Surface protection sheet and processing method

Abstract

The present invention provides a surface protection sheet that, even when used in a process that includes a step of processing the object to be protected in a liquid while the sheet is attached to the object to be protected, is less likely to peel off from the edges due to external forces such as vibrations during the process, and can be peeled off without damaging or deforming the object to be protected. [Solution] The surface protection sheet has a bending stiffness value of 1.0 × 10 at 25°C. -6 ~1.0×10 -2 Pa·m 3 It is within the specified range. Furthermore, the above surface protection sheet has a water peeling force FW0 of 1.0 N / 20 mm or less.

Description

[Technical Field]

[0001] The present invention relates to a surface protection sheet and a processing method. This application claims priority under Japanese Patent Application No. 2021-52064, filed on 25 March 2021, and Japanese Patent Application No. 2021-151206, filed on 16 September 2021, the entire contents of those applications are incorporated herein by reference. [Background technology]

[0002] A technique is known for protecting the surface of various items by adhering a protective sheet (adhesive sheet) to prevent damage (scratches, dirt, corrosion, etc.) to the surface when processing or transporting them. For example, in various processes such as chemically treating glass, semiconductor wafers, and metal plates using chemical solutions (etching solutions) or performing physical treatments such as cutting and polishing, the untreated surface of the object to be protected is protected by attaching a surface protection sheet to the untreated surface. Patent Document 1 is a prior art document relating to protective sheets for chemical treatment. Patent Document 2 is a prior art document relating to water-removable adhesive sheets. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2015-193688 [Patent Document 2] Japanese Patent Application Publication No. 2020-23656 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Surface protection sheets are removed from the adherend (object to be protected) at an appropriate time after achieving their protective purpose. Therefore, surface protection sheets are required to have the adhesive properties necessary to protect the object during the protection period, such as during chemical treatment, and to be easily peeled off when removing them from the object. If the peeling force on the object to be protected is too strong, for example, if the object to be protected is thin, there is a risk that the object to be protected may be damaged or deformed when the surface protection sheet is peeled off from the object due to that peeling force.

[0005] In recent years, electronic devices such as smartphones, tablet computers, and various wearable devices (e.g., portable electronic devices) have become smaller and thinner, and consequently, semiconductor components and optical components such as glass used in these electronic devices are also tending to become thinner. Therefore, surface protection sheets used to protect these components also need to have easy peelability so that the protected object is not damaged or deformed when the surface protection sheet is peeled off.

[0006] For example, the glass panels used as optical components can be thinned by a glass slimming treatment using chemicals such as hydrofluoric acid. In this glass slimming treatment, a surface protection sheet may be used to protect the untreated surface of the glass. When the surface protection sheet used in such applications is peeled off from the glass panel after the treatment, the thinned glass may break due to increased peeling force during the treatment or the manner of peeling, resulting in problems such as a decrease in yield. In particular, window glass and cover glass used in foldable displays and rollable displays are thinned to a thickness of about 100 μm or less in order to provide flexibility. Therefore, the risk of breakage when peeling off the surface protection sheet is greater. If the peeling strength of the surface protection sheet is set low, the load on the adherend during peeling can be reduced, and the risk of breakage or deformation can be reduced, but the adhesion (adhesion) to the protected object will decrease, the chemicals may seep into the protected area, or in severe cases, lifting or peeling may occur from the adherend during the protection period, and the protection purpose may not be achieved. Achieving both the necessary adhesive properties for protection and the ability to easily peel off the substrate without damaging it is even more difficult when dealing with thin, brittle materials such as thin glass.

[0007] Furthermore, one embodiment of surface protection using the above-mentioned surface protection sheet is to attach one surface protection sheet to one or more objects to be processed (e.g., glass plates), and then, using a transport means such as rollers, transport multiple objects to be processed (objects to be protected) continuously or individually into water, such as in a chemical tank or a washing tank, to perform the desired processing. During this transport and subsequent processes (including placement and setting into equipment, etc.), the objects to be processed may be subjected to external forces such as impact, vibration, and deformation, either inevitably or unintentionally. There is a concern that these external forces will act as peeling loads, causing the surface protection sheet to peel off the objects to be processed. In addition, in embodiments where physical processing such as cutting or polishing is performed on objects to be processed, such as semiconductor wafers, the external forces in such physical processing may act as peeling loads, and there is a concern that the edges of the surface protection sheet may peel off. If such edge peeling occurs, there is a risk that chemicals, etc., may seep into the protected area, and the protective purpose may not be achieved.

[0008] The present invention was created in view of the above circumstances, and aims to provide a surface protection sheet that, even when used in a process that includes a step of processing the object to be protected, for example in a liquid, while attached to the object to be protected, is less likely to peel off from the edges due to external forces such as vibrations and physical processing during the process, and can be peeled off without damaging or deforming the object to be protected. Another related object is to provide a processing method using the above surface protection sheet. [Means for solving the problem]

[0009] A surface protection sheet according to one embodiment provided by this specification has a bending stiffness value of 1.0 × 10 at 25°C. -6 ~1.0×10 -2 Pa·m 3 It is within the specified range. Furthermore, the above surface protection sheet is bonded to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, held in an environment of 23°C and 50%RH for 1 hour, then 20 μL of distilled water is supplied between the alkali glass and the adhesive surface, and after the distilled water enters one end of the interface between the alkali glass and the adhesive surface, the water peeling force FW0 measured under conditions of temperature 23°C, peeling angle 180 degrees and speed 300 mm / min is 1.0 N / 20 mm or less.

[0010] The inventors are conducting research and development on an adhesive sheet (water-removable adhesive sheet) that can be easily peeled off using an aqueous liquid such as water, and has improved water resistance reliability during bonding. With such a water-removable adhesive sheet, the adhesive sheet can be removed from the adherend without damaging the adherend or with minimal physical load by water-removal using an aqueous liquid such as water. The technology disclosed herein utilizes the above water-removal. Specifically, the above surface protection sheet has a water-removal force FW0 of 1.0 N / 20 mm or less, so it is possible to achieve peeling (water-removal) without damaging or deforming the adherend (protected object) during peeling. Furthermore, the above surface protection sheet has a bending stiffness value of 1.0 × 10 at 25°C.-6 ~1.0×10 -2 Pa·m 3 Because it is within the specified range, even if external forces such as vibration are applied during a process in which the object to be protected is treated in a liquid such as a chemical solution or water while the above surface protection sheet is attached to the object, the above surface protection sheet is less likely to peel off from the edges in response to such external forces.

[0011] Furthermore, in another embodiment provided by this specification, the surface protection sheet is bonded to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, the adhesive surface of the surface protection sheet is bonded to the surface of the alkali glass, the environment is maintained at 23°C and 50%RH for 1 hour, then 20 μL of distilled water is supplied between the alkali glass and the adhesive surface, the distilled water enters one end of the interface between the alkali glass and the adhesive surface, and the water peel force FW0 measured under conditions of temperature 23°C, peel angle 180 degrees and speed 300 mm / min is 1.0 N / 20 mm or less. Furthermore, the above-mentioned surface protection sheet is bonded to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, held in an environment of 23°C and 50%RH for 24 hours, and then 20 μL of distilled water is dropped between the alkali glass and the adhesive surface. The initial peeling force measured under conditions of 23°C, a peeling angle of 20 degrees, and a speed of 1000 mm / min is 0.5 N / 10 mm or more. The above surface protection sheet has a water peeling force FW0 of 1.0 N / 20 mm or less, so by peeling it off in the presence of water, it is possible to achieve peeling and removal without damaging or deforming the adherend (object to be protected). Furthermore, since the above surface protection sheet has an initial peeling force of 0.5 N / 10 mm or more, even when external forces (also called physical loads or peeling loads) acting in the thickness direction of the surface protection sheet and potentially causing peeling at the edges are applied, such as vibrations during the transport process or physical loads during the physical processing process, peeling from the edges is unlikely to occur.

[0012] In some preferred embodiments, the surface protection sheet has a water peel strength FW0 [N / 20mm] that is 50% or less of the adhesive strength F0 [N / 20mm]. Here, the adhesive strength F0 is the peel strength [N / 20mm] measured under conditions of 23°C, peel angle of 180°C, and speed of 300 mm / min after bonding the adhesive side of the surface protection sheet to the surface of alkali glass having a surface with a water contact angle of 20 degrees or less, and holding it in an environment of 23°C, 50% RH for 1 hour. A surface protection sheet satisfying the above characteristics can be easily peeled off from the object to be protected by performing the peeling in the presence of water, while maintaining a good adhesive state to the object to be protected during protection.

[0013] In some embodiments, the surface protection sheet comprises an adhesive layer and a base layer that supports the adhesive layer. With such a configuration, the surface protection sheet can have a protective function provided by the base layer located on the back side and adhesion to the object to be protected by the adhesive layer.

[0014] In some preferred embodiments, the adhesive layer includes a water-attracting agent. An adhesive layer containing a water-attracting agent makes it easier to obtain an adhesive that satisfactorily balances normal adhesive strength and water-release properties.

[0015] In some preferred embodiments, the thickness (total thickness) of the surface protection sheet is 20 to 200 μm. Having a total thickness greater than a predetermined value tends to improve the ability to prevent peeling at the edges during the process. Furthermore, surface protection sheets with the above total thickness tend to exhibit good protective functions. For example, they tend to provide protection such as preventing chemical penetration.

[0016] The surface protection sheet disclosed herein is suitable, for example, as a surface protection sheet used in a process of chemically and / or physically treating glass or semiconductor wafers in a liquid. In a process including the above processing step, the surface protection sheet attached to the glass or semiconductor wafer, which is the object to be protected, is less prone to peeling from the edges. Furthermore, when peeling after the above process, smooth peeling using water peeling can be achieved from the glass or semiconductor wafer, which is the object to be protected. The surface protection sheet having the above water peeling ability allows for peeling without damaging the object to be protected, even when the object to be protected is a thin, brittle material such as thin glass, based on its water peeling properties. For example, in an embodiment in which the above processing step is a process of thinning glass or semiconductor wafers, the object to be protected at the time of peeling is thinner than when it was attached, and the risk of damage is greater. By using the surface protection sheet disclosed herein in such applications, peeling from the edges is less likely to occur, and easy peeling (easy water peeling) without damaging the object to be protected can be achieved.

[0017] Furthermore, this specification provides a method for processing an adherend. This processing method includes the steps of: attaching a surface protection sheet to the surface of an adherend having a surface with a water contact angle of 20 degrees or less; applying a physical load to the adherend to which the surface protection sheet is attached in the thickness direction of the surface protection sheet; and peeling off and removing the surface protection sheet from the adherend in the presence of water. The surface protection sheet has a water peeling force FW0 of 1.0 N / 20 mm or less and an initial peeling force of 0.5 N / 10 mm or more. [Water-based peeling power FW0] The aforementioned water peeling force FW0 is the water peeling force [N / 20mm] measured under the conditions of a temperature of 23°C, a peeling angle of 180 degrees, and a speed of 300 mm / min, after bonding the adhesive side of a surface protective sheet to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, holding it in an environment of 23°C and 50% RH for 1 hour, supplying 20 μL of distilled water between the alkali glass and the adhesive surface, allowing the distilled water to enter one end of the interface between the alkali glass and the adhesive surface. [Initiating force for separation] The aforementioned initial peeling force is the maximum stress [N / 10mm] at the beginning of peeling, measured under the conditions of 23°C, a peeling angle of 20 degrees, and a speed of 1000 mm / min, after bonding the adhesive side of a surface protective sheet to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, holding it in an environment of 23°C and 50% RH for 24 hours, and then dropping 20 μL of distilled water between the alkali glass and the adhesive surface. In a method for processing an object to which a surface protection sheet is attached, including a step of applying a physical load in the thickness direction of the surface protection sheet, by using a surface protection sheet with an initial peeling force of 0.5 N / 10 mm or more, the surface protection sheet is less likely to peel from the edges when subjected to a physical load applied to its edges. Furthermore, since the surface protection sheet has a water peeling force FW0 of 1.0 N / 20 mm or less, the surface protection sheet can be removed from the object (protected object) without damage or deformation by peeling the surface protection sheet from the object in the presence of water.

[0018] In some preferred embodiments, the surface protection sheet has a water peel strength FW0 [N / 20mm] of 50% or less of the adhesive strength F0 [N / 20mm]. Here, the adhesive strength F0 is the peel strength [N / 20mm] measured under conditions of 23°C, peel angle of 180°C, and speed of 300 mm / min after bonding the adhesive side of the surface protection sheet to the surface of alkali glass having a surface with a water contact angle of 20 degrees or less, and holding it in an environment of 23°C, 50%RH for 1 hour. By using a surface protection sheet that satisfies the above characteristics, the adherend can be subjected to the intended treatment with the surface protection sheet in good adhesion, while in the surface protection sheet removal process, the surface protection sheet can be easily removed from the adherend.

[0019] The surface protection sheet described above preferably consists of an adhesive layer and a base layer that supports the adhesive layer.

[0020] Examples of processes in which a physical load is applied to the adherend to which the surface protection sheet is attached in the thickness direction of the surface protection sheet include a transport process and a physical processing process. The surface protection sheet disclosed herein is less prone to peeling at the edges when subjected to a physical load applied in the thickness direction of the surface protection sheet in a transport process where vibration is likely to occur, or in a processing method that includes physical processing of the adherend such as cutting, and can achieve the desired protection.

[0021] As described above, this specification provides a surface protection sheet for use in any of the methods for treating an adherend disclosed herein. In one embodiment, such a surface protection sheet has a water peel force FW0 of 1.0 N / 20 mm or less and an initial peel force of 0.5 N / 10 mm or more. Therefore, when applied to the processing method disclosed herein, it is possible to achieve both adhesive retention that is resistant to peeling at the edges under physical load applied in the thickness direction of the surface protection sheet, and smooth peeling and removal. Such a surface protection sheet is particularly suitable for the processing method for an adherend disclosed herein. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic cross-sectional view showing one example of a surface protection sheet. [Figure 2] This is a schematic cross-sectional view showing other examples of surface protection sheets. [Modes for carrying out the invention]

[0023] Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein but necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art. Furthermore, in the following drawings, components and parts that perform the same function may be denoted by the same reference numerals and described accordingly, and redundant descriptions may be omitted or simplified. Also, the embodiments shown in the drawings are schematic for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the size or scale of the actual product provided.

[0024] <Example of surface protection sheet configuration> Figure 1 shows the cross-sectional structure of a surface protection sheet according to one embodiment. As shown in Figure 1, the surface protection sheet 1 has an adhesive surface 1A and is in the form of a single-sided adhesive sheet in which an adhesive layer 20 is provided on one side 10A of a sheet-like base material layer (support base material) 10. The surface protection sheet 1 is used by attaching the surface 20A of the adhesive layer 20, which is the adhesive surface 1A, to the adherend (object to be protected). The back surface 10B of the base material layer 10 (the side opposite to the one side 10A) is also the back surface 1B of the surface protection sheet 1 and constitutes the outer surface of the surface protection sheet 1. Before use (i.e., before being attached to the adherend), the surface protection sheet 1 may be in the form of a surface protection sheet 50 with a release liner, in which the adhesive surface 1A is protected by a release liner 30, at least on the side of the adhesive layer 20, which is the release surface. Alternatively, the other side (back surface) 10B of the base layer 10 may be a release surface, and the surface protection sheet 1 may be wound in a roll shape so that the adhesive layer 20 comes into contact with the back surface and protects its surface (adhesive surface 1A).

[0025] Further, as shown in FIG. 2, the surface protection sheet 2 may have a multilayer structure for the base material layer 10. In this embodiment, the surface protection sheet 2 is configured such that an adhesive layer 20 is provided on one surface 10A of a sheet-like base material layer (support base material) 10, and the base material layer 10 has a laminated structure of a first layer 11 and a second layer 12. Specifically, the base material layer 10 includes a first layer 11 that is the main layer of the base material layer 10 and a second layer 12 that constitutes one surface (back surface) 10B of the base material layer 10. In this embodiment, the second layer 12 is an inorganic material-containing layer. The adhesive layer 20 is in close contact with the surface 10A on the first layer 11 side of the base material layer 10. Before use (i.e., before attaching to the adherend), the surface protection sheet 2 can be in the form of a surface protection sheet 50 with a release liner, in which the adhesive surface 2A is protected by a release liner 30 whose at least the adhesive layer 20 side is a release surface. Alternatively, it may be a surface protection sheet in a form in which the other surface (back surface) 10B of the base material layer 10 is a release surface, and the adhesive layer 20 abuts against the back surface when the surface protection sheet 2 is wound in a roll shape to protect its surface.

[0026] <Properties of the surface protection sheet> (Flexural rigidity value at 25°C) In some embodiments, the surface protection sheet has a flexural rigidity value (25°C flexural rigidity value) at 25°C of 1.0×10 -6 ~1.0×10 -2 Pa·m 3 within the range. A surface protection sheet that satisfies this property is less likely to peel from the end portion against an external force such as vibration even when an external force such as vibration is applied in the process of treating the protected object in a liquid such as a chemical solution or water with the surface protection sheet attached to the protected object. Specifically, by giving the surface protection sheet a rigidity within a predetermined range (25°C flexural rigidity) and increasing the stress (peeling stress) against an external force such as vibration that may cause end peeling of the surface protection sheet in the above process, even when an external force such as vibration is applied during the above process, the occurrence of end peeling can be prevented or the risk of end peeling can be reduced. Note that when the above 25°C flexural rigidity value is a predetermined value (for example, 10 -2 Pa·m 3As a result of meeting the following criteria, the surface protection sheet possesses the rigidity suitable for surface protection applications, and is easily peelable and easy to handle. It also tends to improve the surface conformability of the object being protected.

[0027] The above 25°C bending stiffness value D is 5.0 × 10 from the viewpoint of preventing end peeling. -6 Pa·m 3 It may be greater than or equal to 1.0 × 10, preferably 1.0 × 10 -5 Pa·m 3 The above is more comfortable 5.0 × 10 -5 Pa·m 3 More preferably 1.0 × 10 -4 Pa·m 3 That is all, 3.0 × 10 -4 Pa·m 3 The above values ​​are also acceptable. The above 25°C bending stiffness value D is preferably 5.0 × 10 from the viewpoint of preventing end peeling, ease of peeling, and handling. -3 Pa·m 3 The following is more comfortable: 1.0 × 10 -3 Pa·m 3 More preferably 5.0 × 10 -4 Pa·m 3 The following is true: 1.0 × 10 -5 Pa·m 3 The following is also acceptable. A low 25°C bending stiffness value D within a predetermined range is advantageous in terms of improving the surface conformability of the protected object. In some other embodiments, the 25°C bending stiffness value is not particularly limited, and is 1.0 × 10 -6 Pa·m 3 It may be less than 1.0 × 10 -2 Pa·m 3 It's perfectly fine.

[0028] The above 25°C bending stiffness value D[Pa·m] 3 The formula is given by: when the thickness of the substrate layer is h[m], the Poisson's ratio of the substrate is ν, and the tensile modulus of the surface protective sheet at a temperature of 25°C (25°C tensile modulus) is E[Pa]. D=Eh 3 / 12(1-ν 2 ); This value is obtained by [the specified method]. Note that the bending stiffness of the adhesive layer is much smaller than that of the base layer, so the bending stiffness of the surface protection sheet may depend on the bending stiffness of the base layer. Therefore, in this specification, the bending stiffness value D of the surface protection sheet refers to the value converted to per unit cross-sectional area of ​​the base layer constituting the surface protection sheet. The cross-sectional area of ​​the base layer is calculated based on the thickness of the base layer. The thickness h of the base layer is the value obtained by subtracting the thickness of the adhesive layer from the measured thickness of the surface protection sheet. Poisson's ratio ν is a value (dimensionless number) determined by the material of the base layer, and when the material is resin, a value of 0.35 can usually be adopted as the value of ν. The above 25°C bending stiffness value D[Pa·m] 3 The 25°C bending stiffness value can be obtained by substituting the 25°C tensile modulus E [Pa] and the substrate thickness h [m] obtained from the tensile test described in the examples below into the above formula. The above 25°C bending stiffness value may be the 25°C bending stiffness value in the longitudinal direction (MD: Machine Direction), or the 25°C bending stiffness value in the width direction (TD: Transverse Direction, the direction perpendicular to MD), and therefore it may be at least one of the 25°C bending stiffness values ​​of MD and TD, or it may be the 25°C bending stiffness value in any one direction, regardless of whether it is MD or TD. The 25°C bending stiffness value of a surface protection sheet can be obtained primarily by selecting the material and setting the thickness of the base layer constituting the surface protection sheet.

[0029] (Tensile modulus at 25°C) While not particularly limited, in some embodiments, the 25°C tensile modulus of the surface protection sheet may be 100 MPa or more, or 500 MPa or more. In some preferred embodiments, the 25°C tensile modulus is 1000 MPa or more, more preferably 3000 MPa or more, even more preferably 5000 MPa or more, and may be 6000 MPa or more. The higher the 25°C tensile modulus, the higher the 25°C bending stiffness value that can be obtained. The upper limit of the 25°C tensile modulus is not particularly limited and may be, for example, 30 GPa or less, 15 GPa or less, 10 GPa or less, 8000 MPa or less, 6000 MPa or less, or 4500 MPa or less. The lower the 25°C tensile modulus, the lower the 25°C bending stiffness value that can be obtained. Furthermore, surface protection sheets having a 25°C tensile modulus within the above range tend to have good peelability, handling properties, and surface conformability.

[0030] (Stress at 25°C and 100% elongation) In some embodiments, the stress of the surface protective sheet at 100% elongation at 25°C is 10 N / mm². 2 It may be greater than or equal to 30 N / mm 2 The above is appropriate, preferably 50 N / mm 2 More preferably 80 N / mm 2 That's all, 120 N / mm 2 The above values ​​may also be used. The greater the stress at 100% elongation, the more likely the surface protection sheet is to have a rigidity above a certain level, and the easier it is to prevent peeling at the edges. The upper limit of the stress at 100% elongation is, for example, 300 N / mm. 2 The following applies: 200 N / mm 2 The following may also be true: 100 N / mm 2 The following is also acceptable. Surface protection sheets having 100% elongation stress within the above range tend to exhibit good peelability, handling, and surface conformability.

[0031] (Fracture stress at 25°C) Although not particularly limited, in some embodiments, the breaking stress of the surface protection sheet at 25°C is 10 N / mm². 2 It may be greater than or equal to 30 N / mm 2 (For example, 50 N / mm²) 2 The above is appropriate, preferably 100 N / mm 2 More preferably, 120 N / mm 2 That's all, 150 N / mm 2 The above fracture stress may also be greater. The greater the above fracture stress, the more likely the surface protection sheet is to have a rigidity above a certain level, and the easier it is to prevent peeling at the edges. The upper limit of the above fracture stress is, for example, 500 N / mm 2 The following applies: 300 N / mm 2 The following may also be true: 200 N / mm 2 The following is also acceptable: 150 N / mm 2 The following is also acceptable. Surface protection sheets having a breaking stress within the above range tend to exhibit good peelability, handling, and surface conformability.

[0032] (25°C fracture strain) While not particularly limited, in some embodiments, the fracture strain of the surface protection sheet at 25°C may be 500% or less, preferably less than 300%, more preferably 250% or less, and may also be 200% or less. The smaller the fracture strain, the easier it is for the surface protection sheet to have a rigidity above a certain level, and the easier it is to prevent peeling at the edges. The lower limit of the fracture strain is, for example, 120% or more, may also be 150% or more, and may also be 200% or more. Surface protection sheets having a fracture strain within the above range tend to exhibit good peelability, handling, and surface conformability.

[0033] The tensile modulus at 25°C mentioned above is determined from the linear regression of the stress-strain curve obtained from the tensile test described in the examples below. Furthermore, the stress at 100% elongation [N / mm²] is also determined. 2 ], fracture stress [N / mm 2The tensile modulus at 25°C and the fracture strain [%] can also be measured by the tensile test described in the examples below. Note that the mechanical properties of the adhesive layer (tensile modulus, stress at 100% elongation, fracture stress, and fracture strain) are much smaller than the above mechanical properties of the base layer, and the above mechanical properties of the surface protection sheet may depend on the mechanical properties of the base layer. Therefore, in this specification, the tensile modulus, stress at 100% elongation, and fracture stress of the surface protection sheet refer to the values ​​converted per unit area of ​​the base layer constituting the surface protection sheet. The cross-sectional area of ​​the base layer is calculated based on the thickness of the base layer. The thickness of the base layer is the measured thickness of the surface protection sheet minus the thickness of the adhesive layer. The above 25°C tensile modulus may be the 25°C tensile modulus of MD or the 25°C tensile modulus of TD, and therefore may be at least one of the 25°C tensile modulus of MD and the 25°C tensile modulus of TD, or it may be the 25°C tensile modulus of any one direction, regardless of whether it is MD or TD. Similarly, the 100% tensile stress, fracture stress, and fracture strain mentioned above may be MD measurements (100% tensile stress, fracture stress, or fracture strain), TD measurements, and therefore may be at least one of the MD and TD measurements, or they may be any unidirectional measurements, regardless of whether they are MD or TD.

[0034] The above mechanical properties of the surface protection sheet (tensile modulus at 25°C, stress at 100% elongation at 25°C, fracture stress at 25°C, and fracture strain at 25°C) can be set and adjusted primarily by selecting the material of the base layer constituting the surface protection sheet.

[0035] (Normal water separation force FW0) One of the features of the surface protection sheet disclosed herein is that its normal water peeling force FW0 is 1.0 N / 20 mm or less. A surface protection sheet having a water peeling force FW0 of 1.0 N / 20 mm or less adheres well to an adherend, and when peeling, it can be easily removed from the object to be protected by performing water peeling using an aqueous liquid such as water. More specifically, for example, by supplying a small amount of aqueous liquid between the object to be protected and the adhesive layer, and allowing the aqueous liquid to enter the interface between the object to be protected and the adhesive layer, a trigger for peeling can be created, thereby significantly reducing the peeling strength of the adhesive layer from the object to be protected. By utilizing this property, the surface protection sheet can be easily removed from the object to be protected by water peeling using an aqueous liquid such as water, without damaging or deforming the object to be protected. With a surface protection sheet having this characteristic (water peeling characteristic), even if the object to be protected is a thin, brittle material such as thin glass, peeling can be achieved without damaging the adherend during peeling.

[0036] In some preferred embodiments, the normal water peeling force FW0 is, for example, less than 1.0 N / 20 mm, and may be 0.9 N / 20 mm or less, 0.8 N / 20 mm or less, 0.7 N / 20 mm or less, 0.6 N / 20 mm or less, 0.5 N / 20 mm or less, or 0.3 N / 20 mm or less (e.g., 0.1 N / 20 mm or less). The lower limit of the normal water peeling force FW0 is appropriately set to exhibit the desired water peeling properties and is not limited to a specific range. The lower limit of the normal water peeling force FW0 may be 0.0 N / 20 mm, or 0.01 N / 20 mm or more (e.g., 0.1 N / 20 mm or more).

[0037] The normal water peel force FW0 is the water peel force [N / 20mm] measured under the conditions of 23°C, a peel angle of 180 degrees, and a speed of 300 mm / min after bonding the adhesive side of a surface protective sheet to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, holding it in an environment of 23°C and 50% RH for 1 hour, supplying 20 μL of distilled water between the alkali glass and the adhesive surface, allowing the distilled water to enter one end of the interface between the alkali glass and the adhesive surface. More specifically, the normal water peel force FW0 is measured by the method described in the examples below.

[0038] (Normal water-shedding force reduction degree FW0 / F0) Furthermore, in some embodiments, it is preferable that the surface protection sheet has a normal water peeling force FW0 [N / 20mm] that is 50% or less of the normal adhesive force F0 [N / 20mm]. In other words, it is preferable that the surface protection sheet has a normal water peeling force reduction [%] expressed by the formula: FW0 / F0 × 100; that is 50% or less. A surface protection sheet satisfying this characteristic adheres well to the adherend, and when peeling, it can be easily removed from the object to be protected by performing water peeling using an aqueous liquid such as water. With such a surface protection sheet, it is possible to exhibit the adhesion necessary for protection and to achieve peeling without damaging the adherend. In some preferred embodiments, the normal water peeling force reduction is 30% or less, more preferably 20% or less, even more preferably 10% or less, and may be 5% or less (for example, 3% or less). A surface protection sheet exhibiting such a normal water peeling force reduction can better balance adhesive reliability during protection with ease of peeling during removal. Theoretically, the lower limit of the normal water peeling force reduction is 0%, but in practice, it may be approximately 1% or more (for example, 2% or more).

[0039] (Normal adhesive strength F0) In the technologies disclosed herein, it is preferable that the normal adhesive strength F0 of the surface protection sheet is designed to be higher than the normal water peeling strength FW0. The normal adhesive strength F0 may be, for example, 0.5 N / 20 mm or more, and is typically greater than 1.0 N / 20 mm. Surface protection sheets with a normal adhesive strength F0 of a predetermined value or higher tend to exhibit good adhesion to the object to be protected. In some preferred embodiments, the normal adhesive strength F0 is 2.0 N / 20 mm or more, more preferably 3.0 N / 20 mm or more (e.g., greater than 3.0 N / 20 mm), even more preferably 5.0 N / 20 mm or more (e.g., greater than 5.0 N / 20 mm), may be 7.0 N / 20 mm or more, may be 8.0 N / 20 mm or more, may be 9.0 N / 20 mm or more, and may be 10.0 N / 20 mm or more. The higher the normal adhesive strength F0, the easier it is to obtain a high level of protective function. According to the technology disclosed herein, even when a surface protection sheet is attached to an object to be protected with high adhesive strength, when peeling, water peeling is used to smoothly remove the surface protection sheet without damaging or deforming the object to be protected. Therefore, it is possible to set a higher adhesive strength (normal adhesive strength F0) than conventional surface protection sheets that achieve peelability by limiting the adhesive strength. This means that sufficient protection can be ensured based on high adhesive reliability even when used in harsher environments, which is practically beneficial. The upper limit of the normal adhesive strength F0 is set appropriately according to the required adhesiveness, and is not limited to a specific range. For example, it may be approximately 20 N / 20 mm or less, approximately 15 N / 20 mm or less, approximately 10 N / 20 mm or less, or approximately 6 N / 20 mm or less.

[0040] The normal adhesive strength F0 is the peel strength [N / 20mm] measured under the conditions of 23°C, peel angle of 180°C, and speed of 300 mm / min after bonding the adhesive side of a surface protection sheet to the surface of an alkali glass having a water contact angle of 20 degrees or less and holding it in an environment of 23°C, 50% RH for 1 hour. More specifically, the normal adhesive strength F0 is measured by the method described in the examples below.

[0041] (Adhesion strength F1 after soaking in hot water for 30 minutes) The surface protection sheet disclosed herein preferably has an adhesive strength F1 of 0.5 N / 20 mm or more after 30 minutes of immersion in hot water. A surface protection sheet satisfying the above characteristics can maintain the adhesiveness required for protection even when used in a manner in which the object to be protected is treated in a liquid while attached to the object to be protected. For example, even when used in a chemical solution (typically in the form of an aqueous solution) or hot water, a decrease in adhesive strength due to water peelability does not occur, or the decrease in adhesive strength is suppressed, and the state of adhesion to the adherend can be maintained. Such a surface protection sheet can provide excellent protection, such as preventing peeling from the edges during the above liquid treatment. In some embodiments, the adhesive strength F1 after 30 minutes of immersion in hot water is preferably 1.0 N / 20 mm or more, more preferably 1.5 N / 20 mm or more, even more preferably 2.0 N / 20 mm or more, and may be 2.5 N / 20 mm or more, or 3.0 N / 20 mm or more (e.g., 3.5 N / 20 mm or more). The greater the adhesive strength F1 after 30 minutes of immersion in hot water, the more likely it is to maintain a high level of protective function even when used in applications involving liquid treatment such as chemical solutions or hot water. The upper limit of the adhesive strength F1 after 30 minutes of immersion in hot water is set appropriately according to the required adhesion, and is not limited to a specific range. For example, it may be approximately 15 N / 20 mm or less, approximately 10 N / 20 mm or less, or approximately 5 N / 20 mm or less.

[0042] The adhesive strength F1 after 30 minutes of hot water immersion is the peel strength [N / 20mm] measured under the conditions of a temperature of 23°C, a peel angle of 180°C, and a speed of 300 mm / min after bonding the adhesive side of a surface protection sheet to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, immersing it in hot water at 60°C ± 2°C for 30 minutes, then removing it from the hot water and wiping off the adhering water. More specifically, the adhesive strength F1 after 30 minutes of hot water immersion is measured by the method described in the examples below.

[0043] (Decrease in water-shedding strength after 30 minutes of immersion in hot water: FW1 / F1) In some embodiments, it is preferable that the surface protection sheet has a water peeling force FW1 [N / 20mm] after 30 minutes of hot water immersion that is 50% or less of the adhesive force F1 [N / 20mm] after 30 minutes of hot water immersion. In other words, it is preferable that the surface protection sheet has a water peeling force reduction rate [%] after 30 minutes of hot water immersion, expressed by the formula: FW1 / F1 × 100; of 50% or less. A surface protection sheet in which the water peeling force FW1 after 30 minutes of hot water immersion is reduced to 50% or less of the adhesive force F1 after 30 minutes of hot water immersion, while maintaining an adhesive force of 30 minutes of hot water immersion above a predetermined value, even after being used in a chemical solution (typically in the form of an aqueous solution) or hot water while attached to the object to be protected, can achieve peeling (water peeling) without damaging or deforming the object to be protected. A surface protection sheet satisfying the above characteristics can have the necessary adhesion for protection, and even when the object to be protected is a thin, brittle material such as thin glass, it is possible to preferably achieve peeling without damaging the adherend during peeling. In some embodiments, the degree of decrease in water peeling force after 30 minutes of hot water immersion is preferably 30% or less, more preferably 20% or less, even more preferably 10% or less, and particularly preferably 5% or less (e.g., 3% or less). A surface protection sheet exhibiting such a degree of decrease in water peeling force after 30 minutes of hot water immersion can better balance adhesive reliability during protection with ease of peeling during peeling. The lower limit of the degree of decrease in water peeling force after 30 minutes of hot water immersion is theoretically 0%, but in practice it may be approximately 1% or more (e.g., 2% or more).

[0044] (Water peeling force FW1 after 30 minutes of soaking in warm water) In the technologies disclosed herein, it is preferable that the water peeling force FW1 of the surface protective sheet after 30 minutes of hot water immersion is designed to be lower than the peeling force F1 after 30 minutes of hot water immersion. The water peeling force FW1 after 30 minutes of hot water immersion is, for example, 1.0 N / 20 mm or less, may be less than 1.0 N / 20 mm, suitablely 0.9 N / 20 mm or less or 0.8 N / 20 mm or less, and may be 0.6 N / 20 mm or less. In some preferred embodiments, the water peeling force FW1 after 30 minutes of hot water immersion is less than 0.5 N / 20 mm, more preferably less than 0.4 N / 20 mm, even more preferably approximately 0.3 N / 20 mm or less, may be 0.2 N / 20 mm or less, may be 0.15 N / 20 mm or less, and may be 0.10 N / 20 mm or less. The surface protection sheet exhibiting the above-mentioned water peeling force FW1 after 30 minutes of hot water immersion can maintain good water peelability even after being used in liquid treatment such as chemical solutions or hot water. The lower limit of the above-mentioned water peeling force FW1 after 30 minutes of hot water immersion is appropriately set to exhibit the desired water peelability and is not limited to a specific range. The lower limit of the water peeling force FW1 after 30 minutes of hot water immersion may be 0.0 N / 20 mm or higher (for example, 0.05 N / 20 mm or higher).

[0045] The water peeling force FW1 after 30 minutes of hot water immersion is measured by bonding the adhesive side of a surface protection sheet to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, immersing it in hot water at 60°C ± 2°C for 30 minutes, then removing it from the hot water and wiping off the adhering water, supplying 20 μL of distilled water between the alkali glass and the adhesive surface, allowing the distilled water to enter one end of the interface between the alkali glass and the adhesive surface, and then measuring the water peeling force [N / 20 mm] under the conditions of a temperature of 23°C, a peeling angle of 180 degrees, and a speed of 300 mm / min. More specifically, the water peeling force FW1 after 30 minutes of hot water immersion is measured by the method described in the examples below.

[0046] Furthermore, in some embodiments, it is preferable that the surface protection sheet has a water peeling force FW1 after 30 minutes of hot water immersion that is the same as or less than the normal water peeling force FW0. A surface protection sheet configured in this way does not experience an increase in water peeling force due to aging even after 30 minutes of hot water immersion. Therefore, even if the surface protection sheet is exposed to temperatures higher than room temperature (e.g., about 40°C or higher) during the protection period, such as in liquid treatments such as chemical treatment, the adhesive strength of the surface protection sheet to the adherend does not increase, or the increase in adhesive strength is suppressed, making it easier to achieve peeling of the surface protection sheet without damaging the adherend, based on the desired water peeling properties. The water peeling force FW1 after 30 minutes of hot water immersion may be 70% or less, 50% or less, 30% or less, or 10% or less of the normal water peeling force FW0. The water peeling force FW1 after 30 minutes of immersion in hot water is not particularly limited, but it is 0% or more of the normal water peeling force FW0, and may be 1% or more (for example, 3% or more).

[0047] (Underwater triggering separation force) Furthermore, it is preferable that the surface protection sheet disclosed herein has an underwater initial peel force of 0.2 N / 10 mm or more, measured under conditions of a peel angle of 20 degrees and a tensile speed of 1000 mm / min in water at room temperature (23-25°C). Surface protection sheets that satisfy this characteristic tend to have excellent edge peeling prevention properties. In processes such as transportation, external forces such as vibrations that can cause edge peeling of the surface protection sheet are considered to be high-speed peeling loads applied at a relatively shallow angle to the object to be protected. A surface protection sheet exhibiting the above underwater initial peel force of 0.2 N / 10 mm or more, measured under conditions of a peel angle of 20 degrees and a peeling speed of 1000 mm / min, has a stress against the above peeling load that is above a predetermined value. Therefore, even when external forces such as vibrations are applied in a process in which the object to be protected is treated in a liquid such as a chemical solution or water while the surface protection sheet is attached to the object, it can exhibit excellent edge peeling prevention properties against such external forces. The above-mentioned underwater initiation peeling force is more preferably 0.3 N / 10 mm or more, even more preferably 0.5 N / 10 mm or more, and particularly preferably 0.6 N / 10 mm or more (for example, 0.7 N / 10 mm or more) from the viewpoint of improving edge peeling prevention. The upper limit of the above-mentioned underwater initiation peeling force is not particularly limited and may be, for example, 3 N / 10 mm or less, or 2 N / 10 mm or less (for example, 1 N / 10 mm or less). The above-mentioned underwater initiation peeling force can preferably be achieved mainly by setting the 25° bending stiffness value of the surface protection sheet within a predetermined range. More specifically, the above-mentioned underwater initiation peeling force is measured by the method described in the examples below.

[0048] (Initiating force for separation) In some preferred embodiments, the surface protection sheet is bonded to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, held in an environment of 23°C and 50% RH for 24 hours, and then 20 μL of distilled water is dropped between the alkali glass and the adhesive surface. The initial peeling force measured under conditions of 23°C, a peeling angle of 20 degrees, and a speed of 1000 mm / min is 0.5 N / 10 mm or more. A surface protection sheet satisfying the above characteristics is less prone to peeling from the edges, even when subjected to external forces (also called physical loads or peeling loads) acting in the thickness direction of the surface protection sheet and potentially causing peeling at the edges, such as vibrations during the transport process or physical loads during the physical processing process. This edge peeling prevention property can be exhibited against the above physical loads regardless of the presence or absence of water. The above-mentioned initial peeling force is more preferably 0.6 N / 10 mm or more, even more preferably 0.7 N / 10 mm or more, and particularly preferably 0.8 N / 10 mm or more (for example, 0.9 N / 10 mm or more) from the viewpoint of improving edge peel prevention. The upper limit of the above-mentioned initial peeling force is not particularly limited and may be, for example, 3 N / 10 mm or less, or 2 N / 10 mm or less (for example, 1 N / 10 mm or less). The above-mentioned initial peeling force can be achieved based on the adhesive composition (use of tackifiers, selection of tackifier types, type and amount of water affinity agents, etc.). It can also be adjusted by setting the mechanical properties of the surface protection sheet (for example, the 25°C bending stiffness value) within a predetermined range. More specifically, the above-mentioned initial peeling force is measured by the method described in the examples below.

[0049] (moisture permeability) In some embodiments, the surface protection sheet has a moisture permeability of 24 g / m² as measured by the cup method. 2It is preferable that the moisture permeability is less than or equal to 20 g / (m²). By having a configuration with such limited moisture permeability, even if the surface protection sheet comes into contact with an aqueous liquid, such as by being immersed in a liquid while attached to the adherend, the aqueous liquid is less likely to penetrate to the adhesive interface with the adherend, and a decrease in adhesive strength due to water peelability does not occur or is suppressed. As a result, the adhesive strength to the adherend is maintained, and the surface protection sheet can maintain a state of close contact with the adherend. Such a surface protection sheet may not peel off from the edges during liquid treatment, such as chemical treatment. In some preferred embodiments, the moisture permeability of the surface protection sheet is approximately 20 g / (m²). 2 • day) or less, more preferably approximately 16 g / (m 2 • day) or less, more preferably about 12 g / (m 2 • day) or less, preferably about 8 g / (m 2 • day) or less, approximately 5g / (m 2 It may be less than or equal to (day), for example, approximately 3g / (m 2 It may be less than 1 g / (m²). Also, if the surface protective sheet is exposed to heat such as hot water, if the above moisture permeability is excessively low, the water peelability may not be effectively developed due to aging caused by the heating. From this viewpoint, in some embodiments, the moisture permeability of the surface protective sheet is 1 g / (m²). 2 It is appropriate that the amount be 3g / (m³) or more, preferably about 3g / (m³). 2 (day) or more, more preferably 5g / (m 2 • day) is greater than, for example, 6g / (m 2 (Day) Super fine

[0050] More specifically, the above moisture permeability of the surface protection sheet is, for example, 23 g / (m²). 2 • 22g / (m) or more or less per day, or less than or equal to 22g / (m 2 • day) or more or less, 21g / (m 2 • 20g / (m) or more or less per day. 2 • 19g / (m) or more or less per day 2 • 18g / (m) or more or less per day. 2· day) or more or less, 17 g / (m 2 · day) or more or less, 16 g / (m 2 · day) or more or less, 15 g / (m 2 · day) or more or less, 14 g / (m 2 · day) or more or less, 13 g / (m 2 · day) or more or less, 12 g / (m 2 · day) or more or less, 11 g / (m 2 · day) or more or less, 10 g / (m 2 · day) or more or less, 9 g / (m 2 · day) or more or less, 8 g / (m 2 · day) or more or less, 7 g / (m 2 · day) or more or less, 6 g / (m 2 · day) or more or less, 5 g / (m 2 · day) or more or less, 4 g / (m 2 · day) or more or less, 3 g / (m 2 · day) or more or less, 2 g / (m 2 · day) or more or less, or 1 g / (m 2 · day) or more or less may also be acceptable.

[0051] The moisture permeability of the surface protection sheet can be obtained by selecting and using a suitable moisture-impermeable or low-moisture-permeable material (typically a base material). More specifically, the moisture permeability of the surface protection sheet is measured by the method described in the examples below.

[0052] <Adhesive layer> The surface protection sheet disclosed herein typically comprises an adhesive layer. The adhesive layer may be composed of one or more adhesives selected from various adhesives such as acrylic adhesives, rubber adhesives (natural rubber, synthetic rubber, mixtures thereof, etc.), silicone adhesives, polyester adhesives, urethane adhesives, polyether adhesives, polyamide adhesives, and fluorine-based adhesives. Here, acrylic adhesive refers to an adhesive whose main component is an acrylic polymer. The same applies to rubber adhesives and other adhesives.

[0053] In this specification, "acrylic polymer" refers to a polymer derived from a monomer component containing more than 50% by weight of acrylic monomers. The above-mentioned acrylic monomer refers to a monomer having at least one (meth)acryloyl group in one molecule. In this specification, "(meth)acryloyl" comprehensively refers to acryloyl and methacryloyl. Similarly, "(meth)acrylate" comprehensively refers to acrylate and methacrylate, and "(meth)acrylic" comprehensively refers to acrylic and methacrylic. The above-mentioned acrylic polymer may be an acrylic polymer. The above-mentioned acrylic polymer may be an acrylic polymer contained as a base polymer (main constituent polymer) in, for example, a water-dispersible or solvent-type adhesive. In this case, "monomer component constituting the acrylic polymer" in this specification can be replaced with "monomer component constituting the acrylic polymer." In this specification, the content of additive components expressed in relative amounts with respect to "monomer component constituting the polymer" or "monomer component constituting the acrylic polymer" can be replaced with relative amounts with respect to "acrylic polymer."

[0054] (Acrylic adhesive) From the viewpoint of weather resistance and other factors, an acrylic adhesive can be preferably used as the constituent material of the adhesive layer in some embodiments.

[0055] As the acrylic adhesive, for example, those containing an acrylic polymer composed of a monomer component containing more than 35% by weight of an alkyl (meth)acrylate having a linear or branched alkyl group with 1 to 20 carbon atoms at the ester terminal are preferred. Hereinafter, an alkyl (meth)acrylate having an alkyl group with X or more and Y or less carbon atoms at the ester terminal may be referred to as “(meth)acrylic acid C X-Y alkyl ester”. The alkyl (meth)acrylate having the above-mentioned chain-like (used in the sense of including linear and branched) alkyl group can be used alone or in combination of two or more.

[0056] In some embodiments, since it is easy to balance the properties, the proportion of (meth)acrylic acid C 1-20 alkyl ester in the whole monomer component may be, for example, 40% by weight or more, may be 45% by weight or more, or may be 50% by weight or more (for example, 55% by weight or more). For the same reason, the proportion of (meth)acrylic acid C 1-20 alkyl ester in the monomer component may be, for example, 90% by weight or less, may be 70% by weight or less, or may be 65% by weight or less (for example, 55% by weight or less). In some other embodiments, since it is easy to balance the properties, the proportion of (meth)acrylic acid C 1-20 alkyl ester in the whole monomer component may be, for example, 70% by weight or more, may be 80% by weight or more, or may be 90% by weight or more. For the same reason, the proportion of (meth)acrylic acid C 1-20 alkyl ester in the monomer component may be, for example, 99.9% by weight or less, may be 99.5% by weight or less, or may be 99% by weight or less.

[0057] (meth)acrylic acid C 1-20Non-specific examples of alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and i Examples include sooctyl, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0058] Of these, at least (meth)acrylic acid C 4-20 It is preferable to use an alkyl ester, and at least (meth)acrylic acid C 4-18 It is more preferable to use alkyl esters. For example, acrylic adhesives containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) as monomer components are preferred, and acrylic adhesives containing at least BA are particularly preferred. (meth)acrylate C is a preferred choice. 4-20 Other examples of alkyl esters include isononyl acrylate, n-butyl methacrylate (BMA), 2-ethylhexyl methacrylate (2EHMA), and isostearyl acrylate (iSTA).

[0059] In some embodiments, the monomer components constituting the acrylic polymer are (meth)acrylic acid C 4-18It may contain alkyl esters in a proportion of 40% by weight or more. When monomer components containing a relatively large amount of alkyl (meth)acrylate esters having an alkyl group with 4 or more carbon atoms at the ester terminal tend to form highly lipophilic acrylic polymers. Highly lipophilic acrylic polymers easily form an adhesive layer that does not lose adhesive strength even when immersed in water such as hot water. (meth)acrylate C in the monomer component 4-18 The proportion of alkyl ester may be, for example, 60% by weight or more, 70% by weight or more, 75% by weight or more, or 80% by weight or more. (meth)acrylate C in a proportion equal to or greater than any of the lower limits mentioned above. 6-18 The monomer component may also contain an alkyl ester. Furthermore, from the viewpoint of enhancing the cohesiveness of the adhesive layer and preventing cohesive failure, (meth)acrylic acid C is included in the monomer component. 4-18 The proportion of alkyl ester is appropriately 99.5% by weight or less, but may also be 99% by weight or less, 98% by weight or less, or 97% by weight or less. From the viewpoint of improving the cohesiveness of the adhesive layer, in some embodiments, the proportion of (meth)acrylic acid C in the above monomer component is appropriate. 4-18 The proportion of alkyl ester is 95% by weight or less, for example, 90% by weight or less is appropriate. In some other embodiments, the monomer component is (meth)acrylic acid C 4-18 The proportion of alkyl ester may be 85% by weight or less, or 75% by weight or less. (meth)acrylate C in a proportion less than or equal to either of the upper limits mentioned above. 6-18 The monomer component may also contain an alkyl ester.

[0060] In some embodiments, the (meth)acrylate C in the (meth)acrylate ester having the above-mentioned chain alkyl group 1-4 Acrylic polymers formed from monomer components in which the proportion of alkyl esters (preferably BA) exceeds 50% by weight are preferably used. Such acrylic polymers easily yield adhesives with suitable adhesion and cohesive strength for surface protection applications. (Meth)acrylic acid C 1-4Alkyl esters can be used individually or in combination of two or more. (meth)acrylate C in the above-mentioned alkyl (meth)acrylate having a chain-like alkyl group. 1-4 The proportion of alkyl ester is preferably 70% by weight or more, more preferably 85% by weight or more, and may be, for example, 90% by weight or more. (meth)acrylate C in the alkyl (meth)acrylate having the above chain alkyl group 1-4 The upper limit for the proportion of alkyl esters is 100% by weight, but it may be 99% by weight or less, for example, less than 97% by weight.

[0061] In some embodiments, the (meth)acrylate C in the (meth)acrylate ester having the chain alkyl group is 2-4 The proportion of alkyl ester is greater than 50% by weight (for example, 70% or more by weight, or 85% or more by weight, or 90% or more by weight). (meth)acrylate C 2-4 Specific examples of alkyl esters include ethyl acrylate, propyl acrylate, isopropyl acrylate, BA, isobutyl acrylate, s-butyl acrylate, and t-butyl acrylate. (meth)acrylic acid C 2-4 Alkyl esters can be used individually or in combination of two or more. Using acrylic polymers with such monomer compositions makes it easier to realize surface protective sheets with good adhesion to the substrate. In particular, a preferred embodiment is one in which the proportion of BA in the (meth)acrylate alkyl ester having the chain-like alkyl group is greater than 50% by weight (for example, 70% by weight or more, or 85% by weight or more, or 90% by weight or more). 2-4 The proportion of alkyl ester is 100% by weight, but may be 99% by weight or less, for example, less than 97% by weight.

[0062] In some preferred embodiments, the (meth)acrylate C in the (meth)acrylate ester having the chain alkyl group described above... 7-12Acrylic polymers formed from monomer components in which the proportion of alkyl esters exceeds 50% by weight are preferably used. Such acrylic polymers make it easier to realize surface protective sheets with good adhesion to the substrate. The above (meth)acrylic acid C 7-12 Examples of alkyl esters include (meth)acrylate C 8-9 Alkyl esters are preferred, and C acrylate 8-9 Alkyl esters are more preferred, and 2EHA is particularly preferred. (meth)acrylate C 7-12 Alkyl esters can be used individually or in combination of two or more. (meth)acrylate C in the above-mentioned alkyl (meth)acrylate having a chain-like alkyl group. 7-12 The proportion of alkyl ester (preferably 2EHA) is preferably 70% by weight or more, more preferably 85% by weight or more, and may be, for example, 90% by weight or more, or 95% by weight or more. (meth)acrylate C in the above-mentioned alkyl (meth)acrylate having a chain-like alkyl group 7-12 The upper limit for the proportion of alkyl esters is 100% by weight, but it may be 99% by weight or less, for example, less than 97% by weight.

[0063] In some preferred embodiments, the monomer component comprises one or more alkyl methacrylates as (meth)acrylate alkyl esters. By using alkyl methacrylates, acrylic polymers suitable for surface protection applications can be preferably designed. The alkyl methacrylate is C methacrylate. 1-10 Alkyl esters are preferred, and C methacrylate 1-4 (More preferably C 2-4 ) Alkyl esters are more preferred. The above alkyl methacrylate ester may preferably be used in combination with an alkyl acrylate ester. When using an alkyl methacrylate ester and an alkyl acrylate ester in combination, one or more alkyl methacrylate esters (e.g., C methacrylate) are used. 2-4 Weight C of alkyl ester AMand the weight C of one or more alkyl acrylates AA The ratio (C AM :C AA ) is not particularly limited, and in some embodiments, it is usually about 1:9 to 9:1, and is suitable to be about 2:8 to 8:2, preferably about 3:7 to 7:3, and more preferably about 4:6 to 6:4. In some other embodiments, the total amount of alkyl (meth)acrylate (C AM +C AA The weight of alkyl methacrylate (e.g., C1 alkyl methacrylate, i.e., methyl methacrylate (MMA)) in the total amount of C AM The amount is usually appropriate to be approximately 30% by weight or less, or approximately 10% by weight or less, and may also be approximately 5% by weight or less, and more preferably approximately 3% by weight or less. On the other hand, the lower limit may usually be approximately 0.1% by weight or more, or approximately 0.5% by weight or more.

[0064] The monomer components constituting the acrylic polymer may, along with the alkyl (meth)acrylate, optionally include other monomers copolymerizable with the alkyl (meth)acrylate (copolymerizable monomers). As copolymerizable monomers, monomers having polar groups (e.g., carboxyl groups, hydroxyl groups, nitrogen atom-containing rings, etc.) can be suitably used. Monomers having polar groups can be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the adhesive. Copolymerizable monomers can be used individually or in combination of two or more.

[0065] Non-specific examples of copolymerizable monomers include the following: Carboxy group-containing monomers: For example, acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. Monomers containing acid anhydride groups: For example, maleic anhydride, itaconic anhydride. Hydroxypropyl monomers: For example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, hydroxyalkyl (meth)acrylate such as (4-hydroxymethylcyclohexyl)methyl (meth)acrylate, etc. Monomers containing sulfonic acid groups or phosphate groups: for example, styrene sulfonic acid, allyl sulfonic acid, sodium vinyl sulfonate, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, sulfopropyl (meth)acrylate, (meth)acryloyloxynaphthalenesulfonic acid, 2-hydroxyethylacryloyl phosphate, etc. Epoxy group-containing monomers: For example, epoxy group-containing acrylates such as glycidyl (meth)acrylate and 2-ethyl glycidyl ether (meth)acrylate, allyl glycidyl ether, glycidyl (meth)acrylate, etc. Cyano group-containing monomers: for example, acrylonitrile, methacrylonitrile, etc. Monomers containing isocyanate groups: for example, 2-isocyanate ethyl (meth)acrylate, etc. Amide group-containing monomers: for example, (meth)acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, N,N-di(t-butyl)(meth)acrylamide, etc., N,N-dialkyl(meth)acrylamide; N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, Nn-butyl(meth)acrylamide, etc., N-alkyl(meth)acrylamide; N-vinyl carboxylic acid amides such as N-vinylacetamide; monomers having a hydroxyl group and an amide group, for example, N-(2-hydroxyethyl)(meth)acrylamide N-hydroxyalkyl(meth)acrylamides such as N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, N-(4-hydroxybutyl)(meth)acrylamide; monomers having an alkoxy group and an amide group, for example, N-alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide; and others such as N,N-dimethylaminopropyl(meth)acrylamide and N-(meth)acryloylmorpholine. Amino group-containing monomers: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate. Monomers containing epoxy groups: for example, glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, allyl glycidyl ether. Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholindione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, N-vinylpyridazine, etc. (for example, lactams such as N-vinyl-2-caprolactam). Monomers having a succinimide skeleton: for example, N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, N-(meth)acryloyl-8-oxyhexamethylenesuccinimide, etc. Maleimides: For example, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, etc. Itaconimides: For example, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide, etc. (meth)acrylate aminoalkyls: for example, (meth)acrylate aminoethyl, (meth)acrylate N,N-dimethylaminoethyl, (meth)acrylate N,N-diethylaminoethyl, (meth)acrylate t-butylaminoethyl. Alkoxy group-containing monomers: For example, alkoxyalkyl (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; alkoxyalkylene glycols such as methoxyethylene glycol (meth)acrylate and methoxypolypropylene glycol (meth)acrylate. Alkoxysilyl group-containing monomers: for example, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane. Vinyl esters: For example, vinyl acetate, vinyl propionate, etc. Vinyl ethers: For example, vinyl alkyl ethers such as methyl vinyl ether and ethyl vinyl ether. Aromatic vinyl compounds: For example, styrene, α-methylstyrene, vinyltoluene, etc. Olefins: For example, ethylene, butadiene, isoprene, isobutylene, etc. (Meth)acrylic acid esters having alicyclic hydrocarbon groups: for example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, etc. (Meth)acrylic acid esters having aromatic hydrocarbon groups: for example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc. Other examples include heterocyclic (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen-containing (meth)acrylates such as vinyl chloride and fluorine-containing (meth)acrylates, silicon-containing (meth)acrylates such as silicone (meth)acrylate, and (meth)acrylic acid esters obtained from terpene compound derivative alcohols.

[0066] When using such copolymerizable monomers, the amount used is not particularly limited, but it is appropriate to use at least 0.01% by weight of the total monomer components. From the viewpoint of better demonstrating the effects of using copolymerizable monomers, the amount of copolymerizable monomer used may be 0.1% by weight or more of the total monomer components, or 0.5% by weight or more. Furthermore, from the viewpoint of easily balancing the adhesive properties, it is appropriate to use at least 50% by weight of the total monomer components, and preferably at least 40% by weight.

[0067] In some embodiments, the monomer components constituting the acrylic polymer may include monomers having nitrogen atoms. The use of monomers having nitrogen atoms can enhance the cohesive force of the adhesive, thereby favorably improving its adhesive strength. Nitrogen-containing monomers can be used individually or in combination of two or more. A preferred example of a nitrogen-containing monomer is a monomer having a nitrogen-containing ring. Examples of monomers having a nitrogen-containing ring include those exemplified above, for example, general formula (1): [ka] An N-vinyl cyclic amide represented by can be used. Here, in general formula (1), R 1 It is a divalent organic group, specifically -(CH2) n - is an integer between 2 and 7 (preferably 2, 3, or 4). Among these, N-vinyl-2-pyrrolidone can be preferably used. Another preferred example of a monomer having a nitrogen atom is (meth)acrylamide.

[0068] The amount of monomer containing nitrogen atoms (preferably monomers having a nitrogen atom-containing ring) used is not particularly limited and may be, for example, 1% or more by weight of the total monomer component, 3% or more by weight, or even 5% or more by weight or 7% or more by weight. In some embodiments, from the viewpoint of improving adhesion, the amount of monomer containing nitrogen atoms used may be 10% or more by weight of the total monomer component, 12% or more by weight, 15% or more by weight, or 20% or more by weight. Furthermore, it is appropriate for the amount of monomer containing nitrogen atoms to be, for example, 40% or less by weight of the total monomer component, but it may also be 35% or less by weight, 30% or less by weight, or 25% or less by weight. In some other embodiments, the amount of monomer containing nitrogen atoms used may be, for example, 20% or less by weight of the total monomer component, or 16% or less by weight. In some other embodiments, the amount of monomer containing nitrogen atoms used may be, for example, 12% or less by weight of the total monomer component, 8% or less by weight, or 4% or less by weight.

[0069] In some embodiments, the monomer component includes a carboxyl group-containing monomer. Preferred examples of carboxyl group-containing monomers include acrylic acid (AA) and methacrylic acid (MAA). AA and MAA may be used in combination. When AA and MAA are used in combination, their weight ratio (AA / MAA) is not particularly limited and can be, for example, in the range of approximately 0.1 to 10. In some embodiments, the above weight ratio (AA / MAA) may be, for example, approximately 0.3 or more, or approximately 0.5 or more. Also, the above weight ratio (AA / MAA) may be, for example, approximately 4 or less, or approximately 3 or less.

[0070] The use of carboxyl group-containing monomers allows aqueous liquids such as water to quickly adhere to the surface of the adhesive layer. This can help reduce water release strength. The amount of carboxyl group-containing monomer used may be, for example, 0.05% or more by weight of the total monomer component, 0.1% or more by weight, 0.3% or more by weight, 0.5% or more by weight, 0.8% or more by weight, 1.2% or more by weight, or 1.5% or more by weight. By using a predetermined amount or more of carboxyl group-containing monomers, the cohesive force and crosslinking density of the adhesive layer can be increased. The proportion of the above carboxyl group-containing monomer may be, for example, 15% or less by weight, 10% or less by weight, 5% or less by weight, 4.5% or less by weight, 3.5% or less by weight, 3.0% or less by weight, or 2.5% or less by weight. It is preferable not to use too much carboxyl group-containing monomer from the viewpoint of suppressing the diffusion of water into the bulk of the adhesive layer and suppressing the reduction in adhesive strength when in contact with aqueous liquids such as hot water immersion. Furthermore, using an excessive amount of carboxyl group-containing monomer can be advantageous in preventing the water used for measuring water peeling force from being absorbed by the adhesive layer, thus preventing a shortage of water during the peeling process. The technology disclosed herein can also be preferably implemented in a manner in which the monomer component substantially does not contain carboxyl group-containing monomer. From this perspective, the proportion of the carboxyl group-containing monomer in the monomer component may be, for example, less than 1% by weight, less than 0.3% by weight, or less than 0.1% by weight.

[0071] In some embodiments, the monomer component may include a hydroxyl group-containing monomer. The use of a hydroxyl group-containing monomer can adjust the cohesive force and crosslinking density of the adhesive, thereby improving its adhesive strength. Examples of hydroxyl group-containing monomers include those exemplified above, and for example, 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) are preferably used. The hydroxyl group-containing monomer can be used alone or in combination of two or more.

[0072] When using hydroxyl group-containing monomers, the amount used is not particularly limited and may be, for example, 0.01% by weight or more of the total monomer component, 0.1% by weight or more, or 0.5% by weight or more. In some preferred embodiments, the amount of hydroxyl group-containing monomer used is 1% by weight or more of the total monomer component, more preferably 5% by weight or more, even more preferably 10% by weight or more, and may be, for example, 12% by weight or more. Furthermore, from the viewpoint of suppressing the water absorption of the adhesive layer, in some embodiments, the amount of hydroxyl group-containing monomer used is appropriate to be, for example, 40% by weight or less of the total monomer component, may be 30% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, 5% by weight or less, or 3% by weight or less. The technology disclosed herein can also be implemented in a manner in which hydroxyl group-containing monomers are not substantially used as monomer components of the adhesive layer.

[0073] In some preferred embodiments, the monomer component of the acrylic polymer uses a combination of monomers having polar groups (polar group-containing monomers), such as monomers having nitrogen atoms (e.g., amide group-containing monomers such as (meth)acrylamide, monomers having nitrogen atom-containing rings such as NVP), and monomers having hydroxyl groups (e.g., HEA, 4HBA). This can effectively improve adhesive strength. In embodiments where monomers having nitrogen atoms and monomers having hydroxyl groups are used in combination, the amount of monomer having nitrogen atoms A N and the amount of hydroxyl group-containing monomer A OH Weight ratio (A N / A OH ) is not particularly limited, and may be 0.1 or more, 0.5 or more, 0.8 or more, 1.0 or more, or 1.2 or more. Also, the above weight ratio (A N / A OH ) may be, for example, 10 or less, 5 or less, 3 or less, or 1.5 or less.

[0074] In some embodiments, the monomer component may include an alkoxysilyl group-containing monomer. An alkoxysilyl group-containing monomer is typically an ethylenically unsaturated monomer having at least one (preferably two or more, for example, two or three) alkoxysilyl groups in one molecule, and specific examples thereof are as described above. The above alkoxysilyl group-containing monomer can be used alone or in combination of two or more. By using an alkoxysilyl group-containing monomer, a crosslinked structure can be introduced into the adhesive layer by a condensation reaction of silanol groups (silanol condensation). Note that an alkoxysilyl group-containing monomer can also be understood as a silane coupling agent, as described later.

[0075] In embodiments in which the monomer component includes an alkoxysilyl group-containing monomer, the proportion of the alkoxysilyl group-containing monomer to the total monomer component can be, for example, 0.005% by weight or more, and is preferably 0.01% by weight or more. Furthermore, from the viewpoint of improving adhesion to the adherend, the proportion of the alkoxysilyl group-containing monomer may be, for example, 0.5% by weight or less, 0.1% by weight or less, or 0.05% by weight or less.

[0076] Furthermore, in some preferred embodiments of the acrylic polymer, the total proportion of alkoxyalkyl (meth)acrylate and alkoxypolyalkylene glycol (meth)acrylate in the monomer component is limited to less than 20% by weight from the viewpoint of suppressing gelation. The total proportion of alkoxyalkyl (meth)acrylate and alkoxypolyalkylene glycol (meth)acrylate is more preferably less than 10% by weight, even more preferably less than 3% by weight, and particularly preferably less than 1% by weight. In some embodiments, the monomer component is substantially free of alkoxyalkyl (meth)acrylate and alkoxypolyalkylene glycol (meth)acrylate (content of 0-0.3% by weight). Similarly, the monomer components of the acrylic polymers disclosed herein may contain or not contain alkoxy group-containing monomers in a proportion of less than 20% by weight. The amount of alkoxy group-containing monomers in the monomer component is preferably less than 10% by weight, more preferably less than 3% by weight, and even more preferably less than 1% by weight. In a particularly preferred embodiment, the monomer component is substantially free of alkoxy group-containing monomers (content of 0 to 0.3% by weight).

[0077] Furthermore, in some preferred embodiments, the proportion of hydrophilic monomers in the monomer components of the acrylic polymer is set within an appropriate range. This preferably results in good water-release properties. Here, "hydrophilic monomer" as used herein refers to carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, monomers having nitrogen atoms (typically, amide group-containing monomers such as (meth)acrylamide, monomers having nitrogen atom-containing rings such as N-vinyl-2-pyrrolidone), and alkoxy group-containing monomers (typically, alkoxyalkyl (meth)acrylate and alkoxy polyalkylene glycol (meth)acrylate). In this embodiment, the proportion of the above-mentioned hydrophilic monomers in the monomer components of the acrylic polymer is suitable to be 40% by weight or less (for example, 35% by weight or less), preferably 32% by weight or less, and may be, for example, 30% by weight or less, or 28% by weight or less. Although not particularly limited, the proportion of the above-mentioned hydrophilic monomers in the monomer components of the acrylic polymer may be 1% by weight or more, 10% by weight or more, or 20% by weight or more.

[0078] In some embodiments, the monomer components constituting the acrylic polymer may include alicyclic hydrocarbon group-containing (meth)acrylates. This can enhance the cohesive force of the adhesive and improve its bonding strength. Alicyclic hydrocarbon group-containing (meth)acrylates can be used individually or in combination of two or more types. Examples of alicyclic hydrocarbon group-containing (meth)acrylates that can be used include those exemplified above, and for example, cyclohexyl acrylate and isobornyl acrylate are preferably used. The amount of alicyclic hydrocarbon group-containing (meth)acrylate used is not particularly limited and can be, for example, 1% or more, 3% or more, or 5% or more by weight of the total monomer components. In some embodiments, the amount of alicyclic hydrocarbon group-containing (meth)acrylate used may be 10% or more by weight of the total monomer components, or 15% or more by weight. The upper limit for the amount of alicyclic hydrocarbon group-containing (meth)acrylate used should be approximately 40% by weight or less, and may be, for example, 30% by weight or less, or 25% by weight or less (for example, 15% by weight or less, or even 10% by weight or less).

[0079] In some preferred embodiments, the acrylic polymer contains, as a monomer component, 0.05 mol to 0.45 mol of a monomer having a polar group (polar group-containing monomer) per 100 g of the acrylic polymer. This improves adhesion to polar substrates, and allows for the maintenance of high adhesive strength, for example, after immersion in hot water. It is believed that introducing the above polar group into the acrylic polymer improves interfacial adhesion to polar substrates such as glass, based on hydrogen bonding. As the polar group-containing monomer, one or more of the above-mentioned carboxyl group-containing monomers (typically AA, MAA, etc.), hydroxyl group-containing monomers (typically HEA, 4HBA, etc.), and monomers having a nitrogen atom (typically amide group-containing monomers such as (meth)acrylamide, and monomers having a nitrogen atom-containing ring such as NVP) can be used. From the viewpoint of effectively exerting the effects of the polar group-containing monomers, the proportion of polar group-containing monomers in the monomer components of the acrylic polymer is appropriately set to 0.10 mol or more per 100 g of the acrylic polymer, preferably 0.15 mol or more, more preferably 0.20 mol or more, and may be, for example, 0.24 mol or more. Furthermore, the upper limit of the proportion of polar group-containing monomers in the monomer components of the acrylic polymer is appropriately set to 0.40 mol or less per 100 g of the acrylic polymer, preferably 0.35 mol or less, and may be, for example, 0.30 mol or less.

[0080] The composition of the monomer component can be set such that the glass transition temperature (hereinafter also referred to as the "polymer glass transition temperature"), which can be determined by Fox's formula based on the composition of the monomer component, is between -75°C and -10°C. In some embodiments, the glass transition temperature (Tg) of the polymer (e.g., acrylic polymer, typically acrylic polymer) is appropriately -15°C or lower, preferably -20°C or lower, more preferably -25°C or lower, even more preferably -30°C or lower, and may be -40°C or lower (e.g., -55°C or lower). As the Tg of the polymer decreases, the adhesion of the adhesive layer to the substrate layer and the adhesion to the adherend generally tend to improve. With such an adhesive layer, it is easier to suppress water penetration into the interface between the adherend and the adhesive layer in situations where peeling of the adhesive layer is not intended. This can be advantageous from the viewpoint of suppressing a decrease in adhesive strength when in contact with aqueous liquids such as hot water immersion. Furthermore, the Tg of the polymer may be, for example, -70°C or higher, or -65°C or higher, from the viewpoint of easily increasing adhesive strength. In some other embodiments, the above Tg may be, for example, -60°C or higher, or -50°C or higher, or -45°C or -40°C or higher.

[0081] Here, Fox's equation, as shown below, is the relationship between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. 1 / Tg = Σ(Wi / Tgi) In Fox's equation above, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the monomer i homopolymer (unit: K).

[0082] The glass transition temperature of the homopolymer used in calculating Tg shall be the value specified in publicly available documents. For example, for the monomers listed below, the following values ​​shall be used as the glass transition temperature of the homopolymer of the monomer. 2-Ethylhexyl acrylate -70℃ n-butyl acrylate -55℃ n-butyl methacrylate 20℃ Isostearyl acrylate -18℃ Methyl methacrylate 105℃ Methyl acrylate 8℃ Cyclohexyl acrylate 15℃ N-vinyl-2-pyrrolidone 54℃ 2-Hydroxyethyl acrylate -15℃ 4-Hydroxybutyl acrylate -40℃ Dicyclopentanyl methacrylate 175℃ Isobornyl acrylate 94℃ Acrylic acid 106℃ Methacrylic acid 228℃

[0083] For the glass transition temperatures of monomer homopolymers other than those exemplified above, the values ​​listed in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. If multiple values ​​are listed in this document, the highest value shall be adopted.

[0084] For monomers whose glass transition temperature for homopolymers is not listed in the Polymer Handbook mentioned above, the values ​​obtained by the following measurement method shall be used (see Japanese Patent Application Publication No. 2007-51271). Specifically, 100 parts by weight of monomer, 0.2 parts by weight of azobisisobutyronitrile, and 200 parts by weight of ethyl acetate as the polymerization solvent are added to a reactor equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser, and the mixture is stirred for 1 hour while circulating nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. Next, the mixture is cooled to room temperature to obtain a homopolymer solution with a solid content of 33% by weight. Next, this homopolymer solution is cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample is punched out into a 7.9 mm diameter disc shape, sandwiched between parallel plates, and measured using a viscoelasticity tester (ARES, Rheometrics) in shear mode while applying a shear strain of 1 Hz at a frequency of 1 Hz, within a temperature range of -70 to 150°C and a heating rate of 5°C / min. The peak top temperature of tanδ is defined as the Tg of the homopolymer.

[0085] The polymers (e.g., acrylic polymers, typically acrylic polymers) contained in the adhesive layer disclosed herein are not particularly limited, but have an SP value of 23.0 (MJ / m²). 3 ) 1 / 2 The following is preferable. An adhesive containing a polymer having such an SP value can preferably be made to have sufficient adhesive strength while also having excellent water release properties by, for example, including a water-affinity agent as described later. The above SP value is more preferably 21.0 (MJ / m 3 ) 1 / 2 (For example, 20.0 (MJ / m) 3 ) 1 / 2 The following applies. The lower limit of the above SP value is not particularly limited; for example, it is approximately 10.0 (MJ / m). 3 ) 1 / 2 That's all, and also approximately 15.0 (MJ / m 3 ) 1 / 2 It is appropriate for the value to be above this, preferably 18.0 (MJ / m 3 )1 / 2 That's all.

[0086] The SP value of the above polymer is calculated using Fedors' method [see "Polymer Engineering & Science," Vol. 14, No. 2 (1974), pp. 148-154], i.e., formula: SP value δ = (ΣΔe / ΣΔv) 1 / 2 (In the above equation, Δe is the evaporation energy Δe of each atom or group of atoms at 25°C, and Δv is the molar volume of each atom or group of atoms at the same temperature.) It can be calculated according to the above. Polymers having the above SP value can be obtained by appropriately determining the monomer composition based on the common technical knowledge of those skilled in the art.

[0087] The adhesive layer may be formed using an adhesive composition containing monomer components of the above-described composition in the form of polymers, unpolymerized materials (i.e., in a form where polymerizable functional groups are unreacted), or mixtures thereof. The above adhesive composition may take various forms, such as a water-dispersible adhesive composition in which the adhesive (adhesive component) is dispersed in water, a solvent-type adhesive composition in which the adhesive is contained in an organic solvent, an active energy ray-curable adhesive composition (e.g., a photocurable adhesive composition) prepared to form an adhesive by curing with active energy rays such as ultraviolet light or radiation, or a hot-melt adhesive composition that is applied in a heated and molten state and forms an adhesive when cooled to around room temperature.

[0088] In polymerization, known or conventional thermal polymerization initiators or photopolymerization initiators may be used depending on the polymerization method and polymerization mode. Such polymerization initiators can be used individually or in appropriate combinations of two or more.

[0089] While not particularly limited, the following can be used as thermal polymerization initiators: azo-based polymerization initiators, peroxide-based initiators, redox initiators using a combination of peroxide and reducing agent, substituted ethane-based initiators, etc. More specifically, for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methyl Examples of azo initiators include: azo-based initiators such as propionamidine hydrate; persulfates such as potassium persulfate and ammonium persulfate; peroxide-based initiators such as benzoyl peroxide, t-butyl hydroperoxide, and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; redox initiators such as combinations of persulfates and sodium bisulfite, or combinations of peroxides and sodium ascorbate; and are not limited to these. Thermal polymerization can preferably be carried out at a temperature of approximately 20 to 100°C (typically 40 to 80°C).

[0090] While not particularly limited, the following can be used as photopolymerization initiators: ketal-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin ether-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and the like.

[0091] The amount of such thermal polymerization initiator or photopolymerization initiator used can be the usual amount depending on the polymerization method and polymerization mode, and is not particularly limited. For example, approximately 0.001 to 5 parts by weight (typically approximately 0.01 to 2 parts by weight, for example approximately 0.01 to 1 part by weight) of polymerization initiator can be used per 100 parts by weight of the monomer to be polymerized.

[0092] For the above polymerization, various conventionally known chain transfer agents (which may also be known as molecular weight modifiers or degree of polymerization modifiers) can be used as needed. As chain transfer agents, mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, and thioglycolic acid can be used. Alternatively, chain transfer agents that do not contain sulfur atoms (non-sulfur chain transfer agents) may be used. Specific examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; styrenes such as α-methylstyrene and α-methylstyrene dimer; compounds having a benzylidenyl group such as dibenzylideneacetone, cinnamyl alcohol, and cinnamyl aldehyde; hydroquinones such as hydroquinone and naphthohydroquinone; quinones such as benzoquinone and naphthoquinone; olefins such as 2,3-dimethyl-2-butene and 1,5-cyclooctadiene; alcohols such as phenol, benzyl alcohol, and allyl alcohol; and benzyl hydrogens such as diphenylbenzene and triphenylbenzene. The chain transfer agent can be used individually or in combination of two or more types. When using a chain transfer agent, the amount used can be approximately 0.01 to 1 part by weight per 100 parts by weight of the monomer component. The technology disclosed herein can also be preferably implemented in a form that does not use a chain transfer agent.

[0093] The molecular weight of polymers obtained by appropriately employing the above-mentioned polymerization methods (e.g., acrylic polymers, typically acrylic polymers) is not particularly limited and can be set to an appropriate range according to the required performance, etc. The weight-average molecular weight (Mw) of the above polymer is approximately 10 × 10 4 It is appropriate that the above be the case, for example, approximately 15 × 10 4 The above is acceptable. By using a polymer (e.g., an acrylic polymer) having Mw greater than or equal to a predetermined value, a good balance between cohesive force and adhesive force can be achieved. In some embodiments, the above Mw is set to 20 × 10 from the viewpoint of obtaining good adhesive reliability. 4 It may be greater than or equal to 30 x 10 4That's all (use 30 x 10) 4 (Super) is also fine, approximately 40 x 10 4 The above is also acceptable, approximately 50 x 10 4 The above is also acceptable; for example, approximately 55 x 10 4 The above is also acceptable. The upper limit of Mw of the above polymer is not particularly limited, for example, approximately 500 × 10 4 The following (for example, approximately 150 x 10 4 The following may also be acceptable, approximately 75 × 10 4 The following is also acceptable. In some preferred embodiments, the above Mw is 50 × 10 4 It may be less than 40 x 10 4 Less than 35 × 10 4 Less than (for example, 30 x 10) 4 It may also be less than ). Polymers having such Mw tend to make it easier to adjust the 60°C loss modulus of the adhesive to a predetermined range. Here, Mw refers to the value obtained by gel permeation chromatography (GPC) on a standard polystyrene basis. As a GPC apparatus, for example, the model name "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) can be used. The same applies to the examples described later.

[0094] Surface protection sheets according to some embodiments have an adhesive layer formed from a water-dispersible adhesive composition. A typical example of a water-dispersible adhesive composition is an emulsion-type adhesive composition. An emulsion-type adhesive composition typically contains polymers of monomer components and additives used as needed.

[0095] Emulsification polymerization of monomer components is usually carried out in the presence of an emulsifier. The emulsifier used for emulsion polymerization is not particularly limited, and known anionic emulsifiers, nonionic emulsifiers, etc., can be used. The emulsifier can be used alone or in combination of two or more.

[0096] Non-limiting examples of anionic emulsifiers include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene lauryl sulfate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate. Non-limiting examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene polyoxypropylene block polymers. Emulsifiers having reactive functional groups (reactive emulsifiers) may also be used. Examples of reactive emulsifiers include radical polymerizable emulsifiers, which have a structure in which radical polymerizable functional groups such as propenyl groups and allyl ether groups are introduced into the above-mentioned anionic or nonionic emulsifiers.

[0097] The amount of emulsifier used in emulsion polymerization may be, for example, 0.2 parts by weight or more, 0.5 parts by weight or more, 1.0 part by weight or more, or 1.5 parts by weight or more, per 100 parts by weight of monomer components. Furthermore, from the viewpoint of suppressing the decrease in adhesive strength after immersion in hot water, in some embodiments, the amount of emulsifier used is appropriate to be 10 parts by weight or less, preferably 5 parts by weight or less, and may be 3 parts by weight or less, per 100 parts by weight of monomer components. Note that the emulsifier used in emulsion polymerization here may also function as a water affinity agent for the adhesive layer.

[0098] Emulsion polymerization yields a polymerization reaction solution in the form of an emulsion, in which polymers of monomer components are dispersed in water. A water-dispersible adhesive composition used for forming an adhesive layer can preferably be produced using the above polymerization reaction solution.

[0099] In some preferred embodiments, the surface protective sheet has an adhesive layer formed from a solvent-type adhesive composition. The solvent-type adhesive composition typically contains a solution polymer of monomer components and additives as needed. The effects of the techniques disclosed herein can also be effectively demonstrated in a form comprising a solvent-type adhesive layer. The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, one solvent or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); esters such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc. Solution polymerization yields a polymerization reaction solution in which polymers of monomer components are dissolved in the polymerization solvent. The solvent-type adhesive composition used for forming the adhesive layer can preferably be manufactured using the above polymerization reaction solution.

[0100] In another preferred embodiment, the surface protection sheet has an adhesive layer formed from an active energy ray-curable adhesive composition. Herein, "active energy ray" refers to an energy ray with energy capable of causing chemical reactions such as polymerization reactions, crosslinking reactions, and initiator decomposition. Examples of active energy rays include light such as ultraviolet rays, visible light, and infrared rays, and radiation such as alpha rays, beta rays, gamma rays, electron beams, neutron beams, and X-rays. A preferred example of an active energy ray-curable adhesive composition is a photocurable adhesive composition. Photocurable adhesive compositions have the advantage that even thick adhesive layers can be easily formed. Among these, ultraviolet-curable adhesive compositions are preferred. Furthermore, the effects of the techniques disclosed herein can also be effectively demonstrated in a form that includes a photocurable adhesive layer.

[0101] A photocurable adhesive composition typically contains at least a portion of its monomer components (which may be a portion of the types of monomers or a portion of their quantities) in the form of a polymer. The polymerization method used to form the polymer is not particularly limited, and various conventionally known polymerization methods can be used as appropriate. For example, thermal polymerization such as solution polymerization, emulsion polymerization, and bulk polymerization (typically carried out in the presence of a thermal polymerization initiator); photopolymerization carried out by irradiation with light such as ultraviolet light (typically carried out in the presence of a photopolymerization initiator); radiation polymerization carried out by irradiation with radiation such as beta rays and gamma rays; etc., can be used as appropriate. Photopolymerization is preferred among these.

[0102] Some preferred embodiments of photocurable adhesive compositions include a partially polymerized monomer component. Such a partially polymer is typically a mixture of polymer derived from the monomer component and unreacted monomer, and preferably exhibits a syrup-like (viscous liquid) state. Hereinafter, a partially polymer with such properties may be referred to as "monomer syrup" or simply "syrup." The polymerization method for partially polymerizing the monomer component is not particularly limited, and various polymerization methods as described above can be appropriately selected and used. From the viewpoint of efficiency and simplicity, photopolymerization can be preferably employed. With photopolymerization, the polymerization conversion rate (monomer conversion) of the monomer component can be easily controlled by polymerization conditions such as the amount of light irradiation (light intensity).

[0103] The polymerization conversion rate of the monomer mixture in the above-mentioned partial polymer is not particularly limited. The polymerization conversion rate can be, for example, approximately 70% by weight or less, and is preferably approximately 60% by weight or less. From the viewpoint of ease of preparation and coating properties of the adhesive composition containing the above-mentioned partial polymer, the polymerization conversion rate is suitable at approximately 50% by weight or less, and is preferably approximately 40% by weight or less (for example, approximately 35% by weight or less). The lower limit of the polymerization conversion rate is not particularly limited, but is typically approximately 1% by weight or more, and is suitable at approximately 5% by weight or more.

[0104] An adhesive composition containing a partially polymerized monomer component can be obtained, for example, by partially polymerizing a monomer mixture containing the total amount of monomer components used in the preparation of the adhesive composition using a suitable polymerization method (e.g., photopolymerization). Alternatively, the adhesive composition containing a partially polymerized monomer component may be a mixture of a partially polymerized or fully polymerized monomer mixture containing some of the monomer components used in the preparation of the adhesive composition, and the remaining monomer components or their partially polymerized forms. In this specification, "fully polymerized" means a polymerization conversion rate of more than 95% by weight.

[0105] The adhesive composition containing the above-mentioned partially polymerized product may contain other components as needed (e.g., photopolymerization initiators, polyfunctional monomers, crosslinking agents, water affinity agents, etc.). The method of incorporating such other components is not particularly limited; for example, they may be included in the monomer mixture beforehand or added to the above-mentioned partially polymerized product.

[0106] (Water affinity agent) The adhesive layer may optionally contain a water-attracting agent. By including a water-attracting agent in the adhesive layer, the peeling force can be effectively reduced using an aqueous liquid such as water. The reason for this is not particularly limited, but generally, water-attracting agents tend to be unevenly distributed on the surface of the adhesive layer due to their hydrophilic regions, thereby efficiently increasing the water affinity of the adhesive layer surface and effectively reducing the peeling force when the adhesive layer comes into contact with water. Water-attracting agents can be used individually or in combination of two or more types.

[0107] In some embodiments, at least one compound A selected from surfactants and compounds having a polyoxyalkylene skeleton can be used as the water affinity agent. As the surfactant and the compound having a polyoxyalkylene skeleton, one or more known surfactants and compounds having a polyoxyalkylene skeleton can be used without particular limitation. It goes without saying that some of the surfactants mentioned above contain compounds having a polyoxyalkylene skeleton, and vice versa.

[0108] As the surfactant that can be used as compound A, known nonionic surfactants, anionic surfactants, cationic surfactants, etc., can be used. Among these, nonionic surfactants are preferred. One surfactant can be used alone or two or more in combination.

[0109] Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether; polyoxyethylene alkylphenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether; sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan triisostearate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan trioleate; polyoxyethylene glyceryl ether fatty acid esters; and polyoxyethylene-polyoxypropylene block copolymers. These nonionic surfactants can be used individually or in combination of two or more.

[0110] Examples of anionic surfactants include alkylbenzene sulfonates such as nonylbenzenesulfonate and dodecylbenzenesulfonate (e.g., sodium dodecylbenzenesulfonate); alkyl sulfates such as lauryl sulfate (e.g., sodium lauryl sulfate, ammonium lauryl sulfate) and octadecyl sulfate; fatty acid salts; polyoxyethylene alkyl ether sulfates such as polyoxyethylene octadecyl ether sulfate and polyoxyethylene lauryl ether sulfate (e.g., sodium polyoxyethylene alkyl ether sulfate); and polyoxyethylene alkyl phenyl ether sulfates such as polyoxyethylene laurylphenyl ether sulfate (e.g., ammonium polyoxyethylene alkyl phenyl ether sulfate). Examples include polyether sulfates such as sodium ion, polyoxyethylene alkylphenyl ether sulfate sodium, and polyoxyethylene styrene-phenyl ether sulfate; polyoxyethylene alkyl ether phosphates such as polyoxyethylene stearyl ether phosphate and polyoxyethylene lauryl ether phosphate; polyoxyethylene alkyl ether phosphate salts such as sodium salts and potassium salts of the above polyoxyethylene alkyl ether phosphates; sulfosuccinates such as lauryl sulfosuccinate and polyoxyethylene lauryl sulfosuccinate (e.g., sodium polyoxyethylene alkyl sulfosuccinate); and polyoxyethylene alkyl ether acetate. When an anionic surfactant forms a salt, the salt may be a metal salt (preferably a monovalent metal salt) such as a sodium salt, potassium salt, calcium salt, or magnesium salt, an ammonium salt, or an amine salt. Anionic surfactants can be used individually or in combination of two or more.

[0111] In some embodiments, anionic surfactants having at least one of a -POH group, a -COH group, and a -SOH group can be preferably used. Surfactants having a -POH group are preferred. Such surfactants typically contain a phosphate ester structure and may be, for example, a monoester of phosphoric acid (ROP(=O)(OH)2; where R is a monovalent organic group), a diester ((RO)2P(=O)OH; where R is the same or different monovalent organic group), or a mixture containing both monoesters and diesters. A preferred example of a surfactant having a -POH group is polyoxyethylene alkyl ether phosphate ester. The number of carbon atoms in the alkyl group in the polyoxyethylene alkyl ether phosphate ester may be, for example, 6 to 20, 8 to 20, 10 to 20, 12 to 20, or 14 to 20.

[0112] Examples of cationic surfactants include polyetheramines such as polyoxyethylene laurylamine and polyoxyethylene stearylamine. Cationic surfactants can be used individually or in combination of two or more.

[0113] Compounds having a polyoxyalkylene skeleton that can be used as compound A include, for example, polyalkylene glycols such as polyethylene glycol (PEG) and polypropylene glycol (PPG); polyethers containing polyoxyethylene units, polyethers containing polyoxypropylene units, compounds containing oxyethylene units and oxypropylene units (the arrangement of these units may be random or blocky); derivatives thereof; and the like. In addition, compounds having a polyoxyalkylene skeleton from among the surfactants mentioned above can also be used. These can be used individually or in combination of two or more. Among these, it is preferable to use a compound containing a polyoxyethylene skeleton (also called a polyoxyethylene segment), and PEG is more preferable.

[0114] The molecular weight (formula weight) of the compound having a polyoxyalkylene skeleton (e.g., polyethylene glycol) is not particularly limited, but is suitable if it is less than 1000, and is preferably about 600 or less (e.g., 500 or less) from the viewpoint of ease of preparing the adhesive composition. The lower limit of the molecular weight of the compound having a polyoxyalkylene skeleton (e.g., polyethylene glycol) is not particularly limited, but those with a molecular weight of about 100 or more (e.g., about 200 or more, and even more preferably about 300 or more) are preferably used.

[0115] Other examples of water-affinity agents include water-soluble polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylic acid. Water-soluble polymers can be used individually or in combination of two or more. In the techniques disclosed herein, one or more compounds A may be used as the water-affinity agent, one or more water-soluble polymers may be used, or a combination of these may be used.

[0116] The HLB of the water-affinity agent is not particularly limited, and is, for example, 3 or more, approximately 6 or more is suitable, and it may be 8 or more (e.g., 9 or more). In some preferred embodiments, the HLB of the water-affinity agent is 10 or more. This tends to favorably exhibit water-release properties. The above HLB is more preferably 11 or more, even more preferably 12 or more, and particularly preferably 13 or more (e.g., 14 or more). By including a water-affinity agent (typically a surfactant) having an HLB within the above range in the adhesive layer, water-release properties can be more effectively exhibited. The upper limit of the above HLB is 20 or less, and may be, for example, 18 or less, 16 or less, or 15 or less.

[0117] In this specification, HLB refers to the Hydrodrophile-Lipophile Balance according to Griffin, a value representing the degree of affinity of a surfactant to water and oil, expressed as a ratio of hydrophilicity to lipophilicity between 0 and 20. The definition of HLB is as described in WCGriffin: J.Soc. Cosmetic Chemists, 1,311 (1949), and in "Surfactant Handbook," 3rd edition, Kogaku Tosho-sha Publishing, November 25, 1972, pp. 179-182, by Koshimi Takahashi, Yoshiro Nanba, Motoo Koike, and Masao Kobayashi. Water-attracting agents having the above HLB can be selected based on the common technical knowledge of those skilled in the art, taking into account the above references as necessary.

[0118] Such water-attracting agents are preferably contained in the adhesive layer in a free form. From the viewpoint of ease of preparing the adhesive composition, water-attracting agents that are liquid at room temperature (approximately 25°C) are preferably used.

[0119] The adhesive layer containing a water-affinity agent is typically formed from an adhesive composition containing a water-affinity agent. The adhesive composition may be any of the above-mentioned water-dispersible adhesive compositions, solvent-type adhesive compositions, active-energy ray-curable adhesive compositions, hot-melt adhesive compositions, etc. In some preferred embodiments, the adhesive layer containing a water-affinity agent may be formed from a photocurable or solvent-type adhesive composition. In such an adhesive layer, the added effect of the water-affinity agent can be favorably exhibited. The adhesive layer may also be photocurable.

[0120] The content of the water-attracting agent in the adhesive layer is not particularly limited and can be set so as to appropriately exhibit the effects of using the water-attracting agent. In some embodiments, the content of the water-attracting agent can be, for example, 0.001 parts by weight or more per 100 parts by weight of monomer components constituting the polymer (e.g., acrylic polymer) contained in the adhesive layer, and it is appropriate to have 0.01 parts by weight or more, it may also be 0.03 parts by weight or more, it may be 0.07 parts by weight or more, or it may be 0.1 parts by weight or more. In some preferred embodiments, the content of the water-attracting agent can be, for example, 0.2 parts by weight or more per 100 parts by weight of monomer components, and from the viewpoint of obtaining a higher effect, it may be 0.3 parts by weight or more, it may be 0.4 parts by weight or more, it may be 0.5 parts by weight or more, it may be 1.0 part by weight or more, or it may be 1.5 parts by weight or more. Furthermore, from the viewpoint of suppressing excessive water diffusion into the bulk of the adhesive layer, in some embodiments, the amount of water-attracting agent used may be, for example, 20 parts by weight or less, 10 parts by weight or less, preferably 5 parts by weight or less, and may also be 3 parts by weight or less, per 100 parts by weight of monomer component. It is also preferable that the water-attracting agent content is not too high, from the viewpoint of suppressing a decrease in adhesive strength when in contact with aqueous liquids such as hot water immersion. For example, in some embodiments, the water-attracting agent content per 100 parts by weight of monomer component may be less than 2 parts by weight, less than 1 part by weight, less than 0.7 parts by weight, less than 0.3 parts by weight, or less than 0.2 parts by weight. Water-attracting agents with an HLB of 10 or more tend to exhibit good water-release properties even when used in small amounts.

[0121] (Crosslinking agent) The adhesive compositions disclosed herein may optionally contain a crosslinking agent, primarily for the purpose of crosslinking within the adhesive layer or between the adhesive layer and its adjacent surfaces. The crosslinking agent is typically present in the adhesive layer in a post-crosslinking form. The use of a crosslinking agent allows for appropriate adjustment of the cohesive force of the adhesive layer.

[0122] The type of crosslinking agent is not particularly limited, and can be selected from conventionally known crosslinking agents, for example, depending on the composition of the adhesive composition, so that the crosslinking agent exhibits appropriate crosslinking function within the adhesive layer. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, hydrazine-based crosslinking agents, amine-based crosslinking agents, and the like. These can be used individually or in combination of two or more. In water-dispersible adhesive compositions, the use of a crosslinking agent that is soluble or dispersible in water is preferred.

[0123] As isocyanate crosslinking agents, polyfunctional isocyanate compounds with two or more functions can be used. Examples include aromatic isocyanates such as tolylene diisocyanate, xylene diisocyanate, polymethylene polyphenyl diisocyanate, tris(p-isocyanatophenyl)thiophosphate, and diphenylmethane diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. Examples of commercially available isocyanate adducts include trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate L"), trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate HL"), isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX"), trimethylolpropane / xylylene diisocyanate adduct (manufactured by Mitsui Chemicals, trade name "Takenate D-110N"). In water-dispersible adhesive compositions, the use of isocyanate-based crosslinking agents that are soluble or dispersible in water is preferred. For example, water-soluble, water-dispersible, or self-emulsifying isocyanate-based crosslinking agents can be preferred. Blocked isocyanate-type isocyanate-based crosslinking agents, in which the isocyanate group is blocked, can be preferred.

[0124] As an epoxy crosslinking agent, any agent having two or more epoxy groups in one molecule can be used without particular limitation. Epoxy crosslinking agents having 3 to 5 epoxy groups in one molecule are preferred. Specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy crosslinking agents include "TETRAD-X" and "TETRAD-C" from Mitsubishi Gas Chemical Company, "Epiclon CR-5L" from DIC Corporation, "Denacol EX-512" from Nagase ChemteX Corporation, and "TEPIC-G" from Nissan Chemical Industries, Ltd.

[0125] As an oxazoline crosslinking agent, any agent having one or more oxazoline groups in one molecule can be used without particular limitation. In water-dispersible adhesive compositions, it is preferable to use an oxazoline crosslinking agent that is soluble or dispersible in water. The oxazoline group may be any of 2-oxazoline, 3-oxazoline, or 4-oxazoline groups. Typically, oxazoline-based crosslinking agents having a 2-oxazoline group are preferred. For example, water-soluble copolymers or water-dispersible copolymers obtained by copolymerizing addition-polymerizable oxazolines such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline with other monomers can be used as oxazoline-based crosslinking agents. Examples of commercially available oxazoline crosslinking agents include the "Epocross WS" series and "Epocross K" series manufactured by Nippon Shokubai Co., Ltd.

[0126] Examples of aziridine crosslinking agents include trimethylolpropantris[3-(1-aziridinyl)propionate] and trimethylolpropantris[3-(1-(2-methyl)aziridinylpropionate)]. As the carbodiimide crosslinking agent, low-molecular-weight or high-molecular-weight compounds having two or more carbodiimide groups can be used.

[0127] In some embodiments, peroxides may be used as crosslinking agents. Examples of peroxides include di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, t-butylperoxypivalate, dilauroyl peroxide, di-n-octanoyl peroxide, 1,1,3,3-tetramethylbutylperoxyisobutyrate, and dibenzoyl peroxide. Among these, di(4-t-butylcyclohexyl)peroxydicarbonate, dilauroyl peroxide, and dibenzoyl peroxide are particularly excellent in crosslinking reaction efficiency. When peroxides are used as polymerization initiators, any remaining peroxide that is not used in the polymerization reaction can also be used in the crosslinking reaction. In that case, the amount of remaining peroxide should be quantified, and if the proportion of peroxide is less than a predetermined amount, peroxide should be added as needed to reach the predetermined amount. The quantification of peroxide can be carried out by the method described in Japanese Patent Publication No. 4971517.

[0128] The amount of crosslinking agent used (or the total amount if two or more crosslinking agents are used) is not particularly limited. From the viewpoint of realizing an adhesive that exhibits a good balance of adhesive properties such as adhesion and cohesiveness, the amount of crosslinking agent used is, for example, about 10 parts by weight or less per 100 parts by weight of monomer components (e.g., monomer components of acrylic polymers) contained in the adhesive composition, and is appropriate to be approximately 5 parts by weight or less, but may also be 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or less than 1 part by weight. In some embodiments, the amount of crosslinking agent (e.g., isocyanate-based crosslinking agent) used per 100 parts by weight of the above monomer components may be, for example, 0.50 parts by weight or less, 0.40 parts by weight or less, 0.30 parts by weight or less, or 0.20 parts by weight or less. The lower limit of the amount of crosslinking agent used is not particularly limited, and it may be an amount greater than 0 parts by weight per 100 parts by weight of the above monomer components. In some embodiments, the amount of crosslinking agent used may be, for example, 0.001 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.10 parts by weight or more, per 100 parts by weight of the monomer component. In some other embodiments, the amount of crosslinking agent used may be, for example, 0.5 parts by weight or more, 1 part by weight or more, or 1.5 parts by weight or more, per 100 parts by weight of the monomer component.

[0129] Alternatively, the adhesive composition may not contain the crosslinking agent described above. When a photocurable adhesive composition is used as the adhesive composition disclosed herein, the adhesive composition may substantially not contain a crosslinking agent such as an isocyanate-based crosslinking agent. Here, "substantially not containing a crosslinking agent (typically an isocyanate-based crosslinking agent)" means that the amount of the crosslinking agent per 100 parts by weight of the monomer component is less than 0.05 parts by weight (for example, less than 0.01 parts by weight).

[0130] To more effectively advance the crosslinking reaction, a crosslinking catalyst may be used. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, ferric narcem, butyltin oxide, and dioctyltin dilaurate. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of crosslinking catalyst used is not particularly limited. The amount of crosslinking catalyst used can be, for example, approximately 0.0001 parts by weight or more, approximately 0.001 parts by weight or more, approximately 0.005 parts by weight or more, or approximately 1 part by weight or less, approximately 0.1 parts by weight or less, approximately 0.05 parts by weight or less, per 100 parts by weight of the monomer component (e.g., monomer component of an acrylic polymer) contained in the adhesive composition.

[0131] The adhesive composition used to form the adhesive layer may optionally contain a compound that induces keto-enol tautomerism as a crosslinking retarder. For example, in an adhesive composition containing an isocyanate crosslinking agent or an adhesive composition that may be used with an isocyanate crosslinking agent, a compound that induces keto-enol tautomerism can be preferably used. This can extend the pot life of the adhesive composition. Various β-dicarbonyl compounds can be used as compounds that exhibit keto-enol tautomerism. Specific examples include β-diketones such as acetylacetone and 2,4-hexanedione; acetoacetate esters such as methyl acetoacetate and ethyl acetoacetate; propionyl acetate esters such as ethyl propionylacetate; isobutyryl acetate esters such as ethyl isobutyrylacetate; and malonic acid esters such as methyl malonate and ethyl malonate. Among these, acetylacetone and acetoacetate esters are particularly preferred. The compounds exhibiting keto-enol tautomerism can be used individually or in combination of two or more. The amount of compound that produces keto-enol tautomerism may be, for example, 0.1 parts by weight to 20 parts by weight, preferably 0.5 parts by weight to 15 parts by weight, per 100 parts by weight of monomer components (e.g., monomer components of acrylic polymers) contained in the adhesive composition. For example, it may be 1 part by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight.

[0132] (Polyfunctional monomers) Polyfunctional monomers may be used in the adhesive composition (and consequently the adhesive layer) as needed. Polyfunctional monomers can be useful for purposes such as adjusting the cohesive force. When the polyfunctional monomer is formed in the adhesive layer, or after application to the adherend, the ethylenically unsaturated groups of the polyfunctional monomer can be reacted by irradiation with light (e.g., ultraviolet light) to form a crosslinked structure with appropriate flexibility. Therefore, in this specification, "polyfunctional monomer" can be replaced with "crosslinking agent". For example, polyfunctional monomers may be preferably used in adhesive layers formed from photocurable adhesive compositions. As polyfunctional monomers, compounds having two or more ethylenically unsaturated groups may be used. Polyfunctional monomers can be used alone or in combination of two or more.

[0133] Examples of ethylenically unsaturated groups found in polyfunctional monomers include, but are not limited to, acryloyl, methacryloyl, vinyl, and allyl groups. From the viewpoint of photoreactivity, preferred ethylenically unsaturated groups include acryloyl and methacryloyl groups. Among these, acryloyl groups are preferred.

[0134] As polyfunctional monomers, compounds having 2 to 10 ethylenically unsaturated groups in the molecule are preferred, compounds having 2 to 8 ethylenically unsaturated groups in the molecule are more preferred, and compounds having 2 to 6 ethylenically unsaturated groups in the molecule are even more preferred. In some embodiments, compounds having 4 or fewer (specifically 2 to 4, for example 2 or 3, preferably 2) ethylenically unsaturated groups in the molecule can be used as polyfunctional monomers. By using such polyfunctional monomers with a limited number of ethylenically unsaturated groups, it is easier to obtain an adhesive layer that balances elongation and strength.

[0135] Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butyldiol(meth)acrylate, hexyldiol di(meth)acrylate, and the like. Among these, trimethylolpropane tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and dipentaerythritol hexa(meth)acrylate are preferred, with 1,6-hexanediol diacrylate being more preferred.

[0136] The amount of polyfunctional monomer used varies depending on its molecular weight, the number of functional groups, etc., but it is appropriate to use an amount in the range of approximately 0.01 to 3.0 parts by weight per 100 parts by weight of the monomer component that forms the polymer contained in the adhesive layer (typically, an acrylic polymer or the monomer component of said polymer). In some embodiments, the amount of polyfunctional monomer used per 100 parts by weight of the above monomer component may be, for example, 0.02 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, 1.0 part by weight or more, or 2.0 parts by weight or more. Increasing the amount of polyfunctional monomer used tends to result in higher cohesive force. On the other hand, from the viewpoint of avoiding a decrease in adhesion between the adhesive layer and the adjacent layer due to excessive improvement in cohesive force, the amount of polyfunctional monomer used per 100 parts by weight of the above monomer component may be, for example, 10 parts by weight or less, 5.0 parts by weight or less, or 3.0 parts by weight or less. In some embodiments, the amount of polyfunctional monomer used per 100 parts by weight of the monomer component is appropriately 1.0 part by weight or less, preferably 0.5 parts by weight or less, more preferably 0.3 parts by weight or less, and may also be 0.2 parts by weight or less.

[0137] (Adhesion agent) In some preferred embodiments, the adhesive layer includes a tackifier. By including a tackifier in the adhesive layer, the initial peel strength can be improved while maintaining the ability to remove the adhesive from the substrate by water peeling. By utilizing the water peeling technology disclosed herein, a tackifier, which is an adhesion-enhancing component, can be added to achieve a high level of both adhesion during protection, prevention of edge peeling, and water peeling removal. Various components that can improve adhesion can be used as the tackifier without particular limitations. Preferred examples of tackifiers include tackifying resins and acrylic oligomers. The tackifier can be used alone or in combination of two or more types.

[0138] While not particularly limited, tackifiers with an assigned acid value are preferably used. Using a tackifier with an acid value above a predetermined value makes it easier to obtain an improved adhesive strength. For example, adhesion to polar substrates is improved, and high adhesive strength can be maintained even after immersion in hot water. The acid value of the tackifier is, for example, greater than 10 mg KOH / g, greater than 15 mg KOH / g is appropriate, preferably greater than 20 mg KOH / g, and more preferably 23 mg KOH / g or more. The upper limit of the above acid value is usually, for example, 200 mg KOH / g or less, and from the viewpoint of water release properties, it may be 100 mg KOH / g or less, 50 mg KOH / g or less, or 40 mg KOH / g or less. The acid value of the tackifier can be measured by potentiometric titration as specified in JIS K 0070:1992.

[0139] In embodiments using a tackifier, the amount of tackifier used is not particularly limited. From the viewpoint of improving the initial peeling force, the amount of tackifier used can be, for example, 0.1 parts by weight or more, 0.3 parts by weight or more, 1 part by weight or more, 3 parts by weight or more, 5 parts by weight or more, or 10 parts by weight or more, per 100 parts by weight of the monomer component constituting the polymer contained in the adhesive layer. In some preferred embodiments, the amount of tackifier used per 100 parts by weight of the above monomer component may exceed 10 parts by weight, be approximately 11 parts by weight or more, be approximately 12 parts by weight or more, more preferably 15 parts by weight or more, even more preferably 18 parts by weight or more, particularly preferably 20 parts by weight or more (for example 22 parts by weight or more), be 25 parts by weight or more, be 28 parts by weight or more, be 32 parts by weight or more, or be 35 parts by weight or more. Furthermore, the amount of tackifier used per 100 parts by weight of the monomer component is appropriately less than 100 parts by weight, and may be approximately 80 parts by weight or less, 70 parts by weight or less, or 50 parts by weight or less. By limiting the amount of tackifier used to an appropriate range, the tackifier is well compatible with the adhesive, and the effect of adding the tackifier (adhesive properties such as adhesive strength) is easily and effectively exhibited. In some preferred embodiments, the amount of tackifier used per 100 parts by weight of the monomer component is less than 50 parts by weight, more preferably less than 40 parts by weight, even more preferably 35 parts by weight or less, particularly preferably 32 parts by weight or less, and may be 30 parts by weight or less, or 25 parts by weight or less. In some other embodiments, the amount of tackifier used per 100 parts by weight of the monomer component is 20 parts by weight or less, may be less than 10 parts by weight, or may be less than 5 parts by weight.

[0140] In the embodiment using the above tackifier, since the use of the tackifier can improve the prevention of edge peeling, it is not necessary to limit the amount of water-attracting agent used, which may cause a decrease in adhesive strength when in contact with aqueous liquids, and it is even possible to increase the amount of water-attracting agent. By using a tackifier and a water-attracting agent, it is possible to achieve a high level of both adhesion to the object to be protected and peelability. In the embodiment using a tackifier and a water-attracting agent, the amount of tackifier contained in the adhesive layer (C B Amount of water affinity agent (C) A ) ratio (C A / C B ) is not particularly limited, but for example it is 0.0001 or more, 0.001 or more is appropriate, preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, it may be 0.05 or more, or 0.1 or more. By relatively increasing the amount of water affinity agent used relative to the amount of tackifier used, it is possible to maintain the adhesion based on the use of the tackifier within a predetermined range while suppressing the water peel force to a low level and maintaining or improving water peeling and removal properties. The above ratio (C A / C B The upper limit of ) is not particularly limited, for example, 10 or less, 1 or less is appropriate, preferably 0.5 or less, more preferably 0.3 or less, and may be less than 0.15 or less. By limiting the amount of water-affinity agent used to a predetermined range relative to the amount of tackifier used, it is possible to maintain or improve adhesive strength such as initial peeling force while maintaining water-peelability.

[0141] (Acrylic oligomers) The adhesive layer disclosed herein may contain acrylic oligomers from the viewpoint of improving cohesive force, adhesion to the substrate layer, and adhesion to the adherend. According to the technology disclosed herein, even if a surface protection sheet is attached to the object to be protected with high adhesive force, when peeling, the surface protection sheet can be peeled off without damaging or deforming the object to be protected by using water peeling. Therefore, it is possible to improve adhesive reliability and enhance protective function by including adhesion-enhancing components such as acrylic oligomers in the adhesive. An adhesive layer containing an acrylic oligomer can be formed using an adhesive composition containing the acrylic oligomer. Preferably, an acrylic oligomer with a higher Tg than the above-mentioned acrylic polymer (e.g., acrylic polymer) can be used.

[0142] The Tg of the above acrylic oligomer is not particularly limited and may be, for example, between approximately 20°C and 300°C. The above Tg may be, for example, above approximately 30°C, above approximately 40°C, above approximately 60°C, above approximately 80°C, or above approximately 100°C. Generally, as the Tg of the acrylic oligomer increases, the effect of improving cohesive force tends to increase. Furthermore, from the viewpoint of anchoring ability to the substrate layer and shock absorption, the Tg of the acrylic oligomer may be, for example, below approximately 250°C, below approximately 200°C, below approximately 180°C, or below approximately 150°C. Note that the Tg of the acrylic oligomer is a value calculated based on Fox's formula, the same as the Tg of the above acrylic polymer.

[0143] The Mw of the acrylic oligomer is not particularly limited; for example, it may be approximately 1000 or more, approximately 1500 or more is appropriate, approximately 2000 or more, or approximately 3000 or more. Furthermore, the Mw of the acrylic oligomer may be approximately less than 30000, approximately less than 10000 is appropriate, approximately less than 7000, or approximately less than 5000. When the Mw falls within the above range, the cohesiveness and adhesion-enhancing effects of the adhesive layer are favorably exhibited. The Mw of the acrylic oligomer can be measured by GPC and determined as a value equivalent to standard polystyrene. Specifically, for example, it can be measured using a Tosoh HPLC8020 with two TSKgelGMH-H(20) columns at a flow rate of approximately 0.5 mL / min in tetrahydrofuran solvent.

[0144] The monomer components that make up the acrylic oligomers are the various (meth)acrylic acid C compounds mentioned above. 1-20 Examples of (meth)acrylate monomers include alkyl esters; various alicyclic hydrocarbon group-containing (meth)acrylates mentioned above; various aromatic hydrocarbon group-containing (meth)acrylates mentioned above; and (meth)acrylates obtained from terpene compound derivative alcohols. These can be used individually or in combination of two or more.

[0145] From the viewpoint of improving adhesion, it is preferable that acrylic oligomers contain relatively bulky acrylic monomers as monomer units, such as alkyl(meth)acrylates with branched alkyl groups like isobutyl(meth)acrylate and t-butyl(meth)acrylate; alicyclic hydrocarbon group-containing(meth)acrylates; and aromatic hydrocarbon group-containing(meth)acrylates. Furthermore, when ultraviolet light is used during the synthesis of acrylic oligomers or the preparation of adhesive layers, monomers having saturated hydrocarbon groups at the ester terminus are preferred because they are less likely to inhibit polymerization. For example, alkyl(meth)acrylates with branched alkyl groups and saturated alicyclic hydrocarbon group-containing(meth)acrylates can be suitably used.

[0146] The proportion of (meth)acrylate monomers in the total monomer components constituting the acrylic oligomer is typically more than 50% by weight, preferably 60% by weight or more, more preferably 70% by weight or more (e.g., 80% by weight or more, and even more than 90% by weight or more). In some preferred embodiments, the acrylic oligomer has a monomer composition consisting substantially of only one or more (meth)acrylate monomers. The monomer components include alicyclic hydrocarbon group-containing (meth)acrylate and (meth)acrylic acid C 1-20 When alkyl esters are included, their weight ratio is not particularly limited. In some embodiments, alicyclic hydrocarbon group-containing (meth)acrylate / (meth)acrylic acid C 1-20 The weight ratio of alkyl esters can be, for example, 10 / 90 or more, 20 / 80 or more, or 30 / 70 or more, and can also be 90 / 10 or less, 80 / 20 or less, or 70 / 30 or less.

[0147] In addition to the (meth)acrylate monomers mentioned above, functional group-containing monomers can be used as constituent monomers of acrylic oligomers as needed. Examples of functional group-containing monomers include monomers having nitrogen atom-containing heterocycles such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; monomers containing amino groups such as N,N-dimethylaminoethyl (meth)acrylate; monomers containing amide groups such as N,N-diethyl (meth)acrylamide; monomers containing carboxyl groups such as AA and MAA; and monomers containing hydroxyl groups such as 2-hydroxyethyl (meth)acrylate. These functional group-containing monomers can be used individually or in combination of two or more. When functional group-containing monomers are used, the proportion of functional group-containing monomers in the total monomer components constituting the acrylic oligomer can be, for example, 1% or more by weight, 2% or more by weight, or 3% or more by weight, and can also be, for example, 15% or less by weight, 10% or less by weight, or 7% or less by weight. Acrylic oligomers may also be those that do not use functional group-containing monomers.

[0148] Suitable acrylic oligomers include, for example, homopolymers of dicyclopentanyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), dicyclopentanyl acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA), as well as copolymers of DCPMA and MMA, copolymers of DCPMA and IBXMA, copolymers of ADA and methyl methacrylate (MMA), copolymers of CHMA and isobutyl methacrylate (IBMA), copolymers of CHMA and IBXMA, copolymers of CHMA and acryloylmorpholine (ACMO), copolymers of CHMA and diethylacrylamide (DEAA), copolymers of CHMA and AA, and the like.

[0149] Acrylic oligomers can be formed by polymerizing their constituent monomer components. The polymerization method and polymerization mode are not particularly limited, and various conventionally known polymerization methods (e.g., solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be employed in appropriate manner. The types of polymerization initiators that can be used as needed (e.g., azo polymerization initiators) are generally as exemplified for the synthesis of acrylic polymers, and the amount of polymerization initiator and the amount of chain transfer agent (e.g., mercaptans) used as needed are appropriately set based on common technical knowledge to achieve the desired molecular weight, so a detailed explanation is omitted.

[0150] When an acrylic oligomer is included in an adhesive layer or adhesive composition, its content can be, for example, 0.01 parts by weight or more per 100 parts by weight of monomer components of the polymer (typically an acrylic polymer) contained in the adhesive layer. From the viewpoint of obtaining a higher effect, it may be 0.05 parts by weight or more, or 0.1 parts by weight or more, or 0.2 parts by weight or more. In some embodiments, the content of the acrylic oligomer is suitable, for example, 0.5 parts by weight or more per 100 parts by weight of the monomer components, preferably 1 part by weight or more, and may be 2 parts by weight or more. Furthermore, from the viewpoint of compatibility with the polymer (typically an acrylic polymer), the content of the acrylic oligomer per 100 parts by weight of the monomer components is suitable to be less than 50 parts by weight, preferably less than 30 parts by weight, more preferably 25 parts by weight or less, and may be, for example, 10 parts by weight or less, or 5 parts by weight or less, or 1 part by weight or less.

[0151] (Adhesive-forming resin) The adhesive layer may contain a tackifying resin. According to the technology disclosed herein, even if the surface protection sheet is attached to the object to be protected with high adhesive strength, when peeling, the surface protection sheet can be peeled off without damaging or deforming the object to be protected by using water peeling. Therefore, it is possible to improve adhesive reliability and enhance protective function by including adhesion-enhancing components such as tackifying resins in the adhesive. Examples of tackifying resins include rosin-based tackifying resins, rosin derivative tackifying resins, petroleum-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, and ketone-based tackifying resins. These can be used individually or in combination of two or more.

[0152] Examples of the rosin-based tackifying resins mentioned above include rosins such as gum rosin, wood rosin, and tall oil rosin, as well as stabilized rosins (for example, stabilized rosins obtained by disproportionation or hydrogenation treatment of the above rosins), polymerized rosins (for example, polymers of the above rosins, typically dimers), and modified rosins (for example, unsaturated acid-modified rosins modified with unsaturated acids such as maleic acid, fumaric acid, and (meth)acrylic acid). Examples of the rosin derivative tackifying resins mentioned above include esterified rosin-based tackifying resins (for example, rosin esters such as stabilized rosin esters and polymerized rosin esters), phenol-modified rosin-based resins (phenol-modified rosin), and their esterified products (phenol-modified rosin esters). Examples of the above-mentioned petroleum-based tackifying resins include aliphatic petroleum resins, aromatic petroleum resins, copolymer petroleum resins, alicyclic petroleum resins, and their hydrides. Examples of the terpene-based tackifying resins mentioned above include α-pinene resin, β-pinene resin, aromatically modified terpene resin, and hydrogenated terpene resin. The term "terpene-phenol resin" refers to polymers containing terpene and phenol residues, and encompasses both copolymers of terpenes and phenol compounds (terpene-phenol copolymer resins) and phenol-modified homopolymers or copolymers of terpenes (phenol-modified terpene resins). Terpene-phenol resins include hydrogenated terpene-phenol resins. Examples of the phenolic tackifying resins mentioned above include alkylphenol resins obtained from alkylphenols and formaldehyde. Examples of alkylphenol resins include novolac type and resol type. Examples of the ketone-based tackifying resins mentioned above include ketone-based resins formed by the condensation of ketones (e.g., aliphatic ketones such as methyl ethyl ketone, methyl isobutyl ketone, and acetophenone; alicyclic ketones such as cyclohexanone and methylcyclohexanone) with formaldehyde.

[0153] In some embodiments, one or more tackifying resins selected from rosin-based tackifying resins, rosin derivative tackifying resins, and terpene phenol resins can be preferably used. Among these, rosin derivative tackifying resins are preferred, and suitable examples include rosin esters such as stabilized rosin esters and polymerized rosin esters.

[0154] In water-dispersible adhesive compositions, it is preferable to use a water-dispersible tackifying resin in which the tackifying resin described above is dispersed in an aqueous solvent. For example, by mixing an aqueous dispersion of an acrylic polymer with a water-dispersible tackifying resin, an adhesive composition containing these components in a desired proportion can be easily prepared. In some embodiments, from the viewpoint of environmental hygiene, it is preferable to use a water-dispersible tackifying resin that is substantially free of at least aromatic hydrocarbon solvents. It is even more preferable to use a water-dispersible tackifying resin that is substantially free of aromatic hydrocarbon solvents and other organic solvents.

[0155] Examples of commercially available water-dispersible tackifying resins containing rosin esters include the "Super Ester E-720," "Super Ester E-730-55," "Super Ester E-865NT," and "Super Ester NS" series from Arakawa Chemical Industries, Ltd., and the "Hariestar SK-90D," "Hariestar SK-70D," "Hariestar SK-70E," and "Neotol 115E" from Harima Chemicals, Ltd. Furthermore, examples of commercially available terpene phenol resins (which may be in the form of water-dispersible terpene phenol resins) include the "Tamanol E-100," "Tamanol E-200," and "Tamanol E-200NT" from Arakawa Chemical Industries, Ltd.

[0156] The softening point of the tackifying resin is not particularly limited. From the viewpoint of suppressing a decrease in the cohesive force of the adhesive layer, a tackifying resin with a softening point of 80°C or higher may be preferably used. The softening point of the tackifying resin may be 90°C or higher, 100°C or higher, 110°C or higher, or 120°C or higher. A tackifying resin with a softening point of 130°C or higher or 140°C or higher may also be used. Furthermore, from the viewpoint of adhesion to the substrate layer and adhesion to the adherend, a tackifying resin with a softening point of 200°C or lower or 180°C or lower may be preferably used. The softening point of the tackifying resin referred to here may be the nominal value described in literature or catalogs. If there is no nominal value, the softening point of the tackifying resin can be measured based on the softening point test method (ring-ball method) specified in JIS K5902 or JIS K2207.

[0157] From the viewpoint of suitably exhibiting its effects, the amount of tackifying resin used is appropriately 1 part by weight or more per 100 parts by weight of monomer components constituting the polymer contained in the adhesive layer, and may be 5 parts by weight or more, or 10 parts by weight or more. In some preferred embodiments, the amount of tackifying resin used per 100 parts by weight of monomer components is greater than 10 parts by weight, more preferably 15 parts by weight or more, even more preferably 18 parts by weight or more, and particularly preferably 20 parts by weight or more (for example, 22 parts by weight or more), and may be 25 parts by weight or more, 28 parts by weight or more, 32 parts by weight or more, or 35 parts by weight or more. Furthermore, from the viewpoint of achieving a good balance between adhesion and cohesiveness to the substrate layer and adherend, the amount of tackifying resin used per 100 parts by weight of monomer components is appropriately less than 100 parts by weight, and may be 70 parts by weight or less, 50 parts by weight or less, 40 parts by weight or less, 30 parts by weight or less, or 20 parts by weight or less. By limiting the amount of tackifying resin used to an appropriate range, the tackifying resin can be well compatible with the adhesive, and the additive effect of the tackifying resin (adhesive properties such as adhesive strength) can be effectively exhibited. Alternatively, the adhesive layer may not contain substantially any tackifying resin.

[0158] (Silane coupling agent) In some embodiments, the adhesive layer can contain a silane coupling agent. An adhesive layer containing a silane coupling agent can suitably provide a surface protection sheet with high adhesive strength. The silane coupling agent can be used alone or in combination of two or more types.

[0159] Examples of silane coupling agents include silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as acetoacetyl group-containing trimethoxysilane, 3-acryloxypropyltrimethoxysilane, and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatetopropyltriethoxysilane. Among these, preferred examples include 3-glycidoxypropyltrimethoxysilane and acetoacetyl group-containing trimethoxysilane.

[0160] The amount of silane coupling agent used can be set to obtain the desired effect and is not particularly limited. In some embodiments, the amount of silane coupling agent used may be, for example, 0.001 parts by weight or more per 100 parts by weight of monomer components constituting the polymer contained in the adhesive layer, and may be 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.015 parts by weight or more from the viewpoint of obtaining a higher effect. Also, from the viewpoint of improving adhesion, in some embodiments, the amount of silane coupling agent used may be, for example, 3 parts by weight or less, 1 part by weight or less, or 0.5 parts by weight or less per 100 parts by weight of monomer components constituting the adhesive layer. Furthermore, the technology disclosed herein can be implemented in a manner that uses an adhesive composition that substantially does not contain a silane coupling agent. By limiting the use of silane coupling agents or not using silane coupling agents, the increase in adhesive strength over time can be suppressed, and good water release properties can be easily obtained.

[0161] In addition, in embodiments in which the monomer component includes an alkoxysilyl group-containing monomer, the alkoxysilyl group-containing monomer may be used as part or all of the silane coupling agent contained in the adhesive layer.

[0162] (Photopolymerization initiator) The adhesive compositions and photocurable adhesive layers disclosed herein may contain a photopolymerization initiator (also called a photoreaction catalyst) as needed for purposes such as imparting photocurability. As photopolymerization initiators, similar to those exemplified for use in the synthesis of acrylic polymers, ketal-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin ether-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, etc. The photopolymerization initiators may be used individually or in appropriate combinations of two or more types.

[0163] The content of the photopolymerization initiator in the adhesive layer is not particularly limited and can be set so as to appropriately exhibit the desired effect. In some embodiments, the content of the photopolymerization initiator can be, for example, approximately 0.005 parts by weight or more, preferably 0.01 parts by weight or more, preferably 0.05 parts by weight or more, and may also be 0.10 parts by weight or more, 0.15 parts by weight or more, or 0.20 parts by weight or more, per 100 parts by weight of monomer components of the polymer (typically acrylic polymer) contained in the adhesive layer. Increasing the content of the photopolymerization initiator improves the photocurability of the adhesive layer. Furthermore, the content of the photopolymerization initiator per 100 parts by weight of the above monomer components is appropriately 5 parts by weight or less, preferably 2 parts by weight or less, and may also be 1 part by weight or less, 0.7 parts by weight or less, or 0.5 parts by weight or less. Not having too much photopolymerization initiator content can be advantageous from the viewpoint of improving the storage stability (e.g., stability against photodegradation) of the surface protective sheet.

[0164] An adhesive layer containing a photopolymerization initiator can typically be formed using an adhesive composition containing the photopolymerization initiator (e.g., a solvent-based adhesive composition). The adhesive composition containing the photopolymerization initiator can be prepared, for example, by mixing the photopolymerization initiator with other components used in the composition. Furthermore, when preparing an adhesive composition using a polymer (typically an acrylic polymer) synthesized (photopolymerized) in the presence of a photopolymerization initiator, the residue (unreacted material) of the photopolymerization initiator used in synthesizing the polymer may be used as part or all of the photopolymerization initiator contained in the adhesive layer. The same applies when using an acrylic oligomer synthesized in the presence of a photopolymerization initiator, as needed. From the viewpoint of ease of manufacturing control, the adhesive layer disclosed herein can preferably be formed using an adhesive composition prepared by adding the above-mentioned amount of photopolymerization initiator to other components.

[0165] (Other ingredients) The adhesive composition used to form the adhesive layer may, if necessary, contain an acid or base (such as aqueous ammonia) used for purposes such as pH adjustment. Examples of other optional components that may be included in the composition include various additives common in the field of adhesive compositions, such as viscosity modifiers (e.g., thickeners), leveling agents, plasticizers, fillers, colorants such as pigments and dyes, stabilizers, preservatives, and anti-aging agents. Such various additives can be used by conventional methods if they are conventionally known and do not particularly characterize the present invention, so a detailed explanation is omitted. Although not particularly limited, the technology disclosed herein can preferably be carried out in a form that comprises an adhesive layer mainly composed of the above polymer (e.g., acrylic polymer). In some embodiments, the proportion of the above polymer (e.g., acrylic polymer) in the adhesive layer is approximately 85% by weight or more (e.g., 85-100% by weight), and may be 90% by weight or more, or 95% by weight or more.

[0166] (Formation of the adhesive layer) The adhesive layer may be a cured layer of the adhesive composition. That is, the adhesive layer can be formed by applying (e.g., coating) the adhesive composition to a suitable surface and then performing a curing treatment as appropriate. When two or more curing treatments (drying, crosslinking, polymerization, etc.) are performed, these can be performed simultaneously or in multiple stages. In adhesive compositions using partially polymerized monomer components (acrylic polymer syrup), typically, the final copolymerization reaction is performed as the curing treatment. That is, the partially polymerized material is subjected to a further copolymerization reaction to form a complete polymer. For example, in the case of a photocurable adhesive composition, light irradiation is performed. If necessary, curing treatments such as crosslinking and drying may be performed. For example, if drying is necessary for a photocurable adhesive composition, it is preferable to perform photocuring after drying. In adhesive compositions using a complete polymer, typically, as necessary, treatments such as drying (heat drying) and crosslinking are performed as the curing treatment. A multilayer adhesive layer with two or more layers can be made by bonding together pre-formed adhesive layers. Alternatively, an adhesive composition may be applied to a pre-formed first adhesive layer, and the adhesive composition may be cured to form a second adhesive layer.

[0167] The adhesive composition can be applied using conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, and spray coaters. For example, as a method for forming an adhesive layer on a substrate layer, a direct method may be used in which the adhesive composition is directly applied to the substrate layer to form the adhesive layer, or a transfer method may be used in which the adhesive layer formed on the release surface is transferred to the substrate layer.

[0168] The thickness of the adhesive layer is not particularly limited and may be, for example, about 3 μm to 1000 μm. From the viewpoint of ensuring the adhesive layer adheres tightly to the substrate layer or adherend and improving water resistance reliability, in some embodiments, the thickness of the adhesive layer is preferably 5 μm or more (e.g., greater than 5 μm), more preferably 10 μm or more (e.g., greater than 10 μm), even more preferably 15 μm or more, and particularly preferably 20 μm or more. The surface protection sheet disclosed herein has water-peelability and can be smoothly peeled off from the adherend using this water-peelability. Therefore, by increasing the thickness of the adhesive layer, the adhesive strength, such as the initial peeling force, can be increased, thereby maintaining or improving protective properties. Furthermore, from the viewpoint of preventing the generation of adhesive residue due to cohesive breakdown of the adhesive layer, in some embodiments, the thickness of the adhesive layer may be, for example, 500 μm or less, 300 μm or less, 200 μm or less, or 150 μm or less. In some preferred embodiments, the thickness of the adhesive layer is 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. For example, it may be 40 μm or less, or 30 μm or less. By limiting the thickness of the adhesive layer, water penetration from the edges of the adhesive layer is restricted, and a decrease in adhesive strength when immersed in aqueous liquid or hot water can be suppressed. The adhesive layer may be a single layer structure or may have a multilayer structure of two or more layers.

[0169] In some embodiments, the loss modulus of elasticity G″ at 60°C (60°C loss modulus G″) of the adhesive layer is preferably in the range of 10 kPa to 50 kPa. A surface protection sheet comprising an adhesive layer having a 60°C loss modulus G″ within the above range improves resistance to hot water based on the viscosity term (60°C loss modulus G″) of the adhesive. For example, even when used in chemical solutions (typically in the form of aqueous solutions) or hot water, it is easier to maintain adhesion to the adherend, and a decrease in adhesive strength due to water peelability does not occur, or the decrease in adhesive strength is easily suppressed. Therefore, even when the object to be protected is treated in a liquid while the surface protection sheet is attached to the object, the adhesion required for protection can be preferably maintained. Furthermore, in hot water, a peeling load is applied to the edges of the surface protection sheet due to the expansion and contraction of the base layer. However, with an adhesive having a predetermined viscosity term at 60°C, the peeling load can be converted into thermal energy and reduced, thus making it easier to maintain a stable adhesive state. Such surface protection sheets can offer excellent protection, for example, preventing peeling from the edges during the liquid treatment described above.

[0170] In some preferred embodiments, the 60°C loss modulus G'' of the adhesive layer is 12 kPa or more, more preferably 15 kPa or more, may be 18 kPa or more, may be 22 kPa or more, may be 25 kPa or more, may be 28 kPa or more, may be 30 kPa or more, or may be 32 kPa or more, from the viewpoint of adhesion after immersion in chemicals or hot water. By setting a high 60°C loss modulus G'', a high adhesive strength F1 after 30 minutes of hot water immersion can be maintained. In some embodiments, the upper limit of the 60°C loss modulus G'' may be 45 kPa or less, may be 40 kPa or less, or may be 35 kPa or less. By limiting the 60°C loss modulus G'' of the adhesive layer to a predetermined value or less, an adhesive with good adhesive properties suitable for surface protection applications can be easily obtained. In some other embodiments, the 60°C loss modulus G'' of the adhesive layer may be 30 kPa or less, may be 25 kPa or less, or may be 20 kPa or less.

[0171] More specifically, the loss modulus G″ at 60°C of the above adhesive layer may be 11 kPa or more or less, 12 kPa or more or less, 13 kPa or more or less, 14 kPa or more or less, 15 kPa or more or less, 16 kPa or more or less, 17 kPa or more or less, 18 kPa or more or less, 19 kPa or more or less, 20 kPa or more or less, 21 kPa or more or less, 22 kPa or more or less, 23 kPa or more or less, 24 kPa or more or less, 25 kPa or more or less, 26 kPa or more or less, 27 kPa or more or less, 28 kPa or more or less, 29 kPa or more or less, 30 kPa or more or less, 31 kPa or more or less, 32 kPa or more or less, 33 kPa or more or less, 34 kPa or more or less, 35 kPa or more or less, 36 kPa or more or less, 37 kPa or more or less, 38 kPa or more or less, 39 kPa or more or less, 40 kPa or more or less, 41 kPa or more or less, 42 kPa or more or less, 43 kPa or more or less, 44 kPa or more or less, 45 kPa or more or less, 46 kPa or more or less, 47 kPa or more or less, 48 kPa or more or less, 49 kPa or more or less.

[0172] The above loss modulus G″ at 60°C can be mainly obtained by adjusting the molecular weight and molecular weight distribution of the polymer contained in the adhesive. In addition, it can also be adjusted by the crosslink density in the adhesive, etc. The loss modulus G″ at 60°C of the adhesive layer is measured by the method described in the examples below.

[0173] (Resilience) Although not particularly limited, as the adhesive (layer), an adhesive with a peeling distance of 3.0 mm or less 1 hour after pressure bonding to the adherend in the anti-rebound test conducted by the method described in the following examples is preferably used. The adhesive (layer) having such anti-rebound properties is less likely to cause end peeling from the adherend with respect to the physical load (peeling load) in the thickness direction of the surface protection sheet having the adhesive (layer), and can exhibit excellent end peeling prevention properties. The peeling distance (1 hour after pressure bonding) in the above anti-rebound test is preferably 1.0 mm or less, more preferably 0.5 mm or less, still more preferably 0.3 mm or less, particularly preferably 0.2 mm or less, and most preferably 0.0 mm. The above anti-rebound characteristics can be realized based on the adhesive composition (use of tackifier, selection of tackifier type, type and amount of hydrophilic agent, etc.).

[0174] <Base material layer> The surface protection sheet disclosed herein may include a base material layer. Non-limiting examples of the material of the base material layer include various resin films such as polyolefin film, polyester film, and polyvinyl chloride film; foam sheets made of foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; various fibrous substances (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc., which can be single or blended, etc.). Woven and non-woven fabrics; papers such as Japanese paper, fine paper, kraft paper, and crepe paper; metal foils such as aluminum foil, copper foil, and stainless steel (SUS); etc. An appropriate material can be selected from these single types or laminates composed of two or more types and used as the base material layer material. Examples of the base material layer having the above composite structure include, for example, a laminated base material (multilayer structure base material) having a structure in which a metal foil and the above resin film are laminated, and a resin sheet reinforced with inorganic fibers such as glass cloths.

[0175] Various types of films (hereinafter also referred to as "substrate films") can be preferably used as the material for the substrate layer. The substrate film may be a porous film such as a foam film or a nonwoven fabric sheet, or it may be a film with a structure in which a porous layer and a non-porous layer are laminated. In some embodiments, the substrate film may preferably include a resin film that can independently maintain its shape (self-supporting or independent) as the base film. Here, "resin film" means a resin film with a non-porous structure, which is typically substantially free of air bubbles (voidless). Therefore, the resin film is a concept distinct from foam films and nonwoven fabrics. The resin film may have a single-layer structure or a multilayer structure of two or more layers (for example, a three-layer structure).

[0176] Resin materials that make up resin films include, for example, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefins such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers; polycycloolefins derived from monomers having aliphatic ring structures such as norbornene structures; polyamides (PA) such as nylon 6, nylon 66, and partially aromatic polyamides; polyimides (PI) such as transparent polyimide (CPI), polyamide-imide (PAI); polyether ether ketone (PEEK); and polyether ether ketones. Resins such as thrusulfone (PES), polyphenylene sulfide (PPS), polycarbonate (PC), polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), polystyrene, ABS resin, polyvinyl chloride, polyvinylidene chloride, fluororesins such as polytetrafluoroethylene (PTFE), acrylic resins such as polymethyl methacrylate, cellulosic polymers such as diacetylcellulose and triacetylcellulose (TAC), vinyl butyral polymers, arylate polymers, polyoxymethylene polymers, and epoxy polymers can be used. The substrate layer disclosed herein may have a surface composed of the above resin materials. The resin film that can be used as the substrate layer may be formed using a resin material containing one of the above resins alone, or a resin film formed using a blend of two or more of the above resins, and an appropriate material can be selected from these. The above resin film may be a composite resin film in which a resin layer containing one or more resin materials and a resin layer containing the same or different resin materials as the resin layer are laminated. The above resin film may be unstretched or stretched (for example, uniaxially stretched or biaxially stretched).

[0177] In some preferred embodiments, a polyolefin resin film is used as the base layer. By using a polyolefin resin film, a surface protection sheet exhibiting suitable properties at an appropriate thickness can be preferably obtained. Here, polyolefin resin refers to a resin containing polyolefin in a proportion of more than 50% by weight. As the polyolefin resin, one type of polyolefin can be used alone, or two or more types of polyolefin can be used in combination. The polyolefin may be, for example, a homopolymer of α-olefin, a copolymer of two or more types of α-olefin, or a copolymer of one or more types of α-olefin with other vinyl monomers. Specific examples include PE, PP, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene rubber (EPR) and other ethylene-propylene copolymers, ethylene-propylene-butene copolymers, ethylene-butene copolymers, ethylene-vinyl alcohol copolymers, and ethylene-ethyl acrylate copolymers. Both low-density (LD) polyolefins and high-density (HD) polyolefins can be used. Examples of polyolefin resin films include unoriented polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, medium-density polyethylene (MDPE) film, high-density polyethylene (HDPE) film, polyethylene (PE) film made by blending two or more types of polyethylene (PE), and PP / PE blend film made by blending polypropylene (PP) and polyethylene (PE). Among these, OPP film is preferred from the viewpoint of moisture permeability.

[0178] Other suitable examples of resin materials constituting the resin film include polyvinylidene chloride resin, PPS resin, polyurethane resin, EVA resin, and fluororesins such as PTFE. Here, polyvinylidene chloride resin refers to a resin containing polyvinylidene chloride in a proportion exceeding 50% by weight. Similarly, PPS resin refers to a resin containing PPS in a proportion exceeding 50% by weight. The same applies to polyurethane resin, EVA resin, and fluororesins. The polyolefin resins (PE, PP), polyvinylidene chloride resin, PPS resin, polyurethane resin, EVA resin, and fluororesins exemplified above may be used in combination with other materials, or each may be used individually as a base layer.

[0179] The resin film may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, and antiblocking agents, as needed. The amount of additives is not particularly limited and can be set appropriately depending on the application.

[0180] The method for manufacturing the resin film is not particularly limited. For example, conventionally known general resin film molding methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be used as appropriate.

[0181] The above-mentioned substrate layer may be substantially composed of such a resin film. Alternatively, the above-mentioned substrate layer may include auxiliary layers in addition to the resin film. Examples of the above-mentioned auxiliary layers include optical property adjustment layers (e.g., coloring layers, anti-reflective layers), printing layers or lamination layers for providing a desired appearance, antistatic layers, undercoat layers, release layers, and other surface treatment layers.

[0182] In some other embodiments, the substrate layer has a layer containing an inorganic material (inorganic material-containing layer). The effects of the technology disclosed herein can also be achieved by using a substrate layer that includes an inorganic material-containing layer. The placement of an inorganic material-containing layer tends to improve barrier properties (moisture permeability prevention). In some embodiments, the substrate layer having an inorganic material-containing layer includes the above-mentioned resin film or the like as the main substrate layer, and has an inorganic material-containing layer provided on at least one surface of the main substrate layer. In some other embodiments, the substrate layer may consist substantially of an inorganic material-containing layer.

[0183] The inorganic material used in the inorganic material-containing layer can be any material capable of forming a hydrophilic surface, selected from various metallic materials including elemental and alloyed transition metals and metalloids, or inorganic compounds such as inorganic oxides. The inorganic material can be used individually or in combination of two or more. Preferred examples of inorganic materials include oxides (inorganic oxides, typically metal oxides) such as titanium oxide, zinc oxide, magnesium oxide, aluminum oxide, silicon oxide, cerium oxide, chromium oxide, zirconium oxide, manganese oxide, zinc oxide, iron oxide, tin oxide, and niobium oxide. Among these, inorganic oxides such as silicon oxide are particularly preferred. Other preferred examples of inorganic materials include metal foils (metal materials) such as aluminum foil, copper foil, and stainless steel (SUS). In addition to the inorganic material, the inorganic material-containing layer may or may not contain various organic materials, including organic polymer compounds that can be used as coating agents or binders.

[0184] The amount of inorganic material (e.g., inorganic oxides such as silicon dioxide) in the inorganic material-containing layer can be an appropriate amount to obtain the desired hydrophilic surface and is not limited to a specific range. For example, the inorganic material content in the inorganic material-containing layer can be approximately 30% by weight or more, approximately 50% by weight or more (e.g., more than 50% by weight) is appropriate, and it may also be approximately 70% by weight or more. In some preferred embodiments, the inorganic material content in the inorganic material-containing layer is approximately 90-100% by weight (e.g., approximately 95% by weight or more).

[0185] The method for forming the inorganic material-containing layer described above is not particularly limited and can be formed by an appropriate method depending on the desired thickness, etc. For example, inorganic materials formed in layers using known film deposition methods such as vacuum deposition, sputtering, or plating can be used. When using inorganic compounds as the inorganic material, various deposition methods can be used, such as physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating, or chemical vapor deposition (CVD) methods such as atomic layer deposition. The formation of a coating layer containing an inorganic polymer such as polysiloxane can be carried out by selecting an appropriate coating agent from known coating agents that can produce a surface exhibiting the desired water contact angle and using it by a conventional method.

[0186] The thickness of the inorganic material-containing layer is not particularly limited. In embodiments in which the substrate layer has a main substrate layer and an inorganic material-containing layer, from the viewpoint of not impairing the function of the substrate layer itself (main layer of the substrate layer), the thickness of the inorganic material-containing layer is specifically suitable to be approximately 5 μm or less (e.g., less than 5000 nm), and may also be approximately 2 μm or less (e.g., less than 2000 nm). In some embodiments, the thickness of the inorganic material-containing layer is less than 1000 nm, more preferably less than 500 nm, even more preferably less than 100 nm, and particularly preferably less than 50 nm, and may also be approximately 30 nm or less, approximately 20 nm or less, and approximately 15 nm or less (e.g., less than 10 nm). By using such a thin inorganic material-containing layer, desired properties such as barrier properties (moisture permeability prevention) can be impaired to the substrate layer without impairing the function of the substrate layer (main layer of the substrate layer). Using a thin inorganic material-containing layer is also advantageous from the viewpoint of lightness and optical properties. Furthermore, the thickness of the inorganic material-containing layer is suitable to be 1 nm or more (for example, 3 nm or more), but from the viewpoint of lowering moisture permeability, it may be approximately 5 nm or more, or approximately 10 nm or more (for example, 15 nm or more).

[0187] In an embodiment in which the above-mentioned substrate layer has a main substrate layer and an inorganic material-containing layer, the thickness of the main substrate layer (or the total thickness of the layers other than the inorganic material-containing layer if there are multiple layers other than the inorganic material-containing layer) is appropriately 50% or more of the total thickness of the substrate layer, preferably 70% or more, more preferably 90% or more, and may be 97% or more (for example, 99% or more).

[0188] The substrate layer may have a single-layer structure or a multilayer structure of two or more layers. An example of a single-layer substrate layer is a substrate layer made of a resin film. A substrate layer made of a resin film is suitable for surface protection sheets used in chemical treatment applications such as etching solutions. It also tends to have excellent flexibility and pliability. Examples of multilayer substrate layers include a structure made of a multilayer resin film, and a structure having a main substrate layer and an inorganic material-containing layer.

[0189] In some embodiments, the substrate layer (the substrate film used as the substrate layer) has a moisture permeability of 24 g / m² as measured by the cup method. 2 It is preferable that the moisture permeability is less than or equal to 18 g / (m²). By having a configuration with such limited moisture permeability, even when used in applications that come into contact with aqueous liquids, such as chemical treatment or hot water immersion, the presence of the low moisture permeability substrate layer moderately prevents the seepage of aqueous liquids into the adhesive layer, preventing or suppressing a decrease in adhesive strength due to water release. As a result, the adhesive strength to the adherend is maintained, and the surface protection sheet can maintain a state of close contact with the adherend. In some preferred embodiments, the moisture permeability of the substrate layer is approximately 18 g / (m²). 2 • day) or less, more preferably approximately 14 g / (m 2 • day) or less, more preferably about 10 g / (m 2 • day) or less, preferably about 8 g / (m 2 • day) or less, approximately 5g / (m 2 • day) or less (for example, approximately 3g / (m 2It may also be less than or equal to 1 day. Furthermore, if the surface protective sheet is exposed to heat such as hot water, if the above moisture permeability is excessively low, the water peelability may not be effectively exhibited due to aging caused by heat. From such a viewpoint, in some embodiments, the moisture permeability of the substrate layer is 1 g / (m 2 It is appropriate that the amount be 3g / (m³) or more, preferably about 3g / (m³). 2 • day) or more, for example 5g / (m 2 (Day) Super fine

[0190] More specifically, the above moisture permeability of the substrate layer is, for example, 23 g / (m²). 2 • 22g / (m) or more or less per day, or less than or equal to 22g / (m 2 • day) or more or less, 21g / (m 2 • 20g / (m) or more or less per day. 2 • 19g / (m) or more or less per day 2 • 18g / (m) or more or less per day. 2 • 17g / (m) or more or less per day. 2 • 16g / (m) or more or less per day. 2 • 15g / (m) or more or less per day 2 • 14g / (m) or more or less per day. 2 • day) or more or less, 13g / (m 2 • 12g / (m) or more or less per day. 2 • day) or more or less, 11g / (m 2 • 10g / (m) or more or less per day. 2 • 9g / (m) or more or less per day 2 • 8g / (m) or more or less per day 2 • day) or more or less, 7g / (m 2 • 6g / (m) or more or less per day 2 • 5g / (m) or more or less per day 2 • 4g / (m) or more or less per day 2 • 3g / (m) or more or less per day 2 • day) or more or less, 2g / (m 2 • day) or more or less, or 1g / (m2 It may be more than or less than (day)

[0191] The above-mentioned moisture permeability of the substrate layer can be obtained by selecting and using a suitable non-moisture-permeable or low-moisture-permeable substrate material. More specifically, the moisture permeability of the substrate layer is measured by the method described in the examples below.

[0192] The 25°C bending stiffness value of the base layer (the base film used as the base layer) is the same as the range of 25°C bending stiffness values ​​that the surface protection sheet can take, so repeated explanations are omitted. Similarly, the ranges of 25°C tensile modulus, 25°C 100% elongation stress, 25°C fracture stress, and 25°C fracture strain that the base layer can take are the same as the ranges of 25°C tensile modulus, 25°C 100% elongation stress, 25°C fracture stress, and 25°C fracture strain of the surface protection sheet, so repeated explanations are omitted. The 25°C bending stiffness, 25°C tensile modulus, 25°C stress at 100% elongation, 25°C fracture stress, and 25°C fracture strain of the base layer are measured in the same way as those of the surface protection sheet, except that the base layer (the base film used as the base layer) is used as the test specimen. The thickness and cross-sectional area of ​​the test specimen used to calculate the 25°C bending stiffness, 25°C tensile modulus, 25°C stress at 100% elongation, and 25°C fracture stress are those of the base layer. Furthermore, the 25°C bending stiffness value of the base layer may be the 25°C bending stiffness value of MD, the 25°C bending stiffness value of TD, and so on, it may be at least one of the 25°C bending stiffness values ​​of MD and TD, or it may be any unidirectional 25°C bending stiffness value regardless of whether it is MD or TD. Similarly, the 25°C tensile modulus of the base layer may be the 25°C tensile modulus of MD, the 25°C tensile modulus of TD, and so on, it may be at least one of the 25°C tensile modulus of MD and TD, or it may be any unidirectional 25°C tensile modulus regardless of whether it is MD or TD. Similarly, the 100% tensile stress, fracture stress, and fracture strain of the base layer may be MD measurements (100% tensile stress, fracture stress, or fracture strain), TD measurements, and therefore may be at least one of the MD and TD measurements, or they may be any unidirectional measurements, regardless of whether they are MD or TD.

[0193] The thickness of the base layer is not particularly limited and can be selected according to the purpose of protection and the manner of use. The thickness of the base layer may be, for example, approximately 1000 μm or less, approximately 300 μm or less, and from the viewpoint of weight reduction and thinning, approximately 200 μm or less is appropriate, preferably approximately 150 μm or less, more preferably approximately 100 μm or less, and may also be approximately 75 μm or less (typically less than 75 μm), approximately 50 μm or less, 40 μm or less, or 30 μm or less. When the thickness of the base layer is reduced, the flexibility of the surface protection sheet and its ability to conform to the surface shape of the adherend tend to improve. In addition, because the thickness of the base layer is limited, deformation (expansion and contraction) of the base layer due to heating is suppressed, so even when used in a manner in which it is heated, such as immersion in hot water, it tends to maintain adhesion to the adherend. Furthermore, from the viewpoint of handling and processability, the thickness of the base layer may be, for example, 2 μm or more, and may be greater than 5 μm. In some embodiments, the thickness of the substrate layer is suitable to be approximately 10 μm or more, preferably approximately 15 μm or more, more preferably approximately 20 μm or more, and may also be approximately 30 μm or more, 40 μm or more, or 50 μm or more. The greater the thickness of the substrate layer, the easier it is to obtain a high bending rigidity value and the easier it is to improve the resistance to peeling at the edges. In addition, the protective performance of the adherend against chemical penetration and the like tends to improve. In some other embodiments, the thickness of the substrate layer may be greater than 50 μm, greater than 75 μm, or 90 μm or more.

[0194] On the surface of the base material layer on the side of the adhesive layer, if necessary, conventional known surface treatments such as corona treatment, plasma treatment, etc., ultraviolet irradiation treatment, acid treatment, alkali treatment, application of an undercoat agent (primer), etc. may be performed. Such surface treatment can be a treatment for improving the adhesion between the base material layer and the adhesive layer, or in other words, the anchoring property of the adhesive layer to the base material layer. The composition of the primer is not particularly limited and can be appropriately selected from known ones. The thickness of the undercoat layer is not particularly limited, but for example, about 0.01 μm to 1 μm is appropriate, and about 0.1 μm to 1 μm is preferable. Also, on the surface of the main base material layer (typically the surface on the side of the inorganic material-containing layer), surface treatments such as the above-mentioned various surface treatments and antistatic treatment may be performed.

[0195] On the surface of the base material layer on the side opposite to the adhesive layer side (hereinafter also referred to as the back surface), if necessary, conventional known surface treatments such as release treatment, antistatic treatment, etc. may be performed. For example, by surface-treating the back surface of the base material layer with a release treatment agent, the rewinding force of the surface protection sheet in the form of a roll can be reduced. As the release treatment agent, a silicone-based release treatment agent, a long-chain alkyl-based release treatment agent, an olefin-based release treatment agent, a fluorine-based release treatment agent, a fatty acid amide-based release treatment agent, molybdenum sulfide, silica powder, etc. can be used.

[0196] <Total thickness> The thickness of the surface protection sheet disclosed herein (including the adhesive layer and the base layer, but not the release liner) is not particularly limited and can be 3 μm or more, may be 5 μm or more, and 10 μm or more is appropriate. From the viewpoint of adhesion to the adherend, such as the ability to follow steps, it is preferably 20 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, and may be 45 μm or more. When the surface protection sheet has a thickness of a predetermined value or more, the ability to prevent peeling at the edges tends to improve. Also, the greater the thickness of the surface protection sheet, the greater the ability to protect the adherend from chemical penetration, etc. In some embodiments, the thickness of the surface protection sheet may be greater than 50 μm, may be 60 μm or more, may be 70 μm or more, and may be 80 μm or more. In some other embodiments, the thickness of the surface protection sheet may be greater than 50 μm, may be greater than 75 μm, and may be 100 μm or more. The upper limit of the thickness of the surface protection sheet is, for example, 5 mm or less, may be 3 mm or less, and may be 1 mm or less. In some embodiments, the thickness of the surface protection sheet is suitable to be 300 μm or less, preferably 200 μm or less, more preferably 150 μm or less, and may also be 100 μm or less, 75 μm or less, 65 μm or less, or for example, 55 μm or less. By limiting the thickness of the surface protection sheet to a predetermined value or less, deformation (expansion and contraction) caused by heating is suppressed, and the surface protection sheet tends to maintain its adhesion to the substrate. Reducing the thickness of the adhesive sheet is also advantageous in terms of thinning, miniaturization, weight reduction, and resource conservation.

[0197] <Removable Liner> The release liner used in the surface protection sheet disclosed herein is not particularly limited, and for example, a release liner whose surface has been peeled off, such as a resin film or paper, or a release liner made of a low-adhesion material such as a fluoropolymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, polypropylene, etc.) can be used. For the above-mentioned peeling treatment, for example, a silicone-based or long-chain alkyl-based release agent can be used. In some embodiments, a peeled resin film can be preferably used as the release liner.

[0198] <Removal Method> This specification provides a method for peeling a surface protection sheet attached to an adherend (object to be protected). The peeling method includes a water peeling step in which, with an aqueous liquid present at the interface between the adherend and the surface protection sheet at the peeling front of the surface protection sheet from the adherend, the aqueous liquid is allowed to penetrate the interface in accordance with the movement of the peeling front, thereby peeling the surface protection sheet from the adherend. The water peeling step allows the surface protection sheet to be peeled off the adherend by effectively utilizing the aqueous liquid.

[0199] As the aqueous liquid, water or a mixed solvent mainly composed of water, with a small amount of additives as needed, can be used. Other solvents besides water that make up the mixed solvent can be lower alcohols (e.g., ethyl alcohol) or lower ketones (e.g., acetone) that can be uniformly mixed with water. As the additives, known surfactants can be used. From the viewpoint of avoiding contamination of the substrate, in some embodiments, an aqueous liquid substantially free of additives may be preferred. From the viewpoint of environmental hygiene, it is particularly preferable to use water as the aqueous liquid. The water used is not particularly limited, and depending on the application, considering the required purity and availability, for example, distilled water, deionized water, tap water, etc., can be used.

[0200] In some embodiments, the peeling method can preferably be carried out in a manner in which, for example, similar to the measurement of the normal water peeling force FW0, aqueous liquid is supplied to the adherend near the outer edge of the surface protective sheet attached to the adherend, and after the aqueous liquid has entered the interface between the surface protective sheet and the adherend from the outer edge of the surface protective sheet, the peeling of the surface protective sheet can proceed without supplying any new water (i.e., using only the aqueous liquid supplied to the adherend before the start of peeling). If the water that enters the interface between the surface protective sheet and the adherend in accordance with the movement of the peeling front is depleted during the water peeling process, water may be supplied intermittently or continuously after the start of the water peeling process. For example, when the adherend is absorbent, or when aqueous liquid tends to remain on the surface of the adherend or adhesive surface after peeling, it is preferable to supply water after the start of the water peeling process.

[0201] The amount of aqueous liquid supplied before the start of peeling is not particularly limited, as long as it is sufficient to introduce the aqueous liquid to the interface between the surface protection sheet and the adherend from outside the application area of ​​the surface protection sheet. The amount of aqueous liquid may be, for example, 5 μL or more, usually 10 μL or more is appropriate, and may also be 20 μL or more. Furthermore, there is no particular upper limit on the amount of aqueous liquid. In some embodiments, from the viewpoint of improving workability, the amount of aqueous liquid may be, for example, 10 mL or less, 5 mL or less, 1 mL or less, 0.5 mL or less, 0.1 mL or less, or 0.05 mL or less. By reducing the amount of aqueous liquid, the operation of removing the aqueous liquid by drying or wiping after peeling off the surface protection sheet can be omitted or simplified.

[0202] The operation of introducing an aqueous liquid into the interface between the surface protection sheet and the adherend from the outer edge of the surface protection sheet at the start of peeling can be carried out, for example, by inserting the tip of a jig such as a cutter knife or needle into the interface at the outer edge of the surface protection sheet, scratching and lifting the outer edge of the surface protection sheet with a hook or fingernail, or attaching a strong adhesive tape or suction cup to the back surface near the outer edge of the surface protection sheet and lifting the edge of the surface protection sheet. By forcibly introducing an aqueous liquid into the interface from the outer edge of the surface protection sheet in this way, a state in which an aqueous liquid is present at the interface between the adherend and the surface protection sheet can be efficiently created. Furthermore, it is possible to suitably achieve both good water peelability after initiating peeling by forcibly introducing an aqueous liquid into the interface and high water resistance reliability when such an operation is not performed.

[0203] <Application> The surface protection sheet disclosed herein can be used as a surface protection sheet for various applications. For example, in various processes such as chemical treatment with chemical solutions or physical treatment such as cutting and polishing of glass, semiconductor wafers, metal plates, etc., the surface protection sheet disclosed herein can be used by attaching it to, for example, the untreated surface of the object to be protected.

[0204] The type of object to be protected is not particularly limited. The surface protection sheet disclosed herein can be used to protect various components and materials. The surface protection sheet disclosed herein allows for peeling using water peeling, which prevents damage or deformation of the adherend during peeling, making it suitable for protecting glass materials such as alkali glass and semiconductor wafers. These materials typically have limited thickness and are brittle materials (also called hard brittle materials) that are prone to cracking, chipping, or fissures due to external forces during handling or peeling. By applying peeling using water peeling to such adherends, it is possible to effectively prevent damage to the adherend during peeling. The glass material to be protected may be, for example, a glass plate having a surface partially provided with a transparent conductive film (e.g., ITO (indium tin oxide) film) or FPC, such as those used in tablet computers, mobile phones, and organic LEDs (light-emitting diodes). Preferred examples of objects to be protected include glass plates such as window glass and cover glass used in foldable displays and rollable displays. These glass plates are made to be thin (for example, less than 100 μm thick), and are at greater risk of breakage. However, according to the technology disclosed herein, even when the object to be protected is made of such a thin, brittle material, damage to the object to be protected can be prevented during delamination.

[0205] The water contact angle of the surface of the object to be protected to which the surface protection sheet is attached is not particularly limited. In some embodiments, the surface of the object to be protected may be a hydrophilic surface such that the water contact angle is, for example, 60 degrees or less, preferably 50 degrees or less. In some preferred embodiments, the water contact angle of the surface may be, for example, 45 degrees or less, 40 degrees or less, 35 degrees or less, or 30 degrees or less. When the water contact angle is small, water tends to spread more easily along the surface of the adherend, and the desired water-removability tends to be easier to obtain. The surface protection sheet disclosed herein can be preferably used to protect a member having a surface made of a material (for example, a glass such as an alkali glass plate or alkali-free glass) with a water contact angle of about 20 degrees or less (for example, 15 degrees or less, and even 10 degrees or less). The lower limit of the water contact angle of the surface of the object to be protected is, in principle, 0 degrees. In some embodiments, the water contact angle of the surface of the object to be protected may be greater than 0 degrees, 1 degree or more, 3 degrees or more, or 5 degrees or more. In some other embodiments, the water contact angle of the surface of the object to be protected may be greater than 30 degrees, greater than 50 degrees, or greater than 60 degrees (e.g., 70 degrees or more). The surface protection sheets disclosed herein can be used with various materials having different water contact angles. The water contact angle of the surface of the object to be protected is measured by a method similar to the contact angle measurement method described in the embodiments below.

[0206] The thickness of the object to be protected (e.g., a glass plate or semiconductor wafer) is not particularly limited and may be, for example, approximately 1 mm or less, or approximately 500 μm or less, or approximately 300 μm or less. Since the effect of the technology disclosed herein (prevention of damage during peeling) is more effectively exerted on thin objects to be protected, the above thickness may be, for example, approximately 150 μm or less, or approximately 100 μm or less. The lower limit of the above thickness is, for example, approximately 10 μm or more (e.g., 30 μm or more).

[0207] In some preferred embodiments, the surface protection sheet is suitable for use in processes of chemically and / or physically treating objects to be protected, such as glass or semiconductor wafers, in a liquid. In the above applications, the surface protection sheet disclosed herein can have the necessary adhesion to the object to be protected during the processing, and when peeling after processing, it can be smoothly peeled off from the object to be protected (adherent) using water peeling. The above chemical processing includes processing with chemical solutions containing acids or alkalis, such as etching solutions such as hydrofluoric acid aqueous solution. For example, the surface protection sheet disclosed herein can be preferably used in etching processes in which glass is dissolved with a chemical solution (etching solution) to adjust the thickness of glass or to remove burrs or microcracks formed on the cut edges of glass, anti-glare processing, etching processes in which the surface of metal is partially corroded with a chemical solution (etching solution), and plating processes in which connection terminals of circuit boards (printed circuit boards, flexible printed circuit boards (FPCs), etc.) are partially plated with a chemical solution (plating solution). In particular, it can be preferably applied to applications in which etching processes are performed using acidic chemical solutions such as hydrofluoric acid solution. Physical processing also includes polishing and cutting the surface of the object to be protected.

[0208] The surface protection sheet disclosed herein is preferably used in glass slimming processes. For example, a glass plate used as an optical component can be thinned by a glass slimming process using a chemical solution such as an aqueous hydrofluoric acid solution. In this glass slimming process, a surface protection sheet may be used to protect the untreated surface of the glass. Although not particularly limited, in the glass slimming process, the glass plate is thinned to, for example, approximately 150 μm or less (for example, approximately 100 μm or less). The thickness of the glass plate before the glass slimming process is, for example, approximately 0.15 mm to 5 mm, and may be approximately 300 μm or more (for example, approximately 500 μm to 1000 μm). Such thinned glass is prone to cracking due to external forces during peeling. By using the surface protection sheet disclosed herein, the problem of glass breakage when peeling off the surface protection sheet can be eliminated, or the risk can be significantly reduced.

[0209] Furthermore, the surface protection sheet can also be preferably used in the manufacture of semiconductors. The semiconductor wafer may be, for example, a silicon wafer, a silicon carbide (SiC) wafer, a nitride semiconductor wafer (such as silicon nitride (SiN) or gallium nitride (GaN)), or a compound semiconductor wafer such as a gallium arsenide wafer. In the manufacture of the semiconductor, the surface protection sheet disclosed herein can be preferably used in semiconductor wafer processing (typically silicon wafer processing) processes, such as a process to thin the semiconductor wafer (more specifically, a back grinding process to polish the back surface of the semiconductor wafer) or a process to cut the semiconductor wafer (such as a dicing process). Although not particularly limited, in the back grinding process, the semiconductor wafer is thinned to, for example, approximately 150 μm or less (for example, approximately 100 μm or less). The thickness of the semiconductor wafer before back grinding may be approximately 300 μm or more (for example, around 500 μm to 1000 μm). Since the semiconductor manufacturing process described above may involve exposure to temperatures higher than room temperature (e.g., 40°C to 90°C, preferably 40°C to 60°C), the use of a surface protection sheet that can maintain good properties (adhesion and water release properties) against such heating is particularly meaningful. Surface protection sheets used in such applications are sometimes simply called backgrinding sheets or dicing sheets.

[0210] The surface protection sheets used for the various surface protection applications described above can be used in a manner in which one or more objects to be treated (which are also the objects to be protected) are transported continuously or individually into water, such as in a chemical tank or a washing tank, using a transport means such as rollers, with one surface protection sheet attached to one side of each object, and the desired treatment is carried out. During such transport and in the process after transport (including placement and setting into equipment, etc.), the objects to be treated may be subjected to external forces such as shocks, vibrations, and deformations, either inevitably or unintentionally. For example, multiple rollers arranged at predetermined intervals may be used as a transport means in chemical treatment or washing treatment, but in transport using such rollers, a peeling load with a shallow peeling angle is likely to be continuously applied due to the height difference between the rollers, vibrations, etc. The surface protection sheets disclosed herein have excellent resistance to peeling at the edges against external forces such as vibrations, and therefore have the advantage that even when used in a process that includes a step of treating the objects to be treated, for example in a liquid, while the sheets are attached to the objects to be treated as described above, peeling from the edges is less likely to occur due to external forces such as vibrations during the process. Furthermore, in embodiments in which physical processing such as cutting or polishing is performed on objects to be processed, such as semiconductor wafers, the external force in said physical processing becomes a peeling load. With the surface protection sheet disclosed herein, peeling from the edges is less likely to occur even when a physical load is applied during the physical processing step. Note that the vibration in the transport process and the physical load (also called peeling load) in the physical processing process typically include a load applied in the thickness direction of the surface protection sheet.

[0211] Furthermore, the objects to be protected may include, for example, display devices (image display devices) such as liquid crystal displays, organic EL (electroluminescent) displays, PDP (plasma display panels), and electronic paper, as well as equipment (optical equipment) such as input devices such as touch panels, and in particular, components that make up portable electronic devices such as foldable displays and rollable displays.

[0212] Examples of portable electronic devices include, for example, mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear-type devices worn on the wrist like watches, modular devices attached to a part of the body with clips or straps, eyewear-type devices including glasses (monocular and binocular, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information equipment, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" means not merely being able to carry something, but having a level of portability that allows an individual (a typical adult) to carry it relatively easily.

[0213] <Protection method> As described above, this specification provides a surface protection method using a surface protection sheet disclosed herein. This surface protection method includes the steps of: attaching a surface protection sheet to at least a part of an object to be protected (a surface or portion to be protected); performing a treatment on the object to be protected to which the surface protection sheet is attached (e.g., chemical treatment, hot water immersion treatment, water immersion treatment, physical treatment such as cutting or polishing); and peeling the surface protection sheet from the object to be protected after the treatment. Here, the step of peeling the surface protection sheet from the object to be protected preferably includes the water peeling step described above. Since the above protection method includes treatment on the object to be protected (object to be treated), it is also called a treatment method. Details of the surface protection sheet, water peeling step, object to be protected, treatment (glass slimming treatment, semiconductor wafer thinning treatment, etc.), and other matters (applications, etc.) are as described above, so repeated explanations are omitted. Typical examples of objects to be protected include glass plates subjected to treatment such as glass slimming, semiconductor wafers, etc. Therefore, this specification may provide a glass slimming method and a semiconductor manufacturing method including the above steps.

[0214] <Processing method> Furthermore, as described above, this specification provides a processing method using the surface protection sheet disclosed herein. This processing method includes the steps of: attaching the surface protection sheet to the surface of an object; applying a physical load to the object to which the surface protection sheet is attached in the thickness direction of the surface protection sheet; and removing the surface protection sheet from the object. In the object, the surface to which the surface protection sheet is attached is typically a surface with a water contact angle of 20 degrees or less. The step of removing the surface protection sheet from the object is preferably a step of peeling and removing the surface protection sheet from the object in the presence of water. The processing method may also typically include a step of performing a treatment on the object (object to be treated) to which the surface protection sheet is attached. In such a processing step, the object to be treated may come into contact with a liquid (e.g., an aqueous solution). The processing method disclosed herein may also include at least one of the steps of the protection method described above. The surface protection sheet used is the surface protection sheet disclosed herein. In some embodiments, the bending stiffness value at 25°C is 1.0 × 10 -6 ~1.0×10 -2 Pa·m 3A surface protection sheet can be used that is within the specified range and satisfies the requirement that the water peeling force FW0 is 1.0 N / 20 mm or less. In some other embodiments, a surface protection sheet can be used that satisfies the requirement that the water peeling force FW0 is 1.0 N / 20 mm or less and the initial peeling force is 0.5 N / 10 mm or more. Examples of processing include glass slimming and semiconductor processing, and typical examples of objects to be processed include glass plates and semiconductor wafers on which glass slimming or other processing is performed. Typical examples of processes on which a physical load is applied to an object to which the surface protection sheet is attached in the thickness direction of the surface protection sheet include transporting the object and physical processing processes on the object. As described above, a glass slimming method and a semiconductor manufacturing method including the above processes can be provided according to this specification. Details of the surface protection sheet, water peeling, removal process, object (object to be processed), processing (glass slimming process, semiconductor wafer thinning process, etc.), and other matters (applications, etc.) are as described above, so repeated explanations will be omitted. [Examples]

[0215] The following describes several embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments. In the following description, "parts" and "%" refer to weight unless otherwise specified.

[0216] <Evaluation Method> [Normal adhesive force F0] A test specimen is prepared by cutting the surface protection sheet of the object to be measured to a size of 20 mm in width and 100 mm in length. In an environment of 23°C and 50% RH, the release liner covering the adhesive surface (adhesive layer surface) is peeled off from the test specimen, and the exposed adhesive surface is pressed onto an alkali glass plate (the surface of alkali glass having a water contact angle of 20 degrees or less) by passing a 2 kg rubber roller back and forth once. The evaluation sample obtained in this way is then subjected to autoclaving (50°C, 0.5 MPa, 15 minutes). After removing the evaluation sample from the autoclave, it is kept in an environment of 23°C and 50% RH for 1 hour. Then, in the same environment, the peel strength of the test piece from the adherend is measured using a tensile testing machine at a tensile speed of 300 mm / min and a peel angle of 180 degrees, according to JIS Z0237:2009, 10.4.1 Method 1: 180° peel adhesion strength to a test plate. (However, the peel strength is measured until the water peel strength measurement described below is performed, i.e., until distilled water is supplied to the peel interface.) Three measurements are performed, and the average value is taken as the normal adhesive strength F0 [N / 20mm]. The measurement of the normal adhesive strength F0 is performed so that the peel of the test piece attached to the adherend progresses from bottom to top. An alkali glass plate (product name "Micro Slide Glass S200423", manufactured by Matsunami Glass Industry Co., Ltd.) can be used as the adherend. For tensile testing, a universal tensile and compression testing machine (device name "Tensile and Compression Testing Machine, TCM-1kNB", manufactured by Minebea Co., Ltd.) or an equivalent product can be used. For measurement, the test specimen may be reinforced by attaching a suitable backing material to the opposite side of the surface protection sheet (the surface opposite the adhesive side) as needed. As a backing material, for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm can be used.

[0217] [Normal water peeling force FW0] In the measurement of the normal adhesive strength F0 described above, 20 μL of distilled water is supplied to the point where the test piece begins to separate from the adherend (the peeling front) while measuring the peel strength of the test piece from the adherend, and the peel strength after the supply of distilled water is measured. The measurement is performed for each measurement of the normal adhesive strength F0 (i.e., 3 times), and the average value of these measurements is taken as the normal water peel strength FW0 [N / 20 mm]. The measurement conditions for peel strength after supplying distilled water shall conform to JIS Z0237:2009, 10.4.1 Method 1: 180° peel adhesion to the test plate. Specifically, the conditions shall be a tensile testing machine at a test temperature of 23°C with a tensile speed of 300 mm / min and a peel angle of 180 degrees. Furthermore, the measurement of the normal water peel strength FW0 may be performed by measuring the normal adhesive strength F0 and the normal water peel strength FW0 consecutively for each test specimen, or the measurement of the normal adhesive strength F0 and the normal water peel strength FW0 may be performed on different test specimens. For example, when it is difficult to prepare test specimens of sufficient length for continuous measurement, a method of measurement using different test specimens can be adopted. The adherend, tensile testing machine, and other matters are the same as for the measurement of the normal adhesive strength F0.

[0218] [Adhesion strength F1 after 30 minutes immersion in warm water] The adhesive strength F1 after 30 minutes of immersion in hot water is measured in the same manner as the normal adhesive strength F0, except that the evaluation sample (alkali glass plate with a test piece (surface protective sheet) attached) is immersed in hot water at 60°C ± 2°C for 30 minutes, then removed from the hot water, the adhering water is wiped off, and the peel strength is measured. Specifically, similar to the measurement of the normal adhesive strength F0, a test specimen is prepared by cutting the surface protection sheet of the object to be measured to a size of 20 mm in width and 100 mm in length. In an environment of 23°C and 50% RH, the release liner covering the adhesive surface (adhesive layer surface) is peeled off the test specimen, and the exposed adhesive surface is pressed onto an alkali glass plate, which is the adherend, by passing a 2 kg rubber roller back and forth once. The evaluation sample obtained in this way is subjected to autoclaving (50°C, 0.5 MPa, 15 minutes). The evaluation sample removed from the autoclave is immersed in a water bath containing hot water at a set temperature of 60°C ± 2°C for 30 minutes. Ion-exchanged water or distilled water is used as the hot water. In the hot water, the evaluation sample is held horizontally with the adhesive layer side facing upwards. The distance from the top surface of the evaluation sample to the water surface (immersion depth) should be 10 mm or more (for example, about 10 mm to 100 mm). Next, the evaluation sample is removed from the hot water, and any water adhering to it is gently wiped off. Then, in an environment of 23°C and 50% RH, the peel strength of the test piece from the adherend is measured using a tensile testing machine in accordance with JIS Z0237:2009, 10.4.1 Method 1: 180° peel adhesion strength to a test plate, at a tensile speed of 300 mm / min and a peel angle of 180 degrees (however, the peel strength is measured until the water peel strength measurement described below is performed, i.e., until distilled water is supplied to the peel interface). Three measurements are performed, and the average value is taken as the adhesive strength F1 [N / 20mm] after 30 minutes of hot water immersion. The time from removing the evaluation sample from the hot water to measuring the peel strength should be within 10 minutes. The adherend, tensile testing machine, and other matters are the same as for the measurement of the normal adhesive strength F0.

[0219] [Water peeling strength after 30 minutes of soaking in warm water: FW1] The water peeling force FW1 after 30 minutes of immersion in hot water is measured in the same manner as the water peeling force FW0 under normal conditions, except that the evaluation sample (alkali glass plate with a test piece (surface protective sheet) attached) is immersed in hot water at 60°C ± 2°C for 30 minutes, then removed from the hot water, the adhering water is wiped off, and the water peeling force is measured. Specifically, in the measurement of the adhesive strength F1 after 30 minutes of hot water immersion described above, after 30 minutes of hot water immersion, while measuring the peel strength of the test piece from the adherend, 20 μL of distilled water is supplied to the point where the test piece begins to separate from the adherend (the peel front), and the peel strength after the supply of distilled water is measured. The measurement is performed for each measurement of the adhesive strength F1 after 30 minutes of hot water immersion (i.e., 3 times), and the average value of these measurements is taken as the water peel strength FW1 [N / 20mm] after 30 minutes of hot water immersion. The measurement conditions for peel strength after supplying distilled water shall conform to JIS Z0237:2009, 10.4.1 Method 1: 180° peel adhesion to the test plate. Specifically, the conditions shall be a tensile testing machine at a test temperature of 23°C with a tensile speed of 300 mm / min and a peel angle of 180 degrees. Furthermore, the measurement of the water peel strength FW1 after 30 minutes of hot water immersion may be performed consecutively for each test specimen, either by measuring the adhesive strength F1 and the water peel strength FW1 after 30 minutes of hot water immersion, or by measuring the adhesive strength F1 and the water peel strength FW1 on different test specimens. The adherend, tensile testing machine, and other matters are the same as for the measurement of the normal adhesive strength F0.

[0220] In the above measurements (measurements of F0, FW0, F1, and FW1), the adherend used is one in which the contact angle of the surface to which the test piece is bonded with distilled water is 20 degrees or less (e.g., 5 to 10 degrees). Specifically, the adherend can be an alkali glass plate made by the float method, in which the contact angle of the surface to which the test piece is bonded with distilled water is 20 degrees or less (e.g., 5 to 10 degrees). As such an adherend, the alkali glass plate manufactured by Matsunami Glass Industry Co., Ltd. may be used, but is not limited to this, and equivalent products of the alkali glass plate manufactured by Matsunami Glass Industry Co., Ltd. or other alkali glass plates can also be used.

[0221] Furthermore, the contact angle of the alkali glass plate is measured by the following method. Specifically, under a measurement atmosphere of 23°C and 50% RH, the measurement is performed using the droplet method with a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DMo-501", control box "DMC-2", control and analysis software "FAMAS (version 5.0.30)"). The amount of distilled water dropped is 2 μL, and the contact angle is calculated from the image 5 seconds after dropping using the Θ / 2 method (performed at N5).

[0222] Furthermore, the inventors have confirmed that the adhesive strength and water-peelability after immersion in hot water, respectively, show a certain high correlation with the adhesive strength and water-peelability after immersion in hydrofluoric acid aqueous solution. Based on this finding, the adhesive strength and water-peelability after immersion in hot water are used as evaluation indicators for the applicability of surface protection sheets in liquid treatment applications, including chemical immersion.

[0223] [60°C loss modulus G″] The 60°C loss modulus G″[Pa] of the adhesive layer is determined by dynamic viscoelasticity measurement. Specifically, an adhesive layer approximately 2 mm thick is prepared by stacking multiple adhesive layers to be measured. A sample of this adhesive layer, punched into a 7.9 mm diameter disc, is fixed between parallel plates, and dynamic viscoelasticity measurement is performed using a viscoelasticity tester (e.g., ARES or equivalent manufactured by T.A. Instruments) under the following conditions to determine the loss modulus G″[Pa] at 60°C. • Measurement mode: Shear mode Temperature range: -70℃ to 150℃ • Heating rate: 5°C / min ·Measurement frequency: 1Hz The adhesive layer to be measured can be formed by applying the corresponding adhesive composition in layers and then drying or curing it.

[0224] [Moisture permeability] The moisture permeability of the substrate (layer) and surface protective sheet is measured in accordance with the moisture permeability test (cup method) of JIS Z0208. The method for measuring the moisture permeability of the substrate is as follows: Specifically, the substrate for each example is cut into a circle with a diameter of 7 cm and used as the evaluation sample. A predetermined amount of calcium chloride is placed inside a test cup (made of aluminum, a moisture permeable cup specified in JIS Z0208), and the mouth of the cup is sealed with the evaluation sample. Specifically, the evaluation sample is placed on the test cup so as to cover the mouth of the test cup, and an annular packing and lid having the same shape as the rim of the opening of the test cup (a circle with an inner diameter of 6 cm, an outer diameter of 9 cm, and a rim width of 1.5 cm) is placed on top and secured with a special screw to seal the inside of the test cup. Next, the cup covered with the evaluation sample is stored at 40°C and 92% RH for 24 hours, and the change in total weight before and after storage (specifically, the weight change based on the amount of water absorbed by calcium chloride) is measured to determine the moisture permeability [g / (m³]. 2 The moisture permeability of the surface protection sheet is measured in the same way as the moisture permeability measurement method for the substrate, except that the surface protection sheet is placed with the cup side as the adhesive surface, the mouth of the cup is sealed, and the measurement is taken.

[0225] [Tensile test] A test specimen is prepared by cutting the surface protection sheet into strips 10 mm wide. A stress-strain curve is obtained by stretching this test specimen under the following conditions in accordance with JIS K 7161. (Stretching conditions) Measurement temperature: 25℃ Tensile speed: 300 mm / min Chuck spacing: 50mm For tensile testing, a universal tensile and compression testing machine (device name "Tensile and Compression Testing Machine, TCM-1kNB", manufactured by Minebea Co., Ltd.) or an equivalent product can be used. The tensile modulus at 25°C [Pa] is determined from the linear regression of the stress-strain curve described above. The tensile modulus at 25°C is calculated by converting the measured thickness of the surface protection sheet (subtracting the thickness of the adhesive layer) or the thickness of the base material layer itself into a value per unit area of ​​the base material layer. Furthermore, from the above tensile test, the stress at 100% elongation at 25°C [N / mm²] 2 ], fracture stress [N / mm 2 Measure the fracture strain [%]. The stress at 100% elongation mentioned above is the load [N] measured when the test specimen is 100% elongated in the tensile test, measured across the cross-sectional area of ​​the base material layer [mm²] of the test specimen. 2 This is the value obtained by dividing the load [N] at the time of fracture of the test specimen in the tensile test by the cross-sectional area [mm²] of the base material layer of the test specimen. The above fracture stress is calculated by dividing the load [N] at the time of fracture of the test specimen in the above tensile test by the cross-sectional area [mm²] of the base material layer of the test specimen. 2 This value is obtained by dividing by [ ], and the above fracture strain [%] is the elongation [%] of the above test specimen at fracture. In this embodiment, the measured values ​​(tensile modulus, stress at 100% elongation, fracture stress, and fracture strain) are measured for the MD of the surface protection sheet (more specifically, the base layer) with the tensile direction of the tensile test aligned with the MD of the tensile test. However, the tensile test can be performed on the MD of the surface protection sheet, or by changing the way the test specimen is cut, the tensile test can be performed on the TD of the surface protection sheet to obtain the TD measurement value. Alternatively, it is possible to perform the tensile test in any direction, regardless of whether it is the MD or TD, to obtain the measurement value.

[0226] [25°C Bending Stiffness Value] Surface protection sheet bending stiffness value D[Pa·m] at 25°C 3 ] is the formula: D=Eh 3 / 12(1-ν 2 ); It can be calculated from the above equation. In the above equation, E is the 25°C tensile modulus of the surface protection sheet [Pa], and h is the thickness of the base layer [m]. ν is Poisson's ratio, and in the above equation, ν = 0.35. In this embodiment, the 25° bending stiffness value is the 25° bending stiffness value for MD. However, by changing the method of cutting the test specimen as described above, it is possible to obtain not only the 25° bending stiffness value for MD but also the 25° bending stiffness value for TD, or to obtain the 25° bending stiffness value for any one direction, regardless of whether it is MD or TD.

[0227] [Underwater triggering separation force] A test specimen is prepared by cutting the surface protection sheet of the object to be measured to a size of 10 mm in width and 100 mm in length. In an environment of 23°C and 50% RH, the release liner covering the adhesive surface (adhesive layer surface) is peeled off the test specimen, and the exposed adhesive surface is pressed onto an alkali glass plate (the surface of alkali glass having a water contact angle of 20 degrees or less) using a 2 kg rubber roller with one back-and-forth motion. At this time, one end of the test specimen in the longitudinal direction is attached so as to extend beyond the adherend. The evaluation sample obtained in this way is subjected to autoclaving (50°C, 0.5 MPa, 15 minutes). After removing the evaluation sample from the autoclave, it is kept in an environment of 23°C and 50% RH for 1 hour, and then immersed in water at room temperature (23°C to 25°C). Deionized water or distilled water is used as the water. In the water, the evaluation sample is held horizontally with the side to which the test specimen is attached facing upwards. The distance from the top surface of the evaluation sample to the water surface (immersion depth) shall be 10 mm or more (for example, approximately 10 mm to 100 mm). With the evaluation sample placed in the water in this manner, within 1 minute of the start of immersion, a peel test shall be performed using a tensile testing machine at 23°C and 50% RH, starting from one end of the longitudinal direction of the test piece (the end extending beyond the adherend), at a tensile speed of 1000 mm / min and a peel angle of 20 degrees, and the maximum stress applied at the initial stage of peeling shall be recorded. Three measurements shall be taken, and the average of the above maximum stresses shall be taken as the water-induced peel force [N / 10 mm]. If the underwater initial peeling force is 0.2 N / 10 mm or more, it is judged to have excellent resistance to edge peeling against external forces such as vibration during the conveying process. External forces such as vibration that can cause edge peeling of surface protection sheets during conveying and other processes are considered to be high-speed peeling loads applied at a relatively shallow angle to the object being protected. A surface protection sheet that exhibits the above underwater initial peeling force of 0.2 N / 10 mm or more, when performed under the conditions of a peeling angle of 20 degrees and a peeling speed of 1000 mm / min, is judged to have excellent resistance to edge peeling against external forces such as vibration because the stress before peeling due to the above peeling load is large. In the above test, an alkali glass plate (product name "Micro Slide Glass S200423", manufactured by Matsunami Glass Industry Co., Ltd.) is used as the adherend. A universal tensile and compression testing machine (device name "Tensile and Compression Testing Machine, TCM-1kNB", manufactured by Minebea Co., Ltd.) or an equivalent is used as the tensile testing machine. For measurement, the test specimen may be reinforced by attaching a suitable backing material to the opposite side of the surface protection sheet (the surface opposite the adhesive side) as needed. For example, a PET film with a thickness of about 25 μm can be used as the backing material.

[0228] [20-degree trigger peeling force] A test specimen is prepared by cutting the surface protection sheet of the object to be measured to a size of 10 mm in width and 100 mm in length. In an environment of 23°C and 50% RH, the release liner covering the adhesive surface (adhesive layer surface) is peeled off the test specimen, and the exposed adhesive surface is pressed onto an alkali glass plate (the surface of alkali glass having a water contact angle of 20 degrees or less) using a 2 kg rubber roller, moving it back and forth once. At this time, one end of the test specimen in the longitudinal direction is attached so as to extend beyond the adherend. The evaluation sample obtained in this manner is kept in an environment of 23°C and 50%RH for 24 hours. Then, 20 μL of distilled water is dropped between the adhesive surface of the test piece that protrudes from the adherend and the adherend (the end of the adherend). In an environment of 23°C and 50%RH, a peel test is performed using a tensile testing machine from one end in the longitudinal direction of the test piece (the end that protrudes from the adherend) under the conditions of a temperature of 23°C, a peel angle of 20 degrees, and a tensile speed of 1000 mm / min, and the maximum stress applied at the initial stage of peeling is recorded. Three measurements are taken, and the average value of the above maximum stresses is taken as the 20-degree trigger peel force [N / 10 mm]. The 20-degree trigger peeling force mentioned above is measured by dropping water onto the point where peeling begins, but the effect of the presence or absence of water at the start of peeling is negligible. As stated above, the trigger peeling force is the maximum stress applied at the beginning of peeling, and the water peelability (reduction in peeling force due to the presence of water) in the technology disclosed herein is a characteristic that appears after peeling has started (after the trigger peeling force has been detected), and the water peeling force is the peeling strength measured after peeling has started. With a surface protection sheet having a 20-degree trigger peeling force of a predetermined value or higher, peeling from the edges of the surface protection sheet is prevented or suppressed at the edges of the surface protection sheet in response to the physical load applied in the thickness direction of the surface protection sheet, regardless of whether water is present or not. In the above test, an alkali glass plate (product name "Micro Slide Glass S200423", manufactured by Matsunami Glass Industry Co., Ltd.) is used as the adherend. A universal tensile and compression testing machine (device name "Tensile and Compression Testing Machine, TCM-1kNB", manufactured by Minebea Co., Ltd.) or an equivalent is used as the tensile testing machine. For measurement, the test specimen may be reinforced by attaching a suitable backing material to the opposite side of the surface protection sheet (the surface opposite the adhesive side) as needed. For example, a PET film with a thickness of about 25 μm can be used as the backing material.

[0229] [Rebound resistance (aluminum rebound resistance)] The adhesive layer protected by the release film is cut to a size of 10 mm wide and 110 mm long. The surface of an aluminum plate measuring 10 mm wide, 110 mm long, and 0.03 mm thick is cleaned with toluene, the release liner covering one side of the adhesive layer is peeled off, and the exposed adhesive surface is bonded to the surface of the aluminum plate to create a measurement sample (a laminate of aluminum plate and adhesive layer) in which the adhesive layer is backed by the aluminum plate. After leaving this measurement sample standing at 23°C for one day, with the aluminum plate side of the measurement sample facing inward, the longitudinal direction of the measurement sample is curved along the outer circumference of a cylindrical glass tube with a radius of 17 mm for 10 seconds. Next, the release liner covering the adhesive layer of the measurement sample is peeled off, and it is pressed onto the surface of an alkali glass plate (the substrate) using a laminator at a bonding pressure of 0.25 MPa and a bonding speed of 0.3 m / min, and the progress is observed at 23°C and 50% RH. In Experiment 2, described below, the distance [mm] the measurement sample peeled off from the adherend (peel length from one end) one hour after being pressed onto the adherend was measured and recorded as an evaluation result of the rebound resistance. The above rebound resistance test evaluates the resistance of the adhesive to peeling at the edges of the surface protection sheet against a physical load (peeling load) in a direction perpendicular to the surface direction of the surface protection sheet (the thickness direction of the surface protection sheet). In the above rebound resistance test, an adhesive that does not peel at the edges or peels only slightly is evaluated as having excellent edge peeling prevention properties against the physical load applied in the thickness direction. Furthermore, the inventors have confirmed that the peel length in the above rebound resistance test correlates with the 20-degree trigger peel force. Specifically, they have confirmed that the shorter the peel length at the edges in the rebound resistance test, the higher the 20-degree trigger peel force tends to be. This is thought to be because, in peeling at a peel angle of 20 degrees, the proportion of components acting in the vertical direction (90 degrees) is high in the peel stress of the adhesive. In addition, water was not applied in the rebound resistance test in order to eliminate the effects of swelling of the adhesive due to water in the evaluation of rebound resistance over time.

[0230] Experiment 1 <Preparation of adhesive> (Adhesive S1) In a reaction vessel equipped with a condenser, nitrogen inlet tube, thermometer, and stirring device, 72 parts of 2-ethylhexyl acrylate (2EHA), 14 parts of N-vinyl-2-pyrrolidone (NVP), 13 parts of 2-hydroxyethyl acrylate (HEA), and 1 part of methyl methacrylate (MMA) were charged as monomer components, 0.12 parts of α-thioglycerol was added as a chain transfer agent, and ethyl acetate was charged as a polymerization solvent. 0.2 parts of AIBN was added as a thermal polymerization initiator, and solution polymerization was carried out under a nitrogen atmosphere to obtain a solution containing an acrylic polymer s1 with an Mw of 300,000.

[0231] To the solution obtained above, 0.75 parts on a solid basis of isocyanate crosslinking agent (trimethylolpropane / xylylene diisocyanate adduct, manufactured by Mitsui Chemicals, trade name: Takenate D-110N, solid content concentration 75%), 0.01 parts dioctyl tin dilaurate (manufactured by Tokyo Fine Chemical Co., Ltd., trade name: Envirizer OL-1) as a crosslinking accelerator, 3 parts acetylacetone as a crosslinking retarder, and 0.3 parts nonionic surfactant (polyoxyethylene sorbitan monolaurate, HLB 16.7, trade name: Leodol TW-L120, manufactured by Kao Corporation) were added per 100 parts of the monomer component used to prepare the solution, and the mixture was uniformly mixed to prepare solvent-type adhesive composition S1.

[0232] Two release films were prepared: one 38 μm thick polyester film with a release surface on one side (Mitsubishi Plastics, MRF#38) and another 38 μm thick polyester film with a release surface on one side (Mitsubishi Plastics, MRE#38). The solvent-type adhesive composition S1 prepared above was applied to the release surface of one of the release films (MRF#38), and dried at 60°C for 3 minutes, then at 120°C for 3 minutes, to form an adhesive layer with a thickness of 25 μm. The release surface of the other release film (MRE#38) was bonded to this adhesive layer for protection. In this way, an adhesive layer S1 with its surface protected by two release films was obtained.

[0233] (Adhesive E1) An aqueous emulsion of monomer mixtures (monomer emulsion) was prepared by mixing 85 parts of 2EHA, 13 parts of methyl acrylate (MA), 1.2 parts of acrylic acid (AA), 0.75 parts of methacrylic acid (MAA), 0.01 parts of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., KBM-403), 0.05 parts of t-dodecyl mercaptan as a chain transfer agent, and 1.9 parts of an emulsifier (manufactured by Kao Corporation, Latemul E-118B) in 100 parts of deionized water and emulsifying the mixture. The monomer emulsion was placed in a reaction vessel equipped with a condenser, nitrogen inlet tube, thermometer, and stirring device, and stirred at room temperature for at least 1 hour while introducing nitrogen gas. Next, the system was heated to 60°C, and 0.1 parts of 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (Wako Pure Chemical Industries, Ltd., VA-057) was added as a polymerization initiator. The mixture was reacted at 60°C for 6 hours to obtain an aqueous dispersion of acrylic polymer e1. After cooling the system to room temperature, 10 parts of tackifying resin emulsion (Arakawa Chemical Industries, Ltd., Super Ester E-865NT, an aqueous dispersion of polymerized rosin ester with a softening point of 160°C) were added to the aqueous dispersion of acrylic polymer e1 by solids per 100 parts of solids. Furthermore, emulsion-type adhesive composition E1 was prepared by adjusting the pH to approximately 7.5 and the viscosity to approximately 9 Pa·s using 10% aqueous ammonia as a pH adjuster and polyacrylic acid (aqueous solution with 36% non-volatile content) as a thickener.

[0234] Two release films were prepared: one 38 μm thick polyester film with a release surface on one side (Mitsubishi Plastics, MRF#38) and another 38 μm thick polyester film with a release surface on one side (Mitsubishi Plastics, MRE#38). Adhesive composition E1 was applied to the release surface of one of the release films (MRF#38), and dried at 120°C for 3 minutes to form a 25 μm thick adhesive layer E1. The release surface of the other release film (MRE#38) was then bonded to this adhesive layer for protection. In this way, an adhesive layer E1 with its surface protected by two release films was obtained. The 60°C loss modulus G″ of the adhesive layer E1 was 12.3 kPa.

[0235] <Example 1> As the base layer material, a 60 μm thick stretched polypropylene (OPP) film (product name "Trefan #60-2500", manufactured by Toray Industries, Inc., biaxially oriented PP film, moisture permeability 2.1 g / m²) is used. 2 A release liner was prepared. The release liner covering one surface of the adhesive layer S1 with a release liner obtained above was peeled off, and the exposed surface (adhesive surface) was pressed onto the surface of the OPP film by passing a 2 kg rubber roller back and forth twice. In this way, a surface protection sheet (single-sided adhesive sheet with a base layer) with the adhesive surface protected by the release liner was obtained. The 25°C bending stiffness value of the surface protection sheet in this example is 1.2 × 10⁻⁶ -4 Pa·m 3 The tensile modulus at 25°C is 5.8 × 10⁻⁶. 9 The stress at Pa, 25℃, and 100% elongation is 83 N / mm². 2 The fracture stress at 25°C is 131 N / mm². 2 The fracture strain at 25°C was 232%.

[0236] <Example 2> As the base layer material, a 25μm thick OPP film (product name "Trefan #25A-KW37", manufactured by Toray Industries, Inc., biaxially oriented PP film, moisture permeability 6.4g / (m²)) is used. 2 The following was used: (day)). The rest was the same as in Example 1 to obtain the surface protection sheet according to this example. The 25° bending stiffness value of the surface protection sheet in this example is 9.3 × 10 -6 Pa·m 3 The tensile modulus at 25°C is 6.3 × 10⁻⁶. 9 The stress at Pa, 25℃, and 100% elongation is 85 N / mm². 2 The breaking stress at 25°C is 146 N / mm². 2 The fracture strain at 25°C was 239%.

[0237] <Example 3> A 100 μm thick PET film (product name "Lumirror S10", manufactured by Toray Industries, Inc.) was used as the base layer material. The surface protection sheet according to this example was obtained in the same manner as in Example 1. The 25°C bending stiffness value of the surface protection sheet in this example was 3.6 × 10⁻⁶. -4 Pa·m 3The tensile modulus at 25°C is 3.8 × 10⁻⁶. 9 The stress at Pa, 25℃, and 100% elongation is 157 N / mm². 2 The breaking stress at 25°C is 189 N / mm². 2 The fracture strain at 25°C was 175%.

[0238] <Examples 4-6> A surface protection sheet according to each example was obtained in the same manner as in Examples 1 to 3, except that adhesive layer E1 was used instead of adhesive layer S1.

[0239] <Comparative Example 1> A 12 μm thick OPP film (product name "Trefan #12D-KW37", manufactured by Toray Industries, Inc., biaxially oriented PP film) was used as the base layer material. The surface protection sheet according to this example was obtained in the same manner as in Example 1. The 25°C bending stiffness value of the surface protection sheet in this example was 5.9 × 10⁻⁶. -7 Pa·m 3 The tensile modulus at 25°C is 3.6 × 10⁻⁶. 9 The stress at Pa, 25℃, and 100% elongation is 105 N / mm². 2 The breaking stress at 25°C is 156 N / mm². 2 The fracture strain at 25°C was 183%.

[0240] <Performance Evaluation> For each example of surface protection sheet, the adhesive strength F0 [N / 20mm], water peel strength FW0 [N / 20mm], and water-induced peel strength [N / 10mm] were measured. The results are shown in Table 1. Table 1 also includes an overview of each example. Note that the moisture permeability of the surface protection sheet for each example is ±1.5 g / (m²) of the moisture permeability of the substrate (layer). 2 It was within the range of (day).

[0241] [Table 1]

[0242] As shown in Table 1, the bending stiffness value at 25°C is 1.0 × 10⁻⁶. -6 ~1.0×10 -2 Pa·m 3The surface protection sheets according to Examples 1 to 6, which fall within the specified range, all have a water-induced peel force of 0.2 N / 10 mm or more, and a 25°C bending stiffness value of 1.0 × 10 -6 Pa·m 3 Compared to Comparative Example 1, which had a lower performance, the edge peeling prevention was superior. Furthermore, since the surface protection sheets of Examples 1 to 6 showed a water peeling force of 1.0 N / 20 mm or less, it can be seen that peeling is possible without damaging or deforming the adherend. From the above results, the bending stiffness value at 25°C is 1.0 × 10⁻⁶. -6 ~1.0×10 -2 Pa·m 3 According to a surface protection sheet that falls within the specified range and has a water peeling force FW0 of 1.0 N / 20 mm or less, even when used in a process that includes a step of processing the object to be protected in a liquid while the sheet is attached to the object, it is less likely to peel from the edges due to external forces such as vibration during the process, and peeling is possible without damaging or deforming the object to be protected.

[0243] Although not shown in the table, the adhesive strength F1 of the surface protection sheet according to Example 5 after 30 minutes of hot water immersion was 1.4 N / 20 mm, and the water peeling strength FW1 after 30 minutes of hot water immersion was 0.0 N / 20 mm.

[0244] Experiment 2 <Preparation of adhesive> (Adhesive E2) The amount of tackifying resin emulsion (Arakawa Chemical Industries, Ltd., Super Ester E-865NT, an aqueous dispersion of polymerized rosin ester with a softening point of 160°C, hereinafter sometimes referred to as "tackifying resin A") added to the aqueous dispersion of acrylic polymer e1 was changed to 20 parts (solids) per 100 parts of solids. Otherwise, an adhesive layer E2 with a thickness of 25 μm was obtained in the same manner as the preparation of adhesive layer E1 described above.

[0245] (Adhesive E3) An adhesive layer E3 with a thickness of 25 μm was obtained in the same manner as the preparation of adhesive layer E2, except that the amount of tackifying resin A added per 100 parts of solids in the aqueous dispersion of acrylic polymer e1 was changed to 30 parts (solids).

[0246] (Adhesive E4) The monomer composition of the acrylic polymer was changed to 49 parts of 2EHA, 49 parts of n-butyl methacrylate (BMA), and 2 parts of AA. An anionic reactive emulsifier (Aqualon BC2020, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used in 2 parts per 100 parts of the above monomer components. The aqueous emulsion of the monomer mixture (monomer emulsion) was prepared in the same manner as the preparation of acrylic polymer e1 in adhesive E1, and an aqueous dispersion of acrylic polymer e2 was obtained by polymerization reaction. After cooling the system to room temperature, 20 parts of tackifying resin A and 2 parts of oxazoline crosslinking agent (Epocross WS-500, manufactured by Nippon Shokubai Co., Ltd.) were mixed in per 100 parts of the solid content of the aqueous dispersion of acrylic polymer e2. Furthermore, an emulsion-type adhesive composition E4 was prepared by adjusting the pH to approximately 7.5 and the viscosity to approximately 9 Pa·s using 10% aqueous ammonia as a pH adjuster and polyacrylic acid (aqueous solution with 36% non-volatile content) as a thickener. An adhesive layer E4 with a thickness of 25 μm was obtained in the same manner as the preparation of the adhesive layer E2, except that the emulsion-type adhesive composition E4 was used.

[0247] (Adhesive E5) Instead of 20 parts of tackifying resin A, 20 parts of tackifying resin B (Arakawa Chemical Industries, Ltd., Super Ester NS-121, an aqueous dispersion of rosin-based resin (acid value imparting) with a softening point of 120°C) were used in solid content. The rest of the process was the same as for the preparation of adhesive layer E4, and an adhesive layer E5 with a thickness of 25 μm was obtained.

[0248] (Adhesive E6) An adhesive layer E6 with a thickness of 25 μm was obtained in the same manner as the preparation of adhesive layer E2, except that a tackifying resin was not used.

[0249] (Adhesive E7) An adhesive layer E7 with a thickness of 25 μm was obtained in the same manner as the preparation of adhesive layer E4, except that a tackifying resin was not used.

[0250] (Adhesive S2) A solution containing the acrylic polymer s1 was obtained by the method described for adhesive S1. To the solution obtained above, add 20 parts of maleated rosin ester (Harima Chemicals, Haritack 4740, softening point 115-125°C, hereinafter sometimes referred to as "tackifying resin C") as a tackifier, based on solid content, per 100 parts of the monomer components used to prepare the solution, and an isocyanate crosslinking agent (trimethylolpropane / xylylene diisocyanate adduct, Mitsui Chemicals, trade name: Takenate D-110N, solid content concentration 75%). 0.75 parts of ) on a solid content basis, 0.01 parts of dioctyl tin dilaurate (manufactured by Tokyo Fine Chemical Co., Ltd., trade name: Envirizer OL-1) as a crosslinking accelerator, 3 parts of acetylacetone as a crosslinking retarder, and 0.5 parts of a nonionic surfactant (polyoxyethylene sorbitan monolaurate, HLB 16.7, trade name: Leodol TW-L120, manufactured by Kao Corporation) as a water affinity agent were added and uniformly mixed to prepare solvent-type adhesive composition S2. An adhesive layer S2 with a thickness of 25 μm was obtained in the same manner as the preparation of the adhesive layer S1, except that the obtained solvent-type adhesive composition S2 was used.

[0251] (Adhesives S3~S4) Except for changing the amount of water-attracting agent used from 0.3 parts to 0.1 parts (adhesive S3) or 0.5 parts (adhesive S4) per 100 parts of monomer component, adhesive layers S3 and S4 with a thickness of 25 μm were obtained in the same manner as in the preparation of adhesive layer S1.

[0252] <Examples 7-15> As the base layer material, a 60 μm thick OPP film (product name "Trefan #60-2500", manufactured by Toray Industries, Inc., biaxially oriented PP film) was prepared. The release liner covering one surface of the adhesive layers E2-E7 and S2-4 obtained above was peeled off, and the exposed surface (adhesive surface) was pressed onto the surface of the OPP film by passing a 2 kg rubber roller back and forth twice. In this way, surface protection sheets (single-sided adhesive sheets with base layer) for each example were obtained, with the adhesive surface protected by the release liner. The 25°C bending stiffness value of the surface protection sheets for each example was 1.2 × 10⁻⁶. -4 Pa·m 3 The stress at 25°C and 100% elongation is 83 N / mm². 2 The fracture stress at 25°C is 131 N / mm². 2 The fracture strain at 25°C was 232%.

[0253] <Performance Evaluation> For each example of surface protection sheet, the adhesive strength F0 [N / 20mm], water peel strength FW0 [N / 20mm], 20-degree trigger peel strength [N / 10mm], and rebound resistance (peel length [mm] 1 hour after application) were measured. The results are shown in Tables 2 and 3. Tables 2 and 3 also show an overview of each example.

[0254] [Table 2]

[0255] [Table 3]

[0256] As shown in Tables 2-3, the surface protection sheets in Examples 7-15 all had a 20-degree trigger peel force of 0.2 N / 10 mm or more, and the rebound resistance test showed that the peel length at the edges after 1 hour was 1.0 mm or less in all cases, indicating good edge peel resistance. In particular, in Examples 7-12, which used a water-dispersible adhesive, Examples 7-10, which had a tackifier added, had a high 20-degree trigger peel force of 0.5 N / 10 mm or more, and showed superior rebound resistance compared to Examples 11-12, which did not use a tackifier. Similarly, in Examples 13-15, which used a solvent-type adhesive, Example 13, which had a tackifier added, and Example 14, which reduced the amount of water-affinity agent used, both had a high 20-degree trigger peel force of 0.5 N / 10 mm or more, and showed superior rebound resistance compared to Example 15, which did not use a tackifier and used 0.5 parts of water-affinity agent. In Examples 7-10 and 13-14, a 20-degree trigger peel force of 0.5 N / 10 mm or more was achieved based on the adhesive, demonstrating superior rebound resistance. Furthermore, a comparison between Example 14 and Example 15 showed that while increasing the amount of water-attracting agent improved water-peelability, it tended to decrease the adhesive strength F0 and 20-degree trigger peel force, as well as the edge peel prevention performance. However, the results of Example 13 indicate that by using a tackifier, it is possible to improve the adhesive strength F0 and 20-degree trigger peel force even when using a sufficient amount of water-attracting agent, thus achieving a higher level of balance between protective adhesion, edge peel prevention, and water-peel removal performance.

[0257] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. [Explanation of Symbols]

[0258] 1,2 Surface protective sheet 1A, 2A adhesive surface 1B, 2B back 10 Base material layer 10A One side 10B The other side 11 First layer 12 Second layer (layer containing inorganic material) 20 Adhesive layer 20A adhesive surface 30 Release Liner 50 Surface protection sheets with release liner

Claims

1. The bending stiffness value at 25°C is 1.0 × 10⁻⁶. －６ ~1.0 x 10 －２ Pa・m ３ It is within the range, A surface protection sheet having an adhesive surface attached to an alkali glass having a surface with a water contact angle of 20 degrees or less, and after being held in an environment of 23°C and 50% RH for 1 hour, 20 μL of distilled water is supplied between the alkali glass and the adhesive surface, and the distilled water enters one end of the interface between the alkali glass and the adhesive surface, and the water peel force FW0 measured under conditions of temperature 23°C, peel angle 180 degrees and speed 300 mm / min is 1.0 N / 20 mm or less.

2. An alkali glass having a surface with a water contact angle of 20 degrees or less is bonded to the surface of a surface protection sheet, held in an environment of 23°C and 50% RH for 1 hour, then 20 μL of distilled water is supplied between the alkali glass and the adhesive surface, and the distilled water enters one end of the interface between the alkali glass and the adhesive surface. After that, the water peel force FW0 measured under conditions of 23°C, peel angle of 180 degrees, and speed of 300 mm / min is 1.0 N / 20 mm or less. A surface protection sheet having an adhesive surface bonded to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, held in an environment of 23°C and 50% RH for 24 hours, then 20 μL of distilled water is dropped between the alkali glass and the adhesive surface, and the initial peel force measured under conditions of 23°C, peel angle of 20 degrees and speed of 1000 mm / min is 0.5 N / 10 mm or more.

3. The surface protective sheet according to claim 1 or 2, wherein the water peeling force FW0 [N / 20 mm] is 50% or less of the adhesive force F0 [N / 20 mm], where the adhesive force F0 is the peel strength [N / 20 mm] measured under the conditions of temperature 23°C, peeling angle 180°C, and speed 300 mm / min after bonding the adhesive surface of the surface protective sheet to the surface of alkali glass having a surface with a water contact angle of 20 degrees or less, and holding it in an environment of 23°C, 50% RH for 1 hour.

4. A surface protection sheet according to any one of claims 1 to 3, comprising an adhesive layer and a base layer supporting the adhesive layer.

5. The surface protective sheet according to claim 4, wherein the adhesive layer contains a water-affinity agent.

6. A surface protection sheet according to any one of claims 1 to 5, having a thickness of 20 to 200 μm.

7. A surface protection sheet according to any one of claims 1 to 6, used in a process of chemically and / or physically thinning a glass or semiconductor wafer in a liquid.

8. In a method for processing an adherend, A step of attaching a surface protection sheet to the surface of an object having a surface with a water contact angle of 20 degrees or less; A step in which a physical load is applied to the adherend to which the surface protective sheet is attached, in the thickness direction of the surface protective sheet; The process involves peeling and removing the surface protective sheet from the adherend in the presence of water; Includes, The aforementioned surface protection sheet has a water peeling force FW0 of 1.0 N / 20 mm or less, and an initial peeling force of 0.5 N / 10 mm or more, in a processing method. [Water-based peeling force FW0] The aforementioned water peeling force FW0 is the water peeling force [N / 20mm] measured under the conditions of a temperature of 23°C, a peeling angle of 180 degrees, and a speed of 300 mm / min, after bonding the adhesive surface of a surface protection sheet to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, holding it in an environment of 23°C and 50% RH for 1 hour, supplying 20 μL of distilled water between the alkali glass and the adhesive surface, allowing the distilled water to enter one end of the interface between the alkali glass and the adhesive surface. [Initial Separation Force] The aforementioned initial peeling force is the maximum stress [N / 10 mm] at the beginning of peeling, measured under the conditions of 23°C, a peeling angle of 20 degrees, and a speed of 1000 mm / min, after bonding the adhesive side of a surface protective sheet to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, holding it in an environment of 23°C and 50% RH for 24 hours, and then dropping 20 μL of distilled water between the alkali glass and the adhesive surface.

9. The processing method according to claim 8, wherein the surface protective sheet has a water peeling force FW0 [N / 20 mm] that is 50% or less of the adhesive force F0 [N / 20 mm]. [Adhesive force F0] The aforementioned adhesive strength F0 is the peel strength [N / 20mm] measured under the conditions of a temperature of 23°C, a peel angle of 180°C, and a speed of 300 mm / min, after bonding the adhesive side of a surface protection sheet to the surface of an alkali glass having a surface with a water contact angle of 20 degrees or less, and holding it in an environment of 23°C, 50% RH for 1 hour.

10. The processing method according to claim 8 or 9, wherein the surface protection sheet comprises an adhesive layer and a base layer that supports the adhesive layer.

11. The processing method according to any one of claims 8 to 10, wherein the step of applying a physical load in the thickness direction of the surface protective sheet to the adherend to which the surface protective sheet is attached is a transport step or a physical processing step.

12. A surface protection sheet used in the processing method according to any one of claims 8 to 11.

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