Adhesive sheet

Abstract

To provide an adhesive sheet capable of significantly suppressing fine concavo-convex deformation.SOLUTION: Provided is an adhesive sheet having a colored adhesive layer. The adhesive layer contains an acrylic polymer. The gel fraction in the adhesive layer is 25% or more. The adhesive layer has a storage modulus at 23°C of 0.05 MPa or more, and has tanδ at 23°C of 0.31 or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet. [Background technology]

[0002] In general, adhesives (also referred to as pressure-sensitive adhesives; the same applies below) are in a soft solid (viscoelastic) state in a temperature range near room temperature, and have the property of easily adhering to an adherend by pressure. Taking advantage of such properties, adhesives are widely used in various industrial fields, such as portable electronic devices such as smartphones and home appliances, automobiles, and office automation equipment, typically in the form of adhesive sheets containing an adhesive layer, for the purpose of joining parts and protecting surfaces. Suitable examples of applications of such adhesive sheets include joining, fixing, and protecting members in electronic devices. In addition, adhesive sheets having a predetermined light-shielding property and light-reducing property are used for the purpose of preventing light leakage from light sources such as backlight modules of liquid crystal display devices in electronic devices and self-emitting elements such as organic EL (electroluminescence), concealing the adherend, adjusting the appearance of the adherend through the adhesive sheet, and design, etc. Patent Document 1 is an example of a document related to this type of technology. Patent Documents 2 and 3 are prior art documents that disclose adhesives containing acrylic polymers polymerized using heptyl acrylate as a monomer component. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-37657 A [Patent Document 2] International Publication No. 2021 / 125247 [Patent Document 3] International Publication No. 2021 / 125278 Summary of the Invention [Problem to be solved by the invention]

[0004] Adhesive sheets used for the purposes of concealing an adherend, adjusting the appearance, imparting design, etc., achieve the purpose of concealment by covering the entire visible surface of the adherend. Since such adhesive sheets can be viewed from the outside, they are required to have good appearance quality. For example, an adhesive sheet used to conceal a metal member disposed on the back side of an organic EL panel or the like in the display unit of an electronic device is required to conceal the adherend with good appearance quality since it can be seen by the user when the display unit is turned off.

[0005] By the way, before use (i.e., before being attached to an adherend), a pressure-sensitive adhesive sheet is usually handled in the form of a pressure-sensitive adhesive sheet with a release liner, the adhesive surface of which is protected by a release liner, from the viewpoints of productivity, handling, and the like. By protecting the adhesive surface of the pressure-sensitive adhesive sheet with a release liner, the adhesive surface is kept smooth and can adhere well to the surface of the adherend, thereby exhibiting the desired adhesive properties. In addition, a pressure-sensitive adhesive sheet having an adhesive surface protected and kept smooth by a release liner can be attached uniformly to an adherend, and can provide a good appearance when the surface of the adherend is visually observed. Such a pressure-sensitive adhesive sheet with a release liner is, for example, formed into a roll body (pressure-sensitive adhesive sheet roll with a release liner) in which the pressure-sensitive adhesive sheet with a release liner is wound, and is distributed, stored, and processed.

[0006] However, in the manufacturing of the above-mentioned pressure-sensitive adhesive sheet, for example, in the process of winding up the pressure-sensitive adhesive sheet with a release liner into a roll, minute foreign matter may be mixed into the back surface of the release liner, and the pressure inside the roll may cause dents in the pressure-sensitive adhesive sheet due to the foreign matter. There is a concern that such dents remain as minute dents even after the pressure-sensitive adhesive sheet is attached to the adherend, and may cause a decrease in the appearance quality. Such visible uneven deformation does not disappear when the sheet is attached to the adherend and stabilized. In particular, a colored pressure-sensitive adhesive sheet, such as one in which the pressure-sensitive adhesive layer contains a coloring agent, is more likely to have a contrast of uneven deformation than a transparent pressure-sensitive adhesive sheet, and the change in appearance due to the uneven deformation tends to be more noticeable. Furthermore, in recent years, there is a tendency for higher appearance quality to be required depending on the application location of the pressure-sensitive adhesive sheet, such as the display part of an electronic device, and it is expected that a pressure-sensitive adhesive sheet in which fine uneven deformation is suppressed to a level that was not previously considered a problem will be required. If a colored pressure-sensitive adhesive sheet in which the above-mentioned fine uneven deformation is highly suppressed is realized, it is possible to improve the appearance quality of the surface to which the colored pressure-sensitive adhesive sheet is applied, which is useful.

[0007] The present invention has been made in view of the above circumstances, and has an object to provide a pressure-sensitive adhesive sheet that can highly suppress minute uneven deformation. [Means for solving the problem]

[0008] According to this specification, a pressure-sensitive adhesive sheet having a colored pressure-sensitive adhesive layer is provided. The pressure-sensitive adhesive layer includes an acrylic polymer. The pressure-sensitive adhesive layer has a gel fraction of 25% or more. The pressure-sensitive adhesive layer has a storage modulus of 0.05 MPa or more at 23° C. and a tan δ of 0.31 or more at 23° C. Here, tan δ refers to the ratio (G″ / G′) of the loss modulus G″ to the storage modulus G′ of the pressure-sensitive adhesive layer. According to the above configuration, the pressure-sensitive adhesive layer including an acrylic polymer has a gel fraction of 25% or more, a storage modulus of 0.05 MPa or more at 23° C., and an appropriate hardness, so that uneven deformation is unlikely to occur. The pressure-sensitive adhesive layer has a tan δ of 0.31 or more at 23° C., so that it has good relaxation properties. Therefore, when fine uneven deformation such as depressions on the adhesive surface occurs in the pressure-sensitive adhesive layer, the fine uneven deformation is eliminated or alleviated by the relaxation action of the pressure-sensitive adhesive. Since the above-mentioned adhesive sheet has a colored adhesive layer, uneven deformation is easily noticeable. However, if the adhesive sheet has a configuration including an adhesive layer that satisfies the above-mentioned characteristics, minute uneven deformation is highly suppressed, resulting in an excellent appearance quality.

[0009] In some embodiments, the monomer component constituting the acrylic polymer includes an alkyl acrylate having a chain alkyl group with 4 to 8 carbon atoms. 4-8 By using an acrylic polymer containing alkyl acrylate as a monomer component, it is easy to form a pressure-sensitive adhesive layer that satisfies both the above-mentioned 23°C storage modulus and 23°C tan δ. 4-8 This is preferably carried out in an embodiment using an acrylic polymer containing an alkyl acrylate as a monomer component.

[0010] In some preferred embodiments, the monomer component constituting the acrylic polymer includes heptyl acrylate. By using an acrylic polymer including heptyl acrylate as a monomer component, it is easy to form a pressure-sensitive adhesive having a storage modulus at 23° C. of a predetermined value or more and a high tan δ at 23° C.

[0011] In some embodiments, the monomer component constituting the acrylic polymer includes n-butyl acrylate. According to the technology disclosed herein, a pressure-sensitive adhesive that satisfies both the above-mentioned 23°C storage modulus and 23°C tan δ can be obtained by using an acrylic polymer containing n-butyl acrylate as a monomer component.

[0012] In some preferred embodiments, the pressure-sensitive adhesive layer contains a black colorant. The use of a small amount of the black colorant can effectively adjust light transmittance, and can easily provide high concealment of the adherend. The effect of the technology disclosed herein (high suppression of fine uneven deformation) can be effectively exerted in a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a black colorant.

[0013] In some preferred embodiments, the pressure-sensitive adhesive layer contains a black colorant as the first colorant and a metal oxide as the second colorant. By using the two types of colorants, it is possible to preferably achieve the desired design and color while adjusting the optical properties (light transmittance, etc.). The effects of the technology disclosed herein can be effectively exerted in a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the two types of colorants.

[0014] In some preferred embodiments, the pressure-sensitive adhesive layer further comprises a tackifier resin. By incorporating a tackifier resin, the adhesive strength can be improved. According to the technology disclosed herein, a pressure-sensitive adhesive layer that satisfies the above gel fraction, 23°C storage modulus, and 23°C tan δ can be formed with a composition that includes a tackifier resin, thereby achieving the desired effect.

[0015] In some preferred embodiments, the pressure-sensitive adhesive layer further comprises an acrylic oligomer. By including an acrylic oligomer, the adhesive strength can be improved. For example, it is more preferable to use a tackifier resin and an acrylic oligomer in combination. According to the technology disclosed herein, a pressure-sensitive adhesive layer that satisfies the above gel fraction, 23°C storage modulus, and 23°C tan δ can be formed with a composition that includes an acrylic oligomer, thereby achieving the desired effect.

[0016] In some embodiments, the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet made of the pressure-sensitive adhesive layer. The substrate-less double-sided pressure-sensitive adhesive sheet can be made thinner because it does not have a substrate, and can contribute to the miniaturization and space-saving of the product to which the double-sided pressure-sensitive adhesive sheet is applied. In addition, the substrate-less double-sided pressure-sensitive adhesive sheet can maximize the effects of the pressure-sensitive adhesive layer, such as adhesive strength. In addition, the effects of the technology disclosed herein can be effectively exerted in the substrate-less double-sided pressure-sensitive adhesive sheet.

[0017] The adhesive sheet disclosed herein can be preferably used for bonding components of electronic devices including, for example, home appliances, office automation equipment, and mobile electronic devices such as smartphones. For example, electronic devices have parts that are visible to the user, and excellent appearance quality may be required. The adhesive sheet disclosed herein is highly suppressed in fine uneven deformation and has excellent appearance quality, so that it can be applied to visible parts of electronic devices to realize a surface with good appearance quality. As described above, according to this specification, an electronic device using any of the adhesive sheets disclosed herein, in other words, an electronic device including the adhesive sheet, is provided. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to an embodiment. [Diagram 2] FIG. 4 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Diagram 3] FIG. 2 is a cross-sectional view illustrating a schematic configuration example of a laminate. [Figure 4] FIG. 1 is an exploded perspective view illustrating a configuration example of a display device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A preferred embodiment of the present invention will be described below. Matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention can be understood by a person skilled in the art based on the teachings on carrying out the invention described in this specification and the common general knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general knowledge in the field. In addition, in the following drawings, members and parts that perform the same function may be described by using the same reference numerals, and duplicated descriptions may be omitted or simplified. In addition, the embodiments described in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the pressure-sensitive adhesive sheet of the present invention that is actually provided as a product.

[0020] In this specification, the term "adhesive" refers to a material that exhibits a soft solid (viscoelastic) state at temperatures near room temperature and that has the property of easily adhering to an adherend by pressure, as described above. The adhesive referred to here is generally a material having a complex tensile modulus E * (1Hz)<10 7 dyne / cm 2 The material may be a material having the above properties at 25° C.

[0021] In this specification, biomass-derived carbon means carbon (renewable carbon) derived from biomass materials, i.e., materials derived from renewable organic resources. The biomass materials typically refer to materials derived from biological resources (typically plants that perform photosynthesis) that can be reproduced sustainably in the presence of sunlight, water, and carbon dioxide. Therefore, materials derived from fossil resources that are depleted through use after mining (fossil resource-based materials) are excluded from the concept of biomass materials here. The biomass carbon ratio of the pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet, i.e., the proportion of biomass-derived carbon in the total carbon contained in the pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet, can be estimated from the carbon isotope content with mass number 14 measured in accordance with ASTM D6866.

[0022] <Composition of adhesive sheet> The adhesive sheet disclosed herein is configured to include an adhesive layer. The adhesive sheet may be in the form of a substrate-less double-sided adhesive sheet having a first adhesive surface constituted by one surface of the adhesive layer and a second adhesive surface constituted by the other surface of the adhesive layer. Alternatively, the adhesive sheet disclosed herein may be in the form of a substrate-attached adhesive sheet in which the adhesive layer is laminated on one or both surfaces of a supporting substrate. Hereinafter, the supporting substrate may simply be referred to as a "substrate". The concept of the adhesive sheet here may include those referred to as adhesive tapes, adhesive labels, adhesive films, and the like. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, the adhesive sheet may be in the form of an adhesive sheet further processed into various shapes.

[0023] The structure of an adhesive sheet according to one embodiment is shown in FIG. 1. The adhesive sheet 1 is configured as a substrate-less double-sided adhesive sheet made of an adhesive layer 21. The adhesive layer 21 is colored. The adhesive sheet 1 is used by attaching a first adhesive surface 21A, which is configured by one surface (first surface) of the adhesive layer 21, and a second adhesive surface 21B, which is configured by the other surface (second surface) of the adhesive layer 21, to different locations on an adherend. The locations to which the adhesive surfaces 21A and 21B are attached may be locations on different members, or may be different locations within a single member. The adhesive sheet 1 before use (i.e., before being attached to an adherend) may be a component of an adhesive sheet with release liner 100 in a form in which the first adhesive surface 21A and the second adhesive surface 21B are protected by release liners 31 and 32, each of which has a release surface at least on the side facing the adhesive layer 21, as shown in FIG. 1. As the release liners 31 and 32, for example, a sheet-like substrate (liner substrate) configured such that one side serves as a release surface by providing a release layer made of a release treatment agent on the one side can be preferably used. Alternatively, the release liner 32 can be omitted, and a release liner 31 having release surfaces on both sides can be used, which is superimposed on the PSA sheet 1 and rolled up in a spiral shape to form a PSA sheet with a release liner in a form in which the second adhesive surface 21B is protected by contacting the back surface of the release liner 31 (roll form).

[0024] The adhesive sheet 100 with a release liner may be in the form of a roll (adhesive sheet roll with a release liner) 300 as shown in Fig. 1. Such an adhesive sheet roll 300 has the adhesive sheet 100 with a release liner wound around a core (winding core) 150.

[0025] The structure of an adhesive sheet according to another embodiment is shown in FIG. 2. The adhesive sheet 2 is configured as a substrate-attached double-sided adhesive sheet including a sheet-like support substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, a first adhesive layer 21 fixedly provided on the first surface 10A side, and a second adhesive layer 22 fixedly provided on the second surface 10B side. In this embodiment, both the first adhesive layer 21 and the second adhesive layer 22 are colored. The adhesive sheet 2 before use may be a component of an adhesive sheet 200 with a release liner in which the surface (first adhesive surface) 21A of the first adhesive layer 21 and the surface (second adhesive surface) 22A of the second adhesive layer 22 are protected by release liners 31 and 32, as shown in FIG. 2. Alternatively, release liner 32 may be omitted, and a release liner 31 having release surfaces on both sides may be used, which is then superimposed on PSA sheet 2 and rolled up in a spiral shape to form a PSA sheet with a release liner in which second adhesive surface 22A is protected by contact with the back surface of release liner 31 (roll form). Such a double-sided PSA sheet with a substrate is preferred because it has excellent processability, handleability, etc.

[0026] It is not necessary for both the first adhesive layer and the second adhesive layer to be colored, as long as at least one of the first adhesive layer and the second adhesive layer is configured as a colored adhesive layer.

[0027] The technology disclosed herein can be preferably implemented in the form of a substrateless double-sided pressure-sensitive adhesive sheet. Substrateless double-sided pressure-sensitive adhesive sheets do not have a supporting substrate, so they are easy to be thinned, and are also advantageous in that they can maximize the adhesive properties such as adhesive strength and impact resistance. In addition, substrateless double-sided pressure-sensitive adhesive sheets can maximize the thickness of the adhesive layer to reduce fine unevenness generated in the adhesive layer.

[0028] <Adhesive layer> In the adhesive sheet disclosed herein, the adhesive layer (in an embodiment having a first adhesive layer and a second adhesive layer, at least one of the first adhesive layer and the second adhesive layer; the same applies hereinafter unless otherwise specified) is colored. An adhesive sheet having a colored adhesive layer can conceal an adherend. In addition, by adjusting the degree of coloring of the adhesive layer, it is possible to adjust optical properties such as light transmittance, and to impart design and color to the surface of the adherend.

[0029] (Viscoelastic properties) The adhesive layer disclosed herein has a storage modulus at 23°C (23°C storage modulus) of 0.05 MPa or more. An adhesive layer satisfying the above 23°C storage modulus has a moderate hardness, so that uneven deformation of a visible size is unlikely to occur. In some preferred embodiments, the above 23°C storage modulus is about 0.06 MPa or more, may be 0.07 MPa or more, or may be 0.08 MPa or more. An adhesive layer having the above 23°C storage modulus has a moderate cohesive force, so that it tends to easily obtain high adhesion reliability to an adherend. It also tends to be excellent in processability. In some embodiments, the 23°C storage modulus of the adhesive layer is about 0.60 MPa or less, may be about 0.40 MPa or less, or may be about 0.20 MPa or less. An adhesive layer having a 23°C storage modulus of a predetermined value or less tends to easily obtain adhesion to an adherend. In some preferred embodiments, it is approximately 0.18 MPa or less, more preferably 0.15 MPa or less, and even more preferably 0.13 MPa or less, and may be 0.11 MPa or less, less than 0.10 MPa, or may be 0.08 MPa or less.

[0030] The adhesive layer disclosed herein is characterized by having a 23°C storage modulus of 0.05 MPa or more and a tan δ (23°C tan δ) of 0.31 or more at 23°C. The tan δ (loss tangent) refers to the ratio (G″ / G′) of the loss modulus G″ to the storage modulus G′ of the adhesive layer. An adhesive layer having a tan δ of 0.31 or more at 23°C has good relaxation properties, so that minute uneven deformations generated in the adhesive layer, such as depressions on the adhesive surface, are relaxed and eliminated or alleviated within a short period of time due to the relaxation action of the adhesive. In some embodiments, the 23°C tan δ may be 0.40 or more, 0.45 or more, 0.50 or more, or 0.55 or more. In some preferred embodiments, the 23°C tan δ is 0.60 or more, more preferably 0.65 or more, and even more preferably 0.70 or more. Since the 23°C tan δ generally tends to decrease as the 23°C storage modulus increases, it is preferable that the upper limit of the 23°C tan δ is set to an appropriate range that is compatible with the 23°C storage modulus. In some embodiments, the 23°C tan δ is 3 or less, may be 1.5 or less, may be 1.2 or less, or may be 1.0 or less. From the viewpoint of highly suppressing uneven deformation, in some preferred embodiments, the 23°C tan δ is less than 1.0, may be less than 0.95, may be less than 0.90, may be less than 0.85, may be less than 0.80, or may be 0.75 or less. In some other embodiments, the 23°C tan δ may be 0.70 or less, may be 0.65 or less, may be 0.60 or less, or may be 0.55 or less.

[0031] In the technology disclosed herein, the 23°C storage modulus and 23°C tan δ of the adhesive layer can be determined by dynamic viscoelasticity measurement. Specifically, a plurality of adhesive layers to be measured (double-sided adhesive sheets in the case of substrate-less double-sided adhesive sheets) are stacked to prepare an adhesive layer with a thickness of about 2 mm. This adhesive layer is punched into a disk-shaped sample with a diameter of 7.9 mm, which is sandwiched and fixed between parallel plates, and dynamic viscoelasticity measurement is performed under the following conditions using a viscoelasticity tester (e.g., ARES manufactured by TA Instruments or its equivalent) to determine the 23°C storage modulus and 23°C tan δ. Measurement mode: Shear mode Temperature range: -70℃~150℃ Heating rate: 5℃ / min ·Measurement frequency: 1Hz The above method is also used in the Examples described later. The pressure-sensitive adhesive layer to be measured may be one formed by applying the corresponding pressure-sensitive adhesive composition in a layer form and drying or curing it.

[0032] (light transmittance) The light transmittance of the colored adhesive layer varies depending on the purpose of use and the purpose of coloring, and is not limited to a specific range, but the colored adhesive layer usually has a lower light transmittance than the transparent adhesive layer. For example, in some embodiments, the light transmittance of the adhesive layer at a wavelength of 550 nm (550 nm light transmittance, also referred to as visible light transmittance) is less than 80%, and may be less than 70%, less than 60%, less than 50%, or less than 40%. The adhesive sheet in which the visible light transmittance is reduced by coloring the adhesive layer is suitable for concealing the adherend and can also be used to impart design. It can also be used as a light-shielding adhesive sheet for preventing light leakage, etc. In some preferred embodiments, the 550 nm light transmittance of the adhesive layer is 30% or less, may be 20% or less, may be 15% or less, may be 10% or less, may be 8% or less, or may be 6% or less. The lower the visible light transmittance, the better the concealment properties can be exhibited. When higher concealment is required, the 550 nm light transmittance may be less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, or less than 0.5%. The lower limit of the 550 nm light transmittance is not particularly limited, and may be substantially 0%, i.e., below the detection limit, 0.1% or more, 1% or more, 3% or more, or 5% or more. In some embodiments, the 550 nm light transmittance may be 10% or more, more than 20%, or more than 30%. By having a certain degree of visible light transmittance, it is possible to appropriately conceal the adherend, adjust the appearance of the adherend (e.g., metal material), and impart a design and color that retains the texture of the adherend. In addition, a pressure-sensitive adhesive layer having moderate light transmittance is also preferable from the viewpoints of maintaining adhesive properties and productivity.

[0033] Although not particularly limited, the light transmittance of the adhesive layer at a wavelength of 1380 nm (1380 nm light transmittance, also referred to as infrared transmittance) is less than 90%, and may be less than 80%, less than 70%, less than 60%, less than 50%, or less than 40%. In some preferred embodiments, the light transmittance of the adhesive layer at 1380 nm is 30% or less, 20% or less, 15% or less, 10% or less, 5% or less, or 3% or less. The adhesive layer with limited infrared transmittance can block light rays in a wide wavelength range including infrared rays, and is likely to provide excellent light blocking properties. In addition, for example, when used in the vicinity of an infrared sensor, blocking infrared rays can prevent a decrease in the operating accuracy of the sensor. The lower limit of the 1380 nm light transmittance is not particularly limited, and may be substantially 0%, i.e., below the detection limit, 0.1% or more, 1% or more, 3% or more, or 5% or more. In some embodiments, the 1380 nm light transmittance may be 10% or more, 30% or more, or 50% or more.

[0034] The relative relationship between the visible light transmittance and the infrared transmittance of the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the infrared transmittance T IR [%] and visible light transmittance T VL [%] ratio (T IR / T VL ) is, for example, in the range of 0.1 to 10, and may be 5 or less, 3 or less, 0.5 or more, 1 or more (e.g., more than 1), or 2 or more. The ratio (T IR / T VL ) is appropriately set, the desired adhesion hiding property and infrared shielding property can be achieved.

[0035] In this specification, the light transmittance [%] of the adhesive layer and the adhesive sheet is determined by measuring the light transmittance (light transmittance at wavelengths of 550 nm and 1380 nm) in the thickness direction of the adhesive layer and the adhesive sheet peeled off from the release liner using a commercially available spectrophotometer. As the spectrophotometer, a spectrophotometer manufactured by Hitachi (device name "U4150 type spectrophotometer") or an equivalent product is used. The light transmittance at wavelengths of 550 nm and 1380 nm corresponds to the visible light transmittance and the infrared transmittance, respectively. In addition, the above light transmittance of the substrateless double-sided adhesive sheet consisting of the adhesive layer is also the light transmittance of the adhesive layer.

[0036] (Acrylic polymer) The adhesive layer constituting the adhesive sheet disclosed herein contains an acrylic polymer. The above-mentioned adhesive layer is typically an adhesive layer having an acrylic polymer as a base polymer. Such an adhesive layer is also called an acrylic adhesive layer. The base polymer refers to the main component of a rubber-like polymer (a polymer that exhibits rubber elasticity in a temperature range around room temperature) contained in the adhesive layer. In addition, in this specification, the "main component" refers to a component contained in an amount of more than 50% by weight, unless otherwise specified. In addition, the following explanation of the adhesive and the components that may be contained in the adhesive layer are also applicable to the adhesive composition used to form the adhesive (layer) unless otherwise specified.

[0037] In addition, in this specification, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer". Therefore, in this specification, an acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer. In this specification, "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, "(meth)acrylate" refers to acrylate and methacrylate, and "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense.

[0038] The acrylic polymer in the technology disclosed herein is preferably, for example, a polymer of a monomer raw material that contains an alkyl (meth)acrylate as a main monomer and may further contain a sub-monomer copolymerizable with the main monomer. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material.

[0039] As the alkyl(meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used. CH2=C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. 2 is a chain alkyl group having 1 to 20 carbon atoms. Hereinafter, this range of carbon atoms will be referred to as "C 1-20 From the viewpoint of the storage modulus of the adhesive, R 2 C 1-14 (For example, C 1-10 , typically C 4-8 It is appropriate to use alkyl (meth)acrylate, which is a chain alkyl group of the formula (I), as the main monomer.

[0040] R 2 C1-20 Specific examples of the alkyl(meth)acrylate, which is a chain alkyl group, include, but are not limited to, 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, 2-ethylhexyl(meth)acrylate, octyl ... Examples of alkyl (meth)acrylate include isooctyl (meth)acrylate, 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, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylates can be used alone or in combination of two or more.

[0041] The proportion of alkyl (meth)acrylate in the monomer components constituting the acrylic polymer is typically more than 50% by weight, and can be, for example, 70% by weight or more, 85% by weight or more, 90% by weight or more (for example, more than 90% by weight), 92% by weight or more is appropriate, 94% by weight or more, or more than 95% by weight. The upper limit of the proportion of alkyl (meth)acrylate is not particularly limited, but is preferably 99.5% by weight or less (for example, 99% by weight or less), or may be 98% by weight or less (for example, less than 97% by weight) from the viewpoint of favorably exerting the characteristics (for example, cohesive force) based on the secondary monomer such as a carboxyl group-containing monomer. Alternatively, the acrylic polymer may be substantially a polymer of only alkyl (meth)acrylate.

[0042] In some embodiments, R in formula (1) 1 is a hydrogen atom and R 2 C 4-8 Alkyl acrylate, which is a chain alkyl group of 4-8 It is preferable to use alkyl acrylate as the main monomer. 4-8 The acrylic polymer containing alkyl acrylate as a monomer component is likely to form a pressure-sensitive adhesive layer that satisfies both the above-mentioned 23°C storage modulus and 23°C tan δ. 4-8 When an alkyl acrylate is used, the C contained in the monomer component 4-8 The proportion of alkyl acrylate is, for example, more than 50% by weight, preferably 70% by weight or more, more preferably 90% by weight or more (e.g., more than 90% by weight), more preferably 92% by weight or more, and may be 94% by weight or more (e.g., more than 95% by weight). 4-8 The upper limit of the proportion of alkyl acrylate is not particularly limited, but is preferably, for example, 99% by weight or less, and may be 98% by weight or less (for example, less than 97% by weight) from the viewpoint of favorably exerting the properties (for example, cohesive strength) based on the secondary monomer such as the carboxyl group-containing monomer. 4-8 The alkyl acrylates may be used alone or in combination of two or more. 4-8 Suitable examples of alkyl acrylates include n-butyl acrylate (BA), n-heptyl acrylate (n-HpA) and 2-ethylhexyl acrylate (2EHA).

[0043] In some embodiments, the monomer component constituting the acrylic polymer includes BA. The ratio of BA in the monomer components of the acrylic polymer is, for example, more than 50% by weight, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 85% by weight or more, particularly preferably 90% by weight or more (for example, more than 90% by weight), and may be 92% by weight or more, 94% by weight or more, 95% by weight or more, or 96% by weight or more. An acrylic polymer containing BA as a main monomer component is likely to provide a pressure-sensitive adhesive having good adhesion reliability to an adherend. In addition, by using a predetermined amount or more of BA as a monomer component, it is possible to maintain good adhesive properties such as adhesive strength while dispersing a colorant such as a black colorant (for example, carbon black) well in the pressure-sensitive adhesive layer. In addition, the ratio of BA in the monomer components may be 99% by weight or less, or 97% by weight or less, from the viewpoint of copolymerizing other copolymerizable monomers.

[0044] In some preferred embodiments, the monomer component constituting the acrylic polymer contains heptyl acrylate. The acrylic polymer polymerized using a monomer component containing heptyl acrylate has better flexibility than other alkyl acrylate polymers such as n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA), and therefore the adhesive containing such a polymer can have a high 23°C tan δ value, and is likely to achieve both the above-mentioned range of 23°C storage modulus and the above-mentioned range of 23°C tan δ. Heptyl acrylate is considered to be one of the most suitable monomer components for achieving both the above-mentioned 23°C storage modulus and the above-mentioned 23°C tan δ. The reason why the polymer of heptyl acrylate has excellent flexibility is not particularly limited, but is considered to be because the polymer containing heptyl acrylate as a monomer unit has a low glass transition temperature and a relatively large space between the main chains in the adhesive. Among heptyl acrylates, n-heptyl acrylate is preferable from the viewpoint of flexibility. It is believed that an acrylic polymer synthesized containing n-heptyl acrylate as a monomer component has relatively long linear side chains, which tends to result in larger spaces between the main chains.

[0045] The proportion of heptyl acrylate in the monomer component of the acrylic polymer is, for example, 50% by weight or more (e.g., more than 50% by weight) in some embodiments, suitably 70% by weight or more, preferably 80% by weight or more, more preferably 85% by weight or more, even more preferably 90% by weight or more (e.g., more than 90% by weight), particularly preferably 92% by weight or more, may be 94% by weight or more, may be 95% by weight or more, or may be 96% by weight or more. By increasing the amount of heptyl acrylate used, the effect of its use (e.g., improvement of 23°C tan δ of the adhesive, and thus improvement of uneven deformation relaxation) can be effectively expressed. On the other hand, the upper limit of the proportion of heptyl acrylate in the monomer component is 100% by weight, and may be 99% by weight or less, or may be 98% by weight or less. From the viewpoint of copolymerizing a carboxyl group-containing monomer or other monomers, in some embodiments, the proportion of heptyl acrylate in the monomer component is less than 97% by weight. In some preferred embodiments, the proportion of heptyl acrylate in the monomer component is 96% by weight or less, optionally 95% by weight or less, or optionally 94% by weight or less.

[0046] In the embodiment in which heptyl acrylate is used as a monomer component, the acrylic polymer may be copolymerized with an alkyl (meth)acrylate other than heptyl acrylate. The alkyl (meth)acrylate other than heptyl acrylate may be, for example, a compound represented by the above formula (1) and an alkyl (meth)acrylate other than heptyl acrylate. The alkyl (meth)acrylate other than heptyl acrylate may be used alone or in combination of two or more.

[0047] In some embodiments, the proportion of heptyl acrylate in the total amount of alkyl (meth)acrylate contained in the monomer component is, for example, 50% by weight or more (specifically, 50 to 100% by weight, for example, more than 50% by weight), preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and may be 99% by weight or more, or may be 100% by weight. By adopting such a monomer composition, the effect of using heptyl acrylate can be effectively exhibited.

[0048] In some embodiments, the monomer component may contain an alkyl (meth)acrylate having an alkyl group derived from biomass at the ester end (hereinafter also referred to as "biomass alkyl (meth)acrylate"). In recent years, environmental issues such as global warming have become important, and it is desired to reduce the amount of fossil resource-based materials such as petroleum used. Under these circumstances, it is also desired to reduce the amount of fossil resource-based materials used in the field of adhesives. By using a biomass alkyl (meth)acrylate, it is possible to preferably realize an acrylic adhesive that takes into consideration the reduction of dependency on fossil resource-based materials.

[0049] The biomass alkyl (meth)acrylate is not particularly limited, and is, for example, an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived (meth)acrylic acid. Examples of biomass-derived alkanols include biomass ethanol, alkanols derived from plant materials such as palm oil, palm kernel oil, coconut oil, and castor oil. When the biomass-derived alkanol has 3 or more carbon atoms, the alkanol may be linear or branched. In some embodiments, an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate used in the synthesis of an acrylic polymer. In such a biomass alkyl (meth)acrylate, the higher the number of carbon atoms of the alkanol, the higher the ratio of the number of biomass-derived carbons to the total number of carbons contained in the biomass alkyl (meth)acrylate, that is, the biomass carbon ratio of the alkyl (meth)acrylate. Therefore, in the above biomass alkyl (meth)acrylate, it is desirable that the alkyl group derived from biomass has a large number of carbon atoms in terms of reducing the dependency on fossil resource-based materials. On the other hand, if the alkyl group constituting the alkyl (meth)acrylate has too many carbon atoms, it tends to be difficult to obtain adhesive properties such as adhesive strength, and it may also be disadvantageous in terms of productivity such as synthesis, handling, and cost. In an embodiment in which an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate, it is desirable to use a material that has a good balance between adhesive properties and reduced dependency on fossil resource-based materials (more specifically, the biomass carbon ratio of the above alkyl (meth)acrylate).

[0050] In some preferred embodiments, biomass-derived heptyl acrylate (biomass heptyl acrylate) is used as the heptyl acrylate. By using biomass heptyl acrylate, the effect of the technology disclosed herein can be realized while reducing the dependency on fossil resource-based materials. The biomass heptyl acrylate is an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived acrylic acid, and for example, an ester of a biomass-derived alkanol and a non-biomass-derived acrylic acid can be used. In such a compound, only the heptyl group is biomass-derived. As the biomass-derived heptyl acrylate, it is preferable to use biomass-derived n-heptyl acrylate (biomass n-heptyl acrylate).

[0051] The proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) in the monomer components of the acrylic polymer is, for example, 50% by weight or more (e.g., more than 50% by weight) in some embodiments, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 85% by weight or more, particularly preferably 90% by weight or more, may be 92% by weight or more, may be 94% by weight or more, or may be 96% by weight or more. The proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) in the monomer components is less than 97% by weight, and in some embodiments, may be 95% by weight or less, 93% by weight or less, or 91% by weight or less.

[0052] In addition, the monomer component of the acrylic polymer preferably contains a carboxyl group-containing monomer. The carboxyl group-containing monomer can improve the cohesive force based on its polarity. In addition, when a crosslinking agent such as an isocyanate-based or epoxy-based crosslinking agent is used, the carboxyl group can be a crosslinking point of the acrylic polymer. By using the carboxyl group-containing monomer, it is easy to obtain an adhesive having an improved storage modulus at 23°C. In addition, by using the carboxyl group-containing monomer, it is possible to exhibit better adhesion to an adherend such as a highly polar material. Furthermore, by copolymerizing an appropriate amount of the carboxyl group-containing monomer, even when a black colorant such as carbon black is blended into the adhesive, the colorant can be easily dispersed in the layer, and the adhesive properties can be favorably maintained.

[0053] Examples of the carboxyl group-containing monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, crotonic acid, and isocrotonic acid; and ethylenically unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and citraconic acid. The carboxyl group-containing monomer may be a monomer having a metal salt of a carboxyl group (e.g., an alkali metal salt). The carboxyl group-containing monomer may be used alone or in combination of two or more. Among them, preferred carboxyl group-containing monomers include AA and MAA. AA is particularly preferred. When one or more carboxyl group-containing monomers are used, the proportion of AA in the carboxyl group-containing monomer is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. In a particularly preferred embodiment, the carboxyl group-containing monomer is substantially composed of AA alone. Due to the combined effects of AA, such as polarity based on its carboxy group, its role as a crosslinking point, and its Tg (106°C), it is believed to be one of the most suitable monomer materials for achieving a good balance between the properties of the adhesive layer (e.g., storage modulus at 23°C and gel fraction) and adhesive properties such as adhesive strength in the carboxy group-containing monomers disclosed herein.

[0054] The ratio of the carboxyl group-containing monomer in the monomer component of the acrylic polymer is not particularly limited, and may be 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, or 2% by weight or more. In some preferred embodiments, the ratio of the carboxyl group-containing monomer in the monomer component is more than 3% by weight (specifically, more than 3.0% by weight), preferably 4.0% by weight or more, more preferably 4.5% by weight or more, even more preferably 5.0% by weight or more (e.g., more than 5.0% by weight), particularly preferably 5.5% by weight or more, may be 6.0% by weight or more, may be 6.5% by weight or more, or may be 7.0% by weight or more. By increasing the amount of the carboxyl group-containing monomer used, the cohesive force of the pressure-sensitive adhesive layer can be improved based on the action of the carboxyl group-containing monomer. In addition, the amount of the carboxyl group-containing monomer is, for example, appropriately 20% by weight or less of the monomer component, preferably 15% by weight or less, more preferably 12% by weight or less. In some preferred embodiments, the amount of the carboxyl group-containing monomer may be 10% by weight or less, 8% by weight or less, 6% by weight or less, or 5% by weight or less. By appropriately adjusting the amount of the carboxyl group-containing monomer used within the above range, a pressure-sensitive adhesive having good adhesive properties is easily obtained.

[0055] The acrylic polymer may be copolymerized with a functional group-containing monomer (any functional group-containing monomer) other than the carboxy group-containing monomer. Examples of optional functional group-containing monomers that can introduce functional groups that can serve as crosslinking base points into acrylic polymers or contribute to improving adhesive strength include hydroxyl group (OH group)-containing monomers (hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; polypropylene glycol mono(meth)acrylate, etc.), acid anhydride group-containing monomers, amide group-containing monomers ((meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc.), amino group-containing monomers (aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), epoxy group-containing monomers, cyano group-containing monomers, keto group-containing monomers, monomers having nitrogen atom-containing rings (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), alkoxysilyl group-containing monomers, and imide group-containing monomers. The above-mentioned optional functional group-containing monomers may be used alone or in combination of two or more.

[0056] When the monomer component constituting the acrylic polymer contains the above-mentioned optional functional group-containing monomer, the content of the optional functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exerting the effect of using the optional functional group-containing monomer, the content of the optional functional group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, suitably 0.5% by weight or more, and may be 1% by weight or more. Also, for example, in an embodiment in which the monomer component of the acrylic polymer contains heptyl acrylate and a carboxyl group-containing monomer, from the viewpoint of easily balancing the adhesive performance in relation to these monomer components, the content of the optional functional group-containing monomer in the monomer component is suitably 40% by weight or less, preferably 20% by weight or less, and may be 10% by weight or less (for example, 5% by weight or less). In some embodiments, the content of the optional functional group-containing monomer in the monomer component is, for example, less than 3% by weight, may be less than 1% by weight, may be less than 0.5% by weight, may be less than 0.3% by weight, or may be less than 0.1% by weight. The technology disclosed herein can be preferably practiced in an embodiment in which the monomer component of the acrylic polymer is substantially free of any functional group-containing monomer.

[0057] In this specification, the monomer component being substantially free of monomer A (e.g., the optional functional group-containing monomer) means that the monomer A is not used at least intentionally, and it is permissible for the monomer A to be unintentionally included in an amount of, for example, about 0.01% by weight or less.

[0058] In addition, a hydroxyl-containing monomer may be used as the optional functional group-containing monomer. In this case, the content of the hydroxyl-containing monomer in the monomer component is suitably about 10% by weight or less (for example, 0.001 to 10% by weight), preferably about 5% by weight or less, more preferably about 2% by weight or less. In some embodiments, the content of the hydroxyl-containing monomer in the monomer component may be, for example, less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, less than 0.1% by weight, or less than 0.01% by weight. The monomer component of the acrylic polymer may not substantially contain a hydroxyl-containing monomer. In the technology disclosed herein, the desired properties and effects can be preferably realized in a composition in which the amount of the hydroxyl-containing monomer used is limited or not used.

[0059] The proportion of the carboxyl group-containing monomer in the total functional group-containing monomers (total functional group-containing monomers including the carboxyl group-containing monomer) used as a copolymerization component of the acrylic polymer is 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, for example, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99.9% by weight or more). The upper limit of the proportion of the carboxyl group-containing monomer in the total functional group-containing monomer is 100% by weight, and may be, for example, 95% by weight or less.

[0060] The monomer components constituting the acrylic polymer may contain other copolymerization components other than the functional group-containing monomers described above for the purpose of improving cohesive strength, etc. Examples of other copolymerization components include vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate); olefin monomers; chlorine-containing monomers; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and the like. The other copolymerization components may be used alone or in combination of two or more.

[0061] The amount of such other copolymerization components is not particularly limited and may be appropriately selected according to the purpose and use, but from the viewpoint of appropriately exerting the effect of use, it is appropriate to set it to 0.05 wt% or more, and it may be 0.5 wt% or more. In addition, from the viewpoint of easily balancing the adhesive performance, the content of other copolymerization components in the monomer component is appropriate to be 20 wt% or less, and from the viewpoint of appropriately exerting the adhesive properties based on the essential monomer components, it is preferably 10 wt% or less, more preferably 8 wt% or less, and even more preferably less than 5 wt%, for example, it may be less than 3 wt%, or it may be less than 1 wt%. The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer component does not substantially contain other copolymerization components.

[0062] The acrylic polymer may contain a polyfunctional monomer having at least two polymerizable functional groups (typically radically polymerizable functional groups) having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, as another monomer component. By using a polyfunctional monomer as a monomer component, the cohesive force of the adhesive layer can be increased. The polyfunctional monomer can be used as a crosslinking agent. The polyfunctional monomer is not particularly limited, and examples thereof include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, and the like. The polyfunctional monomer can be used alone or in combination of two or more kinds.

[0063] The amount of the polyfunctional monomer used is not particularly limited, and can be appropriately set so that the purpose of using the polyfunctional monomer is achieved. The amount of the polyfunctional monomer used can be about 3% by weight or less of the monomer component, preferably about 2% by weight or less, and more preferably about 1% by weight or less (for example, about 0.5% by weight or less). When using a polyfunctional monomer, the lower limit of the amount used is not particularly limited as long as it is greater than 0% by weight. Usually, the effect of using the polyfunctional monomer can be appropriately exhibited by setting the amount of the polyfunctional monomer used to about 0.001% by weight or more (for example, about 0.01% by weight or more) of the monomer component.

[0064] In a particularly preferred embodiment, an acrylic polymer synthesized using a monomer component consisting essentially of heptyl acrylate (preferably n-heptyl acrylate) and a carboxyl group-containing monomer (preferably acrylic acid) is used as the acrylic polymer. According to the above monomer composition, the action of heptyl acrylate and the carboxyl group-containing monomer is effectively exerted, and a predetermined 23°C storage modulus and 23°C tan δ are both achieved, and a high degree of suppression of fine uneven deformation can be preferably realized. From such a viewpoint, the total ratio of heptyl acrylate and the carboxyl group-containing monomer in the above monomer component is appropriately 90% by weight or more (90 to 100% by weight), preferably 95% by weight or more, more preferably 99% by weight or more, even more preferably more than 99.5% by weight, and particularly preferably more than 99.9% by weight (for example, more than 99.99% by weight), and the total ratio of heptyl acrylate and the carboxyl group-containing monomer in the above monomer component may be 100% by weight.

[0065] The biomass carbon ratio of the monomer components constituting the acrylic polymer (the biomass carbon ratio of the acrylic polymer) may be, for example, 1% or more, suitably 10% or more, preferably 30% or more, more preferably 50% or more (e.g., more than 50%), may be 70% or more, may be 80% or more, or may be 90% to 100%. By designing in this way, an acrylic pressure-sensitive adhesive that takes into consideration the reduction of dependency on fossil resource-based materials can be obtained.

[0066] Although not particularly limited, it is appropriate that the copolymer composition of the acrylic polymer is designed so that the glass transition temperature (Tg) of the polymer is about -15°C or less (for example, about -70°C or more and -15°C or less). Here, the Tg of the acrylic polymer refers to the Tg calculated by the Fox formula based on the composition of the monomer components used in the synthesis of the polymer. The Fox formula, as shown below, is a relational expression between the Tg of the 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 the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i.

[0067] The glass transition temperature of the homopolymer used to calculate Tg is determined from known materials, specifically, from the value described in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). For monomers for which multiple values ​​are described in this document, the highest value is used. If the value is not described in the Polymer Handbook, the value obtained by the measurement method described in JP-A-2007-51271 is used.

[0068] Although not particularly limited, from the viewpoint of impact resistance and adhesion to an adherend, the Tg of the acrylic polymer is advantageously about -25°C or less, preferably about -35°C or less, more preferably about -40°C or less. In some embodiments, from the viewpoint of cohesive strength, the Tg of the acrylic polymer is, for example, about -70°C or more, may be about -65°C or more, may be about -60°C or more, or may be about -55°C or more. The technology disclosed herein can be preferably implemented in an embodiment in which the Tg of the acrylic polymer is about -65°C or more and -35°C or less (for example, about -55°C or more and -40°C or less). The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (i.e., the type and amount ratio of the monomers used in the synthesis of the polymer).

[0069] The method for obtaining an acrylic polymer is not particularly limited, and various polymerization methods known as a synthesis method for an acrylic polymer, such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method, can be appropriately adopted. For example, a solution polymerization method can be preferably adopted. As a monomer supply method when carrying out solution polymerization, a lump-sum charging method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc. can be appropriately adopted. The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0070] The solvent (polymerization solvent) used in the solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one of the following solvents or a mixture of two or more of them can be used: aromatic compounds (typically aromatic hydrocarbons) such as toluene; acetate esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol; ethers such as tert-butyl methyl ether; and ketones such as methyl ethyl ketone.

[0071] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators according to the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide (BPO) and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and the like. Still other examples of polymerization initiators include redox-based initiators obtained by combining peroxides with reducing agents. Such polymerization initiators can be used alone or in combination of two or more. The amount of polymerization initiator used may be a normal amount, and can be selected, for example, from the range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) relative to 100 parts by weight of the total monomer components.

[0072] The weight average molecular weight (Mw) of the acrylic polymer is not particularly limited, and an acrylic polymer having an appropriate Mw that can achieve both the above-mentioned 23° C. storage modulus and 23° C. tan δ is used. For example, the Mw of the acrylic polymer is about 10×10 4 ~500×10 4 From the viewpoint of adhesive performance, the Mw of the base polymer may be in the range of approximately 20×10 4 It may be more than 30×10 4 More than 40 x 10 is fine. 4 More than 50 x 10 is fine. 4or more. In some embodiments, the Mw of the acrylic polymer is greater than 600,000, may be greater than 650,000, is suitably greater than 700,000, and may be greater than 750,000. The greater the Mw of the acrylic polymer, the easier it is to obtain a pressure-sensitive adhesive exhibiting good cohesive strength, and the more the processability tends to improve. In some preferred embodiments, the Mw of the acrylic polymer is greater than 800,000, may be greater than 850,000, may be greater than 900,000, may be greater than 1 million (e.g., greater than 1 million), or may be greater than 1.2 million. For example, a monomer composition containing heptyl acrylate is easy to maintain a low viscosity, so that the synthesis of a high molecular weight substance is good, and an acrylic polymer having the above Mw is easy to obtain. In addition, by using an acrylic polymer containing heptyl acrylate as a monomer unit and having a Mw of a predetermined value or more, the above viscoelastic properties (specifically, the 23°C storage modulus and the 23°C tan δ) are easily satisfied based on the flexibility based on the chemical structure of the polymer and the cohesive strength based on the molecular weight. On the other hand, from the viewpoint of impact resistance, adhesive strength, ease of synthesis, etc., the Mw of the acrylic polymer is usually about 3 million or less, preferably 2.5 million or less, more preferably 2 million or less, even more preferably 1.8 million or less, and may be 1.5 million or less, or may be 1.3 million or less. In some preferred embodiments, the Mw of the acrylic polymer may be 1.1 million or less, 1 million or less, 950,000 or less, or 900,000 or less. In some other preferred embodiments, the Mw of the acrylic polymer may be 800,000 or less, 600,000 or less, less than 500,000, or 450,000 or less. By appropriately limiting the Mw of the acrylic polymer, the 23 ° C. tan δ tends to be improved.

[0073] The Mw of the acrylic polymer can be measured by gel permeation chromatography (GPC) and calculated as a standard polystyrene equivalent. Specifically, it can be measured under the following conditions using a GPC measuring device (trade name: "HLC-8220GPC" manufactured by Tosoh Corporation). The same applies to the examples described below. [GPC measurement conditions] Sample concentration: 0.2% by weight (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40℃ column: Sample column: 1 "TSKguardcolumn SuperHZ-H" + 2 "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: 1 "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0074] (Coloring agent) In the technology disclosed herein, the colored adhesive layer typically contains a colorant. By using a colorant, the adhesive layer can be colored and have the desired optical properties (light transmittance, etc.), concealing properties, design properties, and color. The colorant can be, for example, a black, gray, white, red, blue, yellow, green, yellow-green, orange, purple, gold, silver, pearl color, or other colorant. The colorant can typically be contained in the adhesive layer in a state dispersed (or dissolved) in the constituent material of the adhesive layer. As the colorant, a conventionally known pigment or dye can be used. Examples of the pigment include inorganic pigments and organic pigments. The colorant can be used alone or in combination of two or more types. When the double-sided adhesive sheet disclosed herein contains a non-colored adhesive layer, the adhesive layer does not substantially contain a colorant.

[0075] The colorant is not particularly limited, and may be, for example, a component capable of absorbing and attenuating light traveling through the adhesive layer, and may be a component that reduces the light transmittance of the adhesive layer by including the colorant in the adhesive layer (hence, may be referred to as a "light transmittance reducing component"). As such a colorant (hereinafter also referred to as a "first colorant"), a black colorant may be preferably used, since it can efficiently adjust the concealing property and light blocking property by using a small amount. Specific examples of black colorants include carbon black, graphite, aniline black, perylene black, cyanine black, titanium black, inorganic pigment hematite, activated carbon, molybdenum disulfide, chromium complex, anthraquinone-based colorants, and the like. The black colorant may be used alone or in appropriate combination of two or more kinds.

[0076] In some preferred embodiments, the adhesive layer contains carbon black particles as a colorant (first colorant). As the carbon black particles to be used, those generally called carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, pine soot, etc.) can be used without any particular limitation. In addition, as the carbon black particles, surface-modified carbon black particles having functional groups such as carboxyl groups, amino groups, sulfonic acid groups, and silicon-containing groups (e.g., alkoxysilyl groups, alkylsilyl groups) can also be used. Such surface-modified carbon black particles are also called self-dispersing carbon black, and do not require the addition of a dispersant or can reduce the amount of dispersant added. The above carbon black particles can be used alone or in combination of two or more types.

[0077] Since the light transmittance of the adhesive layer can be efficiently adjusted by using a small amount of the colorant (pigment), a particulate colorant (pigment) can be preferably used. In some preferred embodiments, a colorant (e.g., a particulate black colorant such as carbon black) having an average particle size of about 10 nm or more (e.g., about 30 nm or more) can be used. The average particle size is, for example, about 50 nm or more, may be about 100 nm or more, may be about 150 nm or more, may be about 200 nm or more, may be about 300 nm or more, or may be about 350 nm or more. The upper limit of the average particle size of the colorant is not particularly limited, and may be, for example, about 3000 nm or less, or may be about 1000 nm or less. From the viewpoint of reducing the light transmittance, the average particle size of the colorant is suitably about 500 nm or less, may be about 300 nm or less, or may be 200 nm or less.

[0078] In this specification, the average particle size of the colorant refers to the volume average particle size, and specifically, the particle size at 50% of the integrated value in the particle size distribution measured by a particle size distribution measuring device based on the laser scattering / diffraction method (50% volume average particle size; hereinafter, D 50 As a measuring device, for example, a product named "Microtrac MT3000II" manufactured by Microtrac Bell or an equivalent product can be used.

[0079] In the technology disclosed herein, the form of addition of the colorant (preferably a black colorant such as carbon black particles) to the adhesive composition is not particularly limited. The colorant such as carbon black particles can be added to the adhesive composition in the form of a dispersion in which the particles are dispersed in a dispersion medium. The dispersion medium constituting the dispersion is not particularly limited, and examples thereof include water (ion-exchanged water, reverse osmosis water, distilled water, etc.), various organic solvents (alcohols such as ethanol; ketones such as acetone; ethers such as butyl cellosolve and propylene glycol monomethyl ether acetate; esters such as ethyl acetate; aromatic hydrocarbons such as toluene; and mixed solvents thereof), and aqueous mixed solvents of water and the organic solvents. The dispersion may contain the above-mentioned dispersant. By mixing the dispersion with the adhesive composition, the adhesive composition contains a colorant (preferably a black colorant such as carbon black particles) and may further contain a dispersant.

[0080] In an embodiment in which the adhesive layer contains a first colorant, the content of the first colorant (preferably a black colorant such as carbon black particles) is appropriately set in consideration of the adjustment of the adherend hiding property and optical properties (light transmittance, etc.), the required adhesive properties, etc., and is not limited to a specific range. The content of the first colorant may also vary depending on the adhesive type, the shape and particle size of the first colorant, the compatibility with the adhesive, etc. The content of the first colorant in the adhesive layer is suitably about 0.01 wt% or more, may be 0.05 wt% or more, or may be 0.1 wt% or more, and from the viewpoint of the adherend hiding property, is preferably about 0.3 wt% or more, more preferably about 0.5 wt% or more. In some embodiments, the content of the first colorant is suitably about 1 wt% or more (for example, more than 1 wt%), and may be about 2 wt% or more. In addition, in an embodiment in which the adhesive layer contains a first colorant or does not contain a first colorant, the content of the first colorant (preferably a black colorant such as carbon black particles) can be about 30% by weight or less, suitably about 20% by weight or less, preferably about 10% by weight or less, more preferably about 7% by weight or less, even more preferably about 5% by weight or less, and may be about 3% by weight or less. In some embodiments, the content of the first colorant (preferably a black colorant such as carbon black particles) may be about 2% by weight or less, about 1% by weight or less, or about 0.5% by weight or less (for example, 0.3% by weight or less). By limiting the content of the first colorant, adhesive properties such as adhesive strength tend to be easily maintained.

[0081] In some other embodiments, the adhesive layer may be embodied in such a manner that it contains a second colorant (e.g., a metal oxide) described below as a colorant. The second colorant is defined as a colorant different from the first colorant. For example, when the adhesive layer contains at least two types of colorants, at least one of the multiple colorants used is the first colorant described above, and the other of the colorants is the second colorant described below, and the first colorant and the second colorant are used in combination. In some other embodiments, the adhesive layer may contain the second colorant and be substantially free of the first colorant described above.

[0082] The second colorant is not particularly limited, and may be, for example, a component that reduces the light transmittance of the adhesive layer, as in the first adhesive, or may be a component that can reduce the amount of light entering the adhesive layer. The second colorant may also be a component that imparts a color or hue different from that of the first colorant. Such a second colorant may be selected, for example, from a white colorant or a gray colorant. The second colorant may be one or more selected from inorganic materials (e.g., metals and metal compounds), organic materials, and organic-inorganic composites. Specific examples of the second colorant include metal oxides such as titanium oxide (titanium dioxide such as rutile titanium dioxide and anatase titanium dioxide), zinc oxide, cerium oxide, aluminum oxide, silicon oxide, zirconium oxide, magnesium oxide, calcium oxide, tin oxide, barium oxide, cesium oxide, and yttrium oxide; carbonate compounds such as magnesium carbonate, calcium carbonate (light calcium carbonate, heavy calcium carbonate, etc.), barium carbonate, and zinc carbonate; and hydroxides such as aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide. Examples of the coloring agent include inorganic materials such as aluminum silicate, magnesium silicate, calcium silicate, and other silicate compounds; barium sulfate, calcium sulfate, barium stearate, zinc oxide, zinc sulfide, talc, clay, kaolin, titanium phosphate, mica, gypsum, white carbon, diatomaceous earth, bentonite, lithopone, zeolite, sericite, hydrated halloysite, and the like; and organic materials such as acrylic resins, polystyrene resins, polyurethane resins, amide resins, polycarbonate resins, silicone resins, urea-formaldehyde resins, and melamine resins. The second colorant does not include carbon black particles and can be defined as a colorant different from carbon black particles. Typically, the second colorant does not include a light-absorbing black colorant.

[0083] In some preferred embodiments, the pressure-sensitive adhesive layer contains a metal oxide as the second colorant. By using the first colorant (preferably a black colorant) in combination with a metal oxide, it is possible to obtain a color tone that cannot be obtained by using only one colorant, while adjusting optical properties such as light transmittance. It is also possible to improve the concealment of the adherend. The metal oxide may be selected from the materials described above. Suitable examples include titanium oxide, zinc oxide, cerium oxide, aluminum oxide, silicon oxide, zirconium oxide, magnesium oxide, and calcium oxide, and among these, titanium oxide, silicon oxide, and zirconium oxide are preferred, and titanium oxide is particularly preferred. The metal oxide may be used alone or in combination of two or more.

[0084] In an embodiment in which the second colorant has a particulate shape, the average particle size of the second colorant (e.g., a white colorant, preferably metal oxide particles) is not particularly limited. Particles of an appropriate size that can realize the desired optical properties (light transmittance, etc.) can be used depending on the thickness of the adhesive layer, the type of adhesive, etc. The average particle size of the second colorant can be, for example, about 1 nm or more, and is suitably about 5 nm or more. From the viewpoint of compatibility, handling, etc., the average particle size of the second colorant is preferably about 10 nm or more, may be about 20 nm or more, or may be about 30 nm or more. From the viewpoint of maintaining adhesive properties, etc., the upper limit of the average particle size is, for example, about 300 nm or less, preferably less than 100 nm (e.g., 90 nm or less), more preferably about 70 nm or less, even more preferably about 50 nm or less, and may be about 35 nm or less (e.g., about 25 nm or less).

[0085] In an embodiment in which the adhesive layer contains a second colorant, the content of the second colorant (e.g., a white colorant, preferably a metal oxide) in the adhesive layer is appropriately set in consideration of the effect of containing the second colorant and the required adhesive properties, and is not limited to a specific range. The content of the second colorant may also vary depending on the adhesive type, the shape and particle size of the second colorant, and the compatibility with the adhesive. From the viewpoint of effectively obtaining the effect of containing the second colorant, the content of the second colorant in the adhesive layer is appropriately about 1 wt% or more, preferably about 2 wt% or more, more preferably about 3 wt% or more, and may be about 4 wt% or more, or may be about 5 wt% or more. In addition, in an embodiment in which the adhesive layer includes a second colorant or an embodiment in which the adhesive layer does not include a second colorant, the content of the second colorant in the adhesive layer can be approximately 30% by weight or less, appropriately approximately 25% by weight or less, may be approximately 20% by weight or less, approximately 15% by weight or less, approximately 12% by weight or less, approximately 10% by weight or less, or approximately 8% by weight or less, from the standpoint of compatibility with the adhesive components and maintenance of adhesive properties such as adhesive strength and impact resistance.

[0086] In an embodiment in which the adhesive layer contains a first colorant and a second colorant, the usage ratio of the amount C1 of the first colorant to the amount C2 of the second colorant is appropriately set so as to realize the intended concealment of the adherend, adjustment of optical properties (such as light transmittance), design, and color, and is not limited to a specific range. In some embodiments, the weight ratio (C2 / C1) of the amount C1 of the first colorant (preferably a black colorant) to the amount C2 of the second colorant (e.g., a white colorant, preferably a metal oxide) is approximately 0.01 or more, suitably 0.1 or more, preferably 1 or more (e.g., more than 1), may be 10 or more, may be 30 or more, or may be 50 or more (e.g., 70 or more). The larger the weight ratio (C2 / C1), the more favorably the effect of adding the second colorant is exhibited. In some embodiments, the weight ratio (C2 / C1) is about 1000 or less, suitably 500 or less, preferably 300 or less, and may be 100 or less, 80 or less, or 60 or less. The smaller the weight ratio (C2 / C1), the more favorably the effect of adding the first colorant is exerted. In an embodiment in which the first colorant is a black colorant, the concealment of the adherend tends to be improved.

[0087] In an embodiment in which the adhesive layer includes a black colorant as the first colorant and a metal oxide as the second colorant, the content of the colorant other than the black colorant and the metal oxide is not particularly limited, and can be, for example, less than 30% by weight of the entire adhesive layer, preferably less than 10% by weight, and can be, for example, less than 5.0% by weight, and can be less than 3.0% by weight (for example, less than 2.0% by weight, or even less than 1% by weight). The technology disclosed herein can be implemented in an embodiment in which the adhesive layer is provided with substantially no colorant other than the black colorant and the metal oxide. In this specification, "substantially no" means that it is not intentionally added, and for example, the content in the adhesive layer can be 0.3% by weight or less (for example, 0.1% by weight or less, typically 0.01% by weight or less).

[0088] In addition, from the viewpoint of compatibility with the adhesive component, the colorant may be a material (particulate colorant) exemplified as the colorant above that has been surface-treated with a surface treatment agent. The surface treatment is not limited to a specific treatment, since an appropriate treatment can be selected depending on the type of core particles, the type of dispersion medium, etc.

[0089] The adhesive composition disclosed herein may contain a component that contributes to improving the dispersibility of the colorant. Such a dispersibility-improving component may be, for example, a polymer, an oligomer, a liquid resin, a surfactant (anionic, cationic, nonionic, amphoteric surfactant), etc. The dispersibility-improving component may be used alone or in combination of two or more. The dispersibility-improving component is preferably dissolved in the adhesive composition. The oligomer may be, for example, a low molecular weight polymer (e.g., having a Mw of about 10×10) of a monomer component including one or more of the acrylic monomers exemplified above. 4 Less than 5 x 10 4The liquid resin may be, for example, a tackifier resin (typically a tackifier resin such as a rosin-based, terpene-based, or hydrocarbon-based resin, for example, hydrogenated rosin methyl ester) having a softening point of about 50° C. or less, more preferably about 40° C. or less. Such a dispersibility improving component can suppress uneven dispersion of the colorant (for example, a particulate black colorant such as carbon black), and thus suppress color unevenness in the adhesive layer. Therefore, an adhesive layer with better appearance quality can be formed.

[0090] The form in which the dispersibility-improving component is added is not particularly limited, and the dispersibility-improving component may be included in a liquid containing a colorant (e.g., a black colorant such as carbon black particles) before being blended into the pressure-sensitive adhesive composition, or the dispersibility-improving component may be supplied to the pressure-sensitive adhesive composition at the same time as the colorant, or before or after the addition of the colorant.

[0091] The content of the dispersibility improving component is not particularly limited, and from the viewpoint of suppressing the influence on the adhesive properties (e.g., reduction in cohesiveness), it is appropriate to set it to about 20% by weight or less (preferably about 10% by weight or less, more preferably 7% by weight or less, for example about 5% by weight or less) of the entire adhesive layer. In some embodiments, the content of the dispersibility improving component can be about 10 times or less (preferably about 5 times or less, for example about 3 times or less) the weight of the colorant. On the other hand, from the viewpoint of suitably exerting the effect of the dispersibility improving component, it is appropriate to set the content to about 0.2% by weight or more (typically about 0.5% by weight or more, preferably about 1% by weight or more) of the entire adhesive layer. In some embodiments, the content of the dispersibility improving component can be about 0.2 times or more (preferably about 0.5 times or more, for example 1 time or more) the weight of the colorant.

[0092] The content of the colorant in the adhesive layer (when two or more kinds of colorants are included, the total amount of the two or more kinds, the total content) is appropriately set in consideration of the intended adherend hiding property, optical properties (light transmittance, etc.), design, color, etc., and the required adhesive properties, etc., and is not limited to a specific range. The content of the colorant in the adhesive layer is about 0.1 wt% or more, and appropriately about 0.5 wt% or more, and from the viewpoint of adherend hiding property, etc., is preferably about 1 wt% or more, more preferably about 1.5 wt% or more, and even more preferably about 2 wt% or more. In some embodiments, the content of the colorant in the adhesive layer is appropriately about 3 wt% or more, may be about 5 wt% or more, or may be about 7 wt% or more. The content of the colorant in the adhesive layer can be approximately 30% by weight or less from the standpoint of compatibility with the adhesive components and maintaining adhesive properties such as adhesive strength and impact resistance, and is usually approximately 20% by weight or less. It may also be approximately 15% by weight or less, approximately 10% by weight or less, approximately 8% by weight or less, approximately 6% by weight or less, or approximately 4% by weight or less.

[0093] (tackifier resin) In some preferred embodiments, the adhesive layer includes a tackifier resin. The adhesive strength can be improved by using a tackifier resin. According to the technology disclosed herein, the adhesive layer can have a predetermined viscoelastic property (specifically, 23°C storage modulus and 23°C tan δ) and gel fraction when the composition includes a tackifier resin. Although not particularly limited, the effect of using a tackifier resin can be effectively exhibited in a composition including a high molecular weight acrylic polymer. The tackifier resin is not particularly limited, and various tackifier resins such as rosin-based tackifier resins, terpene-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, phenol-based tackifier resins, and ketone-based tackifier resins can be used. Such tackifier resins can be used alone or in combination of two or more.

[0094] Specific examples of rosin-based tackifying resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; modified rosins obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.; the same applies below); and various other rosin derivatives. Examples of the rosin derivative include rosin esters such as those obtained by esterifying unmodified rosin with alcohols (i.e., esterified products of rosin) and those obtained by esterifying modified rosin with alcohols (i.e., esterified products of modified rosin); unsaturated fatty acid modified rosins obtained by modifying unmodified rosin or modified rosin with unsaturated fatty acid; unsaturated fatty acid modified rosin esters obtained by modifying rosin esters with unsaturated fatty acid; rosin alcohols obtained by reducing the carboxyl groups in unmodified rosin, modified rosin, unsaturated fatty acid modified rosins, or unsaturated fatty acid modified rosin esters; metal salts of rosins (particularly rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; rosin phenolic resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) using an acid catalyst and thermally polymerizing the mixture; and the like. Among these, rosin esters are preferred.

[0095] Although not particularly limited, specific examples of rosin esters include esters of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), such as methyl esters, triethylene glycol esters, glycerin esters, pentaerythritol esters, etc.

[0096] Examples of terpene-based tackifier resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers; modified terpene resins obtained by modifying these terpene resins (phenol-modified, aromatic-modified, hydrogen-modified, hydrocarbon-modified, etc.); etc. An example of the modified terpene resin is a terpene phenol resin.

[0097] Terpene phenolic resin refers to a polymer containing a terpene residue and a phenol residue, and is a concept that includes both a copolymer of a terpene and a phenolic compound (terpene-phenol copolymer resin) and a homopolymer or copolymer of a terpene modified with phenol (phenol-modified terpene resin). Specific examples of terpenes that constitute such terpene phenolic resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d / l-forms (dipentene)). Hydrogenated terpene phenolic resin refers to a hydrogenated terpene phenolic resin having a structure obtained by hydrogenating such a terpene phenolic resin. It is also called hydrogenated terpene phenolic resin.

[0098] Examples of hydrocarbon-based tackifying resins include various hydrocarbon resins such as aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic / aromatic copolymer (C5 / C9) petroleum resins, hydrogenated products thereof (for example, alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), various modified products thereof (for example, maleic anhydride modified products), coumarone resins, and coumarone-indene resins.

[0099] In some embodiments, it is preferable to use at least one selected from rosin-based tackifier resins and terpene-based tackifier resins as the tackifier resin. By incorporating rosin-based tackifier resins and / or terpene-based tackifier resins into an acrylic adhesive, excellent adhesive properties such as adhesive strength can be easily obtained. In some preferred embodiments, the total proportion of the rosin-based tackifier resin and the terpene-based tackifier resin in the entire tackifier resin contained in the adhesive layer can be, for example, more than about 50% by weight (more than 50% by weight and not more than 100% by weight), and may be more than about 70% by weight, more than about 80% by weight, more than about 90% by weight, more than 95% by weight, or more than 99% by weight.

[0100] Some preferred embodiments include an embodiment in which the tackifier resin contains one or more terpene phenol resins. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the total amount of the tackifier resin is about 25% by weight or more (more preferably about 30% by weight or more). The proportion of the terpene phenol resin in the total amount of the tackifier resin may be about 50% by weight or more, about 70% by weight or more, about 80% by weight or more, or about 90% by weight or more. Substantially all of the tackifier resin (for example, about 95% by weight or more and 100% by weight or less, or even about 99% by weight or more and 100% by weight or less) may be a terpene phenol resin.

[0101] The content of the terpene phenol resin in the adhesive layer is not particularly limited as long as the desired properties (viscoelastic properties, etc.) are satisfied. In some embodiments, the content of the terpene phenol resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer from the viewpoint of improving adhesive strength. The more the amount of the terpene phenol resin used, the higher the 23°C storage modulus tends to be. In addition, in some embodiments, the content of the terpene phenol resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, may be 50 parts by weight or less, may be 40 parts by weight or less, or may be 30 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, from the viewpoint of improving the unevenness deformation mitigation properties of the adhesive, the content of the above-mentioned terpene phenol resin is less than 30 parts by weight, more preferably 25 parts by weight or less, even more preferably 22 parts by weight or less, and may be 20 parts by weight or less.

[0102] The softening point of the tackifier resin is not particularly limited. From the viewpoint of improving the cohesive force, a tackifier resin having a softening point (softening temperature) of about 80°C or higher may be preferably used. The softening point of the tackifier resin may be about 100°C or higher, or about 110°C or higher. In addition, from the viewpoint of adhesion to an adherend, a tackifier resin having a softening point of about 200°C or lower (more preferably about 180°C or lower) may be preferably used. In some embodiments, the softening point of the tackifier resin may be lower than 160°C, or may be lower than 150°C.

[0103] The softening point of the tackifier resin in this specification is defined as a value measured based on the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at a low temperature, and is carefully filled into a ring placed on a flat metal plate so as not to create bubbles. After cooling, the part that protrudes from the flat surface including the top end of the ring is cut off with a slightly heated knife. Next, a holder (ring stand) is placed in a glass container (heating bath) with a diameter of 85 mm or more and a height of 127 mm or more, and glycerin is poured to a depth of 90 mm or more. Next, a steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in glycerin without touching each other, and the temperature of the glycerin is kept at 20°C ± 5°C for 15 minutes. Next, a steel ball is placed in the center of the surface of the sample in the ring, and this is placed in a fixed position on the holder. Next, keeping the distance from the top of the ring to the glycerin surface at 50 mm, place a thermometer and align the center of the thermometer's mercury bulb to the same height as the center of the ring, then heat the container. The flame of the Bunsen burner used for heating should be midway between the center of the bottom of the container and its edge, and heating should be uniform. After heating begins and the temperature of the bath reaches 40°C, the rate of increase must be 5.0 ± 0.5°C per minute. The sample gradually softens and flows down the ring, and the temperature is read when it finally touches the bottom plate, and this is the softening point. The softening point is measured for two or more samples at the same time, and the average value is used.

[0104] In some embodiments, the tackifier resin is a tackifier resin T having a softening point of less than 150° C. L Tackifying resin T is used.L By using the tackifier resin T, a higher adhesive strength can be obtained. L The softening point of the tackifier resin T is less than 140° C., more preferably less than 130° C., and even more preferably less than 120° C., and may be 110° C. or less, 100° C. or less, or 90° C. or less. L The lower limit of the softening point of the tackifier resin T is not particularly limited. L From the viewpoint of exerting an appropriate cohesive force, the softening point of the polyurethane foam may be, for example, about 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, or 110°C or higher.

[0105] Tackifying resin T L As the tackifier resin, one type selected from the tackifier resins exemplified above having a softening point of less than 150° C. can be used alone or in combination of two or more types. L It is preferable that the tackifier resin T contains at least one selected from the group consisting of rosin-based tackifier resins and terpene-based tackifier resins. L may contain one type of rosin-based tackifier resin alone, or may contain two or more types of rosin-based tackifiers in combination. L may contain one terpene-based tackifying resin (eg, a terpene phenolic resin) alone, or may contain two or more terpene-based tackifying resins in combination.

[0106] In some embodiments, tackifier resin T L The proportion of the terpene-based tackifier resin (e.g., terpene phenol resin) in the total can be, for example, more than about 50% by weight, or may be about 65% by weight or more, about 75% by weight or more, 85% by weight or more, or 95% by weight or more. LThe composition can be preferably implemented in an embodiment in which substantially all of (for example, approximately 97% by weight or more, or 99% by weight or more, or may be 100% by weight) is a terpene-based tackifying resin.

[0107] Although not particularly limited, tackifier resin T L Examples of rosin-based tackifying resins that can be preferably used as the tackifying resin include rosin esters such as unmodified rosin ester and modified rosin ester. A preferred example of a modified rosin ester is hydrogenated rosin ester. For example, esters of unmodified rosin or modified rosin (e.g. hydrogenated rosin), such as rosin esters such as methyl ester and glycerin ester, can be used as tackifying resin T. L It can be used as:

[0108] In some embodiments, tackifier resin T L may contain hydrogenated rosin ester. L may contain a non-hydrogenated rosin ester. The term "non-hydrogenated rosin ester" as used herein is a general concept that refers to the above-mentioned rosin esters other than the hydrogenated rosin ester. Examples of the non-hydrogenated rosin ester include unmodified rosin ester, disproportionated rosin ester, and polymerized rosin ester. Tackifier resin T L may contain, as rosin esters, a combination of hydrogenated rosin esters and non-hydrogenated rosin esters, may contain only one or more hydrogenated rosin esters, or may contain only one or more non-hydrogenated rosin esters. L As the rosin esters contained in the composition, only one or more hydrogenated rosin esters may be used.

[0109] In addition, tackifier resin T LThe tackifier resin may or may not contain a tackifier resin having a softening point of less than 50° C., more preferably about 40° C. or less (typically a rosin-based, terpene-based, or hydrocarbon-based tackifier resin, for example, hydrogenated rosin methyl ester). Such a low-softening-point tackifier resin may be a liquid tackifier resin that is liquid at 30° C. The liquid tackifier resin may be used alone or in combination of two or more. The content of the liquid tackifier resin is determined based on the tackifier resin T from the viewpoint of cohesive strength, etc. L It can be about 30% by weight or less of the total, suitably about 10% by weight or less (for example, 0 to 10% by weight), may be about 2% by weight or less (0.5 to 2% by weight), or may be less than 1% by weight.

[0110] Tackifying resin T L The content of is not particularly limited, but in some embodiments, it is appropriate to make it about 70 parts by weight or less relative to 100 parts by weight of the acrylic polymer, and it may be 60 parts by weight or less, 50 parts by weight or less, 40 parts by weight or less, or 30 parts by weight or less. In some preferred embodiments, the content of the tackifier resin T L The content of the tackifier resin T is less than 30 parts by weight, more preferably 25 parts by weight or less, and even more preferably 22 parts by weight or less, and may be 20 parts by weight or less, based on 100 parts by weight of the acrylic polymer. L The content of is, for example, 1 part by weight or more, suitably 5 parts by weight or more, preferably 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably 12 parts by weight or more, and may be 15 parts by weight or more, based on 100 parts by weight of the acrylic polymer. L The greater the amount used, the higher the 23°C storage modulus tends to be.

[0111] In some embodiments, the pressure-sensitive adhesive layer contains a tackifier resin T L and a tackifier resin T having a softening point of 150°C or higher (e.g., 150°C to 200°C). HThe tackifier resin T may be used in combination with the above. H As the tackifier resin, one type may be used alone or two or more types may be used in combination from among the tackifier resins exemplified above that have a softening point of 150° C. or higher.

[0112] In some embodiments, tackifier resin T L It is preferable that the tackifier resin T accounts for more than 50% by weight of the total amount of the tackifier resin contained in the pressure-sensitive adhesive layer. L The effect of the inclusion of the tackifier resin T in the total amount of the tackifier resin contained in the adhesive layer is easily manifested. L The ratio of tackifier resin T L From the viewpoint of more effectively exerting the effect of use, the content of the tackifier resin in the pressure-sensitive adhesive layer is preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, and may be 95% by weight or more, or may be 98% by weight or more. In some preferred embodiments, the tackifier resin contained in the pressure-sensitive adhesive layer is substantially tackifier resin T L In this embodiment, the tackifier resin T L The proportion is in the range of 99 to 100% by weight.

[0113] Although not particularly limited, in some embodiments, the tackifier resin may contain a tackifier resin having a hydroxyl value of more than 20 mgKOH / g (e.g., terpene phenol resin). Among them, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more is preferable. Hereinafter, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more may be referred to as a "high hydroxyl value resin". According to a tackifier resin containing such a high hydroxyl value resin, in addition to adhesive strength, a pressure-sensitive adhesive layer having high cohesive strength can be realized by interacting with a crosslinking agent such as an isocyanate-based crosslinking agent. In some embodiments, the tackifier resin may contain a high hydroxyl value resin having a hydroxyl value of 60 mgKOH / g or more (e.g., 70 mgKOH / g or more). In addition, such a high hydroxyl value resin (e.g., terpene phenol resin) is preferably used in combination with an acrylic polymer containing heptyl acrylate as a monomer component, for example, to achieve both adhesive strength and cohesive strength.

[0114] The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with acrylic polymers, the hydroxyl value of the high hydroxyl value resin is usually about 300 mgKOH / g or less, and is preferably about 200 mgKOH / g or less, and is preferably about 180 mgKOH / g or less, more preferably about 160 mgKOH / g or less, and even more preferably about 140 mgKOH / g or less, and may be 120 mgKOH / g or less, 100 mgKOH / g or less, or 80 mgKOH / g or less (for example, 65 mgKOH / g or less). The technology disclosed herein can be preferably implemented in an embodiment in which the tackifier resin contains a high hydroxyl value resin with a hydroxyl value of 30 to 160 mgKOH / g (for example, a terpene tackifier resin, preferably a terpene phenol resin). In some embodiments, a high hydroxyl value resin having a hydroxyl value of 30 to 80 mgKOH / g (eg, 30 to 65 mgKOH / g) can be preferably used.

[0115] Here, the hydroxyl value may be a value measured by potentiometric titration as specified in JIS K0070: 1992. The specific measurement method is as follows. [Method for measuring hydroxyl value] 1. Reagents (1) As the acetylation reagent, take about 12.5 g (about 11.8 mL) of acetic anhydride, add pyridine to make the total volume 50 mL, and stir thoroughly before use. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to make the total volume 100 mL, and stir thoroughly before use. (2) Use a 0.5 mol / L potassium hydroxide ethanol solution as the measurement reagent. (3) In addition, prepare toluene, pyridine, ethanol and distilled water. 2.Operation (1) Accurately weigh out approximately 2 g of sample into a flat-bottom flask, add 5 mL of acetylation reagent and 10 mL of pyridine, and attach an air condenser. (2) Heat the flask in a 100°C bath for 70 minutes, then allow it to cool, add 35 mL of toluene as a solvent from the top of the cooling tube and stir, then add 1 mL of distilled water and stir to decompose the acetic anhydride. Heat again in the bath for 10 minutes to complete the decomposition, then allow it to cool. (3) Wash the cooling tube with 5 mL of ethanol and remove it. Then, add 50 mL of pyridine as a solvent and stir. (4) Add 25 mL of 0.5 mol / L potassium hydroxide ethanol solution using a volumetric pipette. (5) Perform potentiometric titration with 0.5 mol / L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is the endpoint. (6) A blank test is carried out by carrying out steps (1) to (5) above without adding any sample. 3.Calculation The hydroxyl value is calculated according to the following formula. Hydroxyl value (mgKOH / g) = [(BC) x f x 28.05] / S + D Where: B: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test. C: Amount of 0.5 mol / L potassium hydroxide ethanol solution used for the sample (mL), f: Factor of 0.5 mol / L potassium hydroxide ethanol solution, S: weight of sample (g), D: acid number, 28.05: 1 / 2 the molecular weight of potassium hydroxide, 56.11. It is.

[0116] As the high hydroxyl value resin, those having a hydroxyl value of a predetermined value or more among the above-mentioned various tackifier resins can be used. The high hydroxyl value resin can be used alone or in combination of two or more. For example, a terpene phenol resin having a hydroxyl value of 30 mgKOH / g or more can be preferably used as the high hydroxyl value resin. The terpene phenol resin is advantageous because the hydroxyl value can be arbitrarily controlled by the copolymerization ratio of phenol.

[0117] Although not particularly limited, when a high hydroxyl value resin is used, the ratio of the high hydroxyl value resin (e.g., terpene phenol resin) to the entire tackifier resin contained in the adhesive layer may be about 5% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more. In some embodiments, the ratio of the high hydroxyl value resin to the entire tackifier resin is preferably, for example, about 30% by weight or more. This allows the effect of using the high hydroxyl value resin to be preferably exhibited. In some preferred embodiments, the ratio of the high hydroxyl value resin to the entire tackifier resin is about 40% by weight or more, about 50% by weight or more (e.g., more than 50% by weight), about 60% by weight or more, about 70% by weight or more, about 80% by weight or more, or about 90% by weight or more. Substantially all of the tackifier resin (e.g., about 95 to 100% by weight, or even about 99 to 100% by weight) may be a high hydroxyl value resin.

[0118] The softening point of the high hydroxyl value resin is not particularly limited. The softening point of the high hydroxyl value resin may be, for example, about 50°C or more, and from the viewpoint of improving the cohesive force, a high hydroxyl value resin having a softening point (softening temperature) of about 80°C or more may be preferably used. For example, a terpene phenol resin having such a softening point may be preferably used. The softening point of the high hydroxyl value resin may be about 100°C or more, or about 110°C or more. The upper limit of the softening point of the high hydroxyl value resin is not particularly limited. From the viewpoint of adhesion to the adherend, a high hydroxyl value resin having a softening point of about 200°C or less (more preferably about 180°C or less) may be preferably used. In some embodiments, the softening point of the high hydroxyl value resin may be less than 160°C, less than 150°C, less than 145°C, less than 140°C, less than 130°C, or less than 120°C.

[0119] The content of the high hydroxyl value resin in the adhesive layer is not particularly limited as long as the desired characteristics (viscoelasticity, etc.) are satisfied. In some embodiments, the content of the high hydroxyl value resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, and is preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength. In some embodiments, the content of the high hydroxyl value resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, may be 50 parts by weight or less, may be 40 parts by weight or less, or may be 30 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the high hydroxyl value resin is less than 30 parts by weight, more preferably 25 parts by weight or less, and even more preferably 22 parts by weight or less, and may be 20 parts by weight or less.

[0120] When the adhesive layer disclosed herein contains a tackifier resin, a tackifier resin derived from a plant (vegetable tackifier resin) may preferably act as the tackifier resin from the viewpoint of improving the biomass carbon ratio of the adhesive layer. Examples of vegetable tackifier resins include the above-mentioned rosin-based tackifier resin and terpene-based tackifier resin. The vegetable tackifier resin may be used alone or in combination of two or more. When the adhesive layer disclosed herein contains a tackifier resin, the proportion of the vegetable tackifier resin in the total amount of tackifier resins is preferably 30% by weight or more (e.g., 50% by weight or more, typically 80% by weight or more). In some embodiments, the proportion of the vegetable tackifier resin in the total amount of tackifier resins is 90% by weight or more (e.g., 95% by weight or more, typically 99 to 100% by weight). The technology disclosed herein may be preferably implemented in an embodiment that does not substantially contain tackifier resins other than vegetable tackifier resins.

[0121] The content of the tackifier resin in the adhesive layer is not particularly limited as long as the desired properties (viscoelastic properties, etc.) are satisfied. In some embodiments, the content of the tackifier resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, and is preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer from the viewpoint of improving adhesive strength. The more the amount of the tackifier resin used, the higher the 23°C storage modulus tends to be. In some embodiments, the content of the tackifier resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, may be 50 parts by weight or less, may be 40 parts by weight or less, or may be 30 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the tackifier resin is less than 30 parts by weight, more preferably 25 parts by weight or less, even more preferably 22 parts by weight or less, and may be 20 parts by weight or less.

[0122] (Acrylic Oligomer) In some preferred embodiments, the adhesive layer contains an acrylic oligomer. The inclusion of an acrylic oligomer can improve the adhesive strength of the adhesive. According to the technology disclosed herein, the adhesive layer can have a predetermined viscoelastic property (specifically, 23°C storage modulus and 23°C tan δ) and gel fraction when the composition contains an acrylic oligomer. Although not particularly limited, the effect of using an acrylic oligomer can be effectively exhibited in a composition containing a high molecular weight acrylic polymer. The acrylic oligomer can be used alone or in combination of two or more kinds.

[0123] The acrylic oligomer has a Tg of about 0°C or more and about 300°C or less, preferably about 20°C or more and about 300°C or less, more preferably about 40°C or more and about 300°C or less. By having the Tg within the above range, the adhesive strength can be suitably improved. In some preferred embodiments, from the viewpoint of the cohesiveness of the adhesive, the Tg of the acrylic oligomer is about 30°C or more, more preferably about 50°C or more (e.g. about 60°C or more), and from the viewpoint of adhesiveness, it is preferably about 200°C or less, more preferably about 150°C or less, and even more preferably about 100°C or less (e.g. about 80°C or less). In this specification, the Tg of the acrylic oligomer refers to the Tg calculated by the Fox formula based on the composition of the monomer components, similar to the Tg of the above-mentioned acrylic polymer.

[0124] The weight average molecular weight (Mw) of the acrylic oligomer can typically be about 1000 or more and less than about 30000, preferably about 1500 or more and less than about 20000, and more preferably about 2000 or more and less than about 10000. When Mw is within the above range, good adhesive strength is likely to be obtained. In some preferred embodiments, the Mw of the acrylic oligomer is about 2500 or more (e.g., about 3000 or more), and from the viewpoint of adhesiveness, it is preferably about 7000 or less, more preferably about 5000 or less (e.g., about 4500 or less, typically about 4000 or less). The Mw of the acrylic oligomer can be measured by gel permeation chromatography (GPC) and calculated as a value in terms of standard polystyrene. Specifically, it is measured using 2 columns of TSKgel GMH-H (20) on a Tosoh HPLC 8020 at a flow rate of about 0.5 mL / min with tetrahydrofuran solvent.

[0125] Examples of monomers constituting acrylic oligomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, Examples of the (meth)acrylate include alkyl (meth)acrylates such as butyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from alcohols derived from terpene compounds. These (meth)acrylates may be used alone or in combination of two or more.

[0126] The acrylic oligomer preferably contains, as a monomer unit, an acrylic monomer having a relatively bulky structure, typified by alkyl (meth)acrylates in which the alkyl group has a branched structure, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates), such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate; and (meth)acrylates having a cyclic structure, such as aryl (meth)acrylates, such as phenyl (meth)acrylate and benzyl (meth)acrylate, from the viewpoint of further improving the adhesiveness of the pressure-sensitive adhesive layer. In addition, when ultraviolet light is used in synthesizing an acrylic oligomer or preparing an adhesive layer, those having saturated bonds are preferred in that they are less likely to cause polymerization inhibition, and alkyl (meth)acrylates in which the alkyl group has a branched structure, or esters with alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) can be suitably used as monomers constituting the acrylic oligomer. The above-mentioned branched alkyl (meth)acrylates, alicyclic hydrocarbon group (meth)acrylates, and aryl (meth)acrylates all fall under the category of (meth)acrylate monomers in the technology disclosed herein. The alicyclic hydrocarbon group may be a saturated or unsaturated alicyclic hydrocarbon group.

[0127] The proportion of (meth)acrylate monomers (e.g., alicyclic hydrocarbon group-containing (meth)acrylates) in the monomer components constituting the acrylic oligomer is typically more than 50% by weight, preferably 60% by weight or more, and more preferably 70% by weight or more (e.g., 80% by weight or more, or even 90% by weight or more). In some preferred embodiments, the acrylic oligomer has a monomer composition consisting essentially of (meth)acrylate monomers.

[0128] In addition to the (meth)acrylate monomer, functional group-containing monomers can be used as the constituent monomer components of the acrylic oligomer. Suitable examples of the functional group-containing monomer include monomers having a nitrogen atom-containing ring (typically a nitrogen atom-containing heterocycle) such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; amino group-containing monomers such as N,N-dimethylaminoethyl (meth)acrylate; amide group-containing monomers such as N,N-diethyl (meth)acrylamide; carboxy group-containing monomers such as AA and MAA; and hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate. These functional group-containing monomers can be used alone or in combination of two or more. Among them, carboxy group-containing monomers are preferred, and AA is particularly preferred. For example, by using a carboxy group-containing monomer as the functional group-containing monomer, it is easy to improve the adhesive strength to a highly polar adherend.

[0129] When the monomer components constituting the acrylic oligomer contain a functional group-containing monomer, the proportion of the functional group-containing monomer (e.g., a carboxy group-containing monomer such as AA) in the monomer components is suitably about 1 wt % or more, preferably 2 wt % or more, more preferably 3 wt % or more, and is suitably about 15 wt % or less, preferably 10 wt % or less, more preferably 7 wt % or less.

[0130] The acrylic oligomer can be formed by polymerizing its 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 used in an appropriate mode. The type of polymerization initiator (e.g., azo-based polymerization initiator such as AIBN) that can be used as necessary is generally as exemplified in the synthesis of the acrylic polymer, and the amount of the polymerization initiator and the amount of the chain transfer agent, such as n-dodecyl mercaptan, that is optionally used, are appropriately set based on technical common sense so as to obtain a desired molecular weight, so detailed explanations are omitted here.

[0131] From the above viewpoint, 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 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, copolymers of ADA and methyl methacrylate (MMA), copolymers of DCPMA and IBXMA, and copolymers of DCPMA and MMA.

[0132] When the adhesive layer disclosed herein contains an acrylic oligomer, the content is suitably, for example, 0.1 parts by weight or more (for example, 1 part by weight or more) relative to 100 parts by weight of the acrylic polymer. From the viewpoint of better exerting the effect of the acrylic oligomer, the content of the acrylic oligomer is preferably about 3 parts by weight or more, more preferably about 5 parts by weight or more, and may be about 8 parts by weight or more, or may be about 10 parts by weight or more. Also, from the viewpoint of compatibility with the acrylic polymer, in some embodiments, the content of the acrylic oligomer is suitably less than 50 parts by weight (for example, less than 40 parts by weight) relative to 100 parts by weight of the acrylic polymer, preferably less than 30 parts by weight, more preferably about 25 parts by weight or less, and even more preferably about 20 parts by weight or less. In some preferred embodiments, the content of the acrylic oligomer is less than 20 parts by weight, may be 15 parts by weight or less, may be 12 parts by weight or less, may be 10 parts by weight or less, may be 8 parts by weight or less, or may be 6 parts by weight or less, based on 100 parts by weight of the acrylic polymer. By limiting the amount of the acrylic oligomer used in this way, the effects of the technology disclosed herein can be preferably exhibited. In some other embodiments, the content of the acrylic oligomer may be 5 parts by weight or less, may be 1 part by weight or less (for example, less than 1 part by weight) based on 100 parts by weight of the acrylic polymer. The technology disclosed herein can be implemented in an embodiment in which the pressure-sensitive adhesive layer does not substantially contain an acrylic oligomer.

[0133] In some preferred embodiments, the adhesive layer contains one or more of the above-mentioned tackifier resins and one or more of the acrylic oligomers. By using a tackifier resin and an acrylic oligomer in combination in a composition containing an acrylic polymer, excellent adhesion can be obtained. In particular, the effects of the technology disclosed herein can be preferably realized in a composition containing an acrylic polymer containing heptyl acrylate as a monomer component, a tackifier resin, and an acrylic oligomer. Although not particularly limited, the effect of using a tackifier resin and an acrylic oligomer in combination can be effectively exerted in a composition containing a high molecular weight acrylic polymer. Content C of acrylic oligomer in adhesive layer O [wt%] Tackifier resin content C T [weight%] ratio (C T / C O ) is not particularly limited, and is suitably set to, for example, 0.1 or more and 10 or less. In some embodiments, the above ratio (C T / C O The ratio (C) is 0.25 or more, may be 0.4 or more, may be 0.7 or more, or may be 0.8 or more. T / C O The higher the ratio (C T / C O ) is about 1 or more (for example, more than 1.0), more preferably 1.5 or more, even more preferably 2.0 or more, and may be 2.5 or more, 3.0 or more, or 3.5 or more. From the viewpoint of obtaining the effect of adding the acrylic oligomer, in some embodiments, the above ratio (C T / C O ) is about 9 or less, suitably 7 or less, may be 5 or less, or may be 3 or less. In some other embodiments, the ratio (C T / C O ) may be 2 or less, 1.5 or less, or 1.2 or less.

[0134] In some preferred embodiments, from the viewpoint of preferably exerting the effects of the technology disclosed herein, the combined amount (total amount) of the tackifier resin and acrylic oligomer contained in the adhesive layer is suitably approximately 1 part by weight or more per 100 parts by weight of the acrylic polymer, preferably approximately 10 parts by weight or more, more preferably approximately 16 parts by weight or more, even more preferably 20 parts by weight or more, and particularly preferably 25 parts by weight or more, and is suitably less than 120 parts by weight (for example, approximately 80 parts by weight or less), preferably less than 60 parts by weight, more preferably approximately 50 parts by weight or less, even more preferably approximately 40 parts by weight or less, and particularly preferably 35 parts by weight or less, and may be 30 parts by weight or less, 28 parts by weight or less, or 26 parts by weight or less.

[0135] In the technology disclosed herein, the total amount (total amount) of the acrylic polymer, tackifier resin and acrylic oligomer in the adhesive layer is appropriately set so that the effects of the technology disclosed herein are exerted, and is not limited to a specific range. In some preferred embodiments, the total amount (total amount) of the acrylic polymer, tackifier resin and acrylic oligomer in the entire adhesive layer is suitable to be more than 50% by weight, preferably about 70% by weight or more, more preferably about 90% by weight or more, even more preferably 95% by weight or more (for example, 95% by weight or more and 100% by weight or less, or less than 100% by weight), and may be 98% by weight or more, from the viewpoint of preferably exerting the effects of the technology disclosed herein.

[0136] (Crosslinking agent) In the technology disclosed herein, the adhesive composition used to form the adhesive layer may contain a crosslinking agent as necessary. The type of crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. The crosslinking agents may be used alone or in combination of two or more. Among these, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and melamine-based crosslinking agents are preferred, and isocyanate-based crosslinking agents and epoxy-based crosslinking agents are more preferred. By appropriately selecting and using a crosslinking agent, the adhesive layer can obtain a moderate cohesive force, and an adhesive having a good balance between adhesive force and cohesive force can be formed. In addition, the gel fraction and 23°C storage modulus can be increased by increasing the amount of crosslinking agent used. The adhesive layer in the technology disclosed herein may contain the crosslinking agent in a form after crosslinking reaction, a form before crosslinking reaction, a form partially crosslinked, an intermediate or composite form thereof, etc. The crosslinking agent is typically contained in the adhesive layer exclusively in a form after crosslinking reaction.

[0137] As the isocyanate-based crosslinking agent, a polyfunctional isocyanate (which refers to a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. The isocyanate-based crosslinking agent can be used alone or in combination of two or more kinds.

[0138] Examples of the polyfunctional isocyanate include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates. Specific examples of aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

[0139] Specific examples of alicyclic polyisocyanates include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0140] Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, Examples of the diisocyanate include 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

[0141] A preferred polyfunctional isocyanate is one having an average of three or more isocyanate groups per molecule. Such a trifunctional or higher isocyanate may be a multimer (typically a dimer or trimer) of a bifunctional or trifunctional or higher isocyanate, a derivative (for example, an addition reaction product of a polyhydric alcohol and two or more molecules of a polyfunctional isocyanate), a polymer, etc. For example, a dimer or trimer of diphenylmethane diisocyanate, an isocyanurate of hexamethylene diisocyanate (a trimer adduct of an isocyanurate structure), a reaction product of trimethylolpropane and tolylene diisocyanate, a reaction product of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and other polyfunctional isocyanates may be mentioned. Commercially available examples of such polyfunctional isocyanates include those manufactured by Asahi Kasei Chemicals Corporation under the trade names "Duranate TPA-100," and those manufactured by Tosoh Corporation under the trade names "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096."

[0142] The technology disclosed herein can be preferably implemented in an embodiment using at least an isocyanate-based crosslinking agent as a crosslinking agent. The amount of the isocyanate-based crosslinking agent used is not particularly limited. The amount of the isocyanate-based crosslinking agent used can be, for example, about 0.1 parts by weight or more relative to 100 parts by weight of the acrylic polymer. From the viewpoint of achieving both cohesive strength and adhesion, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the acrylic polymer is usually preferably about 0.3 parts by weight or more (for example, 0.5 parts by weight or more). In some preferred embodiments, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the acrylic polymer is about 1.0 part by weight or more, more preferably about 1.5 parts by weight or more, even more preferably about 2.0 parts by weight or more, particularly preferably about 2.5 parts by weight or more, and may be about 2.8 parts by weight or more. By increasing the amount of the isocyanate-based crosslinking agent used, the gel fraction and the 23° C. storage modulus can be improved. From the viewpoint of improving adhesion to the adherend, the amount of the isocyanate-based crosslinking agent used is suitably 10 parts by weight or less per 100 parts by weight of the acrylic polymer, preferably 8 parts by weight or less, more preferably 6 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 4 parts by weight or less, and may be 3.5 parts by weight or less, or may be 3.2 parts by weight or less.

[0143] As the epoxy crosslinking agent, a compound having two or more epoxy groups in one molecule can be used without any particular limitation. An epoxy crosslinking agent having 3 to 5 epoxy groups in one molecule is preferred. The epoxy crosslinking agent can be used alone or in combination of two or more kinds.

[0144] Non-limiting specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc. Commercially available epoxy crosslinking agents include Mitsubishi Gas Chemical Company's product names "TETRAD-C" and "TETRAD-X," DIC Corporation's product name "Epicron CR-5L," Nagase ChemteX Corporation's product name "Denacol EX-512," Nissan Chemical Industries' product name "TEPIC-G," etc.

[0145] The amount of the epoxy crosslinking agent used is not particularly limited. The amount of the epoxy crosslinking agent used can be, for example, more than 0 part by weight and about 1 part by weight or less (typically about 0.001 to 1 part by weight) relative to 100 parts by weight of the acrylic polymer. From the viewpoint of favorably exerting the effect of improving the cohesive force, the amount of the epoxy crosslinking agent used is usually about 0.002 parts by weight or more relative to 100 parts by weight of the acrylic polymer, preferably about 0.005 parts by weight or more, for example, about 0.01 parts by weight or more, or about 0.02 parts by weight or more. By increasing the amount of the epoxy crosslinking agent used, the gel fraction and the 23°C storage modulus can be improved. Also, from the viewpoint of improving adhesion to the adherend, in some embodiments, the amount of the epoxy crosslinking agent used can be about 0.7 parts by weight or less relative to 100 parts by weight of the acrylic polymer, suitably about 0.5 parts by weight or less, preferably about 0.2 parts by weight or less, more preferably about 0.1 parts by weight or less (for example, less than 0.1 parts by weight), and may be 0.07 parts by weight or less, may be 0.04 parts by weight or less, or may be 0.03 parts by weight or less. By limiting the amount of the epoxy crosslinking agent used within a predetermined range, it is easy to maintain sufficient adhesive strength.

[0146] In some preferred embodiments, the crosslinking agent is a combination of an isocyanate-based crosslinking agent and at least one crosslinking agent having a different type of crosslinkable functional group from that of the isocyanate-based crosslinking agent. The technology disclosed herein can be preferably implemented in an embodiment in which a crosslinking agent other than an isocyanate-based crosslinking agent (i.e., a crosslinking agent having a different type of crosslinkable reactive group from that of an isocyanate-based crosslinking agent. Hereinafter, also referred to as a "non-isocyanate-based crosslinking agent") is used in combination with an isocyanate-based crosslinking agent.

[0147] The type of non-isocyanate crosslinking agent that can be used in combination with the isocyanate crosslinking agent is not particularly limited, and can be appropriately selected from the above-mentioned crosslinking agents. The non-isocyanate crosslinking agent can be used alone or in combination of two or more. In some preferred embodiments, an epoxy crosslinking agent can be used as the non-isocyanate crosslinking agent. For example, by using an isocyanate crosslinking agent and an epoxy crosslinking agent in combination, better adhesion properties can be achieved.

[0148] The relationship between the content of the isocyanate crosslinking agent and the content of the nonisocyanate crosslinking agent (preferably an epoxy crosslinking agent) is not particularly limited, and is appropriately set within a range that satisfies a predetermined viscoelasticity property and gel fraction. The content of the isocyanate crosslinking agent is, for example, greater than 1 time the content of the nonisocyanate crosslinking agent (preferably an epoxy crosslinking agent), may be approximately 5 times or more, and is preferably approximately 10 times or more, preferably approximately 50 times or more, more preferably approximately 80 times or more, even more preferably approximately 100 times or more (for example, more than 100 times), and particularly preferably approximately 120 times or more (for example, approximately 140 times or more). Furthermore, from the viewpoint of optimally exerting the effect of using an isocyanate-based crosslinking agent in combination with a non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent), the content of the isocyanate-based crosslinking agent relative to the content of the non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent) is usually, for example, approximately 1000 times or less, appropriately approximately 500 times or less, preferably approximately 300 times or less, more preferably approximately 200 times or less, and even more preferably approximately 180 times or less (for example, approximately 160 times or less).

[0149] The content of the crosslinking agent in the adhesive composition disclosed herein (total amount of crosslinking agent) is not particularly limited. From the viewpoint of cohesion, the content of the crosslinking agent is usually about 0.001 parts by weight or more, preferably about 0.01 parts by weight or more, more preferably about 1 part by weight or more, even more preferably about 2 parts by weight or more, and particularly preferably about 2.5 parts by weight or more, relative to 100 parts by weight of the acrylic polymer. The content of the crosslinking agent in the adhesive composition is usually about 20 parts by weight or less, preferably about 15 parts by weight or less, and preferably about 10 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the crosslinking agent relative to 100 parts by weight of the acrylic polymer is 5.0 parts by weight or less, may be 4.0 parts by weight or less, or may be 3.5 parts by weight or less.

[0150] (Other additives) In addition to the above-mentioned components, the adhesive composition may contain, as necessary, various additives that are common in the field of adhesives, such as leveling agents, crosslinking assistants, plasticizers, softeners, fillers, antistatic agents, antiaging agents, UV absorbers, antioxidants, rust inhibitors, light stabilizers, etc. As for such various additives, conventionally known ones can be used in the usual manner, and they do not particularly characterize the present invention, so detailed explanations will be omitted.

[0151] (Method of forming pressure-sensitive adhesive layer) The adhesive layer (layer made of adhesive) disclosed herein may be an adhesive layer formed from an aqueous adhesive composition, a solvent-based adhesive composition, a hot melt-type adhesive composition, or an active energy ray curable adhesive composition. The aqueous adhesive composition refers to an adhesive composition in a form containing an adhesive (adhesive layer forming component) in a solvent (aqueous solvent) mainly composed of water, and typically includes those called water-dispersed adhesive compositions (compositions in a form in which at least a part of the adhesive is dispersed in water). The solvent-based adhesive composition refers to an adhesive composition in a form containing an adhesive in an organic solvent. As the organic solvent contained in the solvent-based adhesive composition, one or more of the organic solvents exemplified as those usable in the above-mentioned solution polymerization (toluene, ethyl acetate, etc.) can be used without particular limitation. The technology disclosed herein can be preferably implemented in an embodiment having an adhesive layer formed from a solvent-based adhesive composition from the viewpoint of adhesion properties, etc.

[0152] The adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method can be adopted in which an adhesive composition is applied to a surface having releasability (release surface) or a non-release surface and then dried to form an adhesive layer. In the case of an adhesive sheet having a substrate, for example, a method (direct method) can be adopted in which an adhesive composition is directly applied (typically coated) to the substrate and then dried to form an adhesive layer. In addition, a method (transfer method) can be adopted in which an adhesive composition is applied to a surface having releasability (release surface) and then dried to form an adhesive layer on the surface, and the adhesive layer is transferred to a substrate. From the viewpoint of productivity, the transfer method is preferred. As the release surface, the surface of a release liner, the back surface of a substrate that has been subjected to a release treatment, etc. can be used.

[0153] The pressure-sensitive adhesive composition can be applied using a conventionally known coater such as a gravure roll coater, a die coater, a bar coater, etc. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation or curtain coating. From the viewpoints of promoting the crosslinking reaction, improving production efficiency, etc., the pressure-sensitive adhesive composition is preferably dried under heating. The drying temperature can be, for example, about 40 to 150° C., and is usually preferably about 60 to 130° C. After drying the pressure-sensitive adhesive composition, aging may be further performed for the purpose of adjusting the component migration in the pressure-sensitive adhesive layer, advancing the crosslinking reaction, relaxing distortion that may exist in the pressure-sensitive adhesive layer, etc.

[0154] The pressure-sensitive adhesive layer may have a single-layer structure or a multi-layer structure of two or more layers. From the viewpoint of productivity, etc., the pressure-sensitive adhesive layer preferably has a single-layer structure.

[0155] (Thickness) The thickness of the adhesive layer is not particularly limited, and a configuration having an adhesive layer having an appropriate thickness, for example, in the range of 0.1 to 500 μm, can be adopted depending on the application, purpose of use, etc. In some embodiments, from the viewpoint of avoiding excessive thickness of the adhesive sheet, the thickness of the adhesive layer is usually about 100 μm or less, preferably about 70 μm or less, more preferably about 60 μm or less, further preferably about 50 μm or less, and may be about 40 μm or less. The thickness of the adhesive layer can be about 35 μm or less, for example, about 30 μm or less, or may be 20 μm or less (for example, 15 μm or less). An adhesive layer with a limited thickness can be well responsive to the demand for thinning and weight reduction. In addition, by limiting the thickness of the adhesive layer, the processability can be improved. From the viewpoint of adhesion to the adherend, the lower limit of the thickness of the adhesive layer is, in some embodiments, appropriately about 0.5 μm or more, may be about 1 μm or more, and is advantageously about 3 μm or more. In some preferred embodiments, the thickness of the adhesive layer is greater than 5 μm, more preferably about 10 μm or more, even more preferably about 12 μm or more (e.g., more than 12 μm), even more preferably about 15 μm or more, and may be, for example, about 18 μm or more. By making the thickness of the adhesive layer greater than 5 μm, the relaxation effect of the adhesive layer makes it easier to eliminate fine uneven deformation. In addition, the adhesive strength tends to improve as the thickness of the adhesive layer increases. In a more preferred embodiment, the thickness of the adhesive layer may be greater than 20 μm, may be 24 μm or more, may be 27 μm or more, may be about 30 μm or more, or may be about 32 μm or more. In a double-sided adhesive sheet with a substrate having a first adhesive layer and a second adhesive layer on each side of the substrate, the first adhesive layer and the second adhesive layer may be of the same thickness or may be of different thicknesses.

[0156] (Gel fraction) The gel fraction (weight basis) of the adhesive layer disclosed herein is 25% or more. The adhesive layer having the above gel fraction has a moderate hardness, so that uneven deformation of a visible size is unlikely to occur. In some embodiments, the gel fraction may be 35% or more, or 40% or more. In some preferred embodiments, the gel fraction is more than 40%, more preferably 45% or more, even more preferably 50% or more, may be 55% or more, may be 60% or more, may be 65% or more, or may be 70% or more. An adhesive layer having a high gel fraction is likely to provide good processability. In addition, the upper limit of the gel fraction of the adhesive layer is usually appropriate to be less than 90% from the viewpoint of adhesive strength, etc., and may be less than 85%, may be less than 80%, or may be less than 75%. In some preferred embodiments, the gel fraction of the adhesive layer is less than 70%, more preferably less than 65%, even more preferably less than 60%, may be less than 55%, or may be less than 50%. By limiting the gel fraction of the pressure-sensitive adhesive layer to a predetermined value or less, the adhesion to the adherend tends to be improved.

[0157] The gel fraction of the adhesive layer is measured by the following method. That is, about 0.1 g of the adhesive sample (weight Wg1) is wrapped in a porous polytetrafluoroethylene film (weight Wg2) with an average pore size of 0.2 μm in a purse shape, and the opening is tied with a string (weight Wg3). As the porous polytetrafluoroethylene (PTFE) film, the product name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) available from Nitto Denko Corporation or an equivalent product is used. The wrapper is immersed in 50 mL of ethyl acetate and kept at room temperature (about 23 ° C) for 7 days to elute only the sol component in the adhesive layer out of the film, and then the wrapper is taken out and the ethyl acetate adhering to the outer surface is wiped off, the wrapper is dried at 130 ° C for 2 hours, and the weight (Wg4) of the wrapper is measured. The gel fraction of the adhesive layer is obtained by substituting each value into the following formula. Gel fraction (%) = [(Wg4-Wg2-Wg3) / Wg1] x 100 In the examples described later, the measurement is also performed by the above method.

[0158] (Biomass carbon ratio) In some embodiments, the pressure-sensitive adhesive layer contains a biomass-derived material, and the biomass carbon ratio thereof may be a predetermined value or more. The biomass carbon ratio of the pressure-sensitive adhesive layer is, for example, 1% or more, and may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the pressure-sensitive adhesive means that the amount of fossil resource-based materials, such as petroleum, used is small. In this respect, the higher the biomass carbon ratio of the pressure-sensitive adhesive, the more preferable it is. For example, the biomass carbon ratio of the pressure-sensitive adhesive layer may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. The upper limit of the biomass carbon ratio is 100% by definition, and may be 99% or less, and from the viewpoint of material availability, it may be 95% or less, or 90% or less. From the viewpoint of easily exerting good adhesive performance, in some embodiments, the biomass carbon ratio of the pressure-sensitive adhesive layer may be, for example, 90% or less, 85% or less, or 80% or less.

[0159] <Base material> In an embodiment in which the pressure-sensitive adhesive sheet disclosed herein is in the form of a single-sided or double-sided pressure-sensitive adhesive sheet with a substrate, the substrate supporting the pressure-sensitive adhesive layer may be a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, or a composite thereof. Examples of paper include Japanese paper, craft paper, glassine paper, wood-free paper, synthetic paper, and top-coated paper. Examples of cloth include woven fabrics and nonwoven fabrics made by spinning various fibrous materials alone or in combination. Examples of the fibrous material include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyolefin sheets, foamed polyurethane sheets, and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil. The substrate is also called a substrate layer in the pressure-sensitive adhesive sheet.

[0160] The substrate may be formed from a material derived from biomass or a material derived from non-biomass. From the viewpoint of producing a PSA sheet that takes into consideration the reduction of dependency on fossil resource-based materials, a substrate material derived from biomass (typically a resin film) is preferably used.

[0161] The substrate may be formed using a recyclable material or a recycled material (also called a recycled material). A resin film is preferably used as such a recycled material. Since a resin film (for example, a polyester film such as a PET film) is recyclable, it is possible to continuously reproduce the resin film after use, regardless of whether or not a plant-derived material is used, and the environmental load can be reduced by reusing the resin film after use. Such a recyclable resin film or recycled resin film is also called a recycled film. The recycled material (for example, a recycled film) may be formed from a biomass-derived material or a non-biomass-derived material.

[0162] As the substrate constituting the substrate-attached pressure-sensitive adhesive sheet, a substrate containing a resin film as the base film can be preferably used. The above-mentioned base film is typically a member capable of independently maintaining its shape (independent). The substrate in the technology disclosed herein may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the above-mentioned base film. Examples of the above-mentioned auxiliary layer include a colored layer, a reflective layer, an undercoat layer, an antistatic layer, etc., provided on the surface of the above-mentioned base film.

[0163] The resin film is a film containing a resin material as a main component (for example, a component contained in the resin film in an amount of more than 50% by weight). Examples of the resin film include polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester resin films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluororesin films; cellophane; and the like. The resin film may be a rubber film such as a natural rubber film or a butyl rubber film. Among them, from the viewpoint of handling and processability, polyester films are preferred, and PET films are particularly preferred.

[0164] In this specification, the term "resin film" refers to a typically non-porous sheet, and is a concept that is distinguished from so-called nonwoven fabric or woven fabric (in other words, a concept that excludes nonwoven fabric or woven fabric). The resin film may be any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film. In addition, such a resin film may be non-foamed. Here, a non-foamed resin film refers to a resin film that has not been intentionally treated to form a foam. Specifically, a non-foamed resin film may be a resin film with an expansion ratio of less than 1.1 times (for example, less than 1.05 times, typically less than 1.01 times).

[0165] The substrate may be transparent, or may have light-shielding or light-reducing properties. In some embodiments, the substrate (e.g., a resin film) may contain a colorant. This allows the light transmittance (light-shielding properties) of the substrate to be adjusted. Adjusting the light transmittance (e.g., vertical light transmittance) of the substrate can also be useful for adjusting the light transmittance of the substrate and even the light transmittance of a pressure-sensitive adhesive sheet including the substrate.

[0166] As the colorant, a conventionally known pigment or dye can be used, similar to the colorant that can be contained in the adhesive layer. The colorant is not particularly limited, and can be, for example, a black, gray, white, red, blue, yellow, green, yellow-green, orange, purple, gold, silver, pearl color, or the like colorant.

[0167] In some embodiments, a black colorant can be preferably used as the colorant for the substrate, since the light-shielding property (e.g., vertical light transmittance) can be efficiently adjusted with a small amount of the colorant. Specific black colorants include those exemplified as colorants that can be contained in the adhesive layer. In some preferred embodiments, a pigment (e.g., a particulate black colorant such as carbon black) having an average particle size of 10 nm to 500 nm, more preferably 10 nm to 120 nm, can be used.

[0168] The amount of the colorant used in the substrate (e.g., a resin film) is not particularly limited, and can be appropriately adjusted to provide the desired optical properties. The amount of the colorant used is suitably about 0.1 to 30% by weight of the substrate, and can be, for example, 0.1 to 25% by weight (typically 0.1 to 20% by weight).

[0169] The above-mentioned substrate (e.g., resin film) may contain various additives such as fillers (inorganic fillers, organic fillers, etc.), dispersants (surfactants, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, etc. The blending ratio of various additives is about less than 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight).

[0170] The substrate (e.g., resin film) may have a single-layer structure, or may have a multi-layer structure of two, three or more layers. From the viewpoint of shape stability, the substrate preferably has a single-layer structure. In the case of a multi-layer structure, at least one layer (preferably all layers) is preferably a layer having a continuous structure of the resin (e.g., polyester resin). The method for producing the substrate (typically a resin film) is not particularly limited and may be any conventionally known method. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting molding, and calendar roll molding may be appropriately used.

[0171] The substrate may be colored by a colored layer disposed on the surface of a base film (preferably a resin film). In such a substrate having a configuration including a base film and a colored layer, the base film may or may not contain a colorant. The colored layer may be disposed on either one surface of the base film, or may be disposed on both surfaces. In a configuration in which colored layers are disposed on both surfaces of the base film, the configurations of the colored layers may be the same or different.

[0172] Such a colored layer can typically be formed by applying a colored layer forming composition containing a colorant and a binder to a base film. As the colorant, a conventionally known pigment or dye can be used, as with the colorant that can be contained in the adhesive layer or resin film. As the binder, a material known in the field of paint or printing can be used without particular limitation. Examples include polyurethane, phenolic resin, epoxy resin, urea melamine resin, polymethyl methacrylate, and the like. The colored layer forming composition can be, for example, a solvent type, an ultraviolet curing type, a heat curing type, and the like. The colored layer can be formed by employing a means that has been conventionally employed for forming a colored layer without particular limitation. For example, a method of forming a colored layer (printed layer) by printing such as gravure printing, flexographic printing, and offset printing can be preferably employed.

[0173] The colored layer may be a single layer structure consisting of one layer as a whole, or may be a multilayer structure including two, three or more sub-colored layers. A colored layer having a multilayer structure including two or more sub-colored layers can be formed, for example, by repeatedly applying (for example, printing) a colored layer-forming composition. The color and amount of the colorant contained in each sub-colored layer may be the same or different. For a colored layer for imparting light-shielding properties, it is particularly meaningful to have a multilayer structure from the viewpoint of preventing pinholes from occurring and increasing the reliability of preventing light leakage.

[0174] The thickness of the entire colored layer is appropriately about 1 μm to 10 μm, preferably about 1 μm to 7 μm, for example, about 1 μm to 5 μm. In a colored layer including two or more sub-colored layers, the thickness of each sub-colored layer is preferably about 1 μm to 2 μm.

[0175] The surface of the substrate may be subjected to a conventionally known surface treatment such as a corona discharge treatment, a plasma treatment, an ultraviolet irradiation treatment, an acid treatment, an alkali treatment, application of a primer, etc. Such a surface treatment may be a treatment for improving the adhesion between the substrate and the pressure-sensitive adhesive layer, in other words, the anchoring property of the pressure-sensitive adhesive layer to the substrate.

[0176] In addition, when the technology disclosed herein is implemented in the form of a single-sided pressure-sensitive adhesive sheet with a substrate, the back surface of the substrate may be subjected to a release treatment as necessary. The release treatment may be, for example, a treatment in which a general silicone-based, long-chain alkyl-based, fluorine-based or other release treating agent is applied in the form of a thin film typically of about 0.01 μm to 1 μm (for example, 0.01 μm to 0.1 μm). By carrying out such a release treatment, it is possible to obtain an effect such as facilitating unwinding of a roll of the pressure-sensitive adhesive sheet.

[0177] In the pressure-sensitive adhesive sheet of an embodiment including a substrate, the thickness of the substrate is not particularly limited. In order to prevent the pressure-sensitive adhesive sheet from becoming excessively thick, the thickness of the substrate can be, for example, about 200 μm or less, preferably about 150 μm or less, more preferably about 100 μm or less. Depending on the purpose and mode of use of the pressure-sensitive adhesive sheet, the thickness of the substrate may be about 70 μm or less, about 50 μm or less, or about 30 μm or less (for example, about 25 μm or less). In some embodiments, the thickness of the substrate may be about 20 μm or less, about 15 μm or less, or about 10 μm or less (for example, about 5 μm or less). By reducing the thickness of the substrate, the thickness of the pressure-sensitive adhesive layer can be made larger even if the total thickness of the pressure-sensitive adhesive sheet is the same, which can be advantageous in terms of improving adhesion to the adherend or substrate. From the viewpoint of the handleability and processability of the pressure-sensitive adhesive sheet, the thickness of the substrate is usually about 0.5 μm or more (eg, 1 μm or more), preferably about 2 μm or more, for example, about 6 μm or more.

[0178] <Total thickness of adhesive sheet> The total thickness of the adhesive sheet disclosed herein (including the adhesive layer and may further include a base layer, but not including a release liner) is not particularly limited. The total thickness of the adhesive sheet is, for example, about 1 mm or less, may be about 500 μm or less, or may be about 300 μm or less, and from the viewpoint of thinning, is appropriately about 200 μm or less, and may be about 150 μm or less (for example, about 100 μm or less). In some preferred embodiments, the thickness of the adhesive sheet can be about 50 μm or less, and may be, for example, about 35 μm or less. The lower limit of the thickness of the adhesive sheet is, for example, 0.1 μm or more (for example, 0.5 μm or more), is appropriately about 3 μm or more, preferably about 10 μm or more, more preferably about 15 μm or more, even more preferably about 20 μm or more, may be about 30 μm or more, or may be about 50 μm or more. A pressure-sensitive adhesive sheet having a thickness equal to or greater than a certain value is likely to be able to adhere to an adherend and also tends to be easy to handle. In a substrate-less double-sided pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer is the total thickness of the pressure-sensitive adhesive sheet.

[0179] <Release liner> In the technology disclosed herein, a release liner can be used during the formation of the adhesive layer, the preparation of the adhesive sheet, the storage, distribution, and shaping of the adhesive sheet before use. The release liner is not particularly limited, and for example, a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or a release liner made of a fluorine-based polymer (polytetrafluoroethylene, etc.) can be used. The release treatment layer can be formed by surface treating the liner substrate with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. As the liner substrate, a substrate formed using a biomass-derived material or a recycled material (recycled film, etc.) can be preferably used, similar to the substrate of the above-mentioned adhesive sheet.

[0180] As the release liner disclosed herein (in an embodiment in which the double-sided pressure-sensitive adhesive sheet with release liner has two release liners, at least one of the two release liners; the same applies hereinafter unless otherwise specified), one having a release treatment layer on a release liner substrate can be preferably used. The release treatment layer can be formed by surface treating the release liner substrate with a release treatment agent. The release treatment agent can be a known release treatment agent such as a silicone-based release treatment agent, a long-chain alkyl-based release treatment agent, a fluorine-based release treatment agent, molybdenum (IV) sulfide, or the like. In some embodiments, a release liner having a release treatment layer made of a silicone-based release treatment agent can be preferably used. The thickness and method of forming the release treatment layer are not particularly limited, and can be set so that appropriate releasability is exhibited on the adhesive surface of the release liner.

[0181] As the release liner substrate, various plastic films can be used. In this specification, the plastic film is a concept that is typically a non-porous sheet and is distinguished from, for example, a non-woven fabric (i.e., does not include a non-woven fabric). As the release liner substrate, a resin film that has a non-porous structure and typically does not substantially contain air bubbles (voidless) can be preferably used. The resin film may have a single layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0182] Examples of the material of the plastic film include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), polyolefin resins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer, cellulose resins such as triacetyl cellulose, acetate resins, polysulfone resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, and cyclic polyolefin resins such as norbornene resins, (meth)acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, ethylene-vinyl acetate copolymer resins, ethylene-vinyl alcohol copolymer resins, polyarylate resins, and polyphenylene sulfide resins. A release liner substrate formed from one or a mixture of two or more of these resins can be used. Among them, a preferred release liner substrate is a polyester resin film (e.g., a PET film) formed from a polyester resin.

[0183] The plastic film used as the release liner substrate may be any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film. The plastic film may be a single-layer structure or a multi-layer structure including two or more sub-layers. The plastic film may contain known additives that can be used in release liner substrates, such as antioxidants, antiaging agents, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants such as pigments and dyes, lubricants, fillers, antistatic agents, slip agents, antiblocking agents, and nucleating agents. In a multi-layered plastic film, each additive may be contained in all sub-layers, or may be contained in only some sub-layers.

[0184] The thickness of the release liner is not particularly limited, and may be, for example, about 10 μm to 500 μm. From the viewpoint of the strength and dimensional stability of the release liner, the thickness of the release liner is suitably 20 μm or more, preferably 25 μm or more, and may be 30 μm or more, or may be 35 μm or more. When the adhesive surface is protected by a release liner having a sufficient thickness, the smoothness of the adhesive surface is easily maintained. For example, an event in which the adhesive layer is deformed unevenly due to an external force from the back surface of the release liner or a foreign matter present on the back surface of the release liner is unlikely to occur. Such an event may be caused by a foreign matter that is mixed on the back surface of the release liner (for example, between two release liners or between the release liner and the substrate) when the pressure-sensitive adhesive sheet with the release liner is wound into a roll. In addition, from the viewpoint of the handleability of the release liner (for example, ease of rolling), the thickness of the release liner is suitably 300 μm or less, preferably 200 μm or less, and may be 150 μm or less, or may be 100 μm or less. By setting the thickness of the release liner to a predetermined value or less, it is easy to remove the release liner from the adhesive sheet. In some embodiments, the thickness of the release liner may be 75 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, or 30 μm or less. According to the technology disclosed herein, even if the adhesive layer is subjected to fine uneven deformation such as a dent due to an external force from the back side of the release liner or a foreign object, the adhesive layer has excellent uneven deformation mitigation properties, so that the fine uneven deformation is eliminated or alleviated, and good appearance quality can be imparted. In addition, when the adhesive sheet with release liner disclosed herein comprises two release liners, i.e., a first release liner and a second release liner, the thicknesses of the first release liner and the second release liner may be the same or different. From the viewpoint of peeling workability, etc., it is preferable that the first release liner and the second release liner have different thicknesses, and it is preferable that the thickness of the thicker release liner is about 1.1 times or more, for example, about 1.25 times or more, of the thickness of the thinner release liner.

[0185] <Roll body> Also, according to this specification, a roll body (a pressure-sensitive adhesive sheet roll with a release liner) is provided, which includes the pressure-sensitive adhesive sheet with a release liner disclosed herein in a wound form. The uneven deformation mitigation property, which is one of the effects of the technology disclosed herein, is effective against minute uneven deformation of the pressure-sensitive adhesive layer caused by minute foreign matter mixed on the back surface of the release liner when the pressure-sensitive adhesive sheet with a release liner is wound into a roll. The technology disclosed herein is suitable for a pressure-sensitive adhesive sheet that is stored in the form of a roll body before use. The above-mentioned roll body typically includes a core (winding core) and a pressure-sensitive adhesive sheet with a release liner wound around the core. The shape of the core is not particularly limited, and may be, for example, a solid cylindrical shape, a hollow cylindrical shape (i.e., a cylindrical shape), a hollow or solid polygonal prism shape, etc. From the viewpoint of improving the handleability of the roll body, a hollow cylindrical or hollow polygonal prism-shaped core may be preferably adopted. A cylindrical core is particularly preferred.

[0186] <Characteristics of adhesive sheet> (light transmittance) The light transmittance of the pressure-sensitive adhesive sheet varies depending on the purpose of use, the purpose of coloring, etc., and is not limited to a specific range. In some embodiments, the light transmittance of the pressure-sensitive adhesive sheet at a wavelength of 550 nm (550 nm light transmittance, also referred to as visible light transmittance) is less than 80%, and may be less than 70%, less than 60%, less than 50%, or less than 40%. A pressure-sensitive adhesive sheet in which the visible light transmittance is limited to a predetermined value or less by coloring the pressure-sensitive adhesive layer is suitable for concealing an adherend and can also be used to impart design. It can also be used as a light-shielding pressure-sensitive adhesive sheet for preventing light leakage, etc. In some preferred embodiments, the 550 nm light transmittance of the pressure-sensitive adhesive sheet is 30% or less, may be 20% or less, may be 15% or less, may be 10% or less, may be 8% or less, or may be 6% or less. The lower the visible light transmittance, the better the concealment properties can be exhibited. When higher concealment is required, the 550 nm light transmittance may be less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, or less than 0.5%. The lower limit of the 550 nm light transmittance is not particularly limited, and may be substantially 0%, i.e., below the detection limit, 0.1% or more, 1% or more, 3% or more, or 5% or more. In some embodiments, the 550 nm light transmittance may be 10% or more, more than 20%, or more than 30%. By having a certain degree of visible light transmittance, it is possible to appropriately conceal the adherend, adjust the appearance of the adherend (e.g., metal material), and impart a design and color that retains the texture of the adherend. In addition, a pressure-sensitive adhesive sheet having moderate light transmittance is also preferable from the viewpoints of maintaining the adhesive properties and productivity.

[0187] Although not particularly limited, the light transmittance of the adhesive sheet at a wavelength of 1380 nm (1380 nm light transmittance, also referred to as infrared transmittance) is less than 90%, and may be less than 80%, less than 70%, less than 60%, less than 50%, or less than 40%. In some preferred embodiments, the light transmittance of the adhesive sheet at 1380 nm is 30% or less, 20% or less, 15% or less, 10% or less, 5% or less, or 3% or less. In addition, for example, when used around an infrared sensor, the infrared rays can be blocked to prevent a decrease in the operating accuracy of the sensor. The adhesive sheet with limited infrared transmittance can block light rays in a wide wavelength range including infrared rays, and excellent light blocking properties are easily obtained. The lower limit of the 1380 nm light transmittance is not particularly limited, and may be substantially 0%, i.e., below the detection limit, 0.1% or more, 1% or more, 3% or more, or 5% or more. In some embodiments, the 1380 nm light transmittance may be 10% or more, 30% or more, or 50% or more.

[0188] The relative relationship between the visible light transmittance and the infrared transmittance of the pressure-sensitive adhesive sheet is not particularly limited. In some embodiments, the infrared transmittance T IR [%] and visible light transmittance T VL [%] ratio (T IR / T VL ) is, for example, in the range of 0.1 to 10, and may be 5 or less, 3 or less, 0.5 or more, 1 or more (e.g., more than 1), or 2 or more. The ratio (T IR / T VL ) is appropriately set, the desired adhesion hiding property and infrared shielding property can be achieved.

[0189] (Adhesion to SUS) Although not particularly limited, in some embodiments, the adhesive sheet has a 180-degree peel strength (adhesive strength to SUS) against a stainless steel plate of about 1 N / 25 mm or more, and preferably about 5 N / 25 mm or more. In some preferred embodiments, the adhesive strength to SUS is about 10 N / 25 mm or more, and may be about 12 N / 25 mm or more, more preferably about 15 N / 25 mm or more, even more preferably about 18 N / 25 mm or more, and particularly preferably 20 N / 25 mm or more (e.g., 22 N / 25 mm or more). An adhesive sheet exhibiting the above adhesive strength to SUS exerts good adhesive strength to an adherend, and is preferably used for joining and fixing members. The upper limit of the adhesive strength to SUS is not particularly limited, but from the viewpoint of compatibility with other adhesive properties, it is usually about 50 N / 25 mm or less, and in some embodiments, it may be about 30 N / 25 mm or less.

[0190] The adhesive strength to SUS is measured using a SUS plate as an adherend under conditions of 23° C., 50% RH, a pulling speed of 300 mm / min, and a peel angle of 180°. More specifically, it is measured by the following method. [Adhesion to SUS] In a measurement environment of 23°C and 50% RH, a PET film having a thickness of 50 μm is attached to one adhesive surface of a pressure sensitive adhesive sheet (double-sided pressure sensitive adhesive sheet) to provide a backing, and the sheet is cut to a size of 25 mm wide and 100 mm long to prepare a measurement sample. In an environment of 23°C and 50% RH, the other adhesive surface of the measurement sample is pressed against the surface of a stainless steel plate (SUS304BA plate) washed with ethyl acetate by rolling a 2 kg roller back and forth once. After leaving the sample in the same environment for 72 hours, a universal tensile compression tester is used to measure the peel strength (adhesive strength to SUS) [N / 25 mm] in accordance with JIS Z 0237:2000 at a tensile speed of 300 mm / min and a peel angle of 180 degrees. In measuring the peel strength, a universal tensile compression tester manufactured by Minebea Co., Ltd., "Tension and compression tester, TG-1kN" or an equivalent product is used. When performing the above peel strength measurement on a single-sided pressure sensitive adhesive sheet, it is not necessary to back the sheet with a PET film. When the substrate is thin (for example, when the substrate is 25 μm or less), the substrate may be backed with a PET film.

[0191] (Biomass carbon ratio) In some embodiments, the pressure-sensitive adhesive sheet contains a biomass-derived material, and the biomass carbon ratio thereof may be a predetermined value or more. The biomass carbon ratio of the pressure-sensitive adhesive sheet is, for example, 1% or more, and may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the pressure-sensitive adhesive sheet means that the amount of fossil resource-based materials, such as petroleum, used is small. In this respect, the higher the biomass carbon ratio of the pressure-sensitive adhesive sheet, the more preferable it is. For example, the biomass carbon ratio of the pressure-sensitive adhesive sheet may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. The upper limit of the biomass carbon ratio is 100% by definition, and may be 99% or less, and from the viewpoint of material availability, it may be 95% or less, or 90% or less. From the viewpoint of easily exerting good adhesive performance, in some embodiments, the biomass carbon ratio of the pressure-sensitive adhesive sheet may be, for example, 90% or less, 85% or less, or 80% or less.

[0192] <Application> The adhesive sheet disclosed herein has a colored adhesive layer, and can have an adhesive surface with excellent appearance quality, in which fine uneven deformation is highly suppressed, and is suitable for various uses, such as use in which the adhesive sheet attached to the surface of the adherend is visible, for example, uses in which the concealing property of the adhesive sheet is required, uses in which a colored adhesive layer is used to impart design or color, and other uses in which a specific optical property (light transmittance, etc.) is required. For example, some electronic devices, such as portable electronic devices, require the use of an adhesive sheet to conceal components or adjust the appearance. The adhesive sheet disclosed herein is suitable for such electronic devices.

[0193] Non-limiting examples of the portable electronic device include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear type devices worn on the wrist like a wristwatch, modular type devices worn on a part of the body with a clip or strap, eyewear type devices including glasses (monocular type and binocular type devices, including head-mounted type devices), clothing type devices attached to shirts, socks, hats, etc. in the form of accessories, earwear type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio devices (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, electronic books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" does not mean that it is sufficient to simply be portable, but rather that it has a level of portability that allows an individual (average adult) to carry it relatively easily. Examples of the electronic device include personal computers (desktop type, notebook type, tablet type, etc.), televisions, etc. These may include a built-in display device such as a liquid crystal or organic electroluminescence display device.

[0194] In some embodiments, the adhesive sheet can be used for the purpose of fixing the pressure sensor and other members in a portable electronic device equipped with a pressure sensor among the above portable electronic devices. In some embodiments, the adhesive sheet can be used for fixing the pressure sensor and other members in an electronic device (typically a portable electronic device) equipped with a function that enables an absolute position to be specified on a plate (typically a touch panel) corresponding to the screen by a device (typically a pen-type or mouse-type device) for indicating a position on a screen and a device for detecting a position.

[0195] In some preferred embodiments, the pressure-sensitive adhesive sheet is suitable for use in applications in which it is disposed on the back surface of a display screen (display unit) such as a touch panel display in a portable electronic device. By disposing the pressure-sensitive adhesive sheet according to some preferred embodiments on the back surface of the display screen (display unit), it is possible to prevent a decrease in visibility of the display screen regardless of the manner in which the portable electronic device is used.

[0196] In some embodiments, the pressure-sensitive adhesive sheet is suitable for a portable electronic device having a built-in optical sensor. Various devices such as the above-mentioned portable electronic device may be provided with an optical sensor that uses infrared light, visible light, ultraviolet light, or other light rays for the purpose of operating the device, detecting nearby objects, detecting the brightness of the surroundings (ambient light), data communication, or the like. Examples of the optical sensor include, but are not limited to, an acceleration sensor, a proximity sensor, and a brightness sensor (ambient light sensor). Such an optical sensor may have a light receiving element for ultraviolet light, visible light, infrared light, or other light, and may also have a light emitting element for a specific light ray such as infrared light. In other words, the optical sensor may include a light emitting element and / or a light receiving element for a light ray in a specific wavelength range among wavelength ranges including ultraviolet light, visible light, and infrared light. By applying the pressure-sensitive adhesive sheet according to some embodiments to such devices and limiting the entry of light that may be refracted or scattered in the pressure-sensitive adhesive layer, the light in the device can be controlled and the deterioration of the operation accuracy of the sensor can be prevented.

[0197] The material (adherend material) to which the adhesive sheet disclosed herein is attached is not particularly limited, but examples thereof include metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, etc., or alloys containing two or more of these, and various resin materials (typically plastic materials) such as polyimide resins, acrylic resins, polyethernitrile resins, polyethersulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyetheretherketone resins, polyamide resins (so-called aramid resins, etc.), polyarylate resins, polycarbonate resins, and liquid crystal polymers, and inorganic materials such as alumina, zirconia, soda glass, quartz glass, and carbon. Among these, metal materials such as copper, aluminum, and stainless steel, polyester resins such as PET, and resin materials (typically plastic materials) such as polyimide resins, aramid resins, and polyphenylene sulfide resins are widely used. The above materials may be materials for components constituting products such as electronic devices. The adhesive sheet disclosed herein may be attached to a component made of the above materials when used. The above materials may also be materials constituting the object to be fixed such as the pressure-sensitive sensor or the display unit (for example, a back surface member such as an electromagnetic wave shield or a reinforcing plate). The object to be fixed refers to an object to which the adhesive sheet is attached, that is, an adherend. The back surface member refers to a member disposed on the opposite side of the front surface (visible side) of the pressure-sensitive sensor or the display unit in, for example, a portable electronic device, and may be, for example, a member constituting the support unit 540 disposed on the back surface of the display device 500 shown in FIG. 4 described later. The object to be fixed may be in the form of either a single-layer structure or a multi-layer structure, and various surface treatments may be applied to the surface (attaching surface) to which the adhesive sheet is attached. Although not particularly limited, an example of the object to be fixed is a back surface member having a thickness of 1 μm or more (typically 5 μm or more, for example 60 μm or more, or even 120 μm or more) and 1500 μm or less (for example 800 μm or less).

[0198] In some embodiments, the member or material to which the pressure-sensitive adhesive sheet is attached may be light-transmitting (light-transmitting adherend). The adhesive surface of the pressure-sensitive adhesive sheet attached to the light-transmitting adherend can be seen through the light-transmitting adherend, so it is desirable for the adhesive sheet to have good appearance quality. The light transmittance of the light-transmitting adherend may be, for example, greater than 50%, and may be 70% or more. In some preferred embodiments, the light transmittance of the adherend is 80% or more, more preferably 90% or more, and may be 95% or more (for example, 95 to 100%). Such a material may be a resin film (for example, a polyester-based resin film such as a PET film) disposed on the back surface of an image display unit of various devices such as a portable electronic device. The pressure-sensitive adhesive sheet disclosed herein may be preferably used in an embodiment in which the pressure-sensitive adhesive sheet is attached to an adherend (for example, a member) having a light transmittance of a predetermined value or more as described above. The light transmittance is a light transmittance at a wavelength of 550 nm, and may be measured in the same manner as the light transmittance of the pressure-sensitive adhesive sheet at a wavelength of 550 nm.

[0199] In some embodiments, the adhesive sheet is used in a form in which it is attached to a metal member. Examples of materials for the metal member include the metal materials exemplified as the above-mentioned adherend material. Such metal members are, for example, members or articles having a surface (adhesive sheet attachment surface) formed from a metal material such as aluminum or stainless steel, and preferred examples include metal members such as stainless steel members and aluminum members. By attaching the adhesive sheet disclosed herein to an area on the surface of a metal member that needs to be concealed, the area of ​​the metal member can be concealed. The adhesive sheet may cover the entire surface of the metal member, or may cover a part of the surface (for example, a part of the area that needs to be concealed). The metal member may be, for example, a member constituting a support part 540 of a display device 500 shown in FIG. 4 described later. The metal member is preferably one of the adherends of the adhesive sheet.

[0200] From the above, the technology disclosed herein provides a laminate comprising an adhesive sheet and a member to which the adhesive sheet is attached. In some embodiments, the laminate comprising the adhesive sheet is a laminate comprising the adhesive sheet and a metal member (first member). Such a laminate may comprise a metal member and an adhesive sheet covering at least a part of the surface of the metal member. The adhesive sheet may cover the entire surface of the metal member, or may cover a part of the surface (for example, a part of the area to be concealed). Typically, one side (adhesive surface) of the adhesive sheet is attached to the metal member. In some embodiments, the member to which the adhesive sheet is attached may have the light transmittance of the above-mentioned adherend material. In this embodiment, the laminate comprising the adhesive sheet is a laminate comprising the adhesive sheet and a member (second member) having light transparency. In some preferred embodiments, the laminate is a laminate comprising a metal member (first member), an adhesive sheet (specifically a double-sided adhesive sheet), and a member (second member) having light transparency in this order. The substrate-less double-sided pressure-sensitive adhesive sheet is also referred to as a pressure-sensitive adhesive layer in the laminate.

[0201] A configuration example of the laminate is shown in FIG. 3. The laminate 50 shown in FIG. 3 includes a first member 41, an adhesive sheet 1, and a second member 42 in this order. In this configuration example, the adhesive sheet 1 is configured as a substrate-less double-sided adhesive sheet. Specifically, in the laminate 50, one adhesive surface (first adhesive surface) 1A of the substrate-less double-sided adhesive sheet 1 is adhered to the first member 41, and the other adhesive surface (second adhesive surface) 1B of the double-sided adhesive sheet 1 is adhered to the second member 42. In this embodiment, both the first member 41 and the second member 42 have a sheet-like or plate-like shape, and the laminate 50 has a multilayer structure. In this embodiment, the first member 41 is a metal member, and the second member 42 is a light-transmitting member. Details of the members constituting the laminate are as described above as the members, materials, and adherends, so overlapping descriptions will not be repeated.

[0202] In some embodiments, the pressure-sensitive adhesive sheet is preferably used in electronic devices including various light sources such as LEDs (light emitting diodes) and light-emitting elements such as self-emitting organic ELs. For example, it is preferably used in electronic devices (typically portable electronic devices) equipped with organic EL displays or liquid crystal displays that require specific optical characteristics.

[0203] FIG. 4 is an exploded perspective view showing a schematic configuration example of a display device. As shown in FIG. 4, a display device 500 included in a portable electronic device 400 includes a display unit 520 including a cover member, an organic EL unit, and the like, and a support unit 540. The display device 500 is configured to further include an adhesive sheet 530. In this configuration example, the adhesive sheet 530 fixes the members that constitute the display unit 520 and the support unit 540. The support unit 540 is configured to include a substrate (a metal plate such as a stainless steel plate or an aluminum plate) and the like. The adhesive sheet disclosed herein is preferably used as a component of the display device as described above.

[0204] In addition, in some embodiments, the PSA sheet disclosed herein may have a PSA layer containing an acrylic polymer with a high biomass carbon ratio, and therefore may be used as a substitute for a conventional acrylic PSA in various applications in which the acrylic PSA (i.e., an acrylic PSA with a low biomass carbon ratio) is used, thereby contributing to reducing dependency on fossil resource-based materials. The PSA sheet disclosed herein may be preferably used as a PSA sheet with reduced dependency on fossil resource-based materials.

[0205] The matters disclosed by this specification include the following: [1] A display device including a display unit including a cover member and an organic EL unit, and a support unit, An adhesive sheet is bonded to the support portion, The pressure-sensitive adhesive sheet has a colored pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer contains an acrylic polymer, The pressure-sensitive adhesive layer has a gel fraction of 25% or more, A display device, wherein the pressure-sensitive adhesive layer has a storage modulus of 0.05 MPa or more at 23°C and a tan δ of 0.31 or more at 23°C, wherein the tan δ refers to the ratio (G'' / G') of the loss modulus G'' to the storage modulus G' of the pressure-sensitive adhesive layer. [2] The display device according to the above [1], wherein the monomer component constituting the acrylic polymer includes an alkyl acrylate having a chain alkyl group having 4 to 8 carbon atoms. [3] The display device according to the above [1] or [2], wherein a monomer component constituting the acrylic polymer includes heptyl acrylate. [4] The display device according to any one of the above [1] to [3], wherein a monomer component constituting the acrylic polymer contains n-butyl acrylate. [5] The display device according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive layer contains a black colorant. [6] The display device according to any one of the above [1] to [5], wherein the pressure-sensitive adhesive layer contains a black colorant as a first colorant and a metal oxide as a second colorant. [7] The display device according to any one of the above [1] to [6], wherein the pressure-sensitive adhesive layer further contains a tackifier resin. [8] The display device according to any one of the above [1] to [7], wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer. [9] The display device according to any one of the above [1] to [8], wherein the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet made of the pressure-sensitive adhesive layer.

[0206]

[11] A pressure-sensitive adhesive sheet having a colored pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer contains an acrylic polymer, The pressure-sensitive adhesive layer has a gel fraction of 25% or more, A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has a storage modulus of 0.05 MPa or more at 23°C and a tan δ of 0.31 or more at 23°C, wherein the tan δ refers to the ratio (G'' / G') of the loss modulus G'' to the storage modulus G' of the pressure-sensitive adhesive layer.

[12] The pressure-sensitive adhesive sheet according to the above

[11] , wherein the monomer component constituting the acrylic polymer contains an alkyl acrylate having a chain alkyl group having 4 to 8 carbon atoms.

[13] The pressure-sensitive adhesive sheet according to the above

[11] or

[12] , wherein the monomer component constituting the acrylic polymer includes heptyl acrylate.

[14] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[13] , wherein a monomer component constituting the acrylic polymer contains n-butyl acrylate.

[15] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[14] , wherein the pressure-sensitive adhesive layer contains a black colorant.

[16] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[15] , wherein the pressure-sensitive adhesive layer contains a black colorant as a first colorant and a metal oxide as a second colorant.

[17] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[16] , wherein the pressure-sensitive adhesive layer further contains a tackifier resin.

[18] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[17] , wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer.

[19] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[18] , which is a substrate-less double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

[20] The pressure-sensitive adhesive sheet according to any one of

[11] to

[19] above, which is used for fixing components in an electronic device.

[21] An electronic device comprising the pressure-sensitive adhesive sheet according to any one of

[11] to

[20] above.

[22] A pressure-sensitive adhesive sheet with a release liner, comprising the pressure-sensitive adhesive sheet according to any one of

[11] to

[20] above, and a release liner laminated on the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet.

[23] A roll of a pressure-sensitive adhesive sheet with a release liner, in which the pressure-sensitive adhesive sheet with a release liner described in

[22] above is wound.

[0207]

[31] A laminate comprising a metal member (first member) and an adhesive sheet, The pressure-sensitive adhesive sheet has a colored pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer contains an acrylic polymer, The pressure-sensitive adhesive layer has a gel fraction of 25% or more, The pressure-sensitive adhesive layer has a storage modulus of 0.05 MPa or more at 23°C and a tan δ of 0.31 or more at 23°C, wherein the tan δ refers to the ratio (G'' / G') of the loss modulus G'' to the storage modulus G' of the pressure-sensitive adhesive layer.

[32] A laminate comprising a light-transmitting member (second member) and a pressure-sensitive adhesive sheet, The pressure-sensitive adhesive sheet has a colored pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer contains an acrylic polymer, The pressure-sensitive adhesive layer has a gel fraction of 25% or more, The pressure-sensitive adhesive layer has a storage modulus of 0.05 MPa or more at 23°C and a tan δ of 0.31 or more at 23°C, wherein the tan δ refers to the ratio (G'' / G') of the loss modulus G'' to the storage modulus G' of the pressure-sensitive adhesive layer.

[33] A laminate including, in this order, a metal member (first member), an adhesive sheet, and a light-transmitting member (second member), The pressure-sensitive adhesive sheet has a colored pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer contains an acrylic polymer, The pressure-sensitive adhesive layer has a gel fraction of 25% or more, The pressure-sensitive adhesive layer has a storage modulus of 0.05 MPa or more at 23°C and a tan δ of 0.31 or more at 23°C, wherein the tan δ refers to the ratio (G'' / G') of the loss modulus G'' to the storage modulus G' of the pressure-sensitive adhesive layer.

[34] The laminate according to the above

[31] or

[33] , wherein the metal member is an aluminum member or a stainless steel member.

[35] The laminate according to the above

[32] or

[33] , wherein the light transmittance of the light-transmitting member is greater than 50%.

[36] The laminate according to the above

[32] ,

[33] or

[35] , wherein the light-transmitting member is made of a resin film.

[37] The laminate according to any one of the above

[31] to

[36] , wherein the monomer component constituting the acrylic polymer contains an alkyl acrylate having a chain alkyl group having 4 to 8 carbon atoms.

[38] The laminate according to any one of the above

[31] to

[37] , wherein the monomer component constituting the acrylic polymer includes heptyl acrylate.

[39] The laminate according to any one of the above

[31] to

[38] , wherein a monomer component constituting the acrylic polymer contains n-butyl acrylate.

[40] The laminate according to any one of the above

[31] to

[39] , wherein the pressure-sensitive adhesive layer contains a black colorant.

[41] The laminate according to any one of the above

[31] to

[40] , wherein the pressure-sensitive adhesive layer contains a black colorant as a first colorant and a metal oxide as a second colorant.

[42] The laminate according to any one of the above

[31] to

[41] , wherein the pressure-sensitive adhesive layer further contains a tackifier resin.

[43] The laminate according to any one of the above

[31] to

[42] , wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer.

[44] The laminate according to any one of the above

[31] to

[43] , wherein the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

[45] The laminate according to any one of

[31] to

[35] above, which is used in an electronic device. EXAMPLES

[0208] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, the units of content and amount added, "parts" and "%", are based on weight unless otherwise specified.

[0209] <Example 1> (Synthesis of acrylic polymers) In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel, 93 parts of n-heptyl acrylate (n-HpA) and 7 parts of acrylic acid (AA) as monomer components, and ethyl acetate as a polymerization solvent were charged, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and solution polymerization was performed at 60°C to 70°C for 8 hours to obtain a solution of an acrylic polymer. The weight average molecular weight (Mw) of this acrylic polymer was 900,000. The Mw was adjusted by adjusting the concentration of the monomer components during polymerization. The above n-HpA is a compound synthesized using heptyl alcohol derived from biomass and having a heptyl group derived from biomass at the ester end.

[0210] (Preparation of Pressure-Sensitive Adhesive Composition) To the above acrylic polymer solution, 20 parts of terpene phenol resin as a tackifier resin, 5 parts of acrylic oligomer, and 3 parts of isocyanate-based crosslinker A and 0.02 parts of epoxy-based crosslinker as crosslinkers were added per 100 parts of acrylic polymer contained in the solution, and carbon black particles were further added as a colorant (black colorant) so that the content in the adhesive layer was 1.1% (based on solids content), and the mixture was stirred and mixed to prepare an adhesive composition. As the terpene phenol resin (tackifier resin), the product name "YS Polystar T-115" (manufactured by Yasuhara Chemical Co., Ltd., softening point about 115°C, hydroxyl value 30 to 60 mgKOH / g) was used. As the isocyanate-based crosslinking agent A, the product name "Coronate L" (manufactured by Tosoh Corporation, 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct) was used. As the epoxy-based crosslinking agent, the product name "TETRAD-C" (manufactured by Mitsubishi Gas Chemical Co., Ltd., 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) was used. As the carbon black particles, the product name "Multilac A903" (manufactured by Toyo Color Co., Ltd., carbon black particle dispersion, average particle size 400 nm) was used. The acrylic oligomer used was prepared by the following method. Specifically, 95 parts of cyclohexyl methacrylate (CHMA), 5 parts of AA, 10 parts of AIBN as a polymerization initiator, and ethyl acetate as a polymerization solvent were charged into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel, and the mixture was stirred in a nitrogen stream for 1 hour to remove oxygen from the polymerization system, and then heated to 85°C and reacted for 5 hours to obtain an acrylic oligomer with a solid content concentration of 50%. The Mw of the obtained acrylic oligomer was 3600.

[0211] (Preparation of adhesive sheet) The obtained adhesive composition was applied to the release surface of a 38 μm thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) and dried at 100° C. for 2 minutes to form an adhesive layer with a thickness of 35 μm. The release surface of a 25 μm thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) was bonded to this adhesive layer. In this way, a substrate-less double-sided adhesive sheet with a release liner, both sides of which were protected by the above two polyester release liners, was obtained.

[0212] <Examples 2 to 8 and Comparative Examples 1 to 4> The adhesive compositions for each example were prepared in the same manner as in Example 1, except that the monomer composition of the acrylic polymer, the type and amount of colorant in the adhesive layer, the amount of tackifier resin, the amount of acrylic oligomer, the type and amount of crosslinking agent, and the adhesive layer thickness were changed as shown in Table 1, and the adhesive compositions were used to produce double-sided adhesive sheets with release liner for each example. In Table 1, BA represents n-butyl acrylate. In Table 1, isocyanate-based crosslinking agent B represents an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, product name "Coronate HX", 1% ethyl acetate solution of a trifunctional isocyanate compound), and the content shown in Table 1 represents the content of solids (non-volatile content). In Table 1, white colorant represents titanium oxide (TiO2) particles (product name "WHITE PASTE R-2228", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., average particle size 50 nm).

[0213] <Evaluation method> (Evaluation of uneven deformation) The double-sided pressure-sensitive adhesive sheet with release liner according to each example (a laminate of a release liner on the light release side / a double-sided pressure-sensitive adhesive sheet / a release liner on the heavy release side) was wound under the same conditions in the same environment to form a roll body, and after a predetermined time had passed, the sheet unwound from the roll body was cut into a size of 500 mm x 1000 mm to obtain an evaluation sample. In a clean room environment, the back surface of the release liner on the heavy release side was wiped with Kimwipe (manufactured by Nippon Paper Crecia Co., Ltd.) to remove foreign matter, and then the release liner on the light release side was peeled off from the evaluation sample. After 1 hour, the evaluation sample was held flat at the midpoint (a position about 50 cm away from the point light source) between a point light source and a projection screen arranged at a distance of about 100 cm, and the angle of the exposed pressure-sensitive adhesive layer surface of the evaluation sample with respect to the light from the point light source was about 90 degrees. The evaluation sample was arranged with the pressure-sensitive adhesive layer surface from which the release liner on the light release side had been peeled off on the side of the point light source. The point light source was turned on in a dark room with an environment of 23°C and 50% RH, and the image projected onto the screen through the evaluation sample was visually observed to evaluate the presence or absence of uneven deformation (specifically, uneven deformation on the surface of the adhesive layer). For example, a "Xenon Lamp C2577" manufactured by Hamamatsu Photonics KK can be used as the point light source. For each example, 10 evaluation samples were prepared and 10 evaluation tests were performed (N=10), and the number of evaluation tests (pass) in which no uneven deformation was observed was used as the result of uneven deformation evaluation, X ( / 10). If the number of passes was 8 or more (i.e., 8 / 10 or more), it was determined that fine uneven deformation was sufficiently suppressed.

[0214] The outline of each example and the evaluation results are shown in Table 1.

[0215] [Table 1]

[0216] As shown in Table 1, the adhesives according to Examples 1 to 8 were colored, contained an acrylic polymer, had a gel fraction of 25% or more, a 23°C storage modulus of 0.05MPa or more, and a 23°C tan δ of 0.31 or more, and the adhesive sheets containing the above adhesives had a pass rate of 8 / 10 or more in the uneven deformation evaluation. On the other hand, Comparative Example 1, in which the adhesive's 23°C storage modulus was less than 0.05MPa, had a result of uneven deformation evaluation that was inferior to Examples 1 to 8. In Comparative Example 2, in which the adhesive's 23°C tan δ was less than 0.31, uneven deformation equivalent to that of Comparative Example 1 was observed. Comparative Example 3, in which the 23°C tan δ was even lower than Comparative Example 2, had an even worse result. Comparative Example 4, in which the adhesive's gel fraction was less than 25%, also had a poor uneven deformation evaluation. It is considered that in Comparative Examples 1 and 4, the 23°C storage modulus or gel fraction was low, so that relatively large uneven deformation occurred, which was reflected in the evaluation results. The evaluation results of Comparative Examples 2 and 3 are believed to be due to the fact that the uneven deformation occurring in the pressure-sensitive adhesive layer was not sufficiently alleviated, and fine uneven deformation remained. From the above, it can be seen that an adhesive sheet having a colored adhesive layer containing an acrylic polymer, in which the adhesive layer has a gel fraction of 25% or more, a storage modulus at 23°C of 0.05 MPa or more, and a 23°C tan δ of 0.31 or more, can highly suppress fine uneven deformation.

[0217] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above. [Explanation of symbols]

[0218] 1, 2, 530 Adhesive sheet 1A 1st adhesive side 1B 2nd adhesive side 10 Supporting base material 10A 1st side 10B 2nd side 21 Adhesive layer (first adhesive layer) 21A Adhesive surface (1st adhesive surface) 21B 2nd adhesive side 22 Adhesive layer (second adhesive layer) 22A Adhesive surface (second adhesive surface) 31,32 Release liner 41 First member 42 Second member 50 Laminate 100,200 Adhesive sheet with release liner 150 cores 300 Adhesive sheet roll with release liner 400 Portable Electronic Devices 500 display device 520 Display section 540 Support part

Claims

1. A pressure-sensitive adhesive sheet having a colored pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer has a light transmittance of less than 50% for a light ray having a wavelength of 550 nm, the pressure-sensitive adhesive layer contains an acrylic polymer, the monomer components constituting the acrylic polymer do not contain a hydroxyl group-containing monomer or contain a hydroxyl group-containing monomer in an amount of less than 0.01% by weight, the pressure-sensitive adhesive layer has a gel fraction of 25% or more, The pressure-sensitive adhesive layer has a storage modulus of 0.05 MPa or more and 0.15 MPa or less at 23°C, and a tan δ of 0.31 or more at 23°C, wherein the tan δ refers to the ratio (G" / G') of the loss modulus G" to the storage modulus G' of the pressure-sensitive adhesive layer.

2. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the monomer component comprises an alkyl acrylate having a chain alkyl group having 4 to 8 carbon atoms.

3. The pressure-sensitive adhesive sheet according to claim 1 , wherein the monomer component comprises heptyl acrylate.

4. The pressure-sensitive adhesive sheet according to claim 1 , wherein the monomer component comprises n-butyl acrylate.

5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer contains a black colorant.

6. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer contains a black colorant as a first colorant and a metal oxide as a second colorant.

7. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer further comprises a tackifier resin.

8. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer.

9. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

10. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, which is used to fix components in an electronic device.

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