Double-sided sticky sheet

Abstract

To provide a double-sided sticky sheet capable of having a high sticking strength and achieving both a reduction in minute recessed and protruding deformation and processability.SOLUTION: The double-sided sticky sheet has a sticky agent layer containing an acrylic polymer. The acrylic polymer is a polymer of monomer components including heptyl acrylate and carboxyl group-containing monomers, where the monomer components contain 3 wt.% or more of the carboxyl group-containing monomers. The gel fraction of the sticky agent layer is higher than 40%, and the sticky agent layer has a storage modulus of 0.04 MPa or more at 23°C and has tanδ of 0.46 or more at 23°C.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Generally, adhesives (also called pressure-sensitive adhesives; the same applies below) are in a soft solid (viscoelastic) state at temperatures around room temperature and have the property of adhering to an adherend when pressure is applied. Taking advantage of such properties, adhesives are widely used in various industrial fields, from portable electronic devices such as smartphones and home appliances to automobiles and office automation equipment, typically in the form of adhesive sheets containing an adhesive layer, for purposes such as joining parts and protecting surfaces. Patent documents 1 and 2 are cited as technical documents related to adhesive sheets. Patent documents 1 and 2 describe adhesives containing acrylic polymers polymerized using heptyl acrylate as a monomer component. [Prior art documents] [Patent documents]

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

[0004] Pressure-sensitive adhesive sheets are required to have various performance characteristics depending on the application location, the mode of use, etc. For example, when fixing components inside a portable electronic device with a double-sided pressure-sensitive adhesive sheet, the adhesion area is usually small due to restrictions on size, weight, etc. Double-sided pressure-sensitive adhesive sheets used for such applications need to have an adhesive strength that can achieve good fixing even over a small area, and the required performance is at a higher level due to the demand for lighter weight and smaller size.

[0005] In addition, the double-sided pressure-sensitive adhesive sheet used for bonding and fixing can be used in a manner in which it is processed into a predetermined shape (outer shape) so as to fit the shape of the adhesive fixing part, and then attached to the adherend. For example, in fixing the members of the above-mentioned portable electronic device, the double-sided pressure-sensitive adhesive sheet is processed into the shape of the adhesive fixing part, such as a band shape or a frame shape, by a cutting process such as punching, and then used to fix the member. In the double-sided pressure-sensitive adhesive sheet used in such a manner, if the adhesive is too soft, the adhesive will overflow during cutting, which will impair the stability of the adhesive performance, reduce the processing accuracy, and cause defects. Therefore, it is desirable to design the adhesive of the double-sided pressure-sensitive adhesive sheet used after cutting process such as punching to have a sufficient hardness that can withstand the above processing.

[0006] Incidentally, before use (i.e., before being attached to an adherend), a double-sided pressure-sensitive adhesive sheet is usually handled in the form of a double-sided pressure-sensitive adhesive sheet with a release liner, in which each adhesive surface is protected by a release liner, from the viewpoints of productivity, handling, and the like. By protecting the adhesive surface of the double-sided 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. The double-sided pressure-sensitive adhesive sheet is, for example, formed into a roll (double-sided pressure-sensitive adhesive sheet roll with release liner) in which a double-sided pressure-sensitive adhesive sheet with a release liner, each adhesive surface of which is protected by two release liners, is wound, and the sheet is distributed, stored, and processed.

[0007] However, in the production of the double-sided pressure-sensitive adhesive sheet, for example, in the process of winding up a double-sided pressure-sensitive adhesive sheet with a release liner into a roll, minute foreign matter may get mixed in between the two release liners, and the pressure inside the roll may cause dents in the double-sided pressure-sensitive adhesive sheet due to the foreign matter. There is a concern that such dents remain as minute dents even after the double-sided pressure-sensitive adhesive sheet is attached to the adherend and are visible, causing a decrease in appearance quality. Such visible uneven deformation does not disappear once the sheet is attached to the adherend and stabilized. In particular, in recent years, there is a tendency for higher appearance quality to be required depending on the application location of the double-sided pressure-sensitive adhesive sheet, such as the display part of an electronic device, and it is expected that a double-sided 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 the adhesive is designed to be soft, it is thought that the above-mentioned fine uneven deformation will be alleviated to a certain extent, but on the other hand, there is a concern that the processability during processing such as punching will decrease. There is a trade-off between the suppression of the above-mentioned fine uneven deformation and processability, so it is difficult to achieve both.

[0008] As a result of intensive research, the inventors have created a double-sided pressure-sensitive adhesive sheet that uses an acrylic polymer containing heptyl acrylate as a monomer component and that has high adhesive strength suitable for bonding and fixing applications, and that can achieve both the above-mentioned ability to mitigate fine uneven deformation and processability in punching, etc., thereby completing the present invention. That is, an object of the present invention is to provide a double-sided pressure-sensitive adhesive sheet that is capable of having high adhesive strength, and that can achieve both the above-mentioned ability to mitigate fine uneven deformation and processability. [Means for solving the problem]

[0009] According to this specification, a double-sided pressure-sensitive adhesive sheet is provided. The double-sided pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer. The acrylic polymer is a polymer of a monomer component containing heptyl acrylate and a carboxyl group-containing monomer. The monomer component contains 3 wt % or more of the carboxyl group-containing monomer. The pressure-sensitive adhesive layer has a gel fraction of more than 40%. The pressure-sensitive adhesive layer has a storage modulus of 0.04 MPa or more at 23°C and a tan δ of 0.46 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.

[0010] By using an acrylic polymer containing heptyl acrylate as a monomer component and further containing 3% by weight or more of a carboxyl group-containing monomer, the adhesive can have high adhesive strength. In addition, the adhesive layer has a composition containing the above acrylic polymer, a gel fraction higher than 40%, and a storage modulus at 23°C of 0.04 MPa or more, so that it has good processability in cutting processes such as punching. Furthermore, the adhesive layer has a tan δ of 0.46 or more at 23°C, so that it has good relaxation properties, and fine uneven deformations occurring in the adhesive layer, such as dents on the adhesive surface, are eliminated or alleviated by the relaxation action of the adhesive. The compatibility of the above 23°C storage modulus of 0.04 MPa or more and 23°C tan δ of 0.46 or more can be suitably achieved by using an acrylic polymer containing heptyl acrylate as a monomer component. In short, according to the above configuration, it is possible to have high adhesive strength, and it is possible to achieve both relaxation and processability of fine uneven deformation.

[0011] In some preferred embodiments, the pressure-sensitive adhesive layer further comprises a tackifier resin. By including the tackifier resin, the adhesive strength can be improved. As the tackifier resin, at least one selected from a rosin-based tackifier resin and a terpene-based tackifier resin is preferably used.

[0012] In some preferred embodiments, the pressure-sensitive adhesive layer further contains an acrylic oligomer. By including an acrylic oligomer, the adhesive strength can be improved. In particular, it is more preferable to use a tackifier resin and an acrylic oligomer in combination. By using an appropriate amount of a tackifier resin and an acrylic oligomer, a higher adhesive strength can be realized. In the embodiment in which a tackifier resin and an acrylic oligomer are used in combination, the technology disclosed herein can achieve both excellent adhesive strength and relaxation of fine uneven deformation and processability. In some embodiments, the content C of the acrylic oligomer is O The content of the tackifier resin relative to C T Ratio of (C T / C O ) is preferably 1 or more and 10 or less.

[0013] In some preferred embodiments, the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains at least an isocyanate-based crosslinking agent. By using the isocyanate-based crosslinking agent, the cohesive strength of the pressure-sensitive adhesive can be appropriately increased.

[0014] In some preferred embodiments, the thickness of the pressure-sensitive adhesive layer is more than 5 μm and not more than 50 μm. A pressure-sensitive adhesive layer limited to a thickness of 50 μm or less can meet the demand for thinning and weight reduction. In addition, by making the thickness of the pressure-sensitive adhesive layer greater than 5 μm, minute uneven deformation is easily eliminated due to the relaxation effect of the pressure-sensitive adhesive layer. In addition, the adhesive strength tends to improve as the thickness of the pressure-sensitive adhesive layer increases.

[0015] Some preferred embodiments of the double-sided pressure-sensitive adhesive sheet have a 180 degree peel strength against a stainless steel plate (adhesive strength to SUS) of 10 N / 25 mm or more. A double-sided pressure-sensitive adhesive sheet having the above adhesive strength to SUS can exhibit high adhesive strength.

[0016] The double-sided pressure-sensitive adhesive sheet disclosed herein has high adhesive strength and good processability in punching and the like, and can be preferably used in applications where it is processed into a predetermined shape and requires long-term adhesive reliability. For example, it is suitable for fixing members in electronic devices including home appliances, office automation equipment, and mobile electronic devices such as smartphones. As described above, this specification provides an electronic device using any of the double-sided pressure-sensitive adhesive sheets disclosed herein, in other words, an electronic device including the double-sided pressure-sensitive adhesive sheet. [Brief description of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a double-sided pressure-sensitive adhesive sheet according to an embodiment. [Diagram 2] FIG. 4 is a cross-sectional view illustrating a schematic configuration of a double-sided 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

[0018] 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.

[0019] 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 properties satisfying the above (typically, a material having the above properties at 25°C).

[0020] 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.

[0021] <Composition of double-sided adhesive sheet> The double-sided adhesive sheet disclosed herein is configured to include an adhesive layer. The double-sided 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 double-sided adhesive sheet may be in the form of a substrate-attached double-sided adhesive sheet in which the adhesive layer is laminated on each surface of a supporting substrate. Hereinafter, the supporting substrate may be simply referred to as a "substrate". The concept of the adhesive sheet here may include those called adhesive tapes, adhesive labels, adhesive films, etc. 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.

[0022] The structure of a double-sided adhesive sheet according to one embodiment is shown in FIG. 1. This double-sided adhesive sheet 1 is configured as a substrate-less double-sided adhesive sheet made of an adhesive layer 21. The double-sided 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 double-sided adhesive sheet 1 before use (i.e., before being attached to an adherend) may be a component of a double-sided adhesive sheet 100 with a release liner, 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 that side may be preferably used. Alternatively, the 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 the double-sided pressure-sensitive adhesive sheet 1 and rolled up in a spiral shape to form a double-sided pressure-sensitive adhesive sheet with a release liner in a form in which the second adhesive surface 21B is protected by being in contact with the back surface of the release liner 31 (in a roll form).

[0023] Furthermore, double-sided pressure-sensitive adhesive sheet 100 with a release liner may be in the form of a roll (double-sided pressure-sensitive adhesive sheet roll with a release liner) 300 as shown in Fig. 1. Such a double-sided pressure-sensitive adhesive sheet roll 300 has double-sided pressure-sensitive adhesive sheet 100 with a release liner wound around a core (winding core) 150.

[0024] The structure of a double-sided pressure-sensitive adhesive sheet according to another embodiment is shown in FIG. 2. This double-sided pressure-sensitive adhesive sheet 2 is configured as a substrate-attached double-sided pressure-sensitive 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 pressure-sensitive adhesive layer 21 fixedly provided on the first surface 10A side, and a second pressure-sensitive adhesive layer 22 fixedly provided on the second surface 10B side. As shown in FIG. 2, the double-sided pressure-sensitive adhesive sheet 2 before use may be a component of a release-liner-attached double-sided pressure-sensitive adhesive sheet 200 in which the surface (first adhesive surface) 21A of the first pressure-sensitive adhesive layer 21 and the surface (second adhesive surface) 22A of the second pressure-sensitive adhesive layer 22 are protected by release liners 31, 32. Alternatively, the release liner 32 may be omitted, and a release liner 31 having both release surfaces may be used, which is superimposed on the double-sided pressure-sensitive adhesive sheet 2 and wound in a spiral shape to configure a release-liner-attached double-sided pressure-sensitive adhesive sheet in a form (roll form) in which the second adhesive surface 22A is protected by contacting the back surface of the release liner 31. Such a substrate-attached double-sided pressure-sensitive adhesive sheet is preferred because it has excellent processability, handleability, and the like.

[0025] 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 form thin layers, 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. On the other hand, substrateless double-sided pressure-sensitive adhesive sheets are substantially composed of only a viscoelastic body, so they are disadvantageous in terms of processability compared to substrate-attached double-sided pressure-sensitive adhesive sheets, but according to the technology disclosed herein, they can have good processability due to the viscoelastic properties and gel fraction properties of the adhesive layer.

[0026] <Adhesive layer> (Viscoelastic properties) The adhesive layer disclosed herein (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) has a storage modulus at 23°C (23°C storage modulus) of 0.04 MPa or more. An adhesive layer satisfying the above 23°C storage modulus tends to have excellent processability, with the adhesive being prevented from protruding during cutting such as punching. In some preferred embodiments, the 23°C storage modulus is about 0.06 MPa or more, may be 0.08 MPa or more, or may be 0.10 MPa or more. An adhesive layer having the above 23°C storage modulus has a moderate cohesive force, and therefore tends to easily obtain high adhesion reliability to an adherend, and also tends not to cause uneven deformation of a visible size. 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. A pressure-sensitive adhesive layer having a storage modulus at 23° C. of not more than a predetermined value tends to easily obtain adhesion to an adherend. In some preferred embodiments, the storage modulus is about 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, 0.08 MPa or less, or 0.06 MPa or less.

[0027] The adhesive layer disclosed herein is characterized by having a 23°C storage modulus of 0.04 MPa or more and a tan δ at 23°C (23°C tan δ) of 0.46 or more. 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 at 23°C of 0.46 or more 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 is 0.50 or more, and may be 0.55 or more. In some preferred embodiments, the 23°C tan δ is 0.60 or more, more preferably 0.65 or more, even more preferably 0.70 or more, and particularly preferably 0.75 or more (e.g., 0.78 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, and may be 1.5 or less, 1.2 or less, or 1.0 or less. From the viewpoint of compatibility between the uneven deformation relaxation property and the processability based on the 23°C storage modulus, 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.

[0028] 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.

[0029] (Acrylic polymer) The adhesive layer constituting the double-sided pressure-sensitive 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 this specification, the term "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.

[0030] 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.

[0031] The acrylic polymer used in the technology disclosed herein is a polymer of a monomer component containing heptyl acrylate. An 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 an 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 a polymer of heptyl acrylate has excellent flexibility is not particularly limited, but is considered to be because a 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.

[0032] The ratio 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, 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 (e.g., 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. 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, from the viewpoint of copolymerizing a carboxyl group-containing monomer, the ratio of heptyl acrylate in the monomer component is 97% by weight or less. In some preferred embodiments, the ratio of heptyl acrylate in the monomer component is 96% by weight or less, may be 95% by weight or less, or may be 94% by weight or less. Limiting the proportion of heptyl acrylate within the above range is preferable in terms of improving the storage modulus, and can be advantageous in terms of improving processability.

[0033] The acrylic polymer may be copolymerized with an alkyl (meth)acrylate other than heptyl acrylate (hereinafter, also referred to as "any alkyl (meth)acrylate"). As the any 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 (wherein R 1 When is a hydrogen atom, the heptyl group is excluded.

[0034] Examples of the optional alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl methacrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and isooctyl (meth)acrylate. Examples of the alkyl (meth)acrylate include acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (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 may be used alone or in combination of two or more.

[0035] In some embodiments, the ratio of heptyl acrylate to 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. According to the technology disclosed herein, a pressure-sensitive adhesive that realizes high adhesive strength, processability, and uneven deformation relaxation in a well-balanced manner can be formed based on the action of heptyl acrylate without relying on any alkyl (meth)acrylate such as 2EHA or BA. Therefore, the technology disclosed herein can be preferably implemented in an embodiment in which the monomer component does not substantially contain any alkyl (meth)acrylate.

[0036] In this specification, the monomer component being substantially free of monomer A (e.g., any alkyl (meth)acrylate) 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.

[0037] 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.

[0038] 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).

[0039] 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).

[0040] 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.

[0041] 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 become a crosslinking point of the acrylic polymer. By using the carboxyl group-containing monomer, the 23°C storage modulus of the pressure-sensitive adhesive layer can be improved, and excellent processability tends to be obtained. In addition, by using the carboxyl group-containing monomer, better adhesion can be exhibited to an adherend such as a highly polar material.

[0042] 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 the 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 of adhesive properties such as adhesive strength and cohesive strength in the carboxy group-containing monomers disclosed herein.

[0043] The proportion of the carboxyl group-containing monomer in the monomer component of the acrylic polymer is 3% by weight or more (e.g., 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, and may be 6.0% by weight or more, 6.5% by weight or more, or 7.0% by weight or more. By increasing the amount of the carboxyl group-containing monomer used, the cohesive strength of the adhesive layer is improved based on the action of the carboxyl group-containing monomer, so that the 23°C storage modulus and gel fraction of the adhesive can be improved, and an adhesive with excellent processability can be easily obtained. 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] In a particularly preferred embodiment, an acrylic polymer synthesized using a monomer component substantially consisting 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 are effectively exerted, and a predetermined storage modulus at 23°C and tan δ at 23°C are both achieved, and it is possible to preferably achieve both uneven deformation relaxation property and processability while obtaining high adhesive strength. 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.

[0053] 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.

[0054] 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).

[0055] 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.

[0056] 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.

[0057] 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 can 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 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 (for example, greater than 1 million), or may be greater than 1.2 million. According to a monomer composition containing heptyl acrylate, the viscosity is easily maintained low, so that the synthesis of a high molecular weight substance is good, and an acrylic polymer having the above Mw is easily obtained. 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, 23°C storage modulus and 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, and uneven deformation relaxation and processability can be preferably achieved at the same time. 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 is improved, and the uneven deformation relaxation property tends to be improved.

[0058] 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

[0059] (tackifier resin) In some preferred embodiments, the adhesive layer contains a tackifier resin. By using a tackifier resin, high adhesive strength can be obtained. According to the technology disclosed herein, the adhesive layer has a predetermined viscoelastic property (specifically, 23°C storage modulus and 23°C tan δ) and gel fraction in a composition containing a tackifier resin, and can achieve both uneven deformation relaxation and processability. Although not particularly limited, the effect of using a tackifier resin can be effectively exhibited in a composition containing 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 the acrylic adhesive, the adhesive strength can be improved. 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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:

[0074] 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.

[0075] 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.

[0076] 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 of heptyl acrylate used, the higher the storage modulus at 23° C. The acrylic polymer containing heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with tackifier resins, so that desired properties can be achieved by incorporating an appropriate amount of tackifier resin.

[0077] 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). H The 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.

[0078] 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, and 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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, and even more preferably 22 parts by weight or less, and may be 20 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. The acrylic polymer containing heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with tackifier resins, and therefore desired properties can be achieved by incorporating an appropriate amount of tackifier resin.

[0088] (Acrylic Oligomer) In some preferred embodiments, the adhesive layer contains an acrylic oligomer. The adhesive strength of the adhesive can be improved by including an acrylic oligomer. According to the technology disclosed herein, the adhesive layer can have high adhesive strength and both uneven deformation relaxation and processability in a composition containing 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.

[0089] 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, and more preferably about 40°C or more and about 300°C or less. By having a Tg within the above range, the adhesive strength can be suitably improved. In some preferred embodiments, from the viewpoint of the cohesiveness of the pressure-sensitive 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).

[0090] In this specification, the Tg of an acrylic oligomer refers to the Tg calculated by the Fox formula based on the composition of the above-mentioned monomer components. The Fox formula is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 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.

[0091] The glass transition temperature of the homopolymer used to calculate Tg is to be a value listed in a publicly known document. For example, the values ​​listed in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989) are used. For monomers for which multiple values ​​are listed in this document, the highest value is used.

[0092] For monomers for which the glass transition temperature of the homopolymer is not described in the above literature, the value obtained by the following measurement method is used. Specifically, 100 parts by weight of monomer, 0.2 parts by weight of 2,2'-azobisisobutyronitrile, and 200 parts by weight of ethyl acetate as a polymerization solvent are charged into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser tube, and stirred for 1 hour while passing nitrogen gas through it. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. Then, the mixture is cooled to room temperature to obtain a homopolymer solution with a solid content concentration of 33% by weight. Then, the homopolymer solution is cast and applied onto a release liner, and dried to prepare a test sample (sheet-shaped homopolymer) with a thickness of about 2 mm. This test sample was punched out into a disk with a diameter of 7.9 mm, sandwiched between parallel plates, and the viscoelasticity was measured in shear mode using a viscoelasticity tester (TA Instruments Japan, model name "ARES") while applying a shear strain of 1 Hz at a temperature range of -70°C to 150°C and a heating rate of 5°C / min. The temperature corresponding to the peak top temperature of tan δ was taken as the Tg of the homopolymer.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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, and may be 15 parts by weight or less, 12 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, or 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 manner, the effects of the technology disclosed herein can be preferably exhibited.

[0102] 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. In a composition containing an acrylic polymer containing heptyl acrylate as a monomer component, a tackifier resin and an acrylic oligomer can be used in combination to preferably form an adhesive that has excellent adhesive strength while also achieving high levels of uneven deformation relaxation and processability. 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 the acrylic oligomer in the 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.

[0103] 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.

[0104] 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.

[0105] (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, by increasing the amount of the crosslinking agent used, the gel fraction and the 23°C storage modulus can be increased, and the processability can be improved. 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 form or a composite form thereof, etc. The crosslinking agent is typically contained in the adhesive layer exclusively in a form after crosslinking reaction.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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."

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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).

[0118] 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.

[0119] (Coloring agent) The adhesive layer disclosed herein may or may not contain a colorant for the purpose of adjusting optical properties (light transmittance, etc.) and imparting hiding power, design, color, etc. The colorant may be, for example, a black, gray, white, red, blue, yellow, green, yellow-green, orange, purple, gold, silver, pearl color, or other colorant. The above colorant may 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 may be used. As the pigment, an inorganic pigment or an organic pigment may be used. The colorant may be used alone or in combination of two or more.

[0120] The colorant is not particularly limited, and for example, a black colorant can be preferably used because it can efficiently adjust the hiding power and light shielding power by using a small amount.Specific examples of the black colorant include carbon black, graphite, aniline black, perylene black, cyanine black, titanium black, inorganic pigment hematite, activated carbon, molybdenum disulfide, chromium complex, anthraquinone-based colorant, etc.The black colorant can be used alone or in appropriate combination of two or more kinds.

[0121] In addition, as the colorant, a non-black colorant that can be selected from, for example, white colorants and gray colorants can also be preferably used. Such a colorant can be one or more selected from inorganic materials (for example, metals and metal compounds), organic materials, and organic-inorganic composites. Specific examples of the colorant include metal oxides such as titanium oxide (titanium dioxide such as rutile type titanium dioxide and anatase type 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, and the like), barium carbonate, and zinc carbonate; and hydroxides such as aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide. Examples of suitable materials include silicate compounds such as aluminum silicate, magnesium silicate, and calcium silicate; inorganic materials such as 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, and hydrated halloysite; and organic materials such as acrylic resins, polystyrene resins, polyurethane resins, amide resins, polycarbonate resins, silicone resins, urea-formaldehyde resins, and melamine resins.

[0122] In some embodiments, 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, for example, about 0.1 wt% or more, appropriately about 0.5 wt% or more, may be about 1 wt% or more, may be about 2 wt% or more, or may be about 3 wt% or more. In some embodiments, the content of the colorant in the adhesive layer can be about 30 wt% or less from the viewpoint of compatibility with the adhesive component, maintenance of adhesive properties such as adhesive strength, etc., and is usually about 20 wt% or less, may be about 15 wt% or less, may be about 10 wt% or less, or may be about 5 wt% or less. In some preferred embodiments, the content of the colorant in the adhesive layer may be about 3 wt% or less, may be about 1 wt% or less, may be about 0.1 wt% or less, or may be about 0.01 wt% or less. The technology disclosed herein can be preferably implemented in an embodiment in which the adhesive layer does not substantially contain a colorant.

[0123] (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 a leveling agent, a crosslinking assistant, a plasticizer, a softener, a filler, an antistatic agent, an antiaging agent, an ultraviolet absorber, an antioxidant, an antirust agent, a light stabilizer, 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.

[0124] (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.

[0125] 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 a double-sided 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.

[0126] 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.

[0127] 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.

[0128] (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 and purpose of use. In some embodiments, from the viewpoint of avoiding excessive thickness of the double-sided 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 well meet the demand for thinning and weight reduction. In addition, by limiting the thickness of the adhesive layer, the adhesive is less likely to protrude during processing such as punching, and 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.

[0129] (Gel fraction) The gel fraction (weight basis) of the adhesive layer disclosed herein is higher than 40%. The adhesive layer having the above gel fraction tends to have excellent processability, suppressing the adhesive from protruding during cutting such as punching. In addition, the adhesive layer having the above gel fraction has a moderate hardness, and therefore tends not to cause uneven deformation of a visible size. In some preferred embodiments, the gel fraction is 45% or more, more preferably 50% or more, even more preferably 55% or more, and may be 60% or more, 65% or more, 70% or more, or 75% or more. 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.

[0130] 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.

[0131] (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.

[0132] <Base material> In an embodiment in which the double-sided pressure-sensitive adhesive sheet disclosed herein is in the form of a 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, a composite of these, or the like. Examples of paper include Japanese paper, craft paper, glassine paper, wood-free paper, synthetic paper, topcoat paper, and the like. Examples of cloth include woven fabrics and nonwoven fabrics made by spinning various fibrous materials alone or in a mixed manner. Examples of the fibrous material include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber, and the like. 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 double-sided pressure-sensitive adhesive sheet.

[0133] The substrate may be formed from a material derived from biomass or a material derived from non-biomass. From the viewpoint of producing a double-sided 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.

[0134] 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.

[0135] As the substrate constituting the substrate-attached double-sided pressure-sensitive adhesive sheet, one containing a resin film as the base film can be preferably used. The above-mentioned base film is typically a member that can independently maintain 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.

[0136] 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.

[0137] 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).

[0138] 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 further the light transmittance of the double-sided pressure-sensitive adhesive sheet containing the substrate.

[0139] 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.

[0140] 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.

[0141] 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).

[0142] 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).

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] In the double-sided pressure-sensitive adhesive sheet of the embodiment including a substrate, the thickness of the substrate is not particularly limited. In order to prevent the double-sided 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, and more preferably about 100 μm or less. Depending on the purpose and mode of use of the double-sided 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 double-sided pressure-sensitive adhesive sheet is the same, which can be advantageous in terms of improving adhesion to the adherend or substrate. In addition, a substrate with a limited thickness can be a good response to the demand for thinning and weight reduction. The thickness of the substrate is usually about 0.5 μm or more (e.g., 1 μm or more), preferably about 2 μm or more, for example, about 6 μm or more, from the viewpoint of the handling property (handling property) and processability of the double-sided pressure-sensitive adhesive sheet, etc. In some embodiments, the thickness of the substrate can be about 8 μm or more, and may be about 10 μm or more.

[0150] <Total thickness of double-sided adhesive sheet> The total thickness of the double-sided pressure-sensitive adhesive sheet disclosed herein (including a pressure-sensitive adhesive layer and may further include a base layer, but not including a release liner) is not particularly limited. The total thickness of the double-sided pressure-sensitive 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 double-sided pressure-sensitive adhesive sheet can be about 50 μm or less, for example, may be about 35 μm or less. The lower limit of the thickness of the double-sided pressure-sensitive 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 double-sided pressure-sensitive adhesive sheet having a thickness equal to or greater than a certain value tends to be easily adhered 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 double-sided pressure-sensitive adhesive sheet.

[0151] <Release liner> In the technology disclosed herein, a release liner can be used during the formation of the adhesive layer, the preparation of the double-sided pressure-sensitive adhesive sheet, the storage, distribution, and shaping of the double-sided pressure-sensitive 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 double-sided pressure-sensitive adhesive sheet described above.

[0152] 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.

[0153] 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).

[0154] 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.

[0155] 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.

[0156] 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. By protecting the adhesive surface with 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, for example, a foreign matter mixed between the release liners when the double-sided 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 winding), 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 double-sided pressure-sensitive 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 dents due to external force from the back surface of the release liner or foreign matter, the adhesive layer has excellent uneven deformation mitigation properties, so that the fine uneven deformation is eliminated or mitigated, and good appearance quality can be imparted. In addition, when the double-sided pressure-sensitive 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.

[0157] <Roll body> This specification also provides a rolled body (double-sided PSA sheet roll with release liner) containing the double-sided PSA sheet with release liner disclosed herein in a rolled form. The uneven deformation mitigation property, which is one of the effects of the technology disclosed herein, is effective against fine uneven deformation of the PSA layer caused by minute foreign matter mixed between two release liners when the double-sided PSA sheet with release liner is wound into a roll. The technology disclosed herein is suitable for a double-sided PSA sheet that is stored in the form of a roll before use. Such a rolled body typically includes a core (winding core) and a double-sided PSA sheet with 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 rolled body, a hollow cylindrical or hollow polygonal prism-shaped core may be preferably used. A cylindrical core is particularly preferred.

[0158] <Characteristics of double-sided adhesive sheets> (Adhesion to SUS) In some embodiments, the double-sided pressure-sensitive adhesive sheet preferably has a 180-degree peel strength (adhesive strength against SUS) against a stainless steel plate of about 10 N / 25 mm or more. The double-sided pressure-sensitive adhesive sheet having the above adhesive strength against SUS can exhibit high adhesive strength. The above adhesive strength against SUS is 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). The upper limit of the above adhesive strength against SUS is not particularly limited, but from the viewpoint of compatibility with processability and the like, it may usually be, for example, about 50 N / 25 mm or less, and in some embodiments, it may be about 30 N / 25 mm or less. The above adhesive strength against SUS is measured using a SUS plate as an adherend under the conditions of 23°C, 50% RH, a pulling speed of 300 mm / min, and a peel angle of 180 degrees. More specifically, it is measured by the method described in the Examples below.

[0159] (Biomass carbon ratio) In some embodiments, the double-sided PSA sheet contains a biomass-derived material, and the biomass carbon ratio thereof may be equal to or greater than a predetermined value. The biomass carbon ratio of the double-sided PSA 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 double-sided PSA sheet means that the amount of fossil resource-based materials, such as petroleum, used is small. From this perspective, the higher the biomass carbon ratio of the double-sided PSA sheet, the more preferable it is. For example, the biomass carbon ratio of the double-sided PSA 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, may be 95% or less, or 90% or less. From the standpoint of making it easier to exert good adhesive performance, in some embodiments, the biomass carbon ratio of the double-sided PSA sheet may be, for example, 90% or less, 85% or less, or 80% or less.

[0160] <Application> The double-sided pressure-sensitive adhesive sheet disclosed herein is not particularly limited in its use, and can be used in various applications. The double-sided pressure-sensitive adhesive sheet disclosed herein is suitable for bonding and fixing members in applications requiring high adhesive strength and processing into a predetermined shape (outer shape). For example, it can be preferably used for fixing members in various mobile devices (portable devices). In addition, the double-sided pressure-sensitive adhesive sheet disclosed herein is highly suppressed from unevenly deforming the pressure-sensitive adhesive layer, such as dents on the surface of the pressure-sensitive adhesive layer, and is therefore suitable for applications requiring appearance quality, such as applications in which the double-sided pressure-sensitive adhesive sheet attached to the surface of the adherend is visible. For example, depending on the application location of the double-sided pressure-sensitive adhesive sheet, such as the display part of an electronic device, there is a tendency for higher appearance quality to be required. The double-sided pressure-sensitive adhesive sheet disclosed herein is suitable for fixing members in the display part of an electronic device, such as the above-mentioned portable electronic device.

[0161] 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.

[0162] In some embodiments, the double-sided adhesive sheet can be used for the purpose of fixing a pressure-sensitive sensor and other members in a portable electronic device equipped with a pressure-sensitive sensor among the above portable electronic devices. In some embodiments, the double-sided adhesive sheet can be used for fixing a pressure-sensitive 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.

[0163] In some preferred embodiments, the double-sided pressure-sensitive adhesive sheet is suitable for use on the back surface of a display screen (display unit) such as a touch panel display in a portable electronic device. By disposing the double-sided 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.

[0164] The material (adherend material) to which the double-sided pressure-sensitive adhesive sheet disclosed herein is attached is not particularly limited, and 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 double-sided pressure-sensitive 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 double-sided pressure-sensitive 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 the surface (attaching surface) to which the double-sided pressure-sensitive adhesive sheet is attached may be subjected to various surface treatments. 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).

[0165] In some embodiments, the member or material to which the double-sided pressure-sensitive adhesive sheet is attached may be light-transmitting (light-transmitting adherend). The adhesive surface of the double-sided pressure-sensitive adhesive sheet attached to the light-transmitting adherend can be seen through the light-transmitting adherend, so it is desirable to have an adhesive surface with 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 double-sided pressure-sensitive adhesive sheet disclosed herein may be preferably used in an embodiment in which it 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 refers to the light transmittance at a wavelength of 550 nm.

[0166] In some embodiments, the double-sided pressure-sensitive adhesive sheet is used in a manner that 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. The double-sided pressure-sensitive adhesive sheet may cover the entire surface of the metal member, or may cover a part of the surface (for example, a part of an area that needs to be concealed). The above-mentioned metal member may be, for example, a member constituting the support part 540 of the display device 500 shown in FIG. 4 described later. The above-mentioned metal member is preferably one of the adherends of the double-sided pressure-sensitive adhesive sheet.

[0167] From the above, the technology disclosed herein provides a laminate comprising a double-sided adhesive sheet and a member to which the double-sided adhesive sheet is attached. In some embodiments, the laminate comprising the double-sided adhesive sheet is a laminate comprising the double-sided adhesive sheet and a metal member (first member). Such a laminate may comprise a metal member and a double-sided adhesive sheet covering at least a part of the surface of the metal member. The double-sided 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 double-sided adhesive sheet is attached to the metal member. In some embodiments, the member to which the double-sided adhesive sheet is attached may have the light transmittance of the above-mentioned adherend material. In this embodiment, the laminate comprising the double-sided adhesive sheet is a laminate comprising the double-sided 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), 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.

[0168] A configuration example of the laminate is shown in FIG. 3. The laminate 50 shown in FIG. 3 includes a first member 41, a substrate-less double-sided adhesive sheet 1, and a second member 42 in this order. 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 that overlapping descriptions will not be repeated.

[0169] In some embodiments, the double-sided 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 properties.

[0170] FIG. 4 is an exploded perspective view showing a typical example of the configuration 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 a double-sided adhesive sheet 530. In this configuration example, the double-sided 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 double-sided adhesive sheet disclosed herein is preferably used as a component of the display device as described above.

[0171] Furthermore, in some embodiments, the double-sided 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 such an acrylic PSA is used (i.e., an acrylic PSA with a low biomass carbon ratio), thereby contributing to reducing dependency on fossil resource-based materials. The double-sided PSA sheet disclosed herein may be preferably used as a double-sided PSA sheet with reduced dependency on fossil resource-based materials.

[0172] The matters disclosed by this specification include the following: [1] A portable electronic device, a double-sided adhesive sheet is bonded to a member constituting the portable electronic device, the double-sided pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of monomer components including heptyl acrylate and a carboxyl group-containing monomer, the monomer component contains 3% by weight or more of the carboxyl group-containing monomer, The pressure-sensitive adhesive layer has a gel fraction of more than 40%, A portable electronic device, wherein the pressure-sensitive adhesive layer has a storage modulus of 0.04 MPa or more at 23°C and a tan δ of 0.46 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 portable electronic device according to the above-mentioned [1], wherein the adhesive layer further contains a tackifier resin. [3] The mobile electronic device according to the above [1] or [2], wherein the tackifier resin is at least one selected from a rosin-based tackifier resin and a terpene-based tackifier resin. [4] The mobile electronic device according to any one of the above [1] to [3], wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer. [5] The portable electronic device according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive layer contains a tackifier resin and an acrylic oligomer. [6] The content C of the acrylic oligomer O The content C of the tackifier resin relative to T Ratio of (C T / C O ) is 1 or more and 10 or less. [7] The mobile electronic device according to any one of the above [1] to [6], wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains at least an isocyanate-based crosslinking agent. [8] The portable electronic device according to any one of the above [1] to [7], wherein the pressure-sensitive adhesive layer has a thickness of more than 5 μm and not more than 50 μm. [9] The portable electronic device according to any one of the above [1] to [8], wherein the double-sided pressure-sensitive adhesive sheet has a 180 degree peel strength against a stainless steel plate of 10 N / 25 mm or more.

[0173]

[11] A double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of monomer components including heptyl acrylate and a carboxyl group-containing monomer, the monomer component contains 3% by weight or more of the carboxyl group-containing monomer, The pressure-sensitive adhesive layer has a gel fraction of more than 40%, The pressure-sensitive adhesive layer has a storage modulus of 0.04 MPa or more at 23°C and a tan δ of 0.46 or more at 23°C, where 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 double-sided pressure-sensitive adhesive sheet according to

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

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

[11] or

[12] , wherein the tackifier resin is at least one selected from a rosin-based tackifier resin and a terpene-based tackifier resin.

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

[11] to

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

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

[11] to

[14] , wherein the pressure-sensitive adhesive layer contains a tackifier resin and an acrylic oligomer.

[16] The content C of the acrylic oligomer O The content C of the tackifier resin relative to T Ratio of (C T / C O ) is 1 or more and 10 or less.

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

[11] to

[16] , wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains at least an isocyanate-based crosslinking agent.

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

[11] to

[17] , wherein the pressure-sensitive adhesive layer has a thickness of more than 5 μm and not more than 50 μm.

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

[11] to

[18] , which has a 180 degree peel strength against a stainless steel plate of 10 N / 25 mm or more.

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

[11] to

[20] above.

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

[11] to

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

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

[22] is wound.

[0174]

[31] A laminate comprising a metal member (first member) and a double-sided pressure-sensitive adhesive sheet, the double-sided pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of monomer components including heptyl acrylate and a carboxyl group-containing monomer, the monomer component contains 3% by weight or more of the carboxyl group-containing monomer, The pressure-sensitive adhesive layer has a gel fraction of more than 40%, The pressure-sensitive adhesive layer has a storage modulus of 0.04 MPa or more at 23°C and a tan δ of 0.46 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 double-sided pressure-sensitive adhesive sheet, the double-sided pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of monomer components including heptyl acrylate and a carboxyl group-containing monomer, the monomer component contains 3% by weight or more of the carboxyl group-containing monomer, The pressure-sensitive adhesive layer has a gel fraction of more than 40%, The pressure-sensitive adhesive layer has a storage modulus of 0.04 MPa or more at 23°C and a tan δ of 0.46 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), a double-sided pressure-sensitive adhesive sheet, and a light-transmitting member (second member), the double-sided pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of monomer components including heptyl acrylate and a carboxyl group-containing monomer, the monomer component contains 3% by weight or more of the carboxyl group-containing monomer, The pressure-sensitive adhesive layer has a gel fraction of more than 40%, The pressure-sensitive adhesive layer has a storage modulus of 0.04 MPa or more at 23°C and a tan δ of 0.46 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

[31] to

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

[0175] Some 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, "parts" and "%" are by weight unless otherwise specified.

[0176] <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.

[0177] (Preparation of Pressure-Sensitive Adhesive Composition) To the acrylic polymer solution obtained above, 20 parts of a terpene phenol resin (trade name "YS Polystar T-115", terpene phenol resin manufactured by Yasuhara Chemical Co., Ltd., softening point about 115°C, hydroxyl value 30 to 60mgKOH / g) as a tackifier resin, 5 parts of an acrylic oligomer, 3 parts (solid content basis) of an isocyanate crosslinking agent A (trade name "Coronate L", 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation), and 0.02 parts of an epoxy crosslinking agent (trade name "TETRAD-C", 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, manufactured by Mitsubishi Gas Chemical Co., Ltd.) were added per 100 parts of the acrylic polymer contained in the solution, and the mixture was stirred to prepare a pressure-sensitive adhesive composition according to this example. 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.

[0178] (Preparation of double-sided 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.

[0179] <Examples 2 to 9 and Comparative Examples 1 to 3> The adhesive compositions of each example were prepared in the same manner as in Example 1, except that the monomer composition of the acrylic polymer, Mw, amount of tackifier resin, amount of acrylic oligomer, type and amount of crosslinking agent, and thickness of the adhesive layer were changed as shown in Table 1, and the resulting adhesive compositions were used to produce substrate-less double-sided adhesive sheets with release liner of each example in the same manner as in Example 1. The Mw of the acrylic polymer was adjusted by adjusting the concentration of the monomer components during polymerization. In Table 1, BA represents n-butyl acrylate. Also, 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).

[0180] <Example 10> A pressure-sensitive adhesive composition prepared by the method described in Example 1 was prepared, and the pressure-sensitive adhesive composition was applied to one surface (first surface) of a 2 μm-thick PET film (trade name "Lumirror", manufactured by Toray Industries, Inc.) as a base layer, and dried at 100° C. for 2 minutes to form a first pressure-sensitive 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 attached to the first pressure-sensitive adhesive layer. In addition, a 38 μm-thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) was prepared, and the pressure-sensitive adhesive composition was applied to the release surface of the release liner, and dried at 100° C. for 2 minutes to form a second pressure-sensitive adhesive layer with a thickness of 35 μm. This second pressure-sensitive adhesive layer was transferred to the non-pressure-sensitive adhesive layer surface of the base layer on which the first pressure-sensitive adhesive layer was formed. In this manner, a double-sided pressure-sensitive adhesive sheet with a release liner (double-sided pressure-sensitive adhesive sheet with substrate) according to this example was produced.

[0181] <Evaluation method> (Adhesion to SUS) A 50 μm thick PET film was attached to one adhesive surface of the double-sided pressure-sensitive adhesive sheet under a measurement environment of 23° C. and 50% RH, and the sheet was cut to a size of 25 mm wide and 100 mm long to prepare a measurement sample. Under an environment of 23° C. and 50% RH, the other adhesive surface of the measurement sample was 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 was used to measure the peel strength (adhesive strength to SUS) [N / 25 mm] in accordance with JIS Z 0237:2000 under the conditions of 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 was used as the universal tensile compression tester.

[0182] (Punching processability) The double-sided adhesive sheet with release liner was cut to a predetermined size and used as an evaluation sample. A processing blade was inserted from one release liner (the release liner on the light release side) of the evaluation sample, and the other release liner (the release liner on the heavy release side) on the opposite side was processed (cut) to a depth where it was half-cut, and processed into a frame shape with an outer shape of 25 mm x 25 mm and a width of 2 mm, and the part other than the frame-shaped adhesive sheet was removed. After 60 seconds, the one release liner was removed from the double-sided adhesive sheet, and the degree of adhesive overflow at the processed end surface of the exposed double-sided adhesive sheet was observed under a microscope. Those in which adhesive overflow of 0.1 mm or more was observed were evaluated as "x", and those in which adhesive overflow of less than 0.1 mm was evaluated as "○". For each example, 10 evaluation samples were prepared and 10 evaluation tests were performed (N=10), and the number of evaluation tests evaluated as "○" X ( / 10) was used as the evaluation result of punching workability. If the number of evaluation tests rated as ◯ is 5 or more (i.e. 5 / 10 or more), the test is judged as passing.

[0183] (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 (passed) in which no uneven deformation was observed was used as the result of the uneven deformation evaluation, X ( / 10). If the number of passes was 6 or more (i.e., 6 / 10 or more), it was determined that the fine uneven deformation was alleviated.

[0184] The outline of each example and the evaluation results are shown in Table 1.

[0185] [Table 1]

[0186] As shown in Table 1, the adhesives according to Examples 1 to 10 contain heptyl acrylate as a monomer component, and further contain an acrylic polymer containing 3% or more of a carboxyl group-containing monomer, have a gel fraction higher than 40%, a 23°C storage modulus of 0.04 MPa or more, and a 23°C tan δ of 0.46 or more. The double-sided adhesive sheets containing the above adhesives have high adhesion to SUS, good punching processability, and excellent relaxation of fine uneven deformation. On the other hand, Comparative Examples 1 and 2, which used a BA-based polymer, had a 23°C tan δ of less than 0.46 and poor uneven deformation relaxation. Furthermore, Comparative Example 1 had high adhesion to SUS, but had a gel fraction of 40%, and the evaluation results of punching processability were poor. Comparative Example 2 had a higher gel fraction and 23°C storage modulus than Comparative Example 1, and the punching processability was improved, but the adhesive strength was reduced. In Comparative Example 3, an acrylic polymer containing heptyl acrylate as a monomer component was used as in the above-mentioned Examples, but the adhesive strength, punching processability, and uneven deformation relaxation were all inferior to those of the above-mentioned Examples. In Comparative Example 3, the amount of carboxyl group-containing monomer used in the acrylic polymer was less than 3%, so high adhesive strength was not obtained, and the 23°C storage modulus was low at less than 0.04 MPa, so good punching processability was not obtained, and the 23°C tan δ was low at less than 0.46, so it is believed that this resulted in poor uneven deformation relaxation. From the above, it can be seen that a double-sided pressure-sensitive adhesive sheet having an adhesive layer containing heptyl acrylate as a monomer component and further containing an acrylic polymer containing 3 wt% or more of a carboxy group-containing monomer, wherein the adhesive layer has a gel fraction of more than 40%, a storage modulus at 23°C of 0.04 MPa or more, and a 23°C tan δ of 0.46 or more, can have high adhesive strength and can achieve both the ability to mitigate fine uneven deformation and processability.

[0187] 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]

[0188] 1, 2, 530 double-sided 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 Double-sided adhesive sheet with release liner 150 cores 300 Double-sided adhesive sheet roll with release liner 400 Portable Electronic Devices 500 display device 520 Display section 540 Support part

Claims

1. A double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing an acrylic polymer, the acrylic polymer is a polymer of monomer components including heptyl acrylate and a carboxy group-containing monomer, the monomer component contains 3% by weight or more of the carboxy group-containing monomer, the monomer component does not contain a hydroxyl group-containing monomer or contains 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 more than 40%; The pressure-sensitive adhesive layer has a storage modulus of 0.04 MPa or more at 23°C and a tan δ of 0.46 or more at 23°C, wherein 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 double-sided pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive layer further comprises a tackifying resin.

3. The double-sided pressure-sensitive adhesive sheet according to claim 2 , wherein the tackifier resin is at least one selected from the group consisting of rosin-based tackifier resins and terpene-based tackifier resins.

4. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer.

5. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer comprises a tackifier resin and an acrylic oligomer.

6. The content C of the acrylic oligomer Ｏ The content C of the tackifier resin relative to Ｔ The ratio (C Ｔ / C Ｏ 6. The double-sided pressure-sensitive adhesive sheet according to claim 5, wherein ) is 1 or more and 10 or less.

7. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains at least an isocyanate-based crosslinking agent.

8. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the thickness of the pressure-sensitive adhesive layer is more than 5 µm and not more than 50 µm.

9. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, which has a 180 degree peel strength from a stainless steel plate of 10 N / 25 mm or more.

10. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, which is used to fix components in electronic devices.

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