Double-sided adhesive 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 adhesive sheet.

Background Art

[0002] Generally, an adhesive (also referred to as a pressure-sensitive adhesive. The same applies hereinafter) exhibits a state of a soft solid (viscoelastic body) in a temperature range near room temperature and has the property of adhering to an adherend by pressure. Taking advantage of such properties, adhesives are widely used for purposes such as joining parts and surface protection in various industrial fields, typically in the form of an adhesive sheet including an adhesive layer, from portable electronic devices such as smartphones and home appliances to automobiles and OA equipment. As technical documents related to adhesive sheets, Patent Documents 1 and 2 can be cited. Patent Documents 1 and 2 describe an adhesive containing an acrylic polymer polymerized using heptyl acrylate as a monomer component.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Adhesive sheets are required to have various performances depending on the application location, usage mode, etc. For example, fixing members inside a portable electronic device using a double-sided adhesive sheet usually has a small adhesion area due to limitations such as size and weight. The double-sided adhesive sheet used for this application needs to have an adhesive force capable of achieving good fixing even with a small area, and the required performance has become at a higher level due to the demands for weight reduction and miniaturization.

[0005] Furthermore, double-sided adhesive sheets used for bonding and fixing may be used in a manner in which they are processed into a predetermined shape (outer shape) to conform to the shape of the adhesive fixing part, and then attached to the object to be bonded. For example, in fixing components of the above-mentioned portable electronic device, the double-sided adhesive sheet is processed into the shape of the adhesive fixing part, such as a strip shape or a frame shape, by cutting processes such as die-cutting, and then used to fix the component. In double-sided adhesive sheets used in this manner, if the adhesive is too soft, the adhesive may ooze out during cutting, impairing the stability of the adhesive performance, reducing processing accuracy, and causing defects. Therefore, it is desirable that the adhesive of a double-sided adhesive sheet used after cutting processes such as die-cutting be designed to have sufficient hardness to withstand the above-mentioned processing.

[0006] Incidentally, double-sided adhesive sheets are usually handled in the form of double-sided adhesive sheets with release liners, where each adhesive surface is protected by a release liner, before use (i.e., before being attached to a substrate), from the viewpoint of productivity and ease of handling. By protecting the adhesive surface of the double-sided adhesive sheet with a release liner, the adhesive surface is kept smooth, allowing it to adhere well to the substrate surface and exhibit the desired adhesive properties. Furthermore, an adhesive sheet with an adhesive surface protected by a release liner and kept smooth can be uniformly attached to the substrate, providing a good appearance when the substrate surface is visible. The above-mentioned double-sided adhesive sheet is formed, for example, into a roll body (double-sided adhesive sheet roll with release liner) by winding a double-sided adhesive sheet with release liners, where each adhesive surface is protected by two release liners, and then distributed, stored, and used for processing.

[0007] However, in the manufacturing of the above-mentioned double-sided adhesive sheets, for example, in the process of winding the double-sided adhesive sheet with release liner onto a roll, minute foreign matter may get mixed in between the two release liners, and due to the pressure inside the roll, this foreign matter may cause indentations in the double-sided adhesive sheet. Such indentations remain visible as minute indentations even after the double-sided adhesive sheet is attached to the substrate, raising concerns that they may cause a decrease in appearance quality. Such visible-sized uneven deformations do not disappear once the sheet is attached to the substrate and stabilized. In particular, in recent years, depending on the application area of ​​the double-sided adhesive sheet, such as the display parts of electronic devices, there is a growing demand for higher appearance quality, and it is anticipated that there will be a need for double-sided adhesive sheets that suppress minute uneven deformations at a level that was not previously considered a problem. It is thought that designing the adhesive to be softer would mitigate the above minute uneven deformations to some extent, but on the other hand, there are concerns that the processability during processing such as die-cutting will decrease. Since there is a trade-off relationship between suppressing the above minute uneven deformations and processability, it is difficult to achieve both.

[0008] As a result of diligent research, the inventors have created a double-sided adhesive sheet using an acrylic polymer containing heptyl acrylate as a monomer component, which has high adhesive strength suitable for bonding and fixing applications, and which can also achieve both the ability to mitigate the aforementioned fine uneven deformation and processability in die-cutting and other processes, thus completing the present invention. In other words, the present invention aims to provide a double-sided adhesive sheet that can have high adhesive strength and can also achieve the ability to mitigate the aforementioned fine uneven deformation and processability. [Means for solving the problem]

[0009] This specification provides a double-sided adhesive sheet. This double-sided adhesive sheet has an adhesive layer containing an acrylic polymer. The acrylic polymer is a polymer of monomer components containing heptyl acrylate and a carboxyl group-containing monomer. The monomer components also contain 3% by weight or more of the carboxyl group-containing monomer. Furthermore, the gel fraction of the adhesive layer is higher than 40%. The adhesive layer has a storage modulus of 0.04 MPa or higher at 23°C, and a tanδ of 0.46 or higher at 23°C. Here, tanδ refers to the ratio of the loss modulus G'' to the storage modulus G' of the adhesive layer (G'' / G').

[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. Furthermore, the adhesive layer, with the composition containing the above acrylic polymer, has a gel fraction higher than 40% and a storage modulus of 0.04 MPa or higher at 23°C, resulting in good processability in cutting processes such as punching. In addition, the adhesive layer has a tanδ of 0.46 or higher at 23°C, resulting in good relaxation properties. Fine irregularities in the adhesive layer, such as indentations on the adhesive surface, are eliminated or mitigated by the relaxing effect of the adhesive. The simultaneous achievement of a storage modulus of 0.04 MPa or higher at 23°C and a tanδ of 0.46 or higher at 23°C can be suitably achieved by using an acrylic polymer containing heptyl acrylate as a monomer component. In short, the above configuration allows for high adhesive strength while simultaneously achieving both relaxation of fine irregularities and good processability.

[0011] In some preferred embodiments, the adhesive layer further comprises a tackifying resin. By including a tackifying resin, the adhesive strength can be improved. Preferably, at least one selected from rosin-based tackifying resins and terpene-based tackifying resins is used as the tackifying resin.

[0012] In some preferred embodiments, the adhesive layer further comprises an acrylic oligomer. The inclusion of an acrylic oligomer improves adhesion. In particular, the combined use of a tackifying resin and an acrylic oligomer is more preferable. By using appropriate amounts of both the tackifying resin and the acrylic oligomer, higher adhesion can be achieved. The technology disclosed herein, in a combined use of a tackifying resin and an acrylic oligomer, achieves excellent adhesion while simultaneously mitigating fine surface deformation and maintaining processability. In some embodiments, the content of the acrylic oligomer C O Content of the above tackifying resin C T The ratio (C T / C O ) is preferably between 1 and 10.

[0013] In some preferred embodiments, the adhesive composition for forming the adhesive layer comprises at least an isocyanate-based crosslinking agent. By using an isocyanate-based crosslinking agent, the cohesive force of the adhesive can be moderately increased.

[0014] In some preferred embodiments, the thickness of the adhesive layer is greater than 5 μm and less than or equal to 50 μm. An adhesive layer with a thickness limited to 50 μm or less can effectively meet the demands for thinning and weight reduction. Furthermore, by making the thickness of the adhesive layer greater than 5 μm, fine irregularities and deformations are more easily eliminated by the relaxing effect of the adhesive layer. In addition, the adhesive strength tends to improve as the thickness of the adhesive layer increases.

[0015] In some preferred embodiments, the double-sided adhesive sheet has a 180-degree peel strength (adhesion to stainless steel) of 10 N / 25 mm or more against a stainless steel plate. The double-sided adhesive sheet having the above-mentioned adhesion to stainless steel can exhibit high adhesive strength.

[0016] The double-sided adhesive sheets disclosed herein have high adhesive strength and good processability in processes such as die-cutting, and are therefore preferably used in applications where they are processed to a predetermined shape and require long-term adhesive reliability. For example, they are suitable for fixing components in electronic devices, including home appliances, office automation equipment, and portable electronic devices such as smartphones. As described above, this specification provides an electronic device using any of the double-sided adhesive sheets disclosed herein, in other words, an electronic device including said double-sided adhesive sheet. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic cross-sectional view showing the structure of a double-sided adhesive sheet according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing the configuration of a double-sided adhesive sheet according to another embodiment. [Figure 3] This is a schematic cross-sectional view showing one example of the structure of a laminate. [Figure 4] This is a schematic exploded perspective view showing an example of the configuration of a display device. [Modes for carrying out the invention]

[0018] Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein but necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art. Furthermore, in the following drawings, members and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Also, the embodiments shown in the drawings are schematic for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the size or scale of the adhesive sheets of the present invention that are actually provided as products.

[0019] In this specification, "adhesive" refers to a material that, as described above, exhibits a soft solid (viscoelastic) state at temperatures around room temperature and has the property of easily adhering to a substrate under pressure. The adhesive referred to here is generally defined as having a complex tensile modulus E, as defined in "CA Dahlquist, “Adhesion: Fundamentals and Practice”, McLaren & Sons, (1966) p. 143". * (1Hz) < 10 7 dyne / cm 2 It may be a material having properties that satisfy the above conditions (typically, a material having the above properties at 25°C).

[0020] In this specification, biomass-derived carbon means carbon derived from biomass materials, i.e., materials derived from renewable organic resources (renewable carbon). The above biomass materials typically refer to materials derived from biological resources (typically photosynthetic plants) that can be sustainably reproduced if sunlight, water, and carbon dioxide are present. Therefore, materials derived from fossil resources that are depleted by use after extraction (fossil resource-based materials) are excluded from the concept of biomass materials as used herein. The biomass-carbon ratio of the adhesive layer and adhesive sheet, i.e., the proportion of biomass-derived carbon in the total carbon contained in the adhesive layer and 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 composed of an adhesive layer. The double-sided adhesive sheet may be in the form of a substrate-less double-sided adhesive sheet comprising, for example, a first adhesive surface formed by one surface of the adhesive layer and a second adhesive surface formed 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 support substrate. Hereinafter, the support substrate may simply be referred to as the "substrate". The concept of adhesive sheet as used herein may include adhesive tapes, adhesive labels, adhesive films, etc. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be an adhesive sheet processed into various shapes.

[0022] Figure 1 schematically shows the structure of a double-sided adhesive sheet according to one embodiment. This double-sided adhesive sheet 1 is configured as a substrate-less double-sided adhesive sheet consisting of an adhesive layer 21. The double-sided adhesive sheet 1 is used by attaching a first adhesive surface 21A, which is formed by one surface (first surface) of the adhesive layer 21, and a second adhesive surface 21B, which is formed by the other surface (second surface) of the adhesive layer 21, to different locations on an object to be adhered to. The locations to which the adhesive surfaces 21A and 21B are attached may be different locations on different members, or different locations within a single member. Before use (i.e., before being attached to an object to be adhered to), as shown in Figure 1, the double-sided adhesive sheet 1 may be a component of a double-sided adhesive sheet 100 with release liners, in which the first adhesive surface 21A and the second adhesive surface 21B are protected by release liners 31 and 32, each having a release surface on at least the side facing the adhesive layer 21. As the release liners 31 and 32, it is preferable to use, for example, a sheet-like substrate (liner substrate) on which a release layer is provided by a release treatment agent, so that the one side becomes a release surface. Alternatively, the release liner 32 may be omitted, and a release liner 31 with release surfaces on both sides may be used. This release liner and the double-sided adhesive sheet 1 may be overlapped and wound in a spiral shape to form a double-sided adhesive sheet with a release liner in a form (roll form) where the second adhesive surface 21B abuts against and is protected by the back surface of the release liner 31.

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

[0024] Figure 2 schematically shows the structure of a double-sided adhesive sheet according to another embodiment. This double-sided adhesive sheet 2 is configured as a base material-attached double-sided adhesive sheet comprising a sheet-shaped support base material (e.g., resin film) 10 having a first surface 10A and a second surface 10B, a first adhesive layer 21 fixedly provided on the first surface 10A side, and a second adhesive layer 22 fixedly provided on the second surface 10B side. Before use, the double-sided adhesive sheet 2 may be a component of a double-sided adhesive sheet 200 with a release liner, as shown in Figure 2, in which the surface (first adhesive surface) 21A of the first adhesive layer 21 and the surface (second adhesive surface) 22A of the second adhesive layer 22 are protected by release liners 31 and 32. Alternatively, the release liner 32 may be omitted, and a release liner 31 with release surfaces on both sides may be used, and the double-sided adhesive sheet 2 may be superimposed on this and wound in a spiral shape to constitute a double-sided adhesive sheet with a release liner in which the second adhesive surface 22A abuts against and is protected by the back surface of the release liner 31 (roll form). Such double-sided adhesive sheets with a base material are preferable because they offer excellent processability and handling.

[0025] The technology disclosed herein can preferably be implemented in the form of a substrate-less double-sided adhesive sheet. Since a substrate-less double-sided adhesive sheet does not have a supporting substrate, it is easy to make thin, and is also advantageous in that it can maximize the adhesive properties such as adhesive strength and impact resistance. Furthermore, a substrate-less double-sided adhesive sheet can mitigate fine irregularities in the adhesive layer by making maximum use of the thickness of the adhesive layer. On the other hand, since a substrate-less double-sided adhesive sheet is composed substantially only of a viscoelastic material, it is at a disadvantage in terms of processability compared to a substrate-attached double-sided adhesive sheet. However, according to the technology disclosed herein, good processability can be achieved due to the viscoelastic properties and gel fraction properties of the adhesive layer.

[0026] <Adhesive layer> (Viscoelastic properties) The adhesive layer disclosed herein (in embodiments comprising 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 higher. Adhesive layers satisfying the above 23°C storage modulus tend to have excellent processability, suppressing adhesive overflow during cutting processes such as punching. In some preferred embodiments, the above 23°C storage modulus is approximately 0.06 MPa or higher, may be 0.08 MPa or higher, or 0.10 MPa or higher. Adhesive layers having the above 23°C storage modulus tend to have moderate cohesive force, making it easier to obtain high adhesive reliability to the adherend, and also tend to be less prone to visible size irregularities. Furthermore, in some embodiments, the 23°C storage modulus of the adhesive layer is approximately 0.60 MPa or lower, may be approximately 0.40 MPa or lower, or approximately 0.20 MPa or lower. Adhesive layers having a storage modulus of elasticity at 23°C below a predetermined value tend to exhibit good adhesion to the adherend. In some preferred embodiments, the storage modulus is approximately 0.18 MPa or less, more preferably 0.15 MPa or less, even more preferably 0.13 MPa or less, and may also be 0.11 MPa or less, less than 0.10 MPa, 0.08 MPa or less, or 0.06 MPa or less.

[0027] Furthermore, the adhesive layer disclosed herein is characterized by having a 23°C storage modulus of 0.04 MPa or higher, as well as a 23°C tanδ (23°C tanδ) of 0.46 or higher. The tanδ (loss tangent) refers to the ratio of the loss modulus G'' to the storage modulus G' of the adhesive layer (G'' / G'). Since the adhesive layer with a 23°C tanδ of 0.46 or higher has good relaxation properties, fine irregularities and deformations in the adhesive layer, such as indentations on the adhesive surface, are relaxed or mitigated in a short time by the relaxing effect of the adhesive. In some embodiments, the 23°C tanδ is 0.50 or higher, and may be 0.55 or higher. In some preferred embodiments, the 23°C tanδ is 0.60 or higher, more preferably 0.65 or higher, even more preferably 0.70 or higher, and particularly preferably 0.75 or higher (e.g., 0.78 or higher). Since the above 23°C tanδ generally tends to decrease as the above 23°C storage modulus increases, it is preferable that the upper limit of the above 23°C tanδ be within an appropriate range that is compatible with the above 23°C storage modulus. In some embodiments, the above 23°C tanδ is 3 or less, may be 1.5 or less, may be 1.2 or less, or may be 1.0 or less. From the viewpoint of balancing the ability to relax uneven deformation and the processability based on the above 23°C storage modulus, in some preferred embodiments, the above 23°C tanδ 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 above 23°C tanδ is 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 tanδ of the adhesive layer can be determined by dynamic viscoelasticity measurement. Specifically, an adhesive layer with a thickness of approximately 2 mm is prepared by stacking multiple adhesive layers (or double-sided adhesive sheets in the case of substrate-less double-sided adhesive sheets) to be measured. A sample of this adhesive layer, punched into a disc shape with a diameter of 7.9 mm, is sandwiched and fixed between parallel plates, and dynamic viscoelasticity measurement is performed using a viscoelasticity tester (e.g., ARES or equivalent manufactured by T.A. Instruments Inc.) under the following conditions to determine the 23°C storage modulus and 23°C tanδ. • Measurement mode: Shear mode Temperature range: -70℃ to 150℃ • Heating rate: 5°C / min ·Measurement frequency: 1Hz The measurements in the examples described later will also be performed using the method described above. The adhesive layer to be measured may be one formed by applying the corresponding adhesive composition in layers and then drying or curing it.

[0029] (Acrylic polymer) The adhesive layer constituting the double-sided adhesive sheet disclosed herein contains an acrylic polymer. The adhesive layer is typically an adhesive layer with an acrylic polymer as the base polymer. Such an adhesive layer is also called an acrylic adhesive layer. The base polymer refers to the main component of the rubbery polymer (a polymer that exhibits rubber elasticity in the temperature range around room temperature) contained in the adhesive layer. In this specification, unless otherwise specified, "main component" refers to a component contained in more than 50% by weight. Furthermore, the following description of components that may be contained in the adhesive and adhesive layer is also applicable to adhesive compositions used to form the adhesive (layer) unless otherwise specified.

[0030] Furthermore, in this specification, "acrylic polymer" means a polymer that contains monomer units derived from monomers having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, monomers having at least one (meth)acryloyl group in one molecule will also be referred to as "acrylic monomers." Therefore, in this specification, acrylic polymers are defined as polymers that contain monomer units derived from acrylic monomers. In this specification, "(meth)acryloyl" comprehensively refers to acryloyl and methacryloyl. Similarly, "(meth)acrylate" comprehensively refers to acrylate and methacrylate, and "(meth)acrylic" comprehensively refers to acrylic and methacrylic.

[0031] The acrylic polymer used in the technology disclosed herein is a polymer of a monomer component containing heptyl acrylate. Acrylic polymers polymerized using a monomer component containing heptyl acrylate have superior flexibility compared to polymers of other alkyl acrylates such as n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). Therefore, adhesives containing such polymers can have a high 23°C tanδ value, making it easy to achieve both a 23°C storage modulus within the above range and a 23°C tanδ within the above range. Heptyl acrylate is considered to be one of the optimal monomer components for achieving both the above 23°C storage modulus and 23°C tanδ. The reason why polymers of heptyl acrylate have superior flexibility is not particularly limited in interpretation, but it is thought that polymers containing heptyl acrylate as a monomer unit have a low glass transition temperature, as well as relatively large spaces between the main chains within the adhesive. Among heptyl acrylates, n-heptyl acrylate is preferred from the viewpoint of flexibility. Acrylic polymers synthesized with n-heptyl acrylate as a monomer component tend to have relatively long linear side chains, which is thought to lead to larger spaces between the main chains.

[0032] The proportion of heptyl acrylate in the monomer component of the acrylic polymer is, for example, 50% by weight or more (e.g., more than 50% by weight) in some embodiments, preferably 70% by weight or more, more preferably 80% by weight or more, still more preferably 85% by weight or more, particularly preferably 90% by weight or more (e.g., more than 90% by weight), may be 92% by weight or more, may be 94% by weight or more, may be 95% by weight or more, may be 96% by weight or more. By increasing the amount of heptyl acrylate used, its usage effects (e.g., improvement of the 23°C tanδ of the adhesive, and thus improvement of the uneven deformation relaxation property) can be effectively exhibited. On the other hand, from the perspective of copolymerizing the carboxy group-containing monomer, the proportion of heptyl acrylate in the monomer component is 97% by weight or less. In some preferred embodiments, the proportion of heptyl acrylate in the monomer component is 96% by weight or less, may be 95% by weight or less, 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 elastic modulus, and thus can be advantageous in terms of improving the processability.

[0033] In the acrylic polymer, an alkyl (meth)acrylate other than heptyl acrylate (hereinafter, also referred to as "optional alkyl (meth)acrylate") may be copolymerized. As the optional alkyl (meth)acrylate, for example, a compound represented by the following formula (1) can be preferably used. CH2=C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. Also, R 2 is a linear alkyl group having 1 to 20 carbon atoms (however, when R 1 is a hydrogen atom, the heptyl group is excluded).

[0034] Examples of the above optional alkyl (meth)acrylates 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. Examples include acrylates, 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, eicosyl (meth)acrylate, etc. These arbitrary alkyl (meth)acrylates can be used individually or in combination of two or more.

[0035] In some embodiments, the proportion of heptyl acrylate in the total amount of alkyl (meth)acrylate contained in the monomer component is, for example, 50% by weight or more (specifically 50 to 100% by weight, for example, more than 50% by weight), preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and may be 99% by weight or more, or even 100% by weight. By adopting such a monomer composition, the effects of using heptyl acrylate can be effectively realized. According to the technology disclosed herein, an adhesive can be formed that achieves a good balance of high adhesive strength, processability, and unevenness deformation mitigation based on the action of heptyl acrylate, without relying on arbitrary alkyl (meth)acrylate such as 2EHA or BA. Therefore, the technology disclosed herein can preferably be carried out in embodiments in which the monomer component substantially does not contain arbitrary alkyl (meth)acrylate.

[0036] In this specification, "substantially free of monomer A (e.g., the arbitrary alkyl (meth)acrylates mentioned above)" means that monomer A is not used intentionally, and it is permissible for monomer A to be unintentionally included in amounts of, for example, 0.01% by weight or less.

[0037] In some embodiments, the above monomer component may include an alkyl (meth)acrylate having a biomass-derived alkyl group at its ester terminus (hereinafter also referred to as "biomass alkyl (meth)acrylate"). In recent years, environmental issues such as global warming have become a major concern, and there is a desire to reduce the amount of fossil resource-based materials used, such as petroleum. Under these circumstances, there is also a need to reduce the amount of fossil resource-based materials used in the field of adhesives. By using biomass alkyl (meth)acrylate, it is possible to suitably realize an acrylic adhesive that takes into consideration the reduction of reliance on fossil resource-based materials.

[0038] Biomass alkyl (meth)acrylates are not particularly limited and include, for example, esters of biomass-derived alkanols and biomass-derived or non-biomass-derived (meth)acrylic acid. Examples of biomass-derived alkanols include biomass ethanol, alkanols derived from plant raw materials such as palm oil, palm kernel oil, coconut oil, and castor oil. When the number of carbon atoms in the biomass-derived alkanol is three or more, the alkanol may be linear or branched. In some embodiments, esters of biomass-derived alkanols and non-biomass-derived (meth)acrylic acid are used as biomass alkyl (meth)acrylates for the synthesis of acrylic polymers. In such biomass alkyl (meth)acrylates, the more carbon atoms the alkanol has, the higher the ratio of biomass-derived carbons to the total number of carbon atoms in the biomass alkyl (meth)acrylate, i.e., the biomass carbon ratio of the alkyl (meth)acrylate. Therefore, in the biomass alkyl (meth)acrylate described above, a high number of carbon atoms in the alkyl group derived from biomass is desirable in terms of reducing dependence on fossil fuel-based materials. On the other hand, if the number of carbon atoms in the alkyl group constituting the alkyl (meth)acrylate is too high, it tends to become difficult to obtain adhesive properties such as adhesion strength, and it may also be disadvantageous in terms of productivity, such as synthesis, handling, and cost. In embodiments where an ester of biomass-derived alkanol and non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate, it is desirable to use a material that balances adhesive properties with a reduction in dependence on fossil fuel-based materials (more specifically, the biomass carbon ratio of the alkyl (meth)acrylate described above).

[0039] In some preferred embodiments, biomass-derived heptyl acrylate (biomass heptyl acrylate) is used as the heptyl acrylate. By using biomass heptyl acrylate, the effects of the technologies disclosed herein can be achieved while reducing the dependence on fossil fuel-based materials. The biomass heptyl acrylate is an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived acrylic acid. For example, an ester of a biomass-derived alkanol and a non-biomass-derived acrylic acid may be used. In such compounds, only the heptyl group is biomass-derived. As the biomass-derived heptyl acrylate, the use of biomass-derived n-heptyl acrylate (biomass n-heptyl acrylate) is preferred.

[0040] The proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) in the monomer component of the above 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, and may also be 92% by weight or more, 94% by weight or more, or 96% by weight or more. In addition, the proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) in the monomer component 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] Furthermore, the monomer component of the acrylic polymer preferably contains a carboxyl group-containing monomer. Carboxyl group-containing monomers can improve cohesiveness based on their polarity. Also, when using crosslinking agents such as isocyanate-based or epoxy-based crosslinking agents, the carboxyl group can act as a crosslinking point for the acrylic polymer. By using a carboxyl group-containing monomer, the 23°C storage modulus of the adhesive layer can be improved, and excellent processability tends to be easily obtained. In addition, by using a carboxyl group-containing monomer, better adhesion can be achieved to adherends such as highly polar materials.

[0042] Examples of carboxyl group-containing monomers 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. Furthermore, the carboxyl group-containing monomer may also be a monomer having a metal salt (e.g., an alkali metal salt) of the carboxyl group. The carboxyl group-containing monomer can be used alone or in combination of two or more. Among these, AA and MAA are particularly preferred carboxyl group-containing monomers. AA is especially preferred. When using one or more carboxyl group-containing monomers, 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 consists substantially of AA alone. Due to the combined effects of its carboxyl group-based polarity, its role as a crosslinking point, and its Tg (106°C), AA is considered one of the optimal monomer materials for achieving a good balance of adhesive properties such as adhesion and cohesiveness in the carboxyl group-containing monomers disclosed herein.

[0043] The proportion of carboxyl group-containing monomers 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 also 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 carboxyl group-containing monomers used, the cohesive force of the adhesive layer is improved based on the action of the carboxyl group-containing monomers, so the storage modulus of elasticity at 23°C and the gel fraction of the adhesive can be improved, and an adhesive with excellent processability can be easily obtained. Furthermore, the amount of carboxyl group-containing monomers is 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 carboxyl group-containing monomers 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 carboxyl group-containing monomer used within the above range, an adhesive with good tackiness can be easily obtained.

[0044] Acrylic polymers may also be copolymerized with functional group-containing monomers other than carboxyl group-containing monomers (monomers containing arbitrary functional groups). Examples of monomers containing optional functional groups that can be introduced into acrylic polymers to serve as crosslinking sites or contribute to improved adhesive strength include monomers containing hydroxyl groups (OH groups) (hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate; polypropylene glycol mono(meth)acrylate, etc.), monomers containing acid anhydride groups, monomers containing amide groups ((meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc.), monomers containing amino groups (aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, etc.), monomers containing epoxy groups, monomers containing cyano groups, monomers containing keto groups, monomers having nitrogen atom-containing rings (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), monomers containing alkoxysilyl groups, and monomers containing imide groups. The above-mentioned monomers containing any functional group can be used individually or in combination of two or more.

[0045] When the monomer component constituting the acrylic polymer contains the above-mentioned arbitrary functional group-containing monomer, the content of the arbitrary functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exhibiting the effects of using the arbitrary functional group-containing monomer, the content of the arbitrary functional group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, is appropriate to be 0.5% by weight or more, and may be 1% by weight or more. Furthermore, 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 arbitrary functional group-containing monomer in the monomer component is appropriate to be 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 arbitrary functional group-containing monomer in the monomer component can be, 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, and may be less than 0.1% by weight. The techniques disclosed herein can preferably be implemented in which the monomer component of the acrylic polymer substantially does not contain any monomers containing an optional functional group.

[0046] Furthermore, a hydroxyl group-containing monomer may be used as the above-mentioned optional functional group-containing monomer. In that case, the content of the hydroxyl group-containing monomer is appropriately about 10% by weight or less (for example, 0.001 to 10% by weight) in the monomer component, preferably about 5% by weight or less, and more preferably about 2% by weight or less. In some embodiments, the content of the hydroxyl group-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 the hydroxyl group-containing monomer. In the technology disclosed herein, desired properties and effects can be preferably achieved by limiting or omitting the use of the hydroxyl group-containing monomer in the composition.

[0047] The proportion of carboxyl group-containing monomers in the total functional group-containing monomers (including carboxyl group-containing monomers) used as copolymer components of acrylic polymers is preferably 30% by weight or more, more preferably 50% 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. For example, it may be 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 carboxyl group-containing monomers in the total functional group-containing monomers is 100% by weight, but for example, it may be 95% by weight or less.

[0048] The monomer components constituting the acrylic polymer may include other copolymer components other than the functional group-containing monomers mentioned above for purposes such as improving cohesiveness. Examples of other copolymer 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)acrylate (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylate (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylate (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 mentioned above can be used individually or in combination of two or more.

[0049] The amount of such other copolymer components is not particularly limited and can be appropriately selected according to the purpose and application, but from the viewpoint of appropriately exhibiting the effects of use, it is appropriate to set it to 0.05% by weight or more, and may be set to 0.5% by weight or more. Furthermore, from the viewpoint of easily balancing the adhesive performance, it is appropriate to set the content of other copolymer components in the monomer component to 20% by weight or less, and from the viewpoint of suitably exhibiting the adhesive properties based on the essential monomer component, it is preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably less than 5% by weight, and may be, for example, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be preferably implemented in a manner in which the monomer component does not substantially contain other copolymer components.

[0050] Acrylic polymers may also contain polyfunctional monomers as other monomer components, having at least two polymerizable functional groups (typically radical polymerizable functional groups) that have unsaturated double bonds, such as (meth)acryloyl groups or vinyl groups. By using polyfunctional monomers as monomer components, the cohesive force of the adhesive layer can be increased. Polyfunctional monomers can be used as crosslinking agents. Polyfunctional monomers are not particularly limited and include, for example, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, etc. Polyfunctional monomers can be used individually or in combination of two or more.

[0051] The amount of polyfunctional monomer used is not particularly limited and can be appropriately set so as to achieve the purpose of using the polyfunctional monomer. The amount of polyfunctional monomer used can be approximately 3% by weight or less of the monomer component, preferably approximately 2% by weight or less, and more preferably approximately 1% by weight or less (for example, approximately 0.5% by weight or less). The lower limit of the amount used when using polyfunctional monomer is not particularly limited as long as it is greater than 0% by weight. Usually, by using an amount of polyfunctional monomer of approximately 0.001% by weight or more of the monomer component (for example, approximately 0.01% by weight or more), the effect of using the polyfunctional monomer can be appropriately achieved.

[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. With the above monomer composition, the effects of heptyl acrylate and carboxyl group-containing monomer are effectively exerted, and it is possible to achieve both a predetermined 23°C storage modulus and 23°C tanδ, thereby obtaining high adhesive strength while preferably achieving both uneven deformation relaxation and processability. From this viewpoint, the total proportion of heptyl acrylate and carboxyl group-containing monomer in the above monomer component is suitable to be 90% by weight or more (90-100% 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 (e.g., more than 99.99% by weight), and the total proportion of heptyl acrylate and 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 above-mentioned acrylic polymer (the biomass-carbon ratio of the acrylic polymer) may be, for example, 1% or more, 10% or more is appropriate, preferably 30% or more, more preferably 50% or more (for example, more than 50%), and may also be 70% or more, 80% or more, or even 90% to 100%. By designing in this way, an acrylic adhesive that takes into consideration the reduction of reliance on fossil fuel-based materials can be obtained.

[0054] The method for obtaining acrylic polymers is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization can be preferably employed. As for the monomer supply method when performing solution polymerization, a batch supply 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 employed. 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, around 20°C to 170°C (typically around 40°C to 140°C).

[0055] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, one solvent or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetic acid esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

[0056] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide (BPO) and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and so on. Another example of polymerization initiators is a redox initiator, which is a combination of a peroxide and a reducing agent. Such polymerization initiators can be used individually or in combination of two or more. The amount of polymerization initiator used can be the usual amount, for example, it can be selected from a range of approximately 0.005 to 1 part by weight (typically approximately 0.01 to 1 part by weight) per 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 a suitable Mw that can satisfy both the above-mentioned 23°C storage modulus and 23°C tanδ is used. For example, the Mw of the acrylic polymer is approximately 10 × 10 4 ~500×10 4 It can be within this range. From the standpoint of adhesive performance, the Mw of the base polymer is approximately 20 × 10 4 It may be more than that, approximately 30 x 10 4 The above is also acceptable, approximately 40 x 10 4 The above is also acceptable: 50 x 10 4The above values ​​are also acceptable. In some embodiments, the Mw of the acrylic polymer may be greater than 600,000 and greater than 650,000, with 700,000 or more being appropriate and 750,000 or more being acceptable. The larger the Mw of the acrylic polymer, the easier it is to obtain an adhesive that exhibits good cohesive force, and the processability tends to improve. In some preferred embodiments, the Mw of the acrylic polymer is 800,000 or more, may be 850,000 or more, may be 900,000 or more, may be 1,000,000 or more (e.g., over 1,000,000), and may be 1,200,000 or more. With a monomer composition containing heptyl acrylate, it is easy to maintain low viscosity, resulting in good synthesization of high molecular weight products and making it easy to obtain acrylic polymers having the above Mw. Furthermore, by using an acrylic polymer that contains heptyl acrylate as a monomer unit and has an Mw of a predetermined value or higher, it is easier to satisfy the above viscoelastic properties (specifically, the 23°C storage modulus and 23°C tanδ) based on the flexibility based on the chemical structure of the polymer and the cohesive force based on the molecular weight, and it is possible to preferably achieve both uneven deformation relaxation and processability. On the other hand, from the viewpoint of impact resistance, adhesive strength, ease of synthesis, etc., the Mw of the acrylic polymer is usually appropriate to be approximately 3 million or less, preferably 2.5 million or less, more preferably 2 million or less, and even more preferably 1.8 million or less, and may also be 1.5 million or less, or 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 tanδ tends to improve, and the ability to relax uneven deformation tends to improve.

[0058] The Mw of acrylic polymers can be measured by gel permeation chromatography (GPC) and determined as a value equivalent to standard polystyrene. Specifically, it can be measured using the "HLC-8220GPC" (manufactured by Tosoh Corporation) GPC measuring device under the following conditions. The same applies to the examples described later. [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 columns: 1 x "TSKguardcolumn SuperHZ-H" + 2 x "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: Product name "TSKgel SuperH-RC" 1 piece (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0059] (Adhesive-granting resin) In some preferred embodiments, the adhesive layer includes a tackifying resin. Using a tackifying resin allows for high adhesive strength. According to the techniques disclosed herein, a composition including a tackifying resin results in an adhesive layer having predetermined viscoelastic properties (specifically, 23°C storage modulus and 23°C tanδ) and gel fraction, achieving both surface deformation relaxation and processability. While not particularly limited, the effect of using a tackifying resin can be effectively demonstrated in compositions containing high molecular weight acrylic polymers. The tackifying resin is not particularly limited, and various tackifying resins such as rosin-based tackifying resins, terpene-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, elastomer-based tackifying resins, phenol-based tackifying resins, and ketone-based tackifying resins can be used. Such tackifying resins can be used individually or in combination of two or more.

[0060] Specific examples of rosin-based tackifying resins include unmodified rosins (raw rosin) such as gum rosin, wood rosin, and tall oil rosin; modified rosins obtained by hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins; the same applies hereinafter); and various other rosin derivatives. Examples of the above rosin derivatives include rosin esters such as those obtained by esterifying unmodified rosin with alcohols (i.e., rosin esters) and modified rosin with alcohols (i.e., modified rosin esters); unsaturated fatty acid modified rosins obtained by modifying unmodified rosin or modified rosin with unsaturated fatty acids; unsaturated fatty acid modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; 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 (especially rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; and rosinphenol resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and then thermal polymerization. Among these, rosin esters are preferred.

[0061] While 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, glycerol esters, and pentaerythritol esters.

[0062] Examples of terpene-based tackifying resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers; and modified terpene resins obtained by modifying these terpene resins (phenol modification, aromatic modification, hydrogenation modification, hydrocarbon modification, etc.). An example of the above-mentioned modified terpene resin is terpenephenol resin.

[0063] Terpene phenol resins refer to polymers containing terpene and phenol residues, and the concept encompasses both copolymers of terpenes and phenol compounds (terpene-phenol copolymer resins) and homopolymers or copolymers of terpenes modified with phenol (phenol-modified terpene resins). Specific examples of terpenes that constitute such terpene phenol resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-isomers, l-isomers, and d / l-isomers (dipentene)). Hydrogenated terpene phenol resins refer to hydrogenated terpene phenol resins that have a structure obtained by hydrogenating such terpene phenol resins. They are sometimes also called hydrogenated terpene phenol resins.

[0064] Examples of hydrocarbon-based tackifying resins include aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic / aromatic copolymer (C5 / C9) petroleum resins, hydrogenated versions thereof (for example, alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), various modified versions thereof (for example, maleic anhydride modified versions), coumarone resins, coumarone indene resins, and other various hydrocarbon-based resins.

[0065] In some embodiments, it is preferable to use at least one selected from rosin-based tackifying resins and terpene-based tackifying resins as the tackifying resin. By incorporating rosin-based tackifying resins and / or terpene-based tackifying resins into the acrylic adhesive, the adhesive strength can be improved. In some preferred embodiments, the total proportion of rosin-based tackifying resins and terpene-based tackifying resins in the total tackifying resin contained in the adhesive layer can be, for example, more than approximately 50% by weight (more than 50% by weight and 100% by weight or less), more than approximately 70% by weight, more than approximately 80% by weight, more than approximately 90% by weight, more than 95% by weight, or more than 99% by weight.

[0066] Some preferred embodiments include the tackifying resin comprising one or more terpene phenol resins. The techniques disclosed herein can preferably be implemented, for example, in an embodiment in which approximately 25% by weight or more (more preferably approximately 30% by weight or more) of the total amount of the tackifying resin is a terpene phenol resin. The proportion of the terpene phenol resin to the total amount of the tackifying resin may be approximately 50% by weight or more, approximately 70% by weight or more, approximately 80% by weight or more, or approximately 90% by weight or more. Substantially all of the tackifying resin (for example, approximately 95% by weight or more and 100% by weight or less, and even more precisely, approximately 99% by weight or more and 100% by weight or less) may be a terpene phenol resin.

[0067] The content of terpene phenol resin in the adhesive layer is not particularly limited as long as it satisfies the desired properties (viscoelastic properties, etc.). In some embodiments, from the viewpoint of improving adhesive strength, the content of terpene phenol resin is usually about 1 part by weight or more, 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) per 100 parts by weight of acrylic polymer. The storage modulus at 23°C tends to increase as the amount of terpene phenol resin used increases. In addition, in some embodiments, the content of terpene phenol resin in the adhesive layer is, for example, 70 parts by weight or less, 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 per 100 parts by weight of acrylic polymer. In some preferred embodiments, from the viewpoint of improving the ability of the adhesive to mitigate uneven deformation, the content of the 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 tackifying resin is not particularly limited. From the viewpoint of improving cohesive force, a tackifying resin with a softening point (softening temperature) of approximately 80°C or higher may be preferably used. The softening point of the tackifying resin may be approximately 100°C or higher, or approximately 110°C or higher. Furthermore, from the viewpoint of adhesion to the adherend, a tackifying resin with a softening point of approximately 200°C or lower (more preferably approximately 180°C or lower) may be preferably used. In some embodiments, the softening point of the tackifying resin may be less than 160°C or less than 150°C.

[0069] In this specification, the softening point of the tackifying resin is defined as the value measured based on the softening point test method (ring-ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at the lowest possible temperature and carefully filled into a ring placed on a flat metal plate, taking care not to create bubbles. After cooling, the portion raised from the plane including the upper end of the ring is cut off with a slightly heated knife. Next, a support (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 in 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 the glycerin so that they do not come into contact with each other, and the temperature of the glycerin is maintained at 20°C ± 5°C for 15 minutes. Next, the steel ball is placed in the center of the surface of the sample in the ring and placed in a fixed position on the support. Next, maintain a distance of 50 mm from the top of the ring to the glycerin surface, place a thermometer, and position the center of the thermometer's mercury bulb at the same height as the center of the ring, then heat the container. The flame of the Bunsen burner used for heating should be positioned midway between the center and edge of the container's bottom to ensure even heating. After heating begins and the bath temperature reaches 40°C, the rate of increase must be 5.0 ± 0.5°C per minute. Read the temperature when the sample gradually softens, flows out of the ring, and finally contacts the bottom plate; this is defined as the softening point. Two or more softening points should be measured simultaneously, and the average value should be used.

[0070] In some embodiments, the tackifying resin is a tackifying resin T having a softening point of less than 150°C. L The following is used: Tackifying resin TL By using the above-mentioned tackifying resin T, higher adhesive strength can be obtained. In some preferred embodiments, the above-mentioned tackifying resin T L The softening point is less than 140°C, more preferably less than 130°C, even more preferably less than 120°C, and may be 110°C or lower, 100°C or lower, or 90°C or lower. Tackifying resin T L The lower limit of the softening point is not particularly limited. In some embodiments, the tackifying resin T L The softening point may be, for example, approximately 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, from the viewpoint of exhibiting appropriate cohesive force.

[0071] Tackifying resin T L As an example, one type of tackifying resin with a softening point of less than 150°C, as exemplified above, can be used alone or in combination of two or more types. In some embodiments, the tackifying resin T L It is preferable that the tackifying resin contains at least one selected from rosin-based tackifying resins and terpene-based tackifying resins. L This may contain one type of rosin-based tackifying resin alone, or a combination of two or more types of rosin-based tackifying resins. Furthermore, the tackifying resin T L This may contain one type of terpene-based tackifying resin (e.g., terpene phenol resin) alone, or it may contain a combination of two or more types of terpene-based tackifying resins.

[0072] In some embodiments, the tackifying resin T L The proportion of terpene-based tackifying resin (e.g., terpene phenol resin) in the total can be, for example, more than approximately 50% by weight, more than approximately 65% ​​by weight, more than approximately 75% by weight, more than 85% by weight, or more than 95% by weight. The technology disclosed herein relates to the tackifying resin T LThis can preferably be carried out in a manner in which substantially all of it (for example, approximately 97% or more by weight, or 99% or more by weight, and may be 100% by weight) is a terpene-based tackifying resin.

[0073] While not particularly limited, tackifying resin T L Examples of rosin-based tackifying resins that can be preferably used include rosin esters such as unmodified rosin esters and modified rosin esters. 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 methyl esters and glycerin esters, can be used as tackifying resin T L It can be used as such.

[0074] In some embodiments, the tackifying resin T L It may also contain hydrogenated rosin esters. For example, tackifying resin T L This may include non-hydrogenated rosin esters. Here, non-hydrogenated rosin esters are a comprehensive concept that refers to all rosin esters other than hydrogenated rosin esters among the rosin esters mentioned above. Examples of non-hydrogenated rosin esters include unmodified rosin esters, disproportionated rosin esters, and polymerized rosin esters. Tackifying resin T L The rosin esters may include a combination of hydrogenated rosin esters and non-hydrogenated rosin esters, or may contain only one or more hydrogenated rosin esters, or may contain only one or more non-hydrogenated rosin esters. In some embodiments, the tackifying resin T L As the rosin esters included, only one or more hydrogenated rosin esters may be used.

[0075] Also, adhesive resin T LFor example, it may or may not include a tackifying resin having a softening point of less than 50°C, more preferably about 40°C or less (typically rosin-based, terpene-based, hydrocarbon-based, etc., such as hydrogenated rosin methyl ester). Such a low-softening-point tackifying resin may be a liquid tackifying resin that is liquid at 30°C. The liquid tackifying resin can be used alone or in combination of two or more types. The content of the liquid tackifying resin is determined from the viewpoint of cohesive force, etc., of the tackifying resin T L It can be approximately 30% or less of the total weight, and it is appropriate to be approximately 10% or less of the total weight (for example, 0-10%), and it may also be approximately 2% or less of the total weight (0.5-2%), or even less than 1% of the total weight.

[0076] Tackifying resin T L The content is not particularly limited, but in some embodiments, it is appropriate to have about 70 parts by weight or less per 100 parts by weight of acrylic polymer, and 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, tackifying resin T L The content of 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, per 100 parts by weight of the acrylic polymer. Also, in some embodiments, from the viewpoint of improving adhesive strength, the tackifying resin T L The content of is, for example, 1 part by weight or more, preferably 5 parts by weight or more, preferably 8 parts by weight or more, more preferably 10 parts by weight or more, even more preferably 12 parts by weight or more, and may be 15 parts by weight or more, per 100 parts by weight of acrylic polymer. Tackifying resin T having an appropriate softening point L The storage modulus at 23°C tends to increase as the amount used increases. The acrylic polymer containing heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with tackifying resins, so by including an appropriate amount of tackifying resin, desired properties can be achieved.

[0077] In some embodiments, the adhesive layer is made of a tackifying resin T, to the extent that it does not impair the effects of the invention. L And, a tackifying resin T with a softening point of 150°C or higher (for example, 150°C to 200°C) H It may also include a combination of the following: Tackifying resin T H For example, one of the tackifying resins exemplified above with a softening point of 150°C or higher can be used alone or in combination of two or more.

[0078] In some embodiments, the tackifying resin T L Preferably, the tackifying resin T accounts for more than 50% by weight of the total amount of tackifying resin contained in the adhesive layer. L The effect of the contained substance is easily expressed. The tackifying resin T is a percentage of the total amount of tackifying resin contained in the adhesive layer. L The proportion of the tackifying resin T L From the viewpoint of more effectively exhibiting the effects of use, the amount 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 also be 95% by weight or more, or 98% by weight or more. In some preferred embodiments, the tackifying resin contained in the adhesive layer is substantially tackifying resin T L It consists only of the following. In this embodiment, the tackifying resin T is the total amount of tackifying resin contained in the adhesive layer. L The proportion is in the range of 99-100% by weight.

[0079] While not particularly limited, in some embodiments, the tackifying resin may include a tackifying resin with a hydroxyl value higher than 20 mgKOH / g (e.g., terpene phenol resin). Among these, a tackifying resin with a hydroxyl value of 30 mgKOH / g or higher is preferred. Hereinafter, a tackifying resin with a hydroxyl value of 30 mgKOH / g or higher may be referred to as a "high hydroxyl value resin." With a tackifying resin containing such a high hydroxyl value resin, in addition to adhesive strength, a highly cohesive adhesive layer can be realized by interacting with a crosslinking agent such as an isocyanate-based crosslinking agent. In some embodiments, the tackifying resin may include a high hydroxyl value resin with a hydroxyl value of 60 mgKOH / g or higher (e.g., 70 mgKOH / g or higher). Furthermore, 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 a high-hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with acrylic polymers, the hydroxyl value of a high-hydroxyl value resin is usually about 300 mgKOH / g or less, about 200 mgKOH / g or less is appropriate, preferably about 180 mgKOH / g or less, more preferably about 160 mgKOH / g or less, even more preferably about 140 mgKOH / g or less, it 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 preferably be implemented in a form in which the tackifying resin contains a high-hydroxyl value resin (for example, a terpene-based tackifying resin, preferably a terpene phenol resin) with a hydroxyl value of 30 to 160 mgKOH / g. In some embodiments, a high hydroxyl value resin with a hydroxyl value of 30 to 80 mgKOH / g (for example, 30 to 65 mgKOH / g) can be preferably used.

[0081] Here, the hydroxyl value can be the 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 approximately 12.5 g (approximately 11.8 mL) of acetic anhydride, add pyridine to make a total volume of 50 mL, and stir thoroughly before use. Alternatively, take approximately 25 g (approximately 23.5 mL) of acetic anhydride, add pyridine to make a total volume of 100 mL, and stir thoroughly before use. (2) A 0.5 mol / L potassium hydroxide ethanol solution is used as the measurement reagent. (3) Prepare toluene, pyridine, ethanol, and distilled water. 2.Operation (1) Accurately weigh out approximately 2 g of the sample into a flat-bottom flask, add 5 mL of acetylation reagent and 10 mL of pyridine, and attach an air condenser. (2) After heating the flask in a 100°C bath for 70 minutes, allow it to cool, add 35 mL of toluene as a solvent from the top of the condenser and stir, then add 1 mL of distilled water and stir to decompose the acetic anhydride. To complete the decomposition, heat it again in the bath for 10 minutes and allow it to cool. (3) Wash the condenser 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 a 0.5 mol / L potassium hydroxide ethanol solution. The inflection point of the resulting titration curve is taken as the endpoint. (6) For a blank test, perform steps (1) to (5) above without adding a sample. 3.Calculation The hydroxyl value is calculated using the following formula. Hydroxyl value (mgKOH / g) = [(BC) × f × 28.05] / S + D Here, B: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used for the blank test. C: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the sample. f: Factor of 0.5 mol / L potassium hydroxide ethanol solution, S: Weight of the sample (g), D: Acid value, 28.05: Half the molecular weight of potassium hydroxide, 56.11. That is the case.

[0082] As the high hydroxyl value resin, any of the above-mentioned tackifying resins having a hydroxyl value of a predetermined value or higher can be used. The high hydroxyl value resin can be used alone or in combination of two or more types. For example, a terpene phenol resin with a hydroxyl value of 30 mgKOH / g or higher can be preferably used as the high hydroxyl value resin. Terpene phenol resins are advantageous because their hydroxyl value can be arbitrarily controlled by the copolymerization ratio of phenol.

[0083] While not particularly limited, when using a high hydroxyl value resin, the proportion of the high hydroxyl value resin (e.g., terpene phenol resin) to the total tackifying resin contained in the adhesive layer may be approximately 5% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more. In some embodiments, it is preferable that the proportion of the high hydroxyl value resin to the total tackifying resin be approximately 30% by weight or more. This allows the effects of using a high hydroxyl value resin to be favorably exhibited. In some preferred embodiments, the proportion of the high hydroxyl value resin to the total tackifying resin may be approximately 40% by weight or more, approximately 50% by weight or more (e.g., more than 50% by weight), approximately 60% by weight or more, approximately 70% by weight or more, approximately 80% by weight or more, or approximately 90% by weight or more. Substantially all of the tackifying resin (e.g., approximately 95-100% by weight, and even more precisely, approximately 99-100% by weight) may be a high hydroxyl value resin.

[0084] The softening point of the high hydroxyl value resin described above is not particularly limited. The softening point of the high hydroxyl value resin may be, for example, approximately 50°C or higher, and from the viewpoint of improving cohesive force, a high hydroxyl value resin having a softening point (softening temperature) of approximately 80°C or higher may be preferably used. For example, a terpene phenol resin having such a softening point can be preferably used. The softening point of the high hydroxyl value resin may be approximately 100°C or higher, or approximately 110°C or higher. There is no particular upper limit to the softening point of the high hydroxyl value resin. From the viewpoint of adhesion to the adherend, a high hydroxyl value resin having a softening point of approximately 200°C or lower (more preferably approximately 180°C or lower) can 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 it satisfies the desired properties (viscoelastic properties, etc.). In some embodiments, from the viewpoint of improving adhesive strength, the content of the high hydroxyl value resin is usually about 1 part by weight or more, 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) per 100 parts by weight of the acrylic polymer. Also 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, 50 parts by weight or less, 40 parts by weight or less, or 30 parts by weight or less per 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, 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 tackifying resin, a plant-derived tackifying resin (plant-based tackifying resin) may be preferred as the tackifying resin from the viewpoint of improving the biomass carbon ratio of the adhesive layer. Examples of plant-based tackifying resins include the rosin-based tackifying resin and terpene-based tackifying resin mentioned above. One type of plant-based tackifying resin may be used alone or in combination of two or more types. When the adhesive layer disclosed herein contains a tackifying resin, the proportion of the plant-based tackifying resin to the total amount of tackifying resin 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 plant-based tackifying resin to the total amount of tackifying resin is 90% by weight or more (e.g., 95% by weight or more, typically 99-100% by weight). The technology disclosed herein can preferably be implemented in a manner that substantially does not contain tackifying resins other than plant-based tackifying resins.

[0087] The content of the tackifying resin in the adhesive layer is not particularly limited as long as it satisfies the desired properties (viscoelastic properties, etc.). In some embodiments, from the viewpoint of improving adhesive strength, the content of the tackifying resin is usually about 1 part by weight or more, 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) per 100 parts by weight of acrylic polymer. The storage modulus at 23°C tends to increase as the amount of tackifying resin used increases. In some embodiments, the content of the tackifying resin in the adhesive layer is, for example, 70 parts by weight or less, 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, per 100 parts by weight of acrylic polymer. In some preferred embodiments, from the viewpoint of uneven deformation mitigation and processability, the content of the tackifying 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. The acrylic polymer containing heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with tackifying resins, so by including an appropriate amount of tackifying resin, desired properties can be achieved.

[0088] (Acrylic oligomers) In some preferred embodiments, the adhesive layer contains an acrylic oligomer. The inclusion of an acrylic oligomer can improve the adhesive strength of the adhesive. According to the techniques disclosed herein, in compositions containing an acrylic oligomer, the adhesive layer can achieve both high adhesive strength and smooth deformation mitigation and processability. While not particularly limited, the effects of using an acrylic oligomer can be effectively demonstrated in compositions containing high molecular weight acrylic polymers. The acrylic oligomer can be used alone or in combination of two or more types.

[0089] The above acrylic oligomer preferably has a Tg of about 0°C to about 300°C, preferably about 20°C to about 300°C, and more preferably about 40°C to about 300°C. By having a Tg within the above range, the adhesive strength can be suitably improved. In some preferred embodiments, from the viewpoint of adhesive cohesiveness, the Tg of the acrylic oligomer is about 30°C or higher, more preferably about 50°C or higher (e.g., about 60°C or higher), and from the viewpoint of adhesion, it is preferably about 200°C or lower, more preferably about 150°C or lower, and even more preferably about 100°C or lower (e.g., approximately 80°C or lower).

[0090] In this specification, the Tg of an acrylic oligomer refers to the Tg determined by Fox's formula based on the composition of the monomer components. Fox's formula is a relationship between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 1 / Tg = Σ(Wi / Tgi) In Fox's equation above, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the monomer i homopolymer (unit: K).

[0091] The glass transition temperature (Tg) of homopolymers used in calculating Tg shall be the value specified in publicly available sources. For example, the values ​​listed in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. For monomers for which multiple values ​​are listed in this document, the highest value shall be adopted.

[0092] For monomers whose glass transition temperature is not described in the above-mentioned literature, the values ​​obtained by the following measurement method shall be 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 added to a reactor equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser, and the mixture is stirred for 1 hour while circulating nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. Then, it is cooled to room temperature to obtain a homopolymer solution with a solid content of 33% by weight. Next, this homopolymer solution is cast onto a release liner and dried to produce a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample is punched out into a 7.9 mm diameter disc shape, sandwiched between parallel plates, and measured using a viscoelasticity tester (manufactured by T.A. Instruments Japan, model name "ARES") in shear mode while applying a shear strain of 1 Hz at a frequency of 1 Hz, in a temperature range of -70°C to 150°C, with a heating rate of 5°C / min. The temperature corresponding to the peak top temperature of tanδ is defined as the Tg of the homopolymer.

[0093] The weight-average molecular weight (Mw) of the acrylic oligomer is typically between approximately 1000 and less than approximately 30000, preferably between approximately 1500 and less than approximately 20000, and more preferably between approximately 2000 and less than approximately 10000. Having an Mw within this range makes it easier to obtain good adhesive strength. In some preferred embodiments, the Mw of the acrylic oligomer is approximately 2500 or more (e.g., approximately 3000 or more), and from the viewpoint of adhesion, it is preferably approximately 7000 or less, more preferably approximately 5000 or less (e.g., approximately 4500 or less, typically approximately 4000 or less). The Mw of the acrylic oligomer can be measured by gel permeation chromatography (GPC) and determined as a value equivalent to standard polystyrene. Specifically, it is measured using a Tosoh HPLC8020 with two TSKgelGMH-H(20) columns at a flow rate of approximately 0.5 mL / min in tetrahydrofuran solvent.

[0094] Examples of monomers that make up 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, and isononyl (meth)acrylate. Examples of (meth)acrylates include alkyl (meth)acrylates such as acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid with alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate (alicyclic hydrocarbon group-containing (meth)acrylate); aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols. Such (meth)acrylates can be used individually or in combination of two or more.

[0095] As acrylic oligomers, it is preferable from the viewpoint of further improving the adhesion of the adhesive layer if the monomer unit contains acrylic monomers with a relatively bulky structure, such as alkyl(meth)acrylates having a branched alkyl group structure, like isobutyl(meth)acrylate and t-butyl(meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates), like cyclohexyl(meth)acrylate, isobornyl(meth)acrylate, and dicyclopentanyl(meth)acrylate; and aryl(meth)acrylates having a cyclic structure, such as phenyl(meth)acrylate and benzyl(meth)acrylate. Furthermore, when ultraviolet light is used during the synthesis of acrylic oligomers or the preparation of adhesive layers, saturated bonds are preferred because they are less likely to inhibit polymerization. Alkyl (meth)acrylates with branched alkyl groups, or esters with alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates), can be suitably used as monomers constituting acrylic oligomers. Note that the above-mentioned branched-chain alkyl (meth)acrylates, alicyclic hydrocarbon group (meth)acrylates, and aryl (meth)acrylates all correspond to (meth)acrylate monomers in the technology disclosed herein. The alicyclic hydrocarbon group may be saturated or unsaturated.

[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, and even more than 90% by weight or more). In some preferred embodiments, the acrylic oligomer has a monomer composition consisting substantially only of (meth)acrylate monomers.

[0097] In addition to the (meth)acrylate monomers mentioned above, functional group-containing monomers can be used as constituent monomer components of acrylic oligomers. Preferred examples of the functional group-containing monomers include monomers having nitrogen atom-containing rings (typically nitrogen atom-containing heterocycles) 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; carboxyl 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 individually or in combination of two or more. Among these, carboxyl group-containing monomers are preferred, and AA is particularly preferred. For example, using a carboxyl group-containing monomer as a functional group-containing monomer makes it easier to improve adhesion to highly polar substrates.

[0098] When the monomer component constituting the acrylic oligomer includes a functional group-containing monomer, the proportion of the functional group-containing monomer (for example, a carboxyl group-containing monomer such as AA) in the monomer component is appropriately set to approximately 1% by weight or more, preferably 2% by weight or more, more preferably 3% by weight or more, and also appropriately set to approximately 15% by weight or less, preferably 10% by weight or less, and more preferably 7% by weight or less.

[0099] Acrylic oligomers can be formed by polymerizing their constituent monomer components. The polymerization method and polymerization mode are not particularly limited, and various conventionally known polymerization methods (e.g., solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be employed in appropriate manner. The types of polymerization initiators that can be used as needed (e.g., azo polymerization initiators such as AIBN) are generally as exemplified in the synthesis of acrylic polymers, and the amount of polymerization initiator and the amount of chain transfer agent such as n-dodecyl mercaptan used optionally are appropriately set based on common technical knowledge to achieve the desired molecular weight, so a detailed explanation is 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), CHMA and IBXMA, CHMA and acryloylmorpholine (ACMO), CHMA and diethylacrylamide (DEAA), CHMA and AA, ADA and methyl methacrylate (MMA), DCPMA and IBXMA, DCPMA and MMA, and the like.

[0101] When the adhesive layer disclosed herein contains an acrylic oligomer, the content is preferably 0.1 parts by weight or more (e.g., 1 part by weight or more) per 100 parts by weight of the acrylic polymer. From the viewpoint of better exhibiting the effects 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 also be about 8 parts by weight or more, or about 10 parts by weight or more. Furthermore, from the viewpoint of compatibility with the acrylic polymer, etc., in some embodiments, the content of the acrylic oligomer is preferably less than 50 parts by weight (e.g., less than 40 parts by weight) per 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 per 100 parts by weight of the acrylic polymer, 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. By limiting the amount of acrylic oligomer used in this way, the effects of the technology disclosed herein can be preferably achieved.

[0102] In some preferred embodiments, the adhesive layer comprises one or more of the above-mentioned tackifying resins and one or more acrylic oligomers. In a composition containing an acrylic polymer that includes heptyl acrylate as a monomer component, the combined use of a tackifying resin and an acrylic oligomer can preferably form an adhesive that has excellent adhesive strength while achieving a high level of both surface deformation mitigation and processability. Although not particularly limited, the effect of combining a tackifying resin and an acrylic oligomer can be effectively demonstrated in a composition containing a high molecular weight acrylic polymer. Content of acrylic oligomer in the adhesive layer C O Content of tackifying resin per [weight] C T [weight %] ratio (C T / C O ) is not particularly limited, but for example, it is appropriate to set it to 0.1 or more and 10 or less. In some embodiments, the above ratio (C T / C O The above ratio (C) is 0.25 or greater, may be 0.4 or greater, may be 0.7 or greater, and may be 0.8 or greater. T / C O The higher the ratio (C), the more effectively the tackifying resin addition effect can be exhibited. In some preferred embodiments, the above ratio (C) is higher. T / C O ) is approximately 1 or more (for example, greater 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. Furthermore, from the viewpoint of obtaining the effect of adding acrylic oligomers, in some embodiments, the above ratio (C T / C O ) is approximately 9 or less, preferably 7 or less, may be 5 or less, or 3 or less. In some other embodiments, the above ratio (C T / C O ) may be 2 or less, 1.5 or less, or 1.2 or less.

[0103] In some preferred embodiments, the total amount of tackifying resin and acrylic oligomer contained in the adhesive layer is suitable to be approximately 1 part by weight or more per 100 parts by weight of 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 also suitable to be 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 technologies disclosed herein, the total amount of acrylic polymer, tackifying resin, and acrylic oligomer in the adhesive layer is appropriately set to achieve the effects of the technologies disclosed herein and is not limited to a specific range. In some preferred embodiments, the total amount of acrylic polymer, tackifying resin, and acrylic oligomer in the entire adhesive layer is preferably more than 50% by weight, more preferably about 70% by weight or more, more preferably about 90% by weight or more, and even more preferably 95% by weight or more (for example, 95% by weight or more and 100% by weight or less than 100% by weight), and may be 98% by weight or more.

[0105] (Crosslinking agent) In the technology disclosed herein, the adhesive composition used to form the adhesive layer may optionally contain a crosslinking agent. The type of crosslinking agent is not particularly limited and examples include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, peroxide crosslinking agents, urea crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, carbodiimide crosslinking agents, hydrazine crosslinking agents, amine crosslinking agents, silane coupling agents, etc. The crosslinking agent can be used alone or in combination of two or more. Among these, isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, and melamine crosslinking agents are preferred, and isocyanate crosslinking agents and epoxy crosslinking agents are more preferred. By appropriately selecting and using a crosslinking agent, the adhesive layer can obtain appropriate cohesive force, forming an adhesive with a good balance between adhesive strength and cohesive force. Furthermore, by increasing the amount of crosslinking agent used, the gel fraction and the storage modulus at 23°C can be increased, thereby improving processability. The adhesive layer in the technology disclosed herein may contain the crosslinking agent in the form after the crosslinking reaction, in the form before the crosslinking reaction, in a partially crosslinked form, or in intermediate or combined forms therein. Typically, the crosslinking agent is contained in the adhesive layer exclusively in the form after the crosslinking reaction.

[0106] As isocyanate-based crosslinking agents, polyfunctional isocyanates (compounds having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. Isocyanate-based crosslinking agents can be used individually or in combination of two or more.

[0107] Examples of polyfunctional isocyanates 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; and 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, lysine diisocyanate, and the like.

[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'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. Examples include 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropanediisocyanate, m-phenylenediisocyanate, p-phenylenediisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

[0110] Examples of preferred polyfunctional isocyanates include those having an average of three or more isocyanate groups per molecule. Such trifunctional or trifunctional isocyanates may be macromers (typically dimers or trimers) of bifunctional or trifunctional or trifunctional isocyanates, derivatives (e.g., addition reaction products of a polyhydric alcohol and two or more polyfunctional isocyanates), polymers, etc. Examples of polyfunctional isocyanates include dimers and trimers of diphenylmethane diisocyanate, isocyanurates of hexamethylene diisocyanate (trimeric adducts of isocyanurate structures), reaction products of trimethylolpropane and tolylene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and other such polyfunctional isocyanates. Examples of commercially available polyfunctional isocyanates include "Duranate TPA-100" from Asahi Kasei Chemicals, and "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096" from Tosoh Corporation.

[0111] The technologies disclosed herein can preferably be implemented in which at least an isocyanate-based crosslinking agent is used as the crosslinking agent. The amount of isocyanate-based crosslinking agent used is not particularly limited. The amount of isocyanate-based crosslinking agent used can be, for example, approximately 0.1 parts by weight or more per 100 parts by weight of acrylic polymer. From the viewpoint of achieving both cohesive force and adhesion, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of acrylic polymer is usually preferably approximately 0.3 parts by weight or more (for example, 0.5 parts by weight or more). In some preferred embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of acrylic polymer is approximately 1.0 part by weight or more, more preferably approximately 1.5 parts by weight or more, even more preferably approximately 2.0 parts by weight or more, particularly preferably approximately 2.5 parts by weight or more, and may also be approximately 2.8 parts by weight or more. By increasing the amount of isocyanate-based crosslinking agent used, the gel fraction and the storage modulus at 23°C can be improved. Furthermore, from the viewpoint of improving adhesion to the adherend, the amount of isocyanate-based crosslinking agent used is preferably 10 parts by weight or less per 100 parts by weight of acrylic polymer, more 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. It may also be 3.5 parts by weight or less, or 3.2 parts by weight or less.

[0112] As the epoxy crosslinking agent, any compound having two or more epoxy groups in one molecule can be used without particular limitation. Epoxy crosslinking agents having three to five epoxy groups in one molecule are preferred. Epoxy crosslinking agents can be used individually or in combination of two or more.

[0113] While not particularly limited, specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy crosslinking agents include "TETRAD-C" and "TETRAD-X" from Mitsubishi Gas Chemical Company, "Epiclon CR-5L" from DIC Corporation, "Denacol EX-512" from Nagase ChemteX Corporation, and "TEPIC-G" from Nissan Chemical Industries, Ltd.

[0114] The amount of epoxy crosslinking agent used is not particularly limited. For example, the amount of epoxy crosslinking agent used can be greater than 0 parts by weight and less than or equal to approximately 1 part by weight (typically about 0.001 to 1 part by weight) per 100 parts by weight of acrylic polymer. From the viewpoint of suitably exhibiting the effect of improving cohesive force, it is usually appropriate to use about 0.002 parts by weight or more of epoxy crosslinking agent per 100 parts by weight of acrylic polymer, preferably about 0.005 parts by weight or more, for example, it may be about 0.01 parts by weight or more, or about 0.02 parts by weight or more. By increasing the amount of epoxy crosslinking agent used, the gel fraction and the storage modulus at 23°C can be improved. Furthermore, from the viewpoint of improving adhesion to the adherend, in some embodiments, the amount of epoxy crosslinking agent used can be approximately 0.7 parts by weight or less per 100 parts by weight of acrylic polymer, approximately 0.5 parts by weight or less is appropriate, approximately 0.2 parts by weight or less is preferred, approximately 0.1 parts by weight or less (e.g., less than 0.1 parts by weight) is more preferred, it may be 0.07 parts by weight or less, 0.04 parts by weight or less, or 0.03 parts by weight or less. By limiting the amount of epoxy crosslinking agent used within a predetermined range, it is easier to maintain sufficient adhesive strength.

[0115] In some preferred embodiments, an isocyanate-based crosslinking agent is used in combination with at least one crosslinking agent having a different type of crosslinkable functional group than the isocyanate-based crosslinking agent. The techniques disclosed herein can preferably be implemented in a manner 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 than the 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 types of non-isocyanate crosslinking agents that can be used in combination with isocyanate crosslinking agents are not particularly limited, and can be appropriately selected from the crosslinking agents described above. Non-isocyanate crosslinking agents can be used individually or in combination of two or more. In some preferred embodiments, epoxy crosslinking agents can be used as non-isocyanate crosslinking agents. For example, by using an isocyanate crosslinking agent and an epoxy crosslinking agent in combination, better adhesive properties can be achieved.

[0117] The relationship between the content of isocyanate-based crosslinking agents and the content of non-isocyanate-based crosslinking agents (preferably epoxy-based crosslinking agents) is not particularly limited and is appropriately set within a range that satisfies predetermined viscoelastic properties and gel fraction. For example, the content of isocyanate-based crosslinking agents is greater than 1 times the content of non-isocyanate-based crosslinking agents (preferably epoxy-based crosslinking agents), may be approximately 5 times or more, is appropriately approximately 10 times or more, is preferably approximately 50 times or more, more preferably approximately 80 times or more, even more preferably approximately 100 times or more (e.g., more than 100 times), and is particularly preferably approximately 120 times or more (e.g., approximately 140 times or more). Furthermore, from the viewpoint of suitably exhibiting the effects of using an isocyanate-based crosslinking agent and a non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent) in combination, the content of the isocyanate-based crosslinking agent to the content of the non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent) is usually, for example, about 1000 times or less, preferably about 500 times or less, preferably about 300 times or less, more preferably about 200 times or less, and even more preferably about 180 times or less (for example, about 160 times or less).

[0118] The crosslinking agent content (total amount of crosslinking agent) in the adhesive composition disclosed herein is not particularly limited. From the viewpoint of cohesiveness, the crosslinking agent content is usually about 0.001 parts by weight or more per 100 parts by weight of acrylic polymer, preferably about 0.01 parts by weight or more, more preferably about 0.1 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. In addition, the crosslinking agent content in the adhesive composition is usually about 20 parts by weight or less per 100 parts by weight of acrylic polymer, preferably about 15 parts by weight or less, and preferably about 10 parts by weight or less. In some preferred embodiments, the crosslinking agent content per 100 parts by weight of acrylic polymer is 5.0 parts by weight or less, may be 4.0 parts by weight or less, or 3.5 parts by weight or less.

[0119] (Coloring agent) The adhesive layer disclosed herein may or may not contain a coloring agent for the purpose of adjusting optical properties (such as light transmittance), opacity, design, color, etc. The coloring agent may be, for example, black, gray, white, red, blue, yellow, green, yellow-green, orange, purple, gold, silver, pearl, etc. The above coloring agent may typically be contained in the adhesive layer in a dispersed state (or dissolved state) within the constituent material of the adhesive layer. Conventionally known pigments and dyes can be used as coloring agents. Examples of pigments include inorganic pigments and organic pigments. The coloring agent may be used alone or in combination of two or more types.

[0120] The coloring agent is not particularly limited, and for example, black coloring agents can be preferably used because they can efficiently adjust opacity and light-shielding properties with small amounts of use. Specific examples of black coloring agents include carbon black, graphite, aniline black, perylene black, cyanine black, titanium black, inorganic pigment hematite, activated carbon, molybdenum disulfide, chromium complexes, and anthraquinone-based coloring agents. Black coloring agents can be used individually or in appropriate combinations of two or more types.

[0121] Furthermore, non-black colorants, which can be selected from, for example, white colorants or gray colorants, may also be preferably used as colorants. Such colorants may be one or more selected from inorganic materials (e.g., metals, metal compounds), organic materials, or organic-inorganic composites. Specific examples of the above colorants include metal oxides such as titanium dioxide (rutile-type titanium dioxide, anatase-type titanium dioxide, etc.), zinc oxide, cerium oxide, aluminum oxide, silicon oxide, zirconium oxide, magnesium oxide, calcium oxide, tin oxide, barium oxide, cesium oxide, and yttrium oxide; carbonate compounds such as magnesium carbonate, calcium carbonate (light calcium carbonate, heavy calcium carbonate, etc.), barium carbonate, and zinc carbonate; and hydroxides such as aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide. Examples include: silicic acid 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 colorants in the adhesive layer (total amount of two or more colorants, total content if two or more colorants are included) is, for example, approximately 0.1% by weight or more, approximately 0.5% by weight or more is appropriate, it may be approximately 1% by weight or more, it may be approximately 2% by weight or more, or it may be approximately 3% by weight or more. Also, in some embodiments, the content of colorants in the adhesive layer can be approximately 30% by weight or less from the viewpoint of compatibility with the adhesive components and maintaining adhesive properties such as adhesive strength, it is usually appropriate to be approximately 20% by weight or less, it may be approximately 15% by weight or less, it may be approximately 10% by weight or less, or it may be approximately 5% by weight or less. In some preferred embodiments, the content of colorants in the adhesive layer may be approximately 3% by weight or less, it may be approximately 1% by weight or less, it may be approximately 0.1% by weight or less, or it may be approximately 0.01% by weight or less. The technology disclosed herein can preferably be implemented in a manner in which the adhesive layer is substantially free of colorants.

[0123] (Other additives) In addition to the components described above, the adhesive composition may optionally contain various additives common in the field of adhesives, such as leveling agents, crosslinking aids, plasticizers, softeners, fillers, antistatic agents, anti-aging agents, UV absorbers, antioxidants, rust inhibitors, and light stabilizers. Such additives can be used by conventional methods if they are conventionally known, and do not particularly characterize the present invention, so a detailed explanation is omitted.

[0124] (Method for forming an adhesive layer) The adhesive layer (layer consisting of adhesive) disclosed herein may be an adhesive layer formed from an aqueous adhesive composition, a solvent-type adhesive composition, a hot-melt adhesive composition, or an active energy ray-curable adhesive composition. An aqueous adhesive composition refers to an adhesive composition in which an adhesive (adhesive layer forming component) is contained in a solvent (aqueous solvent) mainly composed of water, and typically includes what is called a water-dispersible adhesive composition (a composition in which at least a part of the adhesive is dispersed in water). A solvent-type adhesive composition refers to an adhesive composition in which an adhesive is contained in an organic solvent. As the organic solvent contained in the solvent-type adhesive composition, one or more of the organic solvents exemplified above as those that can be used in solution polymerization (such as toluene and ethyl acetate) can be used without particular limitation. The technology disclosed herein can preferably be implemented in a form comprising an adhesive layer formed from a solvent-type adhesive composition, from the viewpoint of adhesive properties, etc.

[0125] The adhesive layer disclosed herein can be formed by conventionally known methods. For example, a method can be employed in which an adhesive layer is formed by applying an adhesive composition to a peelable surface (release surface) or a non-peelable surface and drying it. In the case of a double-sided adhesive sheet having a substrate, for example, a method can be employed in which an adhesive layer is formed by directly applying (typically coating) the adhesive composition to the substrate and drying it (direct method). Alternatively, a method can be employed in which an adhesive layer is formed on a peelable surface (release surface) by applying an adhesive composition to the surface and drying it, and then the adhesive layer is transferred to the substrate (transfer method). From the viewpoint of productivity, the transfer method is preferred. As the release surface, the surface of a release liner or the back surface of a released substrate can be used.

[0126] The adhesive composition can be applied using conventionally known coaters, such as gravure roll coaters, die coaters, or bar coaters. Alternatively, the adhesive composition may be applied by impregnation or curtain coating methods. From the viewpoint of promoting the crosslinking reaction and improving manufacturing efficiency, it is preferable to dry the adhesive composition under heating. The drying temperature can be, for example, around 40 to 150°C, and is usually preferably around 60 to 130°C. After drying the adhesive composition, aging may be performed for the purpose of adjusting the migration of components within the adhesive layer, promoting the crosslinking reaction, and alleviating any strain that may exist within the adhesive layer.

[0127] The adhesive layer may have a single-layer structure or a multilayer structure of two or more layers. From the viewpoint of productivity, etc., a single-layer structure for the adhesive layer is preferable.

[0128] (thickness) The thickness of the adhesive layer is not particularly limited, and a configuration having an adhesive layer with an appropriate thickness in the range of 0.1 to 500 μm can be adopted depending on the application and intended use. In some embodiments, from the viewpoint of avoiding the double-sided adhesive sheet becoming excessively thick, the thickness of the adhesive layer is usually appropriate to be approximately 100 μm or less, preferably approximately 70 μm or less, more preferably approximately 60 μm or less, even more preferably approximately 50 μm or less, and may also be approximately 40 μm or less. The thickness of the adhesive layer can be approximately 35 μm or less, for example, it may be approximately 30 μm or less, or 20 μm or less (for example, 15 μm or less). An adhesive layer with a limited thickness can be well met in response to the demands for thinning and weight reduction. Furthermore, by limiting the thickness of the adhesive layer, it becomes less likely for the adhesive to overflow during processing such as die-cutting, and processability can be improved. From the viewpoint of adhesion to the adherend, the lower limit of the thickness of the adhesive layer is suitable to be approximately 0.5 μm or more in some embodiments, may be approximately 1 μm or more, and is advantageous to be approximately 3 μm or more. In some preferred embodiments, the thickness of the adhesive layer is greater than 5 μm, more preferably approximately 10 μm or more, even more preferably approximately 12 μm or more (e.g., greater than 12 μm), even more preferably approximately 15 μm or more, and may be approximately 18 μm or more. By making the thickness of the adhesive layer greater than 5 μm, fine irregularities and deformations are more easily resolved by the relaxing effect of the adhesive layer. Also, the adhesive strength tends to improve as the thickness of the adhesive layer increases. In a further 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 approximately 30 μm or more, and may be approximately 32 μm or more. In a double-sided adhesive sheet with a substrate, each surface of the substrate has a first adhesive layer and a second adhesive layer, the first adhesive layer and the second adhesive layer may have the same thickness or may have different thicknesses.

[0129] (Gel fraction) The gel fraction (by weight) of the adhesive layer disclosed herein is higher than 40%. The adhesive layer having the above gel fraction tends to have excellent processability, suppressing adhesive overflow during cutting processes such as die-cutting. Furthermore, the adhesive layer having the above gel fraction has a moderate hardness, so it tends to be less prone to visible irregularities. 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. Also, from the viewpoint of adhesive strength, the upper limit of the gel fraction of the adhesive layer is usually appropriate to be less than 90%, and may be less than 85%, 80%, or 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%, and may be less than 55%, or less than 50%. By limiting the gel fraction of the adhesive layer to below a predetermined value, the adhesion to the substrate tends to improve.

[0130] The gel fraction of the adhesive layer is measured by the following method. Specifically, approximately 0.1 g of adhesive sample (weight Wg1) is wrapped in a drawstring shape with a porous polytetrafluoroethylene membrane (weight Wg2) having an average pore size of 0.2 μm, and the opening is tied with string (weight Wg3). As the porous polytetrafluoroethylene (PTFE) membrane, the product name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent product available from Nitto Denko Corporation is used. This package is immersed in 50 mL of ethyl acetate and kept at room temperature (approximately 23°C) for 7 days to elute only the sol component of the adhesive layer from the membrane. After that, the package is removed, the ethyl acetate adhering to the outer surface is wiped off, and the package is dried at 130°C for 2 hours, and the weight of the package (Wg4) is measured. The gel fraction of the adhesive layer can be determined by substituting each value into the following formula. Gel fraction (%) = [(Wg4 - Wg2 - Wg3) / Wg1] × 100 The measurement will also be performed using the method described above in the examples described later.

[0131] (Biomass carbon ratio) In some embodiments, the adhesive layer contains biomass-derived material, and its biomass-carbon ratio may be above a predetermined value. The biomass-carbon ratio of the adhesive layer is, for example, 1% or more, may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass-carbon ratio of the adhesive means that less fossil resource-based material, such as petroleum, is used. From this viewpoint, a higher biomass-carbon ratio of the adhesive is preferable. For example, the biomass-carbon ratio of the adhesive layer may be 55% or more, may be 60% or more, may be 70% or more, may be 75% or more, may be 80% or more, and may be over 80%. The upper limit of the biomass-carbon ratio is 100% by definition, may be 99% or less, and from the viewpoint of material availability, may be 95% or less, or 90% or less. From the viewpoint of easily exhibiting good adhesive performance, in some embodiments, the biomass-carbon ratio of the adhesive layer may be, for example, 90% or less, may be 85% or less, or 80% or less.

[0132] <Base material> In embodiments of the double-sided adhesive sheet disclosed herein, in the form of a double-sided adhesive sheet with a substrate, the substrate supporting the adhesive layer can be a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, or a composite thereof. Examples of paper include Japanese paper, kraft paper, glassine paper, fine paper, synthetic paper, and topcoat paper. Examples of cloth include woven or nonwoven fabrics made from various fibrous materials individually or in blends. Examples of the fibrous materials include cotton, rayon, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyolefin sheets, foamed polyurethane sheets, and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil. The substrate is also referred to as the substrate layer in a double-sided adhesive sheet.

[0133] The base material may be made from biomass-derived materials or from non-biomass-derived materials. From the viewpoint of producing a double-sided adhesive sheet that takes into consideration the reduction of reliance on fossil fuel-based materials, a biomass-derived base material (typically a resin film) is preferably used.

[0134] Furthermore, the base material may be formed using recyclable materials or recycled materials (also called recycled materials). Resin film is preferably used as such recycled material. Since resin film (for example, polyester film such as PET film) is recyclable, regardless of whether plant-derived materials are used, reuse of used resin film enables sustainable reproduction and reduces environmental impact. Such recyclable resin film or recycled resin film is also called recycled film. The above-mentioned recycled material (e.g., recycled film) may be formed from biomass-derived materials or from non-biomass-derived materials.

[0135] As the base material constituting the double-sided adhesive sheet with a substrate, a resin film is preferably used as the base film. The base film is typically an independently shape-retaining (independent) component. The substrate in the art disclosed herein may be substantially composed of such a base film. Alternatively, the substrate may include auxiliary layers in addition to the base film. Examples of such auxiliary layers include a colored layer, a reflective layer, a primer layer, an antistatic layer, etc., provided on the surface of the base film.

[0136] The above-mentioned resin film is a film whose main component is a resin material (for example, a component that is present in the resin film in an amount exceeding 50% by weight). Examples of resin films 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 also be a rubber film such as natural rubber film or butyl rubber film. Among these, polyester films are preferred from the viewpoint of handling and processability, and PET films are particularly preferred among them.

[0137] In this specification, "resin film" typically refers to a non-porous sheet and is a concept distinct from so-called nonwoven or woven fabrics (in other words, a concept excluding nonwoven or woven fabrics). The above resin film may be an unoriented film, a uniaxially oriented film, or a biaxially oriented film. Furthermore, such a resin film may be non-foamed. Here, a non-foamed resin film refers to a resin film that has not undergone any intentional treatment to become a foam. Specifically, a non-foamed resin film may be a resin film with a foaming 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 it may have light-shielding or light-reducing properties. In some embodiments, the substrate (e.g., a resin film) may contain a colorant. This allows for adjustment of the light transmittance (light-shielding properties) of the substrate. Adjusting the light transmittance (e.g., vertical light transmittance) of the substrate may also be useful for adjusting the light transmittance of the substrate, and further, the light transmittance of the double-sided adhesive sheet containing the substrate.

[0139] As a coloring agent, conventionally known pigments and dyes can be used, similar to the coloring agents that can be contained in the adhesive layer. The coloring agent is not particularly limited and may be, for example, black, gray, white, red, blue, yellow, green, yellow-green, orange, purple, gold, silver, pearl, etc.

[0140] In some embodiments, light-shielding properties (e.g., vertical light transmittance) can be efficiently adjusted with a small amount of colorant, so black colorants can be preferably used as colorants for the substrate. Specific examples of black colorants include those exemplified as colorants that can be contained in the adhesive layer. In some preferred embodiments, pigments with an average particle size of 10 nm to 500 nm, more preferably 10 nm to 120 nm (e.g., particulate black colorants such as carbon black) can be used.

[0141] The amount of colorant used in the substrate (e.g., resin film) is not particularly limited and can be adjusted as appropriate to impart the desired optical properties. The amount of colorant used is appropriately about 0.1 to 30% by weight of the substrate, 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 as needed, such as fillers (inorganic fillers, organic fillers, etc.), dispersants (surfactants, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, and plasticizers. The proportion of each additive is less than 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight).

[0143] The above-mentioned substrate (e.g., resin film) may have a single-layer structure, or it may have a multilayer structure of two, three, or more layers. From the viewpoint of shape stability, a single-layer structure is preferred for the substrate. In the case of a multilayer structure, it is preferable that at least one layer (preferably all layers) is a layer having a continuous structure of the above-mentioned resin (e.g., polyester resin). The method for manufacturing the substrate (typically resin film) is not particularly limited and may be any conventionally known method as appropriate. For example, conventionally known general film molding methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be appropriately employed.

[0144] The substrate may be colored by a colored layer disposed on the surface of a base film (preferably a resin film). In a substrate having a base film and a colored layer, the base film may or may not contain a coloring agent. The colored layer may be disposed on either one surface of the base film, or on both surfaces. In a configuration where colored layers are disposed on both surfaces of the base film, the composition of these 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, conventionally known pigments and dyes can be used, similar to those that can be incorporated into adhesive layers or resin films. As the binder, any material known in the field of paints or printing can be used without particular limitations. Examples include polyurethane, phenolic resin, epoxy resin, urea-melamine resin, and polymethyl methacrylate. The colored layer-forming composition may be solvent-based, UV-curable, or thermosetting. The colored layer can be formed using conventional methods for colored layer formation without particular limitations. For example, a method of forming the colored layer (printed layer) by printing, such as gravure printing, flexographic printing, or offset printing, can be preferred.

[0146] The colored layer may be a single-layer structure consisting of one layer, or it may be a multilayer structure including two, three or more sub-colored layers. A multilayer colored layer including two or more sub-colored layers can be formed, for example, by repeatedly applying (e.g., printing) a colored layer-forming composition. The color and amount of colorant contained in each sub-colored layer may be the same or different. For colored layers intended to provide light-shielding properties, a multilayer structure is particularly beneficial from the viewpoint of preventing the occurrence of pinholes and improving the reliability of light leakage prevention.

[0147] The overall thickness of the colored layer is appropriately about 1 μm to 10 μm, preferably about 1 μm to 7 μm, and can be, for example, about 1 μm to 5 μm. In a colored layer containing 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 conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or application of a primer. Such surface treatments may be intended to improve the adhesion between the substrate and the adhesive layer, in other words, the anchoring ability of the adhesive layer to the substrate.

[0149] In a double-sided adhesive sheet comprising a substrate, the thickness of the substrate is not particularly limited. From the viewpoint of avoiding the double-sided adhesive sheet becoming excessively thick, the thickness of the substrate can be, for example, approximately 200 μm or less, preferably approximately 150 μm or less, and more preferably approximately 100 μm or less. Depending on the purpose and manner of use of the double-sided adhesive sheet, the thickness of the substrate may be approximately 70 μm or less, approximately 50 μm or less, or approximately 30 μm or less (for example, approximately 25 μm or less). In some embodiments, the thickness of the substrate may be approximately 20 μm or less, approximately 15 μm or less, or approximately 10 μm or less (for example, approximately 5 μm or less). By reducing the thickness of the substrate, the thickness of the adhesive layer can be increased even if the total thickness of the double-sided adhesive sheet remains the same, which can be advantageous from the viewpoint of improving adhesion to the adherend or substrate. Furthermore, a substrate with limited thickness can better meet the demands for thinning and weight reduction. The thickness of the substrate is usually about 0.5 μm or more (for example, 1 μm or more), preferably about 2 μm or more, for example, about 6 μm or more, from the viewpoint of handling and processability of the double-sided adhesive sheet. In some embodiments, the thickness of the substrate can be about 8 μm or more, and may even be about 10 μm or more.

[0150] <Total thickness of double-sided adhesive sheet> The total thickness of the double-sided adhesive sheet disclosed herein (including an adhesive layer and possibly a base layer, but not a release liner) is not particularly limited. The total thickness of the double-sided adhesive sheet is, for example, approximately 1 mm or less, may be approximately 500 μm or less, can be approximately 300 μm or less, and from the viewpoint of thinning, approximately 200 μm or less is appropriate, and may be approximately 150 μm or less (for example, approximately 100 μm or less). In some preferred embodiments, the thickness of the double-sided adhesive sheet can be approximately 50 μm or less, for example, approximately 35 μm or less. The lower limit of the thickness of the double-sided adhesive sheet is, for example, 0.1 μm or more (for example, 0.5 μm or more), may be approximately 3 μm or more, preferably approximately 10 μm or more, more preferably approximately 15 μm or more, even more preferably approximately 20 μm or more, may be approximately 30 μm or more, and may be approximately 50 μm or more. Double-sided adhesive sheets with a thickness exceeding a specified value tend to exhibit good adhesion to the substrate and also have superior handling properties. In the case of base material-less double-sided adhesive sheets, the thickness of the adhesive layer becomes the total thickness of the double-sided adhesive sheet.

[0151] <Removable Liner> In the technologies disclosed herein, release liners can be used in the formation of the adhesive layer, the production of double-sided adhesive sheets, storage of double-sided adhesive sheets before use, distribution, and shaping. 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 fluoropolymer (such as polytetrafluoroethylene) can be used. The release treatment layer may 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 for the liner substrate, similar to the substrate of the double-sided adhesive sheet described above, materials made from biomass or recycled materials (such as recycled film) can preferably be used.

[0152] The release liner disclosed herein (in embodiments where the double-sided adhesive sheet with a release liner comprises two release liners, at least one of the two release liners; the same applies hereinafter unless otherwise specified) may preferably have a release treatment layer on the release liner substrate. The release treatment layer may be formed by surface-treating the release liner substrate with a release treatment agent. The release treatment agent may 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, or molybdenum(IV) sulfide. In some embodiments, a release liner having a release treatment layer made of a silicone-based release treatment agent may preferably be used. The thickness and formation method of the release treatment layer are not particularly limited and can be set so that appropriate release properties are exhibited on the adhesive side surface of the release liner.

[0153] Various plastic films can be used as the release liner substrate. In this specification, a plastic film is typically a non-porous sheet and is distinct from, for example, nonwoven fabrics (i.e., does not include nonwoven fabrics). A resin film having a non-porous structure and typically being substantially void-free (void-free) can be preferably used as the release liner substrate. The resin film may have a single-layer structure or a multilayer structure of two or more layers (e.g., a three-layer structure).

[0154] Examples of materials for the above-mentioned 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 triacetylcellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide resins; polyimide resins; norbornene resins; cyclic polyolefin 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 more of these resins can be used. Among these, a polyester resin film (e.g., PET film) formed from a polyester resin is a preferred release liner substrate.

[0155] The plastic film used as the release liner substrate described above may be an unoriented film, a uniaxially oriented film, or a biaxially oriented film. Furthermore, the plastic film may have a single-layer structure or a multilayer structure including two or more sublayers. The plastic film may contain known additives that can be used in release liner substrates, such as antioxidants, anti-aging agents, heat stabilizers, light stabilizers, UV absorbers, colorants such as pigments and dyes, lubricants, fillers, antistatic agents, slip agents, antiblocking agents, and nucleating agents. In a multilayer plastic film, each additive may be incorporated into all sublayers or into only some of the sublayers.

[0156] The thickness of the release liner is not particularly limited and may be, for example, around 10 μm to 500 μm. From the viewpoint of the strength and dimensional stability of the release liner, a thickness of 20 μm or more is appropriate, preferably 25 μm or more, and may also be 30 μm or more, or even 35 μm or more. By protecting the adhesive surface with a release liner of sufficient thickness, the smoothness of the adhesive surface is easily maintained. For example, it is less likely that the adhesive layer will become uneven or deformed due to external forces from the back of the release liner or foreign matter present on the back of the release liner. Such phenomena may be caused, for example, by foreign matter mixed between the release liners when winding the double-sided adhesive sheet with the release liner onto a roll. Furthermore, from the viewpoint of the handling of the release liner (e.g., ease of winding), a thickness of 300 μm or less is appropriate, preferably 200 μm or less, and may also be 150 μm or less, or even 100 μm or less. By setting the thickness of the release liner to a predetermined value or less, it is easier to remove it from the double-sided 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 fine irregularities such as indentations occur in the adhesive layer due to external forces or foreign matter from the back surface of the release liner, the adhesive layer has excellent irregularity deformation mitigation properties, so the fine irregularities are eliminated or mitigated, and good appearance quality can be provided. When the double-sided 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 peelability, 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 approximately 1.1 times or more, for example, approximately 1.25 times or more, than the thickness of the thinner release liner.

[0157] <Rolled form> Furthermore, this specification provides a roll containing the double-sided adhesive sheet with release liner disclosed herein in a wound form (double-sided adhesive sheet roll with release liner). One of the effects of the technology disclosed herein is the ability to mitigate uneven deformation, which is effective against fine uneven deformation of the adhesive layer caused by minute foreign matter mixed between the two release liners when winding the double-sided adhesive sheet with release liner onto a roll. The technology disclosed herein is suitable for double-sided adhesive sheets that are stored in the form of a roll before use. The roll described above typically includes a core and a double-sided adhesive 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., cylindrical shape), a hollow or solid polygonal prism shape, etc. From the viewpoint of improving the handling of the roll, a hollow cylindrical or hollow polygonal prism 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 adhesive sheet preferably has a 180-degree peel strength (adhesion to SUS) of approximately 10 N / 25 mm or more against a stainless steel plate. A double-sided adhesive sheet having the above adhesion to SUS can exhibit high adhesive strength. The above adhesion to SUS is more preferably approximately 15 N / 25 mm or more, even more preferably approximately 18 N / 25 mm or more, and particularly preferably 20 N / 25 mm or more (for example, 22 N / 25 mm or more). There is no particular upper limit to the above adhesion to SUS, but from the viewpoint of compatibility with processability, etc., it may usually be approximately 50 N / 25 mm or less, and in some embodiments, it may be approximately 30 N / 25 mm or less. The above adhesion to SUS is measured using a SUS plate as the adherend, under measurement conditions of 23°C, 50% RH, tensile speed of 300 mm / min, and 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 adhesive sheet contains biomass-derived material, and its biomass-carbon ratio may be above a predetermined value. The biomass-carbon ratio of the double-sided adhesive sheet is, for example, 1% or more, may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass-carbon ratio of the double-sided adhesive sheet means that less fossil resource-based material, such as petroleum, is used. From this viewpoint, a higher biomass-carbon ratio of the double-sided adhesive sheet is preferable. For example, the biomass-carbon ratio of the double-sided adhesive sheet may be 55% or more, may be 60% or more, may be 70% or more, may be 75% or more, may be 80% or more, and may be over 80%. The upper limit of the biomass-carbon ratio is 100% by definition, 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 making it easier to exhibit good adhesive performance, in some embodiments, the biomass carbon ratio of the double-sided adhesive sheet may be, for example, 90% or less, 85% or less, or 80% or less.

[0160] <Application> The applications of the double-sided adhesive sheet disclosed herein are not particularly limited and can be used in a variety of applications. The double-sided adhesive sheet disclosed herein is suitable for bonding and fixing components in applications where high adhesive strength is required and the components can be processed into a predetermined shape (outer shape). For example, it can be preferably used for fixing components in various portable devices. Furthermore, since the double-sided adhesive sheet disclosed herein highly suppresses deformation of the adhesive layer, such as indentations on the surface of the adhesive layer, it is suitable for applications where appearance quality is required, such as applications where the double-sided adhesive sheet attached to the surface of the adherend is visible. For example, depending on the application location of the double-sided adhesive sheet, such as the display part of an electronic device, there is a tendency to require a higher level of appearance quality. The double-sided adhesive sheet disclosed herein is suitable for fixing components in the display part of an electronic device such as the portable electronic device mentioned above.

[0161] Non-limiting examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear-type devices worn on the wrist like watches, modular devices attached to a part of the body with clips or straps, eyewear-type devices including glasses (monocular and binocular, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information systems, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" means not merely being able to be carried, but having a level of portability that allows an individual (a typical adult) to carry it relatively easily. Examples of the above-mentioned electronic devices include personal computers (desktop, notebook, tablet, etc.) and televisions. These may incorporate display devices such as liquid crystal or organic EL.

[0162] In some embodiments, the double-sided adhesive sheet may be used, for example, within a portable electronic device equipped with a pressure sensor, to fix a pressure sensor to other components. In some embodiments, the double-sided adhesive sheet may be used to fix a pressure sensor to other components within an electronic device (typically a portable electronic device) that has the function of enabling the specification of an absolute position on a screen-corresponding plate (typically a touch panel) using a device for indicating a position on a screen (typically a pen-type or mouse-type device) and a device for detecting a position.

[0163] Furthermore, in several preferred embodiments, the double-sided 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 placing the double-sided adhesive sheet according to several preferred embodiments on the back surface of the display screen (display unit), a decrease in the visibility of the display screen can be prevented regardless of how the portable electronic device is used.

[0164] The materials to which the double-sided adhesive sheets disclosed herein are attached (adhered materials) are not particularly limited, but include, for example, metallic materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, etc., or alloys containing two or more of these; various resin 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, liquid crystal polymers, etc. (typically plastic materials); and inorganic materials such as alumina, zirconia, soda glass, quartz glass, and carbon. Among these, metallic materials such as copper, aluminum, and stainless steel, and resin materials such as polyester resins such as PET, polyimide resins, aramid resins, and polyphenylene sulfide resins (typically plastic materials) are widely used. The above materials may be materials for components that make up products such as electronic devices. The double-sided adhesive sheet disclosed herein may be used by being attached to a component made of the above materials. The above materials may also be materials that make up the object to which the pressure sensor or display unit is fixed (for example, a back surface component such as an electromagnetic wave shield or a reinforcing plate). The object to which the sheet is fixed refers to the object to which the double-sided adhesive sheet is attached, i.e., the adherend. The back surface component refers to a component that is located on the opposite side of the front surface (viewing side) of the pressure sensor or display unit in, for example, in a portable electronic device, and may be a component that makes up the support part 540 located on the back surface of the display device 500 shown in Figure 4 below. The object to which the sheet is fixed may be in the form of a single-layer structure or a multi-layer structure, and the surface to which the double-sided adhesive sheet is attached (the adhesive surface) may be subjected to various surface treatments. While not particularly limited, an example of an object to be fixed is a back surface member with a thickness of 1 μm or more (typically 5 μm or more, e.g., 60 μm or more, and even 120 μm or more) and 1500 μm or less (e.g., 800 μm or less).

[0165] In some embodiments, the member or material to which the double-sided adhesive sheet is attached may be light-transmitting (light-transmitting substrate). Since the adhesive surface of the double-sided adhesive sheet attached to the light-transmitting substrate can be seen through the light-transmitting substrate, it is desirable that the adhesive surface has good appearance quality. The light transmittance of the light-transmitting substrate may be greater than, for example, 50%, and 70% or more. In some preferred embodiments, the light transmittance of the substrate may be 80% or more, more preferably 90% or more, and 95% or more (for example, 95-100%). Such a material may be a resin film (for example, a polyester resin film such as PET film) that is placed on the back surface of the image display part of various devices such as portable electronic devices. The double-sided adhesive sheet disclosed herein may preferably be used in a manner in which it is attached to a substrate (e.g., a member) with a light transmittance of a predetermined value or higher. The light transmittance referred to here is the light transmittance at a wavelength of 550 nm.

[0166] Furthermore, in some embodiments, the double-sided adhesive sheet is used in a manner in which it is attached to a metal member. Examples of the material of the metal member include the metal materials exemplified above as adherend materials. Such a metal member is, for example, a member or article having a surface (adhesive sheet attachment surface) formed from a metal material such as aluminum or stainless steel, and preferred examples include metal members made of stainless steel or aluminum. The double-sided adhesive sheet may cover the entire surface of the metal member, or it may cover a part of the surface (for example, a part area that needs to be concealed). The metal member may be, for example, a member constituting the support part 540 of the display device 500 shown in Figure 4, which will be described later. Preferably, the metal member is one of the adherends of the double-sided adhesive sheet.

[0167] As described 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 including 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 the metal member and a double-sided adhesive sheet covering at least a portion of the surface of the metal member. The double-sided adhesive sheet may cover the entire surface of the metal member, or it may cover a portion of the surface (for example, a portion area where concealment is required). Typically, one side (adhesive side) 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 adherend material described above. In this embodiment, the laminate including the double-sided adhesive sheet is a laminate comprising the double-sided adhesive sheet and a light-transmitting member (second member). In some preferred embodiments, the laminate comprises a metal member (first member), a double-sided adhesive sheet, and a light-transmitting member (second member) in this order. Furthermore, a substrate-less double-sided adhesive sheet is also referred to as the adhesive layer in a laminate.

[0168] Figure 3 shows an example of the configuration of the above-described laminate. The laminate 50 shown in Figure 3 comprises a first member 41, a substrate-less double-sided adhesive sheet 1, and a second member 42, in that 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 members, materials, and adherends, so redundant explanations will not be repeated.

[0169] Furthermore, in some embodiments, the double-sided adhesive sheet is preferably used in electronic devices that include various light sources such as LEDs (light-emitting diodes) and light-emitting elements such as self-emitting organic ELs. For example, it can be preferably used in electronic devices (typically portable electronic devices) that are equipped with organic EL display devices or liquid crystal display devices that require predetermined optical characteristics.

[0170] Figure 4 is a schematic exploded perspective view showing an example configuration of a display device. As shown in Figure 4, the display device 500 provided by the portable electronic device 400 comprises a display unit 520 composed of a cover member and an organic EL unit, etc., and a support unit 540. The display device 500 further includes a double-sided adhesive sheet 530. In this example configuration, the double-sided adhesive sheet 530 fixes the components constituting the display unit 520 and the support unit 540. The support unit 540 is composed of a substrate (a metal plate such as a stainless steel plate or an aluminum plate), etc. The double-sided adhesive sheet disclosed herein is preferably used as a component of the display device described above.

[0171] Furthermore, since the double-sided adhesive sheet disclosed herein may, in some embodiments, have an adhesive layer containing an acrylic polymer with a high biomass-carbon ratio, it can be used as a substitute for conventional acrylic adhesives (i.e., acrylic adhesives with a low biomass-carbon ratio) in various applications where such acrylic adhesives are used, thereby contributing to reducing reliance on fossil fuel-based materials. The double-sided adhesive sheet disclosed herein can be preferably used as a double-sided adhesive sheet with reduced reliance on fossil fuel-based materials.

[0172] The matters disclosed in this specification include the following: [1] Portable electronic device, A double-sided adhesive sheet is attached to the component constituting the aforementioned portable electronic device. The aforementioned double-sided adhesive sheet has an adhesive layer containing an acrylic polymer, The aforementioned 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 gel fraction of the aforementioned adhesive layer is higher than 40%. The adhesive layer has a storage modulus of 0.04 MPa or higher at 23°C, and a tanδ of 0.46 or higher at 23°C, where tanδ is the ratio of the loss modulus G'' to the storage modulus G' of the adhesive layer (G'' / G'), in a portable electronic device. [2] The portable electronic device according to [1], wherein the adhesive layer further comprises a tackifying resin. [3] The portable electronic device according to [1] or [2] above, wherein the tackifying resin is at least one selected from rosin-based tackifying resins and terpene-based tackifying resins. [4] The portable electronic device according to any one of [1] to [3] above, wherein the adhesive layer further comprises an acrylic oligomer. [5] The portable electronic device according to any one of [1] to [4] above, wherein the adhesive layer comprises a tackifying resin and an acrylic oligomer. [6] Content C of the acrylic oligomer O Content of the tackifying resin relative to C T The ratio (C T / C O ) is a portable electronic device as described in [5] above, wherein the value is between 1 and 10. [7] The portable electronic device according to any one of [1] to [6] above, wherein the adhesive composition for forming the adhesive layer comprises at least an isocyanate crosslinking agent. [8] The portable electronic device according to any one of [1] to [7] above, wherein the thickness of the adhesive layer is greater than 5 μm and less than or equal to 50 μm. [9] The portable electronic device according to any of [1] to [8] above, wherein the double-sided adhesive sheet has a 180-degree peel strength of 10 N / 25 mm or more against a stainless steel plate.

[0173]

[11] A double-sided adhesive sheet having an adhesive layer containing an acrylic polymer, The aforementioned 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 gel fraction of the aforementioned adhesive layer is higher than 40%. The adhesive layer has a storage modulus of 0.04 MPa or higher at 23°C, and a tanδ of 0.46 or higher at 23°C, where tanδ is the ratio of the loss modulus G'' to the storage modulus G' of the adhesive layer (G'' / G'), and is a double-sided adhesive sheet.

[12] The double-sided adhesive sheet according to

[11] , wherein the adhesive layer further comprises a tackifying resin.

[13] The double-sided adhesive sheet according to

[11] or

[12] above, wherein the tackifying resin is at least one selected from rosin-based tackifying resins and terpene-based tackifying resins.

[14] The double-sided adhesive sheet according to any one of

[11] to

[13] above, wherein the adhesive layer further comprises an acrylic oligomer.

[15] The double-sided adhesive sheet according to any one of

[11] to

[14] above, wherein the adhesive layer comprises a tackifying resin and an acrylic oligomer.

[16] Content C of the acrylic oligomer O Content of the tackifying resin relative to C T The ratio (C T / C O The double-sided adhesive sheet described in

[15] above, wherein the value is between 1 and 10.

[17] The adhesive composition for forming the adhesive layer comprises at least an isocyanate crosslinking agent, and is the double-sided adhesive sheet according to any one of

[11] to

[16] above.

[18] The double-sided adhesive sheet according to any one of

[11] to

[17] above, wherein the thickness of the adhesive layer is greater than 5 μm and less than or equal to 50 μm.

[19] A double-sided adhesive sheet according to any of

[11] to

[18] above, wherein the 180-degree peel strength to stainless steel plate is 10 N / 25 mm or more.

[20] A double-sided adhesive sheet as described in any of

[11] to

[19] above, used for fixing components in electronic equipment.

[21] Electronic device containing a double-sided adhesive sheet as described in any of

[11] to

[20] above.

[22] A double-sided adhesive sheet with a release liner, comprising a double-sided adhesive sheet as described in any of

[11] to

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

[23] A roll of double-sided adhesive sheets with a release liner, on which the double-sided adhesive sheets with a release liner described in

[22] above are wound.

[0174]

[31] A laminate comprising a metal member (first member) and a double-sided adhesive sheet, The aforementioned double-sided adhesive sheet has an adhesive layer containing an acrylic polymer, The aforementioned 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 gel fraction of the aforementioned adhesive layer is higher than 40%. The adhesive layer is a laminate in which the storage modulus at 23°C is 0.04 MPa or higher, and the tanδ at 23°C is 0.46 or higher, where tanδ is the ratio of the loss modulus G'' to the storage modulus G' of the adhesive layer (G'' / G').

[32] A laminate comprising a light-transmitting member (second member) and a double-sided adhesive sheet, The aforementioned double-sided adhesive sheet has an adhesive layer containing an acrylic polymer, The aforementioned 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 gel fraction of the aforementioned adhesive layer is higher than 40%. The adhesive layer is a laminate in which the storage modulus at 23°C is 0.04 MPa or higher, and the tanδ at 23°C is 0.46 or higher, where tanδ is the ratio of the loss modulus G'' to the storage modulus G' of the adhesive layer (G'' / G').

[33] A laminate comprising a metal member (first member), a double-sided adhesive sheet, and a light-transmitting member (second member) in this order, The aforementioned double-sided adhesive sheet has an adhesive layer containing an acrylic polymer, The aforementioned 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 gel fraction of the aforementioned adhesive layer is higher than 40%. The adhesive layer is a laminate in which the storage modulus at 23°C is 0.04 MPa or higher, and the tanδ at 23°C is 0.46 or higher, where tanδ is the ratio of the loss modulus G'' to the storage modulus G' of the adhesive layer (G'' / G').

[34] The laminate according to

[31] or

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

[35] The laminate according to

[32] or

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

[36] The laminate according to

[32] ,

[33] , or

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

[37] A laminate according to any of

[31] to

[35] above, used in electronic equipment. [Examples]

[0175] The following describes several embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments. In the following description, "parts" and "%" refer to weight unless otherwise specified.

[0176] <Example 1> (Synthesis of acrylic polymers) In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, 93 parts of n-heptyl acrylate (n-HpA) and 7 parts of acrylic acid (AA) as monomer components, along with ethyl acetate as the polymerization solvent, were charged and stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this manner, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and solution polymerization was carried out at 60°C to 70°C for 8 hours to obtain a solution of acrylic polymer. The weight-average molecular weight (Mw) of this acrylic polymer was 900,000. The Mw was adjusted by controlling the concentration of the monomer components during polymerization. The above-mentioned n-HpA is a compound synthesized using biomass-derived heptyl alcohol, and has a biomass-derived heptyl group at its ester terminus.

[0177] (Preparation of adhesive composition) To the acrylic polymer solution obtained above, the following were added per 100 parts of the acrylic polymer contained in the solution: 20 parts of terpene phenol resin (trade name "YS Polystar T-115", terpene phenol resin manufactured by Yasuhara Chemical Co., Ltd., softening point approximately 115°C, hydroxyl value 30-60 mg KOH / g), 5 parts of acrylic oligomer, 3 parts (based on solid content) of 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 epoxy crosslinking agent (trade name "TETRAD-C", 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, manufactured by Mitsubishi Gas Chemical Co., Ltd.), and the mixture was stirred to prepare the 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, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel. The mixture was stirred under a nitrogen stream for 1 hour to remove oxygen from the polymerization system, and then the temperature was raised to 85°C and the reaction was carried out for 5 hours to obtain an acrylic oligomer with a solid content of 50%. The Mw of the obtained acrylic oligomer was 3600.

[0178] (Preparation of double-sided adhesive sheets) The obtained adhesive composition was applied to the release surface of a 38 μm thick polyester release liner (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) and dried at 100°C for 2 minutes to form a 35 μm thick adhesive layer. The release surface of a 25 μm thick polyester release liner (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) was then bonded to this adhesive layer. In this way, a substrate-less double-sided adhesive sheet with a release liner, protected on both sides by the two polyester release liners described above, was obtained.

[0179] <Examples 2-9 and Comparative Examples 1-3> Except for changing the monomer composition, Mw, amount of tackifying resin, amount of acrylic oligomer, type and amount of crosslinking agent, and thickness of the adhesive layer of the acrylic polymer as shown in Table 1, adhesive compositions for each example were prepared in basically the same manner as in Example 1. Using the obtained adhesive compositions, substrate-less double-sided adhesive sheets with release liners for each example were prepared in the same manner as in Example 1. The Mw of the acrylic polymer was adjusted by adjusting the concentration of the monomer component during polymerization. In Table 1, BA represents n-butyl acrylate. Also, in Table 1, isocyanate crosslinking agent B represents the isocyanurate form of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a 1% ethyl acetate solution of a trifunctional isocyanate compound), and the content shown in Table 1 represents the solid content (non-volatile content).

[0180] <Example 10> An adhesive composition prepared by the method described in Example 1 was applied to one surface (first surface) of a 2 μm thick PET film (product name "Lumirror", manufactured by Toray Industries, Inc.) as a base layer, and dried at 100°C for 2 minutes to form a 35 μm thick first adhesive layer. The release surface of a 25 μm thick polyester release liner (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) was bonded to the first adhesive layer. A 38 μm thick polyester release liner (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) was also prepared, and the adhesive composition was applied to the release surface of the release liner, and dried at 100°C for 2 minutes to form a 35 μm thick second adhesive layer. This second adhesive layer was transferred to the non-adhesive surface of the base layer on which the first adhesive layer was formed. In this way, a double-sided adhesive sheet with a release liner (double-sided adhesive sheet with base material) according to this example was produced.

[0181] <Evaluation Method> (Adhesion to SUS) Under a measurement environment of 23°C and 50%RH, a 50μm thick PET film was attached to one adhesive side of a double-sided adhesive sheet as a backing, and the sheet was cut to a size of 25mm wide and 100mm long to prepare a measurement sample. Under the same environment of 23°C and 50%RH, the other adhesive side of the measurement sample was pressed onto the surface of a stainless steel plate (SUS304BA plate) that had been cleaned with ethyl acetate by applying pressure with a 2kg roller for one back-and-forth motion. After leaving this in the same environment for 72 hours, the peel strength (adhesion strength against SUS) [N / 25mm] was measured using a universal tensile and compression testing machine in accordance with JIS Z 0237:2000, under conditions of a tensile speed of 300mm / min and a peel angle of 180 degrees. For the measurement of the peel strength, a Minebea "Tensile and Compression Testing Machine, TG-1kN" or an equivalent product was used.

[0182] (Die-cutting properties) A double-sided adhesive sheet with a release liner, cut to a predetermined size, was used as an evaluation sample. A cutting blade was inserted into one side of the evaluation sample (the lightly peeling side), and the cutting was performed to a depth where the other side of the release liner (the heavily peeling side) was half-cut. This created a frame shape with an outer diameter of 25 mm x 25 mm and a width of 2 mm, and the portion 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 edge of the exposed double-sided adhesive sheet was observed under a microscope. Samples with adhesive overflow of 0.1 mm or more were evaluated as "×", and samples with adhesive overflow of less than 0.1 mm were evaluated as "○". For each example, 10 evaluation samples were prepared and the evaluation test was performed 10 times (N=10), and the number of evaluation tests evaluated as "○" X( / 10) was used as the evaluation result for punching processability. If the number of evaluation tests that received a "○" rating is 5 or more (i.e., 5 / 10 or more), the candidate is judged to have passed.

[0183] (Evaluation of uneven deformation) For each example, a double-sided adhesive sheet with a release liner (a laminate of the lightly peelable release liner, the double-sided adhesive sheet, and the heavily peelable release liner) was wound into a roll under the same conditions in the same environment. After a predetermined time, the roll was unwound and cut into 500mm x 1000mm pieces to obtain evaluation samples. In a cleanroom environment, the back surface of the heavily peelable release liner was wiped with a Kimwipe (manufactured by Nippon Paper Crecia Co., Ltd.) to remove foreign matter, and then the lightly peelable release liner was peeled off the evaluation sample. After 1 hour, the evaluation sample was held in a planar position at the midpoint between a point light source and a projection screen, which were positioned at a distance of approximately 100cm (approximately 50cm from the point light source), and positioned so that the angle of the exposed adhesive layer surface of the evaluation sample with respect to the light rays from the point light source was approximately 90 degrees. The evaluation sample was positioned with the adhesive layer surface from which the lightly peelable release liner had been peeled facing the point light source. In a darkroom at 23°C and 50% RH, the above-mentioned point light source was illuminated, and the image projected onto the screen through the evaluation sample was visually observed to evaluate the presence or absence of surface deformation (specifically, surface deformation of the adhesive layer). As a point light source, for example, a "xenon lamp C2577" manufactured by Hamamatsu Photonics can be used. For each example, 10 evaluation samples were prepared and 10 evaluation tests were performed (N=10), and the number of evaluation tests in which no surface deformation was observed (pass) X( / 10) was used as the result of the surface deformation evaluation. If the number of passes was 6 or more (i.e., 6 / 10 or more), it was determined that the fine surface deformation had been mitigated.

[0184] Table 1 shows an overview of each case and its evaluation results.

[0185] [Table 1]

[0186] As shown in Table 1, the adhesives in Examples 1 to 10 contained heptyl acrylate as a monomer component, and further contained an acrylic polymer containing 3% or more of a carboxyl group-containing monomer. The gel fraction was higher than 40%, the 23°C storage modulus was 0.04 MPa or higher, and the 23°C tanδ was 0.46 or higher. The double-sided adhesive sheets containing the above adhesives exhibited high adhesion to SUS, good die-cutting processability, and excellent ability to mitigate fine uneven deformation. On the other hand, Comparative Examples 1 and 2, which used BA-based polymers, had a 23°C tanδ of less than 0.46 and poor ability to mitigate uneven deformation. Furthermore, although Comparative Example 1 had high adhesion to SUS, its gel fraction was 40%, resulting in poor evaluation of die-cutting processability. Comparative Example 2 had a higher gel fraction and 23°C storage modulus compared to Comparative Example 1, resulting in improved die-cutting processability, but a decrease in adhesive strength. Furthermore, Comparative Example 3, like the above examples, used an acrylic polymer containing heptyl acrylate as a monomer component, but its adhesive strength, die-cutting processability, and ability to relax uneven deformation were all inferior to those of the above examples. In Comparative Example 3, the amount of carboxyl group-containing monomer used in the acrylic polymer was less than 3%, resulting in low adhesive strength. The storage modulus at 23°C was low, less than 0.04 MPa, resulting in poor die-cutting processability. The tanδ at 23°C was low, less than 0.46, which is thought to have resulted in poor ability to relax uneven deformation. From the above, it can be seen that a double-sided adhesive sheet having an adhesive layer containing heptyl acrylate as a monomer component, and further containing an acrylic polymer containing 3% by weight or more of carboxyl group-containing monomers, wherein the gel fraction of the adhesive layer is higher than 40%, the storage modulus at 23°C is 0.04 MPa or higher, and the tanδ at 23°C is 0.46 or higher, can have high adhesive strength and can achieve both ease of fine deformation of uneven surfaces and processability.

[0187] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. [Explanation of symbols]

[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-layer structure 100,200 Double-sided adhesive sheets with release liner 150 cores 300 rolls of double-sided adhesive sheets with release liner. 400 Portable Electronic Devices 500 display device 520 Display section 540 Support part

Claims

1. A double-sided adhesive sheet having an adhesive layer containing an acrylic polymer, The aforementioned 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 monomer component either does not contain a hydroxyl group-containing monomer, or contains a hydroxyl group-containing monomer in a proportion of less than 0.01% by weight. The gel fraction of the adhesive layer is higher than 40%. The adhesive layer is a double-sided adhesive sheet having a storage modulus of 0.04 MPa or more and 0.15 MPa or less at 23°C, and a tanδ of 0.46 or more at 23°C, where tanδ is the ratio of the loss modulus G'' to the storage modulus G' of the adhesive layer (G'' / G').

2. The double-sided adhesive sheet according to claim 1, wherein the adhesive layer further comprises a tackifying resin.

3. The double-sided adhesive sheet according to claim 2, wherein the tackifying resin is at least one selected from rosin-based tackifying resins and terpene-based tackifying resins.

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

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

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

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

8. The double-sided adhesive sheet according to any one of claims 1 to 3, wherein the thickness of the adhesive layer is greater than 5 μm and less than or equal to 50 μm.

9. A double-sided adhesive sheet according to any one of claims 1 to 3, wherein the 180-degree peel strength to a stainless steel plate is 10 N / 25 mm or more.

10. A double-sided adhesive sheet according to any one of claims 1 to 3, used for fixing components in electronic equipment.

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