Pressure-sensitive adhesive sheet

Abstract

To provide a pressure-sensitive adhesive sheet which can have the repulsion resistance and the impact resistance both at high levels.SOLUTION: The pressure-sensitive adhesive sheet includes a pressure-sensitive adhesive agent layer comprising an acrylic polymer. The acrylic polymer is a polymer of a monomer ingredient comprising heptyl acrylate. The pressure-sensitive adhesive agent layer has a storage modulus G' at 65°C of 20,000 Pa or more, and tanδ at -20°C of 0.3 or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

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

[0004] Adhesive sheets are required to have various performances depending on the application location and the mode of use. For example, when fixing a member in a portable electronic device with an adhesive sheet, the adhesive area is usually small due to restrictions on size, weight, etc. Adhesive sheets used for this purpose must have an adhesive force that can achieve good fixation even in a small area, and the required performance is at a higher level due to the demand for lighter weight and smaller size. In particular, portable electronic devices equipped with touch panel displays, such as smartphones, are becoming smaller and thinner in size, while the screens are becoming larger in terms of visibility and operability of the displays. Due to this unique situation, the adhesives used are required to have adhesive fixing performance under harsher conditions. Specifically, not only is the adhesive area limited in this application, but measures are taken such as folding an elastic member such as a flexible printed circuit board (FPC) and storing it in a limited internal space in the portable electronic device, positioning it precisely with an adhesive sheet, and fixing it stably. Adhesive sheets used to fix such components are subjected to a sustained peel load in the thickness direction (also referred to as the Z-axis direction) of the adhesive sheet, and are therefore required to have repulsion resistance that can sustainably resist the elastic rebound of the above-mentioned components (specifically, durability against a sustained peel load applied in the thickness direction (Z-axis direction) of the adhesive sheet).

[0005] In recent years, in addition to the above-mentioned weight reduction and miniaturization, the development of portable electronic devices having curved shapes such as three-dimensional shapes has progressed, and the surface shapes tend to become more complex. Adhesive sheets that are attached to complex shapes are required to have the ability to conform well to the shape and adhere closely. For example, in the above-mentioned portable electronic devices, adhesive sheets that fix members such as cover glass having complex surface shapes (which may be curved shapes) tend to be subjected to a larger sustained peel load than before, and adhesive sheets used for such purposes are required to have a higher level of repulsion resistance against sustained peel loads.

[0006] Furthermore, the temperature and humidity inside the portable electronic device may become high, exceeding 50° C., and may also become high humidity due to the influence of not only the heat inside the electronic device but also the external environment. Even under such an environment, the pressure-sensitive adhesive used for this application is required to exhibit stable repulsion resistance in the Z-axis direction.

[0007] In addition, because portable electronic devices are prone to dropping due to the way they are used, there is a strong demand for improved impact resistance for adhesives used in portable electronic devices. Impact resistance can be improved by lowering the elastic modulus of the adhesive, but if the elastic modulus of the adhesive is designed to be low, for example by lowering the degree of crosslinking, the cohesive force required for repulsion resistance is also reduced, making it difficult to obtain good repulsion resistance. In this way, repulsion resistance and impact resistance are contradictory properties, and it is difficult to achieve both. It would be meaningful to provide an adhesive sheet that exhibits good repulsion resistance against the above-mentioned sustained peel load in the thickness direction (resistance to sustained load in the Z-axis direction) and has excellent impact resistance even in harsh environments such as high temperature and high humidity conditions.

[0008] As a result of intensive research, the present inventors have found that a pressure-sensitive adhesive that exhibits good repulsion resistance against sustained load in the Z-axis direction even in harsh environments and also has excellent impact resistance can be obtained by using an acrylic polymer containing heptyl acrylate as a monomer component, and have completed the present invention. That is, the present invention aims to provide a pressure-sensitive adhesive sheet that can achieve both repulsion resistance and impact resistance at a high level. [Means for solving the problem]

[0009] According to this specification, a pressure-sensitive adhesive sheet is provided. This pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer. The acrylic polymer is a polymerization product of a monomer component containing heptyl acrylate. The pressure-sensitive adhesive layer has a storage modulus G' of 20,000 Pa or more at 65°C and a tan δ of 0.3 or more at -20°C. Here, tan δ refers to the ratio (G" / G') of the loss modulus G" to the storage modulus G' of the pressure-sensitive adhesive layer.

[0010] According to the above configuration, the pressure-sensitive adhesive layer has a 65°C storage modulus of 20,000 Pa or more, and therefore can exhibit good repulsion resistance. In addition, the pressure-sensitive adhesive layer has a -20°C tan δ of 0.3 or more, and therefore excellent impact resistance is easily obtained. Achieving both the 65°C storage modulus G' and the -20°C tan δ can be suitably achieved by using an acrylic polymer containing heptyl acrylate as a monomer component. According to the pressure-sensitive adhesive sheet of the above configuration, a high level of both repulsion resistance and impact resistance can be achieved.

[0011] In some preferred embodiments, the weight average molecular weight (Mw) of the acrylic polymer is 700,000 or more. By using an acrylic polymer that contains heptyl acrylate as a monomer unit and has a Mw of 700,000 or more, the above viscoelastic properties (specifically, 65°C storage modulus G' and -20°C tan δ) can be preferably satisfied, and it is easy to achieve both high levels of repulsion resistance and impact resistance.

[0012] In some preferred embodiments, the pressure-sensitive adhesive layer has a glass transition temperature (Tg) in the range of −15° C. to 15° C. Here, the glass transition temperature of the pressure-sensitive adhesive layer refers to a glass transition temperature determined from the peak temperature of tan δ in dynamic viscoelasticity measurement. A pressure-sensitive adhesive layer having a Tg in the range of −15° C. to 15° C. is likely to have both repulsion resistance and impact resistance.

[0013] In some preferred embodiments, the pressure-sensitive adhesive layer further comprises a tackifier resin. The technology disclosed herein is preferably implemented in a configuration in which the pressure-sensitive adhesive layer comprises a tackifier resin. As the tackifier resin, at least one selected from a rosin-based tackifier resin and a terpene-based tackifier resin is preferably used. In some embodiments, the content of the tackifier resin in the pressure-sensitive adhesive layer is 70 parts by weight or less relative to 100 parts by weight of the acrylic polymer. The effects of the technology disclosed herein can be preferably realized in an embodiment in which the content of the tackifier resin in the pressure-sensitive adhesive layer is appropriately adjusted within the above range.

[0014] In some preferred embodiments, the pressure-sensitive adhesive layer further comprises an acrylic oligomer. In the embodiment in which the pressure-sensitive adhesive layer comprises an acrylic oligomer, the technology disclosed herein is preferably implemented. In particular, it is more preferable to use a tackifier resin and an acrylic oligomer in combination.

[0015] In some preferred embodiments, the adhesive composition for forming the adhesive layer includes at least one selected from an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent. By using a crosslinking agent selected from an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent, the cohesive strength of the adhesive can be appropriately increased, and the repulsion resistance can be preferably improved while maintaining impact resistance.

[0016] In some preferred embodiments, the pressure-sensitive adhesive sheet has a 180-degree peel strength against a stainless steel plate (adhesive strength to SUS) of 20 N / 25 mm or more. A pressure-sensitive adhesive sheet having the above-mentioned adhesive strength to SUS can exhibit excellent adhesive strength.

[0017] The adhesive sheet disclosed herein can achieve both repulsion resistance and impact resistance, and is therefore preferably used for bonding components of portable electronic devices that require high repulsion resistance and impact resistance. As described above, this specification provides a portable electronic device using any of the adhesive sheets disclosed herein, in other words, a portable electronic device including the adhesive sheet. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to an embodiment. [Diagram 2] FIG. 4 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Diagram 3] FIG. 4 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Figure 4] 1 is a front view showing a schematic diagram of an example of a portable electronic device including an adhesive sheet. [Diagram 5]FIG. 1 is a schematic diagram illustrating a method for testing repulsion resistance in the Z-axis direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

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

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

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

[0024] The structure of an adhesive sheet according to another embodiment is shown in FIG. 2. The adhesive sheet 2 is configured as a substrate-attached single-sided adhesive sheet including a sheet-like supporting substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, and an adhesive layer 21 provided on the first surface 10A side. The adhesive layer 21 is fixedly provided on the first surface 10A side of the supporting substrate 10, that is, without the intention of separating the adhesive layer 21 from the supporting substrate 10. As shown in FIG. 2, the adhesive sheet 2 before use may be a component of an adhesive sheet 200 with a release liner in a form in which the surface (adhesive surface) 21A of the adhesive layer 21 is protected by a release liner 31, at least the side facing the adhesive layer 21 being a release surface. Alternatively, the release liner 31 may be omitted, and a supporting substrate 10 having a second surface 10B as a release surface may be used, and the adhesive sheet 2 may be rolled up so that the adhesive surface 21A is in contact with the second surface (rear surface) 10B of the supporting substrate 10 and protected.

[0025] The structure of a pressure-sensitive adhesive sheet according to yet another embodiment is shown in FIG. 3. The pressure-sensitive adhesive sheet 3 is configured as a substrate-attached double-sided pressure-sensitive adhesive sheet including a sheet-like support substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, a first pressure-sensitive adhesive layer 21 fixedly provided on the first surface 10A side, and a second pressure-sensitive adhesive layer 22 fixedly provided on the second surface 10B side. As shown in FIG. 3, the pressure-sensitive adhesive sheet 3 before use may be a component of a release-liner-attached pressure-sensitive adhesive sheet 300 in which the surface (first adhesive surface) 21A of the first pressure-sensitive adhesive layer 21 and the surface (second adhesive surface) 22A of the second pressure-sensitive adhesive layer 22 are protected by release liners 31, 32. Alternatively, the release liner 32 may be omitted, and a release liner 31 having both release surfaces may be used, which is then superimposed on the pressure-sensitive adhesive sheet 3 and wound in a spiral shape to form a release-liner-attached pressure-sensitive adhesive sheet in a form (roll form) in which the second adhesive surface 22A is protected by contacting the back surface of the release liner 31.

[0026] In the above-mentioned double-sided pressure-sensitive adhesive sheet with a substrate, at least one of the first and second pressure-sensitive adhesive layers (e.g., the first pressure-sensitive adhesive layer) may be a pressure-sensitive adhesive layer as described below, and the other pressure-sensitive adhesive layer (e.g., the second pressure-sensitive adhesive layer) may be a pressure-sensitive adhesive layer disclosed herein, or may be a pressure-sensitive adhesive layer having a composition different from that of the pressure-sensitive adhesive layer disclosed herein (specifically, the one pressure-sensitive adhesive layer, e.g., the first pressure-sensitive adhesive layer). Such other pressure-sensitive adhesive layer may be formed, for example, from a known or commonly used pressure-sensitive adhesive.

[0027] In addition, although not particularly limited, the technology disclosed herein can achieve both repulsion resistance and impact resistance in a configuration that does not have a foam substrate, which is advantageous for improving impact resistance. Therefore, the technology disclosed herein can be implemented in the form of a substrate-less double-sided adhesive sheet made of an adhesive layer, or in the form of an adhesive sheet with a substrate that has a substrate other than a foam substrate (non-foam substrate). Among these, the form of a substrate-less double-sided adhesive sheet is preferable. A substrate-less double-sided adhesive sheet can be made thinner by not having a substrate, which can contribute to the miniaturization and space saving of products to which the double-sided adhesive sheet is applied. In addition, a substrate-less adhesive sheet can maximize the effects of the adhesive layer, such as repulsion resistance and impact resistance against sustained load in the Z-axis direction.

[0028] <Adhesive layer> (Viscoelastic properties) The adhesive layer disclosed herein (in an embodiment 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 G' at 65°C of 20,000 Pa or more. Adhesives having the above-mentioned storage modulus at 65°C tend to provide good repulsion resistance (particularly repulsion resistance against sustained load in the Z-axis direction in harsh environments such as high temperature conditions). In some preferred embodiments, from the viewpoint of improving repulsion resistance, the 65°C storage modulus is 21,000 Pa or more, may be 22,000 Pa or more, and is suitably 23,000 Pa or more, more preferably 24,000 Pa or more, even more preferably 25,000 Pa or more, particularly preferably 26,000 Pa or more, may be 27,000 Pa or more, may be 28,000 Pa or more, may be 29,000 Pa or more, may be 30,000 Pa or more, may be 31,000 Pa or more, may be 32,000 Pa or more, or may be 33,000 Pa or more. The upper limit of the 65°C storage modulus can be set within an appropriate range that can achieve both repulsion resistance and impact resistance. In some embodiments, the 65°C storage modulus is suitably about 60,000 Pa or less, preferably 50,000 Pa or less, more preferably 40,000 Pa or less, and even more preferably 35,000 Pa or less, and may be 32,000 Pa or less, 30,000 Pa or less, 28,000 Pa or less, or 26,000 Pa or less.

[0029] The pressure-sensitive adhesive layer disclosed herein is characterized by having a storage modulus at 65° C. of 20,000 Pa or more, and a tan δ at −20° C. of 0.3 or more. The tan δ (loss tangent) refers to the ratio (G″ / G′) of the loss modulus G″ to the storage modulus G′ of the pressure-sensitive adhesive layer. −20° C. corresponds to the impact speed range at the time of dropping according to the temperature-speed conversion rule. A pressure-sensitive adhesive having a tan δ of 0.3 or more at −20° C. is likely to provide excellent impact resistance. In some embodiments, the −20° C. tan δ is 0.35 or more, may be 0.40 or more, or may be 0.45 or more. In some preferred embodiments, the −20° C. tan δ is 0.50 or more, more preferably 0.55 or more, and even more preferably 0.60 or more, from the viewpoint of impact resistance. The upper limit of the −20° C. tan δ can be set within an appropriate range that can achieve both repulsion resistance and impact resistance. The -20°C tan δ may be, for example, about 2 or less, 1.8 or less, 1.6 or less, or 1.4 or less. In some embodiments, the -20°C tan δ is suitably 1.2 or less, and from the viewpoint of repulsion resistance, is preferably 1.0 or less, more preferably 0.80 or less, even more preferably 0.70 or less, may be 0.60 or less, or may be 0.55 or less.

[0030] Although not particularly limited, in some preferred embodiments, the glass transition temperature (Tg) of the pressure-sensitive adhesive layer is within the range of -15°C to 15°C. Here, the glass transition temperature of the pressure-sensitive adhesive layer refers to the glass transition temperature determined from the peak temperature of tan δ in dynamic viscoelasticity measurement. By using a pressure-sensitive adhesive having a Tg within the range of -15°C to 15°C, both repulsion resistance and impact resistance can be preferably achieved. From the viewpoint of repulsion resistance, the Tg of the pressure-sensitive adhesive layer is more preferably -12°C or higher, further preferably -10°C or higher, particularly preferably -7°C or higher, and may be -5°C or higher, -3°C or higher, -1°C or higher, 0°C or higher (e.g., above 0°C), or 1°C or higher. Furthermore, from the viewpoint of impact resistance, the Tg of the adhesive layer is preferably 12°C or less, more preferably 10°C or less, even more preferably 7°C or less, and particularly preferably 5°C or less, and may be 3°C or less, 1°C or less, 0°C or less (e.g., less than 0°C), -1°C or less, or -3°C or less.

[0031] In the technology disclosed herein, the 65°C storage modulus, -20°C tan δ, and Tg of the adhesive layer can be determined by dynamic viscoelasticity measurement. Specifically, a plurality of adhesive layers (adhesive sheets in the case of substrate-less adhesive sheets) to be measured are stacked to prepare an adhesive layer having a thickness of about 2 mm. The adhesive layer is punched into a disk shape having a diameter of 7.9 mm, and a sample is sandwiched and fixed between parallel plates. Dynamic viscoelasticity measurement is performed under the following conditions using a viscoelasticity tester (e.g., ARES manufactured by TA Instruments or its equivalent) to determine the 65°C storage modulus, -20°C tan δ, and Tg. Measurement mode: Shear mode Temperature range: -70℃~150℃ Heating rate: 5℃ / min ·Measurement frequency: 1Hz The above method is also used in the Examples described later. The pressure-sensitive adhesive layer to be measured may be one formed by applying the corresponding pressure-sensitive adhesive composition in a layer form and drying or curing it.

[0032] (Acrylic polymer) The adhesive layer constituting the adhesive sheet disclosed herein contains an acrylic polymer. The above-mentioned adhesive layer is typically an adhesive layer having an acrylic polymer as a base polymer. Such an adhesive layer is also called an acrylic adhesive layer. The base polymer refers to the main component of a rubber-like polymer (a polymer that exhibits rubber elasticity in a temperature range around room temperature) contained in the adhesive layer. In addition, in this specification, the "main component" refers to a component contained in an amount of more than 50% by weight, unless otherwise specified. In addition, the following explanation of the adhesive and the components that may be contained in the adhesive layer are also applicable to the adhesive composition used to form the adhesive (layer) unless otherwise specified.

[0033] In addition, in this specification, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer". Therefore, in this specification, an acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer. In this specification, "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, "(meth)acrylate" refers to acrylate and methacrylate, and "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense.

[0034] The acrylic polymer used in the technology disclosed herein is a polymer of a monomer component containing heptyl acrylate. An acrylic polymer polymerized using a monomer component containing heptyl acrylate has better flexibility than other alkyl acrylate polymers such as n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA), and therefore an adhesive containing such a polymer is likely to have a high value of -20°C tan δ and is likely to have excellent impact resistance. The reason for this is not particularly limited, but is considered to be that a polymer containing heptyl acrylate as a monomer unit has a low glass transition temperature and a relatively large space between the main chains in the adhesive. Among heptyl acrylates, n-heptyl acrylate is preferred from the viewpoint of flexibility. An acrylic polymer synthesized containing n-heptyl acrylate as a monomer component has a relatively long linear side chain, and is therefore likely to have a larger space between the main chains.

[0035] The ratio of heptyl acrylate in the monomer component of the acrylic polymer is, for example, 50% by weight or more (e.g., more than 50% by weight) in some embodiments, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 85% by weight or more, particularly preferably 90% by weight or more, may be 92% by weight or more, may be 94% by weight or more, may be 95% by weight or more, or may be 96% by weight or more. By increasing the amount of heptyl acrylate used, the effect of its use (for example, improvement of the -20°C tan δ of the adhesive, and thus improvement of impact resistance) can be effectively expressed. On the other hand, the upper limit of the ratio of heptyl acrylate in the monomer component is 100% by weight, and may be 99% by weight or less, or may be 98% by weight or less. From the viewpoint of copolymerizing a carboxyl group-containing monomer or other monomers, in some embodiments, the ratio of heptyl acrylate in the monomer component is less than 97% by weight. In some preferred embodiments, the proportion of heptyl acrylate in the monomer component is 96% by weight or less, may be 95% by weight or less, or may be 94% by weight or less. Limiting the proportion of heptyl acrylate within the above range is preferable in terms of improving the storage modulus, and may be advantageous in terms of improving repulsion resistance.

[0036] The acrylic polymer may be copolymerized with an alkyl (meth)acrylate other than heptyl acrylate (hereinafter, also referred to as "any alkyl (meth)acrylate"). As the any alkyl (meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used. CH2=C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. 2 is a chain alkyl group having 1 to 20 carbon atoms (wherein R 1 When is a hydrogen atom, the heptyl group is excluded.

[0037] Examples of the optional alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl methacrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and isooctyl (meth)acrylate. Examples of the alkyl (meth)acrylate include acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylates may be used alone or in combination of two or more.

[0038] In some embodiments, the proportion of heptyl acrylate in the total amount of alkyl (meth)acrylate contained in the monomer component is, for example, 50% by weight or more (specifically, 50 to 100% by weight, for example, more than 50% by weight), preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and may be 99% by weight or more, or may be 100% by weight. By adopting such a monomer composition, the effect of using heptyl acrylate can be effectively exhibited. According to the technology disclosed herein, it is possible to achieve both repulsion resistance and impact resistance based on the action of heptyl acrylate without relying on any alkyl (meth)acrylate such as 2EHA or BA. Therefore, the technology disclosed herein can be preferably implemented in an embodiment in which the monomer component does not substantially contain any alkyl (meth)acrylate.

[0039] In this specification, the monomer component being substantially free of monomer A (e.g., any alkyl (meth)acrylate) means that the monomer A is not used at least intentionally, and it is permissible for the monomer A to be unintentionally included in an amount of, for example, about 0.01% by weight or less.

[0040] In some embodiments, the monomer component may contain an alkyl (meth)acrylate having an alkyl group derived from biomass at the ester end (hereinafter also referred to as "biomass alkyl (meth)acrylate"). In recent years, environmental issues such as global warming have become important, and it is desired to reduce the amount of fossil resource-based materials such as petroleum used. Under these circumstances, it is also desired to reduce the amount of fossil resource-based materials used in the field of adhesives. By using a biomass alkyl (meth)acrylate, it is possible to preferably realize an acrylic adhesive that takes into consideration the reduction of dependency on fossil resource-based materials.

[0041] The biomass alkyl (meth)acrylate is not particularly limited, and is, for example, an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived (meth)acrylic acid. Examples of biomass-derived alkanols include biomass ethanol, alkanols derived from plant materials such as palm oil, palm kernel oil, coconut oil, and castor oil. When the biomass-derived alkanol has 3 or more carbon atoms, the alkanol may be linear or branched. In some embodiments, an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate used in the synthesis of an acrylic polymer. In such a biomass alkyl (meth)acrylate, the higher the number of carbon atoms of the alkanol, the higher the ratio of the number of biomass-derived carbons to the total number of carbons contained in the biomass alkyl (meth)acrylate, that is, the biomass carbon ratio of the alkyl (meth)acrylate. Therefore, in the above biomass alkyl (meth)acrylate, it is desirable that the alkyl group derived from biomass has a large number of carbon atoms in terms of reducing the dependency on fossil resource-based materials. On the other hand, if the alkyl group constituting the alkyl (meth)acrylate has too many carbon atoms, it tends to be difficult to obtain adhesive properties such as adhesive strength, and it may also be disadvantageous in terms of productivity such as synthesis, handling, and cost. In an embodiment in which an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate, it is desirable to use a material that has a good balance between adhesive properties and reduced dependency on fossil resource-based materials (more specifically, the biomass carbon ratio of the above alkyl (meth)acrylate).

[0042] In some preferred embodiments, biomass-derived heptyl acrylate (biomass heptyl acrylate) is used as the heptyl acrylate. By using biomass heptyl acrylate, the effect of the technology disclosed herein can be realized while reducing the dependency on fossil resource-based materials. The biomass heptyl acrylate is an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived acrylic acid, and for example, an ester of a biomass-derived alkanol and a non-biomass-derived acrylic acid can be used. In such a compound, only the heptyl group is biomass-derived. As the biomass-derived heptyl acrylate, it is preferable to use biomass-derived n-heptyl acrylate (biomass n-heptyl acrylate).

[0043] The proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) in the monomer components of the acrylic polymer is, for example, 50% by weight or more (e.g., more than 50% by weight) in some embodiments, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 85% by weight or more, particularly preferably 90% by weight or more, may be 92% by weight or more, may be 94% by weight or more, or may be 96% by weight or more. The proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) in the monomer components is less than 97% by weight, and in some embodiments, may be 95% by weight or less, 93% by weight or less, or 91% by weight or less.

[0044] In addition, the monomer component of the acrylic polymer preferably contains a carboxyl group-containing monomer. The carboxyl group-containing monomer can improve the cohesive force based on its polarity. In addition, when a crosslinking agent such as an isocyanate-based or epoxy-based crosslinking agent is used, the carboxyl group can become a crosslinking point of the acrylic polymer. By using the carboxyl group-containing monomer, the 65°C storage modulus of the adhesive can be improved, and an adhesive having excellent repulsion resistance against sustained load in the Z-axis direction is easily obtained. In addition, by using the carboxyl group-containing monomer, better adhesion can be exhibited to an adherend such as a highly polar material.

[0045] Examples of the carboxyl group-containing monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, crotonic acid, and isocrotonic acid; and ethylenically unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and citraconic acid. The carboxyl group-containing monomer may be a monomer having a metal salt of a carboxyl group (e.g., an alkali metal salt). The carboxyl group-containing monomer may be used alone or in combination of two or more. Among them, preferred carboxyl group-containing monomers include AA and MAA. AA is particularly preferred. When one or more carboxyl group-containing monomers are used, the proportion of AA in the carboxyl group-containing monomer is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. In a particularly preferred embodiment, the carboxyl group-containing monomer is substantially composed of AA alone. Due to the combined effects of AA, such as the polarity based on its carboxy group, its role as a crosslinking point, and its Tg (106°C), it is believed to be the optimal monomer material for achieving a good balance between impact resistance and resilience against sustained load in the Z-axis direction in the carboxy group-containing monomers disclosed herein.

[0046] The ratio of the carboxyl group-containing monomer in the monomer component of the acrylic polymer is not particularly limited, and may be 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, or 2% by weight or more. In some preferred embodiments, the ratio of the carboxyl group-containing monomer in the monomer component is more than 3% by weight (specifically, more than 3.0% by weight), preferably 4.0% by weight or more, more preferably 4.5% by weight or more, even more preferably 5.0% by weight or more (e.g., more than 5.0% by weight), particularly preferably 5.5% by weight or more, and may be 6.0% by weight or more. By increasing the amount of the carboxyl group-containing monomer used, the cohesive force of the adhesive layer is improved based on the action of the carboxyl group-containing monomer, so that the 65°C storage modulus of the adhesive can be improved, and an adhesive with excellent repulsion resistance can be easily obtained. In addition, the amount of the carboxyl group-containing monomer is, for example, appropriately 20% by weight or less of the total monomer component, preferably 15% by weight or less, more preferably 12% by weight or less. In some preferred embodiments, the amount of the carboxyl group-containing monomer may be 10% by weight or less, 8% by weight or less, 6% by weight or less, or 5% by weight or less. By reducing the amount of the carboxyl group-containing monomer (e.g., AA) used, the -20°C tan δ tends to be higher. By appropriately adjusting the amount of the carboxyl group-containing monomer used within the above range, it is easy to obtain a pressure-sensitive adhesive that has both repulsion resistance and impact resistance.

[0047] The acrylic polymer may be copolymerized with a functional group-containing monomer (any functional group-containing monomer) other than the carboxy group-containing monomer. Examples of optional functional group-containing monomers that can introduce functional groups that can serve as crosslinking base points into acrylic polymers or contribute to improving adhesive strength include hydroxyl group (OH group)-containing monomers (hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; polypropylene glycol mono(meth)acrylate, etc.), acid anhydride group-containing monomers, amide group-containing monomers ((meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc.), amino group-containing monomers (aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), epoxy group-containing monomers, cyano group-containing monomers, keto group-containing monomers, monomers having nitrogen atom-containing rings (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), alkoxysilyl group-containing monomers, and imide group-containing monomers. The above-mentioned optional functional group-containing monomers may be used alone or in combination of two or more.

[0048] When the monomer component constituting the acrylic polymer contains the above-mentioned optional functional group-containing monomer, the content of the optional functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exerting the effect of using the optional functional group-containing monomer, the content of the optional functional group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, suitably 0.5% by weight or more, and may be 1% by weight or more. Also, for example, in an embodiment in which the monomer component of the acrylic polymer contains heptyl acrylate and a carboxyl group-containing monomer, from the viewpoint of easily balancing the adhesive performance in relation to these monomer components, the content of the optional functional group-containing monomer in the monomer component is suitably 40% by weight or less, preferably 20% by weight or less, and may be 10% by weight or less (for example, 5% by weight or less). In some embodiments, the content of the optional functional group-containing monomer in the monomer component is, for example, less than 3% by weight, may be less than 1% by weight, may be less than 0.5% by weight, may be less than 0.3% by weight, or may be less than 0.1% by weight. The technology disclosed herein can be preferably practiced in an embodiment in which the monomer component of the acrylic polymer is substantially free of any functional group-containing monomer.

[0049] In addition, a hydroxyl-containing monomer may be used as the optional functional group-containing monomer. In this case, the content of the hydroxyl-containing monomer is suitably about 10% by weight or less (for example, 0.001 to 10% by weight) in the total monomer components, preferably about 5% by weight or less, more preferably about 2% by weight or less. In some embodiments, the content of the hydroxyl-containing monomer in the monomer components 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 components of the acrylic polymer may not substantially contain a hydroxyl-containing monomer. In the technology disclosed herein, by limiting the amount of the hydroxyl-containing monomer used or not using it at all, it is possible to achieve both a predetermined 65°C storage modulus G' and -20°C tan δ, and to preferably achieve a high level of both repulsion resistance and impact resistance.

[0050] The proportion of the carboxyl group-containing monomer in the total functional group-containing monomers (total functional group-containing monomers including the carboxyl group-containing monomer) used as a copolymerization component of the acrylic polymer is 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, for example, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99.9% by weight or more). The upper limit of the proportion of the carboxyl group-containing monomer in the total functional group-containing monomer is 100% by weight, and may be, for example, 95% by weight or less.

[0051] The monomer components constituting the acrylic polymer may contain other copolymerization components other than the functional group-containing monomers described above for the purpose of improving cohesive strength, etc. Examples of other copolymerization components include vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate); olefin monomers; chlorine-containing monomers; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and the like. The other copolymerization components may be used alone or in combination of two or more.

[0052] The amount of such other copolymerization components is not particularly limited and may be appropriately selected according to the purpose and use, but from the viewpoint of appropriately exerting the effect of use, it is appropriate to set it to 0.05 wt% or more, and it may be 0.5 wt% or more. In addition, from the viewpoint of easily balancing the adhesive performance, the content of other copolymerization components in the monomer component is appropriate to be 20 wt% or less, and from the viewpoint of appropriately exerting the adhesive properties based on the essential monomer components, it is preferably 10 wt% or less, more preferably 8 wt% or less, and even more preferably less than 5 wt%, for example, it may be less than 3 wt%, or it may be less than 1 wt%. The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer component does not substantially contain other copolymerization components.

[0053] The acrylic polymer may contain a polyfunctional monomer having at least two polymerizable functional groups (typically radically polymerizable functional groups) having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, as another monomer component. By using a polyfunctional monomer as a monomer component, the cohesive force of the adhesive layer can be increased. The polyfunctional monomer can be used as a crosslinking agent. The polyfunctional monomer is not particularly limited, and examples thereof include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, and the like. The polyfunctional monomer can be used alone or in combination of two or more kinds.

[0054] The amount of the polyfunctional monomer used is not particularly limited, and can be appropriately set so that the purpose of using the polyfunctional monomer is achieved. The amount of the polyfunctional monomer used can be about 3% by weight or less of the monomer component, preferably about 2% by weight or less, and more preferably about 1% by weight or less (for example, about 0.5% by weight or less). When using a polyfunctional monomer, the lower limit of the amount used is not particularly limited as long as it is greater than 0% by weight. Usually, the effect of using the polyfunctional monomer can be appropriately exhibited by setting the amount of the polyfunctional monomer used to about 0.001% by weight or more (for example, about 0.01% by weight or more) of the monomer component.

[0055] In a particularly preferred embodiment, an acrylic polymer synthesized using a monomer component consisting essentially of heptyl acrylate (preferably n-heptyl acrylate) and a carboxyl group-containing monomer (preferably acrylic acid) is used as the acrylic polymer. According to the above monomer composition, the action of heptyl acrylate and the carboxyl group-containing monomer is effectively exerted, and a predetermined 65°C storage modulus G' and -20°C tan δ are both achieved, and a high level of both repulsion resistance and impact resistance can be preferably achieved. From this viewpoint, the total ratio of heptyl acrylate and the carboxyl group-containing monomer in the above monomer component is suitably 90% by weight or more (90 to 100% by weight), preferably 95% by weight or more, more preferably 99% by weight or more, even more preferably more than 99.5% by weight, and particularly preferably more than 99.9% by weight (for example, more than 99.99% by weight), and the total ratio of heptyl acrylate and the carboxyl group-containing monomer in the above monomer component may be 100% by weight.

[0056] The biomass carbon ratio of the monomer components constituting the acrylic polymer (the biomass carbon ratio of the acrylic polymer) may be, for example, 1% or more, suitably 10% or more, preferably 30% or more, more preferably 50% or more (e.g., more than 50%), may be 70% or more, may be 80% or more, or may be 90% to 100%. By designing in this way, an acrylic pressure-sensitive adhesive that takes into consideration the reduction of dependency on fossil resource-based materials can be obtained.

[0057] The method for obtaining an acrylic polymer is not particularly limited, and various polymerization methods known as a synthesis method for an acrylic polymer, such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method, can be appropriately adopted. For example, a solution polymerization method can be preferably adopted. As a monomer supply method when carrying out solution polymerization, a lump-sum charging method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc. can be appropriately adopted. The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0058] The solvent (polymerization solvent) used in the solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one of the following solvents or a mixture of two or more of them can be used: aromatic compounds (typically aromatic hydrocarbons) such as toluene; acetate esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol; ethers such as tert-butyl methyl ether; and ketones such as methyl ethyl ketone.

[0059] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators according to the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide (BPO) and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and the like. Still other examples of polymerization initiators include redox-based initiators obtained by combining peroxides with reducing agents. Such polymerization initiators can be used alone or in combination of two or more. The amount of polymerization initiator used may be a normal amount, and can be selected, for example, from the range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) relative to 100 parts by weight of the total monomer components.

[0060] The weight average molecular weight (Mw) of the acrylic polymer is not particularly limited, and an acrylic polymer having an appropriate Mw that satisfies the above 65°C storage modulus and -20°C tan δ is used. In some embodiments, the Mw of the acrylic polymer is greater than 600,000, may be greater than 650,000, is suitable for 700,000 or more, and may be 750,000 or more. The larger the Mw of the acrylic polymer, the easier it is to obtain a pressure-sensitive adhesive that exhibits good cohesive strength, and the repulsion resistance 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, more preferably 1 million or more (e.g., more than 1 million), even more preferably 1.2 million or more, particularly preferably 1.4 million or more, may be 1.5 million or more, or may be 1.6 million or more. A monomer composition containing heptyl acrylate is easy to maintain a low viscosity, so that the synthesis of a high molecular weight substance is good, and an acrylic polymer having the above Mw is easy to obtain. In addition, by using an acrylic polymer containing heptyl acrylate as a monomer unit and having a Mw of a predetermined value or more, the above-mentioned viscoelastic properties (specifically, 65°C storage modulus G' and -20°C tan δ) are easily satisfied based on the flexibility based on the chemical structure of the polymer and the cohesive strength based on the molecular weight, and a high level of both repulsion resistance and impact resistance can be preferably achieved. On the other hand, from the viewpoint of impact resistance, adhesive strength, ease of synthesis, etc., the Mw of the acrylic polymer is usually about 3 million or less, preferably 2.5 million or less, more preferably 2 million or less, even more preferably 1.8 million or less, and may be 1.5 million or less, or 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.

[0061] The Mw of the acrylic polymer can be measured by gel permeation chromatography (GPC) and calculated as a standard polystyrene equivalent. Specifically, it can be measured under the following conditions using a GPC measuring device (trade name: "HLC-8220GPC" manufactured by Tosoh Corporation). The same applies to the examples described below. [GPC measurement conditions] Sample concentration: 0.2% by weight (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40℃ column: Sample column: 1 "TSKguardcolumn SuperHZ-H" + 2 "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: 1 "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0062] (tackifier resin) In some preferred embodiments, the adhesive layer includes a tackifier resin. By using a tackifier resin, high adhesive strength can be obtained. According to the technology disclosed herein, the adhesive layer has a predetermined viscoelastic property (specifically, 65°C storage modulus G' and -20°C tan δ) in a composition containing a tackifier resin, and can exhibit excellent Z-axis direction repulsion resistance. In particular, the effect of using a tackifier resin can be effectively exhibited in a composition containing a high molecular weight acrylic polymer. The tackifier resin is not particularly limited, and various tackifier resins such as rosin-based tackifier resins, terpene-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, phenol-based tackifier resins, and ketone-based tackifier resins can be used. Such tackifier resins can be used alone or in combination of two or more.

[0063] Specific examples of rosin-based tackifying resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; modified rosins obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.; the same applies below); and various other rosin derivatives. Examples of the rosin derivative include rosin esters such as those obtained by esterifying unmodified rosin with alcohols (i.e., esterified products of rosin) and those obtained by esterifying modified rosin with alcohols (i.e., esterified products of modified rosin); unsaturated fatty acid modified rosins obtained by modifying unmodified rosin or modified rosin with unsaturated fatty acid; unsaturated fatty acid modified rosin esters obtained by modifying rosin esters with unsaturated fatty acid; rosin alcohols obtained by reducing the carboxyl groups in unmodified rosin, modified rosin, unsaturated fatty acid modified rosins, or unsaturated fatty acid modified rosin esters; metal salts of rosins (particularly rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; rosin phenolic resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) using an acid catalyst and thermally polymerizing the mixture; and the like. Among these, rosin esters are preferred.

[0064] Although not particularly limited, specific examples of rosin esters include esters of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), such as methyl esters, triethylene glycol esters, glycerin esters, pentaerythritol esters, etc.

[0065] Examples of terpene-based tackifier resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers; modified terpene resins obtained by modifying these terpene resins (phenol-modified, aromatic-modified, hydrogen-modified, hydrocarbon-modified, etc.); etc. An example of the modified terpene resin is a terpene phenol resin.

[0066] Terpene phenolic resin refers to a polymer containing a terpene residue and a phenol residue, and is a concept that includes both a copolymer of a terpene and a phenolic compound (terpene-phenol copolymer resin) and a homopolymer or copolymer of a terpene modified with phenol (phenol-modified terpene resin). Specific examples of terpenes that constitute such terpene phenolic resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d / l-forms (dipentene)). Hydrogenated terpene phenolic resin refers to a hydrogenated terpene phenolic resin having a structure obtained by hydrogenating such a terpene phenolic resin. It is also called hydrogenated terpene phenolic resin.

[0067] Examples of hydrocarbon-based tackifying resins include various hydrocarbon resins such as aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic / aromatic copolymer (C5 / C9) petroleum resins, hydrogenated products thereof (for example, alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), various modified products thereof (for example, maleic anhydride modified products), coumarone resins, and coumarone-indene resins.

[0068] In some embodiments, it is preferable to use at least one selected from rosin-based tackifier resins and terpene-based tackifier resins as the tackifier resin. By incorporating a rosin-based tackifier resin and / or a terpene-based tackifier resin into an acrylic adhesive, excellent repulsion resistance in the Z-axis direction is easily obtained, and adhesive strength can be improved. In some preferred embodiments, the total proportion of the rosin-based tackifier resin and the terpene-based tackifier resin in the entire tackifier resin contained in the adhesive layer can be, for example, more than about 50% by weight (more than 50% by weight and 100% by weight or less), and may be about 70% by weight or more, about 80% by weight or more, about 90% by weight or more, 95% by weight or more, or 99% by weight or more.

[0069] Some preferred embodiments include an embodiment in which the tackifier resin contains one or more terpene phenol resins. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the total amount of the tackifier resin is about 25% by weight or more (more preferably about 30% by weight or more). The proportion of the terpene phenol resin in the total amount of the tackifier resin may be about 50% by weight or more, about 70% by weight or more, about 80% by weight or more, or about 90% by weight or more. Substantially all of the tackifier resin (for example, about 95% by weight or more and 100% by weight or less, or even about 99% by weight or more and 100% by weight or less) may be a terpene phenol resin.

[0070] The content of the terpene phenol resin in the adhesive layer is not particularly limited as long as the desired viscoelastic properties are satisfied. In some embodiments, the content of the terpene phenol resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, and is preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength. In some embodiments, the content of the terpene phenol resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, or may be 50 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the terpene phenol resin is 40 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 25 parts by weight or less, particularly preferably 20 parts by weight or less, and may be 18 parts by weight or less, relative to 100 parts by weight of the acrylic polymer.

[0071] Although not particularly limited, in some embodiments, the tackifier resin may contain a tackifier resin having a hydroxyl value of more than 20 mgKOH / g (e.g., terpene phenol resin). The hydroxyl value of such a tackifier resin may be 30 mgKOH / g or more. Among them, a tackifier resin having a hydroxyl value of 50 mgKOH / g or more is preferable. Hereinafter, a tackifier resin having a hydroxyl value of 50 mgKOH / g or more may be referred to as a "high hydroxyl value resin". According to a tackifier resin containing such a high hydroxyl value resin, in addition to adhesive strength, a pressure-sensitive adhesive layer having high cohesive strength can be realized by interacting with a crosslinking agent such as an isocyanate-based crosslinking agent. In some embodiments, the tackifier resin may contain a high hydroxyl value resin having a hydroxyl value of 60 mgKOH / g or more (more preferably 70 mgKOH / g or more). Furthermore, such high hydroxyl value resins (e.g., terpene phenol resins) are preferably used in combination with, for example, acrylic polymers containing heptyl acrylate as a monomer component, and can exhibit good adhesion to the adherend and repulsion resistance against sustained load in the Z-axis direction.

[0072] The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with acrylic polymers, the hydroxyl value of the high hydroxyl value resin is usually about 300 mgKOH / g or less, and is suitably about 200 mgKOH / g or less, preferably about 180 mgKOH / g or less, more preferably about 160 mgKOH / g or less, and even more preferably about 140 mgKOH / g or less, and may be less than 120 mgKOH / g (for example, 110 mgKOH / g or less). The technology disclosed herein can be preferably implemented in an embodiment in which the tackifier resin contains a high hydroxyl value resin (for example, a terpene tackifier resin, preferably a terpene phenol resin) having a hydroxyl value of 50 to 200 mgKOH / g. In some embodiments, a high hydroxyl value resin having a hydroxyl value of 60 to 140 mgKOH / g (for example, 70 to 110 mgKOH / g) can be preferably used.

[0073] Here, the hydroxyl value may be a value measured by potentiometric titration as specified in JIS K0070: 1992. The specific measurement method is as follows. [Method for measuring hydroxyl value] 1. Reagents (1) As the acetylation reagent, take about 12.5 g (about 11.8 mL) of acetic anhydride, add pyridine to make the total volume 50 mL, and stir thoroughly before use. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to make the total volume 100 mL, and stir thoroughly before use. (2) Use a 0.5 mol / L potassium hydroxide ethanol solution as the measurement reagent. (3) In addition, prepare toluene, pyridine, ethanol and distilled water. 2.Operation (1) Accurately weigh out approximately 2 g of sample into a flat-bottom flask, add 5 mL of acetylation reagent and 10 mL of pyridine, and attach an air condenser. (2) Heat the flask in a 100°C bath for 70 minutes, then allow it to cool, add 35 mL of toluene as a solvent from the top of the cooling tube and stir, then add 1 mL of distilled water and stir to decompose the acetic anhydride. Heat again in the bath for 10 minutes to complete the decomposition, then allow it to cool. (3) Wash the cooling tube with 5 mL of ethanol and remove it. Then, add 50 mL of pyridine as a solvent and stir. (4) Add 25 mL of 0.5 mol / L potassium hydroxide ethanol solution using a volumetric pipette. (5) Perform potentiometric titration with 0.5 mol / L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is the endpoint. (6) A blank test is carried out by carrying out steps (1) to (5) above without adding any sample. 3.Calculation The hydroxyl value is calculated according to the following formula. Hydroxyl value (mgKOH / g) = [(BC) x f x 28.05] / S + D Where: B: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test. C: Amount of 0.5 mol / L potassium hydroxide ethanol solution used for the sample (mL), f: Factor of 0.5 mol / L potassium hydroxide ethanol solution, S: weight of sample (g), D: acid number, 28.05: 1 / 2 the molecular weight of potassium hydroxide, 56.11. It is.

[0074] As the high hydroxyl value resin, those having a hydroxyl value of a predetermined value or more among the above-mentioned various tackifier resins can be used. The high hydroxyl value resin can be used alone or in combination of two or more. For example, a terpene phenol resin having a hydroxyl value of 50 mgKOH / g or more can be preferably used as the high hydroxyl value resin. The terpene phenol resin is advantageous because the hydroxyl value can be arbitrarily controlled by the copolymerization ratio of phenol.

[0075] Although not particularly limited, when a high hydroxyl value resin is used, the ratio of the high hydroxyl value resin (e.g., terpene phenol resin) to the entire tackifier resin contained in the adhesive layer may be about 5% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more. In some embodiments, the ratio of the high hydroxyl value resin to the entire tackifier resin is preferably, for example, about 30% by weight or more. This allows the effect of using a high hydroxyl value resin to be favorably exhibited, and while having impact resistance, the adhesive strength and repulsion resistance against sustained load in the Z-axis direction can be improved. In some preferred embodiments, the ratio of the high hydroxyl value resin to the entire tackifier resin is about 40% by weight or more, about 50% by weight or more (e.g., more than 50% by weight), about 60% by weight or more, about 70% by weight or more, about 80% by weight or more, or about 90% by weight or more. Substantially all of the tackifier resin (for example, about 95 to 100% by weight, or even about 99 to 100% by weight) may be a high hydroxyl value resin.

[0076] The softening point of the high hydroxyl value resin is not particularly limited. The softening point of the high hydroxyl value resin may be, for example, about 50°C or higher, and from the viewpoint of improving the cohesive force, a high hydroxyl value resin having a softening point (softening temperature) of about 80°C or higher may be preferably used. For example, a terpene phenol resin having such a softening point may be preferably used. The softening point of the high hydroxyl value resin may be about 100°C or higher, or about 110°C or higher. In some preferred embodiments, the softening point of the high hydroxyl value resin is about 120°C or higher, about 130°C or higher, or about 135°C or higher (or even about 140°C or higher). The upper limit of the softening point of the high hydroxyl value resin is not particularly limited. From the viewpoint of adhesion to the adherend, a high hydroxyl value resin having a softening point of about 200°C or lower (more preferably about 180°C or lower) may be preferably used. In some embodiments, the softening point of the high hydroxyl value resin may be less than 160°C. In some preferred embodiments, a high hydroxyl value resin having a softening point of less than 150° C. is used as the high hydroxyl value resin. By using a high hydroxyl value resin having a softening point of less than 150° C., a pressure-sensitive adhesive having both repulsion resistance and impact resistance and also excellent adhesive strength can be preferably obtained. The softening point of the high hydroxyl value resin may be 145° C. or less.

[0077] The softening point of the tackifier resin in this specification is defined as a value measured based on the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at a low temperature, and is carefully filled into a ring placed on a flat metal plate so as not to create bubbles. After cooling, the part that protrudes from the flat surface including the top end of the ring is cut off with a slightly heated knife. Next, a holder (ring stand) is placed in a glass container (heating bath) with a diameter of 85 mm or more and a height of 127 mm or more, and glycerin is poured to a depth of 90 mm or more. Next, a steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in glycerin without touching each other, and the temperature of the glycerin is kept at 20°C ± 5°C for 15 minutes. Next, a steel ball is placed in the center of the surface of the sample in the ring, and this is placed in a fixed position on the holder. Next, keeping the distance from the top of the ring to the glycerin surface at 50 mm, place a thermometer and align the center of the thermometer's mercury bulb to the same height as the center of the ring, then heat the container. The flame of the Bunsen burner used for heating should be midway between the center of the bottom of the container and its edge, and heating should be uniform. After heating begins and the temperature of the bath reaches 40°C, the rate of increase must be 5.0 ± 0.5°C per minute. The sample gradually softens and flows down the ring, and the temperature is read when it finally touches the bottom plate, and this is the softening point. The softening point is measured for two or more samples at the same time, and the average value is used.

[0078] The content of the high hydroxyl value resin in the adhesive layer is not particularly limited as long as the desired viscoelastic properties are satisfied. In some embodiments, the content of the high hydroxyl value resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, and is preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength. In some embodiments, the content of the high hydroxyl value resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, or may be 50 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the high hydroxyl value resin is 40 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 25 parts by weight or less, particularly preferably 20 parts by weight or less, and may be 18 parts by weight or less, relative to 100 parts by weight of the acrylic polymer.

[0079] Although not particularly limited, in some embodiments, the tackifier resin may include a tackifier resin having a hydroxyl value of less than 50 mgKOH / g. Hereinafter, a tackifier resin having a hydroxyl value of less than 50 mgKOH / g may be referred to as a "low hydroxyl value resin". Although not particularly limited, a low hydroxyl value resin is preferably used in an embodiment in which it is combined with a high hydroxyl value resin. The hydroxyl value of the low hydroxyl value resin may be less than 40 mgKOH / g. The lower limit of the hydroxyl value of the low hydroxyl value resin is 0 mgKOH / g or more, may be approximately 10 mgKOH / g or more, or may be approximately 15 mgKOH / g or more. As the low hydroxyl value resin, one type appropriately selected from the tackifier resins exemplified above having a hydroxyl value of less than 50 mgKOH / g may be used alone or in combination of two or more types. In some embodiments, the low hydroxyl value resin preferably includes a rosin-based tackifier resin. The low hydroxyl value resin may contain one type of rosin-based tackifying resin alone, or may contain two or more types of rosin-based tackifying resins in combination.

[0080] In some embodiments, the proportion of the rosin-based tackifier resin in the entire low hydroxyl value resin can be, for example, more than about 50% by weight, or may be about 65% by weight or more, about 75% by weight or more, 85% by weight or more, or 95% by weight or more. The technology disclosed herein can be preferably practiced in an embodiment in which substantially all of the low hydroxyl value resin (e.g., about 97% by weight or more, or 99% by weight or more, or even 100% by weight) is a rosin-based tackifier resin.

[0081] The softening point of the low hydroxyl value resin is not particularly limited. From the viewpoint of improving the cohesive force, a low hydroxyl value resin having a softening point (softening temperature) of about 80° C. or more can be preferably used. For example, a rosin-based tackifier resin having such a softening point can be preferably used. The softening point of the low hydroxyl value resin may be about 100° C. or more, about 110° C. or more, or about 120° C. or more. The upper limit of the softening point of the low hydroxyl value resin is not particularly limited. From the viewpoint of adhesion to the adherend, a low hydroxyl value resin having a softening point of about 200° C. or less (more preferably about 180° C. or less) can be preferably used. In some embodiments, the softening point of the low hydroxyl value resin may be about 160° C. or less, about 150° C. or less (for example, less than 150° C.), about 140° C. or less, or 130° C. or less.

[0082] In some embodiments, the tackifier resin is a tackifier resin T having a softening point of less than 150° C. L Tackifying resin T is used. L By using the tackifier resin T, it is possible to obtain a higher adhesive strength to various adherends. L The softening point of the tackifier resin T may be 145° C. or lower. L The lower limit of the softening point of the tackifier resin T is not particularly limited. LFrom the viewpoint of exerting an appropriate cohesive force, the softening point of the tackifier resin may be, for example, about 50° C. or higher, preferably about 80° C. or higher, more preferably about 100° C. or higher, and even more preferably about 110° C. or higher. In some preferred embodiments, the softening point of the tackifier resin is about 120° C. or higher, may be 130° C. or higher, or may be 135° C. or higher (or even about 140° C. or higher).

[0083] Tackifying resin T L As the tackifier resin, one type selected from the tackifier resins exemplified above having a softening point of less than 150° C. can be used alone or in combination of two or more types. L Preferably, the tackifier resin T comprises a terpene phenol resin. L may contain one type of terpene phenol resin alone, or may contain two or more types of terpene phenol resins in combination.

[0084] In some embodiments, tackifier resin T L The proportion of the terpene phenol resin in the total can be, for example, more than about 50% by weight, may be about 65% by weight or more, may be about 75% by weight or more, may be 85% by weight or more, or may be 95% by weight or more. L The present invention can be preferably implemented in an embodiment in which substantially all of the above (for example, approximately 97% by weight or more, or 99% by weight or more, or may be 100% by weight) is a terpene phenol resin.

[0085] In addition, tackifier resin T L The tackifier resin may or may not contain a tackifier resin having a softening point of less than 50° C., more preferably about 40° C. or less (typically a rosin-based, terpene-based, or hydrocarbon-based tackifier resin, for example, hydrogenated rosin methyl ester). Such a low-softening-point tackifier resin may be a liquid tackifier resin that is liquid at 30° C. The liquid tackifier resin may be used alone or in combination of two or more. The content of the liquid tackifier resin is determined based on the tackifier resin T from the viewpoint of cohesive strength, etc.L It can be about 30% by weight or less of the total, suitably about 10% by weight or less (for example, 0 to 10% by weight), may be about 2% by weight or less (0.5 to 2% by weight), or may be less than 1% by weight.

[0086] Tackifying resin T L The content of the tackifier resin T is not particularly limited, but in some embodiments, it is appropriate to set the content to about 70 parts by weight or less per 100 parts by weight of the acrylic polymer. L By limiting the amount of the tackifier resin T to a predetermined amount or less, it is possible to improve the impact resistance while maintaining good repulsion resistance and adhesive strength. L From the viewpoint of impact resistance and the like, the amount of the tackifier resin T used is suitably 60 parts by weight or less, preferably 50 parts by weight or less, more preferably 40 parts by weight or less, and may be 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, or 18 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. L The amount of is, for example, 1 part by weight or more, suitably 5 parts by weight or more, preferably 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably 12 parts by weight or more, and may be 15 parts by weight or more, based on 100 parts by weight of the acrylic polymer. The acrylic polymer containing heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with tackifier resins, so that desired properties can be achieved by incorporating an appropriate amount of tackifier resin.

[0087] In some embodiments, the adhesive layer comprises a tackifier resin T L and a tackifier resin T having a softening point of 150°C or higher (e.g., 150°C to 200°C). H The tackifier resin T may be used in combination with the above. H As the tackifier resin, one type may be used alone or two or more types may be used in combination from among the tackifier resins exemplified above that have a softening point of 150° C. or higher.

[0088] In some embodiments, tackifier resin T L It is preferable that the tackifier resin T accounts for more than 50% by weight of the total amount of the tackifier resin contained in the pressure-sensitive adhesive layer. L The effect of the inclusion of the tackifier resin T in the total amount of the tackifier resin contained in the adhesive layer is easily manifested. L The ratio of tackifier resin T L From the viewpoint of more effectively exerting the effect of use, the content of the tackifier resin in the pressure-sensitive adhesive layer is preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more, and may be 95% by weight or more, or may be 98% by weight or more. In some preferred embodiments, the tackifier resin contained in the pressure-sensitive adhesive layer is substantially tackifier resin T L In this embodiment, the tackifier resin T L The proportion is in the range of 99 to 100% by weight.

[0089] The softening point of the tackifier resin is not particularly limited. From the viewpoint of improving the cohesive force, a tackifier resin having a softening point (softening temperature) of about 80° C. or more can be preferably used. For example, a terpene-based tackifier resin (such as a terpene phenol resin) having such a softening point can be preferably used. The softening point of the tackifier resin may be about 100° C. or more, or about 110° C. or more. In some preferred embodiments, the softening point of the tackifier resin is about 120° C. or more, about 130° C. or more, or about 135° C. or more (or even about 140° C. or more). Among them, the use of a terpene phenol resin having the above softening point is preferred. The upper limit of the softening point of the tackifier resin is not particularly limited. From the viewpoint of adhesion to an adherend, a tackifier resin having a softening point of about 200° C. or less (more preferably about 180° C. or less) can be preferably used. In some embodiments, the softening point of the tackifier resin may be less than 160° C., or less than 150° C.

[0090] When the adhesive layer disclosed herein contains a tackifier resin, a tackifier resin derived from a plant (vegetable tackifier resin) may preferably act as the tackifier resin from the viewpoint of improving the biomass carbon ratio of the adhesive layer. Examples of vegetable tackifier resins include the above-mentioned rosin-based tackifier resin and terpene-based tackifier resin. The vegetable tackifier resin may be used alone or in combination of two or more. When the adhesive layer disclosed herein contains a tackifier resin, the proportion of the vegetable tackifier resin in the total amount of tackifier resins is preferably 30% by weight or more (e.g., 50% by weight or more, typically 80% by weight or more). In some embodiments, the proportion of the vegetable tackifier resin in the total amount of tackifier resins is 90% by weight or more (e.g., 95% by weight or more, typically 99 to 100% by weight). The technology disclosed herein may be preferably implemented in an embodiment that does not substantially contain tackifier resins other than vegetable tackifier resins.

[0091] The content of the tackifier resin in the adhesive layer is not particularly limited as long as the desired viscoelastic properties are satisfied. In some embodiments, the content of the tackifier resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, and is preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength. In some embodiments, the content of the tackifier resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, or may be 50 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the tackifier resin is 40 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 25 parts by weight or less, particularly preferably 20 parts by weight or less, and may be 18 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. The acrylic polymer containing heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with tackifier resins, and therefore desired properties can be achieved by incorporating an appropriate amount of tackifier resin.

[0092] (Acrylic Oligomer) In some preferred embodiments, the adhesive layer contains an acrylic oligomer. The inclusion of an acrylic oligomer can improve the adhesive strength of the adhesive. According to the technology disclosed herein, the adhesive layer has a predetermined viscoelastic property (specifically, 65°C storage modulus G' and -20°C tan δ) in a composition containing an acrylic oligomer, and can exhibit excellent Z-axis direction repulsion resistance. In particular, the effect of using an acrylic oligomer can be effectively exhibited in a composition containing a high molecular weight acrylic polymer.

[0093] The acrylic oligomer has a Tg of about 0°C or more and about 300°C or less, preferably about 20°C or more and about 300°C or less, and more preferably about 40°C or more and about 300°C or less. By having a Tg within the above range, the adhesive strength can be suitably improved. In some preferred embodiments, from the viewpoint of the cohesiveness of the pressure-sensitive adhesive, the Tg of the acrylic oligomer is about 30°C or more, more preferably about 50°C or more (e.g., about 60°C or more), and from the viewpoint of adhesiveness, it is preferably about 200°C or less, more preferably about 150°C or less, and even more preferably about 100°C or less (e.g., about 80°C or less).

[0094] In this specification, the Tg of an acrylic oligomer refers to the Tg calculated by the Fox formula based on the composition of the above-mentioned monomer components. The Fox formula is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 1 / Tg=Σ(Wi / Tgi) In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i.

[0095] The glass transition temperature of the homopolymer used to calculate Tg is to be a value listed in a publicly known document. For example, the values ​​listed in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989) are used. For monomers for which multiple values ​​are listed in this document, the highest value is used.

[0096] For monomers for which the glass transition temperature of the homopolymer is not described in the above literature, the value obtained by the following measurement method is used. Specifically, 100 parts by weight of monomer, 0.2 parts by weight of 2,2'-azobisisobutyronitrile, and 200 parts by weight of ethyl acetate as a polymerization solvent are charged into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser tube, and stirred for 1 hour while passing nitrogen gas through it. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. Then, the mixture is cooled to room temperature to obtain a homopolymer solution with a solid content concentration of 33% by weight. Then, the homopolymer solution is cast and applied onto a release liner, and dried to prepare a test sample (sheet-shaped homopolymer) with a thickness of about 2 mm. This test sample was punched out into a disk with a diameter of 7.9 mm, sandwiched between parallel plates, and the viscoelasticity was measured in shear mode using a viscoelasticity tester (TA Instruments Japan, model name "ARES") while applying a shear strain of 1 Hz at a temperature range of -70°C to 150°C and a heating rate of 5°C / min. The temperature corresponding to the peak top temperature of tan δ was taken as the Tg of the homopolymer.

[0097] The weight average molecular weight (Mw) of the acrylic oligomer can typically be about 1000 or more and less than about 30000, preferably about 1500 or more and less than about 20000, and more preferably about 2000 or more and less than about 10000. It is preferable that Mw is within the above range because good adhesive strength and repulsion resistance can be obtained. In some preferred embodiments, from the viewpoint of repulsion resistance against a sustained load in the Z-axis direction, Mw of the acrylic oligomer is about 2500 or more (e.g., about 3000 or more), and from the viewpoint of adhesiveness, it is preferably about 7000 or less, more preferably about 5000 or less (e.g., about 4500 or less, typically about 4000 or less). Mw of the acrylic oligomer can be measured by gel permeation chromatography (GPC) and calculated as a value in terms of standard polystyrene. Specifically, the measurement is performed using 2 columns of TSKgel GMH-H(20) on a Tosoh HPLC8020 with a tetrahydrofuran solvent at a flow rate of about 0.5 mL / min.

[0098] Examples of monomers constituting acrylic oligomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, Examples of the (meth)acrylate include alkyl (meth)acrylates such as butyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from alcohols derived from terpene compounds. These (meth)acrylates may be used alone or in combination of two or more.

[0099] The acrylic oligomer preferably contains, as a monomer unit, an acrylic monomer having a relatively bulky structure, typified by alkyl (meth)acrylates in which the alkyl group has a branched structure, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates), such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate; and (meth)acrylates having a cyclic structure, such as aryl (meth)acrylates, such as phenyl (meth)acrylate and benzyl (meth)acrylate, from the viewpoint of further improving the adhesiveness of the pressure-sensitive adhesive layer. In addition, when ultraviolet light is used in synthesizing an acrylic oligomer or preparing an adhesive layer, those having saturated bonds are preferred in that they are less likely to cause polymerization inhibition, and alkyl (meth)acrylates in which the alkyl group has a branched structure, or esters with alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) can be suitably used as monomers constituting the acrylic oligomer. The above-mentioned branched alkyl (meth)acrylates, alicyclic hydrocarbon group (meth)acrylates, and aryl (meth)acrylates all fall under the category of (meth)acrylate monomers in the technology disclosed herein. The alicyclic hydrocarbon group may be a saturated or unsaturated alicyclic hydrocarbon group.

[0100] The proportion of (meth)acrylate monomers (e.g., alicyclic hydrocarbon group-containing (meth)acrylates) in all monomer components constituting the acrylic oligomer is typically more than 50% by weight, preferably 60% by weight or more, and more preferably 70% by weight or more (e.g., 80% by weight or more, or even 90% by weight or more). In some preferred embodiments, the acrylic oligomer has a monomer composition consisting essentially of (meth)acrylate monomers.

[0101] As the constituent monomer component of the acrylic oligomer, in addition to the above (meth)acrylate monomer, a functional group-containing monomer can be used. Suitable examples of the functional group-containing monomer include monomers having a nitrogen atom-containing ring (typically a nitrogen atom-containing heterocycle) such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; amino group-containing monomers such as N,N-dimethylaminoethyl (meth)acrylate; amide group-containing monomers such as N,N-diethyl (meth)acrylamide; carboxy group-containing monomers such as AA and MAA; and hydroxy group-containing monomers such as 2-hydroxyethyl (meth)acrylate. These functional group-containing monomers can be used alone or in combination of two or more. Among them, carboxy group-containing monomers are preferred, and AA is particularly preferred.

[0102] When all monomer components constituting the acrylic oligomer contain a functional group-containing monomer, the proportion of the functional group-containing monomer (e.g., a carboxy group-containing monomer such as AA) in the above all monomer components is suitably about 1 wt % or more, preferably 2 wt % or more, more preferably 3 wt % or more, and is suitably about 15 wt % or less, preferably 10 wt % or less, more preferably 7 wt % or less.

[0103] The acrylic oligomer can be formed by polymerizing its constituent monomer components. The polymerization method and polymerization mode are not particularly limited, and various conventionally known polymerization methods (e.g., solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be used in an appropriate mode. The type of polymerization initiator (e.g., azo-based polymerization initiator such as AIBN) that can be used as necessary is generally as exemplified in the synthesis of the acrylic polymer, and the amount of the polymerization initiator and the amount of the chain transfer agent, such as n-dodecyl mercaptan, that is optionally used, are appropriately set based on technical common sense so as to obtain a desired molecular weight, so detailed explanations are omitted here.

[0104] From the above viewpoint, suitable acrylic oligomers include, for example, homopolymers of dicyclopentanyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), dicyclopentanyl acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA), as well as copolymers of CHMA and isobutyl methacrylate (IBMA), copolymers of CHMA and IBXMA, copolymers of CHMA and acryloylmorpholine (ACMO), copolymers of CHMA and diethylacrylamide (DEAA), copolymers of CHMA and AA, copolymers of ADA and methyl methacrylate (MMA), copolymers of DCPMA and IBXMA, and copolymers of DCPMA and MMA.

[0105] When the adhesive layer disclosed herein contains an acrylic oligomer, the content is suitably, for example, 0.1 parts by weight or more (for example, 1 part by weight or more) relative to 100 parts by weight of the acrylic polymer. From the viewpoint of better exerting the effect of the acrylic oligomer, the content of the acrylic oligomer is preferably about 5 parts by weight or more, more preferably about 8 parts by weight or more, even more preferably about 10 parts by weight or more, and particularly preferably about 12 parts by weight or more. In addition, from the viewpoint of compatibility with the acrylic polymer, the content of the acrylic oligomer is suitably less than 50 parts by weight (for example, less than 40 parts by weight) relative to 100 parts by weight of the acrylic polymer, preferably less than 30 parts by weight, more preferably about 25 parts by weight or less, and even more preferably about 20 parts by weight or less.

[0106] In some preferred embodiments, the adhesive layer contains one or more of the above-mentioned tackifier resins and one or more of the acrylic oligomers. In a composition containing an acrylic polymer containing heptyl acrylate as a monomer component, the combination of the tackifier resin and the acrylic oligomer can provide excellent adhesion while exhibiting highly excellent repulsion resistance against sustained load in the Z-axis direction even in a usage mode exposed to harsh conditions such as strong repulsion. In particular, in a composition containing a high molecular weight acrylic polymer, the effect of using the tackifier resin and the acrylic oligomer in combination can be effectively exerted. Content C of the acrylic oligomer in the adhesive layer O [wt%] Tackifier resin content C T [weight%] ratio (C T / C O ) is not particularly limited. T / C O ) is suitably, for example, 0.1 or more and 9 or less, preferably 0.25 or more and 4 or less, more preferably 0.4 or more and 2 or less, further preferably 0.7 or more and 1.5 or less, and may be 0.8 or more and 1.2 or less.

[0107] In some preferred embodiments, from the viewpoint of preferably exerting the effects of the technology disclosed herein, the combined amount (total amount) of tackifier resin and acrylic oligomer contained in the adhesive layer is suitably approximately 1 part by weight or more per 100 parts by weight of acrylic polymer, preferably approximately 10 parts by weight or more, more preferably approximately 16 parts by weight or more, even more preferably 20 parts by weight or more, and particularly preferably 25 parts by weight or more, and is suitably less than 120 parts by weight (for example, approximately 80 parts by weight or less), preferably less than 60 parts by weight, more preferably approximately 50 parts by weight or less, and even more preferably approximately 40 parts by weight or less.

[0108] In the technology disclosed herein, the total amount (total amount) of the acrylic polymer, tackifier resin and acrylic oligomer in the adhesive layer is appropriately set so as to achieve the effects of the technology disclosed herein, and is not limited to a specific range. In some preferred embodiments, the total amount (total amount) of the acrylic polymer, tackifier resin and acrylic oligomer contained in the adhesive layer is suitable to be more than 50% by weight, preferably about 70% by weight or more, more preferably about 90% by weight or more, even more preferably 95% by weight or more (for example, 95% by weight or more and 100% by weight or less, or less than 100% by weight), and may be 98% by weight or more, from the viewpoint of preferably achieving the effects of the technology disclosed herein.

[0109] (Crosslinking agent) In the technology disclosed herein, the adhesive composition used to form the adhesive layer may contain a crosslinking agent as necessary. The type of crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. The crosslinking agents may be used alone or in combination of two or more. Among them, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and melamine-based crosslinking agents are preferred, and isocyanate-based crosslinking agents and epoxy-based crosslinking agents are more preferred. By appropriately selecting and using a crosslinking agent, the adhesive layer can obtain cohesive force, improve repulsion resistance, and preferably achieve both repulsion resistance and impact resistance. The pressure-sensitive adhesive layer in the technology disclosed herein may contain the crosslinking agent in a form after crosslinking reaction, a form before crosslinking reaction, a form partially crosslinked, an intermediate or composite form thereof, etc. The crosslinking agent is typically contained in the pressure-sensitive adhesive layer exclusively in a form after crosslinking reaction.

[0110] As the isocyanate-based crosslinking agent, a polyfunctional isocyanate (which refers to a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. The isocyanate-based crosslinking agent can be used alone or in combination of two or more kinds.

[0111] Examples of the polyfunctional isocyanate include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates. Specific examples of aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

[0112] 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.

[0113] Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, Examples of the diisocyanate include 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

[0114] A preferred polyfunctional isocyanate is one having an average of three or more isocyanate groups per molecule. Such a trifunctional or higher isocyanate may be a multimer (typically a dimer or trimer) of a bifunctional or trifunctional or higher isocyanate, a derivative (for example, an addition reaction product of a polyhydric alcohol and two or more molecules of a polyfunctional isocyanate), a polymer, etc. For example, a dimer or trimer of diphenylmethane diisocyanate, an isocyanurate of hexamethylene diisocyanate (a trimer adduct of an isocyanurate structure), a reaction product of trimethylolpropane and tolylene diisocyanate, a reaction product of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and other polyfunctional isocyanates may be mentioned. Commercially available examples of such polyfunctional isocyanates include those manufactured by Asahi Kasei Chemicals Corporation under the trade names "Duranate TPA-100," and those manufactured by Tosoh Corporation under the trade names "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096."

[0115] The technology disclosed herein can be preferably implemented in an embodiment using at least an isocyanate-based crosslinking agent as a crosslinking agent. By using an isocyanate-based crosslinking agent, it is possible to preferably obtain repulsion resistance against a sustained load in the Z-axis direction.

[0116] The amount of the isocyanate crosslinking agent used is not particularly limited. For example, it can be about 0.1 parts by weight or more relative to 100 parts by weight of the acrylic polymer. From the viewpoint of achieving both cohesive strength and adhesion, the amount of the isocyanate crosslinking agent used relative to 100 parts by weight of the acrylic polymer is usually preferably about 0.3 parts by weight or more (for example, 0.5 parts by weight or more). In some preferred embodiments, the amount of the isocyanate crosslinking agent used relative to 100 parts by weight of the acrylic polymer is about 0.8 parts by weight or more, more preferably about 1.0 parts by weight or more, even more preferably about 1.2 parts by weight or more, and may be about 1.5 parts by weight or more. In addition, the amount of the isocyanate crosslinking agent used is suitably 10 parts by weight or less relative to 100 parts by weight of the acrylic polymer, preferably less than 5 parts by weight, more preferably less than 4.0 parts by weight, even more preferably less than 3.0 parts by weight, particularly preferably 2.5 parts by weight or less, and may be 2.0 parts by weight or less (for example, 1.7 parts by weight or less). By limiting the amount of isocyanate-based crosslinking agent used within a predetermined range, it is possible to obtain repulsion resistance against sustained load in the Z-axis direction based on the use of the isocyanate-based crosslinking agent, while preferably achieving both repulsion resistance and impact resistance.

[0117] As the epoxy crosslinking agent, a compound having two or more epoxy groups in one molecule can be used without any particular limitation. An epoxy crosslinking agent having 3 to 5 epoxy groups in one molecule is preferred. The epoxy crosslinking agent can be used alone or in combination of two or more kinds.

[0118] Non-limiting specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc. Commercially available epoxy crosslinking agents include Mitsubishi Gas Chemical Company's product names "TETRAD-C" and "TETRAD-X," DIC Corporation's product name "Epicron CR-5L," Nagase ChemteX Corporation's product name "Denacol EX-512," Nissan Chemical Industries' product name "TEPIC-G," etc.

[0119] The amount of the epoxy crosslinking agent used is not particularly limited. The amount of the epoxy crosslinking agent used can be, for example, more than 0 parts by weight and about 1 part by weight or less (typically about 0.001 to 1 part by weight) relative to 100 parts by weight of the acrylic polymer. From the viewpoint of favorably exerting the effect of improving the cohesive force, the amount of the epoxy crosslinking agent used is usually about 0.002 parts by weight or more relative to 100 parts by weight of the acrylic polymer, preferably about 0.005 parts by weight or more, and may be, for example, about 0.01 parts by weight or more. In addition, from the viewpoint of improving the adhesion to the adherend, the amount of the epoxy crosslinking agent used is suitable to be about 0.5 parts by weight or less relative to 100 parts by weight of the acrylic polymer, preferably about 0.2 parts by weight or less, more preferably about 0.1 parts by weight or less (for example, less than 0.1 parts by weight), and may be 0.07 parts by weight or less, or may be 0.04 parts by weight or less. In order to avoid a decrease in impact resistance due to excessive crosslinking, the amount of the epoxy crosslinking agent used is usually about 0.03 parts by weight or less, and preferably about 0.02 parts by weight or less, per 100 parts by weight of the acrylic polymer. By limiting the amount of the epoxy crosslinking agent used within a predetermined range, it is easy to maintain sufficient adhesive strength and also easy to obtain repulsion resistance against sustained load in the Z-axis direction.

[0120] In some preferred embodiments, the crosslinking agent is a combination of an isocyanate-based crosslinking agent and at least one crosslinking agent having a different type of crosslinking functional group from that of the isocyanate-based crosslinking agent. According to the technology disclosed herein, a crosslinking agent other than an isocyanate-based crosslinking agent (i.e., a crosslinking agent having a different type of crosslinking reactive group from that of an isocyanate-based crosslinking agent. Hereinafter, also referred to as a "non-isocyanate-based crosslinking agent") is used in combination with an isocyanate-based crosslinking agent, so that both repulsion resistance and impact resistance can be preferably achieved.

[0121] The type of non-isocyanate crosslinking agent that can be used in combination with the isocyanate crosslinking agent is not particularly limited, and can be appropriately selected from the above-mentioned crosslinking agents. The non-isocyanate crosslinking agent can be used alone or in combination of two or more. In some preferred embodiments, an epoxy crosslinking agent can be used as the non-isocyanate crosslinking agent. For example, by using an isocyanate crosslinking agent and an epoxy crosslinking agent in combination, it is possible to better achieve both repulsion resistance and impact resistance against sustained load in the Z-axis direction.

[0122] The relationship between the content of the isocyanate crosslinking agent and the content of the nonisocyanate crosslinking agent (preferably an epoxy crosslinking agent) is not particularly limited, and is appropriately set so as to satisfy the above-mentioned 65°C storage modulus and -20°C tan δ. The content of the isocyanate crosslinking agent is, for example, more than 1 time, preferably about 10 times or more, more preferably about 50 times or more, more preferably about 80 times or more, even more preferably about 100 times or more (e.g., more than 100 times), and particularly preferably about 120 times or more (e.g., about 140 times or more) relative to the content of the nonisocyanate crosslinking agent (preferably an epoxy crosslinking agent). Furthermore, from the viewpoint of optimally exerting the effect of using an isocyanate-based crosslinking agent in combination with a non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent), the content of the isocyanate-based crosslinking agent relative to the content of the non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent) is usually, for example, approximately 1000 times or less, appropriately approximately 500 times or less, preferably approximately 300 times or less, more preferably approximately 200 times or less, and even more preferably approximately 180 times or less (for example, approximately 160 times or less).

[0123] The content of the crosslinking agent in the adhesive composition disclosed herein (total amount of crosslinking agent) is not particularly limited. From the viewpoint of cohesion, the content of the crosslinking agent is usually about 0.001 parts by weight or more, and it is appropriate to set it to about 0.002 parts by weight or more relative to 100 parts by weight of acrylic polymer, and it is preferably about 0.005 parts by weight or more, more preferably about 0.01 parts by weight or more, even more preferably about 0.02 parts by weight or more, and particularly preferably about 0.03 parts by weight or more. In some embodiments, the content of the crosslinking agent relative to 100 parts by weight of acrylic polymer is about 0.1 parts by weight or more, more preferably about 0.5 parts by weight or more, even more preferably about 1.0 parts by weight or more, and it may be about 1.2 parts by weight or more, or it may be about 1.5 parts by weight or more. The content of the crosslinking agent in the pressure-sensitive adhesive composition is usually about 20 parts by weight or less, preferably about 15 parts by weight or less, and preferably about 10 parts by weight or less (for example, about 5 parts by weight or less) relative to 100 parts by weight of the acrylic polymer. In some embodiments, the content of the crosslinking agent relative to 100 parts by weight of the acrylic polymer is 4.0 parts by weight or less, more preferably 3.0 parts by weight or less, even more preferably 2.5 parts by weight or less, and may be 2.0 parts by weight or less (for example, less than 2.0 parts by weight), or may be 1.8 parts by weight or less. By appropriately setting the total amount of the crosslinking agent used within the above range, it is possible to preferably achieve both repulsion resistance and impact resistance.

[0124] (Other additives) In addition to the above-mentioned components, the adhesive composition may contain various additives, as necessary, that are common in the field of adhesives, such as leveling agents, crosslinking assistants, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antiaging agents, UV absorbers, antioxidants, rust inhibitors, light stabilizers, etc. As for such various additives, conventionally known ones can be used in the usual manner, and they do not particularly characterize the present invention, so detailed explanations will be omitted.

[0125] The adhesive layer (layer made of adhesive) disclosed herein may be an adhesive layer formed from an aqueous adhesive composition, a solvent-based adhesive composition, a hot melt-type adhesive composition, or an active energy ray curable adhesive composition. The aqueous adhesive composition refers to an adhesive composition in a form containing an adhesive (adhesive layer forming component) in a solvent (aqueous solvent) mainly composed of water, and typically includes those called water-dispersed adhesive compositions (compositions in a form in which at least a part of the adhesive is dispersed in water). The solvent-based adhesive composition refers to an adhesive composition in a form containing an adhesive in an organic solvent. As the organic solvent contained in the solvent-based adhesive composition, one or more of the organic solvents exemplified as those usable in the above-mentioned solution polymerization (toluene, ethyl acetate, etc.) can be used without particular limitation. The technology disclosed herein can be preferably implemented in an embodiment having an adhesive layer formed from a solvent-based adhesive composition from the viewpoint of adhesion properties, etc.

[0126] The adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method can be adopted in which an adhesive composition is applied to a surface having releasability (release surface) or a non-release surface and dried to form an adhesive layer. In the case of an adhesive sheet having a substrate, for example, a method (direct method) can be adopted in which an adhesive composition is directly applied (typically coated) to the substrate and dried to form an adhesive layer. In addition, a method (transfer method) can be adopted in which an adhesive composition is applied to a surface having releasability (release surface) and dried to form an adhesive layer on the surface, and the adhesive layer is transferred to a substrate. From the viewpoint of productivity, the transfer method is preferred. As the release surface, the surface of a release liner, the back surface of a substrate treated for release, etc. can be used. The adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and may be an adhesive layer formed in a regular or random pattern such as a dotted or striped pattern.

[0127] The pressure-sensitive adhesive composition can be applied using a conventionally known coater such as a gravure roll coater, a die coater, a bar coater, etc. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation or curtain coating. From the viewpoints of promoting the crosslinking reaction, improving production efficiency, etc., the pressure-sensitive adhesive composition is preferably dried under heating. The drying temperature can be, for example, about 40 to 150° C., and is usually preferably about 60 to 130° C. After drying the pressure-sensitive adhesive composition, aging may be further performed for the purpose of adjusting the component migration in the pressure-sensitive adhesive layer, advancing the crosslinking reaction, relaxing distortion that may exist in the pressure-sensitive adhesive layer, etc.

[0128] (Thickness) The thickness of the adhesive layer is not particularly limited, and a configuration having an adhesive layer having an appropriate thickness, for example, in the range of 0.1 to 500 μm, can be adopted depending on the application and purpose of use. In some embodiments, from the viewpoint of avoiding excessive thickness of the adhesive sheet, the thickness of the adhesive layer is usually about 100 μm or less, preferably about 70 μm or less, more preferably about 60 μm or less, and even more preferably about 50 μm or less. The thickness of the adhesive layer can be about 35 μm or less, for example, about 30 μm or less. An adhesive layer with a limited thickness can well meet the demand for thinning and weight reduction. In addition, generally, when the thickness of the adhesive layer is small, the impact resistance and adhesion to the adherend tend to be easily reduced, but according to the technology disclosed herein, a configuration having an adhesive layer with a limited thickness can realize sufficient impact resistance and adhesive strength. From the viewpoint of adhesion to the adherend, the lower limit of the thickness of the adhesive layer is, in some embodiments, appropriately about 0.5 μm or more, may be about 1 μm or more, and is advantageously about 3 μm or more, preferably about 10 μm or more, more preferably about 12 μm or more (e.g., more than 12 μm), even more preferably about 15 μm or more, for example, may be about 18 μm or more. In some preferred embodiments, the thickness of the adhesive layer is more than 20 μm, may be 24 μm or more, or may be 27 μm or more. The adhesive sheet disclosed herein may be an adhesive sheet having an adhesive layer of the above thickness on both sides of a substrate. In addition, in a substrate-attached double-sided adhesive sheet having a first adhesive layer and a second adhesive layer on each side of the substrate, the first adhesive layer and the second adhesive layer may have the same thickness or may have different thicknesses.

[0129] (Biomass carbon ratio) In some embodiments, the pressure-sensitive adhesive layer contains a biomass-derived material, and the biomass carbon ratio thereof may be a predetermined value or more. The biomass carbon ratio of the pressure-sensitive adhesive layer is, for example, 1% or more, and may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the pressure-sensitive adhesive means that the amount of fossil resource-based materials, such as petroleum, used is small. In this respect, the higher the biomass carbon ratio of the pressure-sensitive adhesive, the more preferable it is. For example, the biomass carbon ratio of the pressure-sensitive adhesive layer may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. The upper limit of the biomass carbon ratio is 100% by definition, and may be 99% or less, and from the viewpoint of material availability, it may be 95% or less, or 90% or less. From the viewpoint of easily exerting good adhesive performance, in some embodiments, the biomass carbon ratio of the pressure-sensitive adhesive layer may be, for example, 90% or less, 85% or less, or 80% or less.

[0130] <Base material> In an embodiment in which the adhesive sheet disclosed herein is in the form of a single-sided or double-sided adhesive type adhesive sheet with a substrate, the substrate supporting (backing) the adhesive layer may be a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, a composite of these, or the like. Examples of paper include Japanese paper, craft paper, glassine paper, wood-free paper, synthetic paper, topcoat paper, and the like. Examples of cloth include woven fabrics and nonwoven fabrics made by spinning various fibrous materials alone or in combination. Examples of the fibrous material include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber, and the like. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets, and the like. Examples of foam sheets include foamed polyolefin sheets, foamed polyurethane sheets, and foamed polychloroprene rubber sheets, and the like. Examples of metal foils include aluminum foil and copper foil, and the like. The substrate supporting the adhesive layer is also called the substrate layer in the adhesive sheet.

[0131] The substrate may be formed from a material derived from biomass or a material derived from non-biomass. From the viewpoint of producing a PSA sheet that takes into consideration the reduction of dependency on fossil resource-based materials, a substrate material derived from biomass (typically a resin film) is preferably used.

[0132] The substrate may be formed using a recyclable material or a recycled material (also called a recycled material). A resin film is preferably used as such a recycled material. Since a resin film (for example, a polyester film such as a PET film) is recyclable, it is possible to continuously reproduce the resin film after use, regardless of whether or not a plant-derived material is used, and the environmental load can be reduced by reusing the resin film after use. Such a recyclable resin film or recycled resin film is also called a recycled film. The recycled material (for example, a recycled film) may be formed from a biomass-derived material or a non-biomass-derived material.

[0133] As the substrate constituting the substrate-attached pressure-sensitive adhesive sheet, a substrate containing a resin film as the base film can be preferably used. The above-mentioned base film is typically a member capable of independently maintaining its shape (independent). The substrate in the technology disclosed herein may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the above-mentioned base film. Examples of the above-mentioned auxiliary layer include a colored layer, a reflective layer, an undercoat layer, an antistatic layer, etc., provided on the surface of the above-mentioned base film.

[0134] The resin film is a film containing a resin material as a main component (for example, a component contained in the resin film in an amount of more than 50% by weight). Examples of the resin film include polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester resin films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluororesin films; cellophane; and the like. The resin film may be a rubber film such as a natural rubber film or a butyl rubber film. Among them, from the viewpoint of handling and processability, polyester films are preferred, and PET films are particularly preferred.

[0135] In this specification, the term "resin film" refers to a typically non-porous sheet, and is a concept that is distinguished from so-called nonwoven fabric or woven fabric (in other words, a concept that excludes nonwoven fabric or woven fabric). The resin film may be any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film. In addition, such a resin film may be non-foamed. Here, a non-foamed resin film refers to a resin film that has not been intentionally treated to form a foam. Specifically, a non-foamed resin film may be a resin film with an expansion ratio of less than 1.1 times (for example, less than 1.05 times, typically less than 1.01 times).

[0136] The above-mentioned substrate (e.g., resin film) may contain various additives such as fillers (inorganic fillers, organic fillers, etc.), colorants, dispersants (surfactants, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, etc. The blending ratio of various additives is about less than 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight).

[0137] The substrate (e.g., resin film) may have a single-layer structure, or may have a multi-layer structure of two, three or more layers. From the viewpoint of shape stability, the substrate preferably has a single-layer structure. In the case of a multi-layer structure, at least one layer (preferably all layers) is preferably a layer having a continuous structure of the resin (e.g., polyester resin). The method for producing the substrate (typically a resin film) is not particularly limited and may be any conventionally known method. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting molding, and calendar roll molding may be appropriately used.

[0138] The surface of the substrate may be subjected to a conventionally known surface treatment such as a corona discharge treatment, a plasma treatment, an ultraviolet irradiation treatment, an acid treatment, an alkali treatment, application of a primer, etc. Such a surface treatment may be a treatment for improving the adhesion between the substrate and the pressure-sensitive adhesive layer, in other words, the anchoring property of the pressure-sensitive adhesive layer to the substrate.

[0139] In addition, when the technology disclosed herein is implemented in the form of a single-sided pressure-sensitive adhesive sheet with a substrate, the back surface of the substrate may be subjected to a release treatment as necessary. The release treatment may be, for example, a treatment in which a general silicone-based, long-chain alkyl-based, fluorine-based or other release treating agent is applied in the form of a thin film typically of about 0.01 μm to 1 μm (for example, 0.01 μm to 0.1 μm). By carrying out such a release treatment, it is possible to obtain an effect such as facilitating unwinding of a roll of the pressure-sensitive adhesive sheet.

[0140] In the pressure-sensitive adhesive sheet of an embodiment including a substrate, the thickness of the substrate is not particularly limited. In order to prevent the pressure-sensitive adhesive sheet from becoming excessively thick, the thickness of the substrate can be, for example, about 200 μm or less, preferably about 150 μm or less, more preferably about 100 μm or less. Depending on the purpose and mode of use of the pressure-sensitive adhesive sheet, the thickness of the substrate may be about 70 μm or less, about 50 μm or less, or about 30 μm or less (for example, about 25 μm or less). In some embodiments, the thickness of the substrate may be about 20 μm or less, about 15 μm or less, or about 10 μm or less (for example, about 5 μm or less). By reducing the thickness of the substrate, the thickness of the pressure-sensitive adhesive layer can be made larger even if the total thickness of the pressure-sensitive adhesive sheet is the same. This can be advantageous in terms of improving adhesion to the adherend or substrate. The lower limit of the substrate is not particularly limited. From the viewpoint of the handling property and processability of the pressure-sensitive adhesive sheet, the thickness of the substrate is usually about 0.5 μm or more (e.g., 1 μm or more), preferably about 2 μm or more, for example, about 6 μm or more. In some embodiments, the thickness of the substrate can be about 15 μm or more, and may be about 25 μm or more.

[0141] <Foam base material> In some other embodiments, a foam substrate is used as the substrate. The foam substrate disclosed herein is a substrate having a portion having bubbles (cell structure), and typically includes at least one layer of layered foam (foam layer). The foam substrate may be a substrate composed of one or more foam layers. The foam substrate may be, for example, a substrate substantially composed of only one or more foam layers. Although not particularly limited, a suitable example of a foam substrate in the technology disclosed herein is a foam substrate composed of a single (single) foam layer.

[0142] The thickness of the foam substrate is not particularly limited, and can be appropriately set depending on the strength, flexibility, and intended use of the pressure-sensitive adhesive sheet. From the viewpoint of thinning, the thickness of the foam substrate is usually 1 mm or less, appropriately 0.70 mm or less, preferably 0.40 mm or less, and more preferably 0.30 mm or less. From the viewpoint of processability, etc., the technology disclosed herein can be preferably implemented in an embodiment in which the thickness of the foam substrate is 0.25 mm or less (typically 0.18 mm or less, for example 0.16 mm or less). In addition, from the viewpoint of impact resistance, etc. of the pressure-sensitive adhesive sheet, the thickness of the foam substrate is usually 0.04 mm or more, appropriately 0.05 mm or more, preferably 0.06 mm or more, and more preferably 0.07 mm or more (for example 0.08 mm or more). The technology disclosed herein can be preferably implemented in an embodiment in which the thickness of the foam substrate is 0.10 mm or more (typically more than 0.10 mm, preferably 0.12 mm or more, for example 0.13 mm or more). Increasing the thickness of the foam substrate tends to improve impact resistance.

[0143] The density of the foam base material (meaning apparent density; hereinafter the same applies unless otherwise specified) is not particularly limited, and may be, for example, 0.1 to 0.9 g / cm 3 From the viewpoint of impact resistance, the density of the foam substrate may be 0.8 g / cm 3 The following is appropriate: 0.7g / cm 3 Less than (e.g. 0.6g / cm 3 In one embodiment, the density of the foam substrate is 0.5 g / cm 3 may be less than 0.4 g / cm 3 Less than (e.g. 0.5g / cm 3 From the viewpoint of impact resistance, the density of the foam substrate may be 0.12 g / cm or less. 3 More than 0.15 g / cm is preferable. 3 More preferably, 0.2 g / cm 3 or more (e.g. 0.3g / cm 3 In one embodiment, the density of the foam substrate is 0.4 g / cm or more. 3 or more, and 3 or more (e.g. 0.5g / cm 3and even 0.55 g / cm 3 The density (apparent density) of the foam base material can be measured in accordance with JIS K 6767.

[0144] The average bubble diameter of the foam base material is not particularly limited, but from the viewpoint of stress dispersion, it is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. The lower limit of the average bubble diameter is not particularly limited, but from the viewpoint of step conformability, it is usually appropriate to be 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more (for example, 50 μm or more). In one embodiment, the average bubble diameter may be 55 μm or more, or may be 60 μm or more. The average bubble diameter here refers to the average bubble diameter in terms of a true sphere obtained by observing the cross section of the foam base material with an electron microscope.

[0145] The cell structure of the foam constituting the foam base material disclosed herein is not particularly limited. The cell structure may be any of an open cell structure, a closed cell structure, and a semi-open and semi-closed cell structure. From the viewpoint of impact absorption, a closed cell structure and a semi-open and semi-closed cell structure are preferred.

[0146] 25% compressive strength of foam substrate C 25 is not particularly limited, and may be, for example, 20 kPa or more (typically 30 kPa or more, and even 40 kPa or more). 25 Generally, the pressure-sensitive adhesive sheet is suitably 250 kPa or more, and preferably 300 kPa or more (e.g., 400 kPa or more). A pressure-sensitive adhesive sheet having such a foam substrate can exhibit good durability against impacts such as dropping. For example, the pressure-sensitive adhesive sheet can be better prevented from being torn off by impact. 25 The upper limit of is not particularly limited, but is usually 1300 kPa or less (for example, 1200 kPa or less). 25may be 1000 kPa or less, 800 kPa or less, or even 600 kPa or less (for example, 500 kPa or less), or 360 kPa or less. 25 The pressure-sensitive adhesive sheet can be 20 kPa to 200 kPa (typically 30 kPa to 150 kPa, for example 40 kPa to 120 kPa). A pressure-sensitive adhesive sheet including such a foam substrate can have excellent cushioning properties. For example, the foam substrate can absorb the impact of a drop, thereby more effectively preventing the pressure-sensitive adhesive sheet from peeling off.

[0147] 25% compressive strength of foam substrate C 25 The compressive strength refers to the load (load at a compression rate of 25%) when a measurement sample, which is a 30 mm square cut of the foam substrate and stacked to a thickness of about 2 mm, is sandwiched between a pair of flat plates and compressed by a thickness equivalent to 25% of the original thickness. In other words, it refers to the load when the measurement sample is compressed to a thickness equivalent to 75% of the original thickness. The compressive strength is measured in accordance with JIS K 6767. As a specific measurement procedure, the measurement sample is set at the center of the pair of flat plates, and the gap between the flat plates is narrowed to continuously compress the sample to a predetermined compression rate, and the flat plates are stopped at that point and the load is measured after 10 seconds have passed. The compressive strength of the foam substrate can be controlled, for example, by the degree of crosslinking or density of the material constituting the foam substrate, the size or shape of the air bubbles, etc.

[0148] The tensile elongation of the foam substrate is not particularly limited. For example, a foam substrate having a tensile elongation in the machine direction (MD) of 200% to 800% (more preferably 400% to 600%) can be suitably used. Also, a foam substrate having a tensile elongation in the transverse direction (TD) of 50% to 800% (more preferably 200% to 500%) is preferred. The elongation of the foam substrate is measured in accordance with JIS K 6767. The elongation of the foam substrate can be controlled by, for example, the degree of crosslinking, apparent density (expansion ratio), etc.

[0149] The tensile strength of the foam substrate is not particularly limited. For example, a foam substrate having a tensile strength in the machine direction (MD) of 5 MPa to 35 MPa (preferably 10 MPa to 30 MPa) can be suitably used. A foam substrate having a tensile strength in the transverse direction (TD) of 1 MPa to 25 MPa (more preferably 5 MPa to 20 MPa) is preferred. The tensile strength of the foam substrate is measured in accordance with JIS K 6767. The tensile strength of the foam substrate can be controlled, for example, by the degree of crosslinking, apparent density (expansion ratio), etc.

[0150] The material of the foam substrate is not particularly limited. Usually, a foam substrate including a foam layer formed by a foam of a plastic material (plastic foam) is preferred. The plastic material (meaning including rubber material) for forming the plastic foam is not particularly limited and can be appropriately selected from known plastic materials. The plastic material can be used alone or in appropriate combination of two or more kinds.

[0151] Specific examples of plastic foams include polyolefin resin foams such as PE foams and PP foams; polyester resin foams such as PET foams, PEN foams, and PBT foams; polyvinyl chloride resin foams such as polyvinyl chloride foams; vinyl acetate resin foams; polyphenylene sulfide resin foams; amide resin foams such as aliphatic polyamide (nylon) resin foams and fully aromatic polyamide (aramid) resin foams; polyimide resin foams; polyether ether ketone (PEEK) foams; styrene resin foams such as polystyrene foams; urethane resin foams such as polyurethane resin foams; etc. In addition, rubber resin foams such as polychloroprene rubber foams may be used as the plastic foams.

[0152] A preferred example of the foam is a polyolefin resin foam (hereinafter also referred to as "polyolefin foam"). As the plastic material (i.e., polyolefin resin) constituting the polyolefin foam, various known or commonly used polyolefin resins can be used without any particular limitation. For example, PE such as low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), PP, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, etc. can be mentioned. Examples of LLDPE include Ziegler-Natta catalyst-based linear low density polyethylene, metallocene catalyst-based linear low density polyethylene, etc. Such polyolefin resins can be used alone or in appropriate combination of two or more kinds.

[0153] Suitable examples of the foam substrate in the technology disclosed herein include polyolefin foam substrates such as a PE foam substrate substantially composed of a PE resin foam and a PP foam substrate substantially composed of a PP resin foam from the viewpoint of impact resistance, waterproofness, dustproofness, etc. Here, the PE resin refers to a resin having ethylene as the main monomer (i.e., the main component of the monomers), and may include HDPE, LDPE, LLDPE, etc., as well as ethylene-propylene copolymers and ethylene-vinyl acetate copolymers in which the copolymerization ratio of ethylene exceeds 50% by weight. Similarly, the PP resin refers to a resin having propylene as the main monomer. As the foam substrate in the technology disclosed herein, a PE foam substrate may be preferably used.

[0154] The method for producing the plastic foam (typically a polyolefin foam) is not particularly limited, and various known methods can be appropriately adopted. For example, the plastic foam can be produced by a method including a molding step, a crosslinking step, and a foaming step of the plastic material or the plastic foam. In addition, a stretching step can be included as necessary. Examples of methods for crosslinking the plastic foam include a chemical crosslinking method using an organic peroxide or an ionizing radiation crosslinking method in which ionizing radiation is irradiated, and these methods can be used in combination. Examples of the ionizing radiation include electron beams, α-rays, β-rays, and γ-rays. The dose of ionizing radiation is not particularly limited, and can be set to an appropriate dose in consideration of the target physical properties (e.g., degree of crosslinking) of the foam base material.

[0155] The foam base material may contain various additives, such as fillers (inorganic fillers, organic fillers, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, flame retardants, and surfactants, as necessary.

[0156] The foam substrate in the technology disclosed herein may be colored black, white, etc., in order to impart desired design properties and optical properties (e.g., light blocking properties, light reflectivity, etc.) to a pressure-sensitive adhesive sheet including the foam substrate. For this coloring, known organic or inorganic colorants can be used alone or in appropriate combination of two or more.

[0157] The surface of the foam substrate may be subjected to an appropriate surface treatment as necessary. The surface treatment may be, for example, a chemical or physical treatment for enhancing adhesion to an adjacent material (e.g., a pressure-sensitive adhesive layer). Examples of such surface treatments include corona discharge treatment, chromic acid treatment, ozone exposure, flame exposure, ultraviolet irradiation treatment, plasma treatment, application of a primer, and the like.

[0158] <Release liner> In the technology disclosed herein, a release liner can be used during the formation of the adhesive layer, the preparation of the adhesive sheet, the storage, distribution, and shaping of the adhesive sheet before use. The release liner is not particularly limited, and for example, a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or a release liner made of a fluorine-based polymer (polytetrafluoroethylene, etc.) can be used. The release treatment layer can be formed by surface treating the liner substrate with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. As the liner substrate, a substrate formed using a biomass-derived material or a recycled material (recycled film, etc.) can be preferably used, similar to the substrate of the above-mentioned adhesive sheet.

[0159] <Total thickness of adhesive sheet> The total thickness of the adhesive sheet disclosed herein (including the adhesive layer and may further include a base layer, but not including a release liner) is not particularly limited. The total thickness of the adhesive sheet is, for example, about 1 mm or less, may be about 500 μm or less, or may be about 300 μm or less, and from the viewpoint of thinning, is appropriately about 200 μm or less, and may be about 150 μm or less (for example, about 100 μm or less). In some preferred embodiments, the thickness of the adhesive sheet can be about 50 μm or less, and may be, for example, about 35 μm or less. The lower limit of the thickness of the adhesive sheet is, for example, 0.1 μm or more (for example, 0.5 μm or more), is appropriately about 3 μm or more, preferably about 10 μm or more, more preferably about 15 μm or more, may be about 50 μm or more, or may be about 100 μm or more. An adhesive sheet having a thickness of a predetermined value or more tends to easily obtain adhesion to an adherend and also tends to be excellent in handleability. In addition, in the case of a substrate-less pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer is the total thickness of the pressure-sensitive adhesive sheet.

[0160] <Characteristics of adhesive sheet> In some embodiments, the adhesive sheet preferably has a 180-degree peel strength (adhesive strength to SUS) against a stainless steel plate of about 15 N / 25 mm or more (e.g., 17 N / 25 mm or more). An adhesive sheet exhibiting such adhesive strength to SUS can exhibit excellent adhesive strength. The adhesive strength to SUS is more preferably about 20 N / 25 mm or more, even more preferably about 23 N / 25 mm or more, and particularly preferably 25 N / 25 mm or more (e.g., 26 N / 25 mm or more). The upper limit of the adhesive strength to SUS is not particularly limited, but from the viewpoint of compatibility with other adhesive properties such as repulsion resistance, it may usually be, for example, about 50 N / 25 mm or less. The adhesive strength to SUS is measured using a SUS plate as an adherend under conditions of 23°C, 50% RH, a pulling speed of 300 mm / min, and a peel angle of 180°. More specifically, it is measured by the method described in the Examples below.

[0161] In addition, the adhesive sheet disclosed herein preferably has a lift height of 2.0 mm or less at the end of a repulsion resistance evaluation test performed by the following method. An adhesive sheet satisfying the above characteristics has particularly excellent repulsion resistance against a peel load substantially only in the thickness direction (Z-axis direction) of the adhesive sheet, and is particularly unlikely to peel against a sustained peel load in that direction. In addition, even when an adhesive sheet attached to an adherend (e.g., a portable electronic device or a module that is a component thereof) is exposed to high temperature and high humidity conditions during storage, it can exhibit stable repulsion resistance. The above-mentioned lift height is suitably 1.5 mm or less, preferably 1.0 mm or less, more preferably 0.7 mm or less, even more preferably 0.5 mm or less, and particularly preferably 0.4 mm or less. The above-mentioned lift height is a height including the thickness of the adhesive sheet (30 μm in the examples described later).

[0162] [Rebound resistance evaluation test] A polyethylene terephthalate (PET) film with a length of 70 mm, a width of 10 mm, and a thickness of 75 μm is fixed at one end of the longitudinal direction of the PET film to the lower surface of a polycarbonate plate with a length of 30 mm, a width of 10 mm, and a thickness of 2 mm. Next, the PET film is folded along the longitudinal direction, and the other end of the folded PET film in the longitudinal direction is fixed to the upper surface of the polycarbonate plate with an adhesive sheet with an adhesive area of ​​3 mm × 10 mm. This state is maintained under the condition of 65 ° C, 90% RH, and 72 hours (repulsion resistance evaluation test). Then, after 72 hours (at the end of the test), the floating height [mm] of the adhesive sheet from the polycarbonate plate is measured. More specifically, the repulsion resistance evaluation test is carried out by the method described in the Z-axis direction repulsion resistance test in the Examples below.

[0163] The adhesive sheet disclosed herein has an impact adhesive strength of 0.3 J / cm in an impact resistance test carried out in accordance with JIS K6855. 2 It is preferable that the adhesive sheet has a shear strength of 0.35 J / cm or more. An adhesive sheet that satisfies this characteristic can be a bonding means having excellent durability against impact in the shear direction. Therefore, it can be preferably used as a member fixing means for mobile electronic devices that are expected to be exposed to impact due to dropping or collision, for example. According to the technology disclosed herein, 2 or more (more preferably 0.40 J / cm 2 More preferably, 0.45 J / cm 2 More than 0.50 J / cm 2 The upper limit of the impact adhesive strength is not particularly limited, and may be, for example, 3.00 J / cm. 2 From the viewpoint of easily achieving a high level of compatibility with repulsion resistance, the impact adhesive strength may be, for example, 1.00 J / cm 2 may be less than or equal to 0.80 J / cm 2 Less than 0.60J / cm is acceptable. 2 More specifically, the impact resistance test is carried out by the method described in the impact resistance test in the Examples below.

[0164] In some embodiments, the pressure-sensitive adhesive sheet contains a biomass-derived material, and the biomass carbon ratio thereof may be a predetermined value or more. The biomass carbon ratio of the pressure-sensitive adhesive sheet is, for example, 1% or more, and may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the pressure-sensitive adhesive sheet means that the amount of fossil resource-based materials, such as petroleum, used is small. In this respect, the higher the biomass carbon ratio of the pressure-sensitive adhesive sheet, the more preferable it is. For example, the biomass carbon ratio of the pressure-sensitive adhesive sheet may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. The upper limit of the biomass carbon ratio is 100% by definition, and may be 99% or less, and from the viewpoint of material availability, it may be 95% or less, or 90% or less. From the viewpoint of easily exerting good adhesive performance, in some embodiments, the biomass carbon ratio of the pressure-sensitive adhesive sheet may be, for example, 90% or less, 85% or less, or 80% or less.

[0165] <Application> The use of the adhesive sheet disclosed herein is not particularly limited, and it can be used for various applications.The adhesive sheet disclosed herein can achieve both repulsion resistance and impact resistance, so it is suitable for bonding and fixing members in applications that require high repulsion resistance and impact resistance.For example, it can be preferably used for fixing members in various portable devices (portable devices). Non-limiting examples of the portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear-type devices worn on the wrist like a wristwatch, modular-type devices worn on a part of the body with a clip or strap, eyewear-type devices including glasses-type devices (monocular and binocular types, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. in the form of accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio devices (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, electronic books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" does not mean that it is sufficient to simply be portable, but rather that it has a level of portability that allows an individual (average adult) to carry it relatively easily.

[0166] The adhesive sheet (typically a double-sided adhesive sheet) disclosed herein can be used in the form of a bonding material processed into various shapes to fix members constituting the above-mentioned portable electronic device. In particular, it can be preferably used in a portable electronic device having a liquid crystal display device. For example, the adhesive sheet disclosed herein is preferably used for fixing an elastic adherend in an electronic device (typically a portable electronic device such as a smartphone) having a display unit (which may be the display unit of a liquid crystal display device) such as a touch panel display, in which an elastic member such as an FPC is folded and accommodated in the internal space for the purpose of enlarging the screen, etc. By using the adhesive sheet disclosed herein, the elastic adherend can be stably fixed in a folded state, and the fixed state can be maintained continuously. As a result, the elastic member accommodated in a limited internal space in the portable electronic device in a folded state can be accurately positioned by the adhesive sheet disclosed herein and maintained in a stably fixed state. In addition, examples of materials to be placed inside the portable electronic device as described above include polar and rigid materials such as polycarbonate and polyimide. For this type of material (polar and rigid resin material), the adhesive sheet disclosed herein can preferably exhibit repulsion resistance against sustained load in the Z-axis direction. Alternatively, the adhesive sheet disclosed herein is preferably used in a portable electronic device for fixing a member such as a cover glass having a three-dimensional shape (typically a curved shape) constituting the portable electronic device. The adhesive sheet used for fixing such a member having a three-dimensional surface shape tends to be subjected to a relatively large sustained load in the Z-axis direction. By using the adhesive sheet disclosed herein, even a member having the above-mentioned three-dimensional shape can be stably fixed.

[0167] The development of electronic devices (typically mobile electronic devices such as smartphones and tablet computers) having a display unit such as the above-mentioned touch panel display (which may be a display unit of a liquid crystal display device) has been moving toward both larger screens and higher functionality, particularly in recent years. For larger screens, measures have been taken such as folding and storing elastic members such as the above-mentioned FPCs in the internal space. On the other hand, for higher functionality, new functions such as pressure-sensitive sensors with higher accuracy of pressure sensing performance and face recognition unlocking functions have been implemented, and in order to realize higher performance and higher quality products, it is essential to highly integrate circuits such as FPCs that support these functions. As a means of highly integrating circuits, for example, double-sided FPCs and multi-layer FPCs can be mentioned, but both of these are aimed at increasing the rigidity of the FPC, and it is expected that the required characteristic will be improved repulsion resistance against continuous load in the Z-axis direction, as evaluated in the Z-axis repulsion resistance test described below. Adhesive sheets according to preferred embodiments of the technology disclosed herein can exhibit excellent repulsion resistance under harsh high temperature and high humidity conditions (strong repulsion conditions), such as in the Z-axis repulsion resistance test described below, and are therefore well suited to and preferably used in the above-mentioned next-generation electronic devices equipped with touch panel displays (typically, portable electronic devices equipped with touch panel displays such as smartphones).

[0168] Although not particularly limited, in some embodiments, the pressure-sensitive 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 is preferably used in electronic devices (typically mobile electronic devices) equipped with organic EL displays or liquid crystal displays.

[0169] FIG. 4 is a schematic example of a portable electronic device (smartphone) using the adhesive sheet disclosed herein. As shown in FIG. 4, a battery (heat generating element) 540 is built into a housing 520 of the portable electronic device 500. The portable electronic device 500 is also configured to include an adhesive sheet 550. In this configuration example, the adhesive sheet 550 has the form of a double-sided adhesive sheet (double-sided adhesive sheet) that fixes the members that constitute the portable electronic device 500. The portable electronic device 500 is provided with a touch panel 570 whose display unit also functions as an input unit. The adhesive sheet disclosed herein is preferably used as a component (member joining means) of the portable electronic device described above.

[0170] In addition, in some embodiments, the PSA sheet disclosed herein may have a PSA layer containing an acrylic polymer with a high biomass carbon ratio, and therefore may be used as a substitute for a conventional acrylic PSA in various applications in which the acrylic PSA (i.e., an acrylic PSA with a low biomass carbon ratio) is used, thereby contributing to reducing dependency on fossil resource-based materials. The PSA sheet disclosed herein may be preferably used as a PSA sheet with reduced dependency on fossil resource-based materials.

[0171] The matters disclosed by this specification include the following: [1] A portable electronic device, an adhesive sheet is bonded to a member constituting the portable electronic device, The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of a monomer component including heptyl acrylate, The pressure-sensitive adhesive layer has a storage modulus G' of 20,000 Pa or more at 65°C and a tan δ of 0.3 or more at -20°C, wherein the tan δ refers to the ratio (G" / G') of the loss modulus G" to the storage modulus G' of the pressure-sensitive adhesive layer. [2] The portable electronic device according to [1] above, wherein the weight average molecular weight of the acrylic polymer is 700,000 or more. [3] The mobile electronic device according to the above [1] or [2], wherein the pressure-sensitive adhesive layer has a glass transition temperature within the range of −15° C. to 15° C., and the glass transition temperature of the pressure-sensitive adhesive layer refers to a glass transition temperature determined from a peak temperature of tan δ in a dynamic viscoelasticity measurement. [4] The portable electronic device according to any one of the above [1] to [3], wherein the pressure-sensitive adhesive layer further contains a tackifier resin. [5] The mobile electronic device according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive layer contains at least one selected from a rosin-based tackifier resin and a terpene-based tackifier resin. [6] The portable electronic device according to any one of the above [1] to [5], wherein the content of the tackifier resin in the pressure-sensitive adhesive layer is 70 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. [7] The portable electronic device according to any one of the above [1] to [6], wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer. [8] The mobile electronic device according to any one of the above [1] to [7], wherein the adhesive composition for forming the adhesive layer contains at least one selected from an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent. [9] The portable electronic device according to any one of the above [1] to [8], wherein the pressure-sensitive adhesive sheet has a 180 degree peel strength against a stainless steel plate of 20 N / 25 mm or more.

[0172]

[11] A pressure-sensitive adhesive layer comprising an acrylic polymer, The acrylic polymer is a polymer of a monomer component including heptyl acrylate, The pressure-sensitive adhesive layer has a storage modulus G' of 20,000 Pa or more at 65°C and a tan δ of 0.3 or more at -20°C, wherein the tan δ refers to the ratio (G" / G') of the loss modulus G" to the storage modulus G' of the pressure-sensitive adhesive layer.

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

[11] , wherein the weight average molecular weight of the acrylic polymer is 700,000 or more.

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

[11] or

[12] , wherein the pressure-sensitive adhesive layer has a glass transition temperature within the range of -15°C to 15°C, and the glass transition temperature of the pressure-sensitive adhesive layer refers to a glass transition temperature determined from a peak temperature of tan δ in a dynamic viscoelasticity measurement.

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

[11] to

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

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

[11] to

[14] , wherein the pressure-sensitive adhesive layer contains at least one selected from a rosin-based tackifying resin and a terpene-based tackifying resin.

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

[11] to

[15] , wherein the content of the tackifier resin in the pressure-sensitive adhesive layer is 70 parts by weight or less per 100 parts by weight of the acrylic polymer.

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

[11] to

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

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

[11] to

[17] , wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains at least one selected from an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent.

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

[11] to

[18] , which has a 180 degree peel strength against a stainless steel plate of 20 N / 25 mm or more.

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

[11] to

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

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

[11] to

[20] above. EXAMPLES

[0173] Some examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0174] <Example 1> (Synthesis of acrylic polymers) In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel, 94 parts of n-heptyl acrylate (n-HpA) and 6 parts of acrylic acid (AA) as monomer components, and ethyl acetate as a polymerization solvent were charged, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and solution polymerization was performed at 60°C to 70°C for 8 hours to obtain a solution of an acrylic polymer. The weight average molecular weight (Mw) of this acrylic polymer was 1.2 million. The Mw was adjusted by adjusting the concentration of the monomer components during polymerization. The above n-HpA is a compound synthesized using heptyl alcohol derived from biomass and having a heptyl group derived from biomass at the ester end.

[0175] (Preparation of Pressure-Sensitive Adhesive Composition) To the acrylic polymer solution obtained above, 30 parts of terpene phenol A (trade name "YS Polystar T-115", terpene phenol resin manufactured by Yasuhara Chemical Co., Ltd., softening point about 115°C, hydroxyl value 30-60mgKOH / g) as a tackifier resin, 3 parts (solid content basis) of an isocyanate crosslinking agent (trade name "Coronate L", 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation), and 0.03 parts of an epoxy crosslinking agent (trade name "TETRAD-C", 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, manufactured by Mitsubishi Gas Chemical Co., Ltd.) were added per 100 parts of the acrylic polymer contained in the solution, and the mixture was stirred to prepare a pressure-sensitive adhesive composition according to this example.

[0176] (Preparation of adhesive sheet) The obtained adhesive composition was applied to the release surface of a 38 μm thick polyester release film (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) and dried at 100° C. for 2 minutes to form an adhesive layer having a thickness of 30 μm. The release surface of a 25 μm thick polyester release film (trade name "Diafoil MRF", thickness 25 μm, manufactured by Mitsubishi Chemical Corporation) was attached to this adhesive layer. In this way, a substrateless double-sided adhesive sheet having a thickness of 30 μm, both sides of which were protected by the above two polyester release films, was obtained.

[0177] <Examples 2 to 6 and Comparative Examples 1 to 4> The pressure-sensitive adhesive compositions of each example were prepared in the same manner as in Example 1, except that the monomer composition of the acrylic polymer, Mw, type and amount of tackifier resin, amount of acrylic oligomer, and type and amount of crosslinker were changed as shown in Table 1, and the resulting pressure-sensitive adhesive compositions were used to produce substrate-less double-sided adhesive sheets (thickness 30 μm) of each example in the same manner as in Example 1. The Mw of the acrylic polymer was adjusted by adjusting the concentration of the monomer components during polymerization. In Table 1, 2EHA stands for 2-ethylhexyl acrylate, BA stands for n-butyl acrylate, 4HBA stands for 4-hydroxybutyl acrylate, and HEA stands for hydroxyethyl acrylate. Terpene phenol B is a product of Yasuhara Chemical Co., Ltd. under the trade name "YS Polystar S-145" (a terpene phenol resin with a softening point of about 145°C and a hydroxyl value of 70 to 110 mgKOH / g), and rosin ester is a product of Arakawa Chemical Industries Co., Ltd. under the trade name "Pensel D125" (a polymerized rosin ester with a softening point of 125°C and a hydroxyl value of 32 mgKOH / g). The acrylic oligomer used was prepared by the following method. Specifically, 95 parts of cyclohexyl methacrylate (CHMA), 5 parts of AA, 10 parts of AIBN as a polymerization initiator, and ethyl acetate as a polymerization solvent were charged into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel, and the mixture was stirred in a nitrogen stream for 1 hour to remove oxygen from the polymerization system. The mixture was then heated to 85°C and reacted for 5 hours to obtain an acrylic oligomer with a solid content of 50%. The Mw of the obtained acrylic oligomer was 3600.

[0178] <Evaluation method> [Adhesion to SUS] Under a measurement environment of 23°C and 50% RH, a PET film having a thickness of 50 μm was attached to one adhesive surface of a pressure sensitive adhesive sheet (double-sided pressure sensitive adhesive sheet) to provide a backing, and the sheet was cut to a size of 25 mm wide and 100 mm long to prepare a measurement sample. Under an environment of 23°C and 50% RH, the other adhesive surface of the measurement sample was pressed against the surface of a stainless steel plate (SUS304BA plate) washed with ethyl acetate by rolling a 2 kg roller back and forth once. After leaving the sample in the same environment for 72 hours, a universal tensile compression tester was used to measure the peel strength (adhesive strength to SUS) [N / 25 mm] in accordance with JIS Z 0237:2000 at a tensile speed of 300 mm / min and a peel angle of 180 degrees. In the measurement of the peel strength, a universal tensile compression tester "Tension and compression tester, TG-1kN" manufactured by Minebea Co., Ltd. or an equivalent product was used as the universal tensile compression tester. When the above peel strength measurement is performed on a single-sided pressure sensitive adhesive sheet, it is not necessary to back the sheet with a PET film. When the substrate is thin (for example, when the substrate is 25 μm or less), the substrate may be backed with a PET film.

[0179] [Impact resistance test (pendulum)] Impact resistance (impact adhesive strength) [J / cm2] was measured using a pendulum-type adhesive shear impact tester based on JIS K6855 (corresponding to the international standard ISO 9653). 2The adhesive sheet pieces obtained by cutting the substrate-less double-sided adhesive sheet according to each example into 10 mm squares were used as test pieces, and a 10 mm square, 5 mm thick stainless steel (SUS304) plate was pressure-bonded to another stainless steel plate (SUS304 plate) with a load of 35 N for 10 seconds, and then cured at room temperature for 48 hours. The measurements were performed under the conditions of a hammer energy of 2.75 J and a hammer speed (impact speed) of 3.5 m / sec.

[0180] [Z-axis repulsion resistance test (high temperature and humidity conditions)] 5(a), a polycarbonate (PC) plate 50 measuring 30 mm in length, 10 mm in width, and 2 mm in thickness, and a PET film 60 measuring 70 mm in length, 10 mm in width, and 75 μm in thickness were prepared, and the PC plate 50 and the PET film 60 were overlapped so that one end of each was aligned in the longitudinal direction, and the PC plate 50 and the PET film 60 were fixed together in a state in which the remaining part of the PET film 60 protruded from the other end of the PC plate 50. A commercially available double-sided adhesive tape (manufactured by Nitto Denko Corporation, "No. 5000NS") was used for the above fixation. The adhesive sheet according to each example, both adhesive surfaces of which were protected by two release liners, was cut to a size of 3 mm in width and 10 mm in length to prepare an adhesive sheet sample piece 70. The surface of the PC board 50 opposite to the fixing surface of the PET film was placed on top, one release liner was peeled off from the adhesive sheet sample piece 70, and the width direction of the PC board 50 and the length direction of the adhesive sheet sample piece 70 were aligned, and the adhesive sheet sample piece 70 was attached and fixed to the upper surface of the PC board 50 such that both ends in the width direction of the adhesive sheet sample piece 70 were located on lines 7 mm and 10 mm from the other end on the upper surface of the PC board 50. The above fixing was performed by moving a 2 kg roller back and forth once on the upper surface of the adhesive sheet sample piece 70 protected by the other release liner. Next, in an environment of 23°C and 50% RH, the other release liner of the adhesive sheet sample piece 70 attached to the PC plate 50 was peeled off, and as shown in (b) of Fig. 5, the protruding portion (length 40 mm) of the PET film 60 fixed to the PC plate 50 from the PC plate 50 was folded back to the PC plate 50 side, and the adhesive sheet sample piece 70 and the other end (free end) of the PET film 60 were aligned, and a 0.1 kg roller was moved back and forth once from above the PET film 60, so that the other end of the folded PET film 60 was fixed to the upper surface of the PC plate 50 via the adhesive sheet sample piece 70, and this was exposed to an environment of 65°C and 90% RH. After being exposed to the same environment for 72 hours, it was confirmed whether the adhesive sheet sample piece 70 and the PET film 60 maintained their adhesion state, and the case where the PET film 60 peeled off as shown in (c) of Fig. 5 was judged to be "peeling". When the PET film 60 was held, the floating height [mm] of the PET film 60 from the adhesive sheet sample piece 70 was measured using a microscope. The measurement was performed three times, and the minimum value was recorded. Note that the floating height includes the thickness of the adhesive sheet sample piece 70. Unlike conventional repulsion resistance evaluations, this evaluation method makes it possible to evaluate repulsion resistance against a peel load that is essentially only in the thickness direction of the adhesive sheet (Z-axis direction) under harsh conditions of high temperature and high humidity of 65°C and 90% RH, and furthermore, by observing over time, it is possible to evaluate sustained repulsion resistance.

[0181] Table 1 shows the outline of the pressure-sensitive adhesive sheet and the evaluation results of each example.

[0182] [Table 1]

[0183] As shown in Table 1, the pressure-sensitive adhesives according to Examples 1 to 6 contained an acrylic polymer containing heptyl acrylate as a monomer component, and had a storage modulus G' of 20,000 Pa or more at 65° C. and a tan δ of 0.3 or more at −20° C. The pressure-sensitive adhesive sheets according to Examples 1 to 6 had an impact resistance test result of 0.3 J / cm 2The storage modulus G' of the adhesive of Comparative Examples 3 and 4 was also less than 20,000 Pa at 65°C, and the adhesive peeled off in the Z-axis direction repulsion resistance test (Comparative Example 3) or the lift height in the Z-axis direction repulsion resistance test was greater than those of Examples 1 to 6. The adhesive of Comparative Example 2 did not contain heptyl acrylate and contained an acrylic polymer containing BA as the main monomer, had a tan δ of less than 0.3 at -20°C, and had a lower impact resistance test result than those of Examples 1 to 6.

[0184] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above. [Explanation of symbols]

[0185] 1,2,3 Adhesive sheet 10 Supporting base material 10A front page 10B Second side (back) 21 Adhesive layer (first adhesive layer) 21A Adhesive surface (first adhesive surface) 21B Second adhesive surface 22 Adhesive layer (second adhesive layer) 22A Adhesive surface (second adhesive surface) 31,32 Release liner 100,200,300 Adhesive sheet with release liner

Claims

1. It has an adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of a monomer component containing 80% by weight or more of heptyl acrylate, The monomer component contains a carboxyl group-containing monomer in a proportion of 2% by weight or more and 15% by weight or less, The monomer component either does not contain a hydroxyl group-containing monomer or contains the hydroxyl group-containing monomer in a proportion of less than 0.1% by weight, The weight average molecular weight of the acrylic polymer is 700,000 or more, The adhesive layer further contains a tackifier resin, The adhesive composition used for forming the adhesive layer contains a crosslinking agent, The adhesive layer has a storage elastic modulus G' at 65°C of 20,000 Pa or more and a tanδ at -20°C of 0.3 or more and 1.0 or less, where the tanδ refers to the ratio (G" / G') of the loss elastic modulus G" to the storage elastic modulus G' of the adhesive layer, an adhesive sheet.

2. The adhesive sheet according to claim 1, which is a double-sided adhesive sheet without a base material or an adhesive sheet with a base material containing a base material having a thickness of 30 μm or less.

3. The adhesive sheet according to claim 1 or 2, wherein the total thickness of the adhesive sheet is 50 μm or less.

4. The glass transition temperature of the adhesive layer is in the range of -15°C to 15°C, where the glass transition temperature of the adhesive layer refers to the glass transition temperature determined from the peak temperature of tanδ in dynamic viscoelasticity measurement, the adhesive sheet according to claim 1 or 2.

5. The tackifier resin is at least one selected from rosin-based tackifier resins and terpene-based tackifier resins, the adhesive sheet according to claim 1 or 2.

6. The content of the tackifier resin in the adhesive layer is 70 parts by weight or less with respect to 100 parts by weight of the acrylic polymer, the adhesive sheet according to claim 1 or 2.

7. The crosslinking agent contains at least one selected from isocyanate-based crosslinking agents and epoxy-based crosslinking agents, the adhesive sheet according to claim 1 or 2.

8. The 180-degree peel strength with respect to a stainless steel plate is 20 N / 25 mm or more, the adhesive sheet according to claim 1 or 2.

9. The adhesive sheet according to claim 1 or 2, which is used for fixing members in a portable electronic device.

Images