JP2024007572A - Pressure-sensitive adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: 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

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an adhesive sheet.

Generally, adhesives (also referred to as pressure-sensitive adhesives, hereinafter the same) exhibit a soft solid state (viscoelastic body) in a temperature range around room temperature, and have the property of adhering to an adherend under pressure. Taking advantage of these properties, adhesives are used in various industrial fields, from mobile electronic devices such as smartphones and home appliances to automobiles and OA equipment, typically in the form of adhesive sheets containing an adhesive layer, for bonding parts and other applications. Widely used for purposes such as surface protection. Technical documents regarding pressure-sensitive adhesive sheets include Patent Documents 1 and 2. Patent Documents 1 and 2 describe adhesives containing acrylic polymers polymerized using heptyl acrylate as a monomer component.

International Publication No. 2021/125247 International Publication No. 2021/125278

Adhesive sheets are required to have various performances depending on the location of application and usage mode. For example, when fixing components inside a portable electronic device using an adhesive sheet, the adhesion area is usually small due to size, weight, and other limitations. Adhesive sheets used for this purpose need to have adhesive strength that can achieve good fixation even on a small area, and the required performance has become higher due to demands for lighter weight and smaller size. ing. In particular, mobile electronic devices equipped with touch-panel displays, such as smartphones, are becoming smaller and thinner, while their screens are becoming larger from the viewpoint of display visibility and operability. For these reasons, adhesives used are required to have adhesive fixing performance under harsher conditions. Specifically, in this application, the adhesion area is of course limited, and for example, an elastic member such as a flexible printed circuit board (FPC) can be bent and accommodated in the limited internal space of a portable electronic device. , Measures are being taken to precisely position and stably fix it using an adhesive sheet. In the adhesive sheets used for fixing such members, a continuous peeling load is applied in the thickness direction (also called the Z-axis direction) of the adhesive sheet, so it is necessary to have repulsion resistance that can sustainably resist the elastic repulsion of the above-mentioned members. (specifically, durability against a continuous peeling load applied in the thickness direction (Z-axis direction) of the pressure-sensitive adhesive sheet).

Furthermore, in recent years, in addition to the above-mentioned reductions in weight and size, development of portable electronic devices having curved shapes such as three-dimensional shapes has progressed, and the surface shapes thereof tend to become more complex. Adhesive sheets that are attached to complex shapes are required to have the ability to closely follow and adhere to the shape. For example, in the above-mentioned portable electronic devices, the adhesive sheet that fixes a member such as a cover glass that has a complicated surface shape (which may be a curved surface shape) tends to be subjected to a larger sustained peeling load than before. Adhesive sheets used for such applications are required to have higher levels of repulsion resistance against sustained peeling loads.

Furthermore, the temperature and humidity inside the above-mentioned portable electronic devices are affected not only by the heat inside the electronic device but also by the external environment, and can reach a high temperature of over 50 degrees Celsius. It is also possible. Even under such an environment, the adhesive used for this purpose may be required to exhibit stable repulsion resistance in the Z-axis direction.

Moreover, since portable electronic devices are at risk of falling due to their usage, there is a strong demand for adhesives used in portable electronic devices to have improved impact resistance. 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 cohesion required for repulsion resistance can be improved. The force also decreases, 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. Even in harsh environments such as high temperature and high humidity conditions, it exhibits good repulsion resistance against sustained peeling loads in the thickness direction (repulsion resistance against sustained loads in the Z-axis direction), and It would be significant if a pressure-sensitive adhesive sheet with excellent impact resistance could be provided.

As a result of extensive studies, the present inventors found that a structure using an acrylic polymer containing heptyl acrylate as a monomer component exhibits good repulsion resistance against sustained loads in the Z-axis direction even in harsh environments. It was discovered that an adhesive having excellent impact resistance can be obtained, and the present invention was completed. That is, an object of the present invention is to provide a pressure-sensitive adhesive sheet that can achieve both high levels of repulsion resistance and impact resistance.

According to this specification, an adhesive sheet is provided. This adhesive sheet has an adhesive layer containing an acrylic polymer. The acrylic polymer is a polymer of monomer components containing heptyl acrylate. Further, the 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 elastic modulus G'' to the storage elastic modulus G' of the adhesive layer.

According to the above configuration, the adhesive layer has a 65° C. storage modulus of 20,000 Pa or more, and therefore can exhibit good repulsion resistance. Furthermore, since the -20°C tan δ of the adhesive layer is 0.3 or more, excellent impact resistance is likely to be obtained. Balancing the storage modulus G' at 65° C. and tan δ at −20° C. can be suitably achieved by using an acrylic polymer containing heptyl acrylate as a monomer component. According to the pressure-sensitive adhesive sheet having the above structure, both repulsion resistance and impact resistance can be achieved at a high level.

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

In some preferred embodiments, the glass transition temperature (Tg) of the adhesive layer is within the range of -15°C to 15°C. Here, the glass transition temperature of the adhesive layer refers to the glass transition temperature determined from the peak temperature of tan δ in dynamic viscoelasticity measurement. In an adhesive layer having a Tg within the range of -15°C to 15°C, both repulsion resistance and impact resistance are likely to be achieved.

In some preferred embodiments, the adhesive layer further includes a tackifying resin. The technology disclosed herein is preferably implemented with a configuration in which the adhesive layer contains a tackifying resin. As the tackifying resin, at least one selected from rosin-based tackifying resins and terpene-based tackifying resins is preferably used. In some embodiments, the content of the tackifier resin in the adhesive layer is 70 parts by weight or less based on 100 parts by weight of the acrylic polymer. The effects of the technology disclosed herein can be preferably achieved by appropriately adjusting the content of the tackifier resin in the adhesive layer within the above range.

In some preferred embodiments, the adhesive layer further includes an acrylic oligomer. The technique disclosed herein is preferably implemented in an embodiment in which the adhesive layer contains an acrylic oligomer. Among these, it is more preferable to use a tackifying resin and an acrylic oligomer together.

In some preferred embodiments, the adhesive composition for forming the adhesive layer includes at least one selected from an isocyanate crosslinking agent and an epoxy crosslinking agent. By using a crosslinking agent selected from isocyanate crosslinking agents and epoxy crosslinking agents, the cohesive force of the adhesive can be appropriately increased, and while having impact resistance, it is possible to preferably improve repulsion resistance. can.

Adhesive sheets according to some preferred embodiments have a 180 degree peel strength against a stainless steel plate (adhesive strength against SUS) of 20 N/25 mm or more. The pressure-sensitive adhesive sheet having the above adhesive strength against SUS can exhibit excellent adhesive strength.

The pressure-sensitive adhesive sheet disclosed herein is capable of achieving both repulsion resistance and impact resistance, and is therefore preferably used for joining members of portable electronic devices that may 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.

FIG. 1 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to an embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment. FIG. 1 is a front view schematically showing an example of a portable electronic device including an adhesive sheet. It is a schematic diagram explaining the method of a Z-axis direction repulsion resistance test.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention are based on the teachings regarding carrying out the invention described in this specification and the common general knowledge at the time of filing. can be understood by those skilled in the art. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field. Furthermore, in the following drawings, members and portions that have the same function may be described with the same reference numerals, and overlapping descriptions may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic for clearly explaining the present invention, and do not necessarily accurately represent the size or scale of the adhesive sheet of the present invention that is actually provided as a product. .

As mentioned above, the term "adhesive" as used herein refers to a material that exhibits a soft solid (viscoelastic) state in the temperature range around room temperature and has the property of easily adhering to an adherend under pressure. . The adhesive referred to here generally has a complex tensile modulus E ^* (1Hz) as defined in "CA Dahlquist, "Adhesion: Fundamentals and Practice", McLaren & Sons, (1966) P. 143". <10 ⁷ dyne/cm ² (typically, a material having the above properties at 25° C.).

In this specification, biomass-derived carbon means carbon derived from biomass materials, that is, materials derived from renewable organic resources (renewable carbon). The above-mentioned biomass materials are typically materials derived from biological resources (typically plants that perform photosynthesis) that can be reproduced sustainably in the presence of sunlight, water, and carbon dioxide. means. 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 adhesive layer and the adhesive sheet, that is, the proportion of biomass-derived carbon in the total carbon contained in the adhesive layer and the adhesive sheet, is the carbon isotope content with a mass number of 14 measured in accordance with ASTM D6866. It can be estimated from the amount.

<Configuration of adhesive sheet>
The adhesive sheet disclosed herein includes an adhesive layer. The above-mentioned pressure-sensitive adhesive sheet is, for example, a base material-less double-sided pressure-sensitive adhesive sheet comprising a first pressure-sensitive adhesive surface formed by one surface of the pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive surface formed by the other surface of the pressure-sensitive adhesive layer. It can be in the form of Alternatively, the pressure-sensitive adhesive sheet disclosed herein may be in the form of a pressure-sensitive adhesive sheet with a base material, in which the pressure-sensitive adhesive layer is laminated on one or both sides of a support base material. Hereinafter, the supporting base material may be simply referred to as "base material". Note that the concept of adhesive sheet here may include what is called an adhesive tape, an adhesive label, an adhesive film, and the like. Note that the pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, the adhesive sheet may be further processed into various shapes.

The structure of a pressure-sensitive adhesive sheet according to one embodiment is schematically shown in FIG. This adhesive sheet 1 is configured as a double-sided adhesive sheet without a base material, which includes an adhesive layer 21. The adhesive sheet 1 has a first adhesive surface 21A constituted by one surface (first surface) of the adhesive layer 21 and a second adhesive surface constituted by the other surface (second surface) of the adhesive layer 21. 21B are attached to different parts of the adherend. The locations on which the adhesive surfaces 21A and 21B are attached may be on different members, or may be on different locations within a single member. As shown in FIG. 1, the adhesive sheet 1 before use (that is, before being attached to an adherend) has a first adhesive surface 21A and a second adhesive surface 21B that are peeled off at least on the side facing the adhesive layer 21. It may be a component of the adhesive sheet 100 with a release liner that is protected by the release liners 31 and 32 serving as surfaces. As the release liners 31 and 32, it is preferable to use, for example, a sheet-like base material (liner base material) that is constructed by providing a release layer made of a release treatment agent on one side so that one side becomes a release surface. obtain. Alternatively, the release liner 32 may be omitted and a release liner 31 having release surfaces on both sides may be used, and this and the adhesive sheet 1 may be overlapped and spirally wound so that the second adhesive surface 21B is on the release liner 31. The pressure-sensitive adhesive sheet with a release liner may be configured in a form (roll form) in which the pressure-sensitive adhesive sheet is in a protected form (in the form of a roll) in contact with the back surface of the adhesive sheet.

FIG. 2 schematically shows the structure of a pressure-sensitive adhesive sheet according to another embodiment. This adhesive sheet 2 is a base material comprising a sheet-shaped support base material (for example, 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. It is constructed as a single-sided adhesive sheet. The adhesive layer 21 is fixedly provided on the first surface 10A side of the support base material 10, that is, without the intention of separating the adhesive layer 21 from the support base material 10. As shown in FIG. 2, the pressure-sensitive adhesive sheet 2 before use has a surface (adhesive surface) 21A of the pressure-sensitive adhesive layer 21 protected by a release liner 31 having a release surface at least on the side facing the pressure-sensitive adhesive layer 21. It may be a component of the pressure-sensitive adhesive sheet 200 with a release liner. Alternatively, the release liner 31 may be omitted, the second surface 10B may be the release surface, and the adhesive sheet 2 may be wound so that the adhesive surface 21A is the second surface (back surface) of the support substrate 10. ) 10B may be in a protected form (roll form).

FIG. 3 schematically shows the structure of a pressure-sensitive adhesive sheet according to yet another embodiment. This adhesive sheet 3 includes a sheet-shaped support base material (for example, a resin film) 10 having a first surface 10A and a second surface 10B, and a first adhesive layer 21 fixedly provided on the first surface 10A side. and a second adhesive layer 22 fixedly provided on the second surface 10B side. In the adhesive sheet 3 before use, as shown in FIG. , 32 may be a component of the adhesive sheet 300 with a release liner. Alternatively, the release liner 32 may be omitted and a release liner 31 having release surfaces on both sides may be used, and this and the adhesive sheet 3 may be overlapped and spirally wound so that the second adhesive surface 22A is on the release liner 31. The pressure-sensitive adhesive sheet with a release liner may be in a protected form (roll form) in contact with the back surface of the adhesive sheet.

In addition, in the double-sided pressure-sensitive adhesive sheet with a base material, at least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer (for example, the first pressure-sensitive adhesive layer) may be the pressure-sensitive adhesive layer described below. The other adhesive layer (for example, the second adhesive layer) may be the adhesive layer disclosed herein, and the adhesive layer disclosed herein (specifically, the one adhesive layer described above) may be the adhesive layer disclosed herein. The adhesive layer may have a composition different from that of the adhesive layer (for example, the first adhesive layer). The other pressure-sensitive adhesive layer may be formed from a known or commonly used pressure-sensitive adhesive, for example.

Furthermore, although not particularly limited, according to the technology disclosed herein, it is possible to achieve both repulsion resistance and impact resistance with a structure that does not have a foam base material that is advantageous for improving impact resistance. It is. Therefore, the present invention is disclosed herein in the form of a double-sided pressure-sensitive adhesive sheet without a base material consisting of an adhesive layer, or in the form of a pressure-sensitive adhesive sheet with a base material comprising a base material other than a foam base material (non-foam base material). The technique can be implemented. Among these, the form of a base material-less double-sided pressure-sensitive adhesive sheet is preferred. Since the base material-less double-sided adhesive sheet does not have a base material, it can be made thinner and can contribute to downsizing and space saving of products to which the double-sided adhesive sheet is applied. Moreover, according to the base material-less adhesive sheet, the effects of the adhesive layer such as repulsion resistance and impact resistance against continuous loads in the Z-axis direction can be maximized.

<Adhesive layer>
(Viscoelastic properties)
The adhesive layer disclosed herein (in an embodiment including 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' of 20,000 Pa or more at 65°C. According to the pressure-sensitive adhesive having a storage modulus of 65° C., good repulsion resistance (especially repulsion resistance against a sustained load in the Z-axis direction in a harsh environment such as a high temperature condition) is easily obtained. 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, suitably 23,000 Pa or more, and more Preferably it is 24,000 Pa or more, more preferably 25,000 Pa or more, particularly preferably 26,000 Pa or more, it may be 27,000 Pa or more, it may be 28,000 Pa or more, it may be 29,000 Pa or more, and it may be 30,000 Pa or more. ,000 Pa or more, 31,000 Pa or more, 32,000 Pa or more, or 33,000 Pa or more. The upper limit of the 65° C. storage modulus can be set within an appropriate range that allows both repulsion resistance and impact resistance to be achieved. 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. The pressure may be 32,000 Pa or less, 30,000 Pa or less, 28,000 Pa or less, or 26,000 Pa or less.

Further, the adhesive layer disclosed herein is characterized by having the storage modulus at 65°C of 20,000 Pa or more, and tan δ at -20°C of 0.3 or more. The above tan δ (loss tangent) refers to the ratio (G''/G') of the loss elastic modulus G'' to the storage elastic modulus G' of the adhesive layer. According to the temperature-velocity conversion law, -20°C corresponds to the impact velocity range during a fall. An adhesive having a tan δ of 0.3 or more at −20° C. can easily 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 still more preferably 0.60 or more from the viewpoint of impact resistance. The upper limit of the above-mentioned -20°C tan δ can be set within an appropriate range that can achieve both repulsion resistance and impact resistance. The above-mentioned -20°C tan δ may be, for example, approximately 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, preferably 1.0 or less, more preferably 0.80 or less, and even more preferably 0.70. or less, and may be 0.60 or less, or may be 0.55 or less.

Although not particularly limited, in some preferred embodiments, the glass transition temperature (Tg) of the adhesive layer is within the range of -15°C to 15°C. Here, the glass transition temperature of the adhesive layer refers to the glass transition temperature determined from the peak temperature of tan δ in dynamic viscoelasticity measurement. By using an adhesive having a Tg in 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 adhesive layer is more preferably -12°C or higher, even more preferably -10°C or higher, particularly preferably -7°C or higher, may be -5°C or higher, and -3°C or higher. The temperature may be higher than or equal to -1°C, higher than 0°C (for example, higher than 0°C), or higher than 1°C. In addition, 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, particularly preferably 5°C or less, and particularly preferably 3°C or less. The temperature may be 1°C or lower, 0°C or lower (for example, lower than 0°C), -1°C or lower, or -3°C or lower.

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, an adhesive layer with a thickness of about 2 mm is produced by stacking a plurality of adhesive layers (adhesive sheets in the case of a base material-less adhesive sheet) to be measured. A sample of this adhesive layer was punched into a disk shape with a diameter of 7.9 mm, which was sandwiched and fixed between parallel plates. Dynamic viscoelasticity was measured under the following conditions to determine the storage modulus at 65°C, tan δ at -20°C, and Tg.
・Measurement mode: Shear mode ・Temperature range: -70℃~150℃
・Heating rate: 5℃/min
・Measurement frequency: 1Hz
The above-mentioned method is also used in the Examples described below. Note that the adhesive layer to be measured may be formed by applying a corresponding adhesive composition in a layered manner and drying or curing it.

(acrylic polymer)
The adhesive layer constituting the adhesive sheet disclosed herein contains an acrylic polymer. The pressure-sensitive adhesive layer is typically a pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer. Such an adhesive layer is also referred to as an acrylic adhesive layer. Note that the base polymer refers to the main component of a rubbery polymer (a polymer that exhibits rubber elasticity in a temperature range around room temperature) contained in the adhesive layer. Furthermore, in this specification, the term "main component" refers to a component contained in an amount exceeding 50% by weight, unless otherwise specified. Further, the following description regarding the adhesive and the components that can be included in the adhesive layer is also applicable to the adhesive composition used to form the adhesive (layer) unless otherwise specified.

In addition, as used herein, the term "acrylic polymer" refers to a polymer containing monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule, as monomer units constituting the polymer. . Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule will also be referred to as an "acrylic monomer." Accordingly, an acrylic polymer in this specification is defined as a polymer containing monomer units derived from acrylic monomers. In addition, in this specification, "(meth)acryloyl" refers comprehensively to acryloyl and methacryloyl. Similarly, "(meth)acrylate" comprehensively refers to acrylate and methacrylate, and "(meth)acrylic" comprehensively refers to acrylic and methacrylic.

As the acrylic polymer used in the technique disclosed herein, a polymer of monomer components containing heptyl acrylate is used. Acrylic polymers polymerized using monomer components containing heptyl acrylate are more flexible than polymers of other alkyl acrylates such as n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). Adhesives containing polymers tend to have a high value of -20°C tan δ and tend to have excellent impact resistance. The reason for this is not to be construed as particularly limiting, but polymers containing heptyl acrylate as a monomer unit have a low glass transition temperature and a relatively large space between the main chains within the adhesive. it is conceivable that. Among heptyl acrylates, n-heptyl acrylate is preferred from the viewpoint of flexibility. Acrylic polymers synthesized containing n-heptyl acrylate as a monomer component are considered to have relatively long linear side chains, and therefore tend to have larger spaces between main chains.

For example, in some embodiments, the proportion of heptyl acrylate in the monomer components of the acrylic polymer is 50% by weight or more (for example, more than 50% by weight), preferably 70% by weight or more, more preferably 80% by weight or more. The content is 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, and may be 96% by weight or more. By increasing the amount of heptyl acrylate used, the effects of its use (for example, improvement in −20° C. tan δ of the adhesive and improvement in impact resistance) can be effectively exhibited. On the other hand, the upper limit of the proportion of heptyl acrylate in the monomer component is 100% by weight, and may be 99% by weight or less, or may be 98% by weight or less. From the viewpoint of copolymerizing the carboxyl group-containing monomer and other monomers, in some embodiments, the proportion of heptyl acrylate in the monomer components 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, and may be 94% by weight or less. Limiting the proportion of heptyl acrylate within the above range is preferable in terms of improving storage modulus, and may be advantageous in terms of improving repulsion resistance.

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

Examples of the above-mentioned 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, 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 Acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like. These optional alkyl (meth)acrylates can be used alone or in combination of two or more.

In some embodiments, the proportion of heptyl acrylate in the total amount of alkyl (meth)acrylates 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, still more preferably 90% by weight or more, particularly preferably 95% by weight or more, may be 99% by weight or more, and may be 100% by weight. . By employing such a monomer composition, the effects 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 arbitrary alkyl (meth)acrylates such as 2EHA and BA. Therefore, the technology disclosed herein can be preferably practiced in an embodiment in which the monomer component does not substantially contain any alkyl (meth)acrylate.

In addition, in this specification, when the monomer component does not substantially contain monomer A (for example, the above-mentioned optional alkyl (meth)acrylate), it means that the monomer A is not used, at least intentionally, and when the monomer A is For example, unintentional inclusion of about 0.01% by weight or less is acceptable.

In some embodiments, the monomer component may include an alkyl (meth)acrylate having a biomass-derived alkyl group at an ester end (hereinafter also referred to as "biomass alkyl (meth)acrylate"). In recent years, environmental issues such as global warming have become more important, and it is desired to reduce the amount of fossil resource-based materials such as petroleum used. Under these circumstances, there is a need to reduce the amount of fossil resource-based materials used in the adhesive field as well. By using biomass alkyl (meth)acrylate, it is possible to suitably realize an acrylic pressure-sensitive adhesive that is designed to reduce dependence on fossil resource-based materials.

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 alkanols derived from biomass 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 three 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 the acrylic polymer. In such a biomass alkyl (meth)acrylate, the greater the number of carbon atoms in the alkanol, the greater the number ratio of biomass-derived carbon to the total number of carbons contained in the biomass alkyl (meth)acrylate, that is, the biomass carbon ratio of the alkyl (meth)acrylate. becomes higher. Therefore, in the above-mentioned biomass alkyl (meth)acrylate, it is desirable that the alkyl group derived from biomass has a large number of carbon atoms in order to reduce dependence on fossil resource materials. On the other hand, if the number of carbon atoms in the alkyl group constituting the alkyl (meth)acrylate is too large, it tends to be difficult to obtain adhesive properties such as adhesive strength, and it also has a negative impact on productivity such as synthesis, ease of handling, and cost. It can be disadvantageous. In an embodiment in which an ester of biomass-derived alkanol and non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate, adhesive properties and reduced dependence on fossil resource materials (more specifically, It is desirable to use a material that is compatible with the above-mentioned alkyl (meth)acrylate to biomass carbon ratio) in a well-balanced manner.

In some preferred embodiments, biomass-derived heptyl acrylate (biomass heptyl acrylate) is used as the heptyl acrylate. By using biomass heptyl acrylate, the effects of the technology disclosed herein can be achieved while reducing dependence on fossil resource materials. The biomass heptyl acrylate is an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived acrylic acid. For example, an ester of a biomass-derived alkanol and a non-biomass-derived acrylic acid can be used. In such compounds, only the heptyl groups are derived from biomass. As the biomass-derived heptyl acrylate, it is preferable to use biomass-derived n-heptyl acrylate (biomass n-heptyl acrylate).

In some embodiments, 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 (for example, more than 50% by weight), preferably 70% by weight or more, more preferably 80% by weight or more, further 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, and may be 96% by weight or more. good. Further, the proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) among the monomer components is less than 97% by weight, and in some embodiments may be 95% by weight or less, and may be 93% by weight or less. It may be 91% by weight or less.

Moreover, it is preferable that the monomer component of the acrylic polymer contains a carboxy group-containing monomer. Carboxy group-containing monomers can improve cohesive force based on their polarity. Further, when using a crosslinking agent such as an isocyanate type crosslinking agent or an epoxy type crosslinking agent, the carboxy group can serve as a crosslinking point of the acrylic polymer. By using a carboxyl group-containing monomer, the 65° C. storage modulus of the adhesive can be improved, and it is easy to obtain an adhesive that has excellent repulsion resistance against a sustained load in the Z-axis direction. Further, by using a carboxyl group-containing monomer, better adhesion can be exhibited, for example, to adherends such as highly polar materials.

Carboxy group-containing monomers include, for example, acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, crotonic acid, isocrotonic acid, and other ethylenically unsaturated monocarboxylic acids; maleic acid; acid, ethylenically unsaturated dicarboxylic acids such as itaconic acid and citraconic acid. Further, the carboxy group-containing monomer may be a monomer having a metal salt (for example, an alkali metal salt) of a carboxy group. Carboxy group-containing monomers can be used alone or in combination of two or more. Among these, preferred carboxy group-containing monomers include AA and MAA. AA is particularly preferred. When one or more carboxy group-containing monomers are used, the proportion of AA in the carboxy group-containing monomers is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. It is. In a particularly preferred embodiment, the carboxy group-containing monomer consists essentially of AA. AA has a combination of functions such as polarity based on its carboxyl group, role as a crosslinking point, and Tg (106°C), so in the carboxyl group-containing monomer disclosed herein, AA has excellent impact resistance and long-lasting durability in the Z-axis direction. It is considered to be the optimal monomer material for achieving a good balance between load and repulsion resistance.

The proportion of the carboxy 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, 2% by weight or more. It may be more than % by weight. In some preferred embodiments, the proportion of the carboxy 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, still more preferably 5.0% by weight or more (for example, more than 5.0% by weight), particularly preferably 5.5% by weight or more, and 6.0% by weight or more. Good too. By increasing the amount of the carboxy group-containing monomer used, the cohesive force of the adhesive layer is improved based on the action of the carboxy group-containing monomer, so the 65°C storage modulus of the adhesive can be improved, and the repulsion resistance It is easy to obtain an adhesive with excellent properties. Further, the amount of the carboxyl group-containing monomer is, for example, suitably 20% by weight or less of the total monomer components, preferably 15% by weight or less, more preferably 12% by weight or less. In some preferred embodiments, the amount of the carboxy 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 carboxy group-containing monomer (eg AA) used, -20°C tan δ tends to increase. By appropriately adjusting the amount of the carboxyl group-containing monomer within the above range, it is easy to obtain an adhesive that has both repulsion resistance and impact resistance.

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 (2-hydroxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2- Hydroxyalkyl (meth)acrylates such as hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 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 with nitrogen atom-containing rings (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), alkoxysilyl Examples include group-containing monomers, imide group-containing monomers, and the like. The above arbitrary functional group-containing monomers can be used alone or in combination of two or more.

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 exhibiting 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, and 0.5% by weight or more. It is appropriate that the amount is 1% by weight or more. For example, in an embodiment in which the monomer component of the acrylic polymer includes heptyl acrylate and a monomer containing a carboxy group, from the viewpoint of making it easier to balance the adhesive performance in relation to these monomer components, the optional functional group-containing monomer in the monomer component The content of 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 optional functional group-containing monomers 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, and may be less than 0.3% by weight. % or less than 0.1% by weight. The technique disclosed herein can be preferably carried out in an embodiment in which the monomer component of the acrylic polymer does not substantially contain any functional group-containing monomer.

Furthermore, a hydroxyl group-containing monomer may be used as the optional functional group-containing monomer. In that case, the content of the hydroxyl group-containing monomer is suitably about 10% by weight or less (for example, 0.001 to 10% by weight), preferably about 5% by weight or less, more preferably about 5% by weight or less, based on the total monomer components. It is approximately 2% by weight or less. In some embodiments, the content of hydroxyl group-containing monomer in the monomer component may be less than 1% by weight, may be less than 0.5% by weight, may be less than 0.3% by weight, and may be less than 0.1% by weight. % or less than 0.01% by weight. The monomer component of the acrylic polymer may be substantially free of hydroxyl group-containing monomers. In the technology disclosed herein, by limiting the amount of the hydroxyl group-containing monomer used or not using it, it is possible to achieve both the predetermined 65°C storage modulus G' and -20°C tan δ, and improve the repulsion resistance. It is possible to preferably achieve both a high level of impact resistance and impact resistance.

The ratio of the carboxy group-containing monomer to the total functional group-containing monomers (total functional group-containing monomers including the carboxy group-containing monomer) used as a copolymerization component of the acrylic polymer is determined by the effect of copolymerizing the carboxy group-containing monomer. From the viewpoint of achieving the desired performance, the content is suitably 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, such as It may be 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99.9% by weight or more). The upper limit of the proportion of the carboxy group-containing monomer to the total of the functional group-containing monomers is 100% by weight, and may be, for example, 95% by weight or less.

The monomer components constituting the acrylic polymer may contain copolymerization components other than the above-mentioned functional group-containing monomers for the purpose of improving cohesive force and the like. 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 ) acrylates; aryl (meth)acrylates (e.g. phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g. phenoxyethyl (meth)acrylate), arylalkyl (meth)acrylates (e.g. benzyl (meth)acrylate), etc. Aromatic ring-containing (meth)acrylate; Olefinic monomer; Chlorine-containing monomer; Isocyanate group-containing monomer such as 2-(meth)acryloyloxyethyl isocyanate; Alkoxy such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate Group-containing monomers; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and the like. The other copolymerization components mentioned above can be used alone or in combination of two or more.

The amount of such other copolymerized components is not particularly limited as long as it can be selected as appropriate depending on the purpose and use, but from the viewpoint of appropriately exhibiting the effects of use, it is appropriate to set it to 0.05% by weight or more. , 0.5% by weight or more. In addition, from the viewpoint of making it easier to balance the adhesive performance, it is appropriate that the content of other copolymer components in the monomer component is 20% by weight or less, so that the adhesive properties based on the essential monomer components can be suitably exhibited. From this point of view, it is preferably 10% by weight or less, more preferably 8% by weight or less, still more preferably less than 5% by weight, for example, it may be less than 3% by weight, and may be less than 1% by weight. The technology disclosed herein can also be preferably practiced in an embodiment in which the monomer component does not substantially contain other copolymer components.

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

The amount of the polyfunctional monomer to be used is not particularly limited, and can be appropriately set so that the intended use of the polyfunctional monomer is achieved. The amount of the polyfunctional monomer used can be about 3% by weight or less of the monomer components, 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). The lower limit of the amount used when using a polyfunctional monomer 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 to be approximately 0.001% by weight or more (for example, approximately 0.01% by weight or more) of the monomer components.

In a particularly preferred embodiment, the acrylic polymer is an acrylic polymer synthesized using a monomer component consisting essentially of heptyl acrylate (preferably n-heptyl acrylate) and a carboxy group-containing monomer (preferably acrylic acid). It will be done. According to the above monomer composition, the effects of heptyl acrylate and the carboxyl group-containing monomer are effectively exhibited, achieving both the prescribed 65°C storage modulus G' and -20°C tan δ, and improving repulsion resistance and impact resistance. It is possible to preferably achieve a high level of compatibility with From this point of view, the total proportion of heptyl acrylate and the carboxyl group-containing monomer in the monomer components 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. % by weight or more, more preferably more than 99.5% by weight, particularly preferably more than 99.9% by weight (for example, more than 99.99% by weight), and the total proportion of heptyl acrylate and the carboxy group-containing monomer in the monomer components may be 100% by weight.

The biomass carbon ratio of the monomer component constituting the acrylic polymer (biomass carbon ratio of the acrylic polymer) may be, for example, 1% or more, suitably 10% or more, preferably 30% or more, and more preferably is 50% or more (for example, 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 can be obtained that takes into account the suppression of dependence on fossil resource-based materials.

The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as methods for synthesizing acrylic polymers such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization may be used. may be adopted as appropriate. For example, a solution polymerization method can be preferably employed. As a monomer supply method when performing solution polymerization, a batch 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 selected as appropriate depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and is, for example, about 20°C to 170°C (typically about 40°C to 140°C). I can do it.

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

The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide (BPO) and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and the like. Still another example of the polymerization initiator is a redox initiator using a combination of a peroxide and a reducing agent. Such polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used may be any normal amount, for example, approximately 0.005 to 1 part by weight (typically approximately 0.01 to 1 part by weight) per 100 parts by weight of all monomer components. degree).

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 may be greater than 600,000, greater than 650,000, suitably greater than 700,000, and may be greater than 750,000. The larger the Mw of the acrylic polymer, the easier it is to obtain a pressure-sensitive adhesive that exhibits good cohesive force, 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 (for example, more than 1 million), and even more preferably The number is 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. According to the monomer composition containing heptyl acrylate, the viscosity can be easily maintained at a low level, so the synthesis of the polymer is good, and an acrylic polymer having the above Mw can be easily obtained. In addition, by using an acrylic polymer that contains heptyl acrylate as a monomer unit and has an Mw of a predetermined value or more, the above-mentioned viscoelastic properties ( Specifically, it is easy to satisfy the storage modulus G' at 65° C. and tan δ at −20° C., and it is possible to preferably achieve both high levels of repulsion resistance and impact resistance. On the other hand, from the viewpoint of impact resistance, adhesive strength, ease of synthesis, etc., the Mw of the acrylic polymer is usually approximately 3 million or less, preferably 2.5 million or less, and more preferably 2 million or less. , more preferably 1.8 million or less, may be 1.5 million or less, or may be 1.3 million or less. In some preferred embodiments, the Mw of the acrylic polymer may be 1.1 million or less, 1 million or less, 950,000 or less, or 900,000 or less.

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

(tackifying resin)
In some preferred embodiments, the adhesive layer includes a tackifying resin. By using a tackifying resin, high adhesive strength can be obtained. According to the technology disclosed herein, the adhesive layer has a composition containing a tackifying resin and has predetermined viscoelastic properties (specifically, 65°C storage modulus G' and -20°C tan δ), It can exhibit excellent repulsion resistance in the Z-axis direction. 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 includes, for example, rosin-based tackifier resin, terpene-based tackifier resin, hydrocarbon-based tackifier resin, epoxy-based tackifier resin, polyamide-based tackifier resin, elastomer-based tackifier resin, Various tackifying resins such as phenolic tackifying resins and ketone tackifying resins can be used. Such tackifying resins can be used alone or in combination of two or more.

Specific examples of rosin-based tackifying resins include unmodified rosin (raw rosin) such as gum rosin, wood rosin, and tall oil rosin; Hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosin, etc. (the same applies hereinafter); and other various rosin derivatives. Examples of the above-mentioned rosin derivatives include rosins 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). Esters: Unsaturated fatty acid-modified rosins, which are unmodified rosin or modified rosin modified with unsaturated fatty acids; Unsaturated fatty acid-modified rosin esters, which are rosin esters modified with unsaturated fatty acids; Unmodified rosin, modified rosin, unsaturated Rosin alcohols obtained by reducing the carboxyl group in fatty acid-modified rosins or unsaturated fatty acid-modified rosin esters; metal salts of rosins (especially rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; rosins; Examples include rosin phenol resins obtained by adding phenol to (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and thermally polymerizing them. Among them, rosin ester is preferred.

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 ester, triethylene glycol ester, glycerin ester. , pentaerythritol ester and the like.

Examples of terpene-based tackifying resins include terpene resins such as α-pinene polymer, β-pinene polymer, and dipentene polymer; Modified terpene resins (modified etc.); etc. An example of the above-mentioned modified terpene resin is terpene phenol resin.

Terpene phenol resin refers to a polymer containing terpene residues and phenol residues, and includes copolymers of terpenes and phenol compounds (terpene-phenol copolymer resins), and homopolymers or copolymers of terpenes. This concept includes both phenol-modified products (phenol-modified terpene resins). Specific examples of terpenes constituting such terpene phenol resin include monoterpenes such as α-pinene, β-pinene, and limonene (including d-form, l-form, and d/l-form (dipentene)); can be mentioned. The hydrogenated terpene phenol resin refers to a hydrogenated terpene phenol resin having a structure obtained by hydrogenating such a terpene phenol resin. Sometimes called hydrogenated terpene phenolic resin.

Examples of hydrocarbon-based tackifying resins include aliphatic (C5-based) petroleum resins, aromatic (C9-based) petroleum resins, aliphatic/aromatic copolymerized (C5/C9-based) petroleum resins, and Hydrogenated substances (e.g., alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), various modified products thereof (e.g., maleic anhydride modified products), coumaron-based resins, coumaron-indene-based resins Examples include various hydrocarbon resins such as.

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

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

The content of the terpene phenol resin in the adhesive layer is not particularly limited as long as it satisfies the desired viscoelastic properties. In some embodiments, the content of the terpene phenol resin is usually about 1 part by weight or more, and suitably about 5 parts by weight or more, based on 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength. The amount is preferably about 8 parts by weight or more, more preferably about 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). 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, and may be 50 parts by weight or less, based on 100 parts by weight of the acrylic polymer. It may be less than parts by weight. In some preferred embodiments, from the viewpoint of repulsion resistance, the content of the terpene phenol resin is 40 parts by weight or less, more preferably 30 parts by weight or less, still more preferably 25 parts by weight or less, particularly preferably 20 parts by weight or less. It is not more than 18 parts by weight, and may be not more than 18 parts by weight.

Although not particularly limited, in some embodiments, the tackifying resin may include a tackifying resin (eg, a terpene phenol resin) having a hydroxyl value higher than 20 mg KOH/g. The hydroxyl value of such a tackifying resin may be 30 mgKOH/g or more. Among these, tackifying resins having a hydroxyl value of 50 mgKOH/g or more are preferred. 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 the tackifier resin containing such a high hydroxyl value resin, in addition to the adhesive force, an adhesive layer with high cohesive force can be realized by interacting with a crosslinking agent such as an isocyanate-based crosslinking agent. In some embodiments, the tackifying resin may include a high hydroxyl value resin having a hydroxyl value of 60 mgKOH/g or more (more preferably 70 mgKOH/g or more). In addition, the above-mentioned high hydroxyl value resin (for example, terpene phenol resin) is preferably used in combination with an acrylic polymer containing heptyl acrylate as a monomer component, and has good adhesive strength and Z It can exhibit repulsion resistance against sustained loads in the axial direction.

The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with the acrylic polymer, the hydroxyl value of the high hydroxyl value resin is usually about 300 mgKOH/g or less, suitably about 200 mgKOH/g or less, preferably about 180 mgKOH/g or less, or more. It is preferably about 160 mgKOH/g or less, 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 practiced in an embodiment in which the tackifier resin includes a high hydroxyl value resin (for example, a terpene-based tackifier resin, preferably a terpene phenol resin) with 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 employed.

Here, as the value of the hydroxyl value, a value measured by the potentiometric titration method specified in JIS K0070:1992 can be adopted. The specific measurement method is as shown below.
[Method for measuring hydroxyl value]
1. Reagent (1) As the acetylation reagent, take about 12.5 g (about 11.8 mL) of acetic anhydride, add pyridine to make a total volume of 50 mL, and stir thoroughly. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to make a total volume of 100 mL, stir thoroughly, and use.
(2) A 0.5 mol/L potassium hydroxide ethanol solution is used as the measurement reagent.
(3) Additionally, prepare toluene, pyridine, ethanol, and distilled water.
2. Procedure (1) Accurately weigh about 2 g of sample into a flat bottom flask, add 5 mL of acetylation reagent and 10 mL of pyridine, and attach an air cooling tube.
(2) After heating the above flask in a bath at 100°C for 70 minutes, let it cool, add 35 mL of toluene as a solvent from the upper part of the cooling tube and stir, and then add 1 mL of distilled water and stir to remove acetic anhydride. Disassemble. To complete decomposition, heat again in the bath for 10 minutes and allow to cool.
(3) Wash the cooling tube with 5 mL of ethanol and remove it. Next, 50 mL of pyridine is added as a solvent and stirred.
(4) Add 25 mL of 0.5 mol/L potassium hydroxide ethanol solution using a whole pipette.
(5) Perform potentiometric titration with a 0.5 mol/L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is defined as the end point.
(6) For a blank test, perform (1) to (5) above without adding a sample.
3. Calculation Calculate the hydroxyl value using the following formula.
Hydroxyl value (mgKOH/g)=[(B-C)×f×28.05]/S+D
here,
B: Amount (mL) of 0.5 mol/L potassium hydroxide ethanol solution used in the blank test,
C: Amount (mL) of 0.5 mol/L potassium hydroxide ethanol solution used in the sample,
f: factor of 0.5 mol/L potassium hydroxide ethanol solution,
S: weight of sample (g),
D: acid value,
28.05: 1/2 of the molecular weight of potassium hydroxide, 56.11,
It is.

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

Although not particularly limited, when using a high hydroxyl value resin, the proportion of the high hydroxyl value resin (for example, terpene phenol resin) to the entire tackifying resin contained in the adhesive layer should be approximately 5% by weight or more. The content may be 10% by weight or more, 15% by weight or more, or 20% by weight or more. In some embodiments, the proportion of the high hydroxyl value resin in the entire tackifier resin is preferably about 30% by weight or more, for example. As a result, the effect of using a high hydroxyl value resin can be preferably exhibited, and it is possible to improve adhesive strength and repulsion resistance against a sustained load in the Z-axis direction while maintaining impact resistance. In some preferred embodiments, the proportion of the high hydroxyl value resin in the entire tackifying resin is about 40% by weight or more, and may be about 50% by weight or more (for example, more than 50% by weight), and about 60% by weight. % or more, approximately 70% by weight or more, approximately 80% by weight or more, or approximately 90% by weight or more. Substantially all of the tackifier resin (for example, approximately 95 to 100% by weight, or even approximately 99 to 100% by weight) may be a high hydroxyl value resin.

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, approximately 50°C or higher, and from the viewpoint of improving cohesive force, a high hydroxyl value resin having a softening point (softening temperature) of approximately 80°C or higher may be preferably employed. For example, a terpene phenol resin having such a softening point can be preferably used. The softening point of the high hydroxyl value resin may be approximately 100°C or higher, or approximately 110°C or higher. In some preferred embodiments, the softening point of the high hydroxyl value resin is approximately 120°C or higher, may be approximately 130°C or higher, or may be approximately 135°C or higher (or even approximately 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 approximately 200° C. or lower (more preferably approximately 180° C. or lower) may be preferably used. In some embodiments, the high hydroxyl value resin may have a softening point of 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 with a softening point of less than 150° C., it is possible to preferably obtain an adhesive that has both repulsion resistance and impact resistance, and also has excellent adhesive strength. The softening point of the high hydroxyl value resin may be 145°C or lower.

Note that the softening point of the tackifying 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 the lowest possible temperature, and the sample is carefully filled into a ring placed on a flat metal plate, taking care not to form bubbles. After it has cooled down, use a slightly heated knife to cut off the raised part from the plane including the top of the ring. Next, a supporter (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 into the container to a depth of 90 mm or more. Next, the steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample were immersed in glycerin without coming into contact with each other, and the temperature of the glycerin was maintained at 20°C plus or minus 5°C for 15 minutes. . A steel ball is then placed in the center of the surface of the sample in the ring and placed in position on the support. Next, keeping the distance from the top of the ring to the glycerin surface at 50 mm, place a thermometer, set the center of the mercury bulb of the thermometer at the same height as the center of the ring, and heat the container. The flame of the Bunsen burner used for heating should be halfway between the center of the bottom of the container and the edge to ensure even heating. Note that the rate at which the bath temperature increases after heating starts and reaches 40°C must be 5.0 plus or minus 0.5°C per minute. The sample gradually softens and flows down from the ring, and the temperature at which it finally touches the bottom plate is read, and this is taken as the softening point. The softening point is measured at two or more points at the same time, and the average value is used.

The content of the high hydroxyl value resin in the adhesive layer is not particularly limited as long as it satisfies the desired viscoelastic properties. In some embodiments, the content of the high hydroxyl value resin is usually about 1 part by weight or more, and can be about 5 parts by weight or more, based on 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength. It is suitable, preferably about 8 parts by weight or more, more preferably about 10 parts by weight or more, still more preferably about 12 parts by weight or more (for example, 15 parts by weight or more). In some embodiments, the content of the high hydroxyl value resin in the adhesive layer is, for example, 70 parts by weight or less, and may be 60 parts by weight or less, based on 100 parts by weight of the acrylic polymer. It may be 50 parts by weight or less. In some preferred embodiments, from the viewpoint of repulsion resistance, the content of the high hydroxyl value resin is 40 parts by weight or less, more preferably 30 parts by weight or less, still more preferably 25 parts by weight or less, particularly preferably The amount may be 20 parts by weight or less, and may be 18 parts by weight or less.

Although not particularly limited, in some embodiments, the tackifying resin may include a tackifying resin having a hydroxyl value of less than 50 mg KOH/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, low hydroxyl value resins are preferably used in combination with high hydroxyl value resins. 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 about 10 mgKOH/g or more, or may be about 15 mgKOH/g or more. As the low hydroxyl value resin, one type suitably selected from among the tackifier resins exemplified above having a hydroxyl value of less than 50 mgKOH/g can be used alone or in combination of two or more types. In some embodiments, the low hydroxyl value resin preferably includes a rosin-based tackifying resin. The low hydroxyl value resin may contain one type of rosin-based tackifier resin alone, or may contain a combination of two or more types of rosin-based tackifier resin.

In some embodiments, the proportion of the rosin-based tackifier resin in the entire low hydroxyl value resin can be, for example, about 50% by weight or more, about 65% by weight or more, or about 75% by weight or more. The content may be 85% by weight or more, or may be 95% by weight or more. The technology disclosed herein is an embodiment in which substantially all of the low hydroxyl value resin (for example, approximately 97% by weight or more, or 99% by weight or more, and may be 100% by weight) is a rosin-based tackifier resin. It can be preferably implemented.

The softening point of the low hydroxyl value resin is not particularly limited. From the viewpoint of improving cohesive force, a low hydroxyl value resin having a softening point (softening temperature) of about 80° C. or higher can be preferably employed. For example, a rosin-based tackifying resin having such a softening point can be preferably used. The softening point of the low hydroxyl value resin may be approximately 100°C or higher, approximately 110°C or higher, or approximately 120°C or higher. 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 lower (more preferably about 180° C. or lower) 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 (eg, less than 150°C), about 140°C or less, or about 130°C or less.

In some embodiments, the tackifying resin is a tackifying resin T _L having a softening point of less than 150°C. By using the tackifier resin T _L , higher adhesive strength can be obtained to various adherends. The softening point of the tackifier resin T _L may be 145° C. or lower. The lower limit of the softening point of the tackifier resin T _L is not particularly limited. In some embodiments, the softening point of the tackifier resin T _L may be, for example, approximately 50°C or higher, preferably approximately 80°C or higher, and more preferably approximately 100°C or higher, from the viewpoint of exhibiting appropriate cohesive force. , more preferably about 110°C or higher. In some preferred embodiments, the softening point of the tackifier resin is approximately 120°C or higher, may be 130°C or higher, or may be 135°C or higher (or even approximately 140°C or higher).

As the tackifier resin T _L , one type suitably selected from among 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. In some embodiments, the tackifying resin T _L preferably comprises a terpene phenolic resin. The tackifier resin T _L may contain one type of terpene phenol resin alone, or may contain a combination of two or more types of terpene phenol resin.

In some embodiments, the proportion of the terpene phenol resin in the entire tackifier resin T _L can be, for example, more than about 50% by weight, may be about 65% by weight or more, and may be about 75% by weight or more. , 85% by weight or more, or 95% by weight or more. The technology disclosed herein is preferably in an embodiment in which substantially all of the tackifier resin T _L (for example, approximately 97% by weight or more, or 99% by weight or more, and may be 100% by weight) is a terpene phenol resin. can be implemented.

In addition, as the tackifying resin T _L , for example, a tackifying resin having a softening point of less than 50°C, more preferably approximately 40°C or less (typically a rosin-based, terpene-based, hydrocarbon-based, etc. tackifying resin, e.g. Hydrogenated rosin methyl ester, etc.) may or may not be included. Such a low softening point tackifier resin may be a liquid tackifier resin that exhibits a liquid state at 30°C. The liquid tackifying resin can be used alone or in combination of two or more. The content of the liquid tackifying resin can be approximately 30% by weight or less of the entire tackifier resin T _L from the viewpoint of cohesive force etc., and should be approximately 10% by weight or less (for example, 0 to 10% by weight). is suitable, and may be approximately 2% by weight or less (0.5 to 2% by weight), and may be less than 1% by weight.

The content of the tackifier resin T _L is not particularly limited, but in some embodiments, it is appropriate to set it to about 70 parts by weight or less based on 100 parts by weight of the acrylic polymer. By limiting the amount of the tackifier resin T _L used to a predetermined amount or less, it is possible to improve impact resistance while maintaining good repulsion resistance and adhesive strength. In some preferred embodiments, the amount of the tackifying resin T _L used is suitably 60 parts by weight or less, preferably 50 parts by weight, based on 100 parts by weight of the acrylic polymer, from the viewpoint of impact resistance etc. The amount is not more than 40 parts by weight, more preferably not more than 40 parts by weight, may be not more than 30 parts by weight, not more than 25 parts by weight, not more than 20 parts by weight, and not more than 18 parts by weight. In some embodiments, from the viewpoint of improving adhesive strength, the amount of the tackifier resin T _L used is, for example, 1 part by weight or more, preferably 5 parts by weight or more, based on 100 parts by weight of the acrylic polymer. The amount is preferably 8 parts by weight or more, more preferably 10 parts by weight or more, still more preferably 12 parts by weight or more, and may be 15 parts by weight or more. The acrylic polymer containing heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with the tackifier resin, so it is possible to achieve desired characteristics by incorporating an appropriate amount of the tackifier resin. can.

In some embodiments, the adhesive layer may include a combination of a tackifying resin T _L and a tackifying resin T _H having a softening point of 150° C. or higher (eg, 150° C. to 200° C.). As the tackifier resin T _H , one kind or a combination of two or more kinds of tackifier resins having a softening point of 150° C. or more among the tackifier resins exemplified above can be used.

In some embodiments, it is preferred that the tackifier resin T _L accounts for more than 50% by weight of the total amount of tackifier resins included in the adhesive layer. Thereby, the effect of containing the tackifying resin _TL tends to be effectively expressed. The proportion of the tackifying resin _{T L} in the total amount of the tackifying resin contained in the adhesive layer is preferably 60% by weight or more, more preferably The content is 70% by weight or more, more preferably 80% by weight or more, particularly preferably 90% by weight or more, 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 adhesive layer consists essentially only of tackifier resin _TL . In this embodiment, the proportion of the tackifying resin T _L in the total amount of tackifying resin contained in the adhesive layer is in the range of 99 to 100% by weight.

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

When the adhesive layer disclosed herein contains a tackifier resin, the tackifier resin is preferably a tackifier resin derived from plants (vegetable tackifier resin) from the viewpoint of improving the biomass carbon ratio of the adhesive layer. It can work. Examples of vegetable tackifying resins include the above-mentioned rosin-based tackifying resins and terpene-based tackifying resins. The vegetable tackifying resins can be used alone or in combination of two or more. When the adhesive layer disclosed herein includes a tackifying resin, the proportion of the vegetable tackifying resin in the total amount of the tackifying resin is 30% by weight or more (for example, 50% by weight or more, typically 80% by weight). above) is preferable. In some embodiments, the proportion of vegetable tackifying resin in the total amount of tackifying resin is 90% by weight or more (eg, 95% by weight or more, typically 99-100% by weight). The technology disclosed herein can be preferably implemented in an embodiment that does not substantially contain tackifying resins other than vegetable tackifying resins.

The content of the tackifying resin in the adhesive layer is not particularly limited as long as it satisfies the desired viscoelastic properties. In some embodiments, the content of the tackifier resin is usually about 1 part by weight or more, and suitably about 5 parts by weight or more, based on 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength. The amount is preferably about 8 parts by weight or more, more preferably about 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). 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, and may be 50 parts by weight or less, based on 100 parts by weight of the acrylic polymer. It may be less than parts by weight. In some preferred embodiments, from the viewpoint of repulsion resistance, the content of the tackifying 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. part or less, and may be 18 parts by weight or less. The acrylic polymer containing heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with the tackifying resin, so it is possible to achieve desired characteristics by incorporating an appropriate amount of the tackifying resin. can.

(acrylic oligomer)
In some preferred embodiments, the adhesive layer contains an acrylic oligomer. By containing an acrylic oligomer, the adhesive force of the pressure-sensitive adhesive can be improved. According to the technology disclosed herein, the adhesive layer has a composition containing an acrylic oligomer and has predetermined viscoelastic properties (specifically, 65°C storage modulus G' and -20°C tan δ), It can exhibit excellent repulsion resistance in the Z-axis direction. In particular, the effect of using an acrylic oligomer can be effectively exhibited in a composition containing a high molecular weight acrylic polymer.

It is desirable that 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. When Tg is within the above range, adhesive strength can be suitably improved. In some preferred embodiments, the Tg of the acrylic oligomer is about 30°C or higher, more preferably about 50°C or higher (for example, about 60°C or higher), from the viewpoint of adhesive cohesiveness, and From this point of view, the temperature is preferably about 200°C or less, more preferably about 150°C or less, and even more preferably about 100°C or less (for example, about 80°C or less).

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

As the glass transition temperature of the homopolymer used to calculate Tg, the value described in a known document shall be used. For example, the values described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) are used. For monomers for which multiple types of values are described in this document, the highest value is adopted.

For monomers whose homopolymer glass transition temperature is not described in the above literature, the value obtained by the following measurement method shall be used.
Specifically, 100 parts by weight of monomer, 0.2 parts by weight of 2,2'-azobisisobutyronitrile, and acetic acid as a polymerization solvent were placed in a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser. Add 200 parts by weight of ethyl and stir for 1 hour while passing nitrogen gas. After removing oxygen in the polymerization system in this manner, the temperature was raised to 63° C. and the reaction was allowed to proceed for 10 hours. Next, it is cooled to room temperature to obtain a homopolymer solution with a solid content concentration of 33% by weight. Next, this homopolymer solution is cast onto a release liner and dried to produce a test sample (sheet-like homopolymer) with a thickness of about 2 mm. This test sample was punched into a disk shape with a diameter of 7.9 mm, sandwiched between parallel plates, and subjected to shear strain at a frequency of 1 Hz using a viscoelasticity testing machine (manufactured by TA Instruments Japan, model name "ARES"). The viscoelasticity is measured in the shear mode at a temperature range of -70° C. to 150° C. and a heating rate of 5° C./min while giving the same temperature, and the temperature corresponding to the peak top temperature of tan δ is taken as the Tg of the homopolymer.

The weight average molecular weight (Mw) of the acrylic oligomer is typically about 1,000 or more and less than about 30,000, preferably about 1,500 or more and less than about 20,000, and more preferably about 2,000 or more and less than about 10,000. It is preferable that Mw is within the above range because good adhesive strength and repulsion resistance can be obtained. In some preferred embodiments, the Mw of the acrylic oligomer is about 2,500 or more (for example, about 3,000 or more) from the viewpoint of repulsion resistance against sustained loads in the Z-axis direction, and from the viewpoint of adhesiveness, preferably It is about 7,000 or less, more preferably about 5,000 or less (eg, about 4,500 or less, typically about 4,000 or less). The Mw of the acrylic oligomer can be measured by gel permeation chromatography (GPC) and determined as a value in terms of standard polystyrene. Specifically, the measurement is performed using HPLC8020 manufactured by Tosoh Corporation with two columns of TSKgelGMH-H (20) using tetrahydrofuran solvent at a flow rate of about 0.5 mL/min.

Examples of monomers constituting the acrylic oligomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and 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 Alkyl (meth)acrylates such as , isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate ; Esters of (meth)acrylic acid and alicyclic alcohol such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate (alicyclic hydrocarbon group-containing (meth)acrylate) ; Aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; (meth)acrylates obtained from terpene compound derivative alcohols; and the like. Such (meth)acrylates can be used alone or in combination of two or more.

Examples of acrylic oligomers include alkyl (meth)acrylates in which the alkyl group has a branched structure, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentaacrylate; Esters of (meth)acrylic acid and alicyclic alcohol such as nyl (meth)acrylate (alicyclic hydrocarbon group-containing (meth)acrylate); aryl such as phenyl (meth)acrylate and benzyl (meth)acrylate Containing as a monomer unit an acrylic monomer having a relatively bulky structure, such as (meth)acrylate having a cyclic structure, further improves the adhesiveness of the adhesive layer. It is preferable from the viewpoint that In addition, when using ultraviolet rays when synthesizing acrylic oligomers or preparing adhesive layers, it is preferable to use ultraviolet rays that have saturated bonds because they are less likely to inhibit polymerization, and those that have alkyl groups with a branched structure are preferable. Alkyl (meth)acrylates or esters with alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) can be suitably used as monomers constituting the acrylic oligomer. In addition, all of the above-mentioned branched alkyl (meth)acrylates, alicyclic hydrocarbon group (meth)acrylates, and aryl (meth)acrylates correspond to (meth)acrylate monomers in the technology disclosed herein. The cycloaliphatic hydrocarbon group can be a saturated or unsaturated cycloaliphatic hydrocarbon group.

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

In addition to the above-mentioned (meth)acrylate monomers, functional group-containing monomers can be used as constituent monomer components of the acrylic oligomer. Suitable examples of the functional group-containing monomer include monomers having a nitrogen atom-containing ring (typically a nitrogen atom-containing heterocycle) such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; N,N-dimethylamino Amino group-containing monomers such as ethyl (meth)acrylate; amide group-containing monomers such as N,N-diethyl (meth)acrylamide; carboxy group-containing monomers such as AA and MAA; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate Monomer; is mentioned. These functional group-containing monomers can be used alone or in combination of two or more. Among these, carboxy group-containing monomers are preferred, and AA is particularly preferred.

When all the monomer components constituting the acrylic oligomer include functional group-containing monomers, the proportion of the functional group-containing monomer (for example, a carboxyl group-containing monomer such as AA) in all the monomer components is approximately 1% by weight or more. The content is preferably 2% by weight or more, more preferably 3% by weight or more, and approximately 15% by weight or less, preferably 10% by weight or less, more preferably 7% by weight. It is as follows.

Acrylic oligomers can be formed by polymerizing their constituent monomer components. The polymerization method and polymerization mode are not particularly limited, and various conventionally known polymerization methods (e.g., solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be employed in an appropriate mode. The types of polymerization initiators (for example, azo polymerization initiators such as AIBN) that can be used as necessary are generally the same as those exemplified in the synthesis of acrylic polymers, and the amount of polymerization initiators and the amount of polymerization initiators optionally used may vary. The amount of the chain transfer agent such as n-dodecyl mercaptan is appropriately determined based on common technical knowledge so as to obtain a desired molecular weight, and therefore detailed explanation will be omitted here.

From the above viewpoint, suitable acrylic oligomers include, for example, dicyclopentanyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), dicyclopentanyl In addition to each homopolymer of acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA), a copolymer of CHMA and isobutyl methacrylate (IBMA), a copolymer of CHMA and IBXMA, Copolymer of CHMA and acryloylmorpholine (ACMO), copolymer of CHMA and diethylacrylamide (DEAA), copolymer of CHMA and AA, copolymer of ADA and methyl methacrylate (MMA), DCPMA and IBXMA copolymers of DCPMA and MMA, and copolymers of DCPMA and MMA.

When the adhesive layer disclosed herein contains an acrylic oligomer, the content is preferably, for example, 0.1 part by weight or more (for example, 1 part by weight or more) based on 100 parts by weight of the acrylic polymer. It is. From the viewpoint of better exhibiting the effects 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, still more preferably about 10 parts by weight or more, especially Preferably it is about 12 parts by weight or more. Further, from the viewpoint of compatibility with the acrylic polymer, it is appropriate that the content of the acrylic oligomer is less than 50 parts by weight (for example, less than 40 parts by weight) based on 100 parts by weight of the acrylic polymer. , preferably less than 30 parts by weight, more preferably about 25 parts by weight or less, even more preferably about 20 parts by weight or less.

In some preferred embodiments, the adhesive layer contains one or more of the above-mentioned tackifier resins and one or more acrylic oligomers. In a composition containing an acrylic polymer containing heptyl acrylate as a monomer component, by using a tackifier resin and an acrylic oligomer together, excellent adhesion can be obtained, while the usage mode is exposed to harsh conditions such as strong repulsion. Also, it can exhibit highly excellent repulsion resistance against sustained loads in the Z-axis direction. In particular, in a composition containing a high molecular weight acrylic polymer, the effect of using a tackifying resin and an acrylic oligomer in combination can be effectively exhibited. The ratio (C _T /C _O ) of the tackifying resin content C _T [wt%] to the acrylic oligomer content C _O [wt %] in the adhesive layer is not particularly limited. The above (C _T /C _O ) is suitably set to, 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, and even more preferably 0.7. It is not less than 1.5, and may be not less than 0.8 and not more than 1.2.

In some preferred embodiments, the total amount (total amount) of the tackifier resin and acrylic oligomer contained in the adhesive layer is 100 parts by weight of the acrylic polymer from the viewpoint of preferably exhibiting the effects of the technology disclosed herein. It is appropriate that the amount is approximately 1 part by weight or more, preferably approximately 10 parts by weight or more, more preferably approximately 16 parts by weight or more, still more preferably 20 parts by weight or more, particularly preferably 25 parts by weight or more. Further, it is appropriate that the amount is less than 120 parts by weight (for example, about 80 parts by weight or less), preferably less than 60 parts by weight, more preferably about 50 parts by weight or less, still more preferably about 40 parts by weight or less.

In the technology disclosed herein, the total amount (total amount) of the acrylic polymer, tackifier resin, and acrylic oligomer in the adhesive layer is appropriately set so that the effect of the technology disclosed herein is exhibited, It 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 50% by weight from the viewpoint of preferably exhibiting the effects of the technology disclosed herein. Suitably, it is 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). It may be 98% by weight or more.

(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 include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, peroxide crosslinking agents, urea crosslinking agents, and metals. Examples include alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, carbodiimide crosslinking agents, hydrazine crosslinking agents, amine crosslinking agents, and silane coupling agents. One type of crosslinking agent can be used alone or two or more types can be used in combination. Among these, isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, and melamine crosslinking agents are preferred, and isocyanate crosslinking agents and epoxy crosslinking agents are more preferred. By appropriately selecting and using a crosslinking agent, the adhesive layer can obtain cohesive force, improve repulsion resistance, and preferably achieve both repulsion resistance and impact resistance. The adhesive layer in the technology disclosed herein may contain the crosslinking agent in a form after a crosslinking reaction, a form before a crosslinking reaction, a partially crosslinked form, an intermediate or composite form thereof, etc. May contain. The crosslinking agent is typically contained in the adhesive layer exclusively in the form after crosslinking reaction.

As the isocyanate-based crosslinking agent, polyfunctional isocyanates (referring to compounds having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. The isocyanate crosslinking agents can be used alone or in combination of two or more.

Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and the like.
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; 1,2-tetramethylene diisocyanate; - hexamethylene diisocyanate such as hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,5-hexamethylene diisocyanate; Examples include 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, lysine diisocyanate, and the like.

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; 1,2-cyclopentyl diisocyanate, and 1,3-cyclohexyl diisocyanate; -Cyclopentyl diisocyanates such as cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and the like.

Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate. , 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 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, xylylene-1,3-diisocyanate, and the like.

Preferred polyfunctional isocyanates include polyfunctional isocyanates having an average of three or more isocyanate groups per molecule. Such trifunctional or higher functional isocyanates are polymers (typically dimers or trimers) of bifunctional or trifunctional or higher functional isocyanates, derivatives (for example, a combination of a polyhydric alcohol and two or more molecules of polyfunctional isocyanate). addition reaction products), polymers, etc. For example, dimers and trimers of diphenylmethane diisocyanate, isocyanurates of hexamethylene diisocyanate (trimeric adducts of isocyanurate structures), reaction products of trimethylolpropane and tolylene diisocyanate, and products of the reaction between trimethylolpropane and hexamethylene diisocyanate. Examples include polyfunctional isocyanates such as reaction products with methylene diisocyanate, polymethylene polyphenylisocyanate, polyether polyisocyanate, and polyester polyisocyanate. Commercially available products of such polyfunctional isocyanates include "Duranate TPA-100" manufactured by Asahi Kasei Chemicals, "Coronate L", "Coronate HL", "Coronate HK", and "Coronate HL" manufactured by Tosoh Corporation. Examples include "Coronate 2096" and "Coronate 2096".

The technology disclosed herein can be preferably implemented in an embodiment using at least an isocyanate-based crosslinking agent as the 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.

The amount of the isocyanate crosslinking agent used is not particularly limited. For example, the amount can be approximately 0.1 part by weight or more per 100 parts by weight of the acrylic polymer. From the perspective of achieving both cohesive force and adhesion, the amount of isocyanate crosslinking agent used per 100 parts by weight of the acrylic polymer should usually be approximately 0.3 parts by weight or more (for example, 0.5 parts by weight or more). is preferred. In some preferred embodiments, the amount of the isocyanate crosslinking agent used per 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, and still more preferably about 1.2 parts by weight. The amount may be at least 1.5 parts by weight, and may be approximately 1.5 parts by weight or more. Further, the amount of the isocyanate crosslinking agent used is suitably 10 parts by weight or less per 100 parts by weight of the acrylic polymer, preferably less than 5 parts by weight, more preferably less than 4.0 parts by weight, It is more preferably less than 3.0 parts by weight, particularly preferably 2.5 parts by weight or less, and may be less than 2.0 parts by weight (eg, 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 achieve both repulsion resistance and impact resistance while obtaining repulsion resistance against sustained loads in the Z-axis direction based on the use of isocyanate-based crosslinking agents. can be preferably realized.

As the epoxy crosslinking agent, any compound having two or more epoxy groups in one molecule can be used without particular limitation. Epoxy crosslinking agents having 3 to 5 epoxy groups in one molecule are preferred. The epoxy crosslinking agents can be used alone or in combination of two or more.

Although not particularly limited, specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylene diamine, 1,3-bis(N,N-diglycidylaminomethyl ) cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether and the like. Commercially available epoxy crosslinking agents include Mitsubishi Gas Chemical's product names "TETRAD-C" and "TETRAD-X", DIC's product name "Epicron CR-5L", and Nagase ChemteX's product name Examples include the product name "Denacol EX-512" manufactured by Nissan Chemical Industries, Ltd. and the product name "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd.

The amount of the epoxy crosslinking agent used is not particularly limited. The amount of the epoxy crosslinking agent used may be, for example, more than 0 parts by weight and no more than about 1 part by weight (typically about 0.001 to 1 part by weight) per 100 parts by weight of the acrylic polymer. can. From the viewpoint of suitably exhibiting the effect of improving cohesive force, it is usually appropriate to use the epoxy crosslinking agent in an amount of about 0.002 parts by weight or more per 100 parts by weight of the acrylic polymer, preferably It is about 0.005 parts by weight or more, and may be about 0.01 parts by weight or more, for example. In addition, from the viewpoint of improving adhesion to the adherend, the amount of the epoxy crosslinking agent used is approximately 0.5 parts by weight or less per 100 parts by weight of the acrylic polymer, and approximately 0.2 parts by weight. It is preferably at most 0.1 part by weight (for example less than 0.1 part by weight), more preferably at most 0.07 part by weight, and may be at most 0.04 part by weight. In addition, from the perspective of avoiding reduction in impact resistance due to excessive crosslinking, it is usually appropriate to use the epoxy crosslinking agent in an amount of about 0.03 parts by weight or less per 100 parts by weight of the acrylic polymer. The amount is preferably about 0.02 parts by weight or less. By restricting the amount of the epoxy crosslinking agent used within a predetermined range, it is easy to maintain sufficient adhesive strength and to obtain repulsion resistance against sustained loads in the Z-axis direction.

In some preferred embodiments, as the crosslinking agent, an isocyanate crosslinking agent and at least one crosslinking agent having a different type of crosslinkable functional group from the isocyanate crosslinking agent are used in combination. According to the technology disclosed herein, a crosslinking agent other than an isocyanate crosslinking agent (that is, a crosslinking agent having a different type of crosslinkable reactive group from the isocyanate crosslinking agent; hereinafter also referred to as a "non-isocyanate crosslinking agent") By using it in combination with an isocyanate-based crosslinking agent, repulsion resistance and impact resistance can be preferably achieved at the same time.

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 agents can be used alone or in combination of two or more. In some preferred embodiments, an epoxy crosslinker can be employed as the non-isocyanate crosslinker. For example, by using an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent in combination, it is possible to better achieve both repulsion resistance and impact resistance against a sustained load in the Z-axis direction.

The relationship between the content of the isocyanate-based crosslinking agent and the content of the non-isocyanate-based crosslinking agent (preferably the epoxy-based crosslinking agent) is not particularly limited. is set to The content of the isocyanate crosslinking agent is, for example, more than 1 time, preferably about 10 times or more, relative to the content of the non-isocyanate crosslinking agent (preferably an epoxy crosslinking agent). is about 50 times or more, more preferably about 80 times or more, still more preferably about 100 times or more (for example, more than 100 times), particularly preferably about 120 times or more (for example, about 140 times or more). In addition, from the viewpoint of suitably exhibiting the effect of using an isocyanate crosslinking agent and a non-isocyanate crosslinking agent (preferably an epoxy crosslinking agent) in combination, a non-isocyanate crosslinking agent (preferably an epoxy crosslinking agent) is usually used. The content of the isocyanate crosslinking agent relative to the content of the crosslinking agent (crosslinking agent) is, for example, approximately 1000 times or less, suitably approximately 500 times or less, preferably approximately 300 times or less, and more preferably approximately 200 times or less. , more preferably about 180 times or less (for example, about 160 times or less).

The content of crosslinking agent (total amount of crosslinking agent) in the adhesive composition disclosed herein 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 preferably about 0.002 parts by weight or more, based on 100 parts by weight of the acrylic polymer. Preferably it is about 0.005 part by weight or more, more preferably about 0.01 part by weight or more, still more preferably about 0.02 part by weight or more, particularly preferably about 0.03 part by weight or more. In some embodiments, the content of the crosslinking agent per 100 parts by weight of the acrylic polymer is about 0.1 parts by weight or more, more preferably about 0.5 parts by weight or more, and even more preferably about 1.0 parts by weight or more. The amount may be about 1.2 parts by weight or more, or about 1.5 parts by weight or more. The content of the crosslinking agent in the adhesive composition is usually about 20 parts by weight or less, preferably about 15 parts by weight or less, and about 10 parts by weight, based on 100 parts by weight of the acrylic polymer. It is preferable that the amount is less than (for example, about 5 parts by weight or less). In some embodiments, the content of the crosslinking agent per 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, still more preferably 2.5 parts by weight or less, The amount may be 2.0 parts by weight or less (for example, less than 2.0 parts by weight), or 1.8 parts by weight or less. By appropriately setting the total amount of crosslinking agent used within the above range, repulsion resistance and impact resistance can be preferably achieved at the same time.

(Other additives)
In addition to the above-mentioned components, the adhesive composition may contain a leveling agent, a crosslinking aid, a plasticizer, a softener, a filler, a coloring agent (pigment, dye, etc.), an antistatic agent, and an antiaging agent, as necessary. , ultraviolet absorbers, antioxidants, rust preventives, light stabilizers, and other additives commonly used in the adhesive field. Regarding such various additives, conventionally known ones can be used in a conventional manner, and since they do not particularly characterize the present invention, detailed explanations will be omitted.

The adhesive layer (layer consisting of an adhesive) disclosed herein is formed from a water-based adhesive composition, a solvent-based adhesive composition, a hot-melt adhesive composition, or an active energy ray-curable adhesive composition. It may be an adhesive layer. The aqueous adhesive composition refers to an adhesive composition containing an adhesive (adhesive layer forming component) in a water-based solvent (aqueous solvent), and is typically a water-based adhesive composition. This includes what is called a type adhesive composition (a composition in which at least a portion of an adhesive is dispersed in water). In addition, a solvent-based adhesive composition refers to an adhesive composition 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 (toluene, ethyl acetate, etc.) that can be used in the above-mentioned solution polymerization can be used without particular limitation. The technology disclosed herein can be preferably implemented in an embodiment including an adhesive layer formed from a solvent-based adhesive composition from the viewpoint of adhesive properties and the like.

The adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method can be adopted in which a pressure-sensitive adhesive layer is formed by applying a pressure-sensitive adhesive composition to a surface having peelability (peelability surface) or a non-peelability surface and drying it. For an adhesive sheet having a base material, for example, a method (direct method) of forming an adhesive layer by directly applying (typically coating) an adhesive composition to the base material and drying is adopted. be able to. In addition, a method (transfer method) in which an adhesive composition is applied to a surface that has releasability (release surface) and dried to form an adhesive layer on the surface, and the adhesive layer is transferred to a base material. may be adopted. 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 release-treated base material, etc. can be used. Note that although the adhesive layer disclosed herein is typically formed continuously, it is not limited to this form, and may be formed, for example, in a regular or random pattern such as dots or stripes. It may also be a formed adhesive layer.

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

(thickness)
The thickness of the adhesive layer is not particularly limited, and a configuration having an adhesive layer having an appropriate thickness in the range of, for example, 0.1 to 500 μm may be adopted depending on the use and purpose of use. In some embodiments, from the viewpoint of preventing the adhesive sheet from becoming excessively thick, the thickness of the adhesive layer is usually approximately 100 μm or less, preferably approximately 70 μm or less, more preferably approximately 60 μm or less, More preferably, it is approximately 50 μm or less. The thickness of the adhesive layer can be approximately 35 μm or less, and may be approximately 30 μm or less, for example. An adhesive layer with a limited thickness can meet the demands for thinning and weight reduction. Additionally, in general, as the thickness of the adhesive layer becomes smaller, the impact resistance and adhesion to the adherend tend to decrease, but according to the technology disclosed herein, the adhesive layer can be With this configuration, sufficient impact resistance and adhesive strength can be achieved. In some embodiments, the lower limit of the thickness of the adhesive layer is suitably about 0.5 μm or more, from the viewpoint of adhesion to the adherend, it may be about 1 μm or more, and it may be about 3 μm or more. Advantageously, it is approximately 10 μm or more, more preferably approximately 12 μm or more (eg greater than 12 μm), still more preferably approximately 15 μm or more, and may for example be approximately 18 μm or more. In some preferred embodiments, the thickness of the adhesive layer is greater than 20 μm, may be greater than or equal to 24 μm, and may be greater than or equal to 27 μm. The pressure-sensitive adhesive sheet disclosed herein may be a pressure-sensitive adhesive sheet having pressure-sensitive adhesive layers having the above-mentioned thickness on both sides of a base material. In addition, in a double-sided adhesive sheet with a base material that has a first adhesive layer and a second adhesive layer on each side of the base material, the first adhesive layer and the second adhesive layer have the same thickness. They may have different thicknesses.

(Biomass carbon ratio)
In some embodiments, the adhesive layer may include a biomass-derived material, and the biomass carbon ratio may be greater than or equal to a predetermined value. The biomass carbon ratio of the 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 in the adhesive means that less fossil resource-based materials, such as petroleum, are used. From this point of view, the higher the biomass carbon ratio of the adhesive, the more preferable. For example, the biomass carbon ratio of the adhesive layer may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. good. 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. In some embodiments, from the viewpoint of facilitating good adhesive performance, the biomass carbon ratio of the adhesive layer may be, for example, 90% or less, 85% or less, or 80% or less.

<Base material>
In an embodiment in which the adhesive sheet disclosed herein is in the form of a single-sided adhesive type or double-sided adhesive type adhesive sheet with a base material, the base material that supports (backs) the adhesive layer may be a resin film, paper, cloth, or rubber. Sheets, foam sheets, metal foils, composites thereof, etc. can be used. Examples of paper include Japanese paper, kraft paper, glassine paper, high quality paper, synthetic paper, top coated paper, and the like. Examples of the fabric include woven fabrics and nonwoven fabrics made of various fibrous substances alone or in combination. Examples of the above-mentioned fibrous materials include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets, butyl rubber sheets, and the like. Examples of foam sheets include foamed polyolefin sheets, foamed polyurethane sheets, foamed polychloroprene rubber sheets, and the like. Examples of metal foil include aluminum foil, copper foil, and the like. Note that the base material that supports the adhesive layer is also referred to as a base material layer in the adhesive sheet.

The base material may be formed from a biomass-derived material or a non-biomass-derived material. From the viewpoint of producing a pressure-sensitive adhesive sheet in consideration of reducing dependence on fossil resource-based materials, biomass-derived base materials (typically resin films) are preferably used.

Further, the base material may be formed using a recyclable material or a recycled material (also referred to as recycled material). As such a recycled material, a resin film is preferably used. Resin films (for example, polyester films such as PET films) can be recycled, so whether or not they are made from plant-based materials, reusing the used resin film allows for sustainable reproduction. It is possible to reduce the environmental burden. Such a recyclable resin film or a recycled resin film is also referred to as a recycled film. The recycled material (for example, recycled film) may be formed from a biomass-derived material or a non-biomass-derived material.

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

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 exceeding 50% by weight). Examples of resin films include polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers; polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), etc. Examples include polyester resin film; vinyl chloride resin film; vinyl acetate resin film; polyimide resin film; polyamide resin film; fluororesin film; cellophane; and the like. The resin film may be a rubber film such as a natural rubber film or a butyl rubber film. Among these, polyester films are preferred from the viewpoint of handling and processability, and among these, PET films are particularly preferred.

In addition, in this specification, "resin film" is typically a non-porous sheet, and is a concept that is distinguished from so-called non-woven fabrics and woven fabrics (in other words, a concept excluding non-woven fabrics and woven fabrics). be. The resin film may be an unstretched film, a uniaxially stretched film, or a biaxially stretched film. Also, such resin films may be non-foamed. Here, the non-foamed resin film refers to a resin film that has not been intentionally processed to form a foam. Specifically, the 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).

The above base material (e.g. resin film) may contain fillers (inorganic fillers, organic fillers, etc.), colorants, dispersants (surfactants, etc.), anti-aging agents, antioxidants, ultraviolet rays, etc., as necessary. Various additives such as absorbers, antistatic agents, lubricants, and plasticizers may be blended. The blending ratio of various additives is about less than 30% by weight (for example, less than 20% by weight, typically less than 10% by weight).

The base material (for example, a resin film) may have a single layer structure, or may have a multilayer structure of two layers, three layers, or more. From the viewpoint of shape stability, the base material preferably has a single-layer structure. In the case of a multilayer structure, at least one layer (preferably all layers) is preferably a layer having a continuous structure of the above resin (for example, polyester resin). The method for producing the base material (typically a resin film) is not particularly limited, and any conventionally known method may be appropriately adopted. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting molding, and calender roll molding can be appropriately employed.

The surface of the base material may be subjected to conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and application of an undercoat. Such surface treatment may be a treatment for improving the adhesion between the base material and the adhesive layer, in other words, the ability of the adhesive layer to anchor to the base material.

Further, when the technology disclosed herein is implemented in the form of a single-sided pressure-sensitive adhesive sheet with a base material, the back surface of the base material may be subjected to a peeling treatment as necessary. For example, the peeling treatment is performed by applying a general silicone-based, long-chain alkyl-based, or fluorine-based peeling agent to a thin film, typically about 0.01 μm to 1 μm (for example, 0.01 μm to 0.1 μm). It can be a process to add. By performing such a peeling treatment, effects such as facilitating the unwinding of a roll of the adhesive sheet can be obtained.

In an embodiment of the pressure-sensitive adhesive sheet including a base material, the thickness of the base material is not particularly limited. From the viewpoint of preventing the pressure-sensitive adhesive sheet from becoming too thick, the thickness of the base material can be, for example, approximately 200 μm or less, preferably approximately 150 μm or less, and more preferably approximately 100 μm or less. The thickness of the base material may be approximately 70 μm or less, approximately 50 μm or less, or approximately 30 μm or less (for example, approximately 25 μm or less) depending on the purpose and manner of use of the adhesive sheet. In some embodiments, the thickness of the substrate can be about 20 μm or less, about 15 μm or less, about 10 μm or less (eg, about 5 μm or less). By reducing the thickness of the base material, the thickness of the adhesive layer can be increased even if the total thickness of the adhesive sheet is the same. This can be advantageous from the viewpoint of improving adhesion to adherends and base materials. The lower limit of the base material is not particularly limited. From the viewpoint of handleability and processability of the pressure-sensitive adhesive sheet, the thickness of the base material is usually about 0.5 μm or more (for example, 1 μm or more), preferably about 2 μm or more, for example about 6 μm or more. In some embodiments, the thickness of the substrate can be about 15 μm or more, and can be about 25 μm or more.

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

The thickness of the foam base material is not particularly limited, and can be appropriately set depending on the strength and flexibility of the adhesive sheet, the purpose of use, etc. From the viewpoint of thinning, the thickness of the foam base material is usually 1 mm or less, suitably 0.70 mm or less, preferably 0.40 mm or less, and more preferably 0.30 mm or less. The technology disclosed herein is preferably implemented in an embodiment in which the thickness of the foam base material is 0.25 mm or less (typically 0.18 mm or less, for example 0.16 mm or less) from the viewpoint of processability etc. obtain. In addition, from the viewpoint of impact resistance of the adhesive sheet, the thickness of the foam base material is usually 0.04 mm or more, suitably 0.05 mm or more, preferably 0.06 mm or more, and 0.07 mm or more. More preferably (for example, 0.08 mm or more). The technology disclosed herein is preferably carried out in an embodiment in which the thickness of the foam base material 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). obtain. Increasing the thickness of the foam substrate tends to improve impact resistance.

The density (referring to apparent density; hereinafter the same applies unless otherwise specified) of the foam base material 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 base material is suitably 0.8 g/cm ³ or less, preferably 0.7 g/cm ³ or less (for example, 0.6 g/cm ³ or less). In one embodiment, the density of the foam substrate may be less than 0.5 g/cm ³ , and may be less than 0.4 g/cm ³ (eg, 0.5 g/cm ³ or less). In addition, from the viewpoint of impact resistance, the density of the foam base material is preferably 0.12 g/cm ³ or more, more preferably 0.15 g/cm 3 or more, and 0.2 g/cm ³ or more (for example, 0.3 g/cm ³ or more). /cm ³ or more) is more preferable. In one aspect, the density of the foam substrate can be 0.4 g/cm ^or more, 0.5 g/cm ³ or more (e.g., greater than 0.5 g/cm 3 ), or even 0.5 g/cm ³ or more (e.g., greater than 0.5 g/cm 3 ), It may be .55 g/cm ³ or more. Note that the density (apparent density) of the foam base material can be measured in accordance with JIS K 6767.

The average cell diameter of the foam base material is not particularly limited, but from the viewpoint of stress distribution, 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 cell diameter is not particularly limited, but from the viewpoint of step followability, it is usually suitable 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 aspect, the average cell diameter may be 55 μm or more, or 60 μm or more. In addition, the average cell diameter here refers to the average cell diameter in terms of a perfect sphere, which is obtained by observing the cross section of the foam base material with an electron microscope.

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 shock absorption, closed cell structures and semi-open and semi-closed cell structures are preferred.

The 25% compressive strength _C25 of the foam base material is not particularly limited, and may be, for example, 20 kPa or more (typically 30 kPa or more, and even 40 kPa or more). _C25 is usually suitably 250 kPa or more, preferably 300 kPa or more (for example, 400 kPa or more). A pressure-sensitive adhesive sheet including such a foam base material can exhibit good durability against impacts such as dropping. For example, tearing of the adhesive sheet due to impact can be better prevented. Although the upper limit of _C25 is not particularly limited, it is usually suitable to be 1300 kPa or less (for example, 1200 kPa or less). In one embodiment, C ₂₅ may be 1000 kPa or less, 800 kPa or less, even 600 kPa or less (eg, 500 kPa or less), or 360 kPa or less. In another preferred embodiment, the C ₂₅ of the foam substrate may be between 20 kPa and 200 kPa (typically between 30 kPa and 150 kPa, such as between 40 kPa and 120 kPa). A pressure-sensitive adhesive sheet including such a foam base material can have excellent cushioning properties. For example, if the foam base material absorbs the impact of a fall, peeling of the adhesive sheet can be better prevented.

The 25% compressive strength _C25 of the foam base material is determined by cutting the foam base material into 30 mm squares, stacking them to a thickness of about 2 mm, and sandwiching the measurement sample between a pair of flat plates. It refers to the load when compressed by a thickness corresponding to 25% of the thickness (load at a compression rate of 25%). That is, it refers to the load when the measurement sample is compressed to a thickness corresponding to 75% of its original thickness. The compressive strength is measured in accordance with JIS K 6767. The specific measurement procedure is to set the measurement sample at the center of the pair of flat plates, compress the plate continuously to a predetermined compression rate by narrowing the gap between the plates, and then stop the flat plates for 10 seconds. Measure the load after the elapsed time. The compressive strength of the foam base material can be controlled by, for example, the degree of crosslinking and density of the material constituting the foam base material, the size and shape of the cells, and the like.

The tensile elongation of the foam base material is not particularly limited. For example, a foam base material having a tensile elongation in the machine direction (MD) of 200% to 800% (more preferably 400% to 600%) can be suitably employed. Further, a foam base material having a tensile elongation in the width direction (TD) of 50% to 800% (more preferably 200% to 500%) is preferable. The elongation of the foam base material is measured in accordance with JIS K 6767. The elongation of the foam base material can be controlled, for example, by the degree of crosslinking, apparent density (expansion ratio), and the like.

The tensile strength (tensile strength) of the foam base material is not particularly limited. For example, a foam base material having a tensile strength in the machine direction (MD) of 5 MPa to 35 MPa (preferably 10 MPa to 30 MPa) can be suitably employed. Further, a foam base material having a tensile strength in the width direction (TD) of 1 MPa to 25 MPa (more preferably 5 MPa to 20 MPa) is preferable. The tensile strength of the foam base material is measured in accordance with JIS K 6767. The tensile strength of the foam base material can be controlled, for example, by the degree of crosslinking, apparent density (expansion ratio), and the like.

The material of the foam base material is not particularly limited. Foam substrates comprising a foam layer formed of a foam of plastic material (plastic foam) are usually preferred. The plastic material (which includes rubber materials) for forming the plastic foam is not particularly limited, and can be appropriately selected from known plastic materials. The plastic materials can be used alone or in an appropriate combination of two or more.

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 foam such as polyvinyl chloride foam; vinyl acetate resin foam; polyphenylene sulfide resin foam; aliphatic polyamide (nylon) resin foam, fully aromatic polyamide (aramid) Amide resin foams such as resin foams; Polyimide resin foams; Polyetheretherketone (PEEK) foams; Styrenic resin foams such as polystyrene foams; Polyurethane resin foams, etc. Urethane resin foam; and the like. Further, as the plastic foam, a rubber resin foam such as a polychloroprene rubber foam may be used.

As a preferable foam, a polyolefin resin foam (hereinafter also referred to as "polyolefin foam") is exemplified. As the plastic material (ie, polyolefin resin) constituting the polyolefin foam, various known or commonly used polyolefin resins can be used without particular limitation. Examples include PE such as low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and high density polyethylene (HDPE), PP, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and the like. Examples of LLDPE include Ziegler-Natta catalyst-based linear low-density polyethylene, metallocene-catalyzed linear low-density polyethylene, and the like. Such polyolefin resins can be used alone or in an appropriate combination of two or more.

A preferred example of the foam base material in the technology disclosed herein is a PE foam base material substantially composed of a PE resin foam from the viewpoint of impact resistance, waterproofness, dustproofness, etc. , a polyolefin foam base material such as a PP foam base material substantially composed of a foam of a PP resin. Here, the PE-based resin refers to a resin whose main monomer (that is, the main component among monomers) is ethylene, and includes HDPE, LDPE, LLDPE, etc., as well as ethylene-based resin with an ethylene copolymerization ratio of more than 50% by weight. It may include propylene copolymers, ethylene-vinyl acetate copolymers, and the like. Similarly, PP-based resin refers to a resin whose main monomer is propylene. As the foam base material in the technology disclosed herein, a PE foam base material can be preferably employed.

The method for producing the plastic foam (typically a polyolefin foam) is not particularly limited, and various known methods may be employed as appropriate. For example, it can be manufactured by a method including a molding step, a crosslinking step, and a foaming step of the above plastic material or the above plastic foam. Moreover, a stretching step may be included as necessary.
Examples of methods for crosslinking the plastic foam include a chemical crosslinking method using an organic peroxide or the like, an ionizing radiation crosslinking method involving irradiation with ionizing radiation, and these methods may be used in combination. Examples of the ionizing radiation include electron beams, α rays, β rays, γ rays, and the like. The dose of ionizing radiation is not particularly limited, and can be set to an appropriate dose in consideration of the target physical properties (for example, degree of crosslinking) of the foam base material.

The foam base material may contain fillers (inorganic fillers, organic fillers, etc.), anti-aging agents, antioxidants, ultraviolet absorbers, antistatic agents, lubricants, plasticizers, flame retardants, Various additives such as surfactants may be blended.

The foam base material in the technology disclosed herein may be black or white in order to exhibit desired design properties and optical properties (e.g., light shielding properties, light reflection properties, etc.) in a pressure-sensitive adhesive sheet including the foam base material. It may be colored as such. For this coloring, one kind of known organic or inorganic coloring agent can be used alone or two or more kinds can be used in an appropriate combination.

The surface of the foam base material may be subjected to an appropriate surface treatment, if necessary. This surface treatment can be, for example, a chemical or physical treatment to increase adhesion to adjacent materials (eg, 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.

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

<Total thickness of adhesive sheet>
The total thickness of the adhesive sheet disclosed herein (which includes an adhesive layer and may further include a base layer, but does not include a release liner) is not particularly limited. The total thickness of the adhesive sheet is, for example, approximately 1 mm or less, may be approximately 500 μm or less, and may be approximately 300 μm or less, and from the viewpoint of thinning, approximately 200 μm or less is appropriate, and approximately 150 μm or less. (For example, approximately 100 μm or less). In some preferred embodiments, the thickness of the pressure-sensitive adhesive sheet can be approximately 50 μm or less, for example, approximately 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), suitably about 3 μm or more, preferably about 10 μm or more, more preferably about 15 μm or more, It may be about 50 μm or more, or about 100 μm or more. A pressure-sensitive adhesive sheet having a thickness of a predetermined value or more tends to have good adhesion to an adherend and also tends to have excellent handling properties. In addition, in the adhesive sheet without a base material, the thickness of the adhesive layer becomes the total thickness of the adhesive sheet.

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

Further, the pressure-sensitive adhesive sheet disclosed herein preferably has a floating height of 2.0 mm or less at the end of the test in a repulsion resistance evaluation test conducted by the method described below. A pressure-sensitive adhesive sheet that satisfies the above characteristics has particularly excellent repulsion resistance against a peeling load consisting essentially only in the thickness direction (Z-axis direction) of the pressure-sensitive adhesive sheet, and has a sustained resistance in that direction. Particularly resistant to peeling under peeling loads. It also exhibits stable repulsion resistance even when adhesive sheets attached to adherends (e.g., mobile electronic devices and their component modules) are exposed to high temperature and high humidity conditions during storage. It is possible. The floating 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, particularly preferably 0.4 mm or less. . Note that the above-mentioned floating height is a height that includes the thickness of the adhesive sheet (30 μm in the examples described later).

[Repulsion resistance evaluation test]
A polyethylene terephthalate (PET) film having a length of 70 mm, a width of 10 mm, and a thickness of 75 μm is fixed to the lower surface of a polycarbonate plate having a length of 30 mm, a width of 10 mm, and a thickness of 2 mm at one longitudinal end of the PET film. Next, the PET film is bent along the longitudinal direction, and the other end of the bent PET film in the longitudinal direction is fixed to the upper surface of the polycarbonate plate using an adhesive sheet with an adhesion area of 3 mm x 10 mm. This state is maintained at 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 above-mentioned repulsion resistance evaluation test is carried out by the method described in the Z-axis direction repulsion resistance test in Examples described below.

The adhesive sheet disclosed herein preferably has an impact adhesive strength of 0.3 J/cm ² or more in an impact test conducted in accordance with JIS K6855. A pressure-sensitive adhesive sheet that satisfies this property can serve as a bonding means with excellent durability against impact in the shear direction. Therefore, for example, it can be preferably used as a member fixing means in a portable electronic device that is expected to be exposed to shocks due to drops or collisions. According to the technology disclosed herein, 0.35 J/cm ² or more (more preferably 0.40 J/cm ² or more, still more preferably 0.45 J/cm ² or more, particularly preferably 0.50 J/cm ² or more) A pressure-sensitive adhesive sheet can be provided that exhibits an impact adhesive strength of . The upper limit of the impact adhesive strength is not particularly limited, and may be, for example, 3.00 J/cm ² or less. From the viewpoint of easily achieving both repulsion resistance and repulsion resistance at a higher level, the impact adhesive strength may be, for example, 1.00 J/cm ² or less, 0.80 J/cm ² or less, or 0.60 J. / ^cm2 or less. More specifically, the above-mentioned impact resistance test is carried out by the method described in the impact resistance test of Examples below.

In some embodiments, the adhesive sheet may contain a biomass-derived material, and the biomass carbon ratio may be greater than or equal to a predetermined value. The biomass carbon ratio of the 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 in the adhesive sheet means that less fossil resource-based materials, such as petroleum, are used. From this point of view, 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 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. In some embodiments, from the viewpoint of facilitating good adhesive performance, the biomass carbon ratio of the adhesive sheet may be, for example, 90% or less, 85% or less, or 80% or less.

<Application>
The use of the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and can be used for various purposes. The pressure-sensitive adhesive sheet disclosed herein is capable of achieving both repulsion resistance and impact resistance, and is therefore suitable for adhesively fixing members in applications where high repulsion resistance and impact resistance may be required. For example, it can be preferably used for fixing members in various types of portable equipment. Non-limiting examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, and various wearable devices (e.g., wrist-wear type that is worn on the wrist like a wristwatch, and Modular type that is attached to a part of the body, eyewear type that includes glasses type (monocular type and binocular type, including head-mounted type), clothing type that is attached to shirts, socks, hats, etc. in the form of accessories, and earphones. digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic notebooks, electronic books, and in-vehicle devices. This includes information equipment, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. Note that in this specification, "portable" does not mean that it is sufficient to simply be able to carry it; it also means that it has a level of portability that allows an individual (standard adult) to carry it relatively easily. shall mean.

The adhesive sheet (typically a double-sided adhesive sheet) disclosed herein is in the form of a bonding material processed into various external shapes and can be used for fixing members constituting the above-mentioned portable electronic device. Among these, it can be preferably used for portable electronic devices having a liquid crystal display device. For example, it is an electronic device (typically a portable electronic device such as a smartphone) that has a display section such as a touch panel display (which can be a display section of a liquid crystal display device), and is used to increase the screen size. The adhesive sheet disclosed herein is preferably used for fixing an elastic adherend in a device in which an elastic member such as FPC is folded and accommodated in an internal space. By using the pressure-sensitive adhesive sheet disclosed herein, it is possible to stably fix an elastic adherend in a bent state, and to maintain the fixed state continuously. As a result, the elastic member accommodated in a bent state in the limited internal space of the portable electronic device can be accurately positioned and held in a stable fixed state by the adhesive sheet disclosed herein. In addition, examples of materials disposed inside the above-mentioned portable electronic devices 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 a 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) that constitutes the portable electronic device. . Adhesive sheets used for fixing members having such three-dimensional surface shapes tend 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 a three-dimensional shape as described above can be stably fixed.

In recent years, the development of electronic devices (typically portable electronic devices such as smartphones and tablet computers) that have a display section such as the above-mentioned touch panel display (which can be the display section of a liquid crystal display device) has been particularly important in recent years. The aim is to achieve both advanced technology and high functionality. In order to increase the screen size, measures have been taken such as folding and housing an elastic member such as the above-mentioned FPC in the internal space. On the other hand, with regard to higher functionality, new functions such as pressure-sensitive sensors with more accurate pressure sensing performance and facial recognition unlocking functions are being added, resulting in products with higher performance and higher quality. For this purpose, it is essential that the circuits that play a role in this process, such as FPCs, become highly integrated. Examples of means for increasing circuit integration include double-sided FPC and multilayer FPC, but both increase the rigidity of the FPC, and the Z-axis as evaluated by the Z-axis repulsion test described below. It is expected that improved repulsion resistance against sustained loads in the axial direction will become a required characteristic. The pressure-sensitive adhesive sheet according to a preferred embodiment of the technology disclosed herein may exhibit excellent repulsion resistance under harsh high temperature and high humidity conditions (strong repulsion conditions) as in the Z-axis repulsion resistance test described below. Therefore, it is more suitable for the above-mentioned next-generation touch-panel display-equipped electronic devices (typically, touch-panel display-equipped portable electronic devices such as smartphones), and can be preferably used.

Although not particularly limited, in some embodiments, the adhesive sheet is preferably used, for example, in electronic devices that include various light sources such as LEDs (light emitting diodes) and light emitting elements such as self-luminous organic EL. For example, it can be preferably used in electronic equipment (typically portable electronic equipment) that includes an organic EL display device or a liquid crystal display device.

FIG. 4 is an example schematically showing a portable electronic device (smartphone) using the adhesive sheet disclosed herein. As shown in FIG. 4, a battery (heat generating element) 540 is built inside the casing 520 of the portable electronic device 500. Moreover, the portable electronic device 500 is 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 members constituting the portable electronic device 500. Note that the portable electronic device 500 includes a touch panel 570 whose display section also functions as an input section. The adhesive sheet disclosed herein is preferably used as a component (member joining means) of the above-mentioned portable electronic devices.

Furthermore, since the adhesive sheet disclosed herein may have an adhesive layer containing an acrylic polymer with a high biomass carbon ratio in some embodiments, conventional general acrylic adhesives (i.e. By being used as a substitute for acrylic adhesives in various applications where acrylic adhesives (acrylic adhesives with a low biomass carbon ratio) are used, it can contribute to reducing dependence on fossil resource-based materials. The adhesive sheet disclosed herein can be preferably used as an adhesive sheet with reduced dependence on fossil resource materials.

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

[11] Has an adhesive layer containing an acrylic polymer,
The acrylic polymer is a polymer of monomer components containing heptyl acrylate,
The 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, where the tan δ is the adhesive layer. The ratio of loss elastic modulus G'' to storage elastic modulus G'(G''/G') of an adhesive sheet.
[12] The pressure-sensitive adhesive sheet according to [11] above, wherein the acrylic polymer has a weight average molecular weight of 700,000 or more.
[13] The glass transition temperature of the adhesive layer is within the range of -15°C to 15°C, where the glass transition temperature of the adhesive layer is determined from the peak temperature of tan δ in dynamic viscoelasticity measurement. The adhesive sheet according to [11] or [12] above, which has a glass transition temperature.
[14] The pressure-sensitive adhesive sheet according to any one of [11] to [13] above, wherein the pressure-sensitive adhesive layer further contains a tackifying resin.
[15] The pressure-sensitive adhesive sheet according to any one of [11] to [14] above, wherein the pressure-sensitive adhesive layer contains at least one selected from rosin-based tackifying resins and terpene-based tackifying resins.
[16] The pressure-sensitive adhesive sheet according to any one of [11] to [15] above, wherein the content of the tackifying resin in the pressure-sensitive adhesive layer is 70 parts by weight or less based on 100 parts by weight of the acrylic polymer. .
[17] The pressure-sensitive adhesive sheet according to any one of [11] to [16] above, wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer.
[18] The adhesive composition for forming the adhesive layer includes at least one selected from an isocyanate crosslinking agent and an epoxy crosslinking agent, according to any one of [11] to [17] above. adhesive sheet.
[19] The adhesive sheet according to any one of [11] to [18] above, which has a 180 degree peel strength against a stainless steel plate of 20 N/25 mm or more.
[20] The adhesive sheet according to any one of [11] to [19] above, which is used for fixing members in portable electronic devices.
[21] A portable electronic device comprising the adhesive sheet according to any one of [11] to [20] above.

Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to what is shown in these examples. In the following description, "parts" and "%" are based on weight unless otherwise specified.

<Example 1>
(Synthesis of acrylic polymer)
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 a polymerization solvent were added. and ethyl acetate were added thereto, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen in the polymerization system in this way, 0.2 part of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and solution polymerization was carried out at 60°C to 70°C for 8 hours. An acrylic polymer solution was obtained. The weight average molecular weight (Mw) of this acrylic polymer was 1.2 million. Mw was adjusted by adjusting the concentration of monomer components during polymerization. Note that the above n-HpA is a compound having a biomass-derived heptyl group at the ester end, which was synthesized using biomass-derived heptyl alcohol.

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

(Preparation of adhesive sheet)
The obtained adhesive composition was applied to the release surface of a polyester release film (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) with a thickness of 38 μm, and dried at 100° C. for 2 minutes to form a film with a thickness of 30 μm. An adhesive layer was formed. A release surface of a 25 μm thick polyester release film (trade name “Diafoil MRF”, 25 μm thick, manufactured by Mitsubishi Chemical Corporation) was attached to this adhesive layer. In this way, a substrate-less double-sided pressure-sensitive adhesive sheet having a thickness of 30 μm and having both sides protected by the two polyester release films was obtained.

<Examples 2 to 6 and Comparative Examples 1 to 4>
Basically the same method as in Example 1 except that the monomer composition of the acrylic polymer, Mw, the type and amount of the tackifying resin, the amount of the acrylic oligomer, and the type and amount of the crosslinking agent were changed as shown in Table 1. A pressure-sensitive adhesive composition according to each example was prepared, and using the obtained pressure-sensitive adhesive composition, a substrate-less double-sided adhesive sheet (thickness: 30 μm) according to each example was prepared in the same manner as in Example 1. ) was created. The Mw of the acrylic polymer was adjusted by adjusting the concentration of monomer components during polymerization.
In Table 1, 2EHA represents 2-ethylhexyl acrylate, BA represents n-butyl acrylate, 4HBA represents 4-hydroxybutyl acrylate, and HEA represents hydroxyethyl acrylate. Terpene phenol B is a product name "YS Polyster S-145" manufactured by Yasuhara Chemical Co., Ltd. (a terpene phenol resin with a softening point of approximately 145°C and a hydroxyl value of 70 to 110 mgKOH/g), and the rosin ester is manufactured by Arakawa Chemical Co., Ltd. The product name is "Pensel D125" (polymerized rosin ester with a softening point of 125° C. and a hydroxyl value of 32 mgKOH/g) manufactured by the company.
Moreover, as the acrylic oligomer, one prepared by the following method was used. Specifically, in a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, a reflux condenser, and a dropping funnel, 95 parts of cyclohexyl methacrylate (CHMA) and 5 parts of AA, and 10 parts of AIBN as a polymerization initiator, After charging ethyl acetate as a polymerization solvent and stirring in a nitrogen stream for 1 hour to remove oxygen from the polymerization system, the temperature was raised to 85°C and reacted for 5 hours to form an acrylic oligomer with a solid content concentration of 50%. Obtained. The Mw of the obtained acrylic oligomer was 3,600.

<Evaluation method>
[Adhesive strength to SUS]
Under a measurement environment of 23°C and 50% RH, one adhesive side of an adhesive sheet (double-sided adhesive sheet) was lined with a PET film with a thickness of 50 μm, and cut into a size of 25 mm in width and 100 mm in length. A measurement sample was prepared. In an environment of 23° C. and 50% RH, the other adhesive surface of the measurement sample was pressed onto the surface of a stainless steel plate (SUS304BA plate) that had been cleaned with ethyl acetate by making one reciprocation with a 2 kg roller. After leaving it in the same environment for 72 hours, using a universal tensile compression tester, the peel strength (relative to SUS Adhesive force) [N/25 mm] was measured. In the above peel strength measurement, the universal tensile compression tester used is Minebea's "Tensile Compression Tester, TG-1kN" or its equivalent. Note that when performing the above peel strength measurement on a single-sided adhesive sheet, backing with a PET film is not necessary. When the base material thickness is thin (for example, when the base material thickness is 25 μm or less), it may be lined with a PET film.

[Shock resistance test (pendulum)]
Impact resistance (impact adhesive strength) [J/cm ² ] was measured using a pendulum adhesive shear impact tester based on JIS K6855 (corresponding to international standard ISO 9653). As test pieces, adhesive sheet pieces obtained by cutting the base material-less double-sided adhesive sheets according to each example into 10 mm square pieces were used, and a 10 mm square, 5 mm thick stainless steel (SUS304) plate was attached to another stainless steel plate (SUS304 plate). After pressure bonding was applied to the top with a load of 35 N for 10 seconds, the product was cured at room temperature for 48 hours before use. The measurement was performed under conditions of hammer energy of 2.75 J and hammer speed (impact speed) of 3.5 m/sec.

[Z-axis repulsion resistance test (high temperature and high humidity conditions)]
As shown in FIG. 5(a), a polycarbonate (PC) plate 50 with a length of 30 mm, a width of 10 mm, and a thickness of 2 mm, and a PET film 60 with a length of 70 mm, a width of 10 mm, and a thickness of 75 μm are prepared, The PC board 50 and the PET film 60 were stacked so that one end in the longitudinal direction was aligned, and the PC board 50 and the PET film 60 were fixed with the remaining part of the PET film 60 protruding from the other end of the PC board 50. . A commercially available double-sided adhesive tape (manufactured by Nitto Denko Corporation, "No. 5000NS") was used for the above fixing.
A pressure-sensitive adhesive sheet sample piece 70 was prepared by cutting the pressure-sensitive adhesive sheet according to each example in which both adhesive surfaces were protected with two release liners into a size of 3 mm in width and 10 mm in length. Place the surface of the PC board 50 opposite to the fixed surface of the PET film on the upper side, peel off one release liner from the adhesive sheet sample piece 70, and separate the width direction of the PC board 50 and the longitudinal direction of the adhesive sheet sample piece 70. Attach the adhesive sheet sample piece 70 to the top surface of the PC board 50 so that both ends of the adhesive sheet sample piece 70 in the width direction are on a line 7 mm and 10 mm from the other end on the top surface of the PC board 50. Fixed. 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 pasted on the PC board 50 is peeled off, and the PC board 50 is removed as shown in FIG. 5(b). The protruding portion (length 40 mm) of the PET film 60 fixed on the PC board 50 is folded back toward the PC board 50 side, and the adhesive sheet sample piece 70 and the other end (free end) of the PET film 60 are aligned. The other end of the bent PET film 60 is fixed to the upper surface of the PC board 50 via the adhesive sheet sample piece 70 by moving a 0.1 kg roller back and forth once from above the PET film 60, and then heated at 65°C and 90%. Exposure to RH environment. After being exposed to the same environment for 72 hours, it was confirmed whether the adhesion between the adhesive sheet sample piece 70 and the PET film 60 was maintained, and if the PET film 60 was peeled off as shown in FIG. It was determined that the film had peeled off. 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. Measurements were performed three times and the lowest value was recorded. Note that the floating height is a height that includes the thickness of the adhesive sheet sample piece 70.
According to this evaluation method, unlike conventional repulsion resistance evaluation, the repulsion resistance against peeling load consisting essentially only in the thickness direction (Z-axis direction) of the adhesive sheet can be evaluated at a high temperature and high humidity of 65°C and 90% RH. It is possible to evaluate under the harsh conditions of , and furthermore, continuous repulsion resistance can be evaluated by performing observation over time.

Table 1 shows the outline and evaluation results of the pressure-sensitive adhesive sheets of each example.

As shown in Table 1, the adhesives according to Examples 1 to 6 contain an acrylic polymer containing heptyl acrylate as a monomer component, and have a storage modulus G' at 65° C. of 20,000 Pa or more, Moreover, tan δ at -20°C was 0.3 or more. The pressure-sensitive adhesive sheets according to Examples 1 to 6 had impact resistance test results of 0.3 J/cm ² or more, and Z-axis repulsion resistance test results of floating heights of 2.0 mm or less. On the other hand, the adhesive according to Comparative Example 1 does not contain heptyl acrylate and contains an acrylic polymer containing 2EHA as a main monomer, and has a storage modulus G' at 65° C. of less than 20,000 Pa, It could not withstand the Z-axis repulsion test. The adhesive sheets according to Comparative Examples 3 and 4 also had a storage modulus G' at 65° C. of the adhesive of less than 20,000 Pa, and were peeled off in the Z-axis repulsion test (Comparative Example 3), or The floating height in the directional repulsion resistance test was larger compared to Examples 1 to 6. In addition, the adhesive according to Comparative Example 2 does not contain heptyl acrylate but contains an acrylic polymer containing BA as the main monomer, has a tan δ of less than 0.3 at -20°C, and has passed the impact test. The results were lower than those in Examples 1 to 6.

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

1, 2, 3 Adhesive sheet 10 Supporting base material 10A First side 10B Second side (back side)
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 (10)

Has an adhesive layer containing an acrylic polymer,
The acrylic polymer is a polymer of monomer components containing heptyl acrylate,
The 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, where the tan δ is the adhesive layer. The ratio of loss elastic modulus G'' to storage elastic modulus G'(G''/G') of an adhesive sheet. The adhesive sheet according to claim 1, wherein the acrylic polymer has a weight average molecular weight of 700,000 or more. The glass transition temperature of the adhesive layer is within the range of -15°C to 15°C. Here, the glass transition temperature of the adhesive layer is the glass transition temperature determined from the peak temperature of tan δ in dynamic viscoelasticity measurement. The pressure-sensitive adhesive sheet according to claim 1 or 2. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer further contains a tackifying resin. The adhesive sheet according to claim 4, wherein the tackifying resin is at least one selected from rosin-based tackifying resins and terpene-based tackifying resins. The adhesive sheet according to claim 5, wherein the content of the tackifier resin in the adhesive layer is 70 parts by weight or less based on 100 parts by weight of the acrylic polymer. The adhesive sheet according to claim 1 or 2, wherein the adhesive layer further contains an acrylic oligomer. The adhesive sheet according to claim 1 or 2, wherein the adhesive composition for forming the adhesive layer contains at least one selected from an isocyanate crosslinking agent and an epoxy crosslinking agent. The pressure-sensitive adhesive sheet according to claim 1 or 2, having a 180 degree peel strength of 20 N/25 mm or more against a stainless steel plate. The adhesive sheet according to claim 1 or 2, which is used for fixing a member in a portable electronic device.

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