JP7321328B1 - Adhesive sheet - Google Patents

Abstract

The present invention provides a pressure-sensitive adhesive sheet that adheres well to curved surfaces and does not peel off even when impact such as dropping is applied, and has excellent adhesion reliability. The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer, has a floating height of 2.0 mm or less at the end of a predetermined repulsion resistance evaluation test, and meets impact resistance performed in accordance with JIS K6855. The test impact bond strength is 0.3 J/cm2 or more. [Selection drawing] Fig. 1

Description

The present invention relates to an adhesive sheet.

In general, pressure-sensitive adhesives (also referred to as pressure-sensitive adhesives; hereinafter the same) exhibit a soft solid (viscoelastic) state in a temperature range around room temperature, and have the property of adhering to adherends under pressure. Taking advantage of such properties, adhesives are used in various industrial fields such as mobile electronic devices such as smartphones, home appliances, automobiles, OA equipment, etc., typically in the form of adhesive sheets containing an adhesive layer, for joining parts and It is widely used for purposes such as surface protection. Patent Documents 1 and 2 are cited as technical documents relating to pressure-sensitive adhesive sheets. Patent Documents 1 and 2 describe pressure-sensitive adhesives containing acrylic polymers polymerized using heptyl acrylate as a monomer component.

WO2021/125247 WO2021/125278

A pressure-sensitive adhesive sheet is required to have various performances depending on the application site, the mode of use, and the like. For example, adhesive sheets used to fix components in mobile electronic devices such as mobile phones, smartphones, and tablet computers are required to have higher adhesive reliability as mobile electronic devices become more sophisticated and functional. It is In recent years, in addition to high performance and high functionality, the development of mobile electronic products with high design characteristics such as incorporating curved surfaces such as 3D shapes is progressing, and the surface shape tends to become more complicated. It is in. Adhesive sheets that can be attached to complicated shapes such as curved surfaces are required to follow and adhere well to the shape and exhibit high adhesion reliability. For example, the temperature and humidity in the portable electronic device may be affected by not only the heat inside the electronic device but also the external environment, and may reach a high temperature state exceeding 50 ° C., and when the humidity becomes high. It is possible. In addition, there is a risk of dropping portable electronic devices due to the way they are used. Adhesive with high adhesion reliability that maintains adhesion to the curved surface of the adherend and does not cause problems such as peeling even in the harsh usage environment described above or in usage forms that can be exposed to impact such as dropping. It makes sense if a sheet is provided.

The present invention was created in view of the above circumstances, and has excellent adhesion reliability that adheres well to curved surfaces and does not peel off even when impact such as dropping is applied. The purpose is to provide a sheet.

According to this specification, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is provided. This pressure-sensitive adhesive sheet had a floating height of 2.0 mm or less at the end of the test in a repulsion resistance evaluation test performed by the following method, and an impact adhesive strength in an impact resistance test performed in accordance with JIS K6855. is 0.3 J/cm ² or more.
[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 at one longitudinal end of the PET film 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. Next, the PET film is folded along the longitudinal direction, and the other longitudinal end of the folded PET film is fixed to the upper surface of the polycarbonate plate with an adhesive sheet with an adhesion area of 3 mm×10 mm. This state is maintained under conditions of 65° C. and 90% RH for 72 hours (repulsion resistance evaluation test). Then, after 72 hours have passed (at the end of the test), the floating height [mm] of the pressure-sensitive adhesive sheet from the polycarbonate plate is measured. A pressure-sensitive adhesive sheet that satisfies the above repulsion resistance and impact resistance characteristics adheres well to curved surfaces, and has excellent adhesion reliability that does not cause peeling even when impact such as dropping is applied. can be a thing.

In some preferred embodiments, the adhesive layer contains an acrylic polymer. Also, the acrylic polymer is a polymer of a monomer component containing heptyl acrylate. The above repulsion resistance and impact resistance can be suitably achieved by using an acrylic polymer containing heptyl acrylate as a monomer component. According to the technology disclosed herein, a composition containing an acrylic polymer containing heptyl acrylate as a monomer component preferably achieves both repulsion resistance and impact resistance, which usually have a trade-off relationship.

In some preferred embodiments, the adhesive layer has a glass transition temperature (Tg) in the range of -15°C to 15°C. Here, the glass transition temperature of the pressure-sensitive adhesive layer refers to the glass transition temperature obtained from the peak temperature of tan δ in dynamic viscoelasticity measurement. In a pressure-sensitive adhesive layer having a Tg in the range of -15°C to 15°C, both repulsion resistance and impact resistance can be preferably achieved.

In some preferred embodiments, the adhesive layer further comprises a tackifying resin. The technology disclosed herein is preferably implemented in a configuration in which the pressure-sensitive 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 aspects, the content of the tackifying resin in the pressure-sensitive adhesive layer is 70 parts by weight or less with respect to 100 parts by weight of the base polymer (eg acrylic polymer). The effects of the technique disclosed herein can be preferably realized by appropriately adjusting the content of the tackifying resin in the pressure-sensitive adhesive layer within the above range.

In some preferred embodiments, the pressure-sensitive adhesive layer further contains an acrylic oligomer. The technology disclosed herein is preferably implemented in a mode in which the pressure-sensitive adhesive layer contains an acrylic oligomer. Among them, it is more preferable to use a tackifying resin and an acrylic oligomer together.

In some preferred embodiments, the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains at least one selected from isocyanate-based cross-linking agents and epoxy-based cross-linking agents. By using a cross-linking agent selected from an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent, it is possible to moderately increase the cohesive force of the pressure-sensitive adhesive, and preferably improve the repulsion resistance while maintaining the impact resistance. can.

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

The pressure-sensitive adhesive sheet disclosed herein adheres well to a curved surface shape, and has excellent adhesion reliability that does not cause peeling even when an impact such as a drop is applied. It may have a curved surface shape for high functionality, design, etc., and is preferably used for joining members of portable electronic devices that may be exposed to impacts such as dropping. From the above, according to this specification, a portable electronic device using any adhesive sheet disclosed herein, in other words, a portable electronic device including the adhesive sheet is provided.

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

Preferred embodiments of the present invention are described below. Matters other than the matters specifically mentioned in the present specification, which are necessary for the implementation of the present invention, are based on the teaching of the implementation of the invention described in the present 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 contents disclosed in this specification and common general technical knowledge in the field. Further, in the following drawings, members and portions having the same function may be denoted by the same reference numerals, and redundant description may be omitted or simplified. In addition, the embodiments described in the drawings are schematic for clearly explaining the present invention, and do not necessarily accurately represent the size and scale of the pressure-sensitive adhesive sheet of the present invention that is actually provided as a product. .

As used herein, the term “adhesive” refers to a material that exhibits a soft solid (viscoelastic) state in a temperature range around room temperature and has the property of easily adhering to an adherend under pressure, as described above. . The adhesive referred to herein generally has a complex tensile modulus E ^* (1 Hz) as defined in "CA Dahlquist, "Adhesion: Fundamentals and Practice", McLaren & Sons, (1966) P. 143" It may be a material having properties satisfying <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, ie materials derived from renewable organic resources (renewable carbon). The biomass material is typically a material derived from biological resources (typically photosynthetic plants) that can be sustainably reproduced in the presence of sunlight, water, and carbon dioxide. Say. Therefore, materials derived from fossil resources that are depleted by use after mining (fossil resource-based materials) are excluded from the concept of biomass materials here. The biomass-carbon ratio of the pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet, that is, the ratio of biomass-derived carbon to the total carbon contained in the pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet, is measured according to ASTM D6866 and contains carbon isotopes with a mass number of 14. can be estimated from quantity.

<Structure of Adhesive Sheet>
The adhesive sheet disclosed here includes an adhesive layer. The pressure-sensitive adhesive sheet is, for example, a substrate-less double-sided pressure-sensitive adhesive sheet comprising a first pressure-sensitive adhesive surface configured by one surface of the pressure-sensitive adhesive layer and a second pressure-sensitive adhesive surface configured by the other surface of the pressure-sensitive adhesive layer. can be of the form Alternatively, the pressure-sensitive adhesive sheet disclosed herein may be in the form of a substrate-attached pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is laminated on one or both sides of a supporting substrate. Hereinafter, the supporting substrate may be simply referred to as "substrate". Note that the concept of the adhesive sheet as used herein can include what is called an adhesive tape, an adhesive label, an adhesive film, and the like. The pressure-sensitive adhesive sheet disclosed herein may be roll-shaped or sheet-shaped. Alternatively, it may be a pressure-sensitive adhesive sheet processed into various shapes.

FIG. 1 schematically shows the structure of a pressure-sensitive adhesive sheet according to one embodiment. This pressure-sensitive adhesive sheet 1 is configured as a substrate-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer 21 . The adhesive sheet 1 has a first adhesive surface 21A configured by one surface (first surface) of the adhesive layer 21 and a second adhesive surface configured by the other surface (second surface) of the adhesive layer 21. 21B are attached to different parts of the adherend. The locations where the adhesive surfaces 21A and 21B are attached may be locations on different members or different locations within a single member. As shown in FIG. 1, the pressure-sensitive adhesive sheet 1 before use (that is, before being attached to an adherend) has a first pressure-sensitive adhesive surface 21A and a second pressure-sensitive adhesive surface 21B that are peeled off at least on the side facing the pressure-sensitive adhesive layer 21. It can be a constituent element of the PSA sheet 100 with a release liner in a form protected by the release liners 31 and 32 which are surfaces. As the release liners 31 and 32, for example, one having a sheet-like base material (liner base material) provided with a release layer by a release treatment agent on one side so that the one side becomes a release surface is preferably used. obtain. Alternatively, the release liner 32 is omitted, and a release liner 31 having release surfaces on both sides is used. A release liner-attached pressure-sensitive adhesive sheet in a form (roll form) protected by contacting the back surface of the sheet may be configured.

FIG. 2 schematically shows the structure of a pressure-sensitive adhesive sheet according to another embodiment. The pressure-sensitive adhesive sheet 2 includes a sheet-like support base material (for example, a resin film) 10 having a first surface 10A and a second surface 10B, and a base material provided with an adhesive layer 21 provided on the first surface 10A side. It is configured as a single-sided adhesive sheet with The pressure-sensitive adhesive layer 21 is fixedly provided on the first surface 10A side of the supporting substrate 10 , that is, without the intention of separating the pressure-sensitive adhesive layer 21 from the supporting substrate 10 . In the pressure-sensitive adhesive sheet 2 before use, as shown in FIG. 2, the surface (adhesive surface) 21A of the pressure-sensitive adhesive layer 21 is protected by a release liner 31 having a release surface on at least the side facing the pressure-sensitive adhesive layer 21. It can be a component of the pressure-sensitive adhesive sheet 200 with a release liner. Alternatively, by omitting the release liner 31 and using the supporting substrate 10 whose second surface 10B is the releasing surface, the adhesive sheet 2 is wound so that the adhesive surface 21A becomes the second surface (back surface) of the supporting 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 still another embodiment. This adhesive sheet 3 consists of a sheet-like supporting substrate (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. The pressure-sensitive adhesive sheet 3 before use has a surface (first pressure-sensitive adhesive surface) 21A of the first pressure-sensitive adhesive layer 21 and a surface (second pressure-sensitive adhesive surface) 22A of the second pressure-sensitive adhesive layer 22 as shown in FIG. , 32 can be a component of the pressure-sensitive adhesive sheet 300 with a release liner. Alternatively, the release liner 32 is omitted, and a release liner 31 having release surfaces on both sides is used. A release liner-attached pressure-sensitive adhesive sheet in a form (roll form) protected by contacting the back surface of the adhesive sheet may be configured.

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

In addition, although not particularly limited, according to the technology disclosed herein, it has a configuration that does not have a foam base material that is advantageous for improving impact resistance, and has good adhesion to curved surfaces and impact such as dropping. It is possible to realize adhesion reliability in which peeling does not occur even in the case of being stuck. Therefore, it is disclosed herein in the form of a substrate-less double-sided pressure-sensitive adhesive sheet comprising an adhesive layer, or in the form of a pressure-sensitive adhesive sheet with a substrate having a substrate other than a foam substrate (non-foam substrate). Techniques can be implemented. Among them, the form of a substrate-less double-sided pressure-sensitive adhesive sheet is preferable. Since the substrate-less double-sided PSA sheet does not have a substrate, it can be made thinner, and can contribute to miniaturization and space saving of products to which the double-sided PSA sheet is applied. Further, according to the substrate-less pressure-sensitive adhesive sheet, it is possible to maximize the action of the pressure-sensitive adhesive layer, such as repulsion resistance and impact resistance against continuous load in the Z-axis direction.

<Characteristics of adhesive sheet>
In some embodiments, the pressure-sensitive adhesive sheet has a floating height of 2.0 mm or less at the end of the test (repulsion resistance) in a repulsion resistance evaluation test performed by the following method, and conforms to JIS K6855. It is characterized by satisfying two properties: an impact adhesive strength of 0.3 J/cm ² or more (impact resistance) in an impact resistance test conducted. A pressure-sensitive adhesive sheet that satisfies the above repulsion resistance and impact resistance characteristics adheres well to curved surfaces, and has excellent adhesion reliability that does not cause peeling even when impact such as dropping is applied. can be a thing. Generally, impact resistance can be improved by lowering the elastic modulus of the adhesive. cohesive force is also reduced, making it difficult to obtain good repulsion resistance. As described above, repulsion resistance and impact resistance are contradictory properties, and it is difficult to achieve both. However, according to the technology disclosed herein, it is possible to achieve both repulsion resistance and impact resistance, which are in a trade-off relationship. is.

[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 at one longitudinal end of the PET film 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. Next, the PET film is folded along the longitudinal direction, and the other longitudinal end of the folded PET film is fixed to the upper surface of the polycarbonate plate with an adhesive sheet with an adhesion area of 3 mm×10 mm. This state is maintained under conditions of 65° C. and 90% RH for 72 hours (repulsion resistance evaluation test). Then, after 72 hours have passed (at the end of the test), the floating height [mm] of the pressure-sensitive adhesive sheet from the polycarbonate plate is measured.

The pressure-sensitive adhesive sheet that satisfies the above repulsion resistance property has particularly excellent repulsion resistance against a peeling load substantially only in the thickness direction (Z-axis direction) of the pressure-sensitive adhesive sheet, and maintains the repulsion resistance in that direction. It is particularly resistant to peeling under a moderate peeling load, and can adhere well to curved surfaces. In addition, even when the adhesive sheet attached to the adherend (e.g. mobile electronic device or its component module) is exposed to high temperature and high humidity conditions during storage, it exhibits stable adhesion reliability. can. In some preferred embodiments, the pressure-sensitive adhesive sheet suitably has a floating height of 1.5 mm or less after the repulsion resistance evaluation test, preferably 1.0 mm or less, and more preferably 0.7 mm or less. , more preferably 0.5 mm or less, particularly preferably 0.4 mm or less. The floating height is a height including the thickness of the adhesive sheet (30 μm in Examples described later). More specifically, the above repulsion resistance evaluation test is carried out by the method described in the Z-axis direction repulsion resistance test in Examples below.

In addition, a pressure-sensitive adhesive sheet that satisfies the impact resistance properties described above can serve as a bonding means that is excellent in durability against impact in the shear direction. Therefore, for example, it can be preferably used as member fixing means in a portable electronic device that is expected to be exposed to impact due to dropping or collision. 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, and 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 making it easier to achieve a higher level of compatibility with repulsion resistance, 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. /cm ² or less. More specifically, the impact resistance test is carried out by the method described in the impact resistance test in the examples below.

In addition, the compatibility of the above repulsion resistance and impact resistance depends on the adhesive composition (specifically, the monomer composition and molecular weight of the base polymer such as the use of heptyl acrylate, the type and amount of the tackifier resin and oligomer, the crosslinking agent can be realized by appropriately selecting and adjusting the type and amount of use, etc., or by appropriately setting the thickness of the adhesive layer, the type of base material, and the thickness.

In addition, the pressure-sensitive adhesive sheet disclosed in the present specification includes embodiments in which the above repulsion resistance and/or impact resistance are not limited, and in such embodiments, the pressure-sensitive adhesive sheet is not limited to those having the above properties.

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

In some aspects, the pressure-sensitive adhesive sheet may contain a biomass-derived material and have a biomass-carbon ratio equal to or higher than a predetermined value. The biomass carbon ratio of the adhesive sheet is, for example, 1% or more, may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the pressure-sensitive adhesive sheet means that the amount of fossil resource-based materials such as petroleum used is small. From this point of view, the higher the biomass carbon ratio of the pressure-sensitive adhesive sheet, the better. 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. From the viewpoint of availability of materials, it may be 95% or less or 90% or less. From the viewpoint of facilitating good adhesion performance, in some embodiments, the biomass carbon ratio of the adhesive sheet may be, for example, 90% or less, 85% or less, or 80% or less.

<Adhesive layer>
(base polymer)
In the technology disclosed herein, at least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer in the embodiment comprising the pressure-sensitive adhesive layer (the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer. Unless otherwise specified, the following The same.) is not particularly limited. The adhesives include acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, which can be used in the field of adhesives. It may contain one or more of various rubber-like polymers such as polyamide-based polymers and fluorine-based polymers as an adhesive polymer (in the sense of a structural polymer that forms an adhesive, hereinafter also referred to as "base polymer"). . From the viewpoint of adhesive performance, cost, etc., a pressure-sensitive adhesive containing an acrylic polymer or a rubber-based polymer as a base polymer can be preferably employed. Among them, a pressure-sensitive adhesive having an acrylic polymer as a base polymer (acrylic pressure-sensitive adhesive) is preferable. The technique disclosed here is preferably implemented in a mode using an acrylic pressure-sensitive adhesive.

The base polymer is the main component of the rubber-like polymer (polymer exhibiting rubber elasticity in a temperature range around room temperature) contained in the pressure-sensitive adhesive layer. In this specification, the term "main component" refers to a component contained in an amount exceeding 50% by weight unless otherwise specified. In addition, the following descriptions of components that can be included in the adhesive and adhesive layer are also applicable to the adhesive composition used to form the adhesive (layer) unless otherwise specified.

In the present specification, 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 the monomer units constituting the polymer. . Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as "acrylic monomer". Accordingly, an acrylic polymer in this specification is defined as a polymer containing monomeric units derived from an acrylic monomer. In this specification, "(meth)acryloyl" is meant to comprehensively refer to acryloyl and methacryloyl. Similarly, "(meth)acrylate" is a generic term for acrylate and methacrylate, and "(meth)acrylic" is generic for acrylic and methacrylic.

A pressure-sensitive adhesive layer composed of an acrylic pressure-sensitive adhesive, that is, a pressure-sensitive adhesive sheet having an acrylic pressure-sensitive adhesive layer will be mainly described below. It is not intended to be limited to

(acrylic polymer)
As the acrylic polymer in the technology disclosed herein, for example, a polymer of monomer raw materials containing an alkyl (meth)acrylate as a main monomer and further containing a sub-monomer copolymerizable with the main monomer is preferable. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material.

As the alkyl (meth)acrylate, for example, a compound represented by the following formula (1) can be preferably used.
_CH2 =C( ^R1 ) ^COOR2 (1)
Here, R ¹ in the above formula (1) is a hydrogen atom or a methyl group. R ² is a chain alkyl group having 1 to 20 carbon atoms. Hereinafter, such a carbon atom number range may be expressed as "C _1-20 ". From the viewpoint of the storage elastic modulus of the adhesive, an alkyl (meth)acrylate in which R ² is a C _1-14 (for example, C _1-10 , typically C _4-8 ) chain alkyl group is used as the main monomer. It is appropriate to From the viewpoint of adhesive properties, the main monomer is an alkyl acrylate in which R ¹ is a hydrogen atom and R ² is a C _4-8 chain alkyl group (hereinafter also simply referred to as C _4-8 alkyl acrylate). is preferred.

Specific examples of alkyl (meth)acrylates in which R ² is a C _1-20 chain alkyl group include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) ) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate ) acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate , nonadecyl (meth)acrylate, eicosyl (meth)acrylate and the like. These alkyl (meth)acrylates may be used singly or in combination of two or more. Suitable examples of alkyl (meth)acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

The ratio of the alkyl (meth)acrylate to the monomer components constituting the acrylic polymer is typically more than 50% by weight, and can be, for example, 70% by weight or more, and may be 85% by weight or more, or 90% by weight. % by weight or more. Although the upper limit of the proportion of alkyl (meth)acrylate is not particularly limited, it is preferably 99.5% by weight or less (for example, 99% by weight or less), or properties based on submonomers such as carboxy group-containing monomers (for example, aggregation 98% by weight or less (for example, less than 97% by weight) from the viewpoint of preferably exerting force). Alternatively, the acrylic polymer may be obtained by polymerizing substantially only alkyl (meth)acrylate.

In some preferred embodiments, the acrylic polymer used is a polymer of monomer components including heptyl acrylate. An acrylic polymer polymerized using a monomer component containing heptyl acrylate is more flexible than polymers of other alkyl acrylates such as n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). A pressure-sensitive adhesive containing a polymer has good adhesion to curved surfaces and is likely to have excellent impact resistance. The reason for this is not particularly limited, but the polymer containing heptyl acrylate as a monomer unit has a low glass transition temperature and a relatively large space between main chains in the pressure-sensitive adhesive. it is conceivable that. Among heptyl acrylates, n-heptyl acrylate is preferred from the viewpoint of flexibility. Since an acrylic polymer synthesized by including n-heptyl acrylate as a monomer component has relatively long linear side chains, it is considered that the space between the main chains tends to be larger.

For example, in some embodiments, the proportion of heptyl acrylate in the monomer component of the acrylic polymer is 50% by weight or more (for example, more than 50% by weight), preferably 70% by weight or more, and more preferably 80% by weight or more. , more preferably 85% by weight or more, particularly preferably 90% by weight or more, may be 92% by weight or more, may be 94% by weight or more, may be 95% by weight or more, or may be 96% by weight or more. By increasing the amount of heptyl acrylate used, the effect of use (for example, improved 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 standpoint of copolymerizing carboxy group-containing monomers and other monomers, in some embodiments, the proportion of heptyl acrylate in the monomer component is less than 97% by weight. In some preferred embodiments, the proportion of heptyl acrylate in the monomer component is 96 wt% or less, optionally 95 wt% or less, or 94 wt% or less. By limiting the proportion of heptyl acrylate within the above range, there is a tendency that repulsion resistance is likely to be obtained.

The acrylic polymer may be copolymerized with an alkyl (meth)acrylate other than heptyl acrylate (hereinafter also referred to as “arbitrary alkyl (meth)acrylate”). As the optional alkyl (meth)acrylate, for example, among the compounds represented by the above formula (1), R ¹ in the above formula (1) is a hydrogen atom or a methyl group, and R ² has 1 carbon atom. A compound having a chain alkyl group of up to 20 (however, when R ¹ is a hydrogen atom, excluding a heptyl group) can be preferably used.

In some embodiments, the proportion of heptyl acrylate in the total amount of alkyl (meth)acrylate contained in the monomer component is, for example, 50% by weight or more (specifically, 50 to 100% by weight, for example, more than 50% by weight). Yes, 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, or may be 100% by weight . By adopting such a monomer composition, the effect of using heptyl acrylate can be effectively exhibited. According to the technology disclosed herein, both repulsion resistance and impact resistance can be achieved based on the action of heptyl acrylate without relying on any alkyl (meth)acrylate such as 2EHA or BA. Therefore, the technology disclosed herein can be preferably practiced in a manner in which the monomer component is substantially free of any alkyl (meth)acrylate.

In the present specification, the expression that the monomer component does not substantially contain the monomer A (e.g., the above optional alkyl (meth)acrylate) means that the monomer A is not used at least intentionally, and the monomer A is For example, unintentional inclusion of about 0.01% by weight or less is permissible.

In some embodiments, the monomer component may include an alkyl (meth)acrylate having a biomass-derived alkyl group at the ester end (hereinafter also referred to as “biomass alkyl (meth)acrylate”). In recent years, environmental problems such as global warming have come to be emphasized, and it is desired to reduce the amount of fossil resource-based materials such as petroleum used. Under such circumstances, it is required to reduce the amount of fossil resource-based materials used in the field of pressure-sensitive adhesives as well. By using biomass alkyl (meth)acrylate, it is possible to suitably realize an acrylic pressure-sensitive adhesive that is less dependent 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 biomass-derived alkanols include biomass ethanol, alkanols derived from plant sources such as palm oil, palm kernel oil, coconut oil, castor oil, and the like. When the number of carbon atoms in the biomass-derived alkanol is 3 or more, 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 to synthesize the acrylic polymer. In such a biomass alkyl (meth)acrylate, the greater the number of carbon atoms in the alkanol, the greater the ratio of the number of biomass-derived carbons to the total number of carbons contained in the biomass alkyl (meth)acrylate, that is, the biomass carbon ratio of the alkyl (meth)acrylate. becomes higher. Therefore, in the above biomass alkyl (meth)acrylate, it is desirable that the number of carbon atoms in the biomass-derived alkyl group is large in terms of reducing dependence on fossil resource-based 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. can be disadvantageous. In an embodiment using an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid as the biomass alkyl (meth)acrylate, adhesive properties and reduced dependence on fossil resource-based materials (more specifically, It is desirable to use a material that satisfies both the biomass carbon ratio of the alkyl (meth)acrylate and the biomass carbon ratio of the alkyl (meth)acrylate 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, it is possible to achieve the effects of the technology disclosed herein while reducing dependence on fossil resource-based materials. The biomass heptyl acrylate is an ester of biomass-derived alkanol and biomass-derived or non-biomass-derived acrylic acid, for example, an ester of biomass-derived alkanol and 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, biomass-derived n-heptyl acrylate (biomass n-heptyl acrylate) is preferably used.

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

Moreover, the monomer component of the acrylic polymer preferably contains a carboxy group-containing monomer. Carboxy group-containing monomers can improve cohesion based on their polarity. In addition, when using a cross-linking agent such as an isocyanate-based or epoxy-based cross-linking agent, the carboxy group may become a cross-linking point of the acrylic polymer. By using a carboxy group-containing monomer, repulsion resistance can be improved. In addition, the use of a carboxy group-containing monomer can exhibit better adhesion to adherends such as highly polar materials.

Examples of carboxy group-containing monomers include ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, crotonic acid and isocrotonic acid; Acids, ethylenically unsaturated dicarboxylic acids such as itaconic acid and citraconic acid. Also, the carboxy group-containing monomer may be a monomer having a metal salt (for example, an alkali metal salt) of the carboxy group. A carboxy group-containing monomer can be used individually by 1 type or in combination of 2 or more types. 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 monomer is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight or more. is. In a particularly preferred embodiment, the carboxy group-containing monomer consists essentially of AA. AA balances repulsion resistance and impact resistance in the carboxy group-containing monomer disclosed herein because of its multiple effects such as polarity based on its carboxy group, role as a cross-linking point, and Tg (106 ° C.). It is considered to be the most suitable monomer material for good compatibility.

The ratio 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, or 1% by weight or more. % by weight or more. In some preferred embodiments, the proportion of carboxy group-containing monomers in the monomer component is more than 3% by weight (specifically more than 3.0% by weight), preferably 4.0% by weight or more, It is 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 action of the carboxy group-containing monomer improves the cohesion of the pressure-sensitive adhesive layer, making it easier to obtain a pressure-sensitive adhesive with excellent repulsion resistance. The amount of the carboxy group-containing monomer is, for example, 20% by weight or less, preferably 15% by weight or less, more preferably 12% by weight or less, based on the total monomer components. In some preferred embodiments, the amount of the carboxy group-containing monomer may be 10 wt% or less, 8 wt% or less, 6 wt% or less, or 5 wt% or less. By reducing the amount of the carboxy group-containing monomer (eg, AA) used, the impact resistance tends to increase. By appropriately adjusting the amount of the carboxy group-containing monomer to be used within the above range, it is easy to obtain a pressure-sensitive adhesive having both repulsion resistance and impact resistance.

The acrylic polymer may be copolymerized with a functional group-containing monomer (optional functional group-containing monomer) other than the carboxyl group-containing monomer. Examples of optional functional group-containing monomers that introduce functional groups that can serve as crosslinking base points into acrylic polymers or that can contribute to improving adhesive strength include hydroxyl group (OH group)-containing monomers (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 monomer, cyano group-containing monomer, keto group-containing monomer, monomer having a nitrogen atom-containing ring (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), alkoxysilyl group-containing monomers, imide group-containing monomers, and the like. The arbitrary functional group-containing monomers may be used singly or in combination of two or more.

When the monomer component constituting the acrylic polymer contains the above 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. and may be 1% by weight or more. Further, for example, in an embodiment in which the monomer component of the acrylic polymer contains heptyl acrylate and a carboxyl group-containing monomer, from the viewpoint of easily balancing adhesive performance in relation to these monomer components, an arbitrary functional group-containing monomer in the monomer component is suitably 40% by weight or less, preferably 20% by weight or less, and may be 10% by weight or less (for example, 5% by weight or less). In some embodiments, the content of optional functional group-containing monomer in the monomer component is, for example, less than 3 wt%, may be less than 1 wt%, may be less than 0.5 wt%, may be less than 0.3 wt% % or less than 0.1% by weight. The technology disclosed herein can be preferably practiced in a mode in which the monomer component of the acrylic polymer does not substantially contain any functional group-containing monomer.

A hydroxyl group-containing monomer may also 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, in the total monomer components. It is about 2% by weight or less. In some embodiments, the content of hydroxyl group-containing monomers in the monomer component may be, for example, less than 1 wt%, less than 0.5 wt%, less than 0.3 wt%, or less than 0.1 wt%. % 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 technique disclosed herein, by limiting the amount of the hydroxyl group-containing monomer used or not using it, it is possible to preferably achieve both repulsion resistance and impact resistance.

The ratio of carboxy group-containing monomers to the total functional group-containing monomers (total functional group-containing monomers including carboxy group-containing monomers) used as a copolymerization component for acrylic polymers reflects the effect of copolymerizing carboxy group-containing monomers. From the viewpoint of effective performance, 30% by weight or more is suitable, preferably 50% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and particularly preferably 90% by weight or more. 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 ratio of the carboxy group-containing monomer to the total functional group-containing monomer is 100% by weight, and may be, for example, 95% by weight or less.

The monomer component constituting the acrylic polymer may contain a copolymer component other than the functional group-containing monomer described above for the purpose of improving the cohesive strength and the like. Examples of other copolymer components include vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; ) acrylate; aryl (meth)acrylate (e.g. phenyl (meth)acrylate), aryloxyalkyl (meth)acrylate (e.g. phenoxyethyl (meth)acrylate), arylalkyl (meth)acrylate (e.g. benzyl (meth)acrylate), etc. Aromatic ring-containing (meth)acrylates; olefinic monomers; chlorine-containing monomers; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate group-containing monomers; vinyl ether-based monomers such as methyl vinyl ether and ethyl vinyl ether; The above other copolymer components can be used singly or in combination of two or more.

The amount of such other copolymerization components may be appropriately selected according to the purpose and application and is not particularly limited, but from the viewpoint of appropriately exhibiting the effects of use, it is appropriate to make it 0.05% by weight or more. , 0.5% by weight or more. In addition, from the viewpoint of easily balancing adhesive performance, the content of other copolymer components in the monomer component is suitably 20% by weight or less, so that the adhesive properties based on the essential monomer components are preferably exhibited. From the viewpoint, it is preferably 10% by weight or less, more preferably 8% by weight or less, still more preferably less than 5% by weight, and may be less than 3% by weight or less than 1% by weight. The technology disclosed herein can also be preferably practiced in a mode in which the monomer component does not substantially contain other copolymer components.

Acrylic polymers are polyfunctional having 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 contain a monomer. By using a polyfunctional monomer as the monomer component, the cohesive force of the pressure-sensitive adhesive layer can be increased. Polyfunctional monomers can be used as cross-linking agents. Polyfunctional monomers are not particularly limited, and examples include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and neopentyl glycol di(meth)acrylate. etc. A polyfunctional monomer can be used individually by 1 type or in combination of 2 or more types.

The amount of the polyfunctional monomer to be used is not particularly limited, and can be appropriately set so as to achieve the intended use of the polyfunctional monomer. The amount of the polyfunctional monomer used can be approximately 3% by weight or less, preferably approximately 2% by weight or less, and more preferably approximately 1% by weight or less (for example, approximately 0.5% by weight or less) based on the above monomer components. 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, by setting the amount of the polyfunctional monomer used to about 0.001% by weight or more (for example, about 0.01% by weight or more) of the monomer component, the effect of using the polyfunctional monomer can be appropriately exhibited.

In a particularly preferred embodiment, an acrylic polymer synthesized using a monomer component substantially consisting of heptyl acrylate (preferably n-heptyl acrylate) and a carboxy group-containing monomer (preferably acrylic acid) is used as the acrylic polymer. be done. According to the above monomer composition, the action of heptyl acrylate and the carboxy group-containing monomer is effectively exhibited, and both repulsion resistance and impact resistance can be better achieved. From this point of view, the total proportion of heptyl acrylate and carboxy group-containing monomer in the above monomer component is suitably 90% by weight or more (90 to 100% by weight), preferably 95% by weight or more, more preferably 99% by weight. % 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 ratio of heptyl acrylate and carboxy group-containing monomers in the monomer component 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 (eg, more than 50%), may be 70% or more, may be 80% or more, or may be 90% to 100%. By designing in this way, an acrylic pressure-sensitive adhesive that takes into consideration the suppression of dependence on fossil resource-based materials can be obtained.

The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization. can be adopted as appropriate. For example, a solution polymerization method can be preferably employed. As a method of supplying the monomers when carrying out solution polymerization, it is possible to appropriately adopt a batch charging method in which all the monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, or the like. The polymerization temperature can be appropriately selected 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.). can be done.

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

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

The weight average molecular weight (Mw) of the base polymer (typically an acrylic polymer) is not particularly limited, and a base polymer having an appropriate Mw capable of achieving both repulsion resistance and impact resistance is used. In some embodiments, the Mw of the base polymer is greater than 600,000, may be greater than 650,000, suitably 700,000 or greater, and may be 750,000 or greater. The higher the Mw of the base polymer, the easier it is to obtain a pressure-sensitive adhesive exhibiting good cohesive strength, and the tendency is for the repulsion resistance to be improved. In some preferred embodiments, the Mw of the base polymer is 800,000 or greater, may be 850,000 or greater, may be 900,000 or greater, more preferably 1 million or greater (e.g., greater than 1 million), and more preferably 120 10,000 or more, particularly preferably 1,400,000 or more, may be 1,500,000 or more, or may be 1,600,000 or more. For example, in an aspect in which the base polymer is an acrylic polymer, a monomer composition containing heptyl acrylate tends to maintain a low viscosity, so that high-molecular-weight synthesis is good and an acrylic polymer having the above Mw is easily obtained. . In addition, by using an acrylic polymer that contains heptyl acrylate as a monomer unit and has a Mw of a predetermined value or more, repulsion resistance and impact resistance are achieved based on the flexibility based on the chemical structure of the polymer and the cohesion based on the molecular weight. It is possible to better achieve compatibility with characteristics. On the other hand, from the viewpoint of impact resistance, adhesive strength, ease of synthesis, etc., the Mw of the base polymer is usually about 3 million or less, preferably 2.5 million or less, more preferably 2 million or less. It is 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 base polymer may be 1.1 million or less, 1 million or less, 950,000 or less, or 900,000 or less.

The Mw of a base polymer (typically an acrylic polymer) can be measured by gel permeation chromatography (GPC) and calculated as a value converted to standard polystyrene. Specifically, it can be obtained 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 examples described later.
[Measurement conditions for GPC]
Sample concentration: 0.2% by weight (tetrahydrofuran solution)
Sample injection volume: 10 μL
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: Product name "TSKgel SuperH-RC" 1 column (manufactured by Tosoh Corporation)
Detector: differential refractometer (RI)
Standard sample: Polystyrene

(tackifying resin)
In some preferred embodiments, the adhesive layer comprises a tackifying resin. A high adhesive strength can be obtained by using a tackifying resin. According to the technology disclosed herein, the composition containing the tackifying resin enables the pressure-sensitive adhesive layer to exhibit excellent anti-repulsion properties. Although not particularly limited, in some aspects, the effect of using a tackifying resin can be effectively exhibited in a composition containing a high-molecular-weight acrylic polymer. The tackifier resin is not particularly limited, and examples thereof include rosin-based tackifier resins, terpene-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, Various tackifying resins such as phenol-based tackifying resins and ketone-based tackifying resins can be used. Such tackifying resins can be used singly or in combination of two or more.

Specific examples of rosin-based tackifying resins include unmodified rosins (fresh rosins) such as gum rosin, wood rosin and tall oil rosin; hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosin, etc. (same below); other various rosin derivatives; Examples of the rosin derivative include rosins obtained by esterifying unmodified rosin with alcohols (that is, esterified rosin), and esterifying modified rosin with alcohols (that is, esterified rosin). Esters; Undenatured rosin and rosins modified with unsaturated fatty acids obtained by modifying rosin with unsaturated fatty acids; Rosin esters modified with unsaturated fatty acids obtained by modifying rosin esters with unsaturated fatty acids; Unmodified rosin, modified rosin, unsaturated Rosin alcohols obtained by reducing the carboxy 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 rosin phenol resin obtained by adding phenol to (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and thermally polymerizing; and the like. Among them, rosin ester is preferred.

Specific examples of rosin esters include, but are not limited to, esters of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), such as methyl ester, triethylene glycol ester, and glycerin ester. , pentaerythritol ester and the like.

Examples of terpene-based tackifying resins include terpene resins such as α-pinene polymer, β-pinene polymer, dipentene polymer; modification of these terpene resins (phenol modification, aromatic modification, hydrogenation modification, hydrocarbon modified terpene resin; An example of the modified terpene resin is a terpene phenol resin.

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

Examples of hydrocarbon-based tackifying resins include aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic/aromatic copolymer (C5/C9) petroleum resins, these Hydrogenates (e.g., alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), various modified products thereof (e.g., maleic anhydride-modified products), coumarone-based resins, coumarone-indene-based resins and various other hydrocarbon-based resins.

In some aspects, 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, for example, an acrylic pressure-sensitive adhesive, excellent repulsion resistance can be easily obtained, and adhesive strength can be improved. In some preferred embodiments, the total ratio of the rosin-based tackifying resin and the terpene-based tackifying resin to the total tackifying resin contained in the pressure-sensitive adhesive layer is, for example, approximately more than 50% by weight (more than 50% by weight and 100% by weight or less). ), may be about 70% by weight or more, may be about 80% by weight or more, may be about 90% by weight or more, may be 95% by weight or more, or may be 99% by weight or more.

In some preferred embodiments, the tackifying resin comprises one or more terpene phenolic resins. The technology disclosed herein can be preferably practiced, for example, in a mode in which approximately 25% by weight or more (more preferably approximately 30% by weight or more) of the total amount of tackifying resin is a terpene phenolic resin. The proportion of the terpene phenolic resin in the total amount of the tackifying resin may be approximately 50% by weight or more, approximately 70% by weight or more, approximately 80% by weight or more, or approximately 90% by weight or more. Substantially all of the tackifying resin (eg, approximately 95% to 100% by weight, or even approximately 99% to 100% by weight) may be a terpene phenolic resin.

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

Although not particularly limited, in some embodiments, the tackifying resin can include a tackifying resin with a hydroxyl value greater than 20 mg KOH/g (eg, a terpene phenolic resin). Such tackifying resins may have a hydroxyl value of 30 mg KOH/g or more. Among them, a tackifying resin having a hydroxyl value of 50 mgKOH/g or more is preferable. Hereinafter, a tackifying resin having a hydroxyl value of 50 mgKOH/g or more may be referred to as a "high hydroxyl value resin". A tackifying resin containing such a high hydroxyl value resin can realize a pressure-sensitive adhesive layer with high cohesive strength by interacting with a cross-linking agent such as an isocyanate-based cross-linking agent in addition to the pressure-sensitive adhesive strength. In some embodiments, the tackifying resin may contain a high hydroxyl value resin having a hydroxyl value of 60 mgKOH/g or more (more preferably 70 mgKOH/g or more). In addition, the high hydroxyl value resin (for example, terpene phenol resin) as described above is preferably used in combination with, for example, an acrylic polymer containing heptyl acrylate as a monomer component, and exhibits good adhesive strength and resistance to adherends. Rebound properties can be achieved.

The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with the base polymer (typically an acrylic polymer), the hydroxyl value of the high hydroxyl value resin is usually about 300 mgKOH/g or less, and about 200 mgKOH/g or less is suitable and preferable. is about 180 mg KOH/g or less, more preferably about 160 mg KOH/g or less, even more preferably about 140 mg KOH/g or less, and may be less than 120 mg KOH/g (eg, 110 mg KOH/g or less). The technology disclosed herein can be preferably practiced in a mode in which the tackifying resin contains a high hydroxyl value resin (eg, a terpene-based tackifying resin, preferably a terpene phenolic resin) having a hydroxyl value of 50-200 mgKOH/g. In some embodiments, a high hydroxyl value resin with a hydroxyl value of 60-140 mgKOH/g (eg, 70-110 mgKOH/g) can be preferably employed.

Here, as the value of the hydroxyl value, a value measured by a potentiometric titration method specified in JIS K0070:1992 can be adopted. A specific measuring method is as follows.
[Method for measuring hydroxyl value]
1. Reagent (1) As the acetylation reagent, approximately 12.5 g (approximately 11.8 mL) of acetic anhydride is taken, pyridine is added to bring the total amount to 50 mL, and the mixture is thoroughly stirred and used. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to bring the total amount to 100 mL, and use the mixture after thorough stirring.
(2) A 0.5 mol/L potassium hydroxide ethanol solution is used as a measurement reagent.
(3) In addition, prepare toluene, pyridine, ethanol and distilled water.
2. Operation (1) About 2 g of a sample is accurately weighed and collected in a flat-bottomed flask, 5 mL of an acetylation reagent and 10 mL of pyridine are added, and an air cooling tube is attached.
(2) After heating the flask in a bath at 100°C for 70 minutes, allowing it to cool, adding 35 mL of toluene as a solvent from the top of the cooling tube and stirring, then adding 1 mL of distilled water and stirring to obtain acetic anhydride. decompose. Heat again in the bath for 10 minutes for complete decomposition and allow to cool.
(3) Wash the cooling tube with 5 mL of ethanol and remove. Then, 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 0.5 mol/L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is taken as the end point.
(6) In the blank test, the above (1) to (5) are performed without any sample.
3. Calculation Calculate the hydroxyl value by the following formula.
Hydroxyl value (mgKOH/g) = [(BC) x f x 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 for the sample,
f: factor of 0.5 mol/L potassium hydroxide ethanol solution,
S: weight of sample (g),
D: acid value,
28.05: ½ of the molecular weight of potassium hydroxide, 56.11;
is.

As the high hydroxyl value resin, among the various tackifying resins described above, those having a hydroxyl value equal to or higher than a predetermined value can be used. High hydroxyl value resin can be used individually by 1 type or in combination of 2 or more types. 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. The terpene phenol resin is convenient because the hydroxyl value can be arbitrarily controlled by the copolymerization ratio of phenol.

Although not particularly limited, when a high hydroxyl value resin is used, the ratio of the high hydroxyl value resin (for example, terpene phenol resin) to the total tackifying resin contained in the adhesive layer is about 5% by weight or more. 10% by weight or more, 15% by weight or more, or 20% by weight or more. In some embodiments, the ratio of the high hydroxyl value resin to the total tackifying resin is preferably about 30% by weight or more, for example. As a result, the effect of using the high hydroxyl value resin is preferably exhibited, and the adhesive strength and the repulsion resistance can be improved while maintaining the impact resistance. In some preferred embodiments, the proportion of the high hydroxyl value resin to the total tackifying resin is about 40 wt% or more, may be about 50 wt% or more (e.g., more than 50 wt%), or about 60 wt%. % 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 (eg, about 95-100 weight percent, or even about 99-100 weight percent) 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 the cohesive strength, a high hydroxyl value resin having a softening point (softening temperature) of approximately 80° C. or higher can 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 about 100° C. or higher, or about 110° C. or higher. In some preferred embodiments, the softening point of the high hydroxyl value resin is about 120° C. or higher, may be about 130° C. or higher, or about 135° C. or higher (even about 140° C. or higher). There is no particular upper limit for the softening point of the high hydroxyl value resin. A high hydroxyl value resin having a softening point of about 200° C. or lower (more preferably about 180° C. or lower) can be preferably used from the viewpoint of adhesion to adherends. In some embodiments, the softening point of the high hydroxyl value resin may be less than 160°C. In some preferred embodiments, a high hydroxyl value resin having a softening point of less than 150° C. is used as the high hydroxyl value resin. By using a high hydroxyl value resin having a softening point of less than 150° C., it is possible to preferably obtain a pressure-sensitive adhesive that has both repulsion resistance and impact resistance and is also excellent in adhesive strength. The softening point of the high hydroxyl value resin may be 145° C. or lower.

The softening point of the tackifier resin in this specification is defined as a value measured based on the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at the lowest possible temperature and carefully filled into a ring placed on a flat metal plate to avoid the formation of bubbles. After it cools down, cut off the raised part from the plane including the top of the ring with a slightly heated knife. Next, a supporter (ring base) is placed in a glass container (heating bath) having a diameter of 85 mm or more and a height of 127 mm or more, and glycerin is poured to a depth of 90 mm or more. Next, the steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in the glycerin without touching each other, and the temperature of the glycerin is kept at 20° C.±5° C. for 15 minutes. . A steel ball is then centered on the surface of the sample in the ring and placed in position on the support. Next, the distance from the upper end of the ring to the glycerin surface is kept at 50 mm, a thermometer is placed, the center of the mercury ball of the thermometer is set at the same height as the center of the ring, and the container is heated. The Bunsen burner flame used for heating should be midway between the center and the rim of the bottom of the vessel to ensure even heating. The rate at which the bath temperature rises after reaching 40° C. after heating is started must be 5.0±0.5° C. per minute. The temperature at which the sample gradually softens and flows down the ring and finally touches the bottom plate is read and taken as the softening point. Two or more softening points are measured at the same time, and the average value is adopted.

The content of the high hydroxyl value resin in the pressure-sensitive adhesive layer is not particularly limited as long as the intended properties are satisfied. In some embodiments, the content of the high hydroxyl value resin is usually about 1 part by weight or more, and about 5 parts by weight with respect to 100 parts by weight of the base polymer (for example, an acrylic polymer), from the viewpoint of improving adhesive strength. It is suitable to be above, preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more). In some embodiments, the content of the high hydroxyl value resin in the pressure-sensitive adhesive layer is, for example, 70 parts by weight or less, and 60 parts by weight or less with respect to 100 parts by weight of the base polymer (e.g., acrylic polymer). It may be present, and may be 50 parts by weight or less. In some preferred embodiments, the content of the high hydroxyl value resin is 40 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 25 parts by weight or less, and particularly preferably It is 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 comprise a tackifying resin having a hydroxyl value of less than 50 mg KOH/g. Hereinafter, a tackifying 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, the low hydroxyl value resin is preferably used in combination with the high hydroxyl value resin. The low hydroxyl value resin may have a hydroxyl value of less than 40 mg KOH/g. The lower limit of the hydroxyl value of the low hydroxyl value resin is 0 mgKOH/g or more, may be approximately 10 mgKOH/g or more, or may be approximately 15 mgKOH/g or more. As the low hydroxyl value resin, one 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. In some embodiments, the low hydroxyl value resin preferably comprises a rosin-based tackifying resin. The low hydroxyl value resin may contain one type of rosin-based tackifying resin alone, or may contain two or more types of rosin-based tackifying resin in combination.

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

The softening point of the low hydroxyl value resin is not particularly limited. From the viewpoint of improving the cohesive force, a low hydroxyl value resin having a softening point (softening temperature) of about 80° C. or 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. There is no particular upper limit for the softening point of the low hydroxyl value resin. 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 from the viewpoint of adhesion to adherends. 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 130° C. or less.

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

As the tackifying resin _TL , one selected from those having a softening point of less than 150° C. among the tackifying resins exemplified above can be used singly or in combination of two or more. 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 two or more types of terpene phenol resin in combination.

In some embodiments, the proportion of the terpene phenolic resin in the total tackifying resin T _L can be, for example, greater than about 50 wt%, may be greater than about 65 wt%, and may be greater than or equal to about 75 wt%. , 85% by weight or more, or 95% by weight or more. The technology disclosed herein is preferred in embodiments in which substantially all of the tackifying resin T _L (e.g., approximately 97% by weight or more, or 99% by weight or more, or even 100% by weight) is a terpene phenolic resin. can be implemented.

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

The content of the tackifying resin T _L is not particularly limited, but in some embodiments, it is suitable to be about 70 parts by weight or less with respect to 100 parts by weight of the base polymer (for example, acrylic polymer). By limiting the amount of the tackifier resin _TL used to a predetermined amount or less, impact resistance can be improved while maintaining sufficient 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, with respect to 100 parts by weight of the base polymer, from the viewpoint of impact resistance and the like. parts or less, more preferably 40 parts by weight or less, may be 30 parts by weight or less, may be 25 parts by weight or less, may be 20 parts by weight or less, or may be 18 parts by weight or less. In some embodiments, from the viewpoint of improving adhesive strength, the amount of the tackifying resin T _L used is, for example, 1 part by weight or more, and 5 parts by weight with respect to 100 parts by weight of the base polymer (for example, an acrylic polymer). 10 parts by weight or more, preferably 12 parts by weight or more, and may be 15 parts by weight or more. For example, an acrylic polymer containing heptyl acrylate as a monomer unit that can be used in some embodiments has good compatibility with a tackifying resin. can be done.

In some embodiments, the adhesive layer may comprise 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 tackifying resin _TH , among the tackifying resins exemplified above, those having a softening point of 150° C. or higher can be used singly or in combination of two or more.

In some embodiments, the tackifying resin T _L preferably accounts for more than 50% by weight of the total amount of tackifying resins contained in the adhesive layer. Thereby, the effect of containing the tackifying resin _TL is likely to be effectively exhibited. The ratio of the tackifying resin _TL to the total amount of the tackifying resin contained in the pressure-sensitive adhesive layer is preferably 60% by weight _or more, more preferably 60% by weight or more, more preferably 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 tackifying resin contained in the adhesive layer consists essentially of the tackifying resin _TL . In this embodiment, the ratio of the tackifier resin T _L to the total amount of tackifier resin contained in the adhesive layer is in the range of 99 to 100% by weight.

The softening point of the tackifying resin is not particularly limited. From the viewpoint of improving the cohesive force, a tackifier resin having a softening point (softening temperature) of approximately 80° C. or higher can be preferably employed. For example, a terpene-based tackifying resin (terpene phenolic resin, etc.) having such a softening point can be preferably used. The softening point of the tackifying resin may be about 100° C. or higher, or about 110° C. or higher. In some preferred embodiments, the softening point of the tackifying resin is about 120° C. or higher, may be about 130° C. or higher, or about 135° C. or higher (even about 140° C. or higher). Among them, it is preferable to use a terpene phenol resin having the above softening point. There is no particular upper limit for the softening point of the tackifying resin. From the viewpoint of adhesion to adherends, a tackifier 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 tackifying resin may be less than 160°C, or less than 150°C.

When the pressure-sensitive adhesive layer disclosed herein contains a tackifying resin, the tackifying resin is preferably a plant-derived tackifying resin (vegetable tackifying resin) from the viewpoint of improving the biomass carbon ratio of the pressure-sensitive adhesive layer. can work. Examples of vegetable tackifying resins include, for example, the above-described rosin-based tackifying resins and terpene-based tackifying resins. Vegetable tackifying resins can be used singly or in combination of two or more. When the pressure-sensitive adhesive layer disclosed herein contains a tackifying resin, the proportion of the vegetable tackifying resin in the total amount of the tackifying resin is 30% by weight or more (e.g. 50% by weight or more, typically 80% by weight). above). In some embodiments, the proportion of vegetable tackifying resin to the total amount of tackifying resin is 90% or more (eg, 95% or more, typically 99-100%) by weight. The technology disclosed herein can be preferably practiced in a mode substantially free of tackifying resins other than vegetable tackifying resins.

The content of the tackifying resin in the pressure-sensitive adhesive layer is not particularly limited as long as the intended properties are satisfied. In some aspects, the content of the tackifying resin is usually about 1 part by weight or more, and about 5 parts by weight or more, relative to 100 parts by weight of the base polymer (for example, an acrylic polymer), from the viewpoint of improving adhesive strength. Preferably, it is about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more). In some embodiments, the content of the tackifying resin in the pressure-sensitive adhesive layer is, for example, 70 parts by weight or less, or 60 parts by weight or less, relative to 100 parts by weight of the base polymer (eg, acrylic polymer). 50 parts by weight or less. In some preferred embodiments, the content of the tackifying 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, and particularly preferably 20 parts by weight, from the viewpoint of repulsion resistance. parts or less, and may be 18 parts by weight or less. For example, an acrylic polymer containing heptyl acrylate as a monomer unit that can be used in some embodiments has good compatibility with a tackifying resin. can be done.

(acrylic oligomer)
In some preferred embodiments, the adhesive layer contains an acrylic oligomer. By containing an acrylic oligomer, the adhesive strength of the pressure-sensitive adhesive can be improved. According to the technology disclosed herein, the pressure-sensitive adhesive layer having a composition containing an acrylic oligomer can exhibit excellent repulsion resistance. Although not particularly limited, in some aspects, the effect of using an acrylic oligomer can be effectively exhibited in a composition containing a high-molecular-weight acrylic polymer.

The above acrylic oligomer preferably has a Tg of about 0°C to about 300°C, preferably about 20°C to about 300°C, more preferably about 40°C to about 300°C. When Tg is within the above range, the adhesive strength can be favorably improved. In some preferred embodiments, the acrylic oligomer has a Tg of about 30° C. or higher, more preferably about 50° C. or higher (e.g., about 60° C. or higher), from the viewpoint of cohesiveness of the adhesive. From the point of view, the temperature is preferably about 200° C. or lower, more preferably about 150° C. or lower, and even more preferably about 100° C. or lower (for example, about 80° C. or lower).

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

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

For monomers for which the glass transition temperatures of homopolymers are not described in the above literature, the values obtained by the following measurement methods are used.
Specifically, a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube and a reflux condenser was charged with 100 parts by weight of a monomer, 0.2 parts by weight of 2,2′-azobisisobutyronitrile and acetic acid as a polymerization solvent. 200 parts by weight of ethyl is added, and the mixture is stirred for 1 hour while circulating nitrogen gas. After oxygen is removed from the polymerization system in this manner, the temperature is raised to 63° C. and the reaction is allowed to proceed for 10 hours. Then, it is cooled to room temperature to obtain a homopolymer solution having a solid concentration of 33% by weight. Next, this homopolymer solution is cast-coated on a release liner and dried to prepare a test sample (sheet-like homopolymer) having 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 shear strain at a frequency of 1 Hz using a viscoelasticity tester (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 at a heating rate of 5°C/min while giving , and the temperature corresponding to the peak top temperature of tan δ is taken as the homopolymer Tg.

The weight average molecular weight (Mw) of the acrylic oligomer can typically be from about 1000 to less than about 30000, preferably from about 1500 to less than about 20000, more preferably from about 2000 to less than about 10000. It is preferable that Mw is within the above range because good adhesive strength and repulsion resistance can be obtained. In some preferred embodiments, Mw of the acrylic oligomer is about 2,500 or more (for example, about 3,000 or more) from the viewpoint of repulsion resistance, and preferably about 7,000 or less, more preferably about 7,000 or less from the viewpoint of adhesion. 5000 or less (eg, about 4500 or less, typically about 4000 or less). The Mw of the acrylic oligomer can be measured by gel permeation chromatography (GPC) and calculated as a value converted to standard polystyrene. Specifically, measurement is performed using HPLC8020 manufactured by Tosoh Corporation, using TSKgelGMH-H(20)×2 columns, and using tetrahydrofuran as a solvent at a flow rate of about 0.5 mL/min.

Examples of monomers constituting acrylic oligomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate 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 alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; (meth)acrylates obtained from terpene compound derivative alcohols; and the like. Such (meth)acrylates can be used singly or in combination of two or more.

Examples of acrylic oligomers include alkyl (meth)acrylates having branched alkyl groups such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopenta Esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) such as nyl (meth)acrylate; aryls such as phenyl (meth)acrylate and benzyl (meth)acrylate The inclusion of an acrylic monomer having a relatively bulky structure, typified by a (meth)acrylate having a cyclic structure such as (meth)acrylate, as a monomer unit further improves the adhesiveness of the pressure-sensitive adhesive layer. It is preferable from the viewpoint that In addition, when ultraviolet rays are used when synthesizing an acrylic oligomer or when producing a pressure-sensitive adhesive layer, those having saturated bonds are preferable, and the alkyl groups have a branched structure, in that they are less likely to cause polymerization inhibition. Alkyl (meth)acrylates or esters with alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) can be suitably used as monomers constituting acrylic oligomers. All of the branched-chain alkyl (meth)acrylates, alicyclic hydrocarbon group (meth)acrylates, and aryl (meth)acrylates described above correspond to (meth)acrylate monomers in the technology disclosed herein. Alicyclic hydrocarbon groups can be saturated or unsaturated alicyclic hydrocarbon groups.

The ratio of the (meth)acrylate monomer (e.g., alicyclic hydrocarbon group-containing (meth)acrylate) to 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, further 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 (meth)acrylate monomers, functional group-containing monomers can be used as the constituent monomer components of the acrylic oligomer. Preferable examples of the functional group-containing monomer include monomers having a nitrogen atom-containing ring (typically a nitrogen atom-containing heterocyclic ring) 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; These functional group-containing monomers can be used singly or in combination of two or more. Among them, carboxy group-containing monomers are preferred, and AA is particularly preferred.

When all monomer components constituting the acrylic oligomer contain functional group-containing monomers, the ratio of functional group-containing monomers (for example, carboxy group-containing monomers such as AA) to all the monomer components is about 1% by weight or more. 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 below.

Acrylic oligomers can be formed by polymerizing their constituent monomer components. The polymerization method and polymerization mode are not particularly limited, and conventionally known various polymerization methods (eg, solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be employed in an appropriate mode. The type of polymerization initiator that can be used as necessary (e.g., an azo polymerization initiator such as AIBN) is generally as exemplified in the synthesis of the acrylic polymer, and the amount of the polymerization initiator and the arbitrarily used The amount of the chain transfer agent such as n-dodecyl mercaptan, etc. is appropriately set based on common general technical knowledge so as to obtain the desired molecular weight, and therefore detailed description is 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 Homopolymers of acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA), copolymers of CHMA and isobutyl methacrylate (IBMA), copolymers of CHMA and IBXMA, Copolymers of CHMA and acryloylmorpholine (ACMO), copolymers of CHMA and diethylacrylamide (DEAA), copolymers of CHMA and AA, copolymers of ADA and methyl methacrylate (MMA), DCPMA and IBXMA and a copolymer of DCPMA and MMA, and the like.

When the acrylic oligomer is contained in the pressure-sensitive adhesive layer disclosed herein, the content is, for example, 0.1 parts by weight or more (for example, 1 part by weight) with respect to 100 parts by weight of the base polymer (preferably acrylic polymer). above). From the viewpoint of better exhibiting the effect of the acrylic oligomer, the content of the acrylic oligomer is preferably about 5 parts by weight or more, more preferably about 8 parts by weight or more, still more preferably about 10 parts by weight or more, especially Preferably, it is about 12 parts by weight or more. Also, from the viewpoint of compatibility with the base polymer, the content of the acrylic oligomer is less than 50 parts by weight (for example, less than 40 parts by weight) with respect to 100 parts by weight of the base polymer (preferably acrylic polymer). preferably less than 30 parts by weight, more preferably about 25 parts by weight or less, still more preferably about 20 parts by weight or less.

In some preferred embodiments, the adhesive layer comprises one or more of the tackifying resins described above and one or more of acrylic oligomers. For example, in some embodiments, in a composition containing an acrylic polymer containing heptyl acrylate as a monomer component, a combination of a tackifying resin and an acrylic oligomer can be used to obtain excellent adhesion and particularly excellent repulsion resistance. characteristics can be exhibited. In particular, in a composition containing a high-molecular-weight acrylic polymer, the effect of using the tackifying resin and the acrylic oligomer in combination can be effectively exhibited. The ratio (C _T /C _O ) of the content C _T [% by weight] of the tackifying resin to the content C _O [% by weight] of the acrylic oligomer in the pressure-sensitive adhesive layer is not particularly limited. The above (C _T /C _O ) is, for example, suitably 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 still more preferably 0.7. 1.5 or more, and may be 0.8 or more and 1.2 or less.

In some preferred embodiments, the total amount (total amount) of the tackifying resin and the acrylic oligomer contained in the pressure-sensitive adhesive layer is the base polymer (preferably acrylic system polymer) is about 1 part by weight or more, preferably about 10 parts by weight or more, more preferably about 16 parts by weight or more, still more preferably 20 parts by weight or more, and particularly preferably It is suitably 25 parts by weight or more and 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. It is below the department.

In the technology disclosed herein, the total amount (total amount) of the base polymer (e.g. acrylic polymer), tackifier resin and acrylic oligomer in the adhesive layer is such that the effect of the technology disclosed herein is exhibited. Well set and not limited to any particular range. In some preferred embodiments, the total amount (total amount) of the base polymer, tackifying resin and acrylic oligomer contained in the pressure-sensitive adhesive layer is more than 50% by weight from the viewpoint of preferably exhibiting the effects of the technology disclosed herein. is preferably approximately 70% by weight or more, more preferably approximately 90% by weight or more, and still 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). , 98% by weight or more.

(crosslinking agent)
In the technique disclosed here, the adhesive composition used for forming the adhesive layer may contain a cross-linking agent as needed. The type of cross-linking agent is not particularly limited. Alkoxide cross-linking agents, metal chelate cross-linking agents, metal salt cross-linking agents, carbodiimide cross-linking agents, hydrazine cross-linking agents, amine cross-linking agents, silane coupling agents and the like can be mentioned. A crosslinking agent can be used individually by 1 type or in combination of 2 or more types. Among them, isocyanate-based cross-linking agents, epoxy-based cross-linking agents, oxazoline-based cross-linking agents, aziridine-based cross-linking agents, and melamine-based cross-linking agents are preferable, and isocyanate-based cross-linking agents and epoxy-based cross-linking agents are more preferable. By appropriately selecting and using a cross-linking agent, the pressure-sensitive adhesive layer can obtain cohesive force, and can preferably achieve both repulsion resistance and impact resistance while improving repulsion resistance. The pressure-sensitive adhesive layer in the technology disclosed herein contains the cross-linking agent in the form after the cross-linking reaction, the form before the cross-linking reaction, the form after the cross-linking reaction, the intermediate or composite form thereof, and the like. can contain The cross-linking agent is typically contained in the pressure-sensitive adhesive layer exclusively in the form after the cross-linking reaction.

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

Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.
Specific examples of aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; - hexamethylene diisocyanates such as hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,5-hexamethylene diisocyanate; 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, 1,3 - cyclopentyl diisocyanate 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.

Examples of preferred polyfunctional isocyanates include polyfunctional isocyanates having an average of 3 or more isocyanate groups per molecule. Such tri- or more functional isocyanates are polymers (typically dimers or trimers) of di- or tri- or more functional isocyanates, derivatives (for example, polyhydric alcohols and two or more molecules of polyfunctional isocyanates). addition reaction products), polymers, and the like. For example, dimers and trimers of diphenylmethane diisocyanate, isocyanurate of hexamethylene diisocyanate (trimer adduct of isocyanurate structure), reaction products of trimethylolpropane and tolylene diisocyanate, trimethylolpropane and hexa Polyfunctional isocyanates such as reaction products with methylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and the like can be mentioned. Commercial products of such polyfunctional isocyanates include "Duranate TPA-100" (trade name) manufactured by Asahi Kasei Chemicals, "Coronate L", "Coronate HL", "Coronate HK" and "Coronate HX", "Coronate 2096", and the like.

The technology disclosed herein can be preferably implemented in a mode using at least an isocyanate-based cross-linking agent as the cross-linking agent. By using an isocyanate-based cross-linking agent, the desired repulsion resistance can be preferably achieved.

The amount of the isocyanate-based cross-linking agent used is not particularly limited. For example, it can be about 0.1 part by weight or more per 100 parts by weight of the base polymer (preferably acrylic polymer). From the viewpoint of achieving both cohesion and adhesion, the amount of the isocyanate-based cross-linking agent used relative to 100 parts by weight of the base polymer is usually about 0.3 parts by weight or more (for example, 0.5 parts by weight or more). preferable. In some preferred embodiments, the amount of the isocyanate-based cross-linking agent used is about 0.8 parts by weight or more, more preferably about 1.0 parts by weight or more, and even more preferably about 1.2 parts by weight, based on 100 parts by weight of the base polymer. parts or more, and may be about 1.5 parts by weight or more. The amount of the isocyanate-based cross-linking agent used is suitably 10 parts by weight or less, preferably less than 5 parts by weight, more preferably less than 5 parts by weight, based on 100 parts by weight of the base polymer (preferably acrylic polymer). It is less than 4.0 parts by weight, more preferably less than 3.0 parts by weight, particularly preferably 2.5 parts by weight or less, and may be 2.0 parts by weight or less (for example, 1.7 parts by weight or less). By limiting the amount of the isocyanate-based cross-linking agent to be used within a predetermined range, it is possible to preferably achieve both repulsion resistance and impact resistance while obtaining repulsion resistance based on the use of the isocyanate-based cross-linking agent.

As the epoxy-based cross-linking agent, a compound having two or more epoxy groups in one molecule can be used without particular limitation. An epoxy-based cross-linking agent having 3 to 5 epoxy groups in one molecule is preferred. Epoxy-based cross-linking agents may be used singly or in combination of two or more.

Specific examples of epoxy-based cross-linking agents include, but are not limited to, N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl ) cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether and the like. Commercial products of epoxy-based cross-linking agents include Mitsubishi Gas Chemical Company's trade name "TETRAD-C" and trade name "TETRAD-X", DIC's trade name "Epiclon CR-5L", and Nagase ChemteX Corporation. and "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd. under the trade name of "Denacol EX-512".

The amount of the epoxy-based cross-linking agent used is not particularly limited. The amount of the epoxy-based cross-linking agent used is, for example, more than 0 parts by weight and about 1 part by weight or less (typically about 0.001 to 1 parts by weight). From the viewpoint of suitably exhibiting the effect of improving the cohesive strength, the amount of the epoxy-based cross-linking agent to be used is usually about 0.002 parts by weight or more per 100 parts by weight of the base polymer. It may be 0.005 parts by weight or more, for example about 0.01 parts by weight or more. In addition, from the viewpoint of improving the adhesion to the adherend, the amount of the epoxy-based cross-linking agent to be used is appropriately about 0.5 parts by weight or less with respect to 100 parts by weight of the base polymer, and about 0.2 parts by weight. It is preferably 0.1 parts by weight or less (for example, less than 0.1 parts by weight), may be 0.07 parts by weight or less, or may be 0.04 parts by weight or less. In addition, from the viewpoint of avoiding a decrease in impact resistance due to excessive cross-linking, the amount of the epoxy-based cross-linking agent used is usually about 0.03 parts by weight or less per 100 parts by weight of the base polymer. It is preferably 0.02 parts by weight or less. By limiting the amount of the epoxy-based cross-linking agent to be used within a predetermined range, it is easy to maintain sufficient adhesive strength and to obtain repulsion resistance.

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

The type of non-isocyanate cross-linking agent that can be used in combination with the isocyanate cross-linking agent is not particularly limited, and can be appropriately selected from the cross-linking agents described above. The non-isocyanate-based cross-linking agents may be used singly or in combination of two or more. In some preferred embodiments, an epoxy-based cross-linking agent can be employed as the non-isocyanate-based cross-linking agent. For example, by using an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent in combination, it is possible to achieve both repulsion resistance and impact resistance.

The relationship between the content of the isocyanate-based cross-linking agent and the content of the non-isocyanate-based cross-linking agent (preferably epoxy-based cross-linking agent) is not particularly limited, and is appropriately set so as to satisfy repulsion resistance and impact resistance. be. The content of the isocyanate-based cross-linking agent is, for example, more than 1-fold, preferably about 10-fold or more, relative to the content of the non-isocyanate-based cross-linking agent (preferably epoxy-based cross-linking agent). is about 50 times or more, more preferably about 80 times or more, more preferably about 100 times or more (eg, about 100 times or more), and particularly preferably about 120 times or more (eg, about 140 times or more). In addition, from the viewpoint of suitably exhibiting the effect of using a combination of an isocyanate-based cross-linking agent and a non-isocyanate-based cross-linking agent (preferably an epoxy-based cross-linking agent), a non-isocyanate-based cross-linking agent (preferably an epoxy-based cross-linking agent) is usually used. The content of the isocyanate cross-linking agent relative to the content of the cross-linking agent) is, for example, about 1000 times or less, suitably about 500 times or less, preferably about 300 times or less, more preferably about 200 times or less. , and more preferably about 180 times or less (for example, about 160 times or less).

The content of the cross-linking agent (total amount of cross-linking agent) in the adhesive composition disclosed herein is not particularly limited. From the viewpoint of cohesiveness, the content of the cross-linking agent is usually about 0.001 parts by weight or more, and about 0.002 parts by weight or more with respect to 100 parts by weight of the base polymer (for example, an acrylic polymer). is suitable, preferably about 0.005 parts by weight or more, more preferably about 0.01 parts by weight or more, still more preferably about 0.02 parts by weight or more, and particularly preferably about 0.03 parts by weight or more. In some embodiments, the content of the cross-linking agent relative to 100 parts by weight of the base 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. It may be about 1.2 parts by weight or more, or about 1.5 parts by weight or more. In addition, the content of the cross-linking agent in the pressure-sensitive adhesive composition is usually about 20 parts by weight or less per 100 parts by weight of the base polymer (for example, an acrylic polymer), and is suitably about 15 parts by weight or less. , about 10 parts by weight or less (for example, about 5 parts by weight or less). In some embodiments, the content of the cross-linking agent relative to 100 parts by weight of the base polymer is 4.0 parts by weight or less, more preferably 3.0 parts by weight or less, and even more preferably 2.5 parts by weight or less. 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 the cross-linking agent to be used within the above range, it is possible to preferably achieve both repulsion resistance and impact resistance.

(Other additives)
In addition to the components described above, the pressure-sensitive adhesive composition may optionally contain a leveling agent, a cross-linking aid, a plasticizer, a softening agent, a filler, a coloring agent (pigment, dye, etc.), an antistatic agent, and an anti-aging agent. , ultraviolet absorbers, antioxidants, rust inhibitors, light stabilizers, and other additives commonly used in the field of pressure-sensitive adhesives. As for such various additives, conventionally known ones can be used in a conventional manner, and since they do not particularly characterize the present invention, detailed description thereof will be omitted.

The pressure-sensitive adhesive layer (layer comprising pressure-sensitive adhesive) disclosed herein is formed from a water-based pressure-sensitive adhesive composition, a solvent-based pressure-sensitive adhesive composition, a hot-melt pressure-sensitive adhesive composition, or an active energy ray-curable pressure-sensitive adhesive composition. It can be a pressure-sensitive adhesive layer. The water-based pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition in the form of containing a pressure-sensitive adhesive (adhesive layer-forming component) in a water-based solvent (aqueous solvent), typically water-dispersed. Also included are so-called type adhesive compositions (compositions in which at least part of the adhesive is dispersed in water) and the like. Moreover, the solvent-type adhesive composition refers to an adhesive composition in the form of containing an adhesive in an organic solvent. As the organic solvent contained in the solvent-based pressure-sensitive adhesive composition, one or two or more of the organic solvents (toluene, ethyl acetate, etc.) exemplified as the organic solvent (toluene, ethyl acetate, etc.) that can be used in the above solution polymerization can be used without particular limitation. The technology disclosed herein can be preferably implemented in a mode comprising a pressure-sensitive adhesive layer formed from a solvent-based pressure-sensitive adhesive composition, from the viewpoint of adhesive properties and the like.

The adhesive layer disclosed here can be formed by a conventionally known method. For example, a method of forming a pressure-sensitive adhesive layer by applying a pressure-sensitive adhesive composition to a releasable surface (release surface) or a non-releasable surface and drying can be employed. In a pressure-sensitive adhesive sheet having a substrate, for example, a method (direct method) of forming a pressure-sensitive adhesive layer by directly applying (typically applying) a pressure-sensitive adhesive composition to the substrate and drying it is adopted. be able to. Alternatively, a method of applying a pressure-sensitive adhesive composition to a surface having releasability (release surface) and drying to form a pressure-sensitive adhesive layer on the surface and transferring the pressure-sensitive adhesive layer to a substrate (transfer method). 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 base material subjected to a release treatment, or the like can be used. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form. It may be a formed pressure-sensitive adhesive layer.

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

(thickness)
The thickness of the pressure-sensitive adhesive layer is not particularly limited, and a configuration having a pressure-sensitive adhesive layer having an appropriate thickness in the range of, for example, 0.1 to 500 μm can be employed depending on the application, purpose of use, and the like. In some aspects, from the viewpoint of avoiding excessive thickness of the adhesive sheet, the thickness of the adhesive layer is usually about 100 μm or less, preferably about 70 μm or less, more preferably about 60 μm or less. More preferably, it is about 50 μm or less. The thickness of the pressure-sensitive adhesive layer may be approximately 35 μm or less, for example approximately 30 μm or less. A pressure-sensitive adhesive layer with a limited thickness can well meet demands for thinning and weight reduction. In general, when the thickness of the pressure-sensitive adhesive layer becomes small, the impact resistance and adhesion to the adherend tend to decrease. Sufficient impact resistance and adhesive strength can be achieved with a configuration having From the viewpoint of adhesion to the adherend, the lower limit of the thickness of the pressure-sensitive adhesive layer is appropriately about 0.5 μm or more in some embodiments, may be about 1 μm or more, or about 3 μm or more. is preferably about 10 μm or greater, more preferably about 12 μm or greater (eg, greater than 12 μm), even more preferably about 15 μm or greater, and may be, for example, about 18 μm or greater. In some preferred embodiments, the thickness of the adhesive layer is greater than 20 μm, may be 24 μm or greater, and may be 27 μm or greater. The pressure-sensitive adhesive sheet disclosed herein may be a pressure-sensitive adhesive sheet having pressure-sensitive adhesive layers having the thicknesses described above on both sides of a substrate. Further, in a double-sided pressure-sensitive adhesive sheet with a substrate having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on each side of the substrate, the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer have the same thickness. There may be one, or they may have mutually different thicknesses.

(Viscoelastic properties)
Although not particularly limited, in some embodiments, the pressure-sensitive adhesive layer has a storage modulus G' at 65°C of 20,000 Pa or more. The pressure-sensitive adhesive having a storage modulus of 65° C. tends to provide good repulsion resistance (particularly, repulsion resistance against sustained loads in the Z-axis direction in harsh environments such as high-temperature conditions). In some preferred embodiments, the 65° C. storage modulus is 21,000 Pa or more, may be 22,000 Pa or more, or is suitably 23,000 Pa or more, from the viewpoint of improving repulsion resistance. It is preferably 24,000 Pa or more, more preferably 25,000 Pa or more, particularly preferably 26,000 Pa or more, may be 27,000 Pa or more, may be 28,000 Pa or more, may be 29,000 Pa or more, and may be 30 ,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 elastic modulus can be set within an appropriate range in which both repulsion resistance and impact resistance can 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. Yes, it may be 32,000 Pa or less, 30,000 Pa or less, 28,000 Pa or less, or 26,000 Pa or less.

Also, although not particularly limited, in some aspects, the adhesive layer has a 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 pressure-sensitive adhesive layer. −20° C. corresponds to the impact velocity range at the time of dropping according to the temperature-velocity conversion rule. The pressure-sensitive adhesive having a tan δ at -20°C of 0.3 or more easily provides excellent impact resistance. It is preferable that the tan δ at −20° C. of 0.3 or more is satisfied together with the 65° C. storage modulus of 20,000 Pa or more. 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, still more preferably 0.60 or more, from the viewpoint of impact resistance. The upper limit of −20° C. tan δ can be set within an appropriate range that achieves both repulsion resistance and impact resistance. The -20°C tan δ may be, for example, about 2 or less, 1.8 or less, 1.6 or less, or 1.4 or less. In some embodiments, the -20° C. tan δ is, for example, about 1.2 or less, preferably 1.0 or less, more preferably 0.80 or less, and still more preferably 0 from the viewpoint of repulsion resistance. 0.70 or less, may be 0.60 or less, or may be 0.55 or less.

In some preferred embodiments, the pressure-sensitive adhesive layer has a glass transition temperature (Tg) in the range of -15°C to 15°C, although it is not particularly limited. Here, the glass transition temperature of the pressure-sensitive adhesive layer refers to the glass transition temperature obtained from the peak temperature of tan δ in dynamic viscoelasticity measurement. By using a pressure-sensitive 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 preferably −12° C. or higher, more preferably −10° C. or higher, particularly preferably −7° C. or higher, and may be −5° C. or higher, or −3. C. or higher, -1.degree. C. or higher, 0.degree. C. or higher (for example, higher than 0.degree. C.), or 1.degree. From the viewpoint of impact resistance, the Tg of the pressure-sensitive adhesive layer is preferably 12° C. or lower, more preferably 10° C. or lower, even more preferably 7° C. or lower, particularly preferably 5° C. or lower, and particularly preferably 3° C. or lower. 1° C. or lower, 0° C. or lower (for example, less 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 pressure-sensitive adhesive layer can be determined by dynamic viscoelasticity measurement. Specifically, a pressure-sensitive adhesive layer having a thickness of about 2 mm is prepared by stacking a plurality of pressure-sensitive adhesive layers (in the case of substrate-less pressure-sensitive adhesive sheets, pressure-sensitive adhesive sheets) to be measured. A sample obtained by punching this adhesive layer into a disk shape with a diameter of 7.9 mm is sandwiched between parallel plates and fixed, and a viscoelasticity tester (for example, manufactured by TA Instruments, ARES or its equivalent) is used as follows. Dynamic viscoelasticity measurement is performed under the conditions of 65° C. storage modulus, −20° C. tan δ, and Tg are determined.
・Measurement mode: Shear mode ・Temperature range: -70°C to 150°C
・Temperature increase rate: 5°C/min
・Measurement frequency: 1Hz
It is also measured by the above method in the examples described later. The adhesive layer to be measured may be formed by applying the corresponding adhesive composition in layers and drying or curing.

(biomass carbon ratio)
In some embodiments, the pressure-sensitive adhesive layer may contain a biomass-derived material and have a biomass-carbon ratio equal to or greater than a predetermined value. The biomass carbon ratio of the adhesive layer is, for example, 1% or more, may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the adhesive means that the amount of fossil resource-based materials such as petroleum used is small. From this point of view, the higher the biomass carbon ratio of the adhesive, the better. 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. From the viewpoint of availability of materials, it may be 95% or less or 90% or less. From the viewpoint of facilitating good adhesion performance, in some embodiments, 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 the embodiment in which the pressure-sensitive adhesive sheet disclosed herein is in the form of a single-sided pressure-sensitive adhesive type or double-sided pressure-sensitive adhesive type pressure-sensitive adhesive sheet with a substrate, the substrate that supports (backs) the pressure-sensitive adhesive layer may be resin film, paper, cloth, or rubber. Sheets, foam sheets, metal foils, composites thereof, and the like can be used. Examples of paper include Japanese paper, kraft paper, glassine paper, woodfree paper, synthetic paper, top coat paper, and the like. Examples of fabrics include woven fabrics and non-woven fabrics obtained by spinning various fibrous materials alone or by blending them. Examples of the fibrous substance include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber, and the like. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyolefin sheets, foamed polyurethane sheets, foamed polychloroprene rubber sheets, and the like. Examples of metal foil include aluminum foil and copper foil. The substrate supporting the adhesive layer is also referred to as a substrate layer in the adhesive sheet.

The substrate may be formed from a biomass-derived material, or may be formed from a non-biomass-derived material. A biomass-derived base material (typically a resin film) is preferably used from the viewpoint of pressure-sensitive adhesive sheet production that takes into account the suppression of dependence on fossil resource-based materials.

Also, the base material may be formed using a recyclable material or a recycled material (also referred to as a recycled material). A resin film is preferably used as such a recycled material. Since resin films (e.g., polyester films such as PET films) can be recycled, sustainable reproduction can be achieved by reusing used resin films regardless of whether plant-derived materials are used or not. is possible, and the environmental load can be reduced. Such recyclable resin films and recycled resin films are also called recycled films. The recycled material (for example, recycled film) may be formed from a biomass-derived material, or may be formed from a non-biomass-derived material.

As the base material constituting the pressure-sensitive adhesive sheet with a base material, a base film containing a resin film can be preferably used. The base film is typically an independently shape-maintainable (independent) member. The substrate in the technology disclosed herein can be substantially composed of such a base film. Alternatively, the substrate may contain 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 copolymer; polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and the like. vinyl chloride resin film; vinyl acetate resin film; polyimide resin film; polyamide resin film; fluorine resin film; The resin film may be a rubber-based film such as a natural rubber film or a butyl rubber film. Among them, from the viewpoint of handleability and workability, polyester films are preferable, and among them, PET films are particularly preferable.

In this specification, the term "resin film" is typically a non-porous sheet, and is a concept distinguished from so-called nonwoven fabrics and woven fabrics (in other words, a concept excluding nonwoven fabrics and woven fabrics). be. The resin film may be a non-stretched 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 treated to form a foam. Specifically, the non-foamed resin film may be a resin film having an expansion ratio of less than 1.1 times (for example, less than 1.05 times, typically less than 1.01 times).

If necessary, the base material (for example, resin film) may contain fillers (inorganic fillers, organic fillers, etc.), colorants, dispersants (surfactants, etc.), anti-aging agents, antioxidants, ultraviolet Various additives such as absorbents, antistatic agents, lubricants and plasticizers may be added. 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, resin film) may have a single-layer structure, or may have a multi-layer structure of two layers, three layers, or more. From the viewpoint of shape stability, the substrate 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 resin (for example, polyester resin). A method for manufacturing the substrate (typically a resin film) is not particularly limited, and a conventionally known method may be appropriately adopted. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be employed as appropriate.

The surface of the substrate may be subjected to conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, application of a primer, and the like. Such a surface treatment can be a treatment for improving the adhesion between the substrate and the adhesive layer, in other words, the anchoring property of the adhesive layer to the substrate.

Moreover, when the technology disclosed herein is implemented in the form of a single-sided pressure-sensitive adhesive sheet with a substrate, the back surface of the substrate may be subjected to release treatment as necessary. For the release treatment, for example, general silicone-based, long-chain alkyl-based, and fluorine-based release agents are typically applied to a thin film of about 0.01 μm to 1 μm (eg, 0.01 μm to 0.1 μm). It can be a treatment to give. By performing such a peeling treatment, it is possible to obtain effects such as facilitating the unwinding of the adhesive sheet wound into a roll.

In the pressure-sensitive adhesive sheet containing a substrate, the thickness of the substrate is not particularly limited. From the viewpoint of avoiding excessive thickness of the pressure-sensitive adhesive sheet, the thickness of the substrate can be, for example, approximately 200 μm or less, preferably approximately 150 μm or less, and more preferably approximately 100 μm or less. 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 intended use and usage mode of the pressure-sensitive adhesive sheet. In some embodiments, the thickness of the substrate can be about 20 μm or less, about 15 μm or less, or about 10 μm or less (eg, about 5 μm or less). By reducing the thickness of the substrate, the thickness of the adhesive layer can be increased even if the total thickness of the adhesive sheet is the same. This can be advantageous from the viewpoint of improving adhesion to adherends and substrates. The lower limit of the base material is not particularly limited. From the standpoint of handleability and workability of the pressure-sensitive adhesive sheet, the thickness of the substrate is usually about 0.5 μm or more (eg, 1 μm or more), preferably about 2 μm or more, for example, about 6 μm or more. In some embodiments, the thickness of the substrate can be approximately 15 μm or greater, and can be approximately 25 μm or greater.

<Foam base material>
In some other embodiments, a foam substrate is used as the substrate. The foam substrates disclosed herein are substrates with portions having cells (cell structure), typically substrates comprising at least one layer of stratified foam (foam layer). be. The foam substrate may be a substrate composed of one or more foam layers. The foam substrate may be, for example, a substrate substantially composed of only one or two or more foam layers. Although not particularly limited, a preferred example of the foam base material in the technology disclosed herein is a foam base material composed of a single (one) foam layer.

The thickness of the foam base material is not particularly limited, and can be appropriately set according to the strength and flexibility of the pressure-sensitive adhesive sheet, the purpose of use, and the like. From the viewpoint of thinning, the thickness of the foam substrate 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 technique disclosed herein is preferably implemented in a mode in which the thickness of the foam substrate is 0.25 mm or less (typically 0.18 mm or less, for example 0.16 mm or less) from the viewpoint of workability. obtain. From the viewpoint of the impact resistance of the adhesive sheet, the thickness of the foam substrate is usually 0.04 mm or more, suitably 0.05 mm or more, preferably 0.06 mm or more, and 0.07 mm. 0.08 mm or more (for example, 0.08 mm or more) is more preferable. The technology disclosed herein is preferably implemented in a mode in which the thickness of the foam substrate is 0.10 mm or more (typically more than 0.10 mm, preferably 0.12 mm or more, for example 0.13 mm or more). obtain. Increasing the thickness of the foam substrate tends to improve impact resistance.

The density of the foam substrate (referring to apparent density; hereinafter the same unless otherwise specified) is not particularly limited, and may be, for example, 0.1 to 0.9 g/cm ³ . From the viewpoint of impact resistance, the density of the foam substrate 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 aspect, 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). From the viewpoint of impact resistance, the density of the foam substrate 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 may be 0.4 g/cm ³ or greater, 0.5 g/cm ³ or greater (eg, greater than 0.5 g/cm ³ ), or even 0.5 g/cm 3 or greater. 0.55 g/cm ³ or more. The density (apparent density) of the foam substrate can be measured according to JIS K 6767.

Although the average cell diameter of the foam substrate is not particularly limited, it is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less from the viewpoint of stress dispersion. Although the lower limit of the average bubble diameter is not particularly limited, from the viewpoint of conformability to unevenness, 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, and may be 60 μm or more. In addition, the average cell diameter here refers to the average cell diameter converted to a true sphere obtained by observing the cross section of the foam base material with an electron microscope.

The cell structure of the foam that constitutes the foam substrate disclosed herein is not particularly limited. The cell structure may be an open cell structure, a closed cell structure, or a semi-open and semi-closed cell structure. From the viewpoint of shock absorption, a closed cell structure and a semi-open and semi-closed cell structure are preferred.

The 25% compressive strength _C25 of the foam substrate is not particularly limited and can be, for example, 20 kPa or more (typically 30 kPa or more, or 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 comprising such a foam base material can exhibit good durability against impact 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, 1300 kPa or less (for example, 1200 kPa or less) is usually appropriate. In one aspect, _C25 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 can be from 20 kPa to 200 kPa (typically from 30 kPa to 150 kPa, such as from 40 kPa to 120 kPa). A pressure-sensitive adhesive sheet comprising such a foam base material can have excellent cushioning properties. For example, the foam base material absorbs the drop impact, so that the peeling of the pressure-sensitive adhesive sheet can be better prevented.

The 25% compressive strength C ₂₅ of the foam base material is obtained by stacking the foam base material cut into squares of 30 mm square and stacking the measurement sample to a thickness of about 2 mm between a pair of flat plates. This is 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 sample to be measured is compressed to a thickness corresponding to 75% of the initial thickness. The compressive strength is measured according to JIS K 6767. As a specific measurement procedure, the measurement sample is set at the center of the pair of flat plates, and the flat plates are continuously compressed to a predetermined compression ratio by narrowing the distance between the flat plates, and the flat plates are stopped for 10 seconds. Measure the load after the passage of time. The compressive strength of the foam substrate can be controlled by, for example, the degree of cross-linking and density of the material forming the foam substrate, the size and shape of cells, and the like.

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

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

The material of the foam substrate is not particularly limited. A foam substrate comprising a foam layer formed by a foam of plastic material (plastic foam) is usually preferred. The plastic material (which is meant to include rubber materials) for forming the plastic foam is not particularly limited, and can be appropriately selected from known plastic materials. The plastic material can be used singly or in 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, wholly aromatic polyamide (aramid) Amide resin foams such as resin foams; polyimide resin foams; polyether ether ketone (PEEK) foams; styrene resin foams such as polystyrene foams; polyurethane resin foams, etc. urethane-based resin foam; and the like. As the plastic foam, a foam made of rubber-based resin such as a foam made of polychloroprene rubber may be used.

A preferred foam is a polyolefin resin foam (hereinafter also referred to as "polyolefin foam"). As the plastic material (that is, polyolefin resin) constituting the polyolefin foam, various known or commonly used polyolefin resins can be used without particular limitation. Examples thereof 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 linear low density polyethylene, metallocene catalyst linear low density polyethylene and the like. Such polyolefin-based resins can be used singly or in combination of two or more.

A suitable example of the foam base material in the technique disclosed herein is a PE-based foam base material substantially composed of a PE-based resin foam from the viewpoint of impact resistance, waterproofness, dust resistance, etc. and polyolefin foam substrates such as PP foam substrates substantially composed of PP resin foams. Here, the PE-based resin refers to a resin having ethylene as the main monomer (that is, the main component in the monomer), and in addition to HDPE, LDPE, LLDPE, etc., ethylene- Propylene copolymers, ethylene-vinyl acetate copolymers, and the like may be included. Similarly, a PP-based resin refers to a resin containing propylene as a main monomer. A PE-based foam base material can be preferably employed as the foam base material in the technique disclosed herein.

The method for producing the plastic foam (typically polyolefin foam) is not particularly limited, and various known methods can be appropriately employed. For example, it can be manufactured by a method including a molding step, a cross-linking step and a foaming step of the plastic material or the plastic foam. In addition, a stretching step may be included as necessary.
Examples of the method for cross-linking the plastic foam include a chemical cross-linking method using an organic peroxide, an ionizing radiation cross-linking method using ionizing radiation, and the like, and these methods can 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 irradiation dose in consideration of the target physical properties (for example, the degree of cross-linking) of the foam substrate.

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

The foam base material in the technique disclosed herein is black or white in order to express desired design properties and optical properties (e.g., light shielding properties, light reflectivity, etc.) in the pressure-sensitive adhesive sheet comprising the foam base material. etc. may be colored. For this coloring, known organic or inorganic coloring agents can be used singly or in combination of two or more.

Appropriate surface treatment may be applied to the surface of the foam base material, if necessary. This surface treatment can be, for example, a chemical or physical treatment to enhance 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 in the formation of the adhesive layer, production of the adhesive sheet, storage of the adhesive sheet before use, distribution, shape processing, and the like. The release liner is not particularly limited, and for example, a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, a release liner made of a fluoropolymer (such as polytetrafluoroethylene), or the like is used. be able to. The release treatment layer may be formed by surface-treating the liner base material with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide release agent. As the liner base material, a material formed using a biomass-derived material or a recycled material (recycled film, etc.) can be preferably used, similarly to the base material of the pressure-sensitive adhesive sheet described above.

<Total thickness of adhesive sheet>
The total thickness of the adhesive sheet disclosed herein (including an adhesive layer and may further include a base layer, but not including a release liner) is not particularly limited. The total thickness of the adhesive sheet is, for example, approximately 1 mm or less, may be approximately 500 μm or less, or 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, about 100 μm or less). In some preferred embodiments, the thickness of the adhesive sheet can be approximately 50 μm or less, such as approximately 35 μm or less. The lower limit of the thickness of the pressure-sensitive 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 be excellent in handleability. In addition, in the substrate-less adhesive sheet, the thickness of the adhesive layer is the total thickness of the adhesive sheet.

<Application>
The use of the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and it can be used for various purposes. Since the pressure-sensitive adhesive sheet disclosed herein can achieve both repulsion resistance and impact resistance, it is suitable for adhesively fixing members in applications where high repulsion resistance and impact resistance are required. For example, it can be preferably used for fixing members in various portable electronic devices. The pressure-sensitive adhesive sheet disclosed herein adheres well to a curved surface shape, and has excellent adhesion reliability that does not peel off even when an impact such as a drop is applied. It may have a curved surface shape for high functionality, design, etc., and is preferably used for joining members of portable electronic devices that may be exposed to impact such as dropping. In addition, the adhesion area for fixing a member in a portable electronic device with an adhesive sheet is usually small due to restrictions on size, weight, and the like. The pressure-sensitive adhesive sheets used for such applications must have adhesive strength that can achieve good fixation even in a small area, and the required performance is at a higher level due to the demands for high functionality, weight reduction, and miniaturization. It is a thing. In particular, mobile electronic devices equipped with touch panel displays, as typified by smartphones, are becoming smaller and thinner. For these reasons, the pressure-sensitive adhesive used is required to have adhesion and fixation performance under more severe conditions. The pressure-sensitive adhesive sheet disclosed herein can achieve excellent adhesion reliability when used in portable electronic devices such as those described above.

Non-limiting examples of the above portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wrist wear type worn on the wrist like a wristwatch, Eyewear type including glasses type (monocular type and binocular type, including head-mounted type), clothes type attached to shirts, socks, hats, etc. in the form of accessories, earphones ear-wear type, etc.), 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, vehicle-mounted information equipment, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, the term “portable” means not only being able to be simply carried, but also having a level of portability that allows an individual (a typical adult) to carry it relatively easily. shall mean.

The adhesive sheet disclosed herein (typically a double-sided adhesive sheet) can be used in the form of a bonding material processed into various external shapes to fix members constituting the portable electronic device as described above. For example, the pressure-sensitive adhesive sheet disclosed herein is preferably used for fixing a member such as a cover glass having a three-dimensional shape (typically a curved surface shape) constituting the portable electronic device. . A pressure-sensitive adhesive sheet used for fixing a member having such a three-dimensional surface tends to be subjected to a relatively large continuous 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. Moreover, the pressure-sensitive adhesive sheet disclosed herein can be preferably used for portable electronic devices having a liquid crystal display device. For example, an electronic device (typically a mobile electronic device such as a smartphone) having a display unit such as a touch panel display (which may be the display unit of a liquid crystal display device), and for increasing the screen size etc. The pressure-sensitive adhesive sheet disclosed herein is preferably used for fixing an elastic adherend in a device such as FPC that is folded to accommodate an elastic member in an internal space. By using the pressure-sensitive adhesive sheet disclosed herein, the elastic adherend can be stably fixed in a folded state, and the fixed state can be maintained continuously. Thus, the elastic member, which is folded and accommodated 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. Moreover, as the material arranged inside the portable electronic device as described above, there are polar and rigid materials such as polycarbonate and polyimide. Compared to 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.

The development of electronic devices (typically, mobile electronic devices such as smartphones and tablet personal computers) having a display unit such as the above-mentioned touch panel display (which may be the display unit of a liquid crystal display device) has become particularly popular in recent years. The trend is toward achieving both high efficiency and high functionality. As for the enlargement of the screen, a countermeasure is taken such that the elastic member such as the FPC as described above is folded and accommodated in the internal space. On the other hand, in terms of high functionality, new functions such as a pressure sensor with more accurate pressure sensing performance and a face authentication unlock function have been embodied, realizing higher performance and higher quality products. For this purpose, high integration of circuits such as FPCs that are responsible for it is indispensable. Examples of high integration means for circuits include double-sided FPCs and multilayer FPCs. It is expected that improved rebound resistance against sustained axial loads will be a required property. A pressure-sensitive adhesive sheet according to a preferred embodiment of the technology disclosed herein can exhibit excellent repulsion resistance under severe high-temperature, high-humidity conditions (strong repulsion conditions) as in the Z-axis direction repulsion resistance test described later. Therefore, it is more suitable for the above-mentioned next-generation touch panel type display mounted electronic device (typically, a touch panel type display mounted portable electronic device such as a smart phone) and can be preferably used.

Although not particularly limited, in some embodiments, the pressure-sensitive adhesive sheet is preferably used in electronic devices including various light sources such as LEDs (light emitting diodes) and light-emitting elements such as self-luminous organic ELs. For example, it can be preferably used for electronic equipment (typically portable electronic equipment) equipped with 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, the housing 520 of the portable electronic device 500 incorporates a battery (heat generating element) 540 . Moreover, the portable electronic device 500 is configured including 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 . The portable electronic device 500 includes a touch panel 570 whose display unit also functions as an input unit. The pressure-sensitive adhesive sheet disclosed herein is preferably used as a constituent element (member joining means) of the portable electronic device as described above.

In addition, the pressure-sensitive adhesive sheet disclosed herein, in some aspects, can have a pressure-sensitive adhesive layer containing an acrylic polymer with a high biomass carbon ratio, so a conventional general acrylic pressure-sensitive adhesive (i.e. , Acrylic adhesive with a low biomass carbon ratio) can be used as a substitute for the acrylic adhesive in various applications, thereby contributing to the suppression of 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-based materials.

Matters disclosed by this specification include the following.
[1] A portable electronic device,
A pressure-sensitive adhesive sheet is bonded to a member constituting the portable electronic device,
The adhesive sheet has an adhesive layer,
In the repulsion resistance evaluation test conducted by the following method, the floating height at the end of the test is 2.0 mm or less,
A portable electronic device having an impact adhesive strength of 0.3 J/cm ² or more in an impact resistance test conducted in accordance with JIS K6855.
[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 at one longitudinal end of the PET film 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. Next, the PET film is folded along the longitudinal direction, and the other longitudinal end of the folded PET film is fixed to the upper surface of the polycarbonate plate with an adhesive sheet with an adhesion area of 3 mm×10 mm. This state is maintained under conditions of 65° C. and 90% RH for 72 hours (repulsion resistance evaluation test). Then, after 72 hours have passed (at the end of the test), the floating height [mm] of the pressure-sensitive adhesive sheet from the polycarbonate plate is measured.
[2] The mobile electronic device according to [1] above, wherein the pressure-sensitive adhesive layer contains an acrylic polymer, and the acrylic polymer is a polymer of a monomer component containing heptyl acrylate.
[3] The glass transition temperature of the pressure-sensitive adhesive layer is in the range of −15° C. to 15° C., where the glass transition temperature of the pressure-sensitive adhesive layer is obtained from the peak temperature of tan δ in dynamic viscoelasticity measurement. The portable electronic device according to the above [1] or [2], which refers to the glass transition temperature.
[4] The portable electronic device according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive layer further contains a tackifying resin.
[5] The portable electronic device according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive layer contains at least one selected from rosin-based tackifying resins and terpene-based tackifying resins.
[6] 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 with respect to 100 parts by weight of the base polymer (preferably acrylic polymer). Portable electronic devices as described in .
[7] The portable electronic device according to any one of [1] to [6] above, wherein the pressure-sensitive adhesive layer further contains an acrylic oligomer.
[8] Any one of [1] to [7] above, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains at least one selected from an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent. mobile electronic devices.
[9] The portable electronic device according to any one of [1] to [8] above, wherein the pressure-sensitive adhesive sheet has a 180 degree peel strength against a stainless steel plate of 20 N/25 mm or more.

[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer,
In the repulsion resistance evaluation test conducted by the following method, the floating height at the end of the test is 2.0 mm or less,
A pressure-sensitive adhesive sheet having an impact adhesive strength of 0.3 J/cm ² or more in an impact resistance test conducted according to JIS K6855.
[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 at one longitudinal end of the PET film 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. Next, the PET film is folded along the longitudinal direction, and the other longitudinal end of the folded PET film is fixed to the upper surface of the polycarbonate plate with an adhesive sheet with an adhesion area of 3 mm×10 mm. This state is maintained under conditions of 65° C. and 90% RH for 72 hours (repulsion resistance evaluation test). Then, after 72 hours have passed (at the end of the test), the floating height [mm] of the pressure-sensitive adhesive sheet from the polycarbonate plate is measured.
[12] The pressure-sensitive adhesive sheet according to [11] above, wherein the pressure-sensitive adhesive layer contains an acrylic polymer, and the acrylic polymer is a polymer of a monomer component containing heptyl acrylate.
[13] The glass transition temperature of the pressure-sensitive adhesive layer is in the range of −15° C. to 15° C., where the glass transition temperature of the pressure-sensitive adhesive layer is obtained from the peak temperature of tan δ in dynamic viscoelasticity measurement. The pressure-sensitive adhesive sheet according to [11] or [12] above, which refers to the 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] 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 per 100 parts by weight of the base polymer (preferably acrylic polymer). The adhesive sheet described in .
[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 pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer according to any one of [11] to [17] above, wherein the pressure-sensitive adhesive composition contains at least one selected from an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent. adhesive sheet.
[19] The pressure-sensitive 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 pressure-sensitive adhesive sheet according to any one of [11] to [19] above, which is used for fixing a member in a portable electronic device.
[21] A portable electronic device comprising the adhesive sheet according to any one of [11] to [20] above.

Several examples relating to the present invention are described below, but the present invention is not intended to be limited to those shown in such examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

<Example 1>
(Synthesis of acrylic polymer)
94 parts of n-heptyl acrylate (n-HpA) and 6 parts of acrylic acid (AA) as monomer components were placed in a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser and a dropping funnel, and a polymerization solvent. and ethyl acetate were charged, and the mixture was stirred for 2 hours while nitrogen gas was introduced. After removing oxygen in the polymerization system in this manner, 0.2 parts of 2,2′-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and solution polymerization was carried out at 60° C. to 70° C. for 8 hours. to obtain an acrylic polymer solution. The weight average molecular weight (Mw) of this acrylic polymer was 1,200,000. Mw was adjusted by adjusting the concentration of the monomer component during polymerization. The above n-HpA is a compound having a biomass-derived heptyl group at the ester end, synthesized using biomass-derived heptyl alcohol.

(Preparation of adhesive composition)
Terpene phenol A (trade name “YS Polyster T-115”, Yasuhara Chemical Co., Ltd.) Resin, softening point of about 115 ° C., hydroxyl value of 30 to 60 mg KOH / g) 30 parts, isocyanate cross-linking agent (trade name "Coronate L", 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct , manufactured by Tosoh Corporation) 3 parts (solid content basis), and an epoxy-based cross-linking agent (trade name “TETRAD-C”, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, Mitsubishi Gas Chemical Company (manufacturer) was added and mixed with stirring to prepare a pressure-sensitive adhesive composition according to this example.

(Preparation of adhesive sheet)
The resulting pressure-sensitive adhesive composition was applied to the release surface of a 38 μm thick polyester release film (trade name “Diafoil MRF”, manufactured by Mitsubishi Chemical Corporation) and dried at 100° C. for 2 minutes to form a film having a thickness of 30 μm. to form an adhesive layer. The 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 the pressure-sensitive adhesive layer. Thus, a substrate-less double-sided PSA 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>
The method is basically the same 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 cross-linking agent are changed as shown in Table 1. Then, the pressure-sensitive adhesive composition according to each example was prepared, and the obtained pressure-sensitive adhesive composition was used to prepare a substrate-less double-sided adhesive pressure-sensitive adhesive sheet (thickness: 30 μm) according to each example in the same manner as in Example 1. ) was made. The Mw of the acrylic polymer was adjusted by adjusting the concentration of the monomer component 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. In addition, terpene phenol B is a trade name "YS Polystar S-145" manufactured by Yasuhara Chemical Co., Ltd. (a terpene phenol resin having a softening point of about 145 ° C. and a hydroxyl value of 70 to 110 mgKOH / g), and rosin ester is Arakawa Chemical Industries Co., Ltd. "Pencel D125" (polymerized rosin ester having a softening point of 125°C and a hydroxyl value of 32 mgKOH/g).
Also, 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 inlet tube, a reflux condenser, and a dropping funnel, 95 parts of cyclohexyl methacrylate (CHMA) and 5 parts of AA, 10 parts of AIBN as a polymerization initiator, Ethyl acetate as a polymerization solvent was charged and stirred in a nitrogen stream for 1 hour to remove oxygen in the polymerization system. Obtained. Mw of the obtained acrylic oligomer was 3,600.

<Evaluation method>
[Adhesive strength against SUS]
Under the measurement environment of 23° C. and 50% RH, a PET film having a thickness of 50 μm is adhered to one adhesive surface of the adhesive sheet (double-sided adhesive sheet) for lining, and the sheet is cut into a size of 25 mm in width and 100 mm in length. A measurement sample was produced. In an environment of 23° C. and 50% RH, the other adhesive surface of the measurement sample was press-bonded to the surface of a stainless steel plate (SUS304BA plate) washed with ethyl acetate by reciprocating a 2 kg roller once. After leaving it in the same environment for 72 hours, using a universal tensile compression tester, according to JIS Z 0237: 2000, the peel strength (vs. SUS Adhesive force) [N/25 mm] was measured. In the measurement of the peel strength, as a universal tension/compression tester, "Tensile/compression tester, TG-1kN" manufactured by Minebea Co., Ltd. or its equivalent is used. When performing the peel strength measurement on a single-sided pressure-sensitive adhesive sheet, the backing of the PET film is unnecessary. If the substrate thickness is thin (for example, if the substrate thickness is 25 μm or less), it may be lined with a PET film.

[Impact resistance test (pendulum)]
Impact resistance (impact adhesive strength) [J/cm ² ] was measured using a pendulum type adhesive shear impact tester based on JIS K6855 (corresponding to international standard ISO 9653). As test pieces, adhesive sheet pieces obtained by cutting the substrate-less double-sided adhesive sheet according to each example into 10 mm squares were used, and a 10 mm square, 5 mm thick stainless steel (SUS304) plate was attached to another stainless steel plate (SUS304 plate). After pressing and adhering to the top with a load of 35 N for 10 seconds, the one cured at room temperature for 48 hours was used. 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 direction repulsion resistance test (high temperature and high humidity conditions)]
As shown in (a) of FIG. 5, a polycarbonate (PC) plate 50 having a length of 30 mm, a width of 10 mm, and a thickness of 2 mm, and a PET film 60 having 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 superimposed 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 (“No. 5000NS” manufactured by Nitto Denko Corporation) was used for the fixing.
A pressure-sensitive adhesive sheet sample piece 70 was prepared by cutting the pressure-sensitive adhesive sheet according to each example, the pressure-sensitive adhesive surfaces of which were protected by two release liners, into a size of 3 mm in width and 10 mm in length. The surface of the PC board 50 opposite to the fixing surface of the PET film is placed on the upper side, one release liner is peeled off from the adhesive sheet sample piece 70, and the width direction of the PC board 50 and the longitudinal direction of the adhesive sheet sample piece 70 are separated. The adhesive sheet sample piece 70 is attached to the upper surface of the PC board 50 so that both ends of the adhesive sheet sample piece 70 in the width direction are on the lines of 7 mm and 10 mm from the other end on the upper surface of the PC board 50. Fixed. The fixing was performed by reciprocating the upper surface of the adhesive sheet sample piece 70 protected by the other release liner with a 2 kg roller once.
Next, under an environment of 23° C. and 50% RH, the other release liner of the adhesive sheet sample piece 70 attached to the PC board 50 was peeled off, and the PC board 50 was left as shown in FIG. The protruding part (length 40 mm) from the PC board 50 of the PET film 60 fixed to the base is folded back to 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 folded PET film 60 was fixed to the upper surface of the PC board 50 via the adhesive sheet sample piece 70 by reciprocating a 0.1 kg roller from above the PET film 60 once, and this was held at 65° C. 90%. Exposure to RH environment. After being exposed to the same environment for 72 hours, it was confirmed whether the adhesion state between the adhesive sheet sample piece 70 and the PET film 60 was maintained. 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 in triplicate and the lowest value was recorded. The floating height is the height including the thickness of the adhesive sheet sample piece 70 .
According to this evaluation method, unlike the conventional repulsion resistance evaluation, the repulsion resistance against a peeling load substantially only in the thickness direction (Z-axis direction) of the adhesive sheet is evaluated at a high temperature and high humidity of 65 ° C and 90% RH. It is possible to evaluate under the severe conditions of , and furthermore, by observing over time, it is possible to evaluate sustained repulsion resistance.

[Curved surface adhesion / impact resistance composite evaluation test]
Cut the adhesive sheet (double-sided adhesive sheet) into a size of 10 mm × 80 mm, expose one adhesive surface, and paste it on a stainless steel plate (SUS304 plate) with a thickness of 0.1 mm cut into the same size (10 mm × 80 mm). A test piece was prepared by attaching and lining. This test piece was press-bonded to an adherend using a laminator in a room temperature (23° C.) environment, and then held in the same environment for 24 hours. A stainless steel plate (SUS304 plate) having a thickness of 0.4 mm cut into a size of 20 mm×100 mm was used as the adherend. Next, the longitudinal direction of the adherend (stainless steel plate) to which the test piece was attached was bent so that the chord length was 70 mm, and the adherend was held at room temperature (23° C.) for 30 minutes. After holding for 30 minutes, a test piece that was found to lift from the surface of the adherend was judged to be "failed", and the test was terminated at this point.
For the test pieces that did not lift up, the adherend to which the test piece was attached was released from the curved state and placed on a flat surface with the convex surface (test piece side) facing upward. Then, a 2 kg weight (sphere) was dropped from a height of 5 cm from the test piece. After dropping the weight, the longitudinal direction of the adherend to which the test piece was attached was bent again in a room temperature (23°C) environment so that the chord length was 70 mm, and the presence or absence of lifting at the end of the test piece. observed. A test piece that did not lift up from the adherend surface was judged as "accepted", and a test piece that lifted up from the adherend surface was judged as "failed".

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

As shown in Table 1, the pressure-sensitive adhesive sheets according to Examples 1 to 6 had an impact resistance test result of 0.3 J/cm ² or more and a Z-axis repulsion resistance test floating height of 2.0 mm. In the curved surface adhesion/impact resistance composite evaluation test, no separation from the adherend occurred. On the other hand, in Comparative Examples 1, 3 to 4, the separation occurred in the Z-axis direction repulsion resistance test (Comparative Examples 1 and 3), or the floating height in the Z-axis direction repulsion resistance test exceeded 2.0 mm (Comparative Example 4) The result of the curved surface adhesion/impact resistance composite evaluation test was unacceptable. In Comparative Example 2, the result of the impact resistance test was less than 0.3 J/cm ² , and in the curved surface adhesion/impact resistance composite evaluation test, a lift of about 1 mm occurred after impact was applied, resulting in a failure. .
From the above results, it can be seen that the pressure-sensitive adhesive sheet having a floating height of 2.0 mm or less in the Z-axis direction repulsion resistance test and an impact adhesive strength of 0.3 J/cm ² or more in the impact resistance test has a curved surface shape. It can be seen that it can have excellent adhesion reliability such that it does not peel off even when it is subjected to impact such as dropping.

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

Reference Signs List 1, 2, 3 Adhesive sheet 10 Supporting substrate 10A First surface 10B Second surface (back surface)
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 PSA sheet with release liner

Claims (6)

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer,
The pressure-sensitive adhesive layer contains an acrylic polymer, and the acrylic polymer is a polymer of a monomer component containing 50% by weight or more of heptyl acrylate,
The monomer component contains a carboxy group-containing monomer at a ratio of more than 3.0% by weight and 10% by weight or less,
The monomer component does not contain a hydroxyl group-containing monomer, or contains a proportion of less than 0.5% by weight,
The pressure-sensitive adhesive layer contains a tackifying resin, or contains an acrylic oligomer, or contains a tackifying resin and an acrylic oligomer,
The total amount of the tackifying resin and the acrylic oligomer contained in the adhesive layer is 10 parts by weight or more and less than 60 parts by weight with respect to 100 parts by weight of the acrylic polymer,
The pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive layer contains an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent ,
The content of the isocyanate-based cross-linking agent is 0.8 parts by weight or more and less than 5 parts by weight with respect to 100 parts by weight of the acrylic polymer,
The content of the isocyanate-based cross-linking agent is 50 to 300 times the content of the epoxy-based cross-linking agent,
In the repulsion resistance evaluation test conducted by the following method, the floating height at the end of the test is 2.0 mm or less,
A pressure-sensitive adhesive sheet having an impact adhesive strength of 0.3 J/cm ² or more in an impact resistance test conducted according to JIS K6855.
[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 at one longitudinal end of the PET film 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. Next, the PET film is folded along the longitudinal direction, and the other longitudinal end of the folded PET film is fixed to the upper surface of the polycarbonate plate with an adhesive sheet with an adhesion area of 3 mm×10 mm. This state is maintained under conditions of 65° C. and 90% RH for 72 hours (repulsion resistance evaluation test). Then, after 72 hours have passed (at the end of the test), the floating height [mm] of the pressure-sensitive adhesive sheet from the polycarbonate plate is measured. The glass transition temperature of the pressure-sensitive adhesive layer is in the range of −15° C. to 15° C., where the glass transition temperature of the pressure-sensitive adhesive layer is the glass transition temperature obtained from the peak temperature of tan δ in dynamic viscoelasticity measurement. The pressure-sensitive adhesive sheet according to claim 1 . The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer contains the tackifying resin . The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer contains the acrylic oligomer. 3. The pressure-sensitive adhesive sheet according to claim 1, which has a 180-degree peel strength against a stainless steel plate of 20 N/25 mm or more. The pressure-sensitive adhesive sheet according to claim 1 or 2, which is used for fixing a member in a portable electronic device.

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