JP2023064541A - Adhesive sheet - Google Patents

Abstract

To provide an adhesive sheet that exhibits both tack and holding power despite having a structure comprising a thin adhesive layer.SOLUTION: Provided is an adhesive sheet comprising an adhesive layer having a thickness of 10 μm or less. The adhesive layer is an acrylic adhesive layer containing an acrylic polymer. The adhesive layer has a storage elastic modulus of less than 0.1 MPa at a temperature of 25°C, and a storage elastic modulus of at least 0.025 MPa at a temperature of 80°C.SELECTED DRAWING: Figure 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 being easily adhered to an adherend by pressure. Taking advantage of such properties, the adhesive can be used, for example, in the form of a base-attached pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on a supporting base, or in the form of a base-less pressure-sensitive adhesive sheet without a supporting base, for use in smartphones, etc. It is widely used for the purpose of joining, fixing, and protecting members in portable electronic devices. Patent document 1 is cited as a document disclosing this kind of prior art. Patent Document 1 discloses a pressure-sensitive adhesive sheet used for fixing and covering a ferrite sheet or a graphite sheet, and describes that the thickness of the pressure-sensitive adhesive layer is 1 to 4 μm.

JP 2015-224284 A

The pressure-sensitive adhesive sheet may be required to be thin depending on the application site. For example, pressure-sensitive adhesive sheets used in mobile electronic devices such as smartphones tend to be thinner as mobile electronic devices are becoming smaller and lighter in recent years. However, when the thickness of the adhesive layer is reduced, the tackiness of the adhesive layer surface decreases, resulting in problems such as poor alignment, time required for crimping and curing, and poor adhesion to rough surfaces. easier. One possible way to maintain and improve tackiness is to employ a softer adhesive, but this will lead to the problem of reduced holding power. In the design of thin-layer pressure-sensitive adhesives, there is a trade-off between tackiness and holding power.

The present invention was created in view of the above circumstances, and aims to achieve both tackiness and holding power in a thin pressure-sensitive adhesive. Specifically, a pressure-sensitive adhesive layer having a thickness of 10 μm or less An object of the present invention is to provide a pressure-sensitive adhesive sheet capable of achieving both tackiness and holding power.

According to this specification, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of 10 μm or less is provided. The pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer. The pressure-sensitive adhesive layer has a storage modulus of less than 0.1 MPa at 25°C and a storage modulus of 0.025 MPa or more at 80°C. By setting the 25° C. storage elastic modulus of the pressure-sensitive adhesive layer to less than 0.1 MPa, good tackiness can be obtained in the thin pressure-sensitive adhesive layer. Further, by setting the 80° C. storage elastic modulus of the pressure-sensitive adhesive layer to 0.025 MPa or more, a sufficient holding force can be obtained in a structure provided with a thin pressure-sensitive adhesive layer. Such properties are preferably achieved using an acrylic pressure-sensitive adhesive. That is, in the acrylic pressure-sensitive adhesive layer having a thickness of 10 μm or less, both tack and holding power can be achieved by setting the 25° C. storage elastic modulus to less than 0.1 MPa and the 80° C. storage elastic modulus to 0.025 MPa or more. .

In some preferred embodiments, the monomer component constituting the acrylic polymer contains 75% by weight or more of an alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms. By using an acrylic polymer having the above monomer composition, the effects of the technology disclosed herein are preferably realized.

In some preferred embodiments, the pressure-sensitive adhesive layer contains, as a tackifying resin, a tackifying resin _TL having a softening point of less than 145°C. By using a tackifying resin having a softening point of less than a predetermined value, the 25°C storage modulus is effectively reduced, making it easier to achieve the desired 25°C storage modulus and 80°C storage modulus.

In some preferred embodiments, the adhesive layer comprises a terpene phenolic resin as a tackifying resin. By using a terpene phenolic resin as the tackifying resin, the advantages of the technology disclosed herein are preferably realized.

In some preferred embodiments, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer contains an isocyanate-based cross-linking agent and a non-isocyanate-based cross-linking agent. By using an isocyanate-based cross-linking agent and a non-isocyanate-based cross-linking agent in combination, both tackiness and holding power are preferably achieved. In addition, the combined use of the above two cross-linking agents makes it easier to adjust the storage modulus of the pressure-sensitive adhesive layer to be formed within a desired range, achieving both the desired 25°C storage modulus and 80°C storage modulus. Cheap. An epoxy-based cross-linking agent is preferably used as the non-isocyanate-based cross-linking agent.

In some embodiments, the pressure-sensitive adhesive sheet further has a base layer that supports the pressure-sensitive adhesive layer. A pressure-sensitive adhesive sheet containing a substrate layer tends to provide good workability and workability.

In some embodiments, the adhesive sheet has a total thickness of 20 μm or less. Such a pressure-sensitive adhesive sheet with a limited thickness is advantageous in terms of thinning, miniaturization, weight reduction, resource saving, etc. of products to which the pressure-sensitive adhesive sheet is applied (for example, portable electronic devices such as smartphones). can be.

The pressure-sensitive adhesive sheets according to some embodiments are suitable as pressure-sensitive adhesive sheets that are used by being attached to graphite sheets or ferrite sheets. For example, it is suitable as a pressure-sensitive adhesive sheet used for graphite sheets arranged in mobile electronic devices such as mobile phones and smart phones. Graphite sheets can be placed in various electronic devices as heat radiation sheets that release heat from heat generating elements (batteries, IC chips, etc.). By applying a pressure-sensitive adhesive sheet having a thin pressure-sensitive adhesive layer to a graphite sheet, the heat dissipation effect of the graphite sheet can be sufficiently exhibited. Accordingly, the adhesive sheet provided by this specification can be laminated to a graphite sheet placed within a portable electronic device. As with the graphite sheet application, the pressure-sensitive adhesive sheet disclosed herein is preferably used as a pressure-sensitive adhesive sheet to be attached to a ferrite sheet because it is required to be thin. For example, it is suitable as an adhesive sheet used for ferrite sheets attached to mobile electronic devices such as mobile phones and smart phones. Therefore, the pressure-sensitive adhesive sheet provided by this specification can be laminated to a ferrite sheet placed in a portable electronic device.

The pressure-sensitive adhesive sheet disclosed herein can achieve both tackiness and holding power while having a thin pressure-sensitive adhesive layer, and is preferably used in various applications where thinness is required by taking advantage of this feature. For example, it is preferably used for portable electronic devices that require thinness. Specifically, it can be preferably used for fixing a member of a portable electronic device.

1 is a cross-sectional view schematically showing one configuration example of an adhesive sheet; FIG. FIG. 3 is a cross-sectional view schematically showing another configuration example of the adhesive sheet; 1 is a cross-sectional view schematically showing one configuration example of a laminate; FIG. 1 is an exploded perspective view schematically showing a configuration example of a display device; FIG.

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 sizes and scales of products such as pressure-sensitive adhesive sheets that are actually provided.

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).

<Configuration example of adhesive sheet>
The pressure-sensitive adhesive sheet disclosed herein may be a pressure-sensitive adhesive sheet with a substrate having the above-mentioned pressure-sensitive adhesive layer on one or both sides of a non-releasable substrate (supporting substrate). It may be a substrate-less pressure-sensitive adhesive sheet (that is, a pressure-sensitive adhesive sheet having no non-releasable substrate) such as a form held by a liner. 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.

The adhesive sheet disclosed herein can have, for example, the cross-sectional structure schematically shown in FIG. The adhesive sheet 1 shown in FIG. 1 includes a sheet-like substrate (support) 10 and an adhesive layer 20 provided on one surface 10A of the substrate 10 . In this pressure-sensitive adhesive sheet 1 , the surface of the pressure-sensitive adhesive layer 20 is an adhesive surface (adhesive surface) 1</b>A that constitutes one surface of the pressure-sensitive adhesive sheet 1 . In this adhesive sheet 1, the other surface 10B of the substrate 10 is the other surface (back surface) 1B of the adhesive sheet 1. As shown in FIG. That is, the other surface 10B of the base material 10 also serves as the back surface 1B of the adhesive sheet 1 . The substrate 10 includes a substrate film 12 and a colored layer 14 disposed on the back side of the substrate film 12 (that is, the back surface 1B side of the pressure-sensitive adhesive sheet 1 rather than the substrate film 12; also referred to as the second surface 12B). and further includes a mat layer 16 on the back side of the colored layer 14 . An adhesive layer 20 is arranged on the other surface (first surface 12A) of the base film 12 . In other words, the adhesive layer 20 is provided on the first surface 12A of the base film 12, and the colored layer 14 is provided on the second surface 12B (opposite side of the first surface 12A) of the base film 12. and mat layer 16 are laminated in this order. Therefore, the substrate 10 has a laminated structure in which the substrate film 12, the colored layer 14, and the mat layer 16 are laminated in this order. In this embodiment, the matte layer 16 is the outermost layer of the substrate 10 and the outer surface 16A of the matte layer 16 is the back surface 1B of the pressure-sensitive adhesive sheet 1 .

The pressure-sensitive adhesive sheet 1 before use has a configuration in which the pressure-sensitive adhesive layer 20 is protected by a release liner 50 having a release surface 50B on the pressure-sensitive adhesive layer 20 side. When the adhesive sheet 1 with the release liner 50 is in the form of a roll (adhesive sheet roll) for the purpose of transportation, storage, etc., the outer surface 50A of the release liner 50 (the surface opposite to the release surface 50B) ) and the back surface 1B of the adhesive sheet (in this embodiment, the outer surface 16A of the mat layer 16) are in contact with each other.

In addition, the PSA sheet disclosed herein may be in the form of a double-sided PSA type substrate-less PSA sheet schematically shown in FIG. 2, for example. The pressure-sensitive adhesive sheet 2 shown in FIG. 2 has a configuration in which both surfaces 21A and 21B of a substrate-less pressure-sensitive adhesive layer 21 are protected by release liners 51 and 52, respectively, whose release surfaces are at least on the pressure-sensitive adhesive layer side. Alternatively, the pressure-sensitive adhesive sheet has a configuration in which one surface (adhesive surface, first adhesive surface) of a substrate-less adhesive layer is protected by a release liner having release surfaces on both sides, and is wound. When turned, the other surface (adhesive surface, second adhesive surface) of the adhesive layer comes into contact with the back surface of the release liner, so that the second adhesive surface of the adhesive layer is also protected by the release liner. You may be able to do it with a configuration. The technology disclosed herein can be preferably implemented in such a substrate-less form from the viewpoint of reducing the thickness of the pressure-sensitive adhesive sheet. A substrate-less pressure-sensitive adhesive sheet is advantageous in that it is easy to form a thin layer, and that the pressure-sensitive adhesive properties such as adhesive strength and impact resistance can be maximized.

<Storage Elastic Modulus of Adhesive Layer>
In some preferred embodiments, the pressure-sensitive adhesive layer has a storage modulus at 25°C (25°C storage modulus) of less than 0.1 MPa (specifically, less than 0.10 MPa), and a storage modulus at 80°C ( 80°C storage modulus) is 0.025 MPa or more. By setting the 25° C. storage elastic modulus of the pressure-sensitive adhesive layer to less than 0.1 MPa, good tackiness can be obtained in the thin pressure-sensitive adhesive layer. Further, by setting the 80° C. storage elastic modulus of the pressure-sensitive adhesive layer to 0.025 MPa or more, a sufficient holding force can be obtained in a structure provided with a thin pressure-sensitive adhesive layer. That is, both tackiness and holding power can be achieved in a thin pressure-sensitive adhesive layer. Such characteristics are realized by the monomer composition and molecular weight characteristics of the base polymer (typically acrylic polymer) contained in the adhesive layer, the type and softening point of the tackifying resin, the amount of the tackifier, and the type and amount of the cross-linking agent used. can be

The 25° C. storage elastic modulus of the pressure-sensitive adhesive layer is more preferably 0.09 MPa or less, even more preferably 0.08 MPa or less. The lower limit of the 25° C. storage elastic modulus is not particularly limited, but in some embodiments, the 25° C. storage elastic modulus is, for example, 0.01 MPa or more, preferably 0.02 MPa or more. From the viewpoint of compatibility with the 80° C. storage modulus, it is preferably 0.03 MPa or more, may be 0.05 MPa or more, may be 0.06 MPa or more, or may be 0.07 MPa or more. The higher the 25°C storage modulus, the higher the cohesive strength of the pressure-sensitive adhesive, which tends to improve the holding power.

The 80° C. storage elastic modulus of the pressure-sensitive adhesive layer is more preferably 0.028 MPa or higher, still more preferably 0.030 MPa or higher, and may be 0.032 MPa or higher. The higher the 80°C storage elastic modulus, the easier it is to obtain good holding power (high-temperature holding power) even when exposed to a high temperature state of 80°C or higher, for example. The upper limit of the 80° C. storage modulus is not particularly limited, but in some embodiments, it is, for example, 0.10 MPa or less, and is suitably 0.08 MPa or less, compatible with the 25° C. storage modulus described above. From the viewpoint, it is preferably 0.06 MPa or less, may be 0.05 MPa or less, may be 0.04 MPa or less, or may be 0.035 MPa or less. There is a tendency that the lower the 80° C. storage elastic modulus, the better the tackiness and adhesiveness.

The ratio of the 25° C. storage modulus to the 80° C. storage modulus is not limited to a specific range because it can be set within a range in which each storage modulus is within a desired range. In some embodiments, the ratio ( _G'25 / _G'80 ) of the 25°C storage modulus ( _G'25 ) to the 80°C storage modulus ( _G'80 ) of the pressure-sensitive adhesive layer is preferably 5 or less, more It is preferably 4 or less, more preferably 3 or less. The smaller the ratio ( _G'25 / _G'80 ), the lower the storage modulus at 25°C and the higher the storage modulus at 80°C. are easily compatible. The lower limit of the ratio (G _{' 25} /G' ₈₀ ) may be 1.5 or more, 2 or more, or 2.2 or more from the viewpoint of ease of preparation of the adhesive.

In this specification, the 25° C. storage modulus and the 80° C. storage modulus 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 the following is performed with a viscoelasticity tester (for example, manufactured by TA Instruments Co., Ltd., ARES or its equivalent). Dynamic viscoelasticity measurement is performed under the conditions of , and the storage elastic modulus [MPa] at 25°C and 80°C is 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 pressure-sensitive adhesive layer to be measured can be formed by applying the corresponding pressure-sensitive adhesive composition in layers and drying or curing.

<Adhesive layer>
In some preferred embodiments, the adhesive constituting the adhesive layer consists of an acrylic adhesive containing an acrylic polymer (preferably an acrylic adhesive containing the acrylic polymer as a base polymer). The PSA that satisfies both the 25° C. storage modulus of less than 0.1 MPa and the 80° C. storage modulus of 0.025 MPa or more can be preferably realized by using an acrylic PSA. According to the technology disclosed herein, it is possible to preferably achieve both tackiness and holding power of a thin pressure-sensitive adhesive layer in a configuration using an acrylic pressure-sensitive adhesive. The use of acrylic polymers is also advantageous in terms of adhesion performance, cost, and the like.

The "base polymer" of the pressure-sensitive adhesive refers to the main component of the rubber-like polymer contained in the pressure-sensitive adhesive, and is not to be construed as being limited to anything other than this. The term "rubber-like polymer" refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, the term "main component" refers to a component contained in an amount exceeding 50% by weight unless otherwise specified.
Further, the term "acrylic polymer" refers to a polymer containing monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule 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. A typical example of an acrylic polymer is an acrylic polymer containing more than 50% by weight of the acrylic monomer in the total monomer components used to synthesize the acrylic polymer.
In addition, "(meth)acryloyl" is a generic term for acryloyl and methacryloyl. Similarly, "(meth)acrylate" is a generic term for acrylate and methacrylate, and "(meth)acrylic" is generic for acrylic and methacrylic.

(acrylic polymer)
As the acrylic polymer in the technique 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. The upper limit of the ratio of alkyl (meth)acrylate is not particularly limited, but 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.

Further, when C _4-8 alkyl acrylate is used as a monomer component, the proportion of C _4-8 alkyl acrylate in the alkyl (meth)acrylate contained in the monomer component is preferably 70% by weight or more, It is more preferably 90% by weight or more.

In some aspects, the monomer component constituting the acrylic polymer contains 50% by weight or more of C _1-6 alkyl (meth)acrylate. In other words, the polymerization ratio of C _1-6 alkyl (meth)acrylate in the acrylic polymer may be 50% by weight or more. By using a C _1-6 alkyl (meth)acrylate as a main monomer in this way, there is a tendency to easily obtain holding power. In this embodiment, the ratio of C _1-6 alkyl (meth)acrylate in the monomer component (in other words, polymerization ratio) is preferably 75% by weight or more, more preferably 80% by weight or more, and still more preferably 90% by weight or more ( for example, 92% by weight or more). The upper limit of the ratio of C _1-6 alkyl (meth)acrylate in the monomer component is not particularly limited, and is usually 99% by weight or less, and 97% by weight or less in relation to the proportion of other copolymerizable monomers used. It is suitable that the content is 95% by weight or less. The C _1-6 alkyl (meth)acrylates may be used singly or in combination of two or more. The C _1-6 alkyl (meth)acrylate is preferably a C _1-6 alkyl acrylate, more preferably a C _2-6 alkyl acrylate, and even more preferably a C _4-6 alkyl acrylate. In some other aspects, the C _1-6 alkyl (meth)acrylate is preferably a C _1-4 alkyl acrylate, more preferably a C _2-4 alkyl acrylate. Preferred examples of C _1-6 alkyl (meth)acrylates include BA.

A secondary monomer may be copolymerized with the acrylic polymer in the technology disclosed herein. A carboxyl group-containing monomer, a hydroxyl group (OH group)-containing monomer (2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth)acrylate, etc.), acid anhydride group-containing monomers, amide group-containing monomers ((meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc.), amino group-containing monomers (aminoethyl ( meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), epoxy group-containing monomers, cyano group-containing monomers, keto group-containing monomers, monomers having 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 said submonomer can be used individually by 1 type or in combination of 2 or more types.

When the monomer component constituting the acrylic polymer contains the functional group-containing monomer described above, the content of the functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exhibiting the effect of using the functional group-containing monomer, the content of the functional group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, and should be 0.5% by weight or more. is suitable, and it may be 1% by weight or more. In addition, from the viewpoint of easily balancing the adhesion performance in relation to the main monomer, the content of the functional group-containing monomer in the monomer component is appropriately 40% by weight or less, and is 20% by weight or less. is preferable, and it may be 10% by weight or less (for example, 5% by weight or less).

In some preferred embodiments, an acidic group-containing monomer is used as the monomer copolymerizable with the main monomer alkyl (meth)acrylate. The acidic group-containing monomer can improve cohesiveness based on its polarity and exhibit good bonding strength to polar adherends. When using a cross-linking agent such as an isocyanate-based or epoxy-based cross-linking agent, the acidic group (typically a carboxyl group) can become a cross-linking point of the acrylic polymer.

A carboxy group-containing monomer is preferably used as the acidic group-containing monomer. Examples of carboxy group-containing monomers include ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, crotonic acid and isocrotonic acid; maleic acid, itaconic acid and citraconic acid; ethylenically unsaturated dicarboxylic acids such as and anhydrides thereof (maleic anhydride, itaconic anhydride, etc.). The acidic group-containing monomer may also be a monomer having a metal salt (for example, an alkali metal salt) of a carboxy group. Among them, AA and MAA are preferred, and AA is particularly preferred. The acidic group-containing monomers may be used singly or in combination of two or more.

In the technology disclosed herein, the content of an acidic group-containing monomer (typically a carboxy group-containing monomer) in the monomer component (in other words, the copolymerization ratio of the acidic group-containing monomer in the acrylic polymer) is 1. It is suitable to be 0% by weight or more, may be 2.0% by weight or more, or may be 3.0% by weight or more. By using a predetermined amount or more of the acidic group-containing monomer, the cohesion of the pressure-sensitive adhesive layer tends to be improved. The copolymerization ratio of the acidic group-containing monomer in the acrylic polymer is preferably more than 3.0% by weight, more preferably more than 3.5% by weight, still more preferably more than 4.0% by weight, particularly preferably 4.5% by weight. %. The copolymerization ratio of the acidic group-containing monomer in the acrylic polymer is usually 20% by weight or less, preferably less than 10% by weight, more preferably 8.0% by weight, from the viewpoint of adhesion and the like. less than, more preferably less than 7.0% by weight, particularly preferably less than 6.0% by weight (for example, 5.5% by weight or less).

The acrylic polymer preferably used in the technology disclosed herein may be a copolymer obtained by copolymerizing an alkyl (meth)acrylate as a main monomer and an acidic group-containing monomer as a sub-monomer. In such an acrylic polymer, the proportion of copolymer components other than the alkyl (meth)acrylate and the acidic group-containing monomer may be less than 10% by weight, less than 3% by weight, or less than 1% by weight. Well, less than 0.1 wt%, less than 0.03 wt% (eg less than 0.01 wt%). The monomer component constituting the acrylic polymer may be substantially free of functional group-containing monomers other than the above acidic group-containing monomers. An acrylic polymer substantially composed of an alkyl (meth)acrylate and an acidic group-containing monomer can maximize the effects of the alkyl (meth)acrylate and the acidic group-containing monomer. Preferably, the alkyl (meth)acrylate is a C _1-6 alkyl (meth)acrylate (more preferably BA). The acidic group-containing monomer is preferably a carboxy group-containing monomer (more preferably AA).

The monomer components constituting the acrylic polymer may contain copolymer components other than the sub-monomers described above for the purpose of improving the cohesive force and the like. Examples of other copolymerization 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-mentioned other copolymerization 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 suitable to be 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 copolymerization components in the monomer component is suitably 20% by weight or less, and 10% by weight or less (for example, 5% by weight or less, and further is 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 copolymerization components. Here, the monomer component does not substantially contain other copolymerization components means that other copolymerization components are not used at least intentionally, and other copolymerization components are, for example, 0.01 wt% or less. To some extent, unintentional inclusion is acceptable.

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 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.

The composition of the monomer components constituting the acrylic polymer is designed so that the glass transition temperature (Tg) of the acrylic polymer is approximately −15° C. or lower (for example, approximately −70° C. or higher and −15° C. or lower). is appropriate. Here, the Tg of the acrylic polymer 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 based on weight), 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, for the monomers listed below, the following values are used as the glass transition temperatures of the homopolymers of the monomers.
2-ethylhexyl acrylate -70°C
n-butyl acrylate -55°C
2-hydroxyethyl acrylate -15°C
4-hydroxybutyl acrylate -40°C
Vinyl acetate 32°C
Acrylic acid 106°C
Methacrylic acid 228°C

For the glass transition temperatures of homopolymers of monomers other than those exemplified above, the values described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. For monomers for which multiple values are listed in this document, the highest value is adopted. If it is not described in the above Polymer Handbook, the value obtained by the measurement method described in JP-A-2007-51271 shall be used.

Although not particularly limited, the Tg of the acrylic polymer is advantageously about −25° C. or less, preferably about −35° C. or less, from the viewpoint of impact resistance and adhesion to adherends. , and more preferably about -40°C or lower. In some embodiments, from the viewpoint of cohesive strength, the Tg of the acrylic polymer is, for example, approximately −70° C. or higher, may be approximately −65° C. or higher, may be approximately −60° C. or higher, or may be approximately −55° C. or higher. good. The technology disclosed herein can be preferably carried out in a mode in which the Tg of the acrylic polymer is approximately −65° C. or higher and −35° C. or lower (for example, approximately −55° C. or higher and −40° C. or lower). The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the types and usage ratios of the monomers used in synthesizing the polymer).

The weight-average molecular weight (Mw) of the base polymer (typically an acrylic polymer) in the technique disclosed herein is not particularly limited, and can range, for example, from approximately 10×10 ⁴ to 500×10 ⁴ . From the viewpoint of cohesiveness, the Mw is usually about 30×10 ⁴ or more, and preferably about 45×10 ⁴ or more (for example, about 65×10 ⁴ or more). In addition, the above Mw is usually 300×10 ⁴ or less (more preferably about 200×10 ⁴ or less, for example about 150×10 ⁴ or less), and may be 120×10 ⁴ or less. , less than 100×10 ⁴ . Mw is determined from a standard polystyrene-equivalent value obtained by GPC (gel permeation chromatography). As the GPC apparatus, for example, model name "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) can be used.

The method for obtaining the base polymer (typically an acrylic polymer) is not particularly limited, and is known as a polymer synthesis method such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method. Various polymerization methods known in the art can be appropriately employed. For example, a solution polymerization method can be preferably employed. The polymerization temperature at the time of solution polymerization can be appropriately selected according to the type of monomer and solvent used, the type of polymerization initiator, etc. ° C.).

The solvent (polymerization solvent) used for solution polymerization can be appropriately selected from conventionally known organic solvents (toluene, ethyl acetate, etc.). Depending on the type of polymerization method, the initiator used for polymerization may be a conventionally known polymerization initiator (for example, an azo polymerization initiator such as 2,2'-azobisisobutyronitrile (AIBN) or a peroxide polymerization initiator). initiator, etc.). The amount of the polymerization initiator 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 the monomer component. ).

(tackifying resin)
The adhesive layer in the technology disclosed herein can contain a tackifying resin. Thereby, the adhesive strength of an adhesive sheet can be improved. Examples of tackifying resins include phenol-based tackifying resins, terpene-based tackifying resins, modified terpene-based tackifying resins, rosin-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, One or more selected from tackifier resins such as elastomer-based tackifier resins and ketone-based tackifier resins can be used. Among them, phenol-based tackifying resins, terpene-based tackifying resins, and modified terpene-based tackifying resins are preferable, and phenol-based tackifying resins (preferably terpene phenolic resins) are more preferable.

Examples of phenolic tackifying resins include terpene phenolic resins, hydrogenated terpene phenolic resins, alkylphenolic resins and rosin phenolic resins.
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). Preferred 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)). is 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.
Alkylphenol resins are resins obtained from alkylphenols and formaldehyde (oily phenolic resins). Examples of alkylphenol resins include novolac and resole types.
Rosin phenolic resins are typically rosins or phenol-modified products of the various rosin derivatives described above (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters). Examples of rosin phenol resins include rosin phenol resins obtained by a method of adding phenol to rosins or various rosin derivatives described above with an acid catalyst and thermally polymerizing the mixture.

Examples of terpene-based tackifying resins include polymers of terpenes (typically monoterpenes) such as α-pinene, β-pinene, d-limonene, l-limonene and dipentene. It may be a homopolymer of one kind of terpenes, or a copolymer of two or more kinds of terpenes. One type of terpene homopolymer includes α-pinene polymer, β-pinene polymer, dipentene polymer and the like. Examples of modified terpene resins include those obtained by modifying the above terpene resins. Specific examples include styrene-modified terpene resins and hydrogenated terpene resins.

The concept of rosin-based tackifying resins as used herein includes both rosins and rosin derivative resins. Examples of rosins include unmodified rosins (fresh rosins) such as gum rosin, wood rosin and tall oil rosin; homogenized rosin, polymerized rosin, other chemically modified rosins, etc.);

Rosin derivative resins are typically derivatives of rosins as described above. The term "rosin-based resin" as used herein includes derivatives of unmodified rosin and derivatives of modified rosin (including hydrogenated rosin, disproportionated rosin and polymerized rosin). For example, rosin esters such as undenatured rosin esters, which are esters of undenatured rosin and alcohols, and denatured rosin esters, which are esters of denatured rosin and alcohols; Saturated fatty acid-modified rosins; for example, unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; rosin alcohols obtained by reducing the carboxy group of rosin esters modified with fatty acids; for example, rosins or metal salts of the various rosin derivatives described above; Specific examples of rosin esters include methyl esters, triethylene glycol esters, glycerin esters and pentaerythritol esters of unmodified rosins or modified rosins (hydrogenated rosins, disproportionated rosins, polymerized rosins, etc.).

Examples of hydrocarbon tackifying resins include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic/aromatic petroleum resins (styrene-olefin copolymers, etc. ), aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-based resins, and coumarone-indene-based resins.

The softening point of the tackifying resin is not particularly limited. From the viewpoint of improving cohesive strength, a tackifier resin having a softening point (softening temperature) of about 80° C. or higher (preferably about 100° C. or higher) can be preferably used. For example, a phenol-based tackifying resin (terpene phenol resin, etc.) having such a softening point can be preferably used. There is no particular upper limit for the softening point of the tackifying resin. A tackifying 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 and substrates. The softening point of the tackifying resin can be measured based on the softening point test method (ring and ball method) specified in JIS K2207.

In some preferred embodiments, a tackifying resin T _L having a softening point of less than 145° C. is used as the tackifying resin. By using the tackifying resin T _L having a softening point of less than 145° C., it is possible to preferably form a PSA that has good tackiness and can adhere well to adherends even when it is thin. can. Also, by using a tackifying resin having a softening point of less than a predetermined value, the storage modulus is lowered, making it easier to achieve desired storage modulus properties. The softening point of the tackifier resin T _L is preferably less than 135°C, more preferably less than 125°C, and may be 120°C or less. The lower limit of the softening point of the tackifier resin T _L is not particularly limited, and is, for example, 60° C. or higher (thus solid at 30° C.), suitably 80° C. or higher, preferably 90° C. or higher, more preferably 90° C. or higher. It is 100° C. or higher, and may be 110° C. or higher. As the tackifying resin _TL , an appropriate type can be selected from among the tackifying resins described above, and terpene phenol resins are preferably used. The tackifying resin _TL can be used singly or in combination of two or more.

In the case where the pressure- _sensitive adhesive layer contains the tackifying resin T _L , the content of the tackifying resin T _L should be the base polymer (typically 1 part by weight or more, preferably 5 parts by weight or more, more preferably 10 parts by weight or more, and still more preferably 15 parts by weight or more (for example, 15 parts by weight) per 100 parts by weight of the acrylic polymer). parts by weight), particularly preferably 18 parts by weight or more. From the viewpoint of cohesive force, the amount of tackifier resin T _L per 100 parts by weight of the base polymer is suitably less than 50 parts by weight, and from the viewpoint of holding power, preferably less than 40 parts by weight, more preferably less than 40 parts by weight. is less than 30 parts by weight and may be less than 25 parts by weight.

In embodiments in which a tackifying resin T _L having a softening point of less than 145° C. is used _, the pressure-sensitive adhesive layer contains a high softening point tackifying resin (typically, A tackifying resin ( _TH ) having a softening point of 145° C. or higher may or may not be included. When the pressure-sensitive adhesive layer contains the tackifying resin T _H in addition to the tackifying resin T _L , the content of the tackifying resin T _H should be less than 100 parts by weight with respect to 100 parts by weight of the tackifying resin T _L. is suitable, preferably less than 50 parts by weight, more preferably less than 30 parts by weight, even more preferably less than 10 parts by weight, and may be less than 1 part by weight, or even less than 0.1 parts by weight.

Some preferred embodiments include embodiments in which the tackifying resin comprises one or more phenolic tackifying resins (typically terpene phenolic resins). The technology disclosed herein can be preferably implemented in a mode in which, for example, about 25% by weight or more (more preferably about 30% by weight or more) of the total amount of tackifying resin is 100% by weight is a terpene phenol resin. Approximately 50% by weight or more of the total amount of tackifying resin may be the terpene phenolic resin, and approximately 80% by weight or more (eg, approximately 90% by weight or more) may be the terpene phenolic resin. Substantially all of the tackifying resin (eg, about 95-100 wt%, or even about 99-100 wt%) may be a terpene phenolic resin.

Although not particularly limited, in some embodiments, the tackifying resin may comprise a tackifying resin having a hydroxyl value greater than 20 mg KOH/g. Among them, a tackifying resin having a hydroxyl value of 30 mgKOH/g or more is preferable. Hereinafter, a tackifying resin having a hydroxyl value of 30 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 that has excellent adhesion to adherends and high cohesion. 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, the hydroxyl value of the high hydroxyl value resin is suitably about 200 mgKOH/g or less, preferably about 100 mgKOH/g or less, and may be about 70 mgKOH/g or less. , approximately 65 mg KOH/g or less. High hydroxyl value resin can be used individually by 1 type or in combination of 2 or more types. The technology disclosed herein is preferred in embodiments in which the tackifying resin comprises a high hydroxyl value resin (such as a phenolic tackifying resin, preferably a terpene phenolic resin) with a hydroxyl value greater than 20 mgKOH/g (eg, 30-65 mgKOH/g). can be implemented. In some preferred embodiments, the high hydroxyl value resin can be a tackifying resin T _L having a softening point of less than 145°C. As the value of the hydroxyl value, a value measured by a potentiometric titration method specified in JIS K0070:1992 can be adopted.

When the pressure-sensitive adhesive layer contains a tackifying resin, the amount (total amount) of the tackifying resin used is not particularly limited, and is, for example, 1 to 100 parts by weight based on 100 parts by weight of the base polymer (typically an acrylic polymer). It can be set as appropriate within the range of about a part. From the viewpoint of suitably exhibiting the effect of improving the adhesive strength, the amount of the tackifying resin to be used with respect to 100 parts by weight of the base polymer is suitably 5 parts by weight or more, preferably 10 parts by weight or more. It may be 15 parts by weight or more. From the viewpoint of impact resistance and cohesive strength, the amount of the tackifier resin used with respect to 100 parts by weight of the base polymer is preferably 50 parts by weight or less, may be 40 parts by weight or less, or may be 30 parts by weight or less. may be

(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. 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, isocyanate-based cross-linking agents and epoxy-based cross-linking agents are more preferable, and isocyanate-based cross-linking agents are particularly preferable. . By appropriately selecting and using a cross-linking agent, the cohesive force of the adhesive layer can be obtained, and the adhesive force and the like can be improved while maintaining sufficient holding power (for example, high-temperature holding power). A crosslinking agent can be used individually by 1 type or in combination of 2 or more types. 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, a polyfunctional isocyanate (meaning a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. The isocyanate-based 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 and polyester polyisocyanate can be mentioned. Commercially available polyfunctional isocyanates include "Duranate TPA-100" (trade name) manufactured by Asahi Kasei Chemicals, "Coronate L" (trade name), "Coronate HL", "Coronate HK" (trade name) and "Coronate HK" (trade names) manufactured by Tosoh Corporation. HX", "Coronate 2096", and the like.

The amount of the isocyanate-based cross-linking agent used is not particularly limited. For example, it can be about 0.001 part by weight or more per 100 parts by weight of the base polymer (typically an acrylic polymer). In some preferred embodiments, the amount of the isocyanate cross-linking agent used relative to 100 parts by weight of the base polymer is, for example, 0.01 parts by weight or more, and 0.03 parts by weight, from the viewpoint of coexistence of cohesive strength and adhesive strength. The above is suitable, preferably 0.05 parts by weight or more, may be 0.07 parts by weight or more, or may be 0.1 parts by weight or more. Also, from the viewpoint of improving adhesive strength and tack, the amount of the isocyanate-based cross-linking agent used is suitably 10 parts by weight or less with respect to 100 parts by weight of the base polymer, and in some embodiments, 5 parts by weight parts, may be less than 3 parts by weight, and may be less than 2 parts by weight. In some preferred embodiments, the amount of the isocyanate-based cross-linking agent used is less than 1.0 parts by weight, more preferably 0.5 parts by weight or less, and even more preferably 0.3 parts by weight, based on 100 parts by weight of the base polymer. parts by weight or less, and may be 0.2 parts by weight or less. By limiting the amount of the isocyanate-based cross-linking agent to be used within the above range, good tackiness can be easily obtained.

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 technology 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 tackiness and holding power (for example, high-temperature holding power) 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 easy to achieve both tackiness and holding power. 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. Commercially available epoxy-based cross-linking agents include Mitsubishi Gas Chemical Co., Ltd.'s trade name "TETRAD-C" and trade name "TETRAD-X", DIC's trade name "Epiclon CR-5L", and Nagase ChemteX Corp. 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 0.5 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 appropriately about 0.003 parts by weight or more, and about 0.005 parts by weight with respect to 100 parts by weight of the base polymer. Above is preferable, and about 0.008 parts by weight or more is more preferable. 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 0.2 parts by weight or less with respect to 100 parts by weight of the base polymer, and about 0.1 part by weight. parts by weight or less, more preferably less than 0.05 parts by weight, and even more preferably less than 0.03 parts by weight (for example, 0.02 parts by weight or less). Good tackiness can be easily obtained by limiting the amount of the epoxy-based cross-linking agent to be used within the above range.

In the technology disclosed herein, the relationship between the content of the isocyanate-based cross-linking agent and the content of the non-isocyanate-based cross-linking agent (eg, epoxy-based cross-linking agent) is not particularly limited. In some embodiments, the content of non-isocyanate crosslinkers is less than, for example, the content of isocyanate crosslinkers. From the viewpoint of achieving both adhesion to the adherend and cohesive strength, the content of the non-isocyanate cross-linking agent is about 1/2 or less of the content of the isocyanate cross-linking agent on a weight basis. about 1/3 or less is preferable, about 1/5 or less is more preferable, about 1/7 or less is even more preferable, and about 1/9 or less is also possible. 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 (for example, an epoxy-based cross-linking agent), the content of the non-isocyanate-based cross-linking agent About 1/1000 or more, for example, about 1/500 or more of the content is suitable. In some preferred embodiments, the content of the non-isocyanate cross-linking agent is about 1/100 or more, more preferably about 1/50 or more, and even more preferably about 1/30 or more of the isocyanate cross-linking agent content. and may be approximately 1/20 or more, or may be 1/15 or more.

The total amount (total amount) of the cross-linking agent used is not particularly limited. For example, it can be about 10 parts by weight or less with respect to 100 parts by weight of the base polymer (typically an acrylic polymer), and from the viewpoint of achieving both adhesive strength and cohesive strength in a well-balanced manner, it is preferably about 0.005. It can be selected from the range of up to 10 parts by weight, more preferably from about 0.01 to 5 parts by weight. In some preferred embodiments, the total amount (total amount) of the cross-linking agent used is approximately less than 3 parts by weight, even less than 1 part by weight, relative to 100 parts by weight of the base polymer (preferably acrylic polymer). Well, it may be 0.5 parts by weight or less, 0.3 parts by weight or less, or 0.2 parts by weight or less. In some embodiments, the total amount of the cross-linking agent used relative to 100 parts by weight of the base polymer is, for example, 0.03 parts by weight or more, preferably 0.05 parts by weight or more, and 0.07 parts by weight or more. It may be present, and may be 0.1 parts by weight or more. By limiting the total amount of the cross-linking agent to be used within the above range, good tack can be easily obtained.

(coloring agent)
The pressure-sensitive adhesive layer disclosed herein may be colored in order to exhibit desired design properties and optical properties (for example, light-shielding properties, etc.). For coloring the pressure-sensitive adhesive layer, one or more of known organic or inorganic colorants (pigments, dyes, etc.) can be used in appropriate combination. For example, the pressure-sensitive adhesive layer can be colored black by including a black colorant such as carbon black in the pressure-sensitive adhesive layer. The content of the colorant is not particularly limited, and can be, for example, less than 15 parts by weight with respect to 100 parts by weight of the base polymer (typically an acrylic polymer). From the viewpoint of suppressing a decrease in adhesive properties, the content of the colorant may be about less than 10 parts by weight (for example, less than 5 parts by weight, typically less than 3 parts by weight) with respect to 100 parts by weight of the base polymer. preferable. From the viewpoint of adhesive performance, the technique disclosed herein can be preferably implemented in a mode in which the adhesive layer does not substantially contain inorganic and organic colorants. For example, the content of the colorant is preferably 0 to 1 part by weight with respect to 100 parts by weight of the base polymer.

(Other additives)
The pressure-sensitive adhesive composition may optionally contain adhesive agents such as leveling agents, cross-linking aids, plasticizers, softeners, fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, and the like. Various additives common in the pharmaceutical field may be included. 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 made of pressure-sensitive adhesive) disclosed herein is a water-based pressure-sensitive adhesive composition, a solvent-based pressure-sensitive adhesive composition, a hot-melt pressure-sensitive adhesive composition, and active energy rays such as ultraviolet rays and electron beams. It may be a pressure-sensitive adhesive layer formed from an active energy ray-curable pressure-sensitive adhesive composition that is cured by irradiation. 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. From the viewpoint of adhesive properties, the technology disclosed herein can be preferably practiced in a mode comprising a pressure-sensitive adhesive layer formed from a solvent-based pressure-sensitive adhesive composition. In an embodiment having a solvent-based pressure-sensitive adhesive layer formed from a solvent-based pressure-sensitive adhesive composition, the effects of the technique disclosed herein are preferably achieved.

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 surface having releasability (release surface) and drying can be employed. For 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 can be employed. can. 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. As the release surface, for example, the surface of a release liner, which will be described later, can be preferably 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 adhesive composition can be performed using a conventionally known coater such as a gravure roll coater, a die coater, and a bar coater. 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.degree. C., preferably about 60 to 130.degree. 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.

In the technique disclosed here, the pressure-sensitive adhesive layer is configured to be thin. Specifically, the thickness of the adhesive layer is 10 μm or less. According to the technology disclosed herein, both tackiness and holding power can be achieved in a pressure-sensitive adhesive layer having a thickness of 10 μm or less. A thin pressure-sensitive adhesive layer is also advantageous in terms of making the pressure-sensitive adhesive sheet thinner, smaller, lighter, and resource-saving. Moreover, when the pressure-sensitive adhesive sheet is applied to a graphite sheet, the thickness of the pressure-sensitive adhesive layer is preferably thin from the viewpoint of heat radiation efficiency. From such a viewpoint, the thickness of the pressure-sensitive adhesive layer is more preferably 8 µm or less, still more preferably 5 µm or less, and may be, for example, 3 µm or less. In some embodiments, the thickness of the pressure-sensitive adhesive layer is suitably about 0.5 μm or more, preferably 1 μm or more, and even 1.2 μm or more, from the viewpoint of adhesion performance, coatability, and the like. It may be, for example, 1.5 μm or more. The greater the thickness of the pressure-sensitive adhesive layer, the easier it is to obtain good tack and sufficient adhesive strength. In some other embodiments, the thickness of the adhesive layer is, for example, approximately 3 μm or greater, may be approximately 5 μm or greater, may be approximately 7 μm or greater, or may be approximately 9 μm or greater. By increasing the thickness of the pressure-sensitive adhesive layer, more excellent pressure-sensitive adhesive properties are likely to be obtained. In a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on each side of a substrate, the thickness of each pressure-sensitive adhesive layer may be the same or different.

<Base material (base material layer)>
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 (layer) supporting (backing) the pressure-sensitive adhesive layer may be a resin film, paper, Cloths, rubber sheets, foam sheets, metal foils, composites thereof, and the like can be used. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene/propylene copolymer; polyester films such as polyethylene terephthalate (PET); vinyl chloride resin films; vinyl acetate resin films; resin film; polyamide resin film; fluorine resin film; cellophane and the like. 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, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyurethane sheets and foamed polychloroprene rubber sheets. Examples of metal foil include aluminum foil and copper foil.

(Base film)
In some preferred embodiments, the adhesive sheet has a base film as a base. The substrate film is not particularly limited, and for example, a resin film containing a resin material as a main component (for example, a component containing more than 50% by weight) can be preferably used. As used herein, the term "resin film" typically refers to a substantially non-foamed resin film. That is, the resin film in this specification may be one in which air bubbles are not substantially present (voidless). Therefore, the resin film is a concept distinguished from the so-called foam film. In addition, the resin film is typically a substantially non-porous film, which is a concept distinguished from so-called non-woven fabrics and woven fabrics. A substrate film that does not contain a porous layer such as a foam, non-woven fabric, or woven fabric, that is, a substrate film comprising a non-porous layer can be preferably used. Resin films generally tend to be superior to foams, nonwoven fabrics, and woven fabrics in mechanical strength such as tensile strength. In addition, it is excellent in workability (for example, punching workability). Therefore, a pressure-sensitive adhesive sheet using a substrate containing a resin film is advantageous in terms of workability, dimensional accuracy, and handleability. A substrate containing such a resin film can also be preferably used as a substrate in the technology disclosed herein from the viewpoints of dimensional stability, thickness accuracy, economic efficiency (cost), and the like.

Preferable examples of the resin material that constitutes the resin film disclosed herein include polyolefin-based resins and polyester-based resins. Here, the term "polyolefin resin" refers to a resin containing polyolefin in a proportion of more than 50% by weight. Similarly, a polyester-based resin refers to a resin containing more than 50% by weight of polyester. Examples of polyolefin-based resin films include polyethylene (PE)-based resins, polypropylene (PP)-based resins, ethylene-propylene copolymers, ethylene-butene copolymers, and the like. Polyester-based resins include polyethylene terephthalate (PET)-based resins, polybutylene terephthalate (PBT)-based resins, polyethylene naphthalate-based resins, polybutylene naphthalate-based resins, and the like. Among these, from the viewpoint of anchoring properties (in particular, the anchoring properties of the acrylic pressure-sensitive adhesive layer), polyester resins are preferable, and from the viewpoints of strength and workability, PET resins are particularly preferable.

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

A transparent film (eg, transparent resin film) can be preferably employed as the base film (eg, resin film). From the viewpoint of strength and the like, such a base film may substantially contain no colorant. Here, that the base film does not substantially contain a coloring agent means that the content of the coloring agent is less than 1% by weight, preferably less than 0.1% by weight. Alternatively, the base film in the technology disclosed herein is colored black, white (e.g., milky white), or other colors in order to express desired design properties and optical properties (e.g., light-shielding properties, etc.) in the adhesive sheet. may The above coloring may be carried out, for example, by adding a known organic or inorganic coloring agent (pigment, dye, etc.) to the material constituting the base film.

The base film disclosed herein may have a single layer structure, or may have a multilayer structure of two layers, three layers or more. From the viewpoint of shape stability, the substrate film preferably has a single-layer structure. A method for producing the substrate film (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.

Conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, application of an undercoat (formation of an undercoat layer), etc. are performed on the surface of the base film (for example, resin film). may be applied. Such a surface treatment can be a treatment for improving the adhesion between the base film and the pressure-sensitive adhesive layer and the adhesion between the base film and the colored layer laminated on the back surface thereof. In addition, in the technology disclosed herein, an undercoat layer is not formed between the base film and the pressure-sensitive adhesive layer and/or between the base film and the layer laminated on the back surface thereof, and the base film and the adhesive layer are not formed. Preferably, the pressure-sensitive adhesive layer and/or the base film and the layer laminated on the back surface thereof are in direct contact with each other. A pressure-sensitive adhesive sheet having such a configuration can be thinner.

The thickness of the base film is not particularly limited. In some embodiments, the thickness of the base film is, for example, approximately 200 μm or less, may be approximately 100 μm or less, may be 70 μm or less, may be 50 μm or less. By reducing the thickness of the base film, the pressure-sensitive adhesive sheet is also thin, which can be advantageous in terms of thinning, miniaturization, weight reduction, resource saving, etc. of products to which the pressure-sensitive adhesive sheet is applied. In some preferred embodiments, the thickness of the base film is, for example, 30 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, particularly preferably 5 μm or less, and may be, for example, 3 μm or less. By limiting the thickness of the base film within the above range, for example, when the pressure-sensitive adhesive sheet disclosed herein is used as a heat-dissipating sheet (typically a graphite sheet), the heat-dissipating efficiency of the heat-dissipating sheet can be improved. In addition, in a pressure-sensitive adhesive sheet having a thin base film, the rigidity of the pressure-sensitive adhesive sheet itself is low, and the workability and handling properties tend to deteriorate. There is a great advantage in improving workability and the like. Moreover, the lower limit of the thickness of the base film is preferably about 0.5 μm or more (for example, 1 μm or more) from the viewpoint of handleability, workability, and the like. In some other aspects, the thickness of the base film may be 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more from the viewpoint of handleability.

(Colored layer)
In some embodiments, the substrate may contain a colored layer. In some preferred embodiments, the colored layer is laminated on the back side of the pressure-sensitive adhesive sheet of the base film, and can be arranged between the later-described matte layer and the base film. By arranging the colored layer on the back side of the pressure-sensitive adhesive sheet, the color and transparency of the pressure-sensitive adhesive sheet can be adjusted, and desired design properties, light-shielding properties, and hiding properties can be obtained. The color of the colored layer is not particularly limited, and various colors can be adopted depending on the purpose. In some preferred embodiments, the colored layer may be a black layer (eg, black printed layer) formed by, for example, black printing. A pressure-sensitive adhesive sheet having a black layer as a colored layer can be preferably used for, for example, attaching to a graphite sheet.

The colored layer can be formed, for example, by applying a colored layer-forming composition containing a coloring agent and a binder onto a substrate film. Materials known in the field of coatings or printing can be used as binders without particular limitations. Examples include polyurethane, phenol resin, epoxy resin, urea melamine resin, polymethyl methacrylate, and the like. The colored layer-forming composition may be, for example, a solvent type, an ultraviolet curable type, a heat curable type, or the like. The formation of the colored layer can be carried out by adopting means conventionally used for forming the colored layer without particular limitation. For example, a method of forming a colored layer (printed layer) by printing such as gravure printing, flexographic printing, and offset printing can be preferably employed.

The colored layer may have a single layer structure consisting entirely of one layer, or may have a multilayer structure including two, three or more sub-colored layers. A colored layer having a multi-layer structure including two or more sub-colored layers can be formed, for example, by repeatedly applying (for example, printing) a composition for forming a colored layer. The colors and blending amounts of the colorants contained in each sub-colored layer may be the same or different. From the viewpoint of preventing the occurrence of pinholes and increasing the reliability of light leakage prevention, it is particularly significant to have a multi-layered structure in the colored layer for imparting light-shielding properties.

As the coloring agent used for coloring the colored layer, a known pigment or dye can be appropriately selected according to the desired color. Examples of white pigments include, but are not limited to, titanium dioxide, zinc white, white lead, and the like. Examples of black pigments include carbon black, acetylene black, pine smoke, graphite and the like. These can be used individually by 1 type or in combination of 2 or more types.

The content of the coloring agent is not limited to a specific range because it is set according to the desired color, texture, etc., but it is appropriate to use about 1% by weight or more in the coloring layer. , preferably 2% by weight or more (eg 5% by weight or more), and may be 15% by weight or more. The content of the coloring agent is suitably about 65% by weight or less, preferably 30% by weight or less (for example, 15% by weight or less), and may be 8% by weight or less.

The thickness of the entire colored layer is usually appropriately 0.1 μm or more, preferably 0.5 μm or more, and more preferably 0.7 μm or more. The thickness of the entire colored layer may be about 0.8 μm or more, or about 1 μm or more. In some other embodiments, the thickness of the entire colored layer may be 2 μm or more (for example, 3 μm or more) or 4 μm or more from the viewpoint of obtaining sufficient light shielding properties and hiding properties. The thickness of the entire colored layer is usually 10 μm or less, preferably 7 μm or less, and more preferably 5 μm or less. In some embodiments, the total color layer thickness can be about 3 μm or less, or even about 2 μm or less. In the colored layer including two or more sub-colored layers, the thickness of each sub-colored layer is preferably about 0.5 μm to 2 μm.

(mat layer)
In some embodiments, the substrate may include a matte layer. In some preferred embodiments, the matte layer is laminated on the back side of the pressure-sensitive adhesive sheet of the base film, and can be arranged on the colored layer described above. The matte layer is preferably a layer (topcoat layer) that constitutes the back surface of the substrate and thus the back surface of the pressure-sensitive adhesive sheet. By arranging the matte layer on the back side of the pressure-sensitive adhesive sheet, a desired appearance (specifically, a matte texture with suppressed gloss (reflected light)) can be obtained. In the present specification, the matte layer means a layer that reduces the glossiness of the back surface of the pressure-sensitive adhesive sheet by forming the layer, and is also referred to as a matte treatment layer or matte layer. The presence or absence and degree of reduction in gloss can be determined by measuring a 60° gloss value, which will be described later. Since the surface of the matte layer can be the back surface of the pressure-sensitive adhesive sheet, the 60° gloss value of the surface of the matte layer can take values within the range shown above as the 60° gloss value of the back surface of the pressure-sensitive adhesive sheet.

In some preferred embodiments, the matte layer may be arranged to cover the surface (outer surface) of the colored layer. Thereby, the desired appearance can be obtained by laminating the colored layer and the matte layer to provide design and texture. In addition, the matte layer can also serve as a protective function for the colored layer. The mat layer is preferably transparent (including translucent) from the viewpoint of efficiently adjusting the color of the pressure-sensitive adhesive sheet when viewed from the rear using the colored layer. The matte layer may be a layer whose surface has been subjected to surface treatment such as embossing or sandblasting (layer having a matte-treated surface). It may be a mat layer having properties. The mat layer typically has a single layer structure, but may have a multilayer structure.

The matte layer disclosed herein preferably has matte properties due to its composition. For example, the matte layer may contain a matte material. This makes it possible to impart mattness without additional surface treatment. The matting material is typically particulate and transparent (typically colorless and transparent) is preferably used. The particle shape of the matting material is not particularly limited, and may be spherical or the like.

The mat material may be either organic particles or inorganic particles, or may be a combination of both. Examples of organic particles include acrylic resin particles such as polymethyl methacrylate particles, polystyrene particles, styrene-acrylic resin particles, polycarbonate particles, urethane resin beads, epoxy resin beads, polyester resin beads, polyester Urethane-based resin beads and the like are included. Examples of inorganic particles include silicon dioxide (silica) particles, titanium dioxide particles, barium sulfate particles, calcium carbonate particles, mica, and talc. These may be used individually by 1 type, and may use 2 or more types together. Among them, acrylic resin particles, urethane resin beads, and silica particles are preferable.

The average particle size of the mat material is not particularly limited, and in some embodiments, it is suitable to be approximately 0.1 μm or more, preferably 0.5 μm or more, and may be, for example, 1 μm or more. It may be greater than 1 μm. In some aspects, the average particle size is suitably 20 μm or less, preferably 8 μm or less, and may be, for example, 3 μm or less, or 2 μm or less. The average particle size of the matte material is preferably half or more the thickness of the matte layer, and preferably equal to or larger than the thickness of the matte layer, from the viewpoint of sufficiently expressing the matte property. From the viewpoint of appearance and coatability, the average particle size of the mat material is preferably about 10 times or less (for example, 5 times or less, typically 3 times or less) as large as the thickness of the mat layer. The average particle size of the mat material is the particle size at which the volume-based cumulative particle size is 50% in the particle size distribution obtained by measurement based on the laser diffraction/scattering method, that is, the 50% volume average particle size (50% median diameter).

The content of the mat material is not particularly limited, and in some embodiments, the content of the mat material in the mat layer is suitably about 0.5% by weight or more, preferably 1% by weight or more. , for example, 2% by weight or more, or 3% by weight or more. In some embodiments, the content of the mat material in the mat layer is suitably about 40% by weight or less, preferably 20% by weight or less, and even 10% by weight or less. Well, it may be 8% by weight or less.

The mat layer may contain other additive components such as resin components and dispersants. When the matte layer is transparent, the matte layer may have a composition substantially free of colorants. Here, the fact that the matte layer does not substantially contain a coloring agent means that the content of the coloring agent is less than 1% by weight, preferably less than 0.1% by weight.

Resin components contained in the mat layer include, for example, polyurethane-based resins, phenol-based resins, epoxy-based resins, urea-melamine-based resins, silicone-based resins, phenoxy resins, methacrylic-based resins, acrylic-based resins, polyarylate resins, and polyester-based resins. Resin, polyolefin resin, polystyrene resin, styrene-acrylic resin, styrene-maleic acid resin, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, polyvinyl acetate, polyvinyl chloride vinylidene, polycarbonate, celluloses, polyacetal, alkyd resin, and the like. A polyurethane resin is preferably used. The resin component can be used singly or in combination of two or more. The resin composition for forming the mat layer (mat layer-forming resin composition) may be a solvent-based composition, a thermosetting composition, or an ultraviolet-curable composition. From the point of view, it is preferably a thermosetting type or an ultraviolet curable type. Commercially available matte layer-forming resin compositions that can be used in the technology disclosed herein include products such as "LG6620" and "LG6510" manufactured by Tokyo Ink.

A method for forming a matte layer using the matte layer-forming composition is not particularly limited, and various printing processing methods can be employed. The printing method is not particularly limited, and various known or commonly used methods such as offset printing, silk screen printing, letterpress printing, flexographic printing, and gravure printing can be employed as appropriate. Specifically, the solid content (typically a resin component or a dispersant) constituting the above composition is dissolved or dispersed in an appropriate solvent, and an appropriate method among the above printing processing methods is adopted to obtain a The matte layer can be formed by printing the composition obtained on the black layer.

The thickness of the matte layer is suitably about 0.1 μm or more in consideration of matting properties and coatability, and in some preferred embodiments, about 0.2 μm or more. It may be 0.3 μm or more, 0.5 μm or more, or 0.7 μm or more (for example, 0.9 μm or more). From the viewpoint of thinning, the thickness is suitably about 5 μm or less, and in some preferred embodiments, it is about 3.0 μm or less, and may be, for example, 2 μm or less, or 1.5 μm or less. or less than 1.2 μm.

(other layers)
In addition, the base material may have other layers different from the base film, the black layer and the matte layer. For example, an adhesive layer, an undercoat layer, or the like may be provided in order to obtain interlayer adhesion.

Although not particularly limited, the total thickness of the substrate (layer) in the adhesive sheet disclosed herein is, for example, approximately 200 μm or less, may be approximately 100 μm or less, may be approximately 70 μm or less, or may be 50 μm or less. good. By reducing the total thickness of the base material, the pressure-sensitive adhesive sheet can also be thin, which can be advantageous in terms of thinning, miniaturization, weight reduction, resource saving, etc. of products to which the pressure-sensitive adhesive sheet is applied. In some preferred embodiments, the total thickness of the substrate is, for example, 30 μm or less, more preferably 20 μm or less, still more preferably 12 μm or less, and particularly preferably 6 μm or less (eg, 5 μm or less). By limiting the total thickness of the substrate as described above, it is possible to increase the thickness ratio of the pressure-sensitive adhesive layer and obtain higher pressure-sensitive adhesive performance in a configuration in which the total thickness of the pressure-sensitive adhesive sheet is limited to a predetermined value or less. Further, for example, when the pressure-sensitive adhesive sheet disclosed herein is used as a heat-dissipating sheet (typically a graphite sheet), the heat-dissipating efficiency of the heat-dissipating sheet can be improved. In addition, in a pressure-sensitive adhesive sheet having a thin base material, the rigidity of the pressure-sensitive adhesive sheet itself is low, and the workability and handling properties tend to deteriorate. The merit of improving workability and the like is great. The lower limit of the total thickness of the substrate is not particularly limited, and is, for example, 1 µm or more, usually 2 µm or more, and preferably 3 µm or more (for example, 3.5 µm or more) from the viewpoint of handling property, workability, and the like. . The total thickness of the base material according to some other aspects may be 5 μm or more, 12 μm or more, 16 μm or more, 20 μm or more, or 25 μm or more from the viewpoint of light shielding properties and handling properties. good.

<Characteristics of adhesive sheet>
(Holding force)
In some embodiments, the pressure-sensitive adhesive sheet preferably has a displacement distance of 1.0 mm or less in a holding force test conducted under conditions of a temperature of 80° C., a load of 500 g, and 60 minutes. A pressure-sensitive adhesive sheet that satisfies this property is excellent in holding power (more specifically, high-temperature holding power), so that it can be used for fixing and covering with high adhesion reliability in various applications. A pressure-sensitive adhesive sheet having the above retention properties is particularly suitable for use in portable electronic devices whose interiors can be exposed to high temperatures. The displacement distance in the holding force test is preferably about 0.5 mm or less, more preferably about 0.3 mm or less, even more preferably about 0.2 mm or less, and particularly preferably about 0.1 mm or less. Specifically, the holding force test is carried out by the method described in Examples below.

(probe tack)
In some embodiments, the pressure-sensitive adhesive sheet has a probe tack of 100 kN/m in a probe tack test conducted at a temperature of 23° C. in accordance with ASTM D2979 (test method for pressure-sensitive tackiness of adhesives using an inversion tester). It is preferably ² or more. A pressure-sensitive adhesive sheet that satisfies these properties has good tackiness, so it is easy to position, the time required for crimping and curing can be kept within a predetermined range, and it has good adhesion even to rough surfaces. easy to perform. According to the technology disclosed herein, the tackiness described above is realized in a thin pressure-sensitive adhesive layer. The probe tack may be 120 kN/m ² or more, 150 kN/m ² or more, or 180 kN/m ² or more. In addition, the upper limit of the probe tack is not particularly limited, but in consideration of cohesive force and retention force, it is suitably 240 kN/m ² or less, preferably 220 kN/m ² or less, and 200 kN/m ² or less, 170 kN/m ² or less, 140 kN/m ² or less, 130 kN/m ² or less, 120 kN/m ² or less, or 110 kN/m ² or less. Specifically, the probe tack test is performed by the method described in Examples below.

In some preferred embodiments, the pressure-sensitive adhesive sheet has a displacement distance of 1.0 mm or less in the holding force test and a probe tack value of 100 kN/m ² or more in the probe tack test. According to the pressure-sensitive adhesive sheet satisfying such holding power properties and tack properties, in an embodiment in which the pressure-sensitive adhesive layer is configured to be thin, based on sufficient holding power (more specifically, high-temperature holding power), adhesion reliability is good. Being able to achieve fixation and covering and having good tack tends to improve alignment, productivity, and rough surface adhesion. Therefore, according to the present specification, a pressure-sensitive adhesive sheet having an acrylic pressure-sensitive adhesive layer having a thickness of 10 μm or less, wherein the displacement distance in the holding force test is 1.0 mm or less, and the probe in the probe tack test A PSA sheet having a tack value of 100 kN/m ² or more can be provided.

(Adhesive strength against SUS)
Although not particularly limited, in some aspects, the pressure-sensitive adhesive sheet preferably has a 180-degree peel strength (adhesive strength to SUS) of 1.0 N/25 mm or more to a stainless steel plate. A pressure-sensitive adhesive sheet exhibiting the above properties can adhere well to an adherend (for example, a graphite sheet). Further, for example, it is suitable for a mode of use including handling with a back surface support tape temporarily attached to the back surface. The adhesive strength to SUS is more preferably 1.5 N/25 mm or more, further preferably 2.0 N/25 mm or more, and may be, for example, 2.5 N/25 mm or more, or 3.0 N/ It may be 25 mm or more. In some other aspects, the adhesion to SUS is 5 N/25 mm or more, for example, may be 8 N/25 mm or more, or 12 N/25 mm or more (for example, 15 N/25 mm or more). The upper limit of the adhesion to SUS is not particularly limited, and may be, for example, 30 N/25 mm or less, 20 N/25 mm or less, or 10 N/25 mm or less (eg, 7 N/25 mm or less).

The above adhesive strength to SUS was measured using a stainless steel plate as the adherend under the conditions of 23 ° C. and 50% RH, in accordance with JIS Z 0237: 2000, with a tensile speed of 300 mm / min and a peel angle of 180 degrees. measured. More specifically, it is measured by the following method. That is, the adhesive sheet is cut into a size of 25 mm in width and 100 mm in length to prepare a measurement sample. When the object to be measured is a single-sided pressure-sensitive adhesive sheet, a commercial single-sided pressure-sensitive adhesive tape (for example, trade name "No. 31B", acrylic single-sided pressure-sensitive adhesive tape with a polyester film base manufactured by Nitto Denko) is attached to the back of the single-sided pressure-sensitive adhesive sheet. The thickness of the substrate is about 25 μm and the total thickness is about 53 μm. When the object to be measured is a double-sided pressure-sensitive adhesive sheet, one side (non-measurement surface) of the double-sided pressure-sensitive adhesive sheet is backed with a PET film having a thickness of 50 μm, and then cut into a predetermined size to prepare a measurement sample. For the prepared measurement sample, under an environment of 23° C. and 50% RH, the adhesive surface of the measurement sample was pressed against the surface of a stainless steel plate (SUS304BA plate) washed with ethyl acetate by reciprocating a 2 kg roller once. do. After leaving it in the same environment for 30 minutes, using a tensile tester, the peel strength against the stainless steel plate (relative to SUS adhesive strength) [N/25 mm] is measured. The tensile tester is not particularly limited, and for example, Minebea Co., Ltd. "Tension/compression tester, TG-1kN" or its equivalent is used.

(60° gross value)
Although not particularly limited, in some embodiments, the back surface of the PSA sheet (typically a single-sided PSA sheet) may have a 60° gloss value of 15 or less. Due to such low glossiness, the back surface of the pressure-sensitive adhesive sheet can exhibit a high-quality appearance with suppressed glossiness. The 60° gloss value of the back surface of the pressure-sensitive adhesive sheet is preferably 10 or less (for example, less than 9), more preferably 8 or less, may be 6 or less, or may be 5 or less. The lower limit of the 60° gloss value of the back surface of the pressure-sensitive adhesive sheet is not particularly limited, and in some embodiments, it may be 0.5 or more, 1.0 or more, or 2.0 or more, It may be 3.0 or more, or 4.0 or more. The above gloss value can be adjusted by the composition of the matte layer formed on the back side of the pressure-sensitive adhesive sheet, and matte treatment (surface treatment) methods such as embossing and sandblasting.

The 60° gloss value of the back surface of the pressure-sensitive adhesive sheet is measured at a measurement angle of 60° using a commercially available gloss meter (for example, "High Gloss Gloss Checker IG-410" manufactured by Horiba Ltd.). The same applies to the examples described later.

(light transmittance)
The light transmittance of the adhesive sheet disclosed herein is not particularly limited, and may be, for example, 50% or less, or 30% or less. In some aspects, the light transmittance of the adhesive sheet is preferably 20% or less. As a result, the pressure-sensitive adhesive sheet exhibits good light-shielding properties. In some other embodiments, the light transmittance may be 15% or less, 10% or less, or 5% or less, and has sufficient light shielding properties and masking properties (hiding properties) of the adherend. from the viewpoint of obtaining, it may be 3% or less, 2.5% or less, or less than 1%. In some aspects, the light transmittance may be 0.5% or more, 1% or more, or 5% or more. According to such a pressure-sensitive adhesive sheet, the color of the adherend (for example, graphite sheet) can be moderately reflected, and desired color, texture, and design can be imparted. From such a viewpoint, the light transmittance may be 10% or more, 12% or more, 14% or more, or 15% or more.

The light transmittance of the adhesive sheet is obtained by irradiating one surface of the adhesive sheet with light having a wavelength of 380 to 780 nm perpendicularly using a commercially available spectrophotometer and measuring the intensity of the light transmitted through the other surface. required by As the spectrophotometer, for example, a spectrophotometer manufactured by Hitachi (device name “U4100 spectrophotometer”) can be used. The same applies to the examples described later.

(L ^* a ^* b ^* colorimetric characteristics)
Although not particularly limited, in some embodiments, the back surface of the pressure-sensitive adhesive sheet (typically a single-sided pressure-sensitive adhesive sheet) has a lightness L ^* of 50 or less as defined by the L ^* a ^* b ^* color system. , for example, may be 40 or less, or may be 35 or less. The lightness L ^* is preferably 30 or less, and may be less than 25. A pressure-sensitive adhesive sheet having such lightness can have a tint suitable for various applications where a black color is desired. The pressure-sensitive adhesive sheet having the above brightness is preferably used for application to be attached to a graphite sheet. The lower limit of the lightness L ^* is not particularly limited, and may be set to about 15 or more (for example, 20 or more) from the viewpoint of appearance. The pressure-sensitive adhesive sheet having a back surface in which the 60° gloss value and lightness L ^* of the back surface are appropriately adjusted can exhibit a profound black color with suppressed gloss, so it is particularly suitable for applications requiring such design. It can be preferably applied. For example, the pressure-sensitive adhesive sheet having a back surface can have a color that is in good harmony with its surrounding members (for example, a battery) by being laminated on a graphite sheet.

The chromaticity a ^* defined by the L ^* a ^* b ^* color system of the back surface of the adhesive sheet is not particularly limited, and is the color difference between the part (which can be a member) to which the adhesive sheet is applied and the periphery of it. A range of ±15 (eg ±5, typically ±2) is preferred for harmony considerations. The chromaticity b ^* is not particularly limited, and is preferably in the range of ±15 (eg ±10, typically ±5). In this specification, the term “±X range” is used to mean the range from −X to +X.

The L ^* a ^* b ^* color system used in this specification complies with the 1976 recommendation of the International Commission on Illumination or the JIS Z 8729 standard. Specifically, L ^* a ^* b ^* is measured at multiple points (for example, 5 points or more) on the back of the adhesive sheet using a color difference meter (trade name "CR-400" manufactured by Minolta Co., Ltd.; color difference meter). and use the average value.

(Surface properties on the back of the adhesive sheet)
Although not particularly limited, in some aspects, the surface roughness (Sa) of the back surface of the pressure-sensitive adhesive sheet (typically a single-sided pressure-sensitive adhesive sheet) is in the range of 0.15 μm or more and 0.70 μm or less. Appropriate. Here, the surface roughness (Sa) is the surface roughness (Sa) defined by ISO25178, and is the average value of the height from the average surface obtained by three-dimensional surface texture measurement. By setting the surface roughness (Sa) of the back surface of the pressure-sensitive adhesive sheet within the range of 0.15 to 0.70 μm, it becomes easy to obtain good workability when handling it together with the back support tape. For example, even when different backing tapes are used, it is possible to maintain the peeling workability of the release liner and the removability of the backing tape, thereby obtaining good workability. In maintaining or improving good workability, dependence on the backing tape and release liner can be reduced. In addition, for example, by improving the removability of the back surface removal tape, it is possible to prevent problems such as damage to the adherend when removing the back surface support tape from the back surface of the pressure-sensitive adhesive sheet after attachment to the adherend. It's easy to do. According to some aspects of the technology disclosed herein, for example, when handling with a backing support tape, for example, it is good in a series of processes from removal of the release liner to attachment to the adherend and further removal of the backing support tape. workability is easily obtained.

In some preferred embodiments, the surface roughness (Sa) of the back surface of the pressure-sensitive adhesive sheet may be 0.20 μm or more, 0.25 μm or more, 0.30 μm or more, 0.35 μm or more, or 0.35 μm or more. It may be 0.40 μm or more, or 0.45 μm or more (for example, 0.60 μm or more). As the surface roughness (Sa) of the back surface of the pressure-sensitive adhesive sheet increases, peeling of the back surface support tape from the back surface tends to become easier. In particular, the effect of improving the releasability of the back support tape, which has relatively high adhesive strength, tends to be large. In some preferred embodiments, the surface roughness (Sa) of the back surface of the adhesive sheet may be 0.65 μm or less, 0.60 μm or less, 0.55 μm or less, 0.50 μm or less, or 0.50 μm or less. 0.45 μm or less, 0.40 μm or less, 0.35 μm or less, or 0.30 μm or less. The smaller the surface roughness (Sa) of the back surface of the PSA sheet, the more the release liner tends to be released. tends to be easy.

In some embodiments, the back surface of the PSA sheet (typically a single-sided PSA sheet) has a core void volume (Vvc) of 0.10 to 1.20 μm ³ / in a load curve obtained by three-dimensional surface texture measurement. It is preferably μm ² . Here, the void volume (Vvc) of the core portion on the back of the adhesive sheet is a kind of function (volume) parameter defined by ISO25178, and the load curve (cumulative histogram) of the total height data obtained by three-dimensional surface texture measurement. The volume of voids (spaces, spaces other than rear protrusions) in a region (core portion) corresponding to a load area ratio of 10% to 80% in . When the void volume (Vvc) of the core portion is in the range of 0.10 to 1.20 μm ³ /μm ² , the back support tape can easily adhere to the back surface of the pressure-sensitive adhesive sheet with appropriate adhesiveness, and the release liner can be easily attached. It is easy to achieve both releasability and removability of the back support tape. The reason is more specifically based on the following findings. That is, the adhesive surface of the back support tape adheres so as to fill in the unevenness of the back surface of the adhesive sheet. It is thought that it is related to the part where is in close contact. Therefore, as a result of verifying the relationship between the spatial volume (Vvc) of the core portion and the adhesion of the back support tape, it was found that when the spatial volume (Vvc) of the core portion is within a predetermined range, the adhesion of the back support tape is It has been found that it is possible to control the releasability of the release liner and the removability of the backing support tape within a range that facilitates compatibility. The above description is based on one of the findings and considerations of the present inventors, and the technology disclosed herein is not limited to the above interpretation.

In some preferred embodiments, the void volume (Vvc) of the core portion may be 0.20 μm ³ /μm ² or more, 0.30 μm ³ /μm ² or more, or 0.50 μm ³ /μm ² 0.70 μm ³ /μm ² or more, or 0.90 μm ³ /μm ² or more. In some preferred embodiments, the core void volume (Vvc) may be 1.10 μm ³ /μm ² or less, 1.00 μm ³ /μm ² or less, or 0.80 μm ³ /μm ² It may be less than or equal to 0.60 μm ³ /μm ² or less, or less than or equal to 0.45 μm ³ /μm ² .

The surface roughness (Sa) of the back surface of the pressure-sensitive adhesive sheet and the void volume (Vvc) of the core portion are the three-dimensional surface roughness (Sa) and the void volume (Vvc) of the core portion defined in ISO25178, respectively. Obtained by original surface property measurement. Specifically, the surface roughness (Sa) and the void volume (Vvc) of the core portion can be measured using a 3D measurement laser microscope (for example, Olympus' product name "LEXT OLS4000"). Specific measurement operations and measurement conditions are appropriately set according to the object to be measured and the measurement device. The surface roughness (Sa) and the void volume (Vvc) of the core portion described in the examples described later were measured using Olympus' product name "LEXT OLS4000" with an objective lens of 50x and a measurement area of: It was measured under the condition of 1024 μm×1024 μm.

The surface roughness (Sa) of the back surface of the pressure-sensitive adhesive sheet and the void volume (Vvc) of the core part are determined, for example, by the composition of the mat layer (for example, the content of organic or inorganic particles, the type and particle size of the particles, the content, etc.), It can be adjusted by the matte layer forming method (for example, selection of printing method such as gravure printing, setting of plate size for gravure printing, surface treatment such as embossing and sandblasting on the matte layer surface).

(Total thickness of adhesive sheet)
The total thickness of the pressure-sensitive adhesive sheet disclosed herein (including the pressure-sensitive adhesive layer and the base material, but excluding the release liner) is not particularly limited, and is suitably about 250 μm or less, preferably 150 μm or less. good too. In some embodiments, the total thickness of the adhesive sheet is preferably 100 μm or less, may be 50 μm or less, or may be 30 μm or less. Such a thin pressure-sensitive adhesive sheet is advantageous in terms of thinning, downsizing, weight reduction, resource saving, etc. of products to which the pressure-sensitive adhesive sheet is applied (for example, portable electronic devices such as smartphones). obtain. Further, for example, it is advantageous to handle the pressure-sensitive adhesive sheet having a limited thickness as described above by attaching a back support tape. In some preferred embodiments, the total thickness of the adhesive sheet is 20 μm or less, more preferably 15 μm or less, still more preferably 12 μm or less, particularly preferably 10 μm or less, and may be 8 μm or less, or even 5 μm or less. good. When the pressure-sensitive adhesive sheet disclosed herein is used for attaching to a graphite sheet, the heat-dissipating effect of the graphite sheet can be sufficiently exhibited by forming the pressure-sensitive adhesive sheet thin. In addition, a thin pressure-sensitive adhesive sheet has low rigidity and tends to deteriorate workability and handling properties. Therefore, it is highly advantageous to improve workability and the like by using a back support tape. Also, the lower limit of the total thickness of the adhesive sheet is suitably about 2 μm or more, and may be, for example, 3 μm or more, 5 μm or more, 7 μm or more, or 9 μm or more. Thereby, the constituent elements of the pressure-sensitive adhesive sheet can have a sufficient thickness, and desired properties (adhesive strength, handleability, workability, etc.) can be easily exhibited. In some other embodiments, the total thickness of the adhesive sheet is 10 μm or more, for example, 20 μm, from the viewpoint of handleability and obtaining sufficient adhesive properties (for example, adhesive strength) by increasing the thickness of the adhesive layer. 30 μm or more, or 40 μm or more.

<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. A release liner or the like made of a low-adhesion material such as polypropylene can be used. 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. A release liner used for a single-sided adhesive pressure-sensitive adhesive sheet usually has a release surface (release-treated surface) on the surface in contact with the adhesive surface of the pressure-sensitive adhesive sheet, and the other surface may be a non-release-treated surface. .

The thickness of the release liner (total thickness of the release liner) is not particularly limited, and is preferably about 10 μm or more (more preferably 15 μm or more, for example, 25 μm or more) from the viewpoint of release workability, handleability, strength, and the like. , 500 μm or less (typically 200 μm or less, preferably 100 μm or less, for example, 75 μm or less).

<Back support tape>
In some embodiments, the pressure-sensitive adhesive sheet (typically a single-sided pressure-sensitive adhesive sheet) can be used in a manner in which a back support tape is attached (typically temporarily attached) to the back surface of the adhesive sheet. As a result, while protecting the back surface of the pressure-sensitive adhesive sheet, the workability and handleability up to attachment to the adherend can be improved regardless of the thickness, strength, rigidity, etc. of the pressure-sensitive adhesive sheet.

The back support tape is not particularly limited, and can be appropriately selected from known pressure-sensitive adhesive sheets. Generally, a back support tape having a pressure-sensitive adhesive layer on one side or both sides of a substrate can be used. A preferable example of the back support tape is a single-sided adhesive adhesive tape having an adhesive layer provided on one side of a base material. As the back support tape having such a structure, various types of surface protective films and surface protective sheets are preferably used.

As the substrate constituting the back support tape, resin films, papers, cloths, rubber films, foam films, metal foils, composites and laminates thereof, and the like can be used. For example, a substrate containing a resin film can be preferably employed. Preferable examples of the resin material that constitutes the resin film include polyolefin-based resins (eg, PE-based resins) and polyester-based resins (eg, PET), which are exemplified as the base film of the pressure-sensitive adhesive sheet. The thickness of the base material is not particularly limited, but from the viewpoint of balancing the purpose of supporting the back side with flexibility, it is usually appropriate to use a back supporting tape having a base material having a thickness of about 10 μm or more and 200 μm or less. be. The thickness of the base material of the back support tape may be 20 μm or more, or may be 30 μm or more. Moreover, the thickness may be 100 μm or less, or may be 80 μm or less.

The type of adhesive that constitutes the adhesive layer of the back support tape is not particularly limited. Adhesives such as silicone-based and polyamide-based adhesives may be used. In some aspects, a rubber-based pressure-sensitive adhesive such as a natural rubber-based pressure-sensitive adhesive or an acrylic pressure-sensitive adhesive that is excellent in versatility, cost, etc. is preferably used. In some other embodiments, a silicone pressure-sensitive adhesive can be preferably used from the viewpoint of low staining and removability. The thickness of the pressure-sensitive adhesive layer is not particularly limited, and the pressure-sensitive adhesive layer usually has a thickness of about 2 μm or more and 50 μm or less in consideration of the balance between the adhesiveness to the back surface of the pressure-sensitive adhesive sheet that is the adherend and the removability. Suitable is the use of a backing tape with a The thickness of the pressure-sensitive adhesive layer of the back support tape is preferably 5 μm or more, and may be, for example, 7 μm or more. Moreover, the thickness is preferably 30 μm or less, and may be, for example, 20 μm or less.

(Release force of back support tape)
Although not particularly limited, in some embodiments, the peel force of the back support tape to the back of the pressure-sensitive adhesive sheet disclosed herein is preferably less than 1.4 N/50 mm. When the peeling force from the back surface of the adhesive sheet is less than a predetermined value, the back support tape can be easily peeled off from the back surface of the adhesive sheet, and when the back support tape is removed from the back surface of the adhesive sheet after attachment to the adherend. , it is easy to prevent the occurrence of defects such as damage to the adherend. From such a viewpoint, the peel force of the back support tape is more preferably less than 1.0 N/50 mm, still more preferably less than 0.8 N/50 mm, and particularly preferably less than 0.6 N/50 mm. Also, in some aspects, the peel force of the back support tape is suitably greater than 0.05 N/50 mm. When the peel strength of the back surface support tape is equal to or greater than a predetermined value, the back surface support tape adheres to the back surface of the pressure-sensitive adhesive sheet, and the back surface of the pressure-sensitive adhesive sheet can be favorably protected by the back surface support tape. In addition, the back surface support tape is handled in a state of being in close contact with the back surface of the pressure-sensitive adhesive sheet, so good workability can be achieved. Furthermore, in a state in which the back surface support tape is attached to the back surface of the pressure-sensitive adhesive sheet, the release liner tends to be easily peeled off. From such a point of view, the peel force of the back support tape is preferably more than 0.07 N/50 mm, more preferably more than 0.09 N/50 mm, still more preferably more than 0.10 N/50 mm (for example, 0.12 N/50 mm above).

In embodiments using various back support tapes such as acrylic and natural rubber, various back support tapes (for example, acrylic back support tapes and natural rubber back support tapes) are selected based on the surface roughness (Sa) of the back surface of the pressure-sensitive adhesive sheet. ) can be in the above range. This makes it easy to obtain good workability when peeling off the release liner and when removing the back support tape. In some preferred embodiments, the peel forces of the backing tapes measured using two or more types of backing tapes (an acrylic backing tape and a natural rubber backing tape) that may be used are all within the range described above. preferably in Satisfying these characteristics makes it possible to maintain the peeling workability of the release liner and the removability of the backing support tape even in embodiments in which two or more kinds of backing support tapes are used, thereby obtaining good workability. be able to.

The peeling force of the back support tape was measured by pulling the back support tape attached to the back of the pressure-sensitive adhesive sheet disclosed herein at 23° C. and 50% in an environment of 300 mm/min according to JIS Z 0237. Measured by peeling in a 180 degree direction at speed. More specifically, it is measured by the following method. That is, under an environment of 23° C. and 50%, a transparent PET film having a thickness of 50 μm for reinforcement (trade name “Lumirror”, manufactured by Toray Industries, Inc.) is adhered to the adhesive surface of the single-sided adhesive sheet. Next, a back support tape cut to a width of 50 mm is crimped onto the back of the pressure-sensitive adhesive sheet by reciprocating a 5 kg roller once. After leaving this for 30 minutes in an environment of 23 ° C. and 50%, according to JIS Z 0237 under the same environment, using a tensile tester, the back support tape is stretched at a tensile speed of 300 mm / min in a 180 degree direction. The peel force [N/50mm] of the backing support tape is measured by peeling it off.

Although not particularly limited, the back support tape may be, for example, an adhesive tape having a 180-degree peel strength (adhesive strength to SUS) against a stainless steel plate of approximately 0.1 N/20 mm or more and 5.0 N/20 mm or less (e.g., a surface protective film ) is preferably used. From the viewpoint of adhesion to the back surface of the adhesive sheet, the adhesive strength to SUS may be, for example, 0.5 N/20 mm or more, 0.8 N/20 mm or more, or 1.0 N/20 mm or more. In addition, the adhesive strength of the back support tape to SUS may be 4.0 N/20 mm or less, 3.0 N/20 mm or less, or 2.0 N/20 mm or less (for example, 1.5 N/20 mm or less). . The above adhesive strength to SUS is measured using a stainless steel plate (SUS430BA plate) as an adherend, under an environment of 23 ° C. and 50% RH, according to JIS Z 0237: 2000, a tensile speed of 300 mm / min, a peel angle of 180. Measured in degrees. Appropriate conditions for pressure bonding to the stainless steel plate are 23° C., 50% RH, and one reciprocating pressure with a 2 kg roller.

The thickness of the back support tape is not particularly limited, and from the viewpoint of balancing the purpose of back support and flexibility, it is usually appropriate to use a back support tape having a thickness of 15 μm or more and 250 μm or less. The thickness of the back support tape may be 25 μm or more, for example 35 μm or more. Also, the thickness of the back support tape may be 150 μm or less, for example, 85 μm or less.

<How to use>
Although not particularly limited, in embodiments where the pressure-sensitive adhesive sheet disclosed herein is a single-sided pressure-sensitive adhesive sheet, the single-sided pressure-sensitive adhesive sheet is used, for example, in the following manner. That is, the adhesive sheet (single-sided adhesive sheet) has the adhesive surface of the adhesive layer covered with a release liner, and the back support tape is attached to the back surface of the adhesive layer. As a result, the back surface of the adhesive sheet is protected, and the appearance of the back surface is easily maintained. In addition, by attaching the back support tape, the workability and handleability up to attachment to the adherend can be improved regardless of the thickness, strength, rigidity, etc. of the single-sided pressure-sensitive adhesive sheet. Then, the release liner covering the adhesive surface of the adhesive sheet is peeled off. By using the pressure-sensitive adhesive sheets according to some embodiments disclosed herein, the release liner can be removed satisfactorily without causing separation between the back support tape and the back surface of the pressure-sensitive adhesive sheet. Then, the adhesive surface exposed after the release liner is peeled off is attached to the adherend. In this way, the pressure-sensitive adhesive sheet is attached to the adherend. After the adhesive sheet is attached to the adherend, the back support tape attached to the back surface of the adhesive sheet is peeled off from the adhesive sheet and removed. At this time, according to the pressure-sensitive adhesive sheet, when the back support tape is removed from the back surface of the pressure-sensitive adhesive sheet, it is easy to prevent the occurrence of problems such as damage to the adherend. According to some aspects of the technology disclosed herein, it is possible to maintain or improve the release workability of the release liner and the removability of the back support tape. Good workability can be easily obtained in a series of processes from affixing to removal of the back support tape. Since the details of the release liner and the back support tape are as described above, redundant description is omitted.

As described above, the technology disclosed herein includes the steps of preparing a pressure-sensitive adhesive sheet with a release liner, attaching a back support tape to the back surface of the pressure-sensitive adhesive sheet, and peeling off the release liner covering the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet. A method comprising the steps of: attaching the adhesive surface of the adhesive sheet exposed by peeling off the release liner to an adherend; and removing the back support tape from the back surface of the adhesive sheet. Since the details of such a method are as described above, redundant description will be omitted.

Further, from the above, according to the present specification, there is provided a laminate comprising an adhesive sheet and a back support tape attached to the back surface of the adhesive sheet. In some embodiments, the pressure-sensitive adhesive sheet can be used in the form of a laminate in which a back support tape is laminated on the back surface of the pressure-sensitive adhesive sheet. Such a laminate may be in the form of a laminate with a release liner provided with a release liner covering the adhesive surface of the adhesive sheet before being attached to the adherend. Such a laminate has a laminate structure in which a release liner, an adhesive sheet and a back support tape are arranged in this order. FIG. 3 shows a structural example of the laminate. A laminate 100 shown in FIG. 3 includes an adhesive sheet 1 and a back surface support tape 70 attached to the back surface 1B of the adhesive sheet 1 . The adhesive sheet 1 includes an adhesive layer 20 provided on one surface 10A of the substrate 10 . Moreover, the laminate 100 before use has a configuration in which the adhesive layer 20 is protected by the release liner 50 in which the adhesive layer 20 side of the adhesive sheet 1 is the release surface 50B. The specific configurations of the adhesive sheet 1 and the release liner 50 are as described with reference to FIG. 1, and are omitted here. Although not shown, the back support tape 70 specifically includes a base material and an adhesive layer provided on one side of the base material. It is attached to the back surface 1B of the sheet 1.

<Application>
Since the pressure-sensitive adhesive sheet disclosed herein can achieve both tack and holding power while having a thin pressure-sensitive adhesive layer, it can be used without particular limitation in various applications where a thin pressure-sensitive adhesive layer is required. can be done. For example, the pressure-sensitive adhesive sheet disclosed herein can be preferably applied to portable electronic devices where there is a strong demand for thinner thickness. For example, it is suitable for fixing members of portable electronic devices. Since the internal space of a portable electronic device may become hot, it is desirable to use an adhesive sheet having sufficient high-temperature holding power. Specifically, mobile phones, smartphones, tablet computers, notebook computers, and various wearable devices (for example, wrist wear types that are worn on the wrist like wristwatches, modular types that are worn on parts of the body with clips, straps, etc.) , Eyewear type including eyeglass type (monocular type and binocular type, including head-mounted type), clothing type that is attached to shirts, socks, hats, etc. in the form of accessories, earwear type that is attached to ears like earphones etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic diaries, electronic books, car information equipment, portable radios, mobile phones In mobile electronic devices such as TVs, mobile printers, mobile scanners, mobile modems, etc., protection of various parts, addition of design properties, fixing of various parts, display items such as logos (design characters) and various designs (including various marks) ) can be preferably used for the purpose of fixing. 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.

In some preferred embodiments, the adhesive sheet disclosed herein is used by being attached to a graphite sheet. Graphite sheets are preferably used in various small electronic devices as heat radiation sheets for releasing heat from heat generating elements (batteries, IC chips, etc.). For example, the graphite sheet is arranged at a position adjacent to a power generation element such as a battery or an IC chip in the electronic device or around the power generation element. By applying a pressure-sensitive adhesive sheet having a thin pressure-sensitive adhesive layer to a graphite sheet, the heat dissipation effect of the graphite sheet can be sufficiently exhibited. In addition, since the graphite sheet has an uneven appearance and is easily damaged when it is thin, a pressure-sensitive adhesive sheet is preferably attached to the surface thereof for the purpose of improving the appearance and protecting the graphite sheet. Although the pressure-sensitive adhesive sheet disclosed herein has a thin pressure-sensitive adhesive layer, it has good tackiness and sufficient holding power, so the heat dissipation property of the graphite sheet is impaired. It can reliably adhere to the graphite sheet without the need. In addition, since the pressure-sensitive adhesive sheet according to some aspects has a colored layer and a matte layer on the back side, by applying such a pressure-sensitive adhesive sheet to a graphite sheet, the presence of the colored layer and the matte layer on the back side of the pressure-sensitive adhesive sheet makes it glossy. A restrained, high-quality appearance can be imparted. In particular, when the black layer is used as the colored layer and the structure has low light transmittance, the back surface of the pressure-sensitive adhesive sheet can exhibit a profound black color. obtain. Further, according to the pressure-sensitive adhesive sheets according to some aspects, even when the adherend is a brittle material such as a graphite sheet, the graphite sheet is less likely to be damaged and good workability can be easily obtained. Although not particularly limited, the thickness of the graphite sheet is about 4 to 100 μm.

In some other embodiments, the adhesive sheet disclosed herein is used by attaching it to a ferrite sheet. Ferrite sheets are preferably used in various electronic devices as a magnetic sheet that absorbs electromagnetic waves emitted from electronic devices and the like and absorbs electromagnetic waves that enter electronic devices. For example, the ferrite sheet is arranged at a position close to an antenna coil in an RFID (Radio Frequency Identification) tag in the electronic device, specifically between the antenna coil and the conductive member. Since such a thin ferrite sheet is fragile and easily damaged, an adhesive sheet is preferably attached to the surface thereof for the purpose of protection or the like. By applying the PSA sheet disclosed herein to the ferrite sheet, the ferrite sheet can be well protected. Moreover, since the pressure-sensitive adhesive sheets according to some embodiments have a colored layer and a matte layer on the back surface, an improvement in appearance quality can be preferably achieved.

FIG. 4 is an exploded perspective view schematically showing a configuration example of a display device in a portable electronic device to which the adhesive sheet disclosed herein can be applied. As shown in FIG. 4 , the display device 200 included in the portable electronic device 300 includes a display section 220 including a cover member, an organic EL unit, and the like, and a support section 240 . Display device 200 further includes an adhesive sheet 230 . In this configuration example, the adhesive sheet 230 is in the form of a double-sided adhesive sheet (double-sided adhesive sheet) that fixes the members constituting the display section 220 and the support section 240 . Note that the support portion 240 includes a substrate (a metal plate such as a stainless steel plate or an aluminum plate) and the like. The pressure-sensitive adhesive sheet disclosed herein is preferably used as a component of the display device as described above.

Matters disclosed by this specification include the following.
[1] A portable electronic device comprising a display device including a display portion including a cover member and an organic EL unit, and a support portion,
An adhesive sheet is bonded to the support,
The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer with a thickness of 10 μm or less,
The pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer,
The portable electronic device, wherein the pressure-sensitive adhesive layer has a storage modulus of less than 0.1 MPa at 25°C and a storage modulus of 0.025 MPa or more at 80°C.
[2] The mobile electronic device according to [1] above, wherein the monomer component constituting the acrylic polymer contains 75% by weight or more of an alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms. .
[3] The portable electronic device according to [1] or [2] above, wherein the pressure-sensitive adhesive layer contains, as a tackifying resin, a tackifying resin _TL having a softening point of less than 145°C.
[4] The portable electronic device according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive layer contains a terpene phenol resin as a tackifying resin.
[5] The pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer contains an isocyanate-based cross-linking agent and a non-isocyanate-based cross-linking agent, according to any one of [1] to [4] above. portable electronics.
[6] The portable electronic device according to [5] above, wherein the pressure-sensitive adhesive composition contains an epoxy-based cross-linking agent as the non-isocyanate-based cross-linking agent.
[7] The portable electronic device according to any one of [1] to [6] above, further comprising a substrate layer supporting the pressure-sensitive adhesive layer.
[8] The portable electronic device according to any one of [1] to [7] above, wherein the adhesive sheet has a total thickness of 20 μm or less.
[9] The pressure-sensitive adhesive sheet according to any one of [1] to [8] above, wherein a displacement distance in a holding force test conducted under conditions of a temperature of 80° C., a load of 500 g, and 60 minutes is 1.0 mm or less. portable electronics.
[10] The pressure-sensitive adhesive sheet has a probe tack value of 100 kN/m ² in a probe tack test performed at a temperature of 23 ° C. in accordance with ASTM D2979 (test method for pressure-sensitive adhesiveness of adhesives using an inversion tester). The portable electronic device according to any one of [1] to [9] above.

[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of 10 μm or less,
The pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer,
The pressure-sensitive adhesive layer has a storage modulus of less than 0.1 MPa at 25°C and a storage modulus of 0.025 MPa or more at 80°C.
[12] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of 10 μm or less,
The pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer,
The displacement distance is 1.0 mm or less in a holding force test conducted under the conditions of a temperature of 80 ° C., a load of 500 g, and 60 minutes, and conforms to ASTM D2979 (pressure-sensitive adhesiveness test method for adhesives using a fall tester). and a pressure-sensitive adhesive sheet having a probe tack value of 100 kN/m ² or more in a probe tack test conducted at a temperature of 23°C.
[13] The above-mentioned [11] or [12], wherein the monomer component constituting the acrylic polymer contains 75% by weight or more of an alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms. adhesive sheet.
[14] The pressure-sensitive adhesive sheet according to any one of [11] to [13] above, wherein the pressure-sensitive adhesive layer contains, as a tackifying resin, a tackifying resin T _L having a softening point of less than 145°C.
[15] The pressure-sensitive adhesive sheet according to any one of [11] to [14] above, wherein the pressure-sensitive adhesive layer contains a terpene phenol resin as a tackifying resin.
[16] The pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer contains an isocyanate-based cross-linking agent and a non-isocyanate-based cross-linking agent, according to any one of [11] to [15] above. adhesive sheet.
[17] The pressure-sensitive adhesive sheet according to [16] above, wherein the pressure-sensitive adhesive composition contains an epoxy-based cross-linking agent as the non-isocyanate-based cross-linking agent.
[18] The pressure-sensitive adhesive sheet according to any one of [11] to [17] above, further comprising a substrate layer supporting the pressure-sensitive adhesive layer.
[19] The pressure-sensitive adhesive sheet according to any one of [11] to [18] above, wherein the total thickness of the pressure-sensitive adhesive sheet is 20 μm or less.

[21] The pressure-sensitive adhesive sheet according to any one of [11] to [19] above, which is a single-sided adhesive pressure-sensitive adhesive sheet comprising a substrate film and the pressure-sensitive adhesive layer provided on one surface of the substrate film. adhesive sheet.
[22] The pressure-sensitive adhesive sheet of [21] above, wherein a colored layer and a matte layer are laminated in this order on the other surface of the base film.
[23] The pressure-sensitive adhesive sheet according to [21] or [22] above, wherein the back surface roughness (Sa) of the pressure-sensitive adhesive sheet is in the range of 0.15 µm or more and 0.70 µm or less.
[24] ^The above [21] ^- [ 23].
[25] The pressure-sensitive adhesive sheet as described in any one of [21] to [24] above, wherein the matte layer has a thickness of 0.2 μm or more and 3.0 μm or less.
[26] The pressure-sensitive adhesive sheet according to any one of [21] to [25] above, wherein the total thickness of the pressure-sensitive adhesive sheet is 100 μm or less.
[27] The pressure-sensitive adhesive sheet according to any one of [21] to [26] above, which has a 180 degree peel strength against a stainless steel plate of 1.0 N/25 mm or more.

[28] The pressure-sensitive adhesive sheet according to any one of [11] to [27] above, which is used by being attached to a graphite sheet or ferrite sheet.
[29] The pressure-sensitive adhesive sheet according to any one of [11] to [28] above, which is used in portable electronic devices.
[30] A pressure-sensitive adhesive sheet with a release liner, comprising the pressure-sensitive adhesive sheet according to any one of [11] to [29] above, and a release liner covering the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet.
[31] A laminate comprising the pressure-sensitive adhesive sheet according to any one of [11] to [29] above, and a back support tape attached to the back surface of the pressure-sensitive adhesive sheet.

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>
A reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser and a dropping funnel was charged with 95 parts of n-butyl acrylate (BA) and 5 parts of acrylic acid (AA) as monomer components, and Ethyl acetate was charged, and the mixture was stirred for 2 hours while nitrogen gas was introduced. After removing oxygen in the polymerization system in this way, 0.2 parts of 2,2′-azobisisobutyronitrile (AIBN) is added as a polymerization initiator, and solution polymerization is performed at 60° C. for 8 hours to form an acrylic polymer. A solution of the polymer was obtained. Mw of this acrylic polymer was about 70×10 ⁴ .
For 100 parts of the acrylic polymer contained in the acrylic polymer solution, terpene phenol resin (trade name "YS Polystar T-115", manufactured by Yasuhara Chemical Co., Ltd., softening point about 115 ° C., hydroxyl value 30 to 60 mg KOH / g) of 20 parts, an isocyanate cross-linking agent (trade name “Coronate L”, manufactured by Tosoh Corporation, solid content 75%) 0.1 part based on solid content, an epoxy cross-linking agent (trade name “TETRAD-C”, 0.01 part of 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was added and mixed with stirring to prepare an adhesive composition.

As a release liner, a polyester release film (trade name “Diafoil MRF”, thickness 38 μm, manufactured by Mitsubishi Polyester Co., Ltd.) having one side subjected to release treatment to serve as a release surface was prepared. The pressure-sensitive adhesive composition was applied to the release surface of the release liner so that the thickness after drying was 2 μm, and dried at 100° C. for 2 minutes. Thus, a pressure-sensitive adhesive layer was formed on the release surface of the release liner. The 25° C. storage elastic modulus of the obtained pressure-sensitive adhesive layer was 0.080 MPa, and the 80° C. storage elastic modulus was 0.032 MPa.
A black printed layer with a thickness of about 1 μm is formed by gravure printing on one side (second surface) of a 2 μm thick transparent PET film (trade name “Mylar”, manufactured by Teijin DuPont Films), and the black printed layer is further formed. A back layer-forming substrate film (substrate) having a mat layer having a thickness of about 1 μm formed thereon by gravure printing was prepared. The black printed layer is made of a material available from Dainichiseika Kogyo Co., Ltd. The matte layer is formed by applying a matte layer-forming composition obtained by adding and mixing a matte material to a resin material on the surface of the black printed layer, and is made of a material available from Tokyo Ink Co., Ltd. ing. . In forming the mat layer, the size of the gravure printing plate is controlled to adjust the surface properties of the back surface of the substrate (back surface of the adhesive sheet).
The pressure-sensitive adhesive layer formed on the release liner was adhered to the PET film side surface (first surface of the PET film layer) of the base material to prepare a single-sided pressure-sensitive adhesive sheet according to this example (transfer method). This single-sided pressure-sensitive adhesive sheet includes a base film and a pressure-sensitive adhesive layer provided on one side of the base film, and a colored layer and a matte layer are provided in this order on the other side of the base film. Laminated. The release liner was left on the pressure-sensitive adhesive layer and used to protect the surface (adhesive surface) of the pressure-sensitive adhesive layer.
The surface roughness (Sa) of the back surface of the pressure-sensitive adhesive sheet was 0.66 μm, and the void volume (Vvc) of the core portion was 1.08 μm ³ /μm ² . Further, the 60° gloss value of the back surface of the single-sided pressure-sensitive adhesive sheet of this example was 4.2, the lightness L ^* of the back surface was 24.6, the chromaticity a ^* was -0.4, and the chromaticity b ^* was -0.4. 2 and the light transmittance was 2.4%.

<Examples 2 to 4 and Comparative Example 1>
Using the adhesive composition used in Example 1, the adhesive layer thickness was 3 μm (Example 2), 5 μm (Example 3), 10 μm (Example) and 15 μm (Comparative Example 1). A material-less double-sided pressure-sensitive adhesive sheet was obtained. Specifically, the adhesive composition was applied to the release surface of a 38 μm thick polyester release liner (trade name “Diafoil MRF”, manufactured by Mitsubishi Polyester Co., Ltd.) and dried at 100° C. for 2 minutes. A pressure-sensitive adhesive layer having a thickness shown in 1 was formed. A release surface of a 25 μm-thick polyester release liner (trade name “Diafoil MRF”, manufactured by Mitsubishi Polyester Co., Ltd.) was attached to each pressure-sensitive adhesive layer thus obtained. In this way, a substrate-less double-sided PSA sheet according to each example was obtained, both sides of which were protected by the two polyester release liners.

<Comparative Example 2>
70 parts of BA, 30 parts of 2-ethylhexyl acrylate (2EHA), 3 parts of AA, and 0.4 parts of 4-hydroxybutyl acrylate as monomer components were placed in a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser and dropping funnel. 05 parts and toluene as a polymerization solvent were charged, and stirred for 2 hours while nitrogen gas was introduced. After removing oxygen in the polymerization system in this way, 0.1 part of AIBN as a polymerization initiator is added, solution polymerization is performed at 60 ° C. for 6 hours, and then aging is performed at 80 ° C. for 3 hours to obtain an acrylic polymer. A toluene solution of the polymer was obtained. Mw of this acrylic polymer was about 40×10 ⁴ .
For 100 parts of the acrylic polymer contained in the toluene solution, 30 parts of a polymerized rosin ester (trade name “Pencel D-125”, softening point 120 to 130 ° C., manufactured by Arakawa Chemical Industries, Ltd.) as a tackifying resin and isocyanate cross-linking A pressure-sensitive adhesive composition according to this example was prepared by adding 2 parts (based on solid content) of an agent (trade name “Coronate L”, manufactured by Tosoh Corporation, solid content 75%).
A substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 3, except that the obtained pressure-sensitive adhesive composition was used. The 25° C. storage elastic modulus of the pressure-sensitive adhesive layer according to this example was 0.122 MPa, and the 80° C. storage elastic modulus was 0.023 MPa.

<Comparative Example 3>
100 parts of the acrylic polymer obtained in Example 1, a terpene phenol resin (trade name "YS Polyster S-145", softening point of about 145 ° C., manufactured by Yasuhara Chemical Co., Ltd.) as a tackifying resin 30 parts, and the above isocyanate crosslinked 2 parts of the agent (based on the solid content) and 0.01 part of the above epoxy-based cross-linking agent were added and stirred to mix to prepare a pressure-sensitive adhesive composition according to this example.
A substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 3, except that the obtained pressure-sensitive adhesive composition was used. The 25° C. storage elastic modulus of the adhesive layer according to this example was 0.242 MPa, and the 80° C. storage elastic modulus was 0.049 MPa.

<Evaluation>
[Holding force test]
A measurement sample was prepared by cutting the adhesive sheet into a size of 10 mm in width and 100 mm in length. If the object to be measured is a single-sided adhesive sheet, a commercially available single-sided adhesive tape (trade name "No. 31B", acrylic single-sided adhesive tape with a polyester film substrate manufactured by Nitto Denko Co., Ltd. is attached to the back of the single-sided adhesive sheet. The thickness is about 25 μm and the total thickness is about 53 μm. When the object to be measured was a double-sided pressure-sensitive adhesive sheet, a PET film having a thickness of 50 μm was adhered to one side (non-measurement surface) of the double-sided pressure-sensitive adhesive sheet for backing, and then cut into a predetermined size to prepare a measurement sample.
In an environment of 23° C. and 50% RH, the adhesive surface of the measurement sample was applied to a bakelite plate (phenolic resin plate) as an adherend with a width of 10 mm and a length of 20 mm. It was crimped by reciprocating. The adherend to which the measurement sample was attached in this manner was allowed to stand in an environment of 80° C. for 30 minutes with the length direction of the measurement sample being the vertical direction. Next, a load of 500 g was applied to the free end of the test piece, and the test piece was left under the load at 80° C. for 60 minutes according to JIS Z0237. After 60 minutes, the displacement distance [mm] from the initial attachment position of the measurement sample was measured, and if the measurement sample fell off the adherend within 60 minutes, it was recorded as "fall". In the holding force test, if the displacement distance after 60 minutes is 1.0 mm or less, it is determined that the holding force is sufficient.

[Probe tack test]
Probe tack [kN/m ² ] was measured on the surface of the adhesive layer of the adhesive sheet according to ASTM D2979 (testing method for pressure-sensitive tackiness of adhesives using an inversion tester). Specifically, a circular stainless steel probe (5 mm in diameter) in a fall tester was applied to the surface of the adhesive layer (adhesive surface) exposed by peeling off the release liner under a constant load (20 gf) in an environment of 23 ° C. /5 mmφ), the force required to separate the probe from the adhesive surface in the vertical direction was determined, and this was taken as the probe tack value [kN/m ² ] of the adhesive layer. The probe contact speed and withdrawal speed were 30 mm/min. If the probe tack value is 100 kN/m ² or more, the pressure-sensitive adhesive layer is judged to have sufficient tack.

Evaluation results are shown in Table 1 together with an overview of each example.

As shown in Table 1, it has an acrylic pressure-sensitive adhesive layer with a thickness of 10 μm or less, the pressure-sensitive adhesive layer has a 25° C. storage elastic modulus of less than 0.1 MPa, and an 80° C. storage elastic modulus of 0. The pressure-sensitive adhesive sheets according to Examples 1 to 4, which were .025 MPa or more, had a displacement distance of 1.0 mm or less in the holding force test, and a measured value of probe tack of 100 kN/m ² or more. It was compatible with On the other hand, in Comparative Example 1 in which the thickness of the adhesive layer was more than 10 μm, the 25° C. storage elastic modulus of the adhesive layer was less than 0.1 MPa and the 80° C. storage elastic modulus was 0.025 MPa or more. The gap distance has increased. In addition, in Comparative Example 2 in which the pressure-sensitive adhesive layer having a thickness of 10 μm or less had a 25° C. storage modulus of 0.1 MPa or more and an 80° C. storage modulus of less than 0.025 MPa, both tack and holding power were unsatisfactory. was enough. In addition, although the 80° C. storage elastic modulus of the pressure-sensitive adhesive layer having a thickness of 10 μm or less was 0.025 MPa or more, in Comparative Example 3 in which the 25° C. storage elastic modulus was 0.1 MPa or more, the result of the holding force test was It was a pass level, but the tack was a low value.
From the above results, in the acrylic pressure-sensitive adhesive layer having a thickness of 10 μm or less, by setting the 25° C. storage elastic modulus to less than 0.1 MPa and the 80° C. storage elastic modulus to 0.025 MPa or more, the tack and holding power are improved. It turns out that they can be compatible.

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 Adhesive sheet 1A Adhesive surface 1B Back surface 10 Base material (support)
10A One surface of base material (adhesive layer side surface)
10B The other surface of the substrate (back side surface)
12 Base film 12A First surface 12B of base film Second surface 14 Colored layer 16 Matte layers 20, 21 Adhesive layers 50, 51, 52 Release liner 70 Back support tape 100 Laminate

Claims (10)

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of 10 μm or less,
The pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer,
The pressure-sensitive adhesive layer has a storage modulus of less than 0.1 MPa at 25°C and a storage modulus of 0.025 MPa or more at 80°C. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the monomer component constituting the acrylic polymer contains 75% by weight or more of an alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer contains, as a tackifier resin, a tackifier resin _TL having a softening point of less than 145°C. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer contains a terpene phenol resin as a tackifying resin. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer contains an isocyanate-based cross-linking agent and a non-isocyanate-based cross-linking agent. The pressure-sensitive adhesive sheet according to claim 5, wherein the pressure-sensitive adhesive composition contains an epoxy-based cross-linking agent as the non-isocyanate-based cross-linking agent. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, further comprising a substrate layer that supports the pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, wherein the total thickness of the pressure-sensitive adhesive sheet is 20 µm or less. The pressure-sensitive adhesive sheet according to any one of claims 1 to 8, which is used by being attached to a graphite sheet or ferrite sheet. The pressure-sensitive adhesive sheet according to any one of claims 1 to 9, which is used for portable electronic devices.

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