JP2017052835A - Pressure sensitive adhesive sheet for graphite sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensitive adhesive sheet for a graphite sheet having excellent adhesion stability to a graphite sheet being an adherend, even made thin.SOLUTION: A pressure sensitive adhesive sheet 1 is a one-sided adhesive sheet to be laminated on a graphite sheet. The pressure sensitive adhesive sheet 1 is 12 μm thick or less, and includes a base material film 10 containing a black colorant, and an adhesive layer 20 arranged on one surface of the base material film 10. Total thickness of the pressure sensitive adhesive sheet 1 is 30 μm or less. The adhesive layer 20 accounts for 40% or more in a ratio with regard to the total thickness of the pressure sensitive adhesive sheet 1, and is 1.2 μm thick or more. The pressure sensitive adhesive sheet 1 exhibits 180°C peel strength of 2 N/20 mm or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an adhesive sheet for graphite sheets.

  In general, a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive; the same shall apply hereinafter) is in the form of a soft solid (viscoelastic body) in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure. Taking advantage of such properties, the pressure-sensitive adhesive is, for example, in the form of a pressure-sensitive adhesive sheet with a base material, and is widely used for the purpose of joining, fixing, and protecting members in portable electronic devices such as mobile phones (patents) References 1 and 2). Further, for example, a heat radiating sheet such as a graphite sheet is attached inside the portable electronic device for the purpose of releasing heat from a heat generating element such as a battery. A black-colored pressure-sensitive adhesive sheet is attached to the heat-dissipating sheet (typically, a graphite sheet) for the purpose of protecting the sheet and appearance. The heat-dissipating sheet pressure-sensitive adhesive sheet may be one in which a pressure-sensitive adhesive layer is typically disposed on one side of a base film having a laminated structure of a resin film layer and a colored layer. Patent document 3 is mentioned as a literature which discloses the prior art regarding the adhesive sheet affixed on a graphite sheet.

JP 2007-284551 A JP 2013-146903 A JP 2013-203965 A

  The pressure-sensitive adhesive sheet used for the heat radiating sheet as described above is desirably thin from the viewpoint of sufficiently exhibiting the heat radiating effect of the heat radiating sheet. The thinning of the pressure-sensitive adhesive sheet also meets the demands for downsizing and weight reduction of products (for example, portable electronic devices) in which the pressure-sensitive adhesive sheet is used. However, when the black pressure-sensitive adhesive sheet for the heat-dissipating sheet was actually made thin, it became clear that the adhesion stability was impaired, for example, the end part peeled off from the graphite sheet. As a result of examining the cause, the typical conventional heat-dissipating sheet pressure-sensitive adhesive sheet described in Patent Document 3 has different thermal expansion coefficients between the resin film layer and the colored layer constituting the base film. It has been found that the base film is deformed (curled) by heat from the heat-dissipating sheet or its peripheral region, and this deformation causes a load on the adhesive surface and contributes to peeling off of the end. When this phenomenon is further investigated, the ratio of the thickness of the colored layer to the entire base film becomes relatively large in the thin base film, and the influence of the difference in the thermal expansion coefficient between the resin film layer and the colored layer is affected. Since it becomes easy to express, it is thought that the deformation | transformation effect | action cannot be suppressed with adhesive force but peeling arises. As a background, the thickness of the pressure-sensitive adhesive layer is sufficiently secured with a thin pressure-sensitive adhesive sheet, although the pressure-sensitive adhesive layer needs to have a certain thickness due to the surface roughness of the graphite sheet used as a heat dissipation sheet. There is a circumstance that cannot be done. That is, it can be said that the above-mentioned peeling is a peculiar problem that occurred when the pressure-sensitive adhesive sheet for graphite sheets having a base film with a colored layer is thinned (in particular, thinning of the base film).

  The present invention was created in view of the above circumstances, and an object thereof is to provide a pressure-sensitive adhesive sheet for graphite sheets that is excellent in adhesion stability to a graphite sheet as an adherend even when the thickness is reduced. .

According to the present invention, a single-sided adhesive sheet laminated on a graphite sheet is provided. The pressure-sensitive adhesive sheet includes a base film having a thickness of 12 μm or less and containing a black colorant, and a pressure-sensitive adhesive layer disposed on one surface of the base film.
As described above, by using a black colorant-containing base film as a base film having a thickness equal to or less than a predetermined thickness, a black print layer that has been conventionally provided becomes unnecessary. Thereby, the thermal deformation (curl) of the base film resulting from the black print layer can be prevented, and excellent adhesion stability is realized. Further, by eliminating the black print layer, the thickness can be applied to the pressure-sensitive adhesive layer. Therefore, the adhesiveness with respect to the graphite sheet is improved, and the adhesive stability is also improved in this respect.

  In a preferred aspect of the technology disclosed herein, the total thickness of the pressure-sensitive adhesive sheet is 30 μm or less. By using a thin adhesive sheet, the heat dissipation of the graphite sheet tends to be sufficiently exhibited. Moreover, the adhesive stability by the technique disclosed here is preferably realized in the thin adhesive sheet as described above.

  In a preferred aspect of the technology disclosed herein, the ratio of the thickness of the pressure-sensitive adhesive layer to the total thickness of the pressure-sensitive adhesive sheet is 40% or more. By making the ratio of the thickness of the pressure-sensitive adhesive layer relatively large, even when the pressure-sensitive adhesive sheet is made thin, good adhesion to the graphite sheet can be exhibited.

  In a preferred aspect of the technology disclosed herein, the pressure-sensitive adhesive sheet exhibits a 180 degree peel strength of 2 N / 20 mm or more. By having a peel strength of a predetermined level or more, the pressure-sensitive adhesive sheet can be favorably and stably bonded to the graphite sheet.

  In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive layer has a thickness of 1.2 μm or more. By setting the pressure-sensitive adhesive layer to a predetermined thickness or more, the pressure-sensitive adhesive sheet can exhibit good adhesion performance to the graphite sheet regardless of the surface roughness of the graphite sheet.

  In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer. By using an acrylic pressure-sensitive adhesive, a pressure-sensitive adhesive having a target pressure-sensitive adhesive property can be suitably designed.

  In a preferred aspect of the technology disclosed herein, the adhesive sheet has a vertical light transmittance of 15% or less. The pressure-sensitive adhesive sheet having the above characteristics exhibits good light shielding properties.

In a preferred aspect of the technology disclosed herein, the back surface of the pressure-sensitive adhesive sheet has a lightness L ^* defined by the L ^* a ^* b ^* color system of 40 or less. By applying the technology disclosed here, the lightness of the back surface of the pressure-sensitive adhesive sheet can be within the above range without providing a black print layer. The pressure-sensitive adhesive sheet having the lightness is preferably used for graphite sheet applications.

  In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the base film is a polyethylene terephthalate resin film containing the black colorant. The effect by the technique disclosed here is preferably realized by using a polyethylene terephthalate (PET) resin film as the base film. Moreover, since a PET-type resin film has moderate stiffness, even if it is a case where it is thin, it has relatively good handling properties and processability.

  The pressure-sensitive adhesive sheet disclosed herein can exhibit excellent adhesion stability with respect to a graphite sheet even when it is configured to be thin. Therefore, when the thickness of the pressure-sensitive adhesive sheet is set to a predetermined value or less, the heat dissipation of the graphite sheet as the adherend is sufficiently exhibited while maintaining excellent pressure-sensitive adhesive properties (typically adhesion stability). obtain. Moreover, it can be useful for reducing the size and weight of a product including a graphite sheet. Specifically, it is suitable as an adhesive sheet used in portable electronic devices such as mobile phones and smartphones. Therefore, the pressure-sensitive adhesive sheet provided by this specification can be laminated on a graphite sheet disposed in a portable electronic device.

It is sectional drawing which shows one structural example of an adhesive sheet typically.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention are based on the teachings on the implementation of the invention described in the present specification and the common general technical knowledge at the time of filing. Can be understood by those skilled in the art. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Further, in the following drawings, members / parts having the same action may be described with the same reference numerals, and overlapping descriptions may be omitted or simplified. In addition, the embodiment described in the drawings is schematically illustrated for clearly explaining the present invention, and does not necessarily accurately represent the size and scale of the pressure-sensitive adhesive sheet of the present invention that is actually provided as a product. .

In the present specification, the “pressure-sensitive adhesive” refers to a material that exhibits a soft solid (viscoelastic body) state in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure as described above. . The adhesive here is generally defined as “CA Dahlquist,“ Adhesion: Fundamental and Practice ”, McLaren & Sons, (1966) P. 143”, and generally has a complex tensile modulus E ^* (1 Hz). <10 < ⁷ > dyne / cm < ² > material (typically a material having the above properties at 25 [deg.] C.).

<Configuration of adhesive sheet>
The pressure-sensitive adhesive sheet disclosed herein is a single-sided adhesive pressure-sensitive adhesive sheet with a substrate having a pressure-sensitive adhesive layer on one surface of a substrate film (support). The concept of the pressure-sensitive adhesive sheet herein may include what are called pressure-sensitive adhesive tapes, pressure-sensitive adhesive labels, pressure-sensitive adhesive films and the like. The pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or a single sheet. Or the adhesive sheet of the form processed into various shapes may be sufficient.

  The pressure-sensitive adhesive sheet disclosed herein may have, for example, a cross-sectional structure schematically shown in FIG. The pressure-sensitive adhesive sheet 1 shown in FIG. 1 includes a base film 10 and a pressure-sensitive adhesive layer 20 provided on one surface (non-peelable) 10 </ b> A of the base film 10. The surface of the pressure-sensitive adhesive layer 20 is an adhesive surface 1 </ b> A of the pressure-sensitive adhesive sheet 1. The other surface 10 </ b> B of the base film 10 constitutes the back surface 1 </ b> B of the pressure-sensitive adhesive sheet 1. The pressure-sensitive adhesive sheet 1 has a configuration in which the pressure-sensitive adhesive layer 20 is protected by a release liner 30 having a pressure-sensitive adhesive layer 20 side as a release surface.

<Base film>
The base film disclosed here is a base film containing a black colorant, and is typically a resin film in which a black colorant is kneaded. Here, the base film into which the black colorant is kneaded is a mixture of the black colorant in the main constituent material of the base film (a material most contained in the base film, typically a resin material). The base film made. The black colorant is substantially contained in a dispersed state in the base film. The black colorant in the base film is not required to be completely evenly dispersed, but the black colorant has a base film up to a degree that the transmittance at a plurality of locations (for example, 10 points or more) of the base film is 15% or less. It is preferable that it is dispersed in. By using the black colorant-containing substrate film, excellent adhesion stability is realized. In addition, the black colorant-containing base film has a thickness that is relatively thicker than the conventional base layer film having the same thickness as the base film, and a resin film that is relatively thick compared to the laminated base film. Excellent handling performance until matching. This improvement in handling properties appears particularly when the pressure-sensitive adhesive sheet is made thin, and contributes to the stable expression of adhesion and adhesion stability. Furthermore, in a conventional pressure-sensitive adhesive sheet in which a colored layer (typically a black print layer) is located on the back side, when the sebum adhering to the back side is wiped off with alcohol, a colored layer is also provided together with a top coat layer (such as an anti-fingerprint layer). When there was a problem of being removed, such a problem can be solved by using a black colorant-containing base film.

  The base film is typically a resin film containing a resin material as a main component (for example, a component contained in the base film in an amount exceeding 50% by weight). Examples of resin films include polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene / propylene copolymers; polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), etc. Polyester resin film; vinyl chloride resin film; vinyl acetate resin film; polyimide resin film; polyamide resin film; fluororesin film; The resin film may be a rubber film such as a natural rubber film or a butyl rubber film. Of these, a polyester film is preferable from the viewpoint of handling properties and processability, and a PET film is particularly preferable. In the present specification, the “resin film” is typically a non-porous sheet and is a concept that is distinguished from a so-called nonwoven fabric or woven fabric (in other words, a concept that excludes nonwoven fabric or woven fabric). is there.

  The base film contains a black colorant as described above. In other words, the base film is colored black. This gives a good black appearance to the surface of the graphite sheet to be deposited. Further, by including a black colorant (typically a black pigment), processability (such as punching processability) is also improved.

As the black colorant contained in the base film, organic or inorganic colorants (pigments, dyes, etc.) can be used. Specific examples of black colorants include carbon black, graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite, magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex. And anthraquinone colorants. Of these, carbon black is preferable. A black coloring agent can be used individually by 1 type or in combination of 2 or more types. Although not particularly limited, for example, it is preferable to use carbon black having an average particle size of 10 nm to 500 nm (more preferably 10 nm to 120 nm). In this specification, “average particle size” means, unless otherwise specified, a particle size (50% volume) at an integrated value of 50% in a particle size distribution measured based on a particle size distribution measuring apparatus based on a laser scattering / diffraction method. average particle diameter; _hereinafter refers to also) be abbreviated as _{D 50..}

  The blending amount of the black colorant in the base film is not particularly limited, and is suitably set to, for example, about 0.1 to 30% by weight in consideration of the coloring effect and mechanical properties, and preferably is about 0.1. It can be 1 to 25% by weight (typically 0.1 to 20% by weight). When the inspection property of the graphite sheet is required through the pressure-sensitive adhesive sheet, the blending amount of the black colorant in the base film may be about 15% by weight or less, or 10% by weight or less (for example, 5% by weight or less, Typically, it may be 3% by weight or less, and further 2% by weight or less).

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

  The substrate 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 base film preferably has a single layer structure. In the case of a multilayer structure, at least one layer (preferably all layers) is preferably a layer having a continuous structure of the above resin (for example, a polyester-based resin, typically a black colorant-containing resin). The method for producing the base film (typically a resin film) is not particularly limited as long as a conventionally known method is appropriately employed. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting, and calendar roll molding can be appropriately employed.

  The thickness of the base film disclosed here is 12 μm or less. Thus, it is preferable from a viewpoint of the thermal radiation efficiency of the graphite sheet which functions as a thermal radiation sheet that the thickness of a base film is restrict | limited. And in the adhesive sheet using such a thin base film, the adhesive stability by the technique disclosed here is implement | achieved. The thickness of the base film is preferably about 9 μm or less (for example, 7 μm or less, typically 5 μm or less). In the case where heat dissipation, miniaturization, and weight reduction are particularly important, the thickness of the base film is more preferably 3 μm or less (for example, 2 μm or less, typically 1.5 μm or less). 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 viewpoints of handling properties and workability.

  Further, on the back surface of the base film, a surface treatment layer such as a fingerprint-resistant treatment layer (also referred to as a top coat layer from the arrangement position) may be provided. The top coat layer preferably has a thickness of less than 2 μm from the viewpoint of adhesion stability. The topcoat layer is preferably not a colored layer (printing layer). Since the coloring function is realized by the base film, the pressure-sensitive adhesive sheet disclosed herein typically has no colored layer other than the base film. The pressure-sensitive adhesive sheet disclosed herein may not have the surface treatment layer.

  Moreover, the peeling process may be given to the back surface of the base film as needed. For the release treatment, for example, a general silicone-based, long-chain alkyl-based, fluorine-based release treatment agent is typically formed into a thin film of about 0.01 μm to 1 μm (for example, 0.01 μm to 0.1 μm). It can be a process of giving. By performing such a peeling treatment, effects such as easy rewinding of the wound body obtained by winding the pressure-sensitive adhesive sheet into a roll shape can be obtained.

  For the adhesive layer side surface of the substrate film (the surface indicated by reference numeral 10A in FIG. 1), a corona discharge treatment, a plasma treatment, an ultraviolet irradiation treatment, an acid treatment, an alkali treatment, a primer coating, and the like are conventionally known. Surface treatment may be performed. Such a surface treatment may be a treatment for improving the adhesion between the base film and the pressure-sensitive adhesive layer, in other words, the anchoring property of the pressure-sensitive adhesive layer to the base film.

<Adhesive layer>
In the technology disclosed herein, the type of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited. The above-mentioned pressure-sensitive adhesives are various rubbery polymers such as acrylic polymers, rubber polymers, polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, fluorine polymers and the like known in the field of pressure-sensitive adhesives. 1 type, or 2 types or more may be included as a base polymer. From the viewpoint of adhesive performance and cost, an adhesive containing an acrylic polymer or a rubber polymer as a base polymer can be preferably used. Of these, an adhesive (acrylic adhesive) having an acrylic polymer as a base polymer is preferable. Hereinafter, the pressure-sensitive adhesive layer constituted by the acrylic pressure-sensitive adhesive, that is, the pressure-sensitive adhesive sheet having the acrylic pressure-sensitive adhesive layer will be mainly described. The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein is constituted by the acrylic pressure-sensitive adhesive. It is not intended to be limited.

The “base polymer” of the pressure-sensitive adhesive refers to the main component of the rubbery polymer contained in the pressure-sensitive adhesive. The rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range near room temperature. Further, in this specification, “main component” refers to a component contained in an amount exceeding 50% by weight unless otherwise specified.
The “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 an “acrylic monomer”. Accordingly, the acrylic polymer in this specification is defined as a polymer including monomer units derived from an acrylic monomer. A typical example of the acrylic polymer is an acrylic polymer in which the proportion of the acrylic monomer in all monomer components used for the synthesis of the acrylic polymer is more than 50% by weight.
The term “(meth) acryloyl” means acryloyl and methacryloyl comprehensively. Similarly, “(meth) acrylate” means acrylate and methacrylate, and “(meth) acryl” generically means acrylic and methacryl.

  As the acrylic polymer, for example, a polymer of a monomer raw material that includes alkyl (meth) acrylate as a main monomer and can further include a submonomer copolymerizable with the main monomer is preferable. Here, the main monomer means a component occupying 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.
CH ₂ = C (R ¹ ) COOR ² (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 range of the number of carbon atoms may be expressed as “C _1-20 ”. From the viewpoint of the storage elastic modulus of the pressure-sensitive adhesive and the like, an alkyl (meth) acrylate that is a chain alkyl group in which R ² is C _1-14 (eg, C _2-10 , typically C _4-8 ) is used as a main monomer. It is appropriate to do. From the viewpoint of adhesive properties, the main monomer is alkyl acrylate (hereinafter, also simply referred to as C _4-8 alkyl acrylate) in which R ¹ is a hydrogen atom and R ² is a C _4-8 chain alkyl group. Is preferred.

Examples of the alkyl (meth) acrylate in which R ² is a C _1-20 chain alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, and n-butyl. (Meth) acrylate, isobutyl (meth) acrylate, s-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, undecyl (meth) Acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecyl (meth) acrylate, And eicosyl (meth) acrylate. These alkyl (meth) acrylates can be used alone or in combination of two or more. Preferred alkyl (meth) acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

The proportion of alkyl (meth) acrylate in the total monomer components used for the synthesis of the acrylic polymer is preferably 70% by weight or more, more preferably 85% by weight or more, and further preferably 90% by weight or more. Although the upper limit of the ratio of alkyl (meth) acrylate is not particularly limited, it is usually preferably 99.5% by weight or less (for example, 99% by weight or less). Alternatively, the acrylic polymer may be obtained by polymerizing substantially only alkyl (meth) acrylate. Moreover, when using _C4-8 alkylacrylate as a monomer component, it is preferable that the ratio of _C4-8 alkylacrylate among the alkyl (meth) acrylate contained in this monomer component is 70 weight% or more, It is more preferably 90% by weight or more, and further preferably 95% by weight or more (typically 99 to 100% by weight). The technique disclosed herein can be preferably implemented in an embodiment in which 50% by weight or more (for example, 60% by weight or more, typically 70% by weight or more) of the total monomer components is BA. In a preferred embodiment, the total monomer component may further comprise 2EHA in a proportion less than BA.

  Monomers (other monomers) other than those described above may be copolymerized in the acrylic polymer in the technology disclosed herein within a range that does not significantly impair the effects of the present invention. The other monomers can be used for the purpose of adjusting the glass transition temperature (Tg) of the acrylic polymer, adjusting the adhesive performance (for example, peelability), and the like. Examples of monomers that can improve the cohesive strength and heat resistance of the pressure-sensitive adhesive include sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, vinyl esters, and aromatic vinyl compounds. Preferred examples of these include vinyl esters. Specific examples of vinyl esters include vinyl acetate (VAc), vinyl propionate, vinyl laurate, and the like. Of these, VAc is preferable.

Other monomers that can introduce a functional group that can serve as a cross-linking point to an acrylic polymer or contribute to an improvement in adhesive strength include a hydroxyl group (OH group) -containing monomer, a carboxy group-containing monomer, an acid anhydride group-containing monomer, and an amide. Examples thereof include a group-containing monomer, an amino group-containing monomer, an imide group-containing monomer, an epoxy group-containing monomer, (meth) acryloylmorpholine, and vinyl ethers.
As a preferable example of the acrylic polymer in the technology disclosed herein, an acrylic polymer obtained by copolymerizing a carboxy group-containing monomer as the other monomer may be mentioned. Examples of carboxy group-containing monomers include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Is done. Of these, AA and MAA are preferable.
As another preferred example, an acrylic polymer obtained by copolymerizing a hydroxyl group-containing monomer as the other monomer may be mentioned. Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meta ) Hydroxyalkyl (meth) acrylates such as acrylate; polypropylene glycol mono (meth) acrylate; N-hydroxyethyl (meth) acrylamide and the like. Among these, a preferred hydroxyl group-containing monomer includes hydroxyalkyl (meth) acrylates in which the alkyl group is a straight chain having 2 to 4 carbon atoms.

The “other monomers” may be used alone or in combination of two or more. The total content of other monomers is preferably about 40% by weight or less (typically 0.001 to 40% by weight) of all monomer components, and is preferably about 30% by weight or less (typically 0.01%). -30% by weight, for example, 0.1-10% by weight) is more preferable.
When a carboxy group-containing monomer is used as the other monomer, the content is about 0.1 to 10% by weight of the total monomer component (for example, 0.2 to 8% by weight, typically 0.5 to 5% by weight). ) Is appropriate. When a hydroxyl group-containing monomer is used as the other monomer, the content is about 0.001 to 10% by weight of the total monomer component (for example, 0.01 to 5% by weight, typically 0.02 to 2% by weight). Is appropriate.

  The copolymer composition of the acrylic polymer is suitably designed such that the glass transition temperature (Tg) of the polymer is −15 ° C. or lower (typically −70 ° C. or higher and −15 ° C. or lower). . The Tg of the acrylic polymer is preferably −25 ° C. or lower (eg, −60 ° C. or higher and −25 ° C. or lower), more preferably −40 ° C. or lower (eg, −60 ° C. or higher and −40 ° C. or lower). Setting the Tg of the acrylic polymer to be equal to or lower than the above-described upper limit value is preferable from the viewpoint of workability for attaching the adhesive sheet.

The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the type and amount ratio of monomers used for the synthesis of the polymer). Here, the Tg of the acrylic polymer refers to a Tg determined by the Fox formula based on the composition of the monomer component used for the synthesis of the polymer. The formula of Fox is a relational expression between Tg of a copolymer and 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 equation, Tg is the glass transition temperature (unit: K) of the copolymer, Wi is the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi is the monomer i. Represents the glass transition temperature (unit: K) of the homopolymer.

As the glass transition temperature of the homopolymer used for the calculation of Tg, the values described in known materials are used. For example, for the monomers listed below, the following values are used as the glass transition temperature of the homopolymer of the monomer.
2-Ethylhexyl acrylate -70 ° C
n-Butyl acrylate -55 ° C
Ethyl acrylate -22 ° C
Methyl acrylate 8 ℃
Methyl methacrylate 105 ° C
2-hydroxyethyl acrylate -15 ° C
4-hydroxybutyl acrylate -40 ° C
Vinyl acetate 32 ° C
Styrene 100 ° C
Acrylic acid 106 ℃
Methacrylic acid 228 ° C

  For the glass transition temperatures of homopolymers other than those exemplified above, the values described in the “Polymer Handbook” (3rd edition, John Wiley & Sons, Inc., 1989) are used. The highest value is adopted for the monomer whose values are described in this document.

When the glass transition temperature of the homopolymer is not described in the above document, the value obtained by the following measurement method is used.
Specifically, a reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube and a reflux condenser is charged with 100 parts by weight of monomer, 0.2 part by weight of 2,2′-azobisisobutyronitrile and acetic acid as a polymerization solvent. 200 parts by weight of ethyl is added and stirred for 1 hour while flowing nitrogen gas. After removing oxygen in the polymerization system in this way, the temperature is raised to 63 ° C. and the reaction is carried out for 10 hours. Next, the mixture is cooled to room temperature to obtain a homopolymer solution having a solid concentration of 33% by weight. Next, this homopolymer solution is cast-coated on a release liner and dried to prepare a test sample (sheet-like homopolymer) having a thickness of about 2 mm. This test sample is punched into a disk shape with a diameter of 7.9 mm, sandwiched between parallel plates, and shear strain at a frequency of 1 Hz using a viscoelasticity tester (manufactured by TA Instruments Japan, model name “ARES”). Temperature range -70 ° C. to 150 ° C., the viscoelasticity is measured by a shear mode at a heating rate of 5 ° C./min, and the temperature corresponding to the peak top temperature of the shear loss elastic modulus G ″ (G ″ curve is The maximum temperature) is defined as the Tg of the homopolymer.

  The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthetic methods for acrylic polymers, such as solution polymerization method, emulsion polymerization method, bulk polymerization method, suspension polymerization method, photopolymerization method, etc. Can be adopted as appropriate. For example, a solution polymerization method can be preferably used. As a monomer supply method when performing solution polymerization, a batch charging method, a continuous supply (dropping) method, a divided supply (dropping) method, or the like that supplies all monomer raw materials at once can be appropriately employed. The polymerization temperature can be appropriately selected according to the type of monomer and solvent to be used, the type of polymerization initiator, and the like, for example, about 20 ° C. to 170 ° C. (typically 40 ° C. to 140 ° C.). it can. In a preferred embodiment, a polymerization temperature of about 75 ° C. or less (more preferably about 65 ° C. or less, for example, about 45 ° C. to 65 ° C.) can be employed.

  The solvent (polymerization solvent) used for the solution polymerization can be appropriately selected from conventionally known organic solvents. For example, aromatic compounds such as toluene (typically aromatic hydrocarbons); aliphatic or alicyclic hydrocarbons such as ethyl acetate; halogenated alkanes such as 1,2-dichloroethane; isopropyl alcohol, etc. A lower alcohol (for example, monohydric alcohol having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; Mixed solvents of more than one species can be used.

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

  According to the solution polymerization, a polymerization reaction liquid in a form in which an acrylic polymer is dissolved in an organic solvent is obtained. The pressure-sensitive adhesive layer in the technology disclosed herein may be formed from a pressure-sensitive adhesive composition containing the above-mentioned polymerization reaction liquid or an acrylic polymer solution obtained by subjecting the reaction liquid to an appropriate post-treatment. As said acrylic polymer solution, what prepared the said polymerization reaction liquid to the appropriate viscosity (concentration) as needed can be used. Alternatively, an acrylic polymer solution prepared by synthesizing an acrylic polymer by a polymerization method other than solution polymerization (for example, emulsion polymerization, photopolymerization, bulk polymerization, etc.) and dissolving the acrylic polymer in an organic solvent may be used. Good.

The weight average molecular weight (Mw) of the base polymer (preferably acrylic polymer) in the technique disclosed herein is not particularly limited, and may be, for example, in the range of 10 × 10 ^{4 to} 500 × 10 ⁴ . From the viewpoint of adhesive performance, the Mw of the base polymer is in the range of 10 × 10 ^{4 to} 150 × 10 ⁴ (for example, 20 × 10 ⁴ to 75 × 10 ⁴ , typically 35 × 10 ^{4 to} 65 × 10 ⁴ ). Preferably there is. Here, Mw refers to a value in terms of standard polystyrene obtained by GPC (gel permeation chromatography). As the GPC apparatus, for example, a model name “HLC-8320GPC” (column: TSKgelGMH-H (S), manufactured by Tosoh Corporation) can be used.

  The pressure-sensitive adhesive in the technology disclosed herein can be a composition containing a tackifying resin. The tackifying resin is not particularly limited. For example, rosin tackifying resin, terpene tackifying resin, hydrocarbon tackifying resin, epoxy tackifying resin, polyamide tackifying resin, elastomer tackifying resin, Various tackifying resins such as a phenolic tackifying resin and a ketone tackifying resin can be used. Such tackifier resin can be used individually by 1 type or in combination of 2 or more types. When an acrylic polymer is employed as the base polymer, it is preferable to use a rosin tackifier resin.

  Examples of rosin-based tackifier resins include gum rosin, wood rosin, tall rosin and other unmodified rosins (raw rosin); these unmodified rosins modified by hydrogenation, disproportionation, polymerization, etc. Rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc. The same shall apply hereinafter); other various rosin derivatives. Examples of the rosin derivative include rosins such as those obtained by esterifying an unmodified rosin with an alcohol (that is, an esterified product of rosin) and those obtained by esterifying a modified rosin with an alcohol (that is, an esterified product of a modified rosin). Esters: Unmodified rosins and modified rosins modified with unsaturated fatty acids Unsaturated fatty acid modified rosins; Unmodified rosins, modified rosins, unsaturated rosin esters modified with unsaturated fatty acids Rosin alcohols obtained by reducing carboxyl groups in fatty acid-modified rosins or unsaturated fatty acid-modified rosin esters; metal salts of rosins (particularly rosin esters) such as unmodified rosin, modified rosin and various rosin derivatives; rosins (Unmodified rosin, modified rosin, various rosin derivatives, etc.) Rosin phenol resins obtained by thermal polymerization by adding Lumpur acid catalyst; and the like.

  The softening point (softening temperature) of the tackifying resin used is not particularly limited. For example, those having a softening point of about 100 ° C. or higher (preferably about 120 ° C. or higher) can be preferably used. A rosin tackifying resin having such a softening point (for example, an esterified product of polymerized rosin) can be preferably used. The upper limit of the softening point of the tackifying resin is not particularly limited, and can be about 200 ° C. or lower (typically about 180 ° C. or lower, for example, about 150 ° C. or lower). In addition, the softening point of the tackifier resin here is defined as a value measured by a softening point test method (ring and ball method) defined in either JIS K 5902 or JIS K 2207.

  The amount of the tackifying resin used is not particularly limited, and can be appropriately set according to the target adhesive performance (peel strength, etc.). For example, it is preferable to use the tackifier resin at a ratio of about 10 to 100 parts by weight (more preferably 15 to 80 parts by weight, and further preferably 20 to 60 parts by weight) with respect to 100 parts by weight of the base polymer.

  In the technology disclosed herein, the pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive layer may contain a crosslinking agent as necessary. The kind in particular of a crosslinking agent is not restrict | limited, It can select from a conventionally well-known crosslinking agent suitably and can be used. Examples of such crosslinking agents include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, peroxide crosslinking agents, urea crosslinking agents, metal alkoxides. Examples of the crosslinking agent include a metal chelate crosslinking agent, a metal salt crosslinking agent, a carbodiimide crosslinking agent, and an amine crosslinking agent. A crosslinking agent can be used individually by 1 type or in combination of 2 or more types. Among these, from the viewpoint of improving cohesive strength, the use of an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent is preferable, and the use of an isocyanate-based crosslinking agent is particularly preferable. The amount of the crosslinking agent used is not particularly limited. For example, the amount can be about 10 parts by weight or less, preferably about 0.005 to 10 parts by weight, more preferably about 0.01 to 5 parts by weight with respect to 100 parts by weight of the base polymer (preferably an acrylic polymer). You can select from a range of parts.

  The pressure-sensitive adhesive layer in the technology disclosed herein may be colored in order to express desired design properties and optical properties (for example, light shielding properties). For this coloring, one or more known organic or inorganic coloring agents (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. Content of a coloring agent is not specifically limited, For example, it can be made into less than 15 weight part with respect to 100 weight part of base polymers. From the viewpoint of suppressing the deterioration of the adhesive properties, the content of the colorant may be 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. The technique disclosed here can be preferably implemented in a mode in which the pressure-sensitive adhesive layer substantially does not contain inorganic and organic colorants from the viewpoint of pressure-sensitive adhesive performance. For example, it can be preferably implemented in an embodiment in which the content of the colorant is 0 to 1 part by weight relative to 100 parts by weight of the base polymer.

  The pressure-sensitive adhesive composition is a pressure-sensitive adhesive composition such as a leveling agent, a crosslinking aid, a plasticizer, a softening agent, an antistatic agent, an anti-aging agent, an ultraviolet absorber, an antioxidant, or a light stabilizer, if necessary. Various additives generally used in the field of products may be contained. About such various additives, conventionally well-known things can be used by a conventional method, and since it does not characterize this invention in particular, detailed description is abbreviate | omitted.

  The pressure-sensitive adhesive layer (layer made of pressure-sensitive adhesive) disclosed herein is formed from a water-based pressure-sensitive adhesive composition, a solvent-type pressure-sensitive adhesive composition, a hot-melt pressure-sensitive adhesive composition, and an active energy ray-curable pressure-sensitive adhesive composition. It can be an adhesive layer. The water-based pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition in a form containing a pressure-sensitive adhesive (pressure-sensitive adhesive layer forming component) in a water-based solvent (water-based solvent), and is typically dispersed in water. What is called a type pressure-sensitive adhesive composition (a composition in which at least a part of the pressure-sensitive adhesive is dispersed in water) and the like are included. Moreover, a solvent-type adhesive composition means the adhesive composition of the form which contains an adhesive in an organic solvent. The technique disclosed here can be preferably implemented in an aspect including a pressure-sensitive adhesive layer formed from a solvent-type pressure-sensitive adhesive composition from the viewpoint of pressure-sensitive adhesive properties and the like.

  The pressure-sensitive adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method (direct method) of forming the pressure-sensitive adhesive layer by directly applying (typically applying) the pressure-sensitive adhesive composition to the base film as described above and drying it can be employed. Also, a method (transfer method) in which a pressure-sensitive adhesive composition is applied to a peelable surface (peeling surface) and dried to form a pressure-sensitive adhesive layer on the surface, and the pressure-sensitive adhesive layer is transferred to a base film. ) May be adopted. From the viewpoint of productivity, the transfer method is preferred. As the release surface, the surface of the release liner, the back surface of the substrate film subjected to the release treatment, or the like can be used. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, for example, a regular or random pattern such as a dot or stripe. The formed adhesive layer may be sufficient.

The pressure-sensitive adhesive composition can be applied using a conventionally known coater such as a gravure roll coater, a die coater, or a bar coater. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation or curtain coating.
From the viewpoint of promoting the crosslinking reaction and improving the production efficiency, the pressure-sensitive adhesive composition is preferably dried under heating. A drying temperature can be about 40-150 degreeC, for example, and it is preferable to usually be about 60-130 degreeC. After drying the pressure-sensitive adhesive composition, further aging is performed for the purpose of adjusting the component transfer in the pressure-sensitive adhesive layer, progress of the crosslinking reaction, alleviating the distortion that may exist in the base film or the pressure-sensitive adhesive layer, etc. Also good.

  In a preferred embodiment, the ratio of the thickness of the pressure-sensitive adhesive layer to the total thickness of the pressure-sensitive adhesive sheet is 40% or more. By using the base film disclosed here, the thickness of the pressure-sensitive adhesive layer can be relatively increased in the pressure-sensitive adhesive sheet in which the total thickness is limited. A large thickness of the pressure-sensitive adhesive layer is advantageous in terms of improving the adhesion stability to the graphite sheet. From such a viewpoint, the ratio of the thickness of the pressure-sensitive adhesive layer to the total thickness of the pressure-sensitive adhesive sheet is preferably 50% or more (for example, 70% or more, typically 80% or more). From the viewpoint of productivity and workability of the pressure-sensitive adhesive sheet, the ratio of the thickness of the pressure-sensitive adhesive layer to the total thickness of the pressure-sensitive adhesive sheet is suitably about 95% or less (for example, 90% or less).

  The thickness of the pressure-sensitive adhesive layer disclosed herein is not particularly limited and can be appropriately selected depending on the purpose. Usually, about 1 to 200 μm (for example, 2 to 140 μm, typically 4 to 80 μm) is appropriate from the viewpoint of productivity such as drying efficiency and adhesive performance. From the viewpoint of limiting the total thickness of the pressure-sensitive adhesive sheet, the thickness is preferably about 1 to 40 μm, more preferably 1.2 to 30 μm (for example, 20 μm or less, typically 10 μm or less). The technique disclosed herein can also be carried out in an embodiment in which the thickness of the pressure-sensitive adhesive layer is 5 μm or less (further 3 μm or less). From the viewpoint of heat dissipation efficiency of the graphite sheet, the pressure-sensitive adhesive layer is preferably thin. A thin adhesive layer is also advantageous in terms of reducing the thickness, reducing the size, reducing the weight, and saving resources of the adhesive sheet.

<Release liner>
In the technology disclosed herein, a release liner can be used in forming the pressure-sensitive adhesive layer, preparing the pressure-sensitive adhesive sheet, storing the pressure-sensitive adhesive sheet before use, distributing it, and processing the shape. The release liner is not particularly limited. For example, a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, a fluoropolymer (polytetrafluoroethylene, etc.), a polyolefin resin (polyethylene, A release liner made of a low adhesion material such as polypropylene can be used. The release treatment layer may be formed, for example, by surface-treating the liner base material with a release treatment agent such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide.

<Characteristics of adhesive sheet>
The pressure-sensitive adhesive sheet disclosed herein preferably has a 180-degree peel strength of 2.0 N / 20 mm or more. The pressure-sensitive adhesive sheet exhibiting the above characteristics can be adhered well to the graphite sheet as the adherend. The peel strength is more preferably 3.0 N / 20 mm or more, and further preferably 5.0 N / 20 mm or more (for example, 8.0 N / 20 mm or more). The peeling strength here refers to 180 degree peeling strength (180 degree peeling adhesive strength) with respect to a stainless steel plate.

  The 180 degree peel strength can be measured as follows. Specifically, after attaching a single-sided adhesive tape (trade name “No. 31B”, manufactured by Nitto Denko Corporation, total thickness 50 μm) to the back of the adhesive sheet, the adhesive sheet is made into a size of 20 mm in width and 100 mm in length. With respect to the cut measurement sample, in an environment of 23 ° C. and 50% RH, the adhesion surface of the measurement sample is pressed against the surface of a stainless steel plate (SUS304BA plate) by reciprocating a 2 kg roller once. After leaving this in the same environment for 30 minutes, using a universal tensile compression tester, in accordance with JIS Z 0237: 2000, under conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees, the peel strength (N / 20 mm). As a universal tensile and compression tester, for example, “Tensile and compression tester, TG-1kN” manufactured by Minebea can be used. A similar measurement method is employed in the examples described later.

  The pressure-sensitive adhesive sheet disclosed herein preferably has a vertical light transmittance of 15% or less. As a result, the pressure-sensitive adhesive sheet exhibits good light shielding properties. The vertical light transmittance is preferably less than 15%, more preferably 10% or less, and even more preferably less than 10% (for example, 7% or less, typically 5% or less). Further, from the viewpoint of the inspection property of the graphite sheet to be deposited, the light transmittance may exceed 1% or 3% or more (for example, 4% or more).

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

In a preferred embodiment, the back surface of the pressure-sensitive adhesive sheet may have a lightness L ^* defined by the L ^* a ^* b ^* color system of 50 or less (eg, 40 or less, typically 35 or less). The lightness L ^* is preferably 30 or less. By applying the technique disclosed here, the above-described brightness can be realized without providing a black print layer. Although there is no restriction | limiting in particular about the lower limit of the said lightness L ^* , From viewpoints, such as an external appearance, it can set to about 15 or more (for example, 20 or more). The pressure-sensitive adhesive sheet having the lightness is preferably used for graphite sheet applications.

Note that the “lightness L ^* ” in this specification refers to the lightness L ^* defined in the L ^* a ^* b ^* color system, and is a specification recommended by the International Lighting Commission in 1976 or JIS Z 8729. Shall comply with the provisions of Specifically, the lightness L ^* is measured at a plurality of locations (for example, 5 points or more) on the back side of the adhesive sheet using a color difference meter (trade name “CR-400” manufactured by Minolta Co .; color color difference meter). An average value may be adopted. The same applies to the embodiments described later.

  The total thickness of the pressure-sensitive adhesive sheet (including the pressure-sensitive adhesive layer and the base film but not including the release liner) disclosed herein is not particularly limited, and is approximately 2 to 150 μm (for example, 3 to 100 μm, typically Is suitably in the range of 3 to 50 μm). The total thickness of the PSA sheet according to a preferred embodiment is about 30 μm or less (for example, 20 μm or less, typically 10 μm or less), and the total thickness is 5 μm or less (for example, less than 5 μm, typically less than 4 μm). There may be. By configuring the adhesive sheet to be thin, the heat dissipation effect of the graphite sheet is sufficiently exhibited. In addition, the thin adhesive sheet can be advantageous in terms of reducing the thickness, size, weight, and resource saving of the product to which the adhesive sheet is applied.

<Application>
The pressure-sensitive adhesive sheet disclosed herein is used by being attached to a graphite sheet. The graphite sheet is preferably used in various small electronic devices as a heat radiating sheet for releasing heat from a heat generating element (battery, IC chip, etc.). For example, the graphite sheet is disposed 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. Such a graphite sheet has uneven appearance, and a thin sheet is easily damaged. Therefore, an adhesive sheet is preferably attached to the surface for the purpose of improving the appearance and protecting the graphite sheet. Although the surface of the graphite sheet is not necessarily smooth, the pressure-sensitive adhesive sheet disclosed herein exhibits excellent adhesion stability with respect to such a graphite sheet, and exhibits functions such as appearance imparting and protection. be able to. Although not particularly limited, the pressure-sensitive adhesive sheet disclosed herein is preferably applied to a graphite sheet having a thickness of 5 to 100 μm and / or an arithmetic average surface roughness Ra of 0.005 to 5 μm. Is done.

  In a preferred embodiment, the pressure-sensitive adhesive sheet disclosed herein is applied to an application that is attached to a graphite sheet installed in a portable electronic device. For example, mobile phones, smartphones, tablet computers, laptop computers, various wearable devices (for example, wristwear devices that are worn on the wrist like wristwatches, modular devices that are worn on a part of the body with clips, straps, etc.) (Eyewear type including monocular type and binocular type, including head mounted type), clothing type attached to shirts, socks, hats, etc. in the form of accessories, earwear type attached to ears like earphones, etc.), Digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game machines, electronic dictionaries, electronic notebooks, electronic books, in-vehicle information equipment, portable radios, portable TVs, mobile phones Graphite placed in portable electronic devices such as printers, portable scanners, and portable modems It may be preferably applied to the application to be pasted to the over and. In this specification, “carrying” means that it is not sufficient to be able to carry it alone, but that it has a level of portability that allows an individual (standard adult) to carry it relatively easily. Shall mean.

The matters disclosed by this specification include the following.
(1) A single-sided adhesive sheet laminated on a graphite sheet,
A base film having a thickness of 12 μm or less and containing a black colorant;
An adhesive layer disposed on one surface of the substrate film;
A pressure-sensitive adhesive sheet.
(2) The adhesive sheet according to (1), wherein the total thickness of the adhesive sheet is 30 μm or less.
(3) The pressure-sensitive adhesive sheet according to (1) or (2), wherein a ratio of the thickness of the pressure-sensitive adhesive layer to the total thickness of the pressure-sensitive adhesive sheet is 40% or more.
(4) The pressure-sensitive adhesive sheet according to any one of (1) to (3), which exhibits a 180-degree peel strength of 2N / 20 mm or more.
(5) The adhesive sheet in any one of said (1)-(4) whose thickness of the said adhesive layer is 1.2 micrometers or more.
(6) The pressure-sensitive adhesive sheet according to any one of (1) to (5), wherein the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer.
(7) The adhesive sheet according to any one of (1) to (6), wherein the adhesive sheet has a vertical light transmittance of 15% or less.
(8) The pressure-sensitive adhesive sheet according to any one of (1) to (7), wherein the back surface of the pressure-sensitive adhesive sheet has a lightness L ^* defined by the L ^* a ^* b ^* color system of 40 or less.
(9) The adhesive sheet according to any one of (1) to (8), wherein the base film is a polyethylene terephthalate resin film containing the black colorant.
(10) The pressure-sensitive adhesive sheet according to any one of (1) to (9), which is used for a portable electronic device.

(11) The pressure-sensitive adhesive layer contains an acrylic polymer in a proportion exceeding 50% by weight of the polymer component contained in the pressure-sensitive adhesive layer,
The acrylic polymer has a formula (1):
CH ₂ = C (R ¹ ) COOR ² (1)
(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.) An alkyl (meth) acrylate represented by: The pressure-sensitive adhesive sheet according to any one of (1) to (10), which is contained at a ratio of 70% by weight or more.
(12) The alkyl (meth) acrylate includes methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, s -Butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate , Nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate , Tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecyl (meth) acrylate and eicosyl (meth) acrylate The pressure-sensitive adhesive sheet according to (11), which is at least one selected from the group consisting of:
(13) The pressure-sensitive adhesive sheet according to (11) or (12), wherein the alkyl (meth) acrylate is n-butyl acrylate and 2-ethylhexyl acrylate.
(14) The alkyl (meth) acrylate is n-butyl acrylate and 2-ethylhexyl acrylate, and the 2-ethylhexyl acrylate is contained in the monomer component in a smaller proportion than the n-butyl acrylate (11) -The adhesive sheet in any one of (13).
(15) The acrylic polymer further includes a functional group-containing monomer as the monomer component,
The functional group-containing monomers include acrylic acid, methacrylic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate and 4 -The adhesive sheet in any one of said (11)-(14) which is at least 1 sort (s) selected from the group which consists of hydroxybutyl (meth) acrylate.
(16) The adhesive sheet according to any one of (1) to (15), wherein the base film contains carbon black as the black colorant.
(17) The pressure-sensitive adhesive sheet according to any one of (1) to (16), wherein the base film contains carbon black having an average particle diameter of 10 nm to 500 nm as the black colorant.
(18) The pressure-sensitive adhesive sheet according to any one of (1) to (17), wherein a blending amount of the black colorant in the base film is 0.1 to 30% by weight.
(19) The pressure-sensitive adhesive sheet according to any one of (1) to (18), wherein the base film has a single-layer structure.

(20) A single-sided adhesive sheet laminated on a graphite sheet in a portable electronic device,
A base film having a single layer structure comprising a polyethylene terephthalate-based resin film containing a black colorant;
An acrylic pressure-sensitive adhesive layer disposed on one surface of the base film;
With
The total thickness of the adhesive sheet is 30 μm or less,
The base film has a thickness of 12 μm or less,
The pressure-sensitive adhesive layer has a thickness of 1.2 μm or more,
The ratio of the thickness of the pressure-sensitive adhesive layer in the total thickness of the pressure-sensitive adhesive sheet is 40% or more,
Shows 180 degree peel strength of 2N / 20mm or more,
The vertical light transmittance of the pressure-sensitive adhesive sheet is 15% or less,
The back surface of the pressure-sensitive adhesive sheet has a lightness L ^* defined by L ^* a ^* b ^* color system of 40 or less,
The acrylic pressure-sensitive adhesive layer contains an acrylic polymer in a proportion exceeding 50% by weight of the polymer component contained in the pressure-sensitive adhesive layer,
The acrylic polymer contains, as a monomer component, alkyl (meth) acrylate in a proportion of 70% by weight or more,
The alkyl (meth) acrylate is n-butyl acrylate and 2-ethylhexyl acrylate, and 2-ethylhexyl acrylate is contained in the monomer component in a smaller proportion than n-butyl acrylate,
The acrylic polymer further includes a functional group-containing monomer as the monomer component,
The functional group-containing monomers include acrylic acid, methacrylic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate and 4 -At least one selected from the group consisting of hydroxybutyl (meth) acrylate,
The black colorant is carbon black having an average particle size of 10 nm to 500 nm,
The adhesive amount of the black colorant in the base film is 0.1 to 30% by weight.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on weight unless otherwise specified.

<Example 1>
In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, 70 parts of BA as monomer components, 27 parts of EHA, 3 parts of AA and 0.05 parts of 4-hydroxybutyl acrylate, and a polymerization solvent The toluene was charged with 135 parts of toluene and stirred for 2 hours while introducing nitrogen gas. After removing oxygen in the polymerization system in this way, 0.1 part of AIBN as a polymerization initiator was added, and solution polymerization was performed at 60 ° C. for 6 hours to obtain a toluene solution of an acrylic polymer. 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 the tackifier resin and isocyanate-based crosslinking 2 parts of an agent (trade name “Coronate L”, Nippon Polyurethane Industry Co., Ltd., solid content: 75%) was added to prepare an acrylic pressure-sensitive adhesive composition.

As a release liner, a polyester release film (trade name “Diafoil MRF”, thickness 38 μm, manufactured by Mitsubishi Polyester Co., Ltd.) having a release surface on which one side was release-treated was prepared. The pressure-sensitive adhesive composition was applied to the release surface of the release liner so that the thickness after drying was 25 μm, and dried at 100 ° C. for 2 minutes. Thus, an adhesive layer was formed on the release surface of the release liner.
Subsequently, the pressure-sensitive adhesive layer formed on the release liner was bonded to the surface of a 4.5 μm-thick PET film kneaded with carbon black as a black pigment to produce a pressure-sensitive adhesive sheet according to this example (transfer) Law). The release liner was left on the pressure-sensitive adhesive layer as it was and used to protect the surface (adhesive surface) of the pressure-sensitive adhesive layer. This pressure-sensitive adhesive sheet is a 25 μm-thick pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition on one surface of a 4.5 μm-thick black colorant-containing (black pigment kneaded) PET film (base film). It is a single-sided adhesive sheet having a total thickness of about 29.5 μm.

<Examples 2 to 9>
As the base film, a black colorant-containing (black pigment kneaded) PET film having the thickness shown in Table 1 was used, and the thickness of the pressure-sensitive adhesive layer was changed to the thickness shown in Table 1. In the same manner as in Example 1, adhesive sheets according to the respective examples were produced.

<Example 10>
In this example, a transparent PET film (trade name “Lumirror”, manufactured by Toray Industries, Inc.) having a thickness of 4.5 μm and a black print having a thickness of 5 μm provided on one side of the PET film (base film) are used as the base film. A base film having a total thickness of 9.5 μm consisting of a layer (colored layer) was used. The black print layer was formed by printing using a gravure printing method using an ink composition containing a black colorant.
A pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 1 except that the above-mentioned base film with a black printed layer was used and the thickness of the pressure-sensitive adhesive layer was 20 μm. The total thickness of the pressure-sensitive adhesive sheet is about 29.5 μm, and the pressure-sensitive adhesive layer is formed on the surface of the base film opposite to the black print layer.

<Examples 11 to 14>
A pressure-sensitive adhesive sheet according to each example was prepared in the same manner as in Example 10, except that the thickness of the base film, the thickness of the pressure-sensitive adhesive layer, and the thickness of the black print layer were changed to the contents shown in Table 1.

[Evaluation]
About the adhesive sheet of each example, 180 degree peel strength (N / 20mm), vertical light transmittance (%), and the lightness L ^* of the back were measured. The results are shown in Table 1. Table 1 also shows a schematic configuration of the pressure-sensitive adhesive sheet according to each example.

[Adhesion stability evaluation test]
Prepare a commercially available graphite sheet (trade name “Graphinity 25 μm”, manufactured by Kaneka Corporation, thickness 25 μm), one surface of which is a stainless steel plate 150 mm long × 30 mm wide × 2 mm thick, the same size as the stainless steel plate The double-sided pressure-sensitive adhesive tape (trade name “No. 5000NS”, manufactured by Nitto Denko Corporation) was used. By cutting the pressure-sensitive adhesive sheet according to each example into a size of 100 mm long × 20 mm wide, placing it on the other surface of the graphite sheet, and reciprocating a 2 kg roller from the top of the pressure-sensitive adhesive sheet once at a speed of 5 mm / second. The adhesive sheet was attached to the graphite sheet. Then, it was stored for a predetermined number of days (up to 10 days) under a high temperature condition of a temperature of 80 ° C., and the number of days in which floating or peeling was observed was recorded. The results are shown in Table 1.

[Handling evaluation]
A comparative evaluation was conducted on the handling properties of Examples 3 and 11 having the same total thickness. Specifically, a pressure-sensitive adhesive sheet of about A4 size was prepared as the pressure-sensitive adhesive sheet according to the above example, and was bonded to a stainless steel plate (SUS304BA plate) under conditions of a pressure of 0.3 MPa and a speed of 1.0 m / min. The presence or absence of occurrence of sticking at the time of the bonding was visually confirmed, and the case where there was no sticking was evaluated as “◯”, and the case where sticking was observed was evaluated as “x”. The results are shown in Table 1.

As shown in Table 1, when the adhesion stability in Examples 7 to 9 and Example 14 using the pressure-sensitive adhesive sheet having a total thickness of 4.0 μm or less is compared, Example 7 using the black colorant-containing base film A clear difference was observed between ˜9 and Example 14 in which the black printed layer was formed, with a storage day of 1 day as a boundary. In addition, when Examples 3, 6, 11, 12 and 13 using an adhesive sheet having a total thickness of more than 4.0 μm and 10 μm or less are compared, a black colorant-containing base film is used with a storage period of 3 days as a boundary. A clear difference was observed between Examples 3 and 6 and Examples 11 to 13 in which a black print layer was formed. The same tendency was observed in Examples 1, 4 and 10 using the pressure-sensitive adhesive sheet having a total thickness exceeding 20 μm. It is expected that the same tendency is shown for the pressure-sensitive adhesive sheets (Examples 2 and 5) having a total thickness of more than 10 μm and 20 μm or less. In summary, the pressure-sensitive adhesive sheet according to Examples 1 to 9 using a black colorant-containing base film having a thickness of 12 μm or less is the pressure-sensitive adhesive sheet according to Examples 10 to 14 having the same total thickness in which a black print layer is formed. It can be said that it exhibits superior adhesion stability. The reason why the adhesion stability was inferior in Examples 10 to 14 in which the black print layer was formed is that the thermal deformation of the base film based on the difference in thermal expansion coefficient between the base film and the black print layer This is thought to be because the adhesive force did not hold it down. Moreover, from the comparison between Example 3 and Example 11, when the black print layer was not provided, a tendency to improve handling was recognized.
From the above results, it can be seen that the pressure-sensitive adhesive sheet provided with the black colorant-containing base film having a thickness of 12 μm or less exhibits excellent adhesion stability to the graphite sheet even when the thickness is reduced.

Specific examples of the present invention have been described in detail above, but 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.

DESCRIPTION OF SYMBOLS 1 Adhesive sheet 1A Adhesive surface 1B Back surface 10 Base film 10A One surface of a base film (adhesive layer side surface)
10B The other surface of the base film (the back side surface)
20 Adhesive layer 30 Release liner

Claims (10)

A single-sided adhesive sheet laminated on a graphite sheet,
A base film having a thickness of 12 μm or less and containing a black colorant;
An adhesive layer disposed on one surface of the substrate film;
A pressure-sensitive adhesive sheet.   The pressure-sensitive adhesive sheet according to claim 1, wherein the total thickness of the pressure-sensitive adhesive sheet is 30 μm or less.   The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein a ratio of the thickness of the pressure-sensitive adhesive layer to the total thickness of the pressure-sensitive adhesive sheet is 40% or more.   The adhesive sheet as described in any one of Claims 1-3 which shows 180 degree peel strength of 2 N / 20mm or more.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer has a thickness of 1.2 µm or more.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer.   The adhesive sheet according to any one of claims 1 to 6, wherein the adhesive sheet has a vertical light transmittance of 15% or less. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, wherein the back surface of the pressure-sensitive adhesive sheet has a lightness L ^* defined by the L ^* a ^* b ^* color system of 40 or less.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 8, wherein the base film is a polyethylene terephthalate resin film containing the black colorant.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 9, which is used for a portable electronic device.

Images