JP2024049203A - Adhesive sheet - Google Patents

Abstract

[Problem] To provide a pressure-sensitive adhesive sheet having a thin pressure-sensitive adhesive layer in which deterioration of appearance quality caused by pigments is suppressed. [Solution] To provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 30 μm or less. The pressure-sensitive adhesive layer contains a pigment. The maximum diameter of particles present in the pressure-sensitive adhesive layer is 8 μm or less. In addition, the thickness of the pressure-sensitive adhesive layer is greater than the maximum diameter of the particles. [Selected Figure] Figure 1

Description

The present invention relates to an adhesive sheet.

Generally, adhesives (also called pressure-sensitive adhesives; the same applies below) are in a soft solid (viscoelastic) state at temperatures around room temperature, and have the property of easily adhering to an adherend when pressure is applied. Taking advantage of these properties, adhesives are widely used for purposes such as joining, fixing, and protecting components in electronic devices, including mobile electronic devices such as smartphones. Also, for example, in electronic devices, adhesive sheets having a light-blocking adhesive layer containing a pigment are used for the purposes of preventing light leakage and anti-reflection from light sources such as backlight modules of liquid crystal display devices and self-luminous elements such as organic electroluminescence (EL). Patent Document 1 is an example of a document related to this type of technology.

JP 2020-66655 A

Pigment-containing adhesives can be used not only for the above-mentioned purposes of preventing light leakage and reflection, but also for the purposes of concealing the adherend, adjusting the appearance of the adherend through the adhesive sheet, and design. The above-mentioned pigments achieve the purpose of adjusting the light blocking property and light transmittance by dispersing well in the adhesive, but it is difficult to completely disperse the pigment in the adhesive in the form of primary particles, and some of them aggregate or overlap, and if the degree of aggregation is large, they may be visually recognized as coarse particles. For example, when an adhesive layer containing a pigment is made thin, the size of the pigment becomes relatively large compared to the thickness and volume, so that pigment aggregates in the adhesive layer become more noticeable, and the pigment aggregates are likely to cause unevenness on the adhesive surface. A thin adhesive layer containing a pigment tends to have a low appearance quality.

In recent years, due to the demand for thinner electronic devices such as smartphones, the adhesive sheets used for this purpose tend to be thinner. The pigment-containing adhesive layers used in such adhesive sheets also tend to be thinner, and maintaining the appearance quality is becoming an issue. In addition, depending on the application location of the adhesive sheet, such as the display unit of the electronic device, there is a tendency for a higher appearance quality to be required, and it is expected that the adhesive sheets applied to such locations will also be required to have a high appearance quality.

The present invention was created in consideration of the above circumstances, and aims to provide an adhesive sheet having a thin, pigment-containing adhesive layer that highly suppresses deterioration in appearance quality caused by the pigment, in other words, an adhesive sheet having a thin adhesive layer in which deterioration in appearance quality caused by the pigment is highly suppressed.

According to the present specification, an adhesive sheet having an adhesive layer is provided. The thickness of the adhesive layer is 30 μm or less. The adhesive layer contains a pigment. The maximum diameter of the particles present in the adhesive layer is 8 μm or less. The thickness of the adhesive layer is larger than the maximum diameter of the particles. In a thin adhesive layer containing a pigment, the pigment aggregates contained in the adhesive layer are easily noticeable, and the appearance quality is easily deteriorated due to the pigment. However, in the adhesive layer disclosed herein, the maximum diameter of the particles present in the adhesive layer is 8 μm or less, so the particles are not easily noticeable. In addition, since the thickness of the adhesive layer is larger than the maximum diameter of the particles, the pigment particles are easily dispersed in the adhesive layer, and unevenness of the adhesive surface caused by pigment aggregates is also unlikely to occur. In short, according to the above configuration, deterioration of the appearance quality caused by the pigment can be highly suppressed.

In some embodiments, the pigment is an inorganic pigment. The technology disclosed herein is preferably implemented in an embodiment using an inorganic material as the pigment.

In some preferred embodiments, the pigment is carbon black. The effects of the technology disclosed herein are preferably achieved in embodiments using carbon black as a pigment.

In some preferred embodiments, the content of the pigment in the adhesive layer is 0.1 to 10% by weight. By using the pigment in an amount within the above range, it is possible to obtain the desired pigment addition effects, such as light blocking properties and design properties, while preferably achieving the effects of the technology disclosed herein (high suppression of deterioration in appearance quality caused by the pigment). In addition, by limiting the pigment content within a specified range, it is also easy to maintain adhesive properties such as adhesive strength.

In some embodiments, the pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer. In a configuration having an acrylic pressure-sensitive adhesive layer containing an acrylic polymer, the effects of the technology disclosed herein can be preferably exerted.

In some embodiments, the total light transmittance of the adhesive sheet is 80% or less. By incorporating a pigment into the adhesive layer, an adhesive sheet with a total light transmittance of 80% or less can be obtained.

In some embodiments, the total light transmittance of the adhesive sheet is 10% or more. By incorporating a pigment into the adhesive layer, an adhesive sheet can be obtained in which the total light transmittance is appropriately reduced to a range of 10% or more. Since such an adhesive sheet has a certain level of light transmittance or more, pigment aggregates and the like are easily visible and noticeable, but according to the technology disclosed herein, the coarsening of particles in the adhesive layer is suppressed, so that the adhesive sheet can have good appearance quality.

In some embodiments, the adhesive sheet is a substrate-less double-sided adhesive sheet comprising the above-mentioned adhesive layer. Substrate-less double-sided adhesive sheets can be made thinner since they do not have a substrate, and can contribute to making products to which the double-sided adhesive sheet is applied thinner, more compact, and more space-saving. Furthermore, substrate-less double-sided adhesive sheets can maximize the effects of the adhesive layer, such as adhesive strength.

In some embodiments, the adhesive sheet has a 180-degree peel strength against a stainless steel plate of 7 N/25 mm or more. Adhesive sheets that satisfy this characteristic have good adhesive strength while exhibiting the effects of pigment addition, such as light blocking and design properties, and are therefore preferably used, for example, for joining and fixing components.

The adhesive sheet disclosed herein can be preferably used to join components of electronic devices, including, for example, home appliances, office automation equipment, and portable electronic devices such as smartphones. For example, electronic devices have parts that are visible to the user, and excellent appearance quality may be required. The adhesive sheet disclosed herein highly suppresses deterioration of appearance quality caused by pigments, and can be applied to visible parts of electronic devices to achieve a surface with good appearance quality. As described above, this specification provides an electronic device using any of the adhesive sheets disclosed herein, in other words, an electronic device including the adhesive sheet.

FIG. 2 is a cross-sectional view illustrating a schematic configuration example of a pressure-sensitive adhesive sheet. FIG. 11 is a cross-sectional view showing a schematic configuration example of the pressure-sensitive adhesive sheet. FIG. 1 is an exploded perspective view illustrating a configuration example of a display device.

The following describes preferred embodiments of the present invention. Note that matters other than those specifically mentioned in this specification that are necessary for the implementation of the present invention can be understood by a person skilled in the art based on the teachings on the implementation of the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the field. In addition, in the following drawings, components and parts that perform the same function may be described with the same reference numerals, and duplicated descriptions may be omitted or simplified. In addition, the embodiments described in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the pressure-sensitive adhesive sheet of the present invention that is actually provided as a product.

As used herein, the term "adhesive" refers to a material that exhibits a soft solid (viscoelastic) state in a temperature range near room temperature and that has the property of easily adhering to an adherend by pressure, as described above. The adhesive referred to here may generally be a material that has a complex tensile modulus E ^* (1Hz)< ¹⁰⁷ dyne/ ^cm2 (typically, a material that has the above property at 25°C), as defined in "CA Dahlquist, "Adhesion: Fundamentals and Practice", McLaren & Sons, (1966) P. 143".

<Examples of adhesive sheet configurations>
The adhesive sheet disclosed herein may be a substrate-attached adhesive sheet having the above-mentioned adhesive layer on one or both sides of a non-releasable substrate (support substrate), or may be a substrate-less adhesive sheet (i.e., an adhesive sheet without a non-releasable substrate) having the above-mentioned adhesive layer held by a release liner. The concept of adhesive sheet here may include those called adhesive tape, adhesive label, adhesive film, etc. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be an adhesive sheet in the form of a processed form into various shapes.

Examples of the configuration of a double-sided adhesive type substrate-less adhesive sheet (substrate-less double-sided adhesive sheet) are shown in Figures 1 and 2. The adhesive sheet 1 shown in Figure 1 has a configuration in which both sides 21A and 21B of the substrate-less adhesive layer 21 are protected by release liners 31 and 32, at least the adhesive layer side of which is a release surface. The adhesive sheet 2 shown in Figure 2 has a configuration in which one surface (adhesive surface) 21A of the substrate-less adhesive layer 21 is protected by a release liner 31, both sides of which are release surfaces, and when this is rolled up, the other surface (adhesive surface) 21B of the adhesive layer 21 abuts against the back surface of the release liner 31, so that the other surface 21B is also protected by the release liner 31. The technology disclosed here can be preferably implemented in such a substrate-less form from the viewpoint of reducing the thickness of the adhesive sheet. Substrate-less adhesive sheets are advantageous in that they are easy to form thin layers and can maximize the adhesive properties such as adhesive strength and impact resistance. Alternatively, although not specifically shown, the adhesive sheet disclosed herein may be in the form of a substrate-attached double-sided adhesive sheet having adhesive layers on both sides of a non-removable substrate (support substrate). Substrate-attached double-sided adhesive sheets are preferred because they are easy to process and handle.

<Adhesive Layer>
(Maximum diameter of particles present in adhesive layer)
The adhesive layer disclosed herein contains a pigment, and the maximum diameter of the particles present in the adhesive layer is 8 μm or less. In a thin adhesive layer containing a pigment, the aggregates and conglomerates of the pigment contained in the adhesive layer and the overlapping of the pigment particles are easily noticeable, and the pigment in the adhesive layer is likely to cause a decrease in appearance quality. However, in the adhesive layer disclosed herein, the maximum diameter of the particles present in the adhesive layer is 8 μm or less, so the particles are less noticeable. In addition, unevenness of the adhesive surface caused by pigment aggregates and the like is less likely to occur. Note that the particles present in the adhesive layer are composed of multiple pigment particles, and this concept includes aggregates, conglomerates, and overlaps. According to an adhesive having a maximum diameter of the particles of 8 μm or less, the decrease in appearance quality caused by the pigment can be highly suppressed. From the viewpoint of improving appearance quality, in some preferred embodiments, the maximum diameter of the particles is 7 μm or less, may be 6 μm or less, more preferably 5 μm or less, may be 4 μm or less, even more preferably 3 μm or less, may be 2 μm or less, and particularly preferably 1 μm or less. The maximum diameter of the above particles is not particularly limited, but may be more than about 1 μm or may be 2 μm or more from the viewpoint of productivity, etc.

The maximum diameter of the particles present in the adhesive layer can be adjusted (specifically reduced) mainly by the type of pigment and particle characteristics (average particle diameter, standard deviation, D90, etc.). Although not particularly limited, by selecting a pigment of an appropriate type and particle characteristics for an acrylic adhesive that contains an acrylic polymer and may contain optional adhesive components (e.g., a tackifier resin, etc.), an adhesive in which the maximum diameter of the particles is 8 μm or less can be preferably formed.

The maximum diameter of the particles present in the adhesive layer is the maximum diameter measured using an optical microscope for particles confirmed by projecting the adhesive layer onto a screen or particles confirmed in the convex portion of the adhesive layer surface, and refers to the maximum diameter of the particle with the largest diameter (maximum length; length of the longest part) among the confirmed particles. More specifically, the maximum diameter of the particles present in the adhesive layer is measured by the method described in the Examples below.

(Particle size characteristics of pigment particles in adhesive layer)
Although not particularly limited, the average particle diameter of the pigment particles dispersed in the adhesive layer is suitably about 150 nm or less. The average particle diameter of the pigment particles dispersed in the adhesive layer referred to here refers to the average particle diameter calculated from the particle diameter distribution based on the number of particles observed by TEM, and is specifically measured using a frozen ultrathin section of the adhesive. The small average particle diameter of the pigment particles in the adhesive layer means that the amount of large diameter particles is limited, and the maximum diameter of the particles present in the adhesive layer also tends to be small. In addition, the limited amount of large diameter particles with a relatively small specific surface area means that a certain amount of pigment particles in the adhesive layer has a predetermined or larger light absorption area. This makes it easy to obtain an excellent pigment addition effect. For example, when the pigment is a black pigment such as carbon black, the adhesive layer can have excellent light transmittance reduction properties and therefore light blocking properties. In some preferred embodiments, the average particle diameter is less than 130 nm, and may be about 120 nm or less, about 110 nm or less, about 100 nm or less, or 90 nm or less. The lower limit of the average particle size is not particularly limited, and is suitably about 10 nm or more. From the viewpoint of limiting the amount of small particles with low light absorption that cause diffraction or scattering, the average particle size is preferably about 50 nm or more, more preferably about 70 nm or more, and even more preferably about 80 nm or more, and may be, for example, 90 nm or more. The average particle size determined from the particle size distribution based on the number of particles observed by TEM is specifically measured by the method described in the Examples described later.

(Pigment)
The pigment contained in the adhesive layer disclosed herein is one in which the maximum particle size present in the adhesive layer is a predetermined value or less. Examples of the pigment include inorganic pigments such as carbon black, graphite, activated carbon, ferrite (non-magnetic ferrite, magnetic ferrite, etc.), magnetite, molybdenum disulfide, chromium complex, copper oxide, manganese dioxide, zinc carbonate, zinc oxide, zinc sulfide, talc, kaolin, calcium carbonate, titanium oxide, silica, lithium fluoride, calcium fluoride, barium sulfate, alumina, zirconia, iron oxide, iron hydroxide, chromium oxide, spinel-type fired system, chromate system, chrome vermilion system, Prussian blue system, aluminum powder system, bronze powder system, silver powder system, and calcium phosphate; and organic pigments such as phthalocyanine system, azo system, condensed azo system, azo lake system, anthraquinone system, perylene-perinone system, indigo system, thioindigo system, isoindolinone system, azomethine system, dioxazine system, quinacridone system, aniline black system, and triphenylmethane system. One or more of these pigments may be appropriately selected and used. As the pigment, black pigments such as aniline black, perylene black, titanium black, cyanine black, etc. may be used. Among them, inorganic pigments are preferably used. Inorganic pigments include pigments mainly composed of inorganic materials, and are not limited to those composed only of inorganic materials. From the viewpoint of light shielding properties and reduced light transmittance, black pigments such as carbon black, graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite (non-magnetic ferrite, magnetic ferrite, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, and chromium complexes are preferably used.

In some preferred embodiments, carbon black is used as the pigment. As the carbon black, any carbon black generally referred to as carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, pine soot, etc.) can be used without any particular restrictions. In addition, as the carbon black, it is also possible to use surface-modified carbon black having functional groups such as carboxyl groups, amino groups, sulfonic acid groups, and silicon-containing groups (e.g., alkoxysilyl groups, alkylsilyl groups). Such surface-modified carbon black is also called self-dispersing carbon black, and does not require the addition of a dispersant or can reduce the amount of dispersant added. The above carbon blacks can be used alone or in combination of two or more types. Self-dispersing carbon black can be produced based on the methods described in, for example, JP 2017-171732 A or JP 2018-30968 A and the technical common knowledge of a person skilled in the art, and a suitable one can be selected from commercially available products.

It is preferable to use a pigment having a volume average particle diameter in an appropriate range such that the maximum diameter of the particles present in the adhesive layer is equal to or less than a predetermined value. The volume average particle diameter is a volume average particle diameter based on a laser diffraction/scattering method. Although not particularly limited, in some embodiments, the volume average particle diameter of the pigment is suitably about 185 nm or less, preferably 180 nm or less, more preferably 170 nm or less, even more preferably 160 nm or less, and particularly preferably 150 nm or less. Within the above range, the smaller the volume average particle diameter of the pigment, the smaller the maximum diameter of the particles present in the adhesive layer tends to be. In addition, in some embodiments, the volume average particle diameter of the pigment is usually about 10 nm or more, may be about 50 nm or more, may be 100 nm or more, preferably 110 nm or more, more preferably 120 nm or more, even more preferably 130 nm or more, and may be 140 nm or more. Within the above range, by having a moderately large volume average particle diameter of the pigment, aggregation of fine particles is suppressed, and the particles in the adhesive layer tend not to become coarse. In addition, by using a pigment with an appropriate volume average particle size, the effects of adding the pigment, such as reducing light transmittance, tend to be more effective.

In addition, the cumulative 90% particle size (D90) of the pigment based on the laser diffraction/scattering method is preferably within an appropriate range in which the maximum diameter of the particles present in the adhesive layer is a predetermined value or less. In some preferred embodiments, the D90 of the pigment is approximately 300 nm or less, more preferably 280 nm or less, even more preferably 260 nm or less, particularly preferably 240 nm or less, and may be 230 nm or less. The smaller the D90 of the pigment, the smaller the maximum diameter of the particles present in the adhesive layer tends to be. In some embodiments, the D90 of the pigment is usually approximately 30 nm or more, and may be approximately 100 nm or more, 150 nm or more, 170 nm or more, 190 nm or more, 200 nm or more, or 210 nm or more. In an embodiment using a pigment having a D90 in the above range, the technology disclosed herein can be preferably implemented.

Although not particularly limited, the cumulative 10% particle size (D10) of the pigment based on the laser diffraction/scattering method may be, for example, approximately 10 nm or more, approximately 50 nm or more, approximately 80 nm or more, and may be, for example, approximately 150 nm or less, approximately 120 nm or less, or approximately 100 nm or less. The cumulative 50% particle size (D50) of the pigment based on the laser diffraction/scattering method may be, for example, approximately 10 nm or more, approximately 50 nm or more, approximately 100 nm or more (for example, approximately 120 nm or more), and may be, for example, approximately 170 nm or less, approximately 160 nm or less, or approximately 150 nm or less. The standard deviation of the pigment based on the laser diffraction/scattering method may be, for example, approximately 120 nm or less, approximately 100 nm or less, approximately 90 nm or less (e.g., 75 μm or less), or, for example, approximately 10 nm or more, approximately 30 nm or more, or approximately 50 nm or more. The technology disclosed herein can be preferably implemented in an embodiment using a pigment having D10, D50, and standard deviation within the above ranges.

The volume average particle size, D10, D50, D90, and standard deviation of the above pigments based on the laser diffraction/scattering method are measured values of the pigment before it is blended into the adhesive layer, and can be measured based on the laser diffraction/scattering method of a dispersion liquid containing the pigment. Specifically, they can be measured by the method described in the Examples below.

The content of the pigment in the adhesive layer can be set taking into consideration the dispersibility of the pigment in the adhesive layer, the thickness of the adhesive layer, the optical properties (light transmittance such as light blocking properties) and design properties to be achieved, and the required adhesive properties. In some embodiments, the content of the pigment in the adhesive layer is appropriately about 0.1% by weight or more, and from the viewpoint of effectively obtaining the effect of adding the pigment (e.g., light blocking properties and design properties), it is preferably about 0.5% by weight or more, more preferably about 1% by weight or more, and may be about 3% by weight or more, about 5% by weight or more, or about 7% by weight or more. In some embodiments, the content of the pigment may be about 30% by weight or less, and from the viewpoint of adhesive properties such as adhesive strength, it is preferably about 10% by weight or less (e.g., less than 10% by weight), may be about 8% by weight or less, may be about 6% by weight or less, may be about 5% by weight or less (e.g., less than 5% by weight), may be about 4% by weight or less, may be about 3% by weight or less, may be about 2% by weight or less, may be about 1% by weight or less (e.g., less than 1.0% by weight), may be 0.8% by weight or less, or may be 0.5% by weight or less (e.g., less than 0.5% by weight). The smaller the amount of pigment, the easier it is to improve the dispersibility of the pigment in the adhesive layer, the less likely coarse particles are to be generated, and the appearance quality tends to improve.

(Dispersant)
The adhesive layer disclosed herein may or may not contain a dispersant. When the above-mentioned self-dispersing carbon black is used as the pigment, for example, no dispersant may be used. The dispersant is not particularly limited, but one or more suitable dispersants that can disperse the pigment in the adhesive layer well can be used from among known or commonly used dispersants. For example, one or more suitable dispersants that exhibit good properties can be appropriately selected from the following anionic, cationic, nonionic, and amphoteric surfactants and polymeric compounds (which may be resins). The same applies to the examples described below.

Examples of anionic surfactants used as dispersants include alkyl sulfates such as lauryl sulfate and octadecyl sulfate; fatty acid salts; polysulfonates; polycarboxylates; alkyl benzene sulfonates such as nonyl benzene sulfonate and dodecyl benzene sulfonate; naphthalene sulfonates such as dodecyl naphthalene sulfonate; naphthalene sulfonate-formaldehyde condensates; alkyl diphenyl ether disulfonates such as dodecyl diphenyl ether disulfonate; polyoxyethylene octadecyl ether sulfate and polyoxyethylene lauryl ether sulfate; polyoxyethylene alkyl ether sulfates such as polyoxyethylene lauryl phenyl ether sulfate; polyoxyethylene styrenated phenyl ether sulfate; sulfosuccinates such as lauryl sulfosuccinate and polyoxyethylene lauryl sulfosuccinate; polyoxyethylene alkyl ether phosphates; polyoxyethylene alkyl phosphate sulfonates; polyoxyethylene alkyl ether acetates; and the like. When the anionic surfactant forms a salt, the salt may be, for example, a metal salt such as a sodium salt, potassium salt, calcium salt, or magnesium salt (preferably a salt of a monovalent metal), an ammonium salt, or an amine salt. These anionic surfactants may be used alone or in combination of two or more.

Examples of cationic surfactants used as dispersants include alkylamine salts and quaternary ammonium salts. Specific examples include stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl beef tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyl triethyl ammonium chloride. These cationic surfactants can be used alone or in combination of two or more.

Examples of nonionic surfactants used as dispersants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether; polyoxyethylene alkyl phenyl ethers such as polyoxyethylene octyl phenyl ether and polyoxyethylene nonyl phenyl ether; sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan triisostearate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan trioleate; polyoxyethylene glyceryl ether fatty acid esters; polyoxyethylene-polyoxypropylene block copolymers; and the like. These nonionic surfactants can be used alone or in combination of two or more.

Examples of amphoteric surfactants used as dispersants include alkyl betaines such as alkyl dimethyl amino acetate betaine; amino carboxylates; alkyl imidazolines; and the like. The above amphoteric surfactants can be used alone or in combination of two or more.

In addition, examples of the resin (which may be a polymeric compound) used as a dispersant include polyurethane resins; polyester resins; polyamide resins such as unsaturated polyamides; (meth)acrylic resins such as poly(meth)acrylic acid esters and (meth)acrylic acid-(meth)acrylate copolymers; polycarboxylic acids (salts) such as polyacrylic acid, amine salts and ammonium salts of polycarboxylic acids, and alkylamine salts; styrene copolymers such as (meth)acrylic acid-styrene copolymers and styrene-maleic acid copolymers; polyvinyl alcohol; polyvinylpyrrolidone; polysiloxane; polyalkylene oxide derivatives such as ethylene oxide-propylene oxide adducts; phosphate ester resins; long-chain polyaminoamide phosphate salts; and modified products thereof. These resins can be used alone or in combination of two or more. The polymeric compounds can be either oil-based (typically oil-soluble) or water-based (typically water-soluble).

The form in which the dispersant is added is not particularly limited, and the dispersant may be added to the pigment dispersion before it is mixed into the adhesive composition, or may be added at the same time as the pigment is added to the adhesive composition, or before or after the pigment is added.

The content of the dispersant in the adhesive layer disclosed herein may be set to an appropriate range taking into consideration the dispersibility of the pigment. In some embodiments, the amount of dispersant relative to 100 parts by weight of the pigment in the adhesive layer may be approximately 0.01 parts by weight or more (e.g., approximately 0.1 parts by weight or more), and is suitably approximately 1 part by weight or more, and may be, for example, approximately 2 parts by weight or more, and may be, for example, approximately 3 parts by weight or more, or may be approximately 4 parts by weight or more. Also, in some embodiments, the amount of dispersant relative to 100 parts by weight of the pigment in the adhesive layer may be approximately 100 parts by weight or less, and is suitably approximately 60 parts by weight or less, and may be approximately 30 parts by weight or less, or may be approximately 10 parts by weight or less.

(Base polymer)
In the technology disclosed herein, the type of adhesive constituting the adhesive layer is not particularly limited. The above-mentioned adhesive may contain one or more of various rubber-like polymers such as acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers as base polymers that can be used in the field of adhesives. From the viewpoint of adhesive performance, cost, etc., an adhesive containing an acrylic polymer or a rubber polymer as a base polymer can be preferably adopted. Among them, an adhesive having an acrylic polymer as a base polymer (acrylic adhesive) is preferable. Hereinafter, an adhesive layer composed of an acrylic adhesive, i.e., an adhesive sheet having an acrylic adhesive layer, will be mainly described, but it is not intended to limit the adhesive layer of the adhesive sheet disclosed herein to one composed of an acrylic adhesive.

The "base polymer" of a PSA refers to the main component of the rubber-like polymer (polymer that exhibits rubber elasticity in a temperature range around room temperature) contained in the PSA. In this specification, the term "main component" refers to a component that is contained in an amount of more than 50% by weight, unless otherwise specified.
In addition, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer". Therefore, the acrylic polymer in this specification is defined as a polymer containing a monomer unit derived from an acrylic monomer. A typical example of an acrylic polymer is an acrylic polymer in which the proportion of the acrylic monomer in the total monomer components used in the synthesis of the acrylic polymer is more than 50% by weight.
In addition, the term "(meth)acryloyl" refers collectively to acryloyl and methacryloyl. Similarly, the term "(meth)acrylate" refers collectively to acrylate and methacrylate, and the term "(meth)acrylic" refers collectively to acrylic and methacrylic.

(Acrylic polymer)
The acrylic polymer in the technology disclosed herein is preferably, for example, a polymer of a monomer raw material that contains an alkyl (meth)acrylate as a main monomer and may further contain a sub-monomer copolymerizable with the main monomer, where 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 suitably 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, this range of carbon atoms may be expressed as "C _1-20 ". From the viewpoint of the storage modulus of the adhesive, it is appropriate to use an alkyl (meth)acrylate in which R ² is a chain alkyl group of C _1-14 (e.g., C _1-10 , typically C _4-8 ) as the main monomer. From the viewpoint of adhesive properties, it is preferable to use an alkyl acrylate in which R ¹ is a hydrogen atom and R ² is a chain alkyl group of C _4-8 (hereinafter, also simply referred to as C _4-8 alkyl acrylate) as the main monomer.

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 ... Examples of the alkyl (meth)acrylate include isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)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, and eicosyl (meth)acrylate. These alkyl (meth)acrylates can be used alone or in combination of two or more. Suitable examples of the alkyl (meth)acrylate include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

The proportion of alkyl (meth)acrylate in the monomer components constituting the acrylic polymer is typically more than 50% by weight, and can be, for example, 70% by weight or more, 85% by weight or more, or 90% by weight or more. There is no particular upper limit to the proportion of alkyl (meth)acrylate, but it is usually preferably 99.5% by weight or less (e.g., 99% by weight or less), or it may be 98% by weight or less (e.g., less than 97% by weight) from the viewpoint of favorably exerting the properties (e.g., cohesive strength) based on the secondary monomer such as a carboxyl group-containing monomer. Alternatively, the acrylic polymer may be substantially a polymer of only alkyl (meth)acrylate.

Furthermore, when a _C4-8 alkyl acrylate is used as a monomer component, the proportion of the _C4-8 alkyl acrylate in the alkyl (meth)acrylate contained in the monomer component is preferably 70% by weight or more, and more preferably 90% by weight or more. The technology disclosed herein can be preferably implemented in an embodiment in which 50% by weight or more (typically 60% by weight or more) of the total monomer components is BA. In some preferred embodiments, the proportion of BA in the total monomer components may be 70% by weight or more, 80% by weight or more, or even 90% by weight or more. The total monomer components may further contain 2EHA in a proportion less than BA.

The technology disclosed herein can be preferably implemented in an embodiment in which the monomer component contains 50% by weight or more of C _1-4 alkyl (meth)acrylate. The proportion of C _1-4 alkyl (meth)acrylate in the monomer component may be 70% by weight or more, or may be 85% by weight or more (e.g., 90% by weight or more). On the other hand, from the viewpoint of obtaining good cohesive strength, the proportion of C _1-4 alkyl (meth)acrylate in the monomer component is usually appropriately 99.5% by weight or less, and may be 98% by weight or less (e.g., less than 97% by weight).

The technology disclosed herein can be preferably implemented in an embodiment in which the _monomer component contains 50% by weight or more (e.g., 70% by weight or more, 85% by weight or more, or 90% by weight or more) of a C _{2-4 alkyl acrylate. Specific examples of C 2-4} alkyl acrylate include ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate (BA), isobutyl acrylate, s-butyl acrylate, and t-butyl acrylate. The C _2-4 alkyl acrylate may be used alone or in combination of two or more. According to such an embodiment, a pressure-sensitive adhesive sheet with good adhesion to the adherend is easily realized. Among them, a preferred embodiment includes an embodiment in which the monomer component contains more than 50% by weight (e.g., 70% by weight or more, 85% by weight or more, or 90% by weight or more) of BA. On the other hand, from the viewpoint of obtaining good cohesive strength, the proportion of the C _2-4 alkyl acrylate in the monomer components is usually suitably 99.5% by weight or less, and may be 98% by weight or less (eg, less than 97% by weight).

In some other embodiments, the monomer component may contain 50% by weight or more (e.g., 70% by weight or more, 85% by weight or more, or 90% by weight or more) of a C _5-20 alkyl (meth)acrylate. As the C _5-20 alkyl (meth)acrylate, a C _6-14 alkyl (meth)acrylate may be used. In some embodiments, a C _6-10 alkyl acrylate (e.g., a C _8-10 alkyl acrylate) may be employed.

The acrylic polymer in the technology disclosed herein may be copolymerized with a secondary monomer. Examples of secondary monomers that can introduce a functional group that can be a crosslinking base point into the acrylic polymer or contribute to improving adhesive strength include carboxyl group-containing monomers, hydroxyl group (OH group)-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, keto group-containing monomers, monomers having a nitrogen atom-containing ring, alkoxysilyl group-containing monomers, and imide group-containing monomers. The secondary monomers may be used alone or in combination of two or more.
A preferred example of the acrylic polymer in the technology disclosed herein is an acrylic polymer in which a carboxyl group-containing monomer is copolymerized as the secondary monomer. Examples of the carboxyl group-containing monomer include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. Among these, AA and MAA are preferred.
Other preferred examples include acrylic polymers in which a hydroxyl group-containing monomer is copolymerized as the secondary monomer. Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; polypropylene glycol mono(meth)acrylate; and N-hydroxyethyl (meth)acrylamide. Among these, preferred hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates in which the alkyl group is linear and has 2 to 4 carbon atoms.
Examples of the amide group-containing monomer include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide, N-methoxymethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide.
Examples of amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate.
Examples of the monomer having an epoxy group include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether.
Examples of the cyano group-containing monomer include acrylonitrile and methacrylonitrile.
Examples of the keto group-containing monomer include diacetone (meth)acrylamide, diacetone (meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, and vinyl acetoacetate.
Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-(meth)acryloylmorpholine.
Examples of the alkoxysilyl group-containing monomer include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane.

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 exerting 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 is usually appropriate to be 0.5% by weight or more, and may be 1% by weight or more. In addition, from the viewpoint of easily balancing the adhesive performance in relation to the main monomer, the content of the functional group-containing monomer in the monomer component is usually appropriate to be 40% by weight or less, preferably 20% by weight or less, and may be 10% by weight or less (for example, 5% by weight or less).

In some preferred embodiments, the monomer components constituting the acrylic polymer contain a carboxyl group-containing monomer. When the monomer components contain a carboxyl group-containing monomer, it becomes easier to obtain a pressure-sensitive adhesive sheet that exhibits good adhesive properties (cohesive strength, etc.). This can also be advantageous in improving the adhesion between the pressure-sensitive adhesive layer and the adherend.

In an embodiment in which a carboxyl group-containing monomer is copolymerized with an acrylic polymer, the content of the carboxyl group-containing monomer in the monomer component is not particularly limited, and can be, for example, 0.2% by weight or more (typically 0.5% by weight or more) of the monomer component, and usually 1% by weight or more is appropriate, and may be 2% by weight or more, or 3% by weight or more. By making the content of the carboxyl group-containing monomer more than 3% by weight, a higher effect is exhibited. In some embodiments, the content of the carboxyl group-containing monomer can be 3.2% by weight or more of the monomer component, may be 3.5% by weight or more, may be 4% by weight or more, or may be 4.5% by weight or more. The upper limit of the content of the carboxyl group-containing monomer is not particularly limited, and can be, for example, 15% by weight or less, 12% by weight or less, or 10% by weight or less. The technology disclosed herein can also be preferably implemented in an embodiment in which the content of the carboxyl group-containing monomer is 7% by weight or less of the monomer component (typically less than 7% by weight, for example 6.8% by weight or less, or 6.0% by weight or less).

The monomer components constituting the acrylic polymer may contain other copolymerization components other than the above-mentioned secondary monomers for the purpose of improving cohesive strength, etc. Examples of other copolymerization components include vinyl ester monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrenes (α-methylstyrene, etc.), and vinyl toluene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate); Olefin monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; polyfunctional monomers having two or more (e.g., three or more) polymerizable functional groups (e.g., (meth)acryloyl groups) in one molecule, such as 1,6-hexanediol di(meth)acrylate and trimethylolpropane tri(meth)acrylate; and the like.

The amount of such other copolymerization components may be appropriately selected according to the purpose and application, and is not particularly limited. From the viewpoint of appropriately exerting the effect of use, it is usually appropriate to set it to 0.05% by weight or more, and it may be 0.5% by weight or more. In addition, from the viewpoint of easily balancing the adhesive performance, the content of other copolymerization components in the monomer component is usually appropriate to be 20% by weight or less, and it may be 10% by weight or less (for example, 5% by weight or less). The technology disclosed herein can also be preferably implemented in an embodiment 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 it is acceptable for other copolymerization components to be unintentionally included, for example, about 0.01% by weight or less.

The copolymer composition of the acrylic polymer is suitably designed so that the glass transition temperature (Tg) of the polymer is approximately -15°C or lower (for example, approximately -70°C or higher and -15°C or lower). Here, the Tg of the acrylic polymer refers to the Tg calculated by the Fox formula based on the composition of the monomer components used in the synthesis of the polymer. The Fox formula, as shown below, is a relational expression between the Tg of the copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer.
1/Tg=Σ(Wi/Tgi)
In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature (unit: K) of a homopolymer of monomer i.

The glass transition temperature of the homopolymer used in calculating Tg is a value described in a publicly known document. 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℃
Isononyl acrylate -60℃
n-Butyl acrylate -55℃
Ethyl acrylate -22℃
Methyl acrylate 8℃
Methyl methacrylate 105℃
2-Hydroxyethyl acrylate -15℃
4-Hydroxybutyl acrylate -40℃
Vinyl acetate 32℃
Acrylic acid 106℃
Methacrylic acid 228℃

For the glass transition temperatures of homopolymers of monomers other than those listed above, the values listed 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 shall be used. If the value is not listed in the Polymer Handbook, the value obtained by the measurement method described in JP 2007-51271 A shall be used.

From the viewpoint of adhesion to the adherend, the Tg of the acrylic polymer is advantageously about -25°C or less, preferably about -35°C or less, and more preferably about -40°C or less, although not particularly limited thereto. In some embodiments, from the viewpoint of cohesive strength, the Tg of the acrylic polymer may be, for example, about -65°C or more, about -60°C or more, or about -55°C or more. The technology disclosed herein may be preferably implemented in an embodiment in which the Tg of the acrylic polymer is about -65°C or more and -35°C or less (for example, about -55°C or more and -40°C or less). The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (i.e., the type and amount ratio of the monomers used in the synthesis of the polymer).

The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as methods for synthesizing acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately adopted. For example, the solution polymerization method can be preferably adopted. The polymerization temperature when carrying out the solution polymerization can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

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

The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and the like. Further examples of polymerization initiators include redox-based initiators formed by combining peroxides with reducing agents. Such polymerization initiators can be used alone or in combination of two or more. The amount of polymerization initiator used may be a normal amount, and can be selected from the range of, 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.

According to the solution polymerization, a polymerization reaction liquid in the form of an acrylic polymer dissolved in an organic solvent is obtained. The adhesive layer in the technology disclosed herein may be formed from an adhesive composition containing the polymerization reaction liquid or an acrylic polymer solution obtained by subjecting the reaction liquid to an appropriate post-treatment. The acrylic polymer solution may be prepared by adjusting the polymerization reaction liquid to an appropriate viscosity (concentration) as necessary. Alternatively, an acrylic polymer solution may be prepared by synthesizing an acrylic polymer by a polymerization method other than solution polymerization (e.g., emulsion polymerization, photopolymerization, bulk polymerization, etc.) and dissolving the acrylic polymer in an organic solvent.

The weight average molecular weight (Mw) of the base polymer (preferably an acrylic polymer) in the technology disclosed herein is not particularly limited, and may be, for example, in the range of about 10×10 ⁴ to 500×10 ^4. From the viewpoint of adhesive performance, the Mw of the base polymer is preferably in the range of about 30×10 ⁴ or more (more preferably about 45×10 ⁴ or more, for example about 65×10 ⁴ or more). In addition, the Mw of the base polymer is preferably in the range of about 200×10 ⁴ or less (more preferably about 150×10 ⁴ or less, for example about 130×10 ⁴ or less), and may be 1.1 million or less, 900,000 or less, or 850,000 or less. Here, Mw refers to a value calculated in terms of standard polystyrene obtained by GPC (gel permeation chromatography). As the GPC device, for example, the model name "HLC-8320GPC" (column: TSKgelGMH-H (S), manufactured by Tosoh Corporation) can be used.

(Tackifier resin)
The adhesive layer in the technology disclosed herein can contain a tackifier resin. This can increase the peel strength of the adhesive sheet. As the tackifier resin, one or more types selected from various known tackifier resins such as phenol-based tackifier resins, terpene-based tackifier resins, modified terpene-based tackifier resins, rosin-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, and ketone-based tackifier resins can be used.

Examples of phenolic tackifying resins include terpene phenolic resins, hydrogenated terpene phenolic resins, alkyl phenolic resins, and rosin phenolic resins.
Terpene phenolic resin refers to a polymer containing a terpene residue and a phenol residue, and is a concept that includes both a copolymer of a terpene with a phenolic compound (terpene-phenol copolymer resin) and a homopolymer or copolymer of a terpene modified with phenol (phenol-modified terpene resin). Suitable examples of terpenes constituting such terpene phenolic resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d/l-forms (dipentene)). Hydrogenated terpene phenolic resin refers to a hydrogenated terpene phenolic resin having a structure obtained by hydrogenating such a terpene phenolic resin. It is also called hydrogenated terpene phenolic resin.
Alkylphenol resins are resins (oil-based phenolic resins) obtained from alkylphenols and formaldehyde. Examples of alkylphenol resins include novolac and resol types.
Rosin phenolic resins are typically phenol-modified products of rosins or the above-mentioned various rosin derivatives (including rosin esters, unsaturated fatty acid modified rosins, and unsaturated fatty acid modified rosin esters). Examples of rosin phenolic resins include rosin phenolic resins obtained by adding phenol to rosins or the above-mentioned various rosin derivatives using an acid catalyst and then thermally polymerizing the resulting 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. They may be homopolymers of one type of terpene, or copolymers of two or more types of terpenes. Examples of homopolymers of one type of terpene include α-pinene polymer, β-pinene polymer, and dipentene polymer. 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 here includes both rosins and rosin derivative resins. Examples of rosins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; and modified rosins obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.).

Rosin derivative resins are typically derivatives of rosins as described above. The concept of rosin-based resins here includes derivatives of unmodified rosin and derivatives of modified rosin (including hydrogenated rosin, disproportionated rosin, and polymerized rosin). For example, rosin esters such as unmodified rosin esters, which are esters of unmodified rosin and alcohols, and modified rosin esters, which are esters of modified rosin and alcohols; unsaturated fatty acid modified rosins in which rosins are modified with unsaturated fatty acids; unsaturated fatty acid modified rosin esters in which rosin esters are modified with unsaturated fatty acids; rosin alcohols in which the carboxyl groups of rosins or the various rosin derivatives described above (including rosin esters, unsaturated fatty acid modified rosins, and unsaturated fatty acid modified rosin esters) are reduced; metal salts of rosins or the various rosin derivatives described above; and the like. Specific examples of rosin esters include methyl esters, triethylene glycol esters, glycerin esters, pentaerythritol esters, etc. of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.).

Examples of hydrocarbon-based tackifying resins include various hydrocarbon resins such as 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 resins, and coumarone-indene resins.

The softening point of the tackifier resin is not particularly limited. From the viewpoint of improving the cohesive force, in some embodiments, a tackifier resin having a softening point (softening temperature) of about 80°C or more (preferably about 100°C or more) may be preferably used. The technology disclosed herein may be preferably implemented in an embodiment in which the total amount of tackifier resin contained in the adhesive layer is 100% by weight, and more than 50% by weight (more preferably more than 70% by weight, for example more than 90% by weight) of the tackifier resin has the above softening point. For example, a phenol-based tackifier resin (such as a terpene phenol resin) having such a softening point may be preferably used. The tackifier resin may, for example, contain a terpene phenol resin having a softening point of about 135°C or more (or even about 140°C or more). The upper limit of the softening point of the tackifier resin is not particularly limited. From the viewpoint of improving the adhesion to the adherend, in some embodiments, a tackifier resin having a softening point of about 200°C or less (more preferably about 180°C or less) may be preferably used. In some preferred embodiments, the softening point of the tackifier resin is less than 150° C., and may be less than 140° C., less than 130° C., or less than 120° C. The softening point of the tackifier resin can be measured based on the softening point test method (ring and ball method) specified in JIS K2207.

In some preferred embodiments, the tackifier resin includes one or more phenol-based tackifier resins (typically terpene phenol resins). The technology disclosed herein may be preferably implemented, for example, in an embodiment in which, assuming the total amount of tackifier resins to be 100% by weight, approximately 25% by weight or more (more preferably approximately 30% by weight or more) of the tackifier resins is terpene phenol resin. Approximately 50% by weight or more of the total amount of tackifier resins may be terpene phenol resin, or approximately 80% by weight or more (e.g. approximately 90% by weight or more) may be terpene phenol resin. Substantially all of the tackifier resin (e.g. approximately 95 to 100% by weight, or even approximately 99 to 100% by weight) may be terpene phenol resin.

Although not particularly limited, in some embodiments, the tackifier resin may contain a tackifier resin having a hydroxyl value of more than 20 mgKOH/g. Among them, a tackifier resin having a hydroxyl value of 30 mgKOH/g or more is preferable. Hereinafter, a tackifier resin having a hydroxyl value of 30 mgKOH/g or more may be referred to as a "high hydroxyl value resin". By using a tackifier resin containing such a high hydroxyl value resin, a pressure-sensitive adhesive layer having excellent adhesion to an adherend and high cohesive strength can be realized. In some embodiments, the tackifier resin may contain a high hydroxyl value resin having a hydroxyl value of 50 mgKOH/g or more (more preferably 70 mgKOH/g or more).
As the hydroxyl value, a value measured by potentiometric titration according to JIS K0070:1992 can be used.

As the high hydroxyl value resin, any of the above-mentioned various tackifier resins having a hydroxyl value equal to or greater than a predetermined value can be used. The high hydroxyl value resin can be used alone or in combination of two or more. For example, a phenol-based tackifier resin having a hydroxyl value of 30 mg KOH/g or more can be preferably used as the high hydroxyl value resin. In some preferred embodiments, a terpene phenol resin having a hydroxyl value of at least 30 mg KOH/g or more is used as the tackifier resin. Terpene phenol resins are advantageous because the hydroxyl value can be controlled as desired by the copolymerization ratio of phenol.

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 usually about 200 mgKOH/g or less, preferably about 180 mgKOH/g or less, more preferably about 160 mgKOH/g or less, and even more preferably about 140 mgKOH/g or less. The technology disclosed herein can be preferably implemented in an embodiment in which the tackifier resin contains a high hydroxyl value resin (e.g., a phenolic tackifier resin, preferably a terpene phenol resin) having a hydroxyl value of 30 to 160 mgKOH/g. In some embodiments, a high hydroxyl value resin with a hydroxyl value of 30 to 80 mgKOH/g (e.g., 30 to 65 mgKOH/g) can be preferably used. In some other embodiments, a high hydroxyl value resin with a hydroxyl value of 70 to 140 mgKOH/g can be preferably used.

Although not particularly limited, when a high hydroxyl value resin is used, the proportion of the high hydroxyl value resin (e.g., terpene phenol resin) in the total tackifier resin contained in the adhesive layer can be, for example, approximately 25% by weight or more, preferably approximately 30% by weight or more, and more preferably approximately 50% by weight or more (e.g., approximately 80% by weight or more, typically approximately 90% by weight or more). Substantially all of the tackifier resin (e.g., approximately 95 to 100% by weight, or even approximately 99 to 100% by weight) may be a high hydroxyl value resin.

When the adhesive layer contains a tackifier resin, the amount of the tackifier resin used is not particularly limited and may be set appropriately within the range of about 1 to 100 parts by weight per 100 parts by weight of the base polymer. From the viewpoint of optimally exerting the effect of improving peel strength, the amount of the tackifier resin used per 100 parts by weight of the base polymer (e.g., acrylic polymer) is usually appropriate to be 5 parts by weight or more, preferably 10 parts by weight or more, and may be 15 parts by weight or more. Furthermore, from the viewpoint of cohesive force, the amount of the tackifier resin used per 100 parts by weight of the base polymer (e.g., acrylic polymer) is usually appropriate to be 50 parts by weight or less, may be 40 parts by weight or less, or may be 30 parts by weight or less.

(anti-rust)
In some preferred embodiments, the adhesive layer may contain a rust inhibitor.As the rust inhibitor, an azole-based rust inhibitor may be preferably used.As the azole-based rust inhibitor, a five-membered aromatic compound containing two or more heteroatoms, at least one of which is a nitrogen atom, may be preferably used as an active ingredient.As the azole-based compound, an azole-based compound that has been used as a rust inhibitor for metals such as copper may be appropriately adopted.

Examples of azole compounds include azoles such as imidazole, pyrazole, oxazole, isoxazole, thiazole, isothiazole, selenazole, 1,2,3-triazole, 1,2,4-triazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,3,4-thiadiazole, tetrazole, and 1,2,3,4-thiatriazole; derivatives thereof; amine salts thereof; metal salts thereof; etc. Examples of azole derivatives include compounds having a structure containing an azole ring fused with another ring, such as a benzene ring. Specific examples include indazole, benzimidazole, benzotriazole (i.e., 1,2,3-benzotriazole having a structure in which the azole ring of 1,2,3-triazole is condensed with a benzene ring), benzothiazole, and the like, and further, derivatives thereof such as alkylbenzotriazole (e.g., 5-methylbenzotriazole, 5-ethylbenzotriazole, 5-n-propylbenzotriazole, 5-isobutylbenzotriazole, 4-methylbenzotriazole), alkoxybenzotriazole (e.g., 5-methoxybenzotriazole), alkylaminobenzotriazole, alkylaminosulfonylbenzotriazole, mercaptobenzotriazole, hydroxybenzotriazole, nitrobenzotriazole (e.g., 4-nitrobenzotriazole), halobenzotriazole (e.g., 5-chlorobenzotriazole), hydroxyalkylbenzotriazole, hydroxybenzotriazole, aminobenzotriazole, (substituted aminomethyl)-tolyltriazole, carboxybenzotriazole, N-alkylbenzotriazole, bisbenzotriazole, naphthotriazole, mercaptobenzothiazole, aminobenzothiazole, and the like, amine salts thereof, and metal salts thereof. Other examples of azole derivatives include azole derivatives with a non-condensed ring structure, such as 3-amino-1,2,4-triazole and 5-phenyl-1H-tetrazole, which have a structure with a substituent on the non-condensed azole ring. Azole compounds can be used alone or in combination of two or more.

Suitable examples of compounds that can be used as azole-based rust inhibitors include benzotriazole-based rust inhibitors that contain a benzotriazole-based compound as an active ingredient. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the base polymer is an acrylic polymer and the rust inhibitor is a benzotriazole-based rust inhibitor. In such an embodiment, a pressure-sensitive adhesive sheet that has good metal corrosion prevention properties and excellent adhesion reliability can be preferably realized. Suitable examples of benzotriazole-based compounds include 1,2,3-benzotriazole, 5-methylbenzotriazole, 4-methylbenzotriazole, carboxybenzotriazole, etc.

Although not particularly limited, in some embodiments, the content of the azole-based rust inhibitor in the adhesive layer can be an amount equivalent to 0.2 parts by weight or more per 10 parts by weight of the carboxyl group-containing monomer contained in the monomer component constituting the base polymer. The content of the azole-based rust inhibitor per 10 parts by weight of the carboxyl group-containing monomer may be 0.5 parts by weight or more, 1 part by weight or more, or 1.5 parts by weight or more. The metal corrosion prevention effect tends to be improved by increasing the content of the azole-based rust inhibitor per 10 parts by weight of the carboxyl group-containing monomer. In some embodiments, the content of the azole-based rust inhibitor per 10 parts by weight of the carboxyl group-containing monomer may be, for example, 4 parts by weight or more, or 6 parts by weight or more. In addition, from the viewpoint of achieving both a favorable combination of metal corrosion prevention effect and adhesive reliability, the content of the azole-based rust inhibitor per 10 parts by weight of the carboxyl group-containing monomer may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less (for example, 3 parts by weight or less).

Examples of rust inhibitors other than azole-based rust inhibitors that may be included in the adhesive layer disclosed herein include, but are not limited to, amine compounds, nitrites, ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, urotropine, thiourea, phenyl carbamate, cyclohexylammonium-N-cyclohexylcarbamate (CHC), and the like. These rust inhibitors other than azole-based (non-azole-based rust inhibitors) can be used alone or in combination of two or more. The technology disclosed herein can also be preferably implemented in an embodiment in which non-azole-based rust inhibitors are not substantially used.

Examples of the amine compounds include hydroxyl group-containing amine compounds such as 2-amino-2-methyl-1-propanol, monoethanolamine, monoisopropanolamine, diethylethanolamine, ammonia, and aqueous ammonia; cyclic amines such as morpholine; cyclic alkylamine compounds such as cyclohexylamine; and linear alkylamines such as 3-methoxypropylamine. Examples of nitrites include dicyclohexylammonium nitrite (DICHAN), diisopropylammonium nitrite (DIPAN), sodium nitrite, potassium nitrite, and calcium nitrite.

The content of the rust inhibitor (preferably an azole-based rust inhibitor, for example, a benzotriazole-based rust inhibitor) is not particularly limited, and can be, for example, 0.01 parts by weight or more (typically 0.05 parts by weight or more) per 100 parts by weight of the base polymer. From the viewpoint of obtaining a better metal corrosion prevention effect, the content may be 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. On the other hand, from the viewpoint of increasing the cohesive force of the adhesive, the content of the rust inhibitor is usually appropriate to be less than 8 parts by weight per 100 parts by weight of the base polymer, and may be 6 parts by weight or less, or 5 parts by weight or less.

(Crosslinking Agent)
In the technology disclosed herein, the adhesive composition used to form the adhesive layer may contain a crosslinking agent as necessary. The type of crosslinking agent is not particularly limited, and may be appropriately selected from conventionally known crosslinking agents. Examples of such crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. The crosslinking agents may be used alone or in combination of two or more. Among these, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and melamine-based crosslinking agents are preferred, and isocyanate-based crosslinking agents and epoxy-based crosslinking agents are more preferred. The pressure-sensitive adhesive layer in the technology disclosed herein may contain the crosslinking agent in a form after crosslinking reaction, a form before crosslinking reaction, a form after partial crosslinking reaction, an intermediate or composite form thereof, etc. The crosslinking agent is typically contained in the pressure-sensitive adhesive layer exclusively in a form after crosslinking reaction.

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

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

Specific examples of alicyclic polyisocyanates include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 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, etc.

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

The amount of the isocyanate-based crosslinking agent used is not particularly limited. For example, it can be about 0.5 parts by weight or more per 100 parts by weight of the base polymer. From the viewpoint of obtaining a higher cohesive strength (particularly heat-resistant cohesive strength), the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the base polymer can be, for example, 1.0 parts by weight or more, and may be 1.5 parts by weight or more. In some preferred embodiments, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the base polymer is about 2.0 parts by weight or more, more preferably about 2.5 parts by weight or more, and may be about 2.8 parts by weight or more. On the other hand, from the viewpoint of improving adhesion to the adherend, the amount of the isocyanate-based crosslinking agent used is usually appropriate to be 10 parts by weight or less per 100 parts by weight of the base polymer, may be 8 parts by weight or less, preferably 6 parts by weight or less, more preferably 5 parts by weight or less, and even more preferably 4 parts by weight or less, may be 3.5 parts by weight or less, or may be 3.2 parts by weight or less. In some embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the base polymer can be about 1 part by weight or more and about 7 parts by weight or less (e.g., about 1.5 parts by weight or more and about 5 parts by weight or less).

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

Specific examples of epoxy crosslinking agents include, but are not limited to, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc. Commercially available epoxy crosslinking agents include "TETRAD-C" and "TETRAD-X" manufactured by Mitsubishi Gas Chemical Company, Inc., "Epicron CR-5L" manufactured by DIC Corporation, "Denacol EX-512" manufactured by Nagase ChemteX Corporation, and "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd.

The amount of the epoxy crosslinking agent used is not particularly limited. The amount of the epoxy crosslinking agent used can be, 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) relative to 100 parts by weight of the base polymer. From the viewpoint of favorably exerting the effect of improving the cohesive force, the amount of the epoxy crosslinking agent used is usually about 0.002 parts by weight or more relative to 100 parts by weight of the base polymer, preferably about 0.005 parts by weight or more, and more preferably about 0.008 parts by weight or more. Also, from the viewpoint of improving the adhesion to the adherend, the amount of the epoxy crosslinking agent used is usually about 0.2 parts by weight or less relative to 100 parts by weight of the base polymer, preferably about 0.1 parts by weight or less, more preferably about 0.05 parts by weight or less, and even more preferably about 0.03 parts by weight or less (for example, about 0.025 parts by weight or less).

In some preferred embodiments, an isocyanate-based crosslinking agent is used in combination with at least one crosslinking agent having a different type of crosslinkable functional group from that of the isocyanate-based crosslinking agent. According to the technology disclosed herein, by using a crosslinking agent other than an isocyanate-based crosslinking agent (i.e., a crosslinking agent having a different type of crosslinkable reactive group from that of an isocyanate-based crosslinking agent; hereinafter also referred to as a "non-isocyanate-based crosslinking agent") in combination with an isocyanate-based crosslinking agent, excellent cohesive strength can be exhibited. For example, in a composition containing a rust inhibitor such as an azole-based rust inhibitor, high heat-resistant cohesive strength and excellent metal corrosion prevention properties can be suitably achieved at the same time.

The type of non-isocyanate crosslinking agent that can be used in combination with the isocyanate crosslinking agent is not particularly limited, and can be appropriately selected from the crosslinking agents described above. The non-isocyanate crosslinking agent can be used alone or in combination of two or more. In some preferred embodiments, an epoxy crosslinking agent can be used as the non-isocyanate crosslinking agent.

In the technology disclosed herein, the relationship between the content of the isocyanate-based crosslinking agent and the content of the nonisocyanate-based crosslinking agent (e.g., epoxy-based crosslinking agent) is not particularly limited. The content of the nonisocyanate-based crosslinking agent can be, for example, approximately 1/50 or less of the content of the isocyanate-based crosslinking agent. From the viewpoint of more suitably achieving both adhesion and cohesive strength to the adherend, the content of the nonisocyanate-based crosslinking agent is suitably approximately 1/75 or less of the content of the isocyanate-based crosslinking agent on a weight basis, and preferably approximately 1/100 or less (e.g., 1/150 or less). In addition, from the viewpoint of suitably exerting the effect of using an isocyanate-based crosslinking agent and a nonisocyanate-based crosslinking agent (e.g., epoxy-based crosslinking agent) in combination, it is usually suitable that the content of the nonisocyanate-based crosslinking agent is approximately 1/1000 or more of the content of the isocyanate-based crosslinking agent, for example, approximately 1/500 or more.

The amount (total amount) of the crosslinking agent used is not particularly limited. For example, it can be about 10 parts by weight or less per 100 parts by weight of the base polymer (preferably an acrylic polymer), and can be selected from the range of preferably about 0.005 to 10 parts by weight, and more preferably about 0.01 to 5 parts by weight.

(Other additives)
In addition to the above-mentioned components, the adhesive composition may contain various additives commonly used in the field of adhesives, such as a leveling agent, a crosslinking aid, a plasticizer, a softener, a dye, an antistatic agent, an antiaging agent, an ultraviolet absorber, an antioxidant, and a light stabilizer, as necessary. The adhesive composition may also contain an oligomer (e.g., an acrylic oligomer having a Mw of about 1000 to less than 30000) for the purpose of improving adhesive strength, etc. As for such various additives, those conventionally known can be used in a conventional manner, and detailed description thereof will be omitted since they do not particularly characterize the present invention.

The adhesive layer (layer made of adhesive) disclosed herein may be an adhesive layer formed from an aqueous adhesive composition, a solvent-based adhesive composition, a hot melt-type adhesive composition, or an active energy ray curable adhesive composition that acts upon irradiation with active energy rays such as ultraviolet rays or electron beams. The aqueous adhesive composition refers to an adhesive composition in a form containing an adhesive (adhesive layer forming component) in a solvent (aqueous solvent) whose main component is water, and typically includes those called aqueous dispersion-type adhesive compositions (compositions in which at least a part of the adhesive is dispersed in water). The solvent-type adhesive composition refers to an adhesive composition in a form containing an adhesive in an organic solvent. The technology disclosed herein may be preferably implemented in an embodiment having an adhesive layer formed from a solvent-type adhesive composition from the viewpoint of adhesive properties, etc.

In the technology disclosed herein, the form of adding the pigment to the adhesive composition is not particularly limited. The pigment may be added to the adhesive composition in the form of a dispersion in which the particles are dispersed in a dispersion medium at an appropriate concentration. The dispersion medium constituting the dispersion is not particularly limited, and examples thereof include water (ion-exchanged water, reverse osmosis water, distilled water, etc.), various organic solvents (alcohols such as ethanol; ketones such as acetone; ethers such as butyl cellosolve and propylene glycol monomethyl ether acetate; esters such as ethyl acetate; aromatic hydrocarbons such as toluene; and mixtures thereof), and aqueous mixtures of water and the above organic solvents. The above dispersion may contain the above-mentioned dispersant.

(Formation of Pressure-Sensitive Adhesive Layer)
The adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method of forming an adhesive layer by applying an adhesive composition to a surface (release surface) having releasability and drying it can be adopted. In the case of an adhesive sheet having a supporting substrate, for example, a method (direct method) of forming an adhesive layer by directly applying (typically applying) an adhesive composition to the supporting substrate and drying it can be adopted. In addition, a method (transfer method) of forming an adhesive layer on a surface (release surface) having releasability by applying an adhesive composition to the surface and drying it, and transferring the adhesive layer to a supporting substrate can be adopted. For example, the surface of a release liner described later can be preferably used as the release surface. The adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and may be an adhesive layer formed in a regular or random pattern such as a dotted or striped pattern.

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

In the technology disclosed herein, the thickness of the adhesive layer is 30 μm or less. In a thin adhesive layer having a thickness of 30 μm or less, the pigment aggregates contained in the adhesive layer are easily noticeable, and the deterioration of the appearance quality is easily caused by the pigment. However, according to the technology disclosed herein, in a thin adhesive layer as described above, the generation of coarse particles is suppressed and the particles are less noticeable, and the deterioration of the appearance quality caused by the pigment can be highly suppressed. In some embodiments, the thickness of the adhesive layer may be, for example, approximately 25 μm or less, approximately 20 μm or less, approximately 15 μm or less, or approximately 12 μm or less. An adhesive layer having the above thickness can be well responsive to the demand for thinning and weight reduction. In addition, although not particularly limited, the thickness of the adhesive layer may be approximately 3 μm or more, or approximately 5 μm or more. In some preferred embodiments, the thickness of the adhesive layer is advantageously greater than about 5 μm, and is about 8 μm or more (e.g., more than 8 μm), and is suitably about 10 μm or more (e.g., more than 10 μm), and may be about 15 μm or more, about 20 μm or more, or may be about 25 μm or more. The thicker the adhesive layer, the easier it is for the pigment particles to disperse in the adhesive layer, and the less likely it is that unevenness on the adhesive surface due to pigment aggregates or the like will occur, and the deterioration of appearance quality due to the pigment tends to be highly suppressed. In addition, the thicker the adhesive layer, the more likely it is that the adhesive strength is improved. Furthermore, for example, in a light-shielding adhesive layer, the thicker the adhesive layer, the more likely it is that high light-shielding properties are obtained. In a substrate-attached double-sided adhesive sheet having a first adhesive layer and a second adhesive layer on each side of the substrate, the first adhesive layer and the second adhesive layer may have the same thickness, or may have different thicknesses.

The thickness of the adhesive layer is greater than the maximum diameter of the particles present in the adhesive layer. Specifically, the thickness T [μm] of the adhesive layer is greater than the maximum diameter P _MAX [μm] of the particles present in the adhesive layer, i.e., T>P _MAX . An adhesive layer that satisfies T>P _MAX has a sufficient thickness and volume relative to the pigment particle size, so that the pigment is easily dispersed in the adhesive layer, and unevenness of the adhesive surface caused by pigment aggregates and the like is unlikely to occur, and deterioration of appearance quality caused by the pigment can be highly suppressed. In some embodiments, the difference (T-P MAX) between the thickness T of the adhesive layer and the maximum _diameter P _MAX of the particles present in the adhesive layer is approximately 1 μm or more, may be approximately 3 μm or more, or may be approximately 5 μm or more. In some preferred embodiments, the difference (T-P _MAX ) is about 8 μm or more, more preferably about 10 μm or more, even more preferably about 12 μm or more, and may be about 15 μm or more, about 20 μm or more, or about 25 μm or more. In some embodiments, the ratio (T/P _MAX ) of the thickness T of the pressure-sensitive adhesive layer to the maximum diameter P _MAX of particles present in the pressure-sensitive adhesive layer is about 1.2 or more, may be about 1.5 or more, or may be about 3 or more. In some preferred embodiments, the ratio (T/P _MAX ) is about 5 or more, may be about 7 or more, may be about 10 or more, may be about 15 or more, may be about 20 or more, or may be about 25 or more.

The total light transmittance of the adhesive layer formed as described above may vary depending on the purpose of adding the pigment (light blocking properties, design properties, etc.). In some embodiments, the total light transmittance of the adhesive layer is approximately 80% or less. By adding a pigment to the adhesive layer, an adhesive layer with a reduced total light transmittance can be formed. The total light transmittance of the adhesive layer may be approximately 70% or less, approximately 60% or less, approximately 50% or less (e.g., less than 50%), approximately 40% or less, 30% or less, 20% or less, or 10% or less. In some preferred embodiments, the total light transmittance of the adhesive layer is less than 10%, may be less than 5%, may be less than 3%, may be less than 1%, may be less than 0.5% (e.g., less than 0.1%), or may be substantially 0%, i.e., below the detection limit. An adhesive sheet having an adhesive layer exhibiting the above total light transmittance can exhibit excellent light blocking properties. In some embodiments, the total light transmittance of the adhesive layer is 10% or more. By adding an appropriate amount of pigment to the adhesive layer, an adhesive layer with a moderately reduced total light transmittance can be formed. In an adhesive sheet having such an adhesive layer, since it has a certain level of light transmittance or more, pigment aggregates and the like are easily visible and easily noticeable, but according to the technology disclosed herein, since the maximum diameter of the particles in the adhesive layer is a predetermined value or less, it can have good appearance quality. The total light transmittance of the adhesive layer may be about 15% or more, about 20% or more, about 25% or more, about 30% or more, about 35% or more, about 40% or more, about 45% or more, about 50% or more (e.g., more than 50%), about 55% or more, about 60% or more, about 65% or more, or about 70% or more. The total light transmittance of the pressure-sensitive adhesive layer can be measured in the same manner as the total light transmittance of the pressure-sensitive adhesive sheet described below.

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

The term "nonwoven fabric" as used herein refers to a nonwoven fabric for adhesive sheets that is used mainly in the field of adhesive tapes and other adhesive sheets, and typically refers to a nonwoven fabric (sometimes called "paper") that is produced using a general papermaking machine. The term "resin film" as used herein refers to a typically nonporous resin sheet that is distinguished from, for example, nonwoven fabric or woven fabric (i.e., does not include nonwoven fabric or woven fabric). Such a resin film may be non-foamed. The term "non-foamed resin film" as used herein refers to a resin film that has not been intentionally treated to be a foamed body. Specifically, the non-foamed resin film may be a resin film with an expansion ratio of less than 1.1 times (for example, less than 1.05 times, typically less than 1.01 times). The resin film may be any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film.

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

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

A colorant can be added to the resin film. This allows the light transmittance (light blocking properties, etc.) of the resin film to be adjusted. Adjusting the light transmittance (e.g., vertical light transmittance) of the resin film can also be useful for adjusting the light transmittance of a substrate containing the resin film, and even the light transmittance of a pressure-sensitive adhesive sheet containing the substrate. As the colorant, conventionally known pigments and dyes can be used. There are no particular limitations on the color of the colorant, and it may be colored or colorless.

In some embodiments, a black colorant may be preferably used because the light blocking properties (e.g., vertical light transmittance) can be efficiently adjusted with a small amount of colorant. Specific black colorants include those exemplified as colorants that can be contained in the adhesive layer. Although not particularly limited, in some embodiments, a pigment (e.g., a particulate black colorant such as carbon black) having an average particle size of 10 nm to 500 nm, more preferably 10 nm to 120 nm, can be used. In other embodiments, the resin film may contain a white colorant such as titanium oxide. The amount of colorant used in the resin film is not particularly limited, and can be appropriately adjusted so as to impart the desired optical properties. The amount of colorant used is usually about 0.1 to 30% by weight of the resin film, and can be, for example, 0.1 to 25% by weight (typically 0.1 to 20% by weight).

The resin film may contain various additives such as fillers (inorganic fillers, organic fillers, etc.), dispersants (surfactants, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, etc., as necessary. The blending ratio of the various additives is usually less than 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight).

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

The supporting substrate may be colored by a colored layer disposed on the surface of a base film (preferably a resin film). In such a substrate having a configuration including a base film and a colored layer, the base film may or may not contain a colorant. The colored layer may be disposed on either one surface of the base film, or on both surfaces. In a configuration in which a colored layer is disposed on each of the surfaces of the base film, the configurations of the colored layers may be the same or different.

The colored layer may be a single layer structure consisting of one layer as a whole, or may be a multilayer structure including two, three or more sub-colored layers. A multilayer structure including two or more sub-colored layers can be formed, for example, by repeatedly applying (e.g., printing) a colored layer-forming composition. The color and amount of colorant contained in each sub-colored layer may be the same or different. For a colored layer intended to impart light-shielding properties, it is particularly useful to have a multilayer structure from the viewpoint of preventing pinholes from occurring and increasing the reliability of preventing light leakage.

The overall thickness of the colored layer is usually about 1 μm to 10 μm, preferably about 1 μm to 7 μm, and can be, for example, about 1 μm to 5 μm. In a colored layer that includes two or more sub-colored layers, the thickness of each sub-colored layer is usually preferably about 1 μm to 2 μm.

The thickness of the support substrate is not particularly limited. In order to avoid the adhesive sheet becoming excessively thick, the thickness of the support substrate can be, for example, approximately 200 μm or less (e.g., approximately 100 μm or less). Depending on the purpose and mode of use of the adhesive sheet, the thickness of the support substrate may be approximately 70 μm or less, approximately 30 μm or less, or approximately 10 μm or less (e.g., approximately 5 μm or less). There is no particular lower limit to the thickness of the support substrate. In terms of the handleability and processability of the adhesive sheet, the thickness of the support substrate is usually approximately 2 μm or more, and is preferably approximately 5 μm or more, for example, approximately 10 μm or more.

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

<Release Liner>
In the technology disclosed herein, a release liner can be used during the formation of the adhesive layer, the preparation of the adhesive sheet, the storage, distribution, and shaping of the adhesive sheet before use. The release liner is not particularly limited, and for example, a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or a release liner made of a low-adhesion material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin (polyethylene, polypropylene, etc.) can be used. The release treatment layer can be formed by surface-treating the liner substrate with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide.

<Adhesive sheet>
The total thickness of the adhesive sheet disclosed herein (including the adhesive layer, and further including the supporting substrate in the configuration having the supporting substrate, but not including the release liner) is not particularly limited. The total thickness of the adhesive sheet can be, for example, about 300 μm or less, and from the viewpoint of thinning, it is usually appropriate to be about 200 μm or less, and may be about 100 μm or less (for example, about 70 μm or less). In some embodiments, the thickness of the adhesive sheet can be about 50 μm or less, for example, about 35 μm or less, preferably about 30 μm or less, for example, about 25 μm or less, about 20 μm or less, about 15 μm or less, or about 12 μm or less. The adhesive sheet can be, for example, in the form of a substrateless double-sided adhesive sheet having the above thickness. The adhesive sheet having the above thickness can be well responsive to the demand for thinning and weight reduction. The thickness of the adhesive sheet may also be about 3 μm or more, or about 5 μm or more. In some embodiments, the thickness of the adhesive sheet is advantageously greater than 5 μm, and is suitably about 8 μm or more (e.g., more than 8 μm), and may be about 10 μm or more (e.g., more than 10 μm), about 15 μm or more, about 20 μm or more, or about 25 μm or more. An adhesive sheet having a thickness of a predetermined value or more can have a sufficient thickness of the adhesive layer, so that the properties based on the adhesive layer (e.g., adhesive properties such as adhesive strength) are easily obtained, and also tends to be excellent in handleability. In addition, in a substrate-less adhesive sheet, the thickness of the adhesive layer is the total thickness of the adhesive sheet.

The adhesive sheet disclosed herein has an adhesive layer containing a pigment, and therefore may have lower light transmittance than a transparent adhesive sheet. The total light transmittance of the adhesive sheet may vary depending on the purpose of adding the pigment to the adhesive layer (light blocking properties, design properties, etc.). In some embodiments, the total light transmittance of the adhesive sheet is about 80% or less, may be about 70% or less, may be about 60% or less, may be about 50% or less (e.g., less than 50%), may be about 40% or less, may be 30% or less, may be 20% or less, or may be 10% or less. In some preferred embodiments, the total light transmittance of the adhesive sheet is less than 10%, may be less than 5%, may be less than 3%, may be less than 1%, may be less than 0.5% (e.g., less than 0.1%), or may be substantially 0%, i.e., below the detection limit. An adhesive sheet exhibiting the above total light transmittance may exhibit excellent light blocking properties. In some embodiments, the total light transmittance of the adhesive sheet is 10% or more. In such a pressure-sensitive adhesive sheet, since it has a certain level of light transmittance or more, pigment aggregates and the like are easily visible and noticeable, but according to the technology disclosed herein, since the maximum diameter of the particles in the pressure-sensitive adhesive layer is a predetermined value or less, it is possible to have good appearance quality. The total light transmittance of the pressure-sensitive adhesive sheet may be about 15% or more, about 20% or more, about 25% or more, about 30% or more, about 35% or more, about 40% or more, about 45% or more, about 50% or more (e.g., more than 50%), about 55% or more, about 60% or more, about 65% or more, or about 70% or more. The total light transmittance of the pressure-sensitive adhesive sheet can be measured by the method described in the Examples below.

The 180-degree peel strength of the adhesive sheet disclosed herein may be approximately 3 N/25 mm or more. From the viewpoint of obtaining good adhesion to the adherend, it is appropriate that the 180-degree peel strength is approximately 5 N/25 mm or more. In addition, according to the technology disclosed herein, the pigment is well dispersed in the adhesive layer, so that the target light blocking properties, design properties, etc. can be achieved by using a relatively small amount of pigment. In other words, excellent pigment addition effects can be achieved while maintaining adhesive properties such as adhesive strength. Therefore, the 180-degree peel strength is preferably approximately 7 N/25 mm or more, more preferably approximately 8 N/25 mm or more, even more preferably approximately 10 N/25 mm or more, and particularly preferably approximately 12 N/25 mm or more. According to the adhesive sheet, it is possible to achieve the above-mentioned predetermined adhesive strength while having a total light transmittance of a predetermined value or less. The above-mentioned 180-degree peel strength is the 180-degree peel strength against a stainless steel plate measured based on JIS Z 0237, and specifically, it can be measured by the method described in the examples described later.

<Applications>
The adhesive sheet disclosed herein has an adhesive layer containing a pigment and can have high appearance quality, so it is suitable for various uses, such as those in which the adhesive sheet attached to the surface of the adherend is visible, for example, those in which the concealing properties of the adhesive sheet are required, those in which a colored adhesive layer is used to impart design and color, and those in which a specific optical property (such as light transmittance) is required. For example, electronic devices have parts that are visible to the user and require excellent appearance quality, but the adhesive sheet disclosed herein is highly suppressed from deteriorating in appearance quality due to the pigment, so it can be applied to visible parts of the electronic device to achieve a surface with good appearance quality. The adhesive sheet disclosed herein is suitable for, for example, those in which components of electronic devices, including home appliances, office automation devices, and mobile electronic devices such as smartphones, are joined, and those in which optical properties (such as light blocking properties) are imparted to the electronic devices.

Non-limiting examples of the portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear devices worn on the wrist like a wristwatch, modular devices worn on a part of the body with a clip or strap, eyewear devices including glasses (monocular or binocular, including head-mounted devices), clothing devices attached to shirts, socks, hats, etc. in the form of accessories, earwear devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio devices (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, electronic books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" does not mean that it is simply possible to carry it around, but rather that it has a level of portability that allows an individual (average adult) to carry it around relatively easily. Examples of the electronic devices include personal computers (desktop, notebook, tablet, etc.), televisions, etc. These may have built-in display devices such as liquid crystal or organic electroluminescence.

In some embodiments, the adhesive sheet may be used for the purpose of fixing a pressure sensor to other members in an electronic device equipped with a pressure sensor, such as the above-mentioned portable electronic device. In some embodiments, the adhesive sheet may be used for fixing a pressure sensor to other members in an electronic device (typically a portable electronic device) equipped with a function that allows an absolute position to be specified on a plate (typically a touch panel) corresponding to the screen using a device (typically a pen-type or mouse-type device) for indicating a position on a screen and a device for detecting the position.

The adhesive sheet disclosed herein is also suitable for use in applications in which it is disposed on the back surface of a display screen (display unit) such as a touch panel display in an electronic device such as a portable electronic device. By disposing the adhesive sheet according to some embodiments on the back surface of the display screen (display unit), it is possible to prevent a decrease in visibility of the display screen regardless of the manner in which the electronic device is used. For example, it can be disposed on the back surface of a display screen (display unit) such as a touch panel display in the electronic device to prevent reflection of light through the display screen. The above-mentioned reflection can be caused by a metal member disposed on the back side of the display screen, but by using the adhesive sheet according to some embodiments, for example, to bond the metal member to the display unit, it is possible to simultaneously achieve bonding of the members and imparting light blocking properties.

Materials (adherend materials) to which the adhesive sheet disclosed herein is attached include, but are not limited to, metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, etc., or alloys containing two or more of these, and various resin materials (typically plastic materials) such as polyimide resins, acrylic resins, polyethernitrile resins, polyethersulfone resins, polyester resins (polyethylene terephthalate resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyether ether ketone resins, polyamide resins (so-called aramid resins, etc.), polyarylate resins, polycarbonate resins, and liquid crystal polymers, and inorganic materials such as alumina, zirconia, soda glass, quartz glass, and carbon. Among them, metal materials such as copper, aluminum, and stainless steel, and resin materials (typically plastic materials) such as polyimide resins, aramid resins, and polyphenylene sulfide resins are widely used. The above materials can be materials for components constituting products such as electronic devices. The adhesive sheet disclosed herein can be used by being attached to a member made of the above-mentioned material. The above-mentioned material can be a material constituting the object to be fixed such as the pressure-sensitive sensor or the display unit (for example, a back surface member such as an electromagnetic wave shield or a reinforcing plate). The object to be fixed refers to an object to which the adhesive sheet is attached, that is, an adherend. The back surface member refers to a member arranged on the opposite side of the front surface (visible side) of the pressure-sensitive sensor or the display unit in, for example, a portable electronic device, and can be, for example, a member constituting the support part 540 arranged on the back surface of the display device 500 shown in FIG. 3 described later. The object to be fixed may be in the form of either a single layer structure or a multilayer structure, and the surface (attaching surface) to which the adhesive sheet is attached may be subjected to various surface treatments. Although not particularly limited, an example of the object to be fixed is a back surface member having a thickness of 1 μm or more (typically 5 μm or more, for example 60 μm or more, or even 120 μm or more) and 1500 μm or less (for example 800 μm or less).

In some embodiments, the member or material to which the pressure-sensitive adhesive sheet is attached may be light-transmitting (light-transmitting adherend). The adhesive surface of the pressure-sensitive adhesive sheet attached to the light-transmitting adherend can be visible through the light-transmitting adherend, so it is desirable for the adhesive sheet to have good appearance quality. The total light transmittance of the light-transmitting adherend may be, for example, greater than 50%, and may be 70% or more. In some preferred embodiments, the total light transmittance of the adherend is 80% or more, more preferably 90% or more, and may be 95% or more (for example, 95 to 100%). Such a material may be a resin film (for example, a polyester-based resin film such as a PET film) that is placed on the back surface of the image display unit of various devices such as portable electronic devices. The pressure-sensitive adhesive sheet disclosed herein may be preferably used in an embodiment in which it is attached to an adherend (for example, a member) having a total light transmittance of a predetermined value or more as described above. The total light transmittance may be measured in the same manner as the total light transmittance of the pressure-sensitive adhesive sheet.

In some embodiments, the adhesive sheet is used in a manner that it is attached to a metal member. Examples of materials for the metal member include the metal materials exemplified as the above-mentioned adherend material. Such metal members are, for example, members or articles having a surface (adhesive sheet attachment surface) formed from a metal material such as aluminum or stainless steel, and preferred examples include metal members such as stainless steel members and aluminum members. By attaching the above-mentioned adhesive sheet to an area of the metal member surface that needs to be concealed, the above-mentioned area of the metal member can be concealed. The adhesive sheet may cover the entire surface of the metal member, or may cover a part of the above-mentioned surface (for example, a part of the area that needs to be concealed). The above-mentioned metal member may be, for example, a member that constitutes the support part 540 of the display device 500 shown in FIG. 3 described later. The above-mentioned metal member is preferably one of the adherends of the adhesive sheet.

As described above, according to the present specification, a laminate comprising an adhesive sheet and a member to which the adhesive sheet is attached is provided. In some embodiments, the laminate comprising the adhesive sheet is a laminate comprising the adhesive sheet and a metal member (first member). Such a laminate may comprise a metal member and an adhesive sheet covering at least a part of the surface of the metal member. The adhesive sheet may cover the entire surface of the metal member, or may cover a part of the surface (for example, a part of the area to be concealed). Typically, one side (adhesive surface) of the adhesive sheet is attached to the metal member. In some embodiments, the member to which the adhesive sheet is attached may have the light transmittance of the above-mentioned adherend material. In this embodiment, the laminate comprising the adhesive sheet is a laminate comprising the adhesive sheet and a member (second member) having light transmittance. In some preferred embodiments, the laminate is a laminate comprising a metal member (first member), an adhesive sheet (specifically a double-sided adhesive sheet), and a member (second member) having light transmittance, in this order. In addition, the substrate-less double-sided adhesive sheet is also called the adhesive layer in the laminate.

The pressure-sensitive adhesive sheet according to some embodiments can be preferably used in electronic devices (typically portable electronic devices) that require, for example, specific optical properties. For example, the pressure-sensitive adhesive sheet can be preferably used in electronic devices that include various light sources such as LEDs (light emitting diodes) and light-emitting elements such as self-emitting organic EL. For example, the pressure-sensitive adhesive sheet can be preferably used in electronic devices (typically portable electronic devices) that include organic EL display devices or liquid crystal display devices that require specific optical properties.

Figure 3 is an exploded perspective view showing a typical example of the configuration of a display device. As shown in Figure 3, the display device 500 included in the portable electronic device 400 includes a display unit 520 including a cover member, an organic EL unit, and the like, and a support unit 540. The display device 500 is further configured to include an adhesive sheet 530. In this configuration example, the adhesive sheet 530 fixes the members that constitute the display unit 520 and the support unit 540. The support unit 540 is configured to include a substrate (a metal plate such as a stainless steel plate or an aluminum plate) and the like. The adhesive sheet disclosed herein is preferably used as a component of the display device as described above.

The matters disclosed by this specification include the following:
[1] A display device including a display unit including a cover member and an organic EL unit, and a support unit,
An adhesive sheet is attached to the support portion,
The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer having a thickness of 30 μm or less,
The pressure-sensitive adhesive layer contains a pigment,
The maximum diameter of the particles present in the pressure-sensitive adhesive layer is 8 μm or less,
A display device, wherein the thickness of the pressure-sensitive adhesive layer is greater than the maximum diameter of the particles.
[2] The display device according to the above [1], wherein the pigment is an inorganic pigment.
[3] The display device according to the above [1] or [2], wherein the pigment is carbon black.
[4] The display device according to any one of the above [1] to [3], wherein the content of the pigment in the adhesive layer is 0.1 to 10 wt %.
[5] The display device according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer.
[6] The display device according to any one of the above [1] to [5], wherein the pressure-sensitive adhesive sheet has a total light transmittance of 80% or less.
[7] The display device according to any one of [1] to [6] above, wherein the pressure-sensitive adhesive sheet has a total light transmittance of 10% or more.
[8] The display device according to any one of the above [1] to [7], wherein the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet made of the pressure-sensitive adhesive layer.
[9] The display device according to any one of the above [1] to [8], wherein the pressure-sensitive adhesive sheet has a 180 degree peel strength against a stainless steel plate of 7 N/25 mm or more.

[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 30 μm or less,
The pressure-sensitive adhesive layer contains a pigment,
The maximum diameter of the particles present in the pressure-sensitive adhesive layer is 8 μm or less,
A pressure-sensitive adhesive sheet, wherein the thickness of the pressure-sensitive adhesive layer is greater than the maximum diameter of the particles.
[12] The pressure-sensitive adhesive sheet according to the above [11], wherein the pigment is an inorganic pigment.
[13] The pressure-sensitive adhesive sheet according to the above [11] or [12], wherein the pigment is carbon black.
[14] The pressure-sensitive adhesive sheet according to any one of [11] to [13] above, wherein the content of the pigment in the pressure-sensitive adhesive layer is 0.1 to 10 wt %.
[15] The pressure-sensitive adhesive sheet according to any one of [11] to [14] above, wherein the pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer.
[16] The pressure-sensitive adhesive sheet according to any one of the above [11] to [15], which has a total light transmittance of 80% or less.
[17] The pressure-sensitive adhesive sheet according to any one of the above [11] to [16], which has a total light transmittance of 10% or more.
[18] The pressure-sensitive adhesive sheet according to any one of [11] to [17] above, which is a substrateless double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.
[19] The pressure-sensitive adhesive sheet according to any one of the above [11] to [18], which has a 180 degree peel strength against a stainless steel plate of 7 N/25 mm or more.
[20] The pressure-sensitive adhesive sheet according to any one of [11] to [19] above, which is used for fixing members in an electronic device.

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

<Evaluation method>
(180 degree peel strength)
Under a measurement environment of 23°C and 50% RH, a 50 μm thick polyethylene terephthalate (PET) film is attached to one adhesive surface of a pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet) to provide a backing, and the sheet is cut to a size of 25 mm wide and 100 mm long to prepare a measurement sample. The prepared measurement sample is then pressure-bonded to the surface of a stainless steel plate (SUS304BA plate) by rolling a 2 kg roller back and forth once under an environment of 23°C and 50% RH. After leaving the sample in the same environment for 30 minutes, a universal tensile compression tester is used to measure the peel strength [N/25 mm] under the conditions of a tensile speed of 300 mm/min and a peel angle of 180 degrees in accordance with JIS Z 0237:2000. As the universal tensile compression tester, for example, Minebea's "tensile compression tester, TG-1kN" or an equivalent product is used. In addition, in the case of a single-sided pressure-sensitive adhesive sheet, the backing of the PET film is not necessary.

(Total light transmittance)
The total light transmittance [%] is measured in accordance with JIS K 7136: 2000 using a commercially available transmittance meter. As the transmittance meter, a product name "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or an equivalent product is used.

(Measurement of pigment particle size in adhesive layer)
The adhesive sample is rapidly frozen under a liquid nitrogen atmosphere, and the sample is cut to a thickness of about 100 nm under a freezing atmosphere of -30°C using an ultramicrotome (model "UC7" manufactured by Leica Corporation) to obtain an ultrathin section. The obtained ultrathin section is observed using a transmission electron microscope (TEM; manufactured by Hitachi High-Technologies Corporation, accelerating voltage 100 kV). Image processing (binarization) is performed on one field of view (6 μm x 6 μm square) of a TEM image enlarged by about 3,000 times to identify particles, and the area fraction of each particle is calculated for all identified particles. Then, the circle equivalent diameter is calculated from the area of each particle. The circle equivalent diameter refers to the diameter of a circle (perfect circle) having the same area as the area of one particle to be measured. This operation is performed in four different fields of view in the TEM image (N = 4), and the particles classified by the circle equivalent diameter are histogrammed on a number basis to obtain a particle size distribution (number basis). The number of particles that is the basis for calculating the particle size distribution is obtained by counting the number of particles present within the above-mentioned one field of view. From the obtained particle size distribution, the average particle size based on TEM observation (TEM average particle size) [nm] is obtained. Note that when identifying particles, particles on the edge of the image are omitted during analysis. As the image analysis software, for example, ImageJ can be used.

(Evaluation of maximum particle size in adhesive layer)
The release liner-attached PSA sheet is cut into a size of 500 mm x 1000 mm to obtain an evaluation sample. The release liner (in the case of a double-sided PSA sheet with a release liner having two release liners, the release liner on the light release side) is peeled off from the evaluation sample, and the evaluation sample is held flat at the midpoint (a position about 50 cm away from the point light source) between a point light source arranged at a distance of about 100 cm and a projection screen, and the evaluation sample is arranged so that the angle of the exposed PSA layer surface of the evaluation sample with respect to the light from the point light source is about 90 degrees. The evaluation sample is arranged with the PSA layer surface from which the release liner has been peeled off on the side of the point light source. In a dark room with an environment of 23°C and 50% RH, the point light source is turned on, and the image projected onto the screen through the evaluation sample is visually observed to detect the largest particle (largest particle) present in the PSA layer (screen projection inspection). In the case where the light-shielding property of the adhesive sheet is high and it is difficult to visually recognize the particles from the image projected on the screen, the part where the light from the point light source is reflected and the surface of the adhesive layer is convex is detected. For example, a "Xenon Lamp C2577" manufactured by Hamamatsu Photonics KK can be used as the point light source. For each example, 10 evaluation samples are prepared and the above-mentioned screen projection inspection is performed, and the part where the largest particle was confirmed and the part where the adhesive layer surface is convex are extracted, and the diameter (maximum length) of the particle (maximum particle) present in the part is measured using an optical microscope, and the largest diameter in the evaluation sample is regarded as the maximum diameter of the particle present in the adhesive layer. For example, a "VHX-S750" manufactured by KEYENCE INC. can be used as the optical microscope.

(Appearance quality evaluation)
The release liner-attached adhesive sheet is cut into a size of 500 mm x 1000 mm to obtain an evaluation sample. The release liner (in the case of a double-sided adhesive sheet with a release liner having two release liners, the release liner on the light release side) is peeled off from the evaluation sample, and the evaluation sample is held flat at the midpoint (a position about 50 cm away from the point light source) between the point light source and the projection screen, which are arranged at a distance of about 100 cm, and the exposed adhesive layer surface of the evaluation sample is arranged at an angle of about 90 degrees with respect to the light from the point light source. The evaluation sample is arranged with the adhesive layer surface from which the release liner has been peeled off on the point light source side. In a dark room in an environment of 23 ° C. and 50% RH, the point light source is turned on, and the image projected onto the screen through the evaluation sample is visually observed to evaluate the presence and number of visible coarse particles and uneven deformation in the adhesive layer. For example, a "xenon lamp C2577" manufactured by Hamamatsu Photonics KK can be used as the point light source. For each example, 10 evaluation samples were prepared and the above evaluation was performed. If the number of samples in which visible coarse particles and uneven deformation were confirmed was 0, the sample was rated as "◎", if 1 to 2 particles were confirmed, the sample was rated as "◯", and if 3 or more particles were confirmed, the sample was rated as "×" (fail).

<Materials used>
Carbon black dispersions A to D were prepared, each consisting of about 25% carbon black, about 1 to 15% dispersant, and the remainder being a solvent (ethyl acetate). For carbon black dispersions A to D, particle size distributions were obtained based on a laser diffraction/scattering method (using a Microtrac MT3000II manufactured by Microtrac-Bell, Inc.; dispersion medium: ethyl acetate), and the volume average particle diameter [nm], standard deviation [nm], cumulative 10% particle diameter (D10) [nm], cumulative 50% particle diameter (D50) [nm], and cumulative 90% particle diameter (D90) [nm] were measured. The measured values are shown in Table 1. D10, D50, and D90 refer to the particle diameters at the points where the cumulative volume from the smaller particle diameter side is 10%, 50%, and 90%, respectively, in a cumulative volume distribution in which the total volume of the particle diameter distribution of the particles calculated on a volume basis is taken as 100%.

<Examples 1 to 20>
(Preparation of Acrylic Polymer)
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser and a dropping funnel, 95 parts of n-butyl acrylate (BA) and 5 parts of acrylic acid (AA) as monomer components, and 233 parts of ethyl acetate as a polymerization solvent were charged, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 0.2 parts of 2,2'-azobisisobutyronitrile was added as a polymerization initiator, and the mixture was solution polymerized at 60°C for 8 hours to obtain a solution of an acrylic polymer. The Mw of this acrylic polymer was about 70 x ¹⁰⁴ .

(Preparation of Pressure-Sensitive Adhesive Composition)
To the acrylic polymer solution, 0.8 parts of 1,2,3-benzotriazole (product name "BT-120", manufactured by Johoku Chemical Industry Co., Ltd.) was added relative to 100 parts of the acrylic polymer contained in the solution, 20 parts of a terpene phenol resin (product name "YS Polystar T-115", softening point about 115°C, hydroxyl value 30 to 60 mgKOH/g, manufactured by Yasuhara Chemical Co., Ltd.) as a tackifier resin, 3 parts of an isocyanate-based crosslinking agent (product name "Coronate L", 75% ethyl acetate solution of trimethylolpropane/tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation) as a crosslinking agent, 0.01 parts of an epoxy-based crosslinking agent (product name "TETRAD-C", 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a crosslinking agent, and any one of carbon black dispersions A to D was added, stirred and mixed to prepare a pressure-sensitive adhesive composition according to each example. Carbon black dispersions A to D were blended so that the solid content of carbon black in the adhesive layer was the content shown in Tables 2 to 3.

(Preparation of adhesive sheet)
The above-mentioned adhesive composition was applied to the release surface of a 38 μm thick polyester release liner (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) and dried at 100° C. for 2 minutes to form an adhesive layer according to each example having the thickness shown in Tables 2 and 3. The release surface of a 25 μm thick polyester release liner (product name "Diafoil MRF", thickness 25 μm, manufactured by Mitsubishi Chemical Corporation) was bonded to this adhesive layer. In this way, a substrate-less double-sided adhesive sheet according to each example, both sides of which were protected by the above-mentioned two polyester release liners, was obtained.

The overview and evaluation results of each example are shown in Tables 2 and 3.

As shown in Tables 2 and 3, the pressure-sensitive adhesive sheets according to Examples 1 to 15 had a pressure-sensitive adhesive layer thickness greater than the maximum diameter of the particles present in the pressure-sensitive adhesive layer and 30 μm or less, the maximum diameter of the particles was 8 μm or less, and had an acceptable level of appearance quality. On the other hand, in Examples 16 to 20, in which the maximum diameter of the particles present in the pressure-sensitive adhesive layer was greater than 8 μm, the results of the appearance quality evaluation were all unacceptable.
The 180 degree peel strengths of the pressure-sensitive adhesive sheets of Examples 9, 12, 15 and 20 were 11.4 N/25 mm, 12.2 N/25 mm, 10.8 N/25 mm and 9.6 N/25 mm, respectively.
From the above results, it can be seen that by using an adhesive sheet in which the adhesive layer contains a pigment, the thickness of the adhesive layer is greater than the maximum diameter of the particles present in the adhesive layer and is 30 μm or less, and the maximum diameter of the particles present in the adhesive layer is 8 μm or less, deterioration in appearance quality caused by the pigment can be highly suppressed.

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 variations of the specific examples given above.

1, 2 Adhesive sheet 21 Adhesive layer 21A, 21B Adhesive surface 31, 32 Release liner

Claims (10)

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 30 μm or less,
The pressure-sensitive adhesive layer contains a pigment,
The maximum diameter of the particles present in the pressure-sensitive adhesive layer is 8 μm or less,
A pressure-sensitive adhesive sheet, wherein the thickness of the pressure-sensitive adhesive layer is greater than the maximum diameter of the particles. The adhesive sheet according to claim 1, wherein the pigment is an inorganic pigment. The adhesive sheet according to claim 1, wherein the pigment is carbon black. The adhesive sheet according to any one of claims 1 to 3, wherein the content of the pigment in the adhesive layer is 0.1 to 10% by weight. The adhesive sheet according to any one of claims 1 to 3, wherein the adhesive layer contains an acrylic polymer as a base polymer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, having a total light transmittance of 80% or less. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, having a total light transmittance of 10% or more. The adhesive sheet according to any one of claims 1 to 3, which is a substrateless double-sided adhesive sheet consisting of the adhesive layer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, which has a 180-degree peel strength against a stainless steel plate of 7 N/25 mm or more. The adhesive sheet according to any one of claims 1 to 3, which is used to fasten components in electronic devices.

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