Adhesive sheet, display device and laminate

Abstract

To provide an adhesive sheet having a structure with limited thickness, capable of maintaining a sufficient adhesive force as a structural material even if exposed to an acidic liquid and an alkaline liquid.SOLUTION: An adhesive sheet is 100 μm thick or less. The adhesive sheet includes an adhesive layer containing an acrylic polymer. The acrylic polymer is a polymer of monomer components containing 60 wt.% or more alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal. The monomer components include a monomer having a nitrogen atom-containing ring and carboxy group-containing monomer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet, a display device, and a laminate. [Background technology]

[0002] Generally, adhesives (also referred to as pressure-sensitive adhesives; the same applies hereinafter) are in a soft solid (viscoelastic) state at temperatures near room temperature and have the property of adhering to an adherend when pressure is applied. Taking advantage of this property, adhesives are widely used in various industrial fields, from home appliances to automobiles and office automation equipment, for purposes such as joining parts and protecting surfaces, in the form of substrate-attached adhesive sheets having an adhesive layer on a supporting substrate, or in the form of substrate-less adhesive sheets without a supporting substrate. Patent documents related to adhesive sheets include Patent Documents 1 to 3. Patent Document 1 discloses an adhesive sheet used inside a touch panel. Patent Document 2 discloses an adhesive sheet having a supporting layer made of a viscoelastic material layer having a thickness of 200 μm or more. Patent Document 3 discloses a backgrinding tape used to fix and protect semiconductor wafers in the backgrinding step of semiconductor wafer processing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-34655 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-147870 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-212441 Summary of the Invention [Problem to be solved by the invention]

[0004] Pressure-sensitive adhesive sheets are widely used as structural materials (e.g., Patent Document 1), which bond or secure components and are incorporated into articles together with the components, or as processing materials (e.g., Patent Document 3), which are temporarily attached to adherends during the manufacture, processing, or transportation of various adherends and are removed from the adherend after achieving their intended purpose. Unlike processing materials, which require removability from the adherend, pressure-sensitive adhesive sheets used as structural materials typically require long-term adhesive reliability so that they will not peel from the adherend throughout the life of the product in which they are incorporated. For example, pressure-sensitive adhesive sheets used to secure components in portable electronic devices tend to have a small adhesive area and a limited thickness due to the trend toward lighter, smaller, and thinner portable electronic devices. Typically, as the thickness of a pressure-sensitive adhesive sheet decreases, its adhesive strength decreases, so improving adhesive reliability and reducing the thickness of the pressure-sensitive adhesive sheet are in a trade-off relationship. Despite these limitations, it is necessary to maintain a good adhesive state for a long period of time.

[0005] Furthermore, various components of the above-mentioned portable electronic devices may be subjected to processing such as perforation. For example, organic electroluminescence (EL) panels and metal components used in portable electronic devices may be provided with openings for various sensors such as fingerprint sensors and camera lenses. While the processing of the above-mentioned components is usually performed before the adhesive sheet is attached, it may be beneficial in terms of production efficiency if it can be performed with the adhesive sheet attached (e.g., with the components bonded by the adhesive sheet). In such processing steps, the adhesive sheet must maintain good adhesion to the adherend even after the processing step on the adherend while attached to the adherend. For example, processing such as forming openings in a metal component may include a chemical processing step such as an etching treatment in which the non-processed portion of the metal component is masked and then immersed in an acidic etching solution. After immersion in the etching solution, the metal component may be washed with an alkaline cleaning solution or the like. Therefore, a pressure-sensitive adhesive sheet that is attached to a metal member and used in a processing step for the metal member may be exposed to an acidic etching solution or an alkaline cleaning solution together with the metal member that is the adherend, and therefore needs to have properties (acid resistance and alkali resistance) that allow it to maintain a good adhesive state, be resistant to swelling, and not lift or peel off even when exposed to acidic and alkaline liquids. If such a pressure-sensitive adhesive sheet for structural materials with excellent acid and alkali resistance were to be realized, it would be able to process the adherend while attached to the adherend, and would be practically useful.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a pressure-sensitive adhesive sheet that can maintain sufficient adhesive strength as a structural material even when exposed to acidic and alkaline liquids in a configuration with a limited thickness. Another related aim is to provide a display device and a laminate that include the pressure-sensitive adhesive sheet. [Means for solving the problem]

[0007] According to this specification, a pressure-sensitive adhesive sheet having a thickness of 100 μm or less is provided. This pressure-sensitive adhesive sheet includes a pressure-sensitive adhesive layer containing an acrylic polymer. The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of an alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at the ester terminal. The monomer component further includes a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer. With this configuration, despite having a limited thickness of 100 μm or less, the sheet can maintain sufficient adhesive strength as a structural material even when exposed to acidic and alkaline liquids.

[0008] The effect of the above-mentioned configuration is not particularly limited, but is thought to be as follows. Specifically, by using a combination of a nitrogen-containing ring-containing monomer and a carboxyl-containing monomer as monomer components of the acrylic polymer contained in the adhesive layer, a pressure-sensitive adhesive suitable for preventing the penetration of acidic and alkaline liquids into the adhesive can be formed. The combination of the nitrogen-containing ring-containing monomer and the carboxyl-containing monomer increases the cohesive strength of the adhesive. However, by using one or more suitable alkyl (meth)acrylates having an alkyl group with five or more carbon atoms at the ester terminus as the main monomer, the desired adhesive strength is more easily achieved than when using n-butyl acrylate (BA) having an alkyl group with four carbon atoms at the ester terminus. Furthermore, the wettability of the adhesive surface is improved, preventing or suppressing the penetration of acidic and alkaline liquids from the edge of the adhesive sheet to the adhesive interface. It is thought that these effects enable the adhesive sheet to maintain sufficient adhesive strength as a structural material even when exposed to acidic and alkaline liquids, despite the overall thickness being limited to 100 μm or less. The above considerations are based on the inventors' considerations on the experimental results of the examples described below, and the technology disclosed herein is not limited to the above interpretations.

[0009] In some preferred embodiments, the total amount of the nitrogen-containing ring-containing monomer and the carboxyl-containing monomer in the monomer components is 6.5% by weight or more and 40% by weight or less. In the synthesis of an acrylic polymer, by appropriately setting the total amount of the nitrogen-containing ring-containing monomer and the carboxyl-containing monomer within the above range, a pressure-sensitive adhesive having sufficient adhesive strength and capable of preventing or suppressing penetration of acidic and alkaline liquids can be preferably obtained.

[0010] In some preferred embodiments, the content of the carboxyl group-containing monomer (A C The content of the monomer having a nitrogen atom-containing ring (A N ) ratio (A N / A C ) is within the range of 1 to 40. In the synthesis of the acrylic polymer, by appropriately setting the ratio of the monomer having a nitrogen atom-containing ring and the carboxy group-containing monomer to be used within the above range, it is possible to preferably obtain a pressure-sensitive adhesive that has sufficient adhesive strength and can prevent or inhibit the penetration of acidic and alkaline liquids.

[0011] In some preferred embodiments, the monomer component contains 10% by weight or less of a hydroxyl group-containing monomer. The effects of the technology disclosed herein can be preferably realized in embodiments using an acrylic polymer containing 10% by weight or less of a hydroxyl group-containing monomer as a monomer component.

[0012] A pressure-sensitive adhesive sheet according to some embodiments is a substrate-less double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer. Substrate-less double-sided pressure-sensitive adhesive sheets can be made thinner because they do not have a substrate, which can contribute to the miniaturization and space-saving of products to which the double-sided pressure-sensitive adhesive sheet is applied. Furthermore, substrate-less pressure-sensitive adhesive sheets can maximize the effects of the pressure-sensitive adhesive layer, such as adhesive strength and impact resistance. The technology disclosed herein realizes a pressure-sensitive adhesive sheet that, without relying on a substrate, can maintain sufficient adhesive strength as a structural material even when exposed to acidic or alkaline liquids, based on the chemical structure of the acrylic polymer contained in the pressure-sensitive adhesive layer.

[0013]

[0013] In some other embodiments, the PSA sheet is a substrate-attached double-sided PSA sheet further comprising a substrate layer, and the PSA layer is provided on each side of the substrate layer. For example, a substrate-attached PSA sheet comprising a substrate such as a resin film substrate has excellent handleability and processability, and can be used in various applications by being processed into various shapes.

[0014] The pressure-sensitive adhesive sheet disclosed herein is suitable for use in fixing components constituting a portable electronic device. Specifically, the pressure-sensitive adhesive sheet can achieve highly reliable bonding and fixing even with a thickness of 100 μm or less, making it suitable for use in portable electronic devices where miniaturization and thinning are strongly desired. Furthermore, for example, various components constituting a portable electronic device, such as metal components, can be processed, for example, by forming openings for various sensors or camera lenses after the pressure-sensitive adhesive sheet is attached. Such processing steps can include steps using acidic or alkaline liquids, such as immersion in an acidic etching solution or cleaning with an alkaline cleaning solution. The pressure-sensitive adhesive sheet disclosed herein can maintain sufficient adhesive strength as a structural material even when used in a manner in which it is exposed to acidic or alkaline liquids while fixing components.

[0015] This specification also provides a display device including a display unit including a cover member and an organic EL unit, and a support unit. In this display device, an adhesive sheet having a thickness of 100 μm or less is attached to the support unit. The adhesive sheet also includes an adhesive layer containing an acrylic polymer. The acrylic polymer is a polymer of a monomer component containing 60 wt % or more of an alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at the ester terminal. The monomer component includes a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer. The adhesive sheet disclosed herein is preferably used as a component (structural material, specifically, a member joining means) of the above-mentioned display device.

[0016] This specification also provides a laminate comprising a metal member and a pressure-sensitive adhesive sheet attached to the surface of the metal member. In this laminate, the pressure-sensitive adhesive sheet has a thickness of 100 μm or less. The pressure-sensitive adhesive sheet also comprises a pressure-sensitive adhesive layer containing an acrylic polymer. The acrylic polymer is a polymer of a monomer component containing 60 wt % or more of an alkyl (meth)acrylate having an alkyl group with 5 or more carbon atoms at the ester terminal. The monomer component includes a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer. The pressure-sensitive adhesive sheet disclosed herein can be preferably used in the form of a laminate attached to a metal member that may be exposed to acidic or alkaline liquids. With this laminate, the pressure-sensitive adhesive sheet can maintain good adhesion to the metal member even when exposed to acidic or alkaline liquids for processing the metal member, even when the thickness is limited. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view schematically showing one example of the configuration of a pressure-sensitive adhesive sheet. [Figure 2] FIG. 10 is a cross-sectional view schematically showing another example of the configuration of the pressure-sensitive adhesive sheet. [Figure 3] FIG. 2 is a cross-sectional view schematically illustrating an example of a configuration of a laminate. [Figure 4] FIG. 1 is an exploded perspective view schematically illustrating a configuration example of a display device. DETAILED DESCRIPTION OF THE INVENTION

[0018] Preferred embodiments of the present invention are described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings for carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic 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.

[0019] As used herein, the term "adhesive" refers to a material that exhibits a soft solid (viscoelastic) state in a temperature range around room temperature and has the property of easily adhering to an adherend by pressure, as described above. The adhesive referred to here is generally a material having a complex tensile modulus E * (1Hz)<10 7 dyne / cm 2 The material may be a material having the properties satisfying the above (typically, a material having the above properties at 25°C).

[0020] <Adhesive sheet composition> The PSA sheet disclosed herein may be a substrate-attached PSA sheet having the PSA layer on one or both sides of a non-releasable substrate (support substrate), or may be a substrate-less PSA sheet (i.e., a PSA sheet without a non-releasable substrate) in which the PSA layer is supported on a release liner. In some preferred embodiments, the PSA sheet is in the form of a double-sided PSA sheet. Double-sided PSA sheets can be bonded to adherends by attaching each side to the adherend, and are therefore preferably used as structural materials for bonding or fixing components. The concept of PSA sheet here may include those referred to as PSA tapes, PSA labels, PSA films, etc. The PSA sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, the PSA sheet may be processed into various shapes.

[0021] An example of the structure of a double-sided adhesive substrateless PSA sheet (substrateless double-sided PSA sheet) is shown in FIG. 1. The PSA sheet 1 shown in FIG. 1 has a configuration in which both sides 21A and 21B of a substrateless PSA layer 21 are protected by release liners 31 and 32, respectively, with at least the PSA layer side serving as a release surface. Alternatively, the PSA sheet may have a configuration in which one surface (adhesive surface, first adhesive surface) of the substrateless PSA layer is protected by a release liner with both surfaces serving as release surfaces, and when rolled up, the other surface (adhesive surface, second adhesive surface) of the PSA layer abuts against the back surface of the release liner, thereby enabling the second adhesive surface of the PSA layer to also be protected by the release liner. The technology disclosed herein can be preferably implemented in such a substrateless form from the perspective of reducing the thickness of the PSA sheet. Substrateless PSA sheets are advantageous in that they are easily thinned and can maximize the PSA properties, such as adhesive strength and impact resistance.

[0022] The pressure-sensitive adhesive sheet disclosed herein may have, for example, the cross-sectional structure shown schematically in FIG. 2. The pressure-sensitive adhesive sheet 2 shown in FIG. 2 has a configuration in which pressure-sensitive adhesive layers 21 and 22 (also referred to as first pressure-sensitive adhesive layer 21 and second pressure-sensitive adhesive layer 22, respectively) are provided on each side (both of which are non-releasable) of a substrate (substrate layer) 10, and these pressure-sensitive adhesive layers are protected by release liners 31 and 32, at least the pressure-sensitive adhesive layer side of which serves as a release surface. Alternatively, the pressure-sensitive adhesive sheet may have a configuration in which pressure-sensitive adhesive layers (first pressure-sensitive adhesive layer and second pressure-sensitive adhesive layer) are provided on each side (both of which are non-releasable) of the substrate, and one of these pressure-sensitive adhesive layers (first pressure-sensitive adhesive layer) is protected by a release liner having release surfaces on both sides. This type of pressure-sensitive adhesive sheet can be configured so that the other pressure-sensitive adhesive layer (second pressure-sensitive adhesive layer) is also protected by the release liner by rolling the pressure-sensitive adhesive sheet and abutting the other pressure-sensitive adhesive layer (second pressure-sensitive adhesive layer) against the back surface of the release liner.

[0023] <Adhesive layer> (acrylic polymer) The pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet disclosed herein contains an acrylic polymer. The pressure-sensitive adhesive layer is typically a pressure-sensitive adhesive layer in which the acrylic polymer is the base polymer (the main component of the polymer components, i.e., a component accounting for 50% by weight or more). Such a pressure-sensitive adhesive layer is also called an acrylic pressure-sensitive adhesive layer. The base polymer refers to the main component of the rubber-like polymer (a polymer that exhibits rubber elasticity in a temperature range around room temperature) contained in the pressure-sensitive adhesive layer. In this specification, unless otherwise specified, the term "main component" refers to a component that is contained in an amount of more than 50% by weight.

[0024] In this specification, "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, and is also referred to as an acrylic polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule will also be referred to as an "acrylic monomer." Furthermore, "(meth)acryloyl" refers collectively to acryloyl and methacryloyl. Similarly, "(meth)acrylate" refers collectively to acrylate and methacrylate, and "(meth)acrylic" refers collectively to acrylic and methacrylic, respectively.

[0025] The acrylic polymer disclosed herein is a polymer of a monomer component containing an alkyl(meth)acrylate having an alkyl group having 5 or more carbon atoms at the ester terminal (hereinafter also referred to as "C5 or higher alkyl(meth)acrylate"). The C5 or higher alkyl(meth)acrylate can also be represented by the following formula (1): CH2=C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. 2 is a linear alkyl group having 5 or more carbon atoms. By using an acrylic polymer containing a C5 or higher alkyl (meth)acrylate as the main monomer component, sufficient adhesive strength is easily obtained, the wettability of the adhesive surface is improved, and the penetration of acidic and alkaline liquids from the edge of the adhesive sheet to the adhesive interface is suppressed. The number of carbon atoms in the alkyl group of the C5 or higher alkyl (meth)acrylate is typically 5 to 20 (hereinafter, this range of carbon atoms may be referred to as "C5-20"). The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate may be, for example, 18 or less, and from the viewpoint of the storage modulus of the adhesive, it is appropriate to have 14 or less, preferably 12 or less, and more preferably 10 or less (e.g., 9 or less). The number of carbon atoms may also be 6 or more, or 7 or more, and is typically 8.

[0026] Specific examples of C5 or higher alkyl (meth)acrylates include, but are not limited to, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, 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. The alkyl (meth)acrylates can be used alone or in combination of two or more. A suitable example of the alkyl (meth)acrylate is 2-ethylhexyl acrylate (2EHA).

[0027] The proportion of C5 or higher alkyl (meth)acrylate in the monomer components constituting the acrylic polymer is 60% by weight or more. This allows the effects of using C5 or higher alkyl (meth)acrylate to be fully realized. The proportion of C5 or higher alkyl (meth)acrylate is suitably 65% ​​by weight or more, preferably 70% by weight or more (e.g., more than 70% by weight), and may be 75% by weight or more. The upper limit of the proportion of C5 or higher alkyl (meth)acrylate is set in consideration of the properties (e.g., cohesive strength) based on the copolymerization of a nitrogen atom-containing ring-containing monomer and a carboxy group-containing monomer, which will be described later. For example, it is suitably 95% by weight or less. From the viewpoint of adhesive strength, cohesive strength, etc., it may be 93.5% by weight or less, preferably 90% by weight or less, more preferably 85% by weight or less, for example, 80% by weight or less.

[0028] The acrylic polymer disclosed herein may contain, as a monomer component, one or more alkyl(meth)acrylates having an alkyl group having 4 or less carbon atoms at the ester terminal (C1-4 alkyl(meth)acrylates). Specific examples of C1-4 alkyl(meth)acrylates include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, and t-butyl(meth)acrylate.

[0029] The proportion of C5 or higher alkyl (meth)acrylate in the entire alkyl (meth)acrylate having a chain alkyl group at the ester terminal, which is contained as a monomer component of the acrylic polymer (hereinafter simply referred to as "alkyl (meth)acrylate"), is, for example, more than 70% by weight, and from the viewpoint of effectively exhibiting the effects of using the C5 or higher alkyl (meth)acrylate, is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more (e.g., 99% by weight or more). The upper limit of the proportion of C5 or higher alkyl (meth)acrylate in the entire alkyl (meth)acrylate is 100% by weight, and may be, for example, 95% by weight or less, or 90% by weight or less.

[0030] The monomer components constituting the acrylic polymer include a monomer having a nitrogen atom-containing ring (hereinafter also referred to as "N-ring-containing monomer") and a carboxyl group-containing monomer. By using the N-ring-containing monomer and the carboxyl group-containing monomer together as the monomer components, the cohesive strength of the PSA is improved, and in combination with the effects of both monomers, a PSA can be obtained that prevents or suppresses the penetration of acidic and alkaline liquids into the PSA.

[0031] The N-ring-containing monomer refers to a monomer having a polymerizable group and a nitrogen-atom-containing ring. Examples of the polymerizable group include a (meth)acryloyl group and a vinyl group. The nitrogen-atom-containing ring refers to a cyclic structure containing a nitrogen atom (N) as a ring-constituting atom. The nitrogen-atom-containing ring typically has a heterocyclic structure containing a nitrogen atom (N) and a carbon atom (C) as ring-constituting atoms, and is preferably one further containing an oxygen atom (O) as a ring-constituting atom. Examples of the nitrogen-atom-containing ring include lactam structures such as pyrrolidone, morpholine rings, piperidine rings, pyrrolidine rings, piperazine rings, pyridine rings, piperidone rings, pyrimidine rings, pyrazine rings, pyrrole rings, imidazole rings, and oxazole rings. Among these, lactam structures and morpholine rings are preferred, and morpholine rings are particularly preferred. The N-ring-containing monomers can be used alone or in combination of two or more.

[0032] Examples of N-ring-containing monomers include lactam vinyl monomers such as N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, and N-vinyl-ε-caprolactam; vinylpyridine; vinylpiperidone; vinylpyrimidine; vinylpiperazine; vinylpyrazine; vinylpyrrole; vinylimidazole; vinyloxazole; vinylmorpholine; N-(meth)acryloylmorpholine; N-(meth)acryloylpiperidine; N-(meth)acryloylpyrrolidine; and the like. Among these, lactam vinyl monomers and N-(meth)acryloylmorpholine are preferred, and N-vinyl-2-pyrrolidone (NVP) and N-acryloylmorpholine (ACMO) are more preferred. Using NVP tends to provide higher adhesive strength, while using ACMO makes it easier to achieve a good balance between adhesive strength and cohesive strength.

[0033] The amount of the N-ring-containing monomer used is set within a range that ensures the effect of its combined use with the carboxyl group-containing monomer. The content of the N-ring-containing monomer is, for example, 5% by weight or more of the total monomer components, preferably 10% by weight or more, more preferably 16% by weight or more, even more preferably 20% by weight or more, particularly preferably 22% by weight or more, and may be 28% by weight or more (e.g., 32% by weight or more). The greater the amount of the N-ring-containing monomer used, the more improved the cohesive strength and the more effectively the pressure-sensitive adhesive can be prevented from permeating acidic and alkaline liquids. The content of the N-ring-containing monomer is, for example, 40% by weight or less of the total monomer components, and may be 35% by weight or less, or even 30% by weight or less. Limiting the amount of the N-ring-containing monomer used within an appropriate range makes it easy to achieve both adhesive strength and cohesive strength.

[0034] Furthermore, the use of a carboxyl group-containing monomer as a monomer component facilitates the production of a pressure-sensitive adhesive sheet that exhibits favorable adhesive properties (such as cohesive strength), which can be advantageous in improving the adhesion between the pressure-sensitive adhesive layer and the adherend. The acid resistance of the pressure-sensitive adhesive also tends to improve. Furthermore, in embodiments in which a black colorant such as carbon black is blended into the pressure-sensitive adhesive, copolymerizing an appropriate amount of a carboxyl group-containing monomer facilitates favorable dispersion of the colorant within the layer, thereby maintaining favorable adhesive properties.

[0035] Examples of carboxyl group-containing monomers that can be used include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Of these, AA and MAA are preferred. The carboxyl group-containing monomers can be used alone or in combination of two or more.

[0036] The content of the carboxyl group-containing monomer in the monomer component is set within a range that ensures the effect of its combined use with the N-ring-containing monomer. The carboxyl group-containing monomer can be, for example, 0.2% by weight or more (typically 0.5% by weight or more) of the monomer component, suitably 1% by weight or more, preferably 1.5% by weight or more, more preferably 2.0% by weight or more, and even more preferably 2.5% by weight or more. By increasing the content of the carboxyl group-containing monomer, even greater effects are exhibited. There is no particular upper limit to the content of the carboxyl group-containing monomer, and it can be, for example, 10% by weight or less, suitably 7% by weight or less, preferably 5% by weight or less, more preferably 4.5% by weight or less, even more preferably 4.0% by weight or less, and may be, for example, 3.5% by weight or less.

[0037] In some embodiments, the total proportion of the N-ring-containing monomer and the carboxyl group-containing monomer in the monomer component is, for example, in the range of 5% by weight to 40% by weight, preferably 6.5% by weight to 40% by weight. By appropriately setting the total amount of the N-ring-containing monomer and the carboxyl group-containing monomer, a PSA having sufficient adhesive strength and improved cohesive strength, suitable for preventing the penetration of acidic and alkaline liquids, can be preferably obtained. In some preferred embodiments, the total proportion of the N-ring-containing monomer and the carboxyl group-containing monomer in the monomer component is 8% by weight or more, more preferably 12% by weight or more, even more preferably 15% by weight or more, particularly preferably 18% by weight or more, and may be 21% by weight or more, 23% by weight or more, or even 26% by weight or more. Furthermore, the total proportion of the N-ring-containing monomer and the carboxyl group-containing monomer in the monomer component is suitably 36% by weight or less, preferably 32% by weight or less, or even 30% by weight or less. By limiting the total amount of the N-ring-containing monomer and the carboxyl group-containing monomer within an appropriate range, adhesive strength and cohesive strength can be more effectively achieved.

[0038] The ratio of the N-ring-containing monomer to the carboxyl group-containing monomer is set within a range in which the effects of the technology disclosed herein are exhibited. In some embodiments, the content of the carboxyl group-containing monomer used as a monomer component (A C The content of N-ring-containing monomers (A N ) ratio (A N / A C The ratio (A) can be set within the range of 1 to 40 by weight. By appropriately setting the ratio of the N-ring-containing monomer and the carboxyl group-containing monomer used within the above range, it is possible to obtain a pressure-sensitive adhesive that has sufficient adhesive strength and is suitable for preventing the penetration of acidic and alkaline liquids. N / A C From the viewpoint of effectively exerting the effect of using the N-ring-containing monomer, the ratio (A) is preferably 3 or more, more preferably 5 or more, and even more preferably 7 or more, and may be 8 or more. N / A C ) is preferably 30 or less, more preferably 25 or less, even more preferably 20 or less, particularly preferably 15 or less, and may be 10 or less, from the viewpoint of effectively exerting the effects of using the carboxy group-containing monomer.

[0039] In some embodiments, the monomer component may contain a hydroxyl group-containing monomer. Use of a hydroxyl group-containing monomer can adjust the cohesive strength and crosslink density of the adhesive, thereby adjusting the adhesive strength and cohesive strength within a preferred range. Examples of hydroxyl group-containing monomers 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. One type of hydroxyl group-containing monomer can be used alone, or two or more types can be used in combination.

[0040] The monomer components may or may not contain a hydroxyl group-containing monomer. In some embodiments, the content of the hydroxyl group-containing monomer is, for example, less than 15% by weight of the total monomer components, suitably 10% by weight or less, 8% by weight or less, 5% by weight or less, or 3% by weight or less. According to the technology disclosed herein, the desired effect can be achieved with or without the use of a small amount of hydroxyl group-containing monomer. In some preferred embodiments, the amount of hydroxyl group-containing monomer is less than 2% by weight of the total monomer components, or may be less than 1.0% by weight, less than 0.5% by weight, or less than 0.3% by weight. Furthermore, when a hydroxyl group-containing monomer is used, the amount used is not particularly limited, and the content of the hydroxyl group-containing monomer may be, for example, 0.01% by weight or more, 0.03% by weight or more, 0.05% by weight or more, or 0.1% by weight or more of the total monomer components.

[0041] The acrylic polymer in the technology disclosed herein may be copolymerized with other copolymerizable monomers (monomers other than linear alkyl (meth)acrylates, N-ring-containing monomers, carboxyl group-containing monomers, and hydroxyl group-containing monomers) within the scope that does not impair the effects of the invention. Examples of other copolymerizable monomers that can be used include functional group-containing monomers such as 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, alkoxysilyl group-containing monomers, and imide group-containing monomers. The above functional group-containing monomers may be used alone or in combination of two or more.

[0042] Other examples of copolymerizable monomers include vinyl ester monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene, etc.), and vinyltoluene; 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-based 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-based monomers such as methyl vinyl ether and ethyl vinyl ether; and 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.

[0043] The monomer components constituting the acrylic polymer may or may not contain the other copolymerizable monomers. The amount of the other copolymerizable monomers is not particularly limited and may be appropriately selected depending on the purpose and application. The content of the other copolymerizable monomers in the monomer components is, for example, suitably less than 30% by weight, preferably less than 10% by weight, more preferably less than 5% by weight, and may be less than 3% by weight (e.g., less than 1% by weight). The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer components are substantially free of other copolymerizable monomers. Here, "substantially free of other copolymerizable monomers" means that other copolymerizable monomers are not used at least intentionally, and the unintentional inclusion of other copolymerizable monomers, for example, at about 0.01% by weight or less, is acceptable.

[0044] The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization can be preferably employed. The polymerization temperature during solution polymerization can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, and the like, and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0045] The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents (toluene, ethyl acetate, etc.). The initiator used in polymerization can be appropriately selected from conventionally known polymerization initiators (for example, azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN), peroxide-based initiators, etc.) depending on the type of polymerization method. The amount of polymerization initiator used may be a normal amount, and can be selected, for example, from the range of 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 components.

[0046] The molecular weight of the acrylic polymer obtained by appropriately employing the above-mentioned various polymerization methods is not particularly limited and can be set within an appropriate range depending on the required performance, etc. In some embodiments, the weight-average molecular weight (Mw) of the polymer is about 10 × 10 4 ~500×10 4 From the viewpoint of achieving a good balance between adhesive strength and cohesive strength, the Mw may be in the range of about 30×10 4 From the viewpoint of adhesive reliability, it is preferable that the thickness is about 50×10 4 More preferably, approximately 70×10 4 More preferably, approximately 90×10 4 That's 100 x 10 4 The upper limit of Mw of the polymer may be approximately 300 × 10 4 It may be less than 200 × 10 4 Below (for example, approximately 150 x 10 4 For example, the Mw of the polymer obtained by solution polymerization can preferably be in the above range. Here, Mw refers to a value calculated as standard polystyrene by GPC (gel permeation chromatography). As the GPC apparatus, for example, a model "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) can be used. The same applies to the examples described later.

[0047] (tackifying resin) The pressure-sensitive adhesive layer can contain a tackifying resin, thereby increasing the adhesive strength of the pressure-sensitive adhesive sheet. The tackifying resin can be one or more selected from various known tackifying resins, such as rosin-based tackifying resins, phenol-based tackifying resins, terpene-based tackifying resins, modified terpene-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, elastomer-based tackifying resins, and ketone-based tackifying resins. For example, rosin-based tackifying resins, phenol-based tackifying resins, terpene-based tackifying resins, modified terpene-based tackifying resins, and hydrocarbon-based tackifying resins are preferred, with rosin-based tackifying resins being more preferred.

[0048] Specific examples of rosin-based tackifying resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; modified rosins obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.; the same applies hereinafter); and various other rosin derivatives. Examples of the rosin derivatives include rosin esters such as those obtained by esterifying unmodified rosin with alcohols (i.e., esterified rosin) and those obtained by esterifying modified rosin with alcohols (i.e., esterified modified rosin); unsaturated fatty acid-modified rosins obtained by modifying unmodified rosin or modified rosin with unsaturated fatty acid; unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acid; rosin alcohols obtained by reducing the carboxyl groups of unmodified rosin, modified rosin, unsaturated fatty acid-modified rosin, or unsaturated fatty acid-modified rosin esters; metal salts of rosins (particularly rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; and rosin phenolic resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) using an acid catalyst and then thermally polymerizing the resulting mixture. Although not particularly limited, specific examples of rosin esters include esters of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), such as methyl ester, triethylene glycol ester, glycerin ester, pentaerythritol ester, etc. Among these, rosin ester is preferred. The rosin-based tackifying resins can be used alone or in combination of two or more.

[0049] Examples of phenolic tackifying resins include terpene phenolic resins, hydrogenated terpene phenolic resins, and alkyl phenolic resins. Terpene phenolic resin refers to a polymer containing terpene residues and phenol residues, and is a concept that encompasses both copolymers of terpenes and phenolic compounds (terpene-phenol copolymer resins) and phenol-modified terpene homopolymers or copolymers of terpenes (phenol-modified terpene resins). Suitable examples of terpenes that constitute such terpene phenolic resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d / l- (dipentene) forms). Hydrogenated terpene phenolic resins have a structure obtained by hydrogenating such terpene phenolic resins. They are also sometimes called hydrogenated terpene phenolic resins. Alkylphenol resins are resins (oil-based phenolic resins) obtained from alkylphenols and formaldehyde. Examples of alkylphenol resins include novolac and resol types.

[0050] 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 polymers, β-pinene polymers, and dipentene polymers. Examples of modified terpene resins include those obtained by modifying the above-mentioned terpene resins. Specific examples include styrene-modified terpene resins and hydrogenated terpene resins.

[0051] Examples of hydrocarbon-based tackifying resins include various hydrocarbon-based 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.

[0052] A suitable example of the tackifier resin is a rosin-based tackifier resin. Among these, rosin esters are preferably used. The proportion of the rosin-based tackifier resin in the total tackifier resin contained in the PSA layer can be, for example, more than approximately 50% by weight, or may be approximately 70% by weight or more, or may be approximately 80% by weight or more. The technology disclosed herein can be preferably implemented in an embodiment in which substantially all of the tackifier resin (for example, approximately 97% by weight or more, or 99% by weight or more, or even 100% by weight) is a rosin-based tackifier resin.

[0053] The softening point of the tackifier resin is not particularly limited. From the viewpoint of exerting an appropriate cohesive force, the softening point of the tackifier resin may be, for example, about 50°C or higher, preferably about 60°C or higher, or may be about 70°C or higher. The upper limit of the softening point of the tackifier resin is not particularly limited. From the viewpoint of improving adhesion to the adherend, in some embodiments, a tackifier resin having a softening point of about 200°C or lower (more preferably about 150°C or lower, for example, less than 130°C) can be preferably used.

[0054] In some preferred embodiments, the tackifier resin is a tackifier resin T having a softening point of 110° C. or less. L Tackifying resin T L By using this tackifier resin, adhesion to the adherend (initial adhesion, etc.) is improved, good adhesive strength is easily obtained, and it is easy to prevent the penetration of acidic or alkaline liquids into the adhesive interface. L The softening point of the tackifier resin T is suitably less than 110°C, preferably about 105°C or less, more preferably about 100°C or less, even more preferably about 95°C or less (for example, less than 95°C), and particularly preferably about 90°C or less (for example, about 85°C or less). L The lower limit of the softening point of the tackifier resin T L From the viewpoint of exerting an appropriate cohesive force, the softening point of the adhesive may be, for example, about 50°C or higher, about 60°C or higher, about 65°C or higher, or about 70°C or higher.

[0055] Although not particularly limited, tackifier resin T L Examples of rosin-based tackifying resins that can be preferably used as the tackifying resin include rosin esters such as unmodified rosin ester and modified rosin ester. A preferred example of a modified rosin ester is hydrogenated rosin ester. For example, rosin esters such as methyl ester and glycerin ester of unmodified rosin or modified rosin (e.g., hydrogenated rosin) can be used as the tackifying resin T. L In some preferred embodiments, the pressure-sensitive adhesive layer can be formed by using a tackifying resin T L Contains hydrogenated rosin ester. Tackifying resin T L may contain only one or more hydrogenated rosin esters as the rosin esters.

[0056] Tackifying resin T L The tackifying resin may contain other tackifying resins in addition to the rosin-based tackifying resin. The other tackifying resins may be selected from the tackifying resins exemplified above, each having a softening point of 110°C or less, and may be used singly or in combination of two or more.

[0057] In some embodiments, tackifying resin T L The proportion of the rosin-based tackifying resin in the total can be, for example, more than about 50% by weight, or may be about 65% by weight or more, or may be about 75% by weight or more. L This can be preferably implemented in an embodiment in which substantially all of (for example, approximately 97% by weight or more, or 99% by weight or more, or even 100% by weight) is a rosin-based tackifying resin.

[0058] The adhesive layer is made of tackifying resin T L The tackifier resin T may or may not be included. L The amount of tackifier resin T used (the total amount when two or more types of tackifier resins are used) is set so as to achieve the effects of the technology disclosed herein. LThe content of the tackifier resin T can be appropriately set, for example, within a range of about 60 parts by weight or less per 100 parts by weight of the acrylic polymer, and from the viewpoint of cohesive strength, etc., it is suitably 50 parts by weight or less, preferably 45 parts by weight or less, more preferably 40 parts by weight or less, and may be 35 parts by weight or less. L In an embodiment comprising the above, the tackifier resin T L The amount of tackifier resin T L In order to ensure the effect of the inclusion, it is appropriate to add about 1 part by weight or more, and in some preferred embodiments, from the viewpoint of improving adhesive strength, it is appropriate to add 5 parts by weight or more, and it may be 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, or 25 parts by weight or more. In some other embodiments, the adhesive layer contains tackifier resin T L In this embodiment, the pressure-sensitive adhesive layer is substantially free of tackifying resin T L It is acceptable for the content to be about 0.3% by weight or less (for example, 0.1% by weight or less, typically 0.01% by weight or less).

[0059] In some embodiments, the pressure-sensitive adhesive layer comprises a tackifying resin T having a softening point of 110°C or less. L and tackifying resin T having a softening point of more than 110°C (typically more than 110°C and up to 200°C). H Tackifying resin T may be contained in combination. L and tackifying resin T H By using it in combination with Tackifying Resin T, it is easy to achieve higher adhesive strength. H As the tackifier resin, one of the tackifier resins exemplified above, which have a softening point of more than 110°C, can be used alone or in combination of two or more. H Preferably, the tackifying resin T contains one or more rosin-based tackifying resins. L and tackifying resin T H It is more preferable that both of the adhesive and the tackifier contain a rosin-based tackifier resin.

[0060] Tackifying resin T HFrom the viewpoint of improving cohesive strength, the softening point of the tackifier resin T may be about 115°C or higher, about 120°C or higher, about 130°C or higher, or about 140°C or higher. H There is no particular upper limit to the softening point of the tackifier resin, and from the viewpoint of adhesion to the adherend, a tackifier resin having a softening point of about 200°C or less (more preferably about 160°C or less, even more preferably 145°C or less, for example, about 130°C or less) can be preferably used.

[0061] The adhesive layer is made of tackifying resin T H The tackifier resin T may or may not be included. H The amount of tackifier resin T used (the total amount when two or more types of tackifier resins are used) is set so as to achieve the effects of the technology disclosed herein. H The content of the tackifier resin T is suitably, for example, less than 30 parts by weight, preferably less than 20 parts by weight, and may be 18 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. H In an embodiment comprising the above, the tackifier resin T H The amount of tackifier resin T H In order to ensure the effect of the inclusion, it is appropriate to add about 1 part by weight or more, and in some embodiments, from the viewpoint of improving adhesive strength, it is appropriate to add 5 parts by weight or more, and it may be 10 parts by weight or more, or even 12 parts by weight or more. H It can also be preferably implemented in an embodiment that is substantially free of

[0062] The softening point of the tackifying resin is defined as the value measured using the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at the lowest possible temperature and carefully filled into a ring placed on a flat metal plate, avoiding the formation of bubbles. After cooling, the raised portion of the ring, including the top edge, is cut off with a slightly heated knife. Next, a holder (ring stand) is placed in a glass container (heating bath) with a diameter of at least 85 mm and a height of at least 127 mm, and glycerin is poured into it to a depth of at least 90 mm. Next, a steel ball (9.5 mm diameter, 3.5 g weight) and the ring filled with the sample are immersed in the glycerin without touching each other, and the glycerin temperature is maintained at 20°C ± 5°C for 15 minutes. Next, the steel ball is placed in the center of the surface of the sample in the ring and placed in its fixed position on the holder. Next, keeping the distance from the top of the ring to the glycerin surface at 50 mm, place a thermometer, and heat the container with the center of the thermometer's mercury bulb at the same height as the center of the ring. The flame of the Bunsen burner used for heating should be aimed halfway between the center of the bottom and the edge of the container, and heating should be uniform. After heating begins and the temperature reaches 40°C, the rate of increase in the bath temperature must be 5.0 ± 0.5°C per minute. The sample gradually softens and flows down the ring, and the temperature is read when it finally touches the bottom plate, and this is the softening point. The softening point should be measured for two or more samples at the same time, and the average value should be used.

[0063] The technology disclosed herein can be implemented in both embodiments in which the PSA layer contains a tackifier resin and embodiments in which the PSA layer does not contain a tackifier resin. The amount of tackifier resin used (the combined amount (total amount) when two or more tackifier resins are used) is set so as to achieve the effects of the technology disclosed herein. The content of the tackifier resin in the PSA layer can be appropriately set within a range of, for example, about 100 parts by weight or less per 100 parts by weight of the acrylic polymer. From the viewpoint of cohesive strength, etc., it is appropriate to set it to 60 parts by weight or less, and preferably 50 parts by weight or less (e.g., 40 parts by weight or less). In embodiments in which the PSA layer contains a tackifier resin, the content of the tackifier resin per 100 parts by weight of the acrylic polymer is appropriate to be about 1 part by weight or more so that the effects of the tackifier resin are achieved. In some preferred embodiments, from the viewpoint of improving adhesive strength, etc., it is appropriate to set it to 5 parts by weight or more, preferably 10 parts by weight or more, and may be 15 parts by weight or more, 20 parts by weight or more, or 25 parts by weight or more. In some other embodiments, the PSA layer is substantially free of tackifier resins. In these embodiments, it is acceptable for the PSA layer to contain about 0.3% by weight or less (e.g., 0.1% by weight or less, typically 0.01% by weight or less) of tackifier resins.

[0064] (Crosslinking agent) In the technology disclosed herein, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer may contain a crosslinking agent, if necessary. By using an appropriate type and amount of crosslinking agent relative to other components (such as an acrylic polymer or a tackifying resin) in the pressure-sensitive adhesive layer, the properties of the pressure-sensitive adhesive can be adjusted, allowing for the creation of a pressure-sensitive adhesive with desired properties. The type of crosslinking agent is not particularly limited, and an appropriate crosslinking agent can be 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, 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, hydrazine-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. 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, with isocyanate-based crosslinking agents and epoxy-based crosslinking agents being more preferred. The crosslinking agent can be used alone or in combination of two or more. The crosslinking agent is contained in the pressure-sensitive adhesive layer in the form after crosslinking reaction, the form before crosslinking reaction, the form after partial crosslinking reaction, or an intermediate or composite form thereof. The crosslinking agent is typically contained in the pressure-sensitive adhesive layer exclusively in the form after crosslinking reaction.

[0065] In some preferred embodiments, an isocyanate-based crosslinking agent is used as the crosslinking agent. Polyfunctional isocyanates (compounds having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used as the isocyanate-based crosslinking agent. The isocyanate-based crosslinking agents can be used alone or in combination of two or more.

[0066] Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates. Specific examples of aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 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.

[0067] 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.

[0068] 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, Examples of the diisocyanate include 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, and xylylene-1,3-diisocyanate.

[0069] A preferred example of a polyfunctional isocyanate is one 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 (for example, 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 those manufactured by Asahi Kasei Chemicals Corporation under the trade name "Duranate TPA-100," and those manufactured by Tosoh Corporation under the trade names "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096."

[0070] The amount of the isocyanate crosslinking agent used is not particularly limited. For example, it can be approximately 0.5 parts by weight or more per 100 parts by weight of the acrylic polymer. From the viewpoints of achieving both cohesive strength and adhesiveness and impact resistance, the amount of the isocyanate crosslinking agent used per 100 parts by weight of the acrylic polymer can be, for example, 1.0 part by weight or more, and may be 1.5 parts by weight or more (e.g., 2.0 parts by weight or more). On the other hand, from the viewpoint of improving adhesiveness to the adherend, the amount of the isocyanate crosslinking agent used is suitably 10 parts by weight or less per 100 parts by weight of the acrylic polymer, and may be 8 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less (e.g., less than 3 parts by weight).

[0071] Other suitable examples of the crosslinking agent include epoxy-based crosslinking agents. As the epoxy-based crosslinking agent, a compound having two or more epoxy groups in one molecule can be used without any particular limitation. Epoxy-based crosslinking agents having 3 to 5 epoxy groups in one molecule are preferred. The epoxy-based crosslinking agents can be used alone or in combination of two or more.

[0072] Non-limiting examples of epoxy crosslinking agents include 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 Mitsubishi Gas Chemical Company, Inc.'s trade names "TETRAD-C" and "TETRAD-X," DIC Corporation's trade name "Epiclon CR-5L," Nagase ChemteX Corporation's trade name "Denacol EX-512," and Nissan Chemical Industries, Ltd.'s trade name "TEPIC-G."

[0073] The amount of epoxy-based crosslinking agent used is not particularly limited. For example, the amount of epoxy-based crosslinking agent used can be more than 0 part by weight and approximately 1 part by weight or less (typically, approximately 0.001 to 0.5 parts by weight) per 100 parts by weight of the acrylic polymer. From the viewpoint of optimally exhibiting the effect of improving cohesive strength, the amount of epoxy-based crosslinking agent used is suitably approximately 0.005 parts by weight or more per 100 parts by weight of the acrylic polymer, preferably approximately 0.01 parts by weight or more, more preferably approximately 0.02 parts by weight or more, and even more preferably approximately 0.03 parts by weight or more. Furthermore, from the viewpoint of improving adhesion to the adherend, the amount of epoxy-based crosslinking agent used is suitably approximately 0.5 parts by weight or less per 100 parts by weight of the acrylic polymer, preferably approximately 0.2 parts by weight or less, more preferably less than 0.1 parts by weight, and even more preferably 0.07 parts by weight or less (for example, approximately 0.05 parts by weight or less). Impact resistance also tends to improve by reducing the amount of epoxy-based crosslinking agent used.

[0074] In some preferred embodiments, the crosslinking agent is a combination of an isocyanate-based crosslinking agent and 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.

[0075] 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. For example, by using an isocyanate crosslinking agent and an epoxy crosslinking agent in combination, it is easy to achieve both cohesion and impact resistance.

[0076] In the technology disclosed herein, the relationship between the content of the isocyanate crosslinking agent and the content of the non-isocyanate crosslinking agent (e.g., epoxy crosslinking agent) is not particularly limited. The content of the non-isocyanate crosslinking agent can be, for example, approximately 1 / 10 or less of the content of the isocyanate crosslinking agent. From the viewpoint of more suitably achieving both adhesion to the adherend and cohesive strength, the content of the non-isocyanate crosslinking agent is suitably approximately 1 / 20 or less of the content of the isocyanate crosslinking agent on a weight basis, and preferably approximately 1 / 30 or less (e.g., 1 / 40 or less). Furthermore, from the viewpoint of optimally exerting the effect of using an isocyanate-based crosslinking agent in combination with a non-isocyanate-based crosslinking agent (for example, an epoxy-based crosslinking agent), the content of the non-isocyanate-based crosslinking agent is suitably approximately 1 / 1000 or more of the content of the isocyanate-based crosslinking agent, for example, approximately 1 / 500 or more, and may also be approximately 1 / 300 or more, approximately 1 / 100 or more, or approximately 1 / 60 or more.

[0077] The total amount of the crosslinking agent used (total quantity) is not particularly limited, and can be, for example, about 10 parts by weight or less, preferably about 0.005 to 10 parts by weight, and more preferably about 0.01 to 5 parts by weight, per 100 parts by weight of the acrylic polymer.

[0078] (coloring agent) The pressure-sensitive adhesive layer may or may not contain a colorant. The inclusion of a colorant allows the optical transparency (light-blocking properties) of the pressure-sensitive adhesive layer to be adjusted. Adjusting the optical transparency of the pressure-sensitive adhesive layer can also be useful for adjusting the optical transparency of a pressure-sensitive adhesive sheet containing the pressure-sensitive adhesive layer. The colorant can be any of a variety of materials capable of attenuating light traveling through the pressure-sensitive adhesive layer by reflecting and / or absorbing it. The color of the colorant is not particularly limited and may be, for example, black, gray, white, red, blue, yellow, green, yellow-green, orange, purple, gold, silver, pearlescent, etc. The colorant is typically contained in the pressure-sensitive adhesive layer in a dispersed state (which may be dissolved) in the constituent materials of the pressure-sensitive adhesive layer.

[0079] Various pigments and dyes can be used as colorants. Examples of pigments include inorganic pigments such as 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, calcined spinel, chromate, chrome vermilion, Prussian blue, aluminum powder, bronze powder, silver powder, and calcium phosphate, and organic pigments such as phthalocyanine, azo, condensed azo, azo lake, anthraquinone, perylene-perinone, indigo, thioindigo, isoindolinone, azomethine, dioxazine, quinacridone, aniline black, triphenylmethane, and carbon black. Examples of dyes include azo dyes, anthraquinone, quinophthalone, styryl, diphenylmethane, triphenylmethane, oxazine, triazine, xanthan, methane, azomethine, acridine, and diazine. The colorants can be used alone or in appropriate combination of two or more.

[0080] Black colorants are preferred because light-blocking properties can be efficiently adjusted with a small amount of colorant. Specific examples of black colorants include carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, pine soot, etc.), graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, hematite, activated carbon, ferrite (non-magnetic ferrite, magnetic ferrite, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complexes, and anthraquinone-based colorants. These can be used alone or in appropriate combinations of two or more. Carbon black is particularly preferred. Surface-modified carbon black particles having functional groups such as carboxy groups, amino groups, sulfonic acid groups, and silicon-containing groups (e.g., alkoxysilyl groups and alkylsilyl groups) can also be used as carbon black particles. Such surface-modified carbon black particles, also known as self-dispersing carbon black, eliminate the need for or reduce the amount of dispersant added. The carbon black particles can be used alone or in combination of two or more.

[0081] Since the light-blocking properties of the pressure-sensitive adhesive layer can be efficiently adjusted with a small amount of colorant, a particulate colorant (pigment) can be preferably used. In some preferred embodiments, a colorant (e.g., a particulate black colorant such as carbon black) having an average particle size of about 10 nm or more (e.g., about 30 nm or more) can be used. The average particle size is, for example, about 50 nm or more, or may be about 100 nm or more, or may be about 150 nm or more. There is no particular upper limit to the average particle size of the colorant, and it may be, for example, about 3000 nm or less, or may be about 1000 nm or less. From the viewpoint of improving light-blocking properties, the average particle size of the colorant is suitably about 500 nm or less.

[0082] The average particle size of the colorant in this specification refers to the volume average particle size, and specifically refers to the particle size at 50% of the cumulative value in the particle size distribution measured using a particle size distribution measuring device based on the laser scattering and diffraction method (50% volume average particle size; hereinafter, D50 As a measuring device, for example, the product name "Microtrac MT3000II" manufactured by Microtrac Bell or an equivalent product can be used.

[0083] The content of the colorant is not limited to a specific range. From the viewpoint of obtaining the effect of adding the colorant, the content of the colorant in the adhesive layer can be about 0.1 wt % or more, and suitably about 0.5 wt % or more. From the viewpoint of light-shielding properties, the content is preferably about 1 wt % or more, more preferably about 2 wt % or more, and even more preferably about 3 wt % or more (for example, about 5 wt % or more). Furthermore, the upper limit of the content of the colorant in the adhesive layer can be, for example, less than 15 wt %, and suitably less than 10 wt %, preferably less than 8 wt %, and more preferably less than 7 wt %. Limiting the amount of colorant used in the adhesive layer is also preferred from the viewpoint of suppressing deterioration of adhesive properties and maintaining the intended performance.

[0084] (rust inhibitor) The pressure-sensitive adhesive layer according to some preferred embodiments may contain a rust inhibitor. Examples of the rust inhibitor include, but are not limited to, azole-based rust inhibitors, amine compounds, nitrites, ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, urotropine, thiourea, phenyl carbamate, and cyclohexylammonium-N-cyclohexylcarbamate (CHC). The rust inhibitors may be used alone or in combination of two or more.

[0085] As the rust inhibitor, an azole-based rust inhibitor can be preferably used. As the azole-based rust inhibitor, one having as its active ingredient an azole-based compound that is a five-membered ring aromatic compound containing two or more heteroatoms, at least one of which is a nitrogen atom, can be preferably used. A suitable example of a compound that can be used as the azole-based rust inhibitor is a benzotriazole-based rust inhibitor that has as its active ingredient a benzotriazole-based compound. Suitable examples of the benzotriazole-based compound include 1,2,3-benzotriazole, 5-methylbenzotriazole, 4-methylbenzotriazole, carboxybenzotriazole, etc.

[0086] The content of the 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 acrylic 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 even 0.5 parts by weight or more. On the other hand, from the viewpoint of increasing the cohesive strength of the adhesive, the content of the rust inhibitor is suitably less than 8 parts by weight per 100 parts by weight of the acrylic polymer, and may be 5 parts by weight or less, or may be 2 parts by weight or less.

[0087] (Other additives) The pressure-sensitive adhesive composition may contain, as necessary, various additives commonly used in the field of pressure-sensitive adhesives, such as leveling agents, crosslinking aids, plasticizers, softeners, fillers, antistatic agents, antioxidants, UV absorbers, antioxidants, and light stabilizers. The pressure-sensitive adhesive composition may also contain any polymer (e.g., rubber-based polymer) or oligomer (e.g., acrylic oligomer with Mw of about 1,000 or more and less than 30,000) other than acrylic polymers, as long as the effects of the invention are not impaired. Conventionally known additives can be used in the usual manner for such various additives, and detailed description thereof will be omitted since they do not particularly characterize the present invention.

[0088] (Adhesive composition) The pressure-sensitive adhesive layer (layer comprising a pressure-sensitive adhesive) disclosed herein may be a pressure-sensitive adhesive layer formed from an aqueous pressure-sensitive adhesive composition, a solvent-based pressure-sensitive adhesive composition, a hot-melt pressure-sensitive adhesive composition, or an active energy ray-curable pressure-sensitive adhesive composition that cures upon exposure to active energy rays such as ultraviolet light or electron beams. The aqueous pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive (a pressure-sensitive adhesive layer-forming component) in a solvent (aqueous solvent) primarily composed of water, and typically includes what are called water-dispersed pressure-sensitive adhesive compositions (compositions in which at least a portion of the pressure-sensitive adhesive is dispersed in water). Furthermore, the solvent-based pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive in an organic solvent. The organic solvent contained in the solvent-based pressure-sensitive adhesive composition may be one or more of the organic solvents exemplified above as those usable in solution polymerization (e.g., toluene, ethyl acetate, etc.), without particular limitation. From the viewpoint of adhesive properties, etc., the technology disclosed herein is preferably implemented in an embodiment having a pressure-sensitive adhesive layer formed from a solvent-based pressure-sensitive adhesive composition. In an embodiment having a solvent-based pressure-sensitive adhesive layer formed from a solvent-based pressure-sensitive adhesive composition, the refractive index-enhancing effect of the technology disclosed herein is preferably realized.

[0089] (Formation of adhesive layer) The PSA layer disclosed herein can be formed by a conventionally known method. For example, a method can be employed in which a PSA composition is applied to a surface (release surface) having releasability and then dried to form a PSA layer. For PSA sheets having a substrate, a method (direct method) can be employed in which a PSA composition is directly applied (typically coated) to the substrate and then dried to form a PSA layer. Alternatively, a method (transfer method) can be employed in which a PSA composition is applied to a surface (release surface) having releasability and then dried to form a PSA layer on the surface, and then the PSA layer is transferred to the substrate. The release surface can preferably be, for example, the surface of a release liner described below. The PSA layer disclosed herein is typically formed continuously, but is not limited to this form. For example, the PSA layer may be formed in a regular or random pattern, such as a dotted or striped pattern.

[0090] 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 preferably about 60 to 130° C. After drying the pressure-sensitive adhesive composition, aging may be further carried out for the purposes of adjusting component migration within the pressure-sensitive adhesive layer, promoting the crosslinking reaction, and alleviating distortion that may exist within the pressure-sensitive adhesive layer.

[0091] The pressure-sensitive adhesive layer disclosed herein may have a single-layer structure or a multi-layer structure of two or more layers. From the viewpoint of productivity, etc., the pressure-sensitive adhesive layer preferably has a single-layer structure.

[0092] The thickness of the pressure-sensitive adhesive layer is set so that the total thickness of the pressure-sensitive adhesive sheet is 100 μm or less. For example, the thickness of the pressure-sensitive adhesive layer is suitably approximately 100 μm or less, preferably approximately 70 μm or less, and more preferably approximately 50 μm or less. The thickness of the pressure-sensitive adhesive layer can be approximately 35 μm or less. A pressure-sensitive adhesive layer with a limited thickness can effectively meet the demands for thinner and lighter weight. Furthermore, according to the technology disclosed herein, a pressure-sensitive adhesive having acid resistance and alkali resistance and sufficient adhesive strength can be obtained with a thickness-limited configuration as described above. There is no particular lower limit for the thickness of the pressure-sensitive adhesive layer. From the viewpoint of adhesion to the adherend, it is advantageous to set it to approximately 1 μm or more, and it is appropriate to set it to approximately 3 μm or more, preferably approximately 10 μm or more, more preferably approximately 15 μm or more, and even more preferably approximately 20 μm or more. It may also be approximately 30 μm or more, approximately 35 μm or more, or approximately 40 μm or more. Increasing the thickness of the adhesive layer tends to provide better adhesive properties. Furthermore, increasing the thickness of the adhesive layer tends to improve the ability to prevent acidic and alkaline liquids from penetrating in the thickness direction. In an adhesive sheet having adhesive layers (first and second adhesive layers) on each side of a substrate, the thicknesses of the adhesive layers may be the same or different.

[0093] <Base material (base material layer)> In embodiments in which the PSA sheet disclosed herein is in the form of a single-sided or double-sided PSA sheet with a substrate, the substrate supporting (backing) the PSA layer can 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, kraft paper, glassine paper, fine paper, synthetic paper, and top-coated paper. Examples of cloth include woven fabrics and nonwoven fabrics made from various fibrous materials, either alone or in combination. Examples of the fibrous materials include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyurethane sheets and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil.

[0094] The term "nonwoven fabric" as used herein refers primarily to nonwoven fabrics for adhesive sheets used in the field of adhesive tapes and other adhesive sheets, and typically refers to nonwoven fabrics (sometimes referred to as "paper") produced using a general papermaking machine. The term "resin film" as used herein typically refers to a non-porous resin sheet that is substantially bubble-free (void-free). Therefore, the resin film is distinct from foam films, nonwoven fabrics, and woven fabrics (i.e., does not include foams, nonwoven fabrics, or woven fabrics). The resin film may be a non-stretched film, a uniaxially stretched film, or a biaxially stretched film.

[0095] As the substrate constituting the substrate-attached PSA sheet, a substrate containing a resin film as the base film can be preferably used. The base film is typically a member that can independently maintain its shape (independent). The substrate in the technology disclosed herein may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include a colored layer, a reflective layer, an undercoat layer, an antistatic layer, etc., provided on the surface of the base film.

[0096] The resin film is a film whose main component is a resin material (e.g., a component contained in the resin film in an amount exceeding 50% by weight). Examples of resin films include polyolefin-based resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; 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 also be a rubber-based film such as a natural rubber film or a butyl rubber film. Among these, polyester films are preferred from the viewpoints of handleability and processability, and PET films are particularly preferred.

[0097] The substrate may be transparent, or may have light-shielding or light-reducing properties. In some embodiments, a colorant may be contained in the substrate (e.g., a resin film). This allows the light transmittance (light-shielding properties) of the substrate to be adjusted. Adjusting the light transmittance (e.g., perpendicular light transmittance) of the substrate can also be useful for adjusting the light transmittance of the substrate and, further, the light transmittance of a pressure-sensitive adhesive sheet including the substrate.

[0098] As with the colorants that can be contained in the pressure-sensitive adhesive layer, conventionally known pigments and dyes can be used as the colorant. The colorant is not particularly limited and may be, for example, a colorant of black, gray, white, red, blue, yellow, green, yellow-green, orange, purple, gold, silver, pearl color, or the like.

[0099] The substrate (e.g., 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. The blending ratio of the various additives is about less than 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight).

[0100] The substrate (e.g., a resin film) may have a single-layer structure, or a multi-layer structure of two, three, or more layers. From the viewpoint of shape stability, the substrate preferably has a single-layer structure. In the case of a multi-layer structure, at least one layer (preferably all layers) preferably has a continuous structure of the resin (e.g., a polyester-based resin). The method for producing the substrate (typically a 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, and calendar roll molding may be used.

[0101] The 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 may be disposed on both surfaces. In a configuration in which colored layers are disposed on both surfaces of the base film, the configurations of the colored layers may be the same or different.

[0102] The surface of the substrate may be subjected to a conventionally known 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 substrate and the pressure-sensitive adhesive layer, in other words, the anchoring ability of the pressure-sensitive adhesive layer to the substrate.

[0103] Furthermore, when the technology disclosed herein is implemented in the form of a single-sided PSA sheet with a substrate, the back surface of the substrate may be subjected to a release treatment, if necessary. The release treatment may be, for example, a treatment in which a typical silicone-based, long-chain alkyl-based, or fluorine-based release agent is applied in the form of a thin film, typically about 0.01 μm to 1 μm (e.g., 0.01 μm to 0.1 μm). By applying such a release treatment, it is possible to obtain effects such as facilitating the unwinding of a roll of the PSA sheet.

[0104] The thickness of the substrate is set so that the total thickness of the pressure-sensitive adhesive sheet is 100 μm or less. In some embodiments, depending on the intended use and manner of use of the pressure-sensitive adhesive sheet, the thickness of the substrate may be approximately 70 μm or less, approximately 30 μm or less, or approximately 15 μm or less (e.g., approximately 8 μm or less). A substrate with a limited thickness can effectively meet the demand for thinner and lighter weight. Furthermore, a pressure-sensitive adhesive sheet having a substrate with a limited thickness tends to exhibit the function of the pressure-sensitive adhesive layer more effectively. There is no particular lower limit for the thickness of the substrate. From the viewpoint of the handleability and processability of the pressure-sensitive adhesive sheet, the thickness of the substrate is suitably approximately 2 μm or more, preferably approximately 5 μm or more, for example approximately 10 μm or more.

[0105] <Release liner> In the technology disclosed herein, a release liner can be used during the formation of the adhesive layer, the production of the adhesive sheet, and the storage, distribution, and shaping of the adhesive sheet before use. The release liner is not particularly limited, and examples that can be used include release liners having a release treatment layer on the surface of a liner substrate such as a resin film or paper, and release liners made of low-adhesion materials such as fluorine-based polymers (polytetrafluoroethylene, etc.) and polyolefin-based resins (polyethylene, polypropylene, etc.). 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.

[0106] <Characteristics of adhesive sheets> (Normal adhesive strength F0) The 180-degree peel strength (normal adhesive strength) F0 of the adhesive sheet disclosed herein against a stainless steel plate may vary depending on the intended use and the application location. From the viewpoint of achieving good adhesive reliability to the adherend, the normal adhesive strength F0 of an adhesive sheet used as a structural material is, for example, suitably about 2.0 N / 5 mm or more, preferably about 3.0 N / 5 mm or more, more preferably about 3.5 N / 5 mm or more, even more preferably 4.0 N / 5 mm or more, particularly preferably 4.5 N / 5 mm or more, and may even be about 5.0 N / 5 mm or more. An adhesive sheet having the above adhesive strength has an adhesive strength suitable for bonding and fixing, and is suitable for applications such as portable electronic devices that require high adhesive reliability despite limited adhesive area and thickness. The upper limit of the adhesive strength F0 is not particularly limited, and may be about 10 N / 5 mm or less (e.g., 8 N / 5 mm or less). The adhesive strength F0 is the peel strength against a stainless steel plate measured at a tensile speed of 300 mm / min and a peel angle of 180° in accordance with JIS Z 0237, and more specifically, is measured by the method described in the Examples below. In the case of a double-sided PSA sheet having adhesive surfaces on both sides, the adhesive strength F0 on each adhesive surface may be the same or different.

[0107] (Adhesion strength F1 after immersion in acidic solution) The pressure-sensitive adhesive sheet disclosed herein maintains an adhesive strength (F1) after immersion in an acidic solution of at least a predetermined value. The adhesive strength (F1) after immersion in an acidic solution is, for example, approximately 2.0 N / 5 mm or more, suitably approximately 2.4 N / 5 mm or more, preferably approximately 3.0 N / 5 mm or more, more preferably approximately 3.5 N / 5 mm or more, even more preferably 4.0 N / 5 mm or more, and particularly preferably 4.5 N / 5 mm or more. A pressure-sensitive adhesive sheet exhibiting the above-described adhesive strength (F1) after immersion in an acidic solution can maintain a good adhesion state to an adherend even when used in a manner that exposes it to an acidic liquid such as an acid etching solution. The technology disclosed herein provides such a pressure-sensitive adhesive sheet with excellent acid resistance. The upper limit of the adhesive strength (F1) after immersion in an acidic solution is not particularly limited, and may be approximately 10 N / 5 mm or less (e.g., 8 N / 5 mm or less). The adhesive strength F1 after immersion in an acidic solution is the peel strength [N / 5 mm] measured under conditions of a pulling rate of 300 mm / min and a peel angle of 180° after a 5 mm wide adhesive sheet attached to a stainless steel plate as an adherend is immersed in an aqueous iron chloride solution (5% FeCl2 aqueous solution) for 30 minutes in an environment of 50°C, and more specifically, is measured by the method described in the Examples below. In the case of a double-sided adhesive sheet having adhesive surfaces on both sides, the adhesive strength F1 after immersion in an acidic solution on each adhesive surface may be the same or different.

[0108] (Adhesion strength after immersion in alkaline solution F2) The PSA sheet disclosed herein maintains an adhesive strength F2 after immersion in an alkaline solution of at least a predetermined value. The adhesive strength F2 after immersion in an alkaline solution is, for example, approximately 2.0 N / 5 mm or more, suitably approximately 2.4 N / 5 mm or more, preferably approximately 3.0 N / 5 mm or more, more preferably approximately 3.5 N / 5 mm or more, even more preferably 4.0 N / 5 mm or more, and particularly preferably 4.5 N / 5 mm or more. PSA sheets exhibiting such an adhesive strength F2 after immersion in an alkaline solution can maintain a good adhesion state to an adherend, even when used in a manner that exposes them to alkaline liquids such as alkaline cleaning solutions. The technology disclosed herein provides such PSA sheets with excellent alkali resistance. The upper limit of the adhesive strength F2 after immersion in an alkaline solution is not particularly limited, and may be approximately 10 N / 5 mm or less (e.g., 8 N / 5 mm or less). The adhesive strength F2 after immersion in an alkaline solution is the peel strength [N / 5 mm] measured under conditions of a pulling rate of 300 mm / min and a peel angle of 180° after a 5 mm wide adhesive sheet attached to a stainless steel plate as an adherend is immersed in an aqueous sodium hydroxide solution (50% NaOH aqueous solution) for 30 minutes in an environment of 50°C, and more specifically, is measured by the method described in the Examples below. In the case of a double-sided adhesive sheet having adhesive surfaces on both sides, the adhesive strength F2 after immersion in an alkaline solution on each adhesive surface may be the same or different.

[0109] (Adhesive strength retention rate after immersion in acidic solution / alkaline solution) The PSA sheets disclosed herein typically have an adhesive strength retention rate of 80% or higher after immersion in an acidic solution and an adhesive strength retention rate of 80% or higher after immersion in an alkaline solution. The adhesive strength retention rate [%] after immersion in an acidic solution is calculated from the ratio of the adhesive strength F1 [N / 5mm] after immersion in an acidic solution to the normal adhesive strength F0 [N / 5mm] (F1 / F0 × 100), and the adhesive strength retention rate [%] after immersion in an alkaline solution is calculated from the ratio of the adhesive strength F2 [N / 5mm] after immersion in an alkaline solution to the normal adhesive strength F0 [N / 5mm] (F2 / F0 × 100). PSA sheets that satisfy the above characteristics maintain sufficient adhesive strength for use as structural materials, and can exhibit excellent adhesive reliability, being resistant to swelling and not prone to lifting or peeling, even when exposed to acidic and alkaline liquids. At least one (preferably both) of the adhesive strength retention rate after immersion in an acidic solution and the adhesive strength retention rate after immersion in an alkaline solution is preferably 85% or more, more preferably 90% or more, even more preferably 95% or more, and particularly preferably 100% or more. There are no particular limitations on the upper limits of the adhesive strength retention rate after immersion in an acidic solution and the adhesive strength retention rate after immersion in an alkaline solution, and the upper limits may be, for example, 300% or less, 200% or less, or 150% or less. In the case of a double-sided PSA sheet having adhesive surfaces on both sides, the adhesive strength retention rate after immersion in an acidic solution and the adhesive strength retention rate after immersion in an alkaline solution on each adhesive surface may be the same or different.

[0110] (Total thickness of adhesive sheet) The thickness (total thickness) of the adhesive sheet disclosed herein (including an adhesive layer, and in configurations having a substrate layer, further including the substrate layer, but excluding a release liner) is 100 μm or less. Adhesive sheets with such limited thickness well meet the demand for thin and lightweight devices, and are suitable for use in portable electronic devices, which are in strong demand for miniaturization and thinness. Furthermore, the technology disclosed herein makes it possible to obtain an adhesive sheet with a limited thickness as described above that has acid resistance and alkali resistance and can maintain sufficient adhesive strength. The thickness of the adhesive sheet is preferably approximately 70 μm or less, more preferably approximately 50 μm or less, and may be, for example, approximately 35 μm or less. The lower limit of the thickness of the adhesive sheet is not particularly limited, and can be approximately 1 μm or more, for example, approximately 3 μm or more, preferably approximately 6 μm or more, more preferably approximately 10 μm or more (e.g., approximately 15 μm or more), and even more preferably approximately 20 μm or more. A PSA sheet having a thickness equal to or greater than a predetermined value tends to be easy to handle and to have excellent adhesive strength and ability to prevent acidic and alkaline liquids from penetrating in the thickness direction. In a substrate-less PSA sheet, the thickness of the PSA layer is the total thickness of the PSA sheet.

[0111] <Application> The pressure-sensitive adhesive sheet disclosed herein can achieve highly reliable bonding and fixation even with a thickness of 100 μm or less, and is suitable for use as a structural material for various applications requiring acid- and alkali-resistant bonding and fixation. Pressure-sensitive adhesive sheets used as structural materials are typically not intended to be peeled off from the adherend and are maintained semi-permanently attached to the adherend. The pressure-sensitive adhesive sheet disclosed herein can achieve highly reliable bonding and fixation even with a thickness of 100 μm or less, making it suitable for use in portable electronic devices, which require high miniaturization and thinning. Furthermore, various components, such as metal components, that make up portable electronic devices can be processed, for example, by forming openings for various sensors such as fingerprint sensors or camera lenses. Such processing steps can include processes using acidic or alkaline liquids, such as immersion in an acidic etching solution or cleaning with an alkaline cleaning solution. Therefore, by applying the pressure-sensitive adhesive sheet disclosed herein to achieve bonding and fixation with excellent acid and alkali resistance, components can be processed with the pressure-sensitive adhesive sheet attached. The pressure-sensitive adhesive sheet is particularly suitable for fixing components for portable electronic devices that undergo such processing.

[0112] 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 eyeglasses (monocular and binocular, including head-mounted devices), clothing devices attached to shirts, socks, hats, etc. as accessories, earwear devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, e-books, in-car information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" does not simply mean that the device is portable, but rather means that the device has a level of portability that allows an individual (average adult) to carry it relatively easily.

[0113] The adhesive sheet disclosed herein can be used, for example, in such portable electronic devices that include a pressure-sensitive sensor, for the purpose of fixing the pressure-sensitive sensor to other members. In some embodiments, the adhesive sheet can be used to fix the pressure-sensitive sensor to other members in an electronic device (typically a portable electronic device) that has a function that enables an absolute position to be specified on a plate (typically a touch panel) corresponding to the screen using a device for indicating a position on the screen (typically a pen-type or mouse-type device) and a device for detecting the position.

[0114] The adhesive sheet disclosed herein is also suitable for use on the backside of a display screen (display unit) such as a touch panel display in a portable electronic device. For example, some electronic devices such as portable electronic devices include light-emitting elements for purposes such as image display, and the adhesive sheet may be required to have limited light transmittance (e.g., light-blocking properties) to prevent light leakage, etc. For such electronic devices, an adhesive sheet having a predetermined light-blocking property can be used. For example, the adhesive sheet can be used in electronic devices including various light sources such as LEDs (light emitting diodes) and light-emitting elements such as self-luminous organic electroluminescence (EL). The electronic device may be an electronic device equipped with an organic electroluminescence display device or a liquid crystal display device (typically a portable electronic device). For example, the adhesive sheet disclosed herein is suitable for use on the backside of a display screen (display unit) such as a touch panel display in a portable electronic device.

[0115] The adhesive sheet disclosed herein is also suitable for portable electronic devices incorporating various sensors such as fingerprint sensors and cameras. The adhesive sheet disclosed herein allows processing (opening processing) of an adherend, such as a metal member, while attached to the adherend, making it suitable for bonding and fixing members that form openings for sensors and camera lenses that constitute portable electronic devices. Examples of the sensor (optical sensor) include acceleration sensors, proximity sensors, and brightness sensors (ambient light sensors). Such sensors have light-receiving elements for ultraviolet light, visible light, infrared light, and the like, and may also have light-emitting elements for specific light rays such as infrared light.

[0116] Materials (adherend materials) to which the pressure-sensitive adhesive sheets disclosed herein can be 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 metals; various resin materials (typically plastic materials) such as polyimide resins, acrylic resins, polyethernitrile resins, polyethersulfone resins, polyester resins (PET resins, PEN resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyetheretherketone 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 these, metal materials such as copper, aluminum, and stainless steel; polyester resins such as PET; and resin materials (typically plastic materials) such as polyimide resins, aramid resins, and polyphenylene sulfide resins are widely used. The PSA sheets disclosed herein can be used by being attached to components made of the above-mentioned materials. PSA sheets (specifically, double-sided PSA sheets) used as structural materials have adhesive surfaces (first and second adhesive surfaces) that adhere well to adherends made of different materials, and can be preferably used to join two or more different materials to the various adherend materials mentioned above.

[0117] The above materials may be materials for components constituting products such as electronic devices. The above materials may also be materials constituting the fixing object (e.g., backside members such as electromagnetic wave shields and reinforcing plates) of the pressure-sensitive sensor, display unit, or other fixing object. The fixing object refers to the object to which the adhesive sheet is attached, i.e., the adherend. The backside member refers to a member disposed on the opposite side of the front surface (viewing side) of the pressure-sensitive sensor or display unit in, for example, a portable electronic device. For example, it may be a member constituting the support member 240 disposed on the backside of the display device 200 shown in FIG. 4 (described later). The fixing object may have either a single-layer structure or a multilayer structure, and the surface to which the adhesive sheet is attached (the attachment surface) may be subjected to various surface treatments. Although not particularly limited, an example of the fixing object is a backside member having a thickness of 1 μm or more (typically 5 μm or more, e.g., 60 μm or more, or even 120 μm or more) and 1500 μm or less (e.g., 800 μm or less).

[0118] The pressure-sensitive adhesive sheet disclosed herein is also suitable for applications in which it is attached to a member having a surface (adhesive sheet attachment surface) formed from a metal material. Examples of such adherends include members having a surface made of the various metal materials (e.g., aluminum, stainless steel, etc.) exemplified above as the adherend material. Suitable examples include metal members such as stainless steel members and aluminum members. The metal members, in the form of a laminate to which the pressure-sensitive adhesive sheet is attached, may be exposed to acidic and alkaline liquids for purposes such as opening processing. It is preferable to use an acid- and alkali-resistant pressure-sensitive adhesive sheet as a component of such a laminate. The pressure-sensitive adhesive sheet can maintain good adhesion to the metal member even when exposed to acidic and alkaline liquids for processing the metal member. The metal member may be, for example, a member constituting the support portion 240 of the display device 200 shown in FIG. 4 (described below). In an embodiment in which the pressure-sensitive adhesive sheet is a double-sided pressure-sensitive adhesive sheet and different adherends (members or articles) are attached to each side of the sheet, it is preferable that one of the adherends is a metal member. Furthermore, the pressure-sensitive adhesive sheet used for the above-mentioned applications may have holes formed in advance by punching or the like at locations corresponding to the processed portions (opening formation portions, etc.) of the metal member.

[0119] Furthermore, the member or material to which the PSA sheet is attached (in the case of a double-sided PSA sheet, at least one of the adherends) may be light-transmitting. The light transmittance of the adherend may be, for example, greater than 50%, and may be 70% or greater. In some preferred embodiments, the light transmittance of the adherend is 80% or greater, more preferably 90% or greater, and may be 95% or greater (e.g., 95 to 100%). Such a material may be a resin film (e.g., a polyester resin film such as a PET film) disposed on the back surface of an image display unit of various devices such as a portable electronic device. The PSA sheet disclosed herein may be preferably used in an embodiment in which it is attached to an adherend (e.g., a member) having a light transmittance equal to or greater than a predetermined value. The light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000.

[0120] As described above, the technology disclosed herein provides a laminate comprising a pressure-sensitive adhesive sheet and a member to which the pressure-sensitive adhesive sheet is attached. In some embodiments, the laminate comprising the pressure-sensitive adhesive sheet is a laminate comprising the pressure-sensitive adhesive sheet and a metal member (first member). In some embodiments, an adherend material having the above-mentioned light transmittance is attached to the side of the pressure-sensitive adhesive sheet opposite to the surface to which the metal member is attached. In this embodiment, the laminate comprising the pressure-sensitive adhesive sheet is a laminate comprising the pressure-sensitive adhesive sheet and a member (second member) having optical transparency. In some preferred embodiments, the laminate is a laminate comprising a metal member (first member), a pressure-sensitive adhesive sheet, and a member (second member) having optical transparency, in this order. The pressure-sensitive adhesive sheet is also referred to as a pressure-sensitive adhesive layer in the laminate.

[0121] In some embodiments, the laminate including the pressure-sensitive adhesive sheet is a laminate including the pressure-sensitive adhesive sheet and a light-transmitting member (second member). In such a configuration, the pressure-sensitive adhesive sheet is typically a double-sided adhesive sheet. In this embodiment, one adhesive surface of the pressure-sensitive adhesive sheet is attached to the light-transmitting member. Such a laminate is also called a pressure-sensitive adhesive sheet with a light-transmitting member. In addition, the other adhesive surface of the pressure-sensitive adhesive sheet can be attached to the metal member.

[0122] An example of the configuration of the laminate is shown in Fig. 3. The laminate 50 shown in Fig. 3 includes a first member 41, a substrate-less adhesive sheet 1, and a second member 42, in this order. Specifically, in the laminate 50, one adhesive surface (first adhesive surface) 1A of the substrate-less adhesive sheet 1 is adhered to the first member 41, and the other adhesive surface (second adhesive surface) 1B of the adhesive sheet 1 is adhered to the second member 42. In this embodiment, the first member 41 and the second member 42 both have a sheet-like or plate-like shape, and the laminate 50 has a multilayer structure. Details of the members constituting the laminate are the same as those described above for the members, materials, and adherends, and therefore will not be described again.

[0123] In some preferred embodiments, the first member 41 is a metal member, and the metal materials or metal members exemplified above as the adherend material are used. Such a metal member may be, for example, a member constituting the support portion 240 of the display device 200 shown in FIG. 4 described below. In some preferred embodiments, the second member 42 is a light-transmitting member and has the light transmittance of the light-transmitting adherend described above. The second member 42 is preferably a member made of a resin film, more preferably a polyester-based resin film (more specifically, a PET-based resin film). The second member 42 may be, for example, a member disposed on the back side of a display unit in a display device. The laminate 50 as described above may typically be a component of an organic electroluminescence display device, a liquid crystal display device, or the like. The laminate 50 is suitable for use, for example, in applications where it is disposed on the back side of an image display unit (which may be a display unit such as a touch panel display) of various devices such as portable electronic devices.

[0124] The pressure-sensitive adhesive sheet disclosed herein is preferably used in electronic devices including various light sources such as LEDs, and light-emitting elements such as self-emitting organic EL devices. For example, it is preferably used in electronic devices (typically portable electronic devices) equipped with organic EL display devices or liquid crystal display devices that require specific optical properties.

[0125] FIG. 4 is an exploded perspective view schematically illustrating an exemplary configuration of a display device. As shown in FIG. 4, the display device 200 included in the portable electronic device 100 includes a display unit 220 including a cover member, an organic EL unit, etc., and a support unit 240. The display device 200 is configured to further include an adhesive sheet 230. In this exemplary configuration, the adhesive sheet 230 is in the form of a double-sided adhesive sheet (double-sided adhesive sheet) that fixes the members that make up the display unit 220 and the support unit 240. The support unit 240 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 described above.

[0126] 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 thickness of the pressure-sensitive adhesive sheet is 100 μm or less, the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal, The display device, wherein the monomer component includes a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer. [2] The display device according to the above [1], wherein the total ratio of the monomer having a nitrogen atom-containing ring and the carboxy group-containing monomer in the monomer components is 6.5% by weight or more and 40% by weight or less. [3] The content of the carboxyl group-containing monomer (A C The content of the monomer having a nitrogen atom-containing ring (A N ) ratio (A N / A C ) is in the range of 1 to 40. [4] The display device according to any one of the above [1] to [3], wherein the monomer component contains a hydroxyl group-containing monomer in a proportion of 10% by weight or less. [5] The display device according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet made of the pressure-sensitive adhesive layer. [6] The display device according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive sheet is a substrate-attached double-sided pressure-sensitive adhesive sheet further comprising a base layer and having the pressure-sensitive adhesive layer on each side of the base layer. [7] The display device according to any one of the above [1] to [6], wherein the pressure-sensitive adhesive sheet has a 180-degree peel strength F0 against a stainless steel plate of 3.0 N / 5 mm or more. [8] The display device according to any one of [1] to [7] above, wherein the adhesive sheet has an adhesive strength retention rate after immersion in an acidic solution and an adhesive strength retention rate after immersion in an alkaline solution of 80% or more.

[0127]

[11] A pressure-sensitive adhesive sheet having a thickness of 100 μm or less, A pressure-sensitive adhesive layer containing an acrylic polymer is provided, The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal, The monomer component includes a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer.

[12] The pressure-sensitive adhesive sheet according to

[11] above, wherein the total amount of the monomer having a nitrogen atom-containing ring and the carboxy group-containing monomer in the monomer component is 6.5% by weight or more and 40% by weight or less.

[13] The content of the carboxyl group-containing monomer (A C The content of the monomer having a nitrogen atom-containing ring (A N ) ratio (A N / A C ) is in the range of 1 to 40.

[14] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[13] , wherein the monomer component contains a hydroxyl group-containing monomer in a proportion of 10% by weight or less.

[15] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[14] , which is a substrateless double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

[16] The pressure-sensitive adhesive sheet according to any one of

[11] to

[14] above, which is a substrate-attached double-sided pressure-sensitive adhesive sheet further comprising a substrate layer and having the pressure-sensitive adhesive layer on each side of the substrate layer.

[17] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[16] , which has a 180-degree peel strength F0 against a stainless steel plate of 3.0 N / 5 mm or more.

[18] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[17] , wherein the adhesive strength retention rate after immersion in an acidic solution and the adhesive strength retention rate after immersion in an alkaline solution are both 80% or more.

[19] The pressure-sensitive adhesive sheet according to any one of

[11] to

[18] above, which is used for fixing components of a portable electronic device.

[0128]

[21] A laminate comprising a metal member (first member) and an adhesive sheet attached to the surface of the metal member, The thickness of the pressure-sensitive adhesive sheet is 100 μm or less, the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal, The monomer component comprises a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer.

[22] A laminate (also referred to as a pressure-sensitive adhesive sheet with a light-transmitting member) comprising a light-transmitting member (second member) and a double-sided adhesive sheet, The thickness of the pressure-sensitive adhesive sheet is 100 μm or less, the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal, The monomer component comprises a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer.

[23] A laminate including a metal member (first member), an adhesive sheet, and a light-transmitting member (second member) in this order, The thickness of the pressure-sensitive adhesive sheet is 100 μm or less, the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal, The monomer component comprises a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer.

[24] The laminate according to any one of the above

[21] to

[23] , wherein the metal member is an aluminum member or a stainless steel member.

[25] The laminate according to the above

[22] or

[23] , wherein the light transmittance of the light-transmitting member is greater than 50%.

[26] The laminate according to the above

[22] ,

[23] or

[25] , wherein the optically transparent member is made of a resin film.

[27] The laminate according to any one of

[21] to

[26] above, wherein the total ratio of the monomer having a nitrogen atom-containing ring and the carboxy group-containing monomer in the monomer components is 6.5% by weight or more and 40% by weight or less.

[28] The content of the carboxyl group-containing monomer (A C The content of the monomer having a nitrogen atom-containing ring (A N ) ratio (A N / A C ) is in the range of 1 to 40.

[29] The laminate according to any one of the above

[21] to

[28] , wherein the monomer component contains a hydroxyl group-containing monomer in a proportion of 10% by weight or less.

[30] The laminate according to any one of the above

[21] to

[29] , wherein the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

[31] The laminate according to any one of

[21] to

[29] above, wherein the pressure-sensitive adhesive sheet is a substrate-attached double-sided pressure-sensitive adhesive sheet further comprising a substrate layer and having the pressure-sensitive adhesive layer on each side of the substrate layer.

[32] The laminate according to any one of the above

[21] to

[31] , wherein the pressure-sensitive adhesive sheet has a 180-degree peel strength against a stainless steel plate of 3.0 N / 5 mm or more.

[33] The laminate according to any one of

[21] to

[32] above, wherein the pressure-sensitive adhesive sheet has an adhesive strength retention rate after immersion in an acidic solution and an adhesive strength retention rate after immersion in an alkaline solution of 80% or more.

[34] The laminate according to any one of

[21] to

[33] above, which is used in a portable electronic device. [Example]

[0129] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" are by weight unless otherwise specified.

[0130] <Evaluation method> [Normal adhesive strength F0] A 50 μm thick PET film is attached to one adhesive side of a double-sided PSA sheet at 23°C and 50% RH, and the sheet is then cut to a size of 5 mm wide and 50 mm long to prepare a measurement sample. Under the same conditions, the adhesive surface (surface to be measured) of the prepared measurement sample is pressed against the surface of a stainless steel plate (SUS304BA plate, 10 cm x 10 cm) using a 2 kg roller, moving back and forth once. This sample is then left in a 50°C thermostatic chamber for 30 minutes. Then, under conditions of 23°C and 50% RH, a tensile tester is used to measure the peel strength (normal adhesive strength F0) [N / 5 mm] in accordance with JIS Z 0237:2000 at a pulling speed of 300 mm / min and a peel angle of 180°. For example, a Shimadzu "Tensilon" tensile tester or an equivalent can be used. Note that the PET film backing is not necessary for single-sided PSA sheets.

[0131] [Adhesion strength F1 after immersion in acidic solution] A 5mm wide, 50mm long measurement sample (adhesive sheet) backed with a PET film was prepared in the same manner as for the measurement of normal adhesive strength F0. The adhesive surface (surface to be measured) of the measurement sample was pressed onto the surface of a 10cm x 10cm stainless steel plate. The stainless steel plate was placed horizontally with the bottom facing downwards, and an iron chloride solution (5% FeCl2 aqueous solution) was dripped onto the entire edge (four sides) of the measurement sample attached to the stainless steel plate until the edge of the measurement sample was no longer exposed, immersing the edge of the measurement sample in the iron chloride solution. The entire measurement sample on the stainless steel plate was covered with a PET film to prevent moisture evaporation, and then left in a 50°C thermostatic chamber for 30 minutes. The measurement sample attached to the stainless steel plate was then removed from the thermostatic chamber, the PET film was removed, the iron chloride solution was rinsed off with tap water, and the moisture on the measurement sample and stainless steel plate was wiped off with a cloth. Then, using a tensile tester, measure the adhesive strength F1 [N / 5mm] after immersion in the acidic solution under the same conditions as for measuring the normal adhesive strength F0. The time between immersion in the iron chloride aqueous solution for 30 minutes and measuring the adhesive strength should be within 10 minutes.

[0132] [Adhesion strength after immersion in alkaline solution F2] A 5mm wide, 50mm long measurement sample (adhesive sheet) backed with a PET film was prepared in the same manner as for measuring the normal adhesive strength F0. The adhesive surface (surface to be measured) of the measurement sample was pressed onto the surface of a 10cm x 10cm stainless steel plate. The stainless steel plate was placed horizontally with the bottom facing downwards, and a sodium hydroxide solution (50% NaOH solution) was dripped onto the entire edge (all four sides) of the measurement sample attached to the stainless steel plate until the edge of the measurement sample was no longer exposed, immersing the edge of the measurement sample in the sodium hydroxide solution. The entire measurement sample on the stainless steel plate was covered with a PET film to prevent moisture evaporation, and then left in a 50°C thermostatic chamber for 30 minutes. The measurement sample attached to the stainless steel plate was then removed from the thermostatic chamber, the PET film was removed, the sodium hydroxide solution was rinsed off with tap water, and the moisture on the measurement sample and stainless steel plate was wiped off with a cloth. Then, using a tensile tester, measure the adhesive strength F2 [N / 5mm] after immersion in the alkaline solution under the same conditions as measuring the normal adhesive strength F0. The time between immersion in the sodium hydroxide solution for 30 minutes and measuring the adhesive strength should be within 10 minutes.

[0133] [Adhesion retention rate] The adhesive strength retention rate after immersion in an acidic solution and the adhesive strength retention rate after immersion in an alkaline solution of each example were calculated as the ratio [%] of the adhesive strength F1 [N / 5mm] after immersion in an acidic solution to the normal adhesive strength F0 [N / 5mm], and the ratio [%] of the adhesive strength F2 [N / 5mm] after immersion in an alkaline solution to the normal adhesive strength F0 [N / 5mm], respectively. If both the adhesive strength retention rate after immersion in an acidic solution and the adhesive strength retention rate after immersion in an alkaline solution were 80% or higher, the sheet was judged to pass.

[0134] [Evaluation of edge lifting after immersion in acidic and alkaline solutions] In measuring the adhesive strength F1 after immersion in the acidic solution, the measurement sample is immersed in an aqueous iron chloride solution, washed with tap water, and the adhering water is wiped off with a cloth. The adhesive surface between the measurement sample and the stainless steel plate is visually inspected for edge lift (evaluation of edge lift after immersion in an acidic solution). In addition, in measuring the adhesive strength F2 after immersion in the alkaline solution, the measurement sample is immersed in an aqueous sodium hydroxide solution, washed with tap water, and the adhering moisture is wiped off with a cloth. The adhesive surface between the measurement sample and the stainless steel plate is visually inspected for edge lift (evaluation of edge lift after immersion in alkaline solution). If no edge lifting was observed after immersion in the acidic solution or the alkaline solution, the sample was judged as "good" (passed), and if edge lifting was observed, the sample was judged as "poor."

[0135] <Example 1> (Preparation of Acrylic Polymer) A reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel was charged with 75 parts of 2-ethylhexyl acrylate (2EHA), 3 parts of acrylic acid (AA), 0.1 parts of 2-hydroxyethyl acrylate (HEA), and 25 parts of acryloylmorpholine (ACMO) as monomer components, and ethyl acetate as a polymerization solvent. 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 (AIBN) was added as a polymerization initiator, and the mixture was solution polymerized at 60 °C for 8 hours to obtain a solution of acrylic polymer (A1). The Mw of this acrylic polymer (A1) was approximately 110 × 10 4 It was.

[0136] (Preparation of Pressure-Sensitive Adhesive Composition) To the acrylic polymer (A1) solution, 0.03 parts of an epoxy-based crosslinking agent (trade name "TETRAD-C", manufactured by Mitsubishi Gas Chemical Co., Inc., 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) was added as a crosslinking agent per 100 parts of the acrylic polymer (A1) contained in the solution, and the mixture was stirred and mixed to prepare a pressure-sensitive adhesive composition.

[0137] (Preparation of adhesive sheet) The above-mentioned pressure-sensitive adhesive composition was applied to the release surface of a 38 μm thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Polyester Corporation) and dried at 100°C for 2 minutes to form a 35 μm thick pressure-sensitive adhesive layer. The release surface of a 25 μm thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Polyester Corporation) was then bonded to this pressure-sensitive adhesive layer. In this way, a 35 μm thick substrateless double-sided pressure-sensitive adhesive sheet was obtained, both sides of which were protected by the two polyester release liners.

[0138] <Example 2> To the acrylic polymer (A1) solution prepared in Example 1, 30 parts of tackifier resin (B1) (product name "Haritac SE10", manufactured by Harima Chemicals, hydrogenated rosin glycerin ester, softening point 75-85°C) were added per 100 parts of the acrylic polymer (A1) contained in the solution, and 2 parts of an isocyanate-based crosslinking agent (product name "Coronate L", manufactured by Tosoh Corporation, 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct) and 0.04 parts of an epoxy-based crosslinking agent (product name "TETRAD-C", manufactured by Mitsubishi Gas Chemical Co., Inc., 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) were added as crosslinkers. A pressure-sensitive adhesive composition was prepared by stirring and mixing. A substrateless double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 1, except that the resulting pressure-sensitive adhesive composition was used.

[0139] <Example 3> To the acrylic polymer (A1) solution prepared in Example 1, 30 parts of the tackifier resin (B1) and 2 parts of the isocyanate-based crosslinking agent and 0.05 parts of the epoxy-based crosslinking agent were added per 100 parts of the acrylic polymer (A1) contained in the solution, and carbon black particles (manufactured by Toyocolor Co., Ltd., product name "Multilac A903", average particle size 400 nm) were added so that the adhesive layer accounted for 6.58% of the total, and the mixture was stirred and mixed to prepare a pressure-sensitive adhesive composition. A substrateless double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 1, except that the resulting pressure-sensitive adhesive composition was used.

[0140] <Example 4> To the acrylic polymer (A1) solution prepared in Example 1, 10 parts of the tackifier resin (B1) and 15 parts of tackifier resin (B2) (product name "Haritac PCJ", manufactured by Harima Chemicals, polymerized rosin ester, softening point approximately 118-128°C) were added per 100 parts of the acrylic polymer (A1) contained in the solution, and 2 parts of the isocyanate crosslinking agent and 0.07 parts of the epoxy crosslinking agent were added as crosslinking agents, followed by stirring and mixing to prepare a pressure-sensitive adhesive composition. A substrateless double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 1, except that the resulting pressure-sensitive adhesive composition was used.

[0141] <Example 5> A solution of acrylic polymer (A2) was obtained in the same manner as in preparation of acrylic polymer (A1), except that the monomer components were changed to 80 parts of 2EHA, 3 parts of AA, 0.1 parts of HEA, and 20 parts of ACMO. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, except that the obtained acrylic polymer (A2) solution was used. A substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using this pressure-sensitive adhesive composition in the same manner as in Example 1.

[0142] <Example 6> A solution of acrylic polymer (A3) was obtained in the same manner as in preparation of acrylic polymer (A1), except that the monomer components were changed to 65 parts of 2EHA, 3 parts of AA, 0.1 parts of HEA, and 35 parts of ACMO. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, except that the obtained acrylic polymer (A3) solution was used. A substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using this pressure-sensitive adhesive composition in the same manner as in Example 1.

[0143] <Example 7> A solution of acrylic polymer (A4) was obtained in the same manner as in preparation of acrylic polymer (A1), except that the monomer components were changed to 90 parts of 2EHA, 3 parts of AA, 0.1 parts of HEA, and 10 parts of ACMO. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, except that the obtained acrylic polymer (A4) solution was used. A substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using this pressure-sensitive adhesive composition in the same manner as in Example 1.

[0144] <Example 8> A solution of acrylic polymer (A5) was obtained in the same manner as in the preparation of acrylic polymer (A1), except that the monomer components were changed to 75 parts of 2EHA, 3 parts of AA, 0.1 parts of HEA, and 25 parts of N-vinyl-2-pyrrolidone (NVP). A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, except that the obtained acrylic polymer (A5) solution was used. Using this pressure-sensitive adhesive composition, a substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 1.

[0145] <Example 9> A solution of acrylic polymer (A6) was obtained in the same manner as in the preparation of acrylic polymer (A1), except that the monomer components were changed to 95 parts of 2EHA and 5 parts of AA. To the resulting acrylic polymer (A6) solution, 20 parts of tackifier resin (B3) (trade name "YS Polystar T-115", manufactured by Yasuhara Chemical Co., Ltd., terpene phenol resin, softening point approximately 115°C) and 0.03 parts of the above-mentioned epoxy-based crosslinking agent were added per 100 parts of the acrylic polymer (A6) contained in the solution, and the mixture was stirred and mixed to prepare a pressure-sensitive adhesive composition. A substrateless double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 1, except that the resulting pressure-sensitive adhesive composition was used.

[0146] <Example 10> A solution of acrylic polymer (A7) was obtained in the same manner as in the preparation of acrylic polymer (A1), except that the monomer components were changed to 63 parts of 2EHA, 13 parts of HEA, 15 parts of NVP, and 9 parts of methyl methacrylate (MMA). To the resulting acrylic polymer (A7) solution, 20 parts of the tackifier resin (B1) and 1 part of the isocyanate-based crosslinking agent were added per 100 parts of the acrylic polymer (A7) contained in the solution, and the mixture was stirred and mixed to prepare a pressure-sensitive adhesive composition. A substrate-less double-sided PSA sheet according to this example was produced in the same manner as in Example 1, except that the resulting PSA composition was used.

[0147] <Example 11> A solution of acrylic polymer (A8) was obtained in the same manner as in preparation of acrylic polymer (A1), except that the monomer components were changed to 75 parts of n-butyl acrylate (BA), 3 parts of AA, 0.1 parts of HEA, and 25 parts of ACMO. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, except that the obtained acrylic polymer (A8) solution was used. A substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using this pressure-sensitive adhesive composition in the same manner as in Example 1.

[0148] <Example 12> A solution of acrylic polymer (A9) was obtained in the same manner as in the preparation of acrylic polymer (A1), except that the monomer components were changed to 95 parts BA and 5 parts AA. To the obtained acrylic polymer (A9) solution, 20 parts of the tackifier resin (B3) and 3 parts of the isocyanate-based crosslinking agent and 0.01 part of the epoxy-based crosslinking agent were added per 100 parts of the acrylic polymer (A9) contained in the solution, and the mixture was stirred and mixed to prepare a pressure-sensitive adhesive composition. A substrateless double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 1, except that the obtained pressure-sensitive adhesive composition was used.

[0149] Table 1 shows an overview of the pressure-sensitive adhesive sheets according to the examples and the evaluation results.

[0150] [Table 1]

[0151] As shown in Table 1, in the PSA sheets of Examples 1 to 12 having a thickness of 100 μm or less, Examples 1 to 8, which used an acrylic polymer containing 60 wt% or more of an alkyl(meth)acrylate having an alkyl group of 5 or more carbon atoms at the ester terminal (C5 or higher alkyl(meth)acrylate) as the monomer component, a monomer having a nitrogen atom-containing ring (N-ring-containing monomer), and a carboxyl group-containing monomer as the PSA component, had a normal adhesive strength F0 of 3.0 N / 5 mm or more, and an adhesive strength retention rate after both immersion in an acidic solution and immersion in an alkaline solution of 80% or more. On the other hand, Examples 9 to 12, which used an acrylic polymer not containing any one of a C5 or higher alkyl(meth)acrylate, an N-ring-containing monomer, and a carboxyl group-containing monomer as the PSA component, had a normal adhesive strength F0 of less than 3.0 N / 5 mm, or an adhesive strength retention rate after immersion in an acidic solution or an alkaline solution of less than 80%.

[0152] More specifically, Example 9, which used an acrylic polymer with a monomer composition that did not contain an N-ring-containing monomer, showed a decreased adhesive strength retention rate after immersion in an alkaline solution, while Example 10, which used an acrylic polymer with a monomer composition that did not contain a carboxyl group-containing monomer, showed a decreased adhesive strength retention rate after immersion in an acidic solution. In Example 9, the cohesive strength decreased because an N-ring-containing monomer and a carboxyl group-containing monomer were not used in combination, and in Example 10, the absence of a carboxyl group-containing monomer is thought to have prevented the penetration of acidic liquids into the adhesive from being sufficiently suppressed. Furthermore, Example 11, which used a monomer composition that did not contain a C5 or higher alkyl (meth)acrylate, did not have a sufficient normal adhesive strength F0. It is thought that the wettability of the adhesive surface was insufficient, preventing sufficient adhesive strength from being developed. Furthermore, Example 12, in which the main monomer was changed from Example 9 to BA, showed a tendency for the adhesive strength retention rate after immersion in an acidic solution and after immersion in an alkaline solution to further decrease. Comparing Example 9 with Example 12, it is believed that an acrylic polymer containing a C5 or higher alkyl (meth)acrylate as a monomer component improves the wettability of the adhesive surface compared to when a BA with an alkyl group having 4 carbon atoms is used, and inhibits the penetration of acidic and alkaline solutions from the edge of the adhesive sheet to the adhesive interface.

[0153] The above results show that by using an adhesive containing an acrylic polymer containing as a monomer component at least 60% by weight of an alkyl (meth)acrylate having an alkyl group with 5 or more carbon atoms at the ester end, and a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer, it is possible to maintain sufficient adhesive strength as a structural material even after exposure to acidic and alkaline liquids, even if the thickness of the adhesive sheet is limited to 100 μm or less.

[0154] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0155] 1 adhesive sheet 1A 1st adhesive side 1B 2nd adhesive side 10 Base material (base material layer) 21 adhesive layer (first adhesive layer) 21A Adhesive surface, 1st adhesive surface 21B Adhesive surface, 2nd adhesive surface 22 Adhesive layer (second adhesive layer) 31,32 Release liner 41 First member 42 Second member 50 laminate 100 Portable electronic devices 200 Display device 220 Display section 240 Support part

Claims

1. A pressure-sensitive adhesive sheet used as a structural material for a portable electronic device to fix components of the portable electronic device, comprising: A pressure-sensitive adhesive sheet having a thickness of 100 μm or less, A pressure-sensitive adhesive layer containing an acrylic polymer is provided, The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal, the monomer components include a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer, The pressure-sensitive adhesive sheet has a 180-degree peel strength of 3.0 N / 5 mm or more against a stainless steel plate.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the total amount of the monomer having a nitrogen atom-containing ring and the carboxy group-containing monomer in the monomer component is 6.5% by weight or more and 40% by weight or less.

3. The content of the carboxyl group-containing monomer (A Ｃ The content of the monomer having a nitrogen atom-containing ring (A Ｎ ) ratio (A Ｎ / A Ｃ 3. The pressure-sensitive adhesive sheet according to claim 1, wherein ) is in the range of 1 to 40.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the monomer component contains a hydroxyl group-containing monomer in a proportion of 10% by weight or less.

5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, which is a substrate-less double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

6. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, which is a substrate-attached double-sided pressure-sensitive adhesive sheet, further comprising a substrate layer, and having the pressure-sensitive adhesive layer on each side of the substrate layer.

7. A display device including a display unit including a cover member and an organic EL unit, and a support unit, an adhesive sheet having a thickness of 100 μm or less is attached to the support portion; the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal, the monomer components include a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer, A display device, wherein the adhesive sheet has a 180-degree peel strength of 3.0 N / 5 mm or more against a stainless steel plate.

8. A laminate used as a component of a portable electronic device, The device comprises a metal member and an adhesive sheet attached to a surface of the metal member, The thickness of the pressure-sensitive adhesive sheet is 100 μm or less, the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer containing an acrylic polymer, The acrylic polymer is a polymer of a monomer component containing 60% by weight or more of alkyl (meth)acrylate having an alkyl group having 5 or more carbon atoms at an ester terminal, the monomer components include a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer, A laminate, wherein the 180-degree peel strength of the pressure-sensitive adhesive sheet against a stainless steel plate is 3.0 N / 5 mm or more.

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