Adhesive sheet and laminate

Abstract

To provide an adhesive composition that can form an adhesive sheet exhibiting excellent durability, and to provide an adhesive sheet and a laminate formed from the adhesive composition.SOLUTION: The adhesive sheet of the present invention is an adhesive sheet for attaching a touch sensor, which is used for bonding a touch sensor, and contains a cured product of an adhesive composition, the adhesive composition including an acrylic polymer and a polycarbodiimide, wherein the acrylic polymer is composed of acrylic monomer units including no carboxyl group, and the polycarbodiimide includes a carbodiimide group within its molecule and has a weight average molecular weight of 500 or more.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] A pressure-sensitive adhesive sheet is a pressure-sensitive adhesive material formed by forming a sheet of a pressure-sensitive adhesive composition containing an acrylic polymer as a main component, and is used for bonding optical components such as touch panels, liquid crystal displays (LCDs), and other displays. Such pressure-sensitive adhesive sheets are required to have not only adhesive performance but also, for example, high durability. For example, in display applications, displays may be placed in high-temperature environments, and therefore pressure-sensitive adhesive sheets that are less likely to cause appearance defects even in such high-temperature environments are required.

[0003] For example, Patent Document 1 discloses a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing an acrylic resin containing a predetermined amount of carboxyl group-containing monomer units and a carbodiimide compound, which is said to be capable of imparting durability in high-temperature environments and corrosion resistance in high-temperature, high-humidity environments. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-143211 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in recent years, there has been a demand for pressure-sensitive adhesive sheets that can provide even greater durability. However, the pressure-sensitive adhesive sheet described in Patent Document 1 contains carboxyl groups, which sometimes results in insufficient durability, leaving room for improvement. In particular, coatings having urethane bonds, amide bonds, or nurate structures are often formed on the surfaces of metal vapor-deposited films and metal nanowires that make up touch sensors. These coatings are prone to deterioration at high temperatures, so such touch sensors are more susceptible to deterioration in high-temperature environments. Therefore, there is a strong demand for pressure-sensitive adhesive sheets that can improve the durability of touch sensors that have such coatings even in high-temperature environments.

[0006] The present invention has been made in view of the above, and aims to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive sheet having durability, and a pressure-sensitive adhesive sheet and laminate formed from the pressure-sensitive adhesive composition. [Means for solving the problem]

[0007] As a result of extensive research into achieving the above object, the present inventors have discovered that the above object can be achieved by using a specific acrylic polymer and a specific polycarbodiimide as essential components, and have thus completed the present invention.

[0008] That is, the present invention includes, for example, the subject matter described in the following sections. Item 1 An adhesive sheet for attaching a touch sensor, which is used to attach a touch sensor, Contains a cured product of the pressure-sensitive adhesive composition, The pressure-sensitive adhesive composition contains an acrylic polymer and a polycarbodiimide, The acrylic polymer is composed of acrylic monomer units having no carboxyl group, The pressure-sensitive adhesive sheet, wherein the polycarbodiimide has a carbodiimide group in the molecule and has a weight-average molecular weight of 500 or more. Section 2 Item 2. The pressure-sensitive adhesive sheet according to Item 1, wherein the surface of the touch sensor is coated with a film having an amide bond, a urethane bond, or a nurate structure. Section 3 Item 2. The pressure-sensitive adhesive sheet according to Item 1, wherein the pressure-sensitive adhesive composition is substantially free of solvent. Section 4 Item 2. The pressure-sensitive adhesive composition according to item 1, wherein the acrylic polymer has a glass transition temperature of 0°C or lower. Section 5 Item 2. The pressure-sensitive adhesive sheet according to item 1, wherein the pressure-sensitive adhesive composition has a hydroxyl value of 30 mgKOH / g or more and 250 mgKOH / g or less. Section 6 Item 2. The pressure-sensitive adhesive sheet according to item 1, wherein the pressure-sensitive adhesive composition further contains a tackifier. Section 7 Item 7. A laminate comprising the pressure-sensitive adhesive sheet according to any one of items 1 to 6 and a touch sensor. [Effects of the Invention]

[0009] The pressure-sensitive adhesive sheet of the present invention can impart excellent durability by being attached to a touch sensor, and can be suitably used for touch sensors. DETAILED DESCRIPTION OF THE INVENTION

[0010]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0011] 1. Adhesive sheet The pressure-sensitive adhesive sheet of the present invention is an adhesive sheet for attaching a touch sensor, which is used to attach a touch sensor, and contains a cured product of a pressure-sensitive adhesive composition. In particular, the pressure-sensitive adhesive composition contains an acrylic polymer and a polycarbodiimide, the acrylic polymer being composed of acrylic monomer units having no carboxyl groups, and the polycarbodiimide having a carbodiimide group in the molecule and having a weight-average molecular weight of 500 or more.

[0012] The pressure-sensitive adhesive sheet of the present invention can be provided with excellent durability by being attached to a touch sensor, and can be suitably used for touch sensors. Here, excellent durability means that air bubbles are unlikely to form between the pressure-sensitive adhesive sheet and the adherend (such as a touch sensor) and peeling is also unlikely to occur, even in a high-temperature, high-humidity environment.

[0013] The pressure-sensitive adhesive sheet of the present invention contains a cured product of the pressure-sensitive adhesive composition, and such a cured product can exhibit adhesive performance in the pressure-sensitive adhesive sheet. Each component contained in the pressure-sensitive adhesive composition will be described below.

[0014] (acrylic polymer) The PSA composition contains an acrylic polymer as an essential component. The acrylic polymer is the main component of the PSA composition and is a component that imparts adhesive properties to the PSA sheet. In the PSA composition, the acrylic polymer can exist, for example, in the form of a solution dissolved in an acrylic monomer. In other words, the PSA composition can contain a solution (so-called syrup) in which the acrylic polymer is dissolved in the acrylic monomer. The acrylic polymer may also be in a form other than syrup, for example, a solution dissolved in a solvent (excluding the acrylic monomer), i.e., the PSA composition may be a solvent-based PSA.

[0015] The acrylic polymer may be any of the acrylic polymers contained in known pressure-sensitive adhesive sheets, as long as it is a polymer formed from acrylic monomer units having no carboxyl group. For example, an example of the acrylic polymer is an acrylic copolymer obtained by polymerizing a mixed monomer containing an acrylic monomer having no carboxyl group.

[0016] Examples of the acrylic monomer not having a carboxyl group include various monofunctional monomers, such as an acrylic monomer having a hydroxyl group, an acrylic monomer having a nitrogen atom, and an acrylic monomer M other than these. Examples of the acrylic monomer M include an acrylic monomer having a linear or branched alkyl group and an acrylic monomer having a ring structure in the side chain.

[0017] Among these, the acrylic polymer is preferably a polymer of at least one mixed monomer selected from the group consisting of an acrylic monomer having a linear or branched alkyl group, an acrylic monomer having a ring structure in the side chain, and an acrylic monomer having a hydroxyl group. In other words, the acrylic polymer preferably has at least one structural unit selected from the group consisting of an acrylic monomer unit having a linear or branched alkyl group, an acrylic monomer unit having a ring structure in the side chain, and an acrylic monomer unit having a hydroxyl group.

[0018] In this specification, the term "monomer unit" refers to the smallest unit (i.e., structural unit) formed by polymerization (radical polymerization) of a monomer.

[0019] The acrylic polymer is composed of acrylic monomer units that do not have a carboxyl group, i.e., does not contain acrylic monomer units that have a carboxyl group, thereby improving the durability of the pressure-sensitive adhesive sheet.

[0020] Because the acrylic polymer does not contain a carboxyl group, even when the PSA sheet is attached to the surface of a touch sensor, the touch sensor surface is less likely to corrode. Furthermore, because the carboxyl group does not react with the carbodiimide group in the polycarbodiimide, the adhesion-improving effect of the polycarbodiimide is easily maintained. Therefore, because the acrylic polymer does not contain a carboxyl group, the PSA sheet exhibits enhanced adhesion to adherends, particularly to touch sensors coated with a urethane material, as described below. While this interpretation is not necessarily restrictive, it is believed that the presence of a carboxyl group in the acrylic polymer may be due to the reaction of the polycarbodiimide, as described below, with the carboxyl group, which may impair the performance of the polycarbodiimide.

[0021] The acrylic monomer having a linear or branched alkyl group may be a (meth)acrylate having a linear or branched alkyl group. In this specification, "(meth)acrylic" means "acrylic" or "methacrylic", and "(meth)acrylate" means "acrylate" or "methacrylate".

[0022] In a (meth)acrylate having a linear or branched alkyl group, the alkyl group may have, for example, 1 to 20 carbon atoms, preferably 1 to 15 carbon atoms, more preferably 2 to 14 carbon atoms, and even more preferably 3 to 12 carbon atoms.

[0023] Specific examples of (meth)acrylates having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isopropyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate.

[0024] Examples of acrylic monomers having a ring structure in the side chain include (meth)acrylates having a ring structure in the side chain. Of these, (meth)acrylates having an alicyclic or aromatic ring in the side chain are preferred, and (meth)acrylic monomers having an alicyclic ring are more preferred. Examples of alicyclic rings include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, cyclododecane, norbornene, norbornadiene, dicyclopentane, isobornyl, tetrahydrofuran, and tetrahydropyran. The alicyclic ring may have a spiro structure. Examples of aromatic rings include benzene, naphthalene, anthracene, pyridine, furan, benzofuran, pyrrole, thiophene, imidazole, and oxazole. Of these, the ring structure is preferably an alicyclic ring, more preferably at least one selected from cyclohexane, dicyclopentane, isobornyl, and benzene, and particularly preferably cyclohexane or isobornyl.

[0025] The ring structure may further have a substituent, for example, a substitutable substituent selected from a halogen atom, a halogenated alkyl group, an alkyl group, an alkenyl group, an acyl group, a hydroxy group, a hydroxyalkyl group, an alkoxy group, an aryl group, a heteroaryl group, an alicyclic group, a cyano group, an epoxy group, an oxetanyl group, a mercapto group, an amino group, a (meth)acryloyl group, and the like.

[0026] The (meth)acrylate having a ring structure in the side chain preferably has a structure in which a monovalent group having a ring structure is bonded to the ester oxygen of the (meth)acrylate, and in this case, the monovalent group having a ring structure preferably has 3 to 12 carbon atoms, more preferably 4 to 10 carbon atoms, and even more preferably 4 to 8 carbon atoms.

[0027] Specific examples of (meth)acrylates having a ring structure in the side chain include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, 3-phenoxybenzyl (meth)acrylate, O-phenylphenoxyethyl (meth)acrylate, etc. Among these, the (meth)acrylate having a ring structure in the side chain is more preferably one or more selected from the group consisting of cyclohexyl (meth)acrylate and isobornyl (meth)acrylate, and particularly preferably cyclohexyl (meth)acrylate, in terms of particularly improving the adhesion between the pressure-sensitive adhesive sheet and the glass substrate and particularly improving the durability.

[0028] The acrylic monomer having a hydroxyl group can be exemplified by (meth)acrylate having a hydroxyl group. Examples of the (meth)acrylate having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy3-phenoxypropyl (meth)acrylate, 2,2-dimethyl-2-hydroxyethyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 2-hydroxy3-phenoxypropyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and polyalkylene glycol mono(meth)acrylate. Among these, the (meth)acrylate having a hydroxyl group is preferably 4-hydroxybutyl (meth)acrylate.

[0029] The acrylic polymer preferably contains both acrylic monomer units having a linear or branched alkyl group and acrylic monomer units having a hydroxyl group, or preferably contains both acrylic monomer units having a ring structure in the side chain and acrylic monomer units having a hydroxyl group, and more preferably contains all of acrylic monomer units having a linear or branched alkyl group, acrylic monomer units having a ring structure in the side chain, and acrylic monomer units having a hydroxyl group. In this case, the durability of the pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition can be further improved.

[0030] The acrylic copolymer may have a functional group having an active hydrogen atom in addition to the hydroxyl group resulting from the hydroxyl group-containing acrylic monomer unit, and examples thereof include an amino group, an amide group, a sulfo group, a sulfonic acid group, a sulfinic acid group, a sulfenic acid group, and a thiol group.

[0031] However, it is preferable that the acrylic polymer does not contain an acrylic monomer unit having a nitrogen atom. That is, it is preferable that the acrylic polymer does not have a group having a nitrogen atom. This makes it easier to particularly improve the durability of the pressure-sensitive adhesive sheet. Examples of nitrogen-atom-containing acrylic monomers include nitrogen-atom-containing monomers such as nitrogen-containing (meth)acrylates such as N-vinylpyrrolidone, as well as (meth)acrylamide and allylamine.

[0032] The acrylic polymer preferably contains 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more of acrylic monomer units having a linear or branched alkyl group, and more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less.

[0033] The acrylic polymer preferably contains 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more of acrylic monomer units having a ring structure in a side chain, and preferably contains 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less.

[0034] The acrylic polymer preferably contains 10% by mass or more of acrylic monomer units having a hydroxyl group, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less.

[0035] The acrylic polymer preferably contains 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 99% by mass or more, of acrylic monomer units having a linear or branched alkyl group, acrylic monomer units having a ring structure in the side chain, and acrylic monomer units having a hydroxyl group. The acrylic polymer may consist solely of acrylic monomer units having a linear or branched alkyl group, acrylic monomer units having a ring structure in the side chain, and acrylic monomer units having a hydroxyl group.

[0036] The ratio (molar ratio) of each unit contained in the acrylic polymer can be considered to be the same as the molar ratio of each monomer used in producing the acrylic polymer.

[0037] The weight-average molecular weight of the acrylic polymer is preferably greater than 10,000, more preferably greater than 100,000, and even more preferably greater than 200,000. The weight-average molecular weight of the acrylic polymer is preferably not greater than 2,000,000, more preferably not greater than 1,500,000, and even more preferably not greater than 1,200,000.

[0038] The weight-average molecular weight referred to in the present invention refers to the weight-average molecular weight measured in terms of polystyrene by gel permeation chromatography (GPC). There are no particular limitations on the GPC equipment used in the GPC method. Commercially available GPC measuring instruments, such as the LC-2000Plus series manufactured by JASCO Corporation, with detectors such as RI-2031Plus and UV-2075Plus, can be used. In this case, for example, a GPC column consisting of four columns connected together, including "Shodex KF801," "Shodex KF803L," "Shodex KF800L," and "Shodex KF800D" manufactured by Showa Denko K.K., can be used. The column temperature can be set to 40°C. Tetrahydrofuran is used as the eluent, and measurements are performed at a flow rate of 1.0 ml / min. Typically, a calibration curve is prepared using standard polystyrene, and the weight-average molecular weight (Mw) can be calculated in terms of polystyrene.

[0039] The acrylic polymer preferably has a glass transition temperature of 0°C or lower. In this case, the pressure-sensitive adhesive sheet of the present invention has good adhesion to substrates such as touch sensors, and is also likely to have increased durability. The glass transition temperature of the acrylic polymer is more preferably -10°C or lower, more preferably -20°C or lower, and more preferably -30°C or lower, and is preferably -80°C or higher, more preferably -70°C or higher, and even more preferably -65°C or higher.

[0040] The method for adjusting the glass transition temperature of the acrylic polymer is not particularly limited, and the glass transition temperature can be adjusted to a desired range by, for example, changing the type and composition ratio of the monomers constituting the acrylic polymer. In the present invention, the glass transition temperature of the acrylic polymer refers to Tg, which is calculated by the following Fox formula based on the composition of the monomers used in synthesizing the polymer. Fox formula: 1 / Tg = (W1 / Tg1) + (W2 / Tg2) + + (Wm / Tgm) where W1+W2+···+Wm=1 In the formula, Tg is the glass transition temperature (unit: K) of the acrylic polymer, Tg1, Tg2, ..., Tgm are the glass transition temperatures of the respective homopolymers of m types of monomers (m is an integer) that make up the acrylic polymer, and W1, W2, ..., Wm are the mass fractions of each structural unit in the acrylic polymer. Note that Tg1 and W1 correspond to each other; that is, the monomer that makes up the homopolymer that exhibits the glass transition temperature of Tg1 is the same as the monomer that forms the structural unit whose mass fraction is W1. Similarly, Tg2 and W2, ..., Tgm and Wm correspond to each other.

[0041] The glass transition temperature of the homopolymer can be determined, for example, from the value described in the Polymer Handbook, 4th Edition (Wiley-Interscience, 2003). If no such reference is found, the glass transition temperature of the homopolymer can be measured, for example, by a differential scanning calorimeter (DSC). The DSC measurement conditions are as follows: 5 mg of sample, under a nitrogen atmosphere, the temperature is increased from -100°C to 200°C at a rate of 5°C / min in the first measurement (1st run), then cooled to -100°C at a rate of 5°C / min, and then increased from -100°C to 200°C at a rate of 5°C / min in the second measurement (2nd run). Here, the glass transition temperature refers to the intersection of the extension of the baseline on the lower temperature side of the region where the baseline of the DSC curve measured when the temperature is raised from -100°C to 200°C changes to a sigmoid shape in the endothermic direction and the tangent to the inflection point of the sigmoid.

[0042] The acrylic polymer can be produced by a known method. For example, the acrylic polymer can be produced by polymerizing a monomer mixture for forming each structural unit in the acrylic polymer by a known polymerization method. As the polymerization method, for example, solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, etc. can be used. The acrylic polymer can also be obtained from a commercial product, etc.

[0043] As described above, the PSA composition preferably contains a so-called syrup, in which the acrylic polymer is dissolved in an acrylic monomer. Examples of the acrylic monomer for forming the syrup include various monomers used to form the acrylic polymer. In particular, a mixture of the same monomers as the monomer units constituting the acrylic polymer is preferred. From this perspective, the acrylic monomer for forming the syrup preferably includes all of an acrylic monomer having a linear or branched alkyl group, an acrylic monomer having a ring structure in the side chain, and an acrylic monomer having a hydroxyl group. The content ratio of each monomer in the syrup can be the same as or nearly the same as the content ratio of the corresponding monomer constituting the acrylic polymer.

[0044] The content of the acrylic polymer in the syrup can be 1 to 50% by mass, and preferably 5 to 30% by mass, based on the total mass of the acrylic polymer and the acrylic monomer. The syrup may consist of only the acrylic polymer and the acrylic monomer.

[0045] (Polycarbodiimide) Polycarbodiimide is a compound having a carbodiimide group (-N=C=N-), and in particular, a compound having two or more carbodiimide groups in one molecule. It is also preferable that the polycarbodiimide contains three or more carbodiimide groups in one molecule.

[0046] The weight-average molecular weight of the polycarbodiimide is 500 or more, preferably 1000 or more, more preferably 1500 or more, and even more preferably 2000 or more. If the weight-average molecular weight of the polycarbodiimide is less than 500, the durability of the pressure-sensitive adhesive sheet may be impaired. The carbodiimide equivalent is preferably 100 or more, more preferably 200 or more. The carbodiimide equivalent is preferably 2000 or less, and even more preferably 1000 or less. The carbodiimide equivalent refers to the chemical formula weight per 1 mole of carbodiimide groups.

[0047] Specific examples of polycarbodiimides include poly(4,4'-dicyclohexylmethanecarbodiimide), poly(4,4'-diphenylmethanecarbodiimide), poly(3,5'-dimethyl-4,4'-biphenylmethanecarbodiimide), poly(p-phenylenecarbodiimide), poly(m-phenylenecarbodiimide), poly(3,5'-dimethyl-4,4'-diphenylmethanecarbodiimide), poly(naphthylenecarbodiimide), poly(1,3-diisopropylphenylenecarbodiimide), poly(1-methyl-3,5-diisopropylphenylenecarbodiimide), poly(1,3,5-triethylphenylenecarbodiimide), poly(triisopropylphenylenecarbodiimide), p-phenylene-bis(2,6-xylylcarbodiimide), and the like. The pressure-sensitive adhesive composition may contain one type of polycarbodiimide alone or two or more types of polycarbodiimide.

[0048] The method for producing polycarbodiimide is not particularly limited, and for example, a wide variety of known methods can be employed. Polycarbodiimide can be obtained, for example, by subjecting an isocyanate compound such as a monoisocyanate or a diisocyanate to a carbodiimidization reaction in the presence of a carbodiimidization catalyst (such as a phospholene).

[0049] Polycarbodiimide can also be obtained from commercially available products, such as Carbodilite V-02 (manufactured by Nisshinbo Chemical), Carbodilite V-02B (manufactured by Nisshinbo Chemical), Carbodilite V-02-L2 (manufactured by Nisshinbo Chemical), Carbodilite V-03 (manufactured by Nisshinbo Chemical), Carbodilite V-04 (manufactured by Nisshinbo Chemical), Carbodilite V-05 (manufactured by Nisshinbo Chemical), Stabackzol P (manufactured by Lanxess), and Elastostab H01 (manufactured by BASF).

[0050] The polycarbodiimide can be present in the PSA sheet without forming a crosslinked structure with other components such as the acrylic polymer, etc. This allows the PSA sheet to have excellent adhesion to the adherend, and in particular, particularly enhanced adhesion to a touch sensor coated with a urethane material, which will be described later.

[0051] The content of polycarbodiimide in the pressure-sensitive adhesive composition is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, particularly preferably 0.2 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, particularly preferably 1 part by mass or less, relative to 100 parts by mass of the total mass of the acrylic polymer and the acrylic monomer that dissolves the acrylic polymer (hereinafter referred to as "total mass M"). In this case, the durability of the pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition can be further improved.

[0052] (tackifier) The PSA composition may further contain a tackifier, in which case the PSA sheet is more likely to have excellent adhesion to the adherend.

[0053] Examples of the tackifier include a wide range of tackifiers used in pressure-sensitive adhesive sheets, and among these, an acrylic tackifier can be mentioned. The type of acrylic tackifier is not particularly limited, and for example, a wide range of acrylic tackifiers used in known pressure-sensitive adhesive sheets can be used.

[0054] The structural units contained in the acrylic tackifier may include a monomer unit having an alicyclic ring. When the acrylic tackifier includes a monomer unit having an alicyclic ring, the carbon number constituting the alicyclic ring is preferably 6 or more. Examples of alicyclic rings having 6 or more carbon atoms include cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, cyclododecane, norbornene, norbornadiene, isobornyl, and dicyclopentane. Examples of preferred monomers having an alicyclic ring include isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyl (meth)acrylate.

[0055] The acrylic tackifier can contain alkyl (meth)acrylate units instead of or in addition to the alicyclic monomer units. Examples of alkyl (meth)acrylates include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate. Among these, it is preferable that the acrylic tackifier contains methyl (meth)acrylate.

[0056] The acrylic tackifier is preferably a copolymer containing both an alicyclic monomer unit and an alkyl(meth)acrylate unit. In order to easily improve the adhesion between the pressure-sensitive adhesive sheet and the adherend, the content of the alkyl(meth)acrylate unit relative to the total mass of the acrylic tackifier is preferably 2% by mass or more, more preferably 5% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less.

[0057] The acrylic tackifier may contain other monomer units as needed. The other monomers may be any monomers copolymerizable with the alkyl (meth)acrylates described above, such as (meth)acrylonitrile, vinyl acetate, vinyl chloride, and ethyl vinyl ether. The content of other monomer units in the acrylic tackifier is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0058] Examples of acrylic tackifiers include resins with a glass transition temperature of 20° C. or higher. The glass transition temperature of the acrylic tackifier is preferably 30° C. or higher, more preferably 40° C. or higher, and even more preferably 50° C. or higher, and is preferably 200° C. or lower, more preferably 180° C. or lower, and even more preferably 150° C. or lower. By adjusting the glass transition temperature of the acrylic tackifier within the above range, the adhesion of the pressure-sensitive adhesive sheet to the adherend can be improved.

[0059] The weight-average molecular weight of the acrylic tackifier is preferably 3,000 or more, more preferably 3,200 or more, and even more preferably 3,500 or more. The weight-average molecular weight of the acrylic tackifier may be 20,000 or less, more preferably 15,000 or less, and even more preferably 10,000 or less. The weight-average molecular weight of the acrylic tackifier is measured by gel permeation chromatography (GPC) and converted using a calibration curve prepared using standard polystyrenes with known molecular weights. Such resins may be commercially available or synthesized by known methods.

[0060] The content of the acrylic tackifier in the pressure-sensitive adhesive composition is not particularly limited. In order to easily improve the adhesion of the pressure-sensitive adhesive sheet to an adherend, the content of the acrylic tackifier is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, relative to the total mass M of 100 parts by mass.

[0061] The tackifier may be formed solely from an acrylic tackifier, or may contain components other than the acrylic tackifier. The tackifier contained in the pressure-sensitive adhesive composition may be one type alone or two or more types.

[0062] (photoinitiator) The pressure-sensitive adhesive composition may further contain a photoinitiator. In this case, the pressure-sensitive adhesive composition has, for example, ultraviolet curability. The photoinitiator initiates polymerization of the acrylic monomer in the syrup when irradiated with active energy rays. In this specification, "active energy rays" refers to electromagnetic waves or charged particle rays that have an energy quantum, and examples thereof include ultraviolet rays, electron beams, visible light, X-rays, and ion beams. Among these, ultraviolet rays or electron beams are preferred from the viewpoint of versatility, and ultraviolet rays are particularly preferred.

[0063] The type of photoinitiator is not particularly limited, and a wide range of known photoinitiators can be used. Examples of the photoinitiator include acetophenone-based photoinitiators such as 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropanone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-methylpropanone, and 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methyl-1-propanone, acylphosphine oxide-based photoinitiators such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 2,4,6-trimethylbenzoyl)phenylphosphine oxide, intramolecular hydrogen abstraction photoinitiators such as methyl benzoylformate and 4-methylbenzophenone, and oil-soluble polymerization initiators such as oxime ester-based photoinitiators and cationic photoinitiators.

[0064] Commercially available acetophenone-based photoinitiators include EsacureOne (oligo(2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenylpropanone], photoinitiator manufactured by IGM Resins BV), Omnirad 651 (2,2-dimethoxy-2-phenylacetophenone, manufactured by IGM Resins BV), Omnirad 184 (1-hydroxycyclohexylphenylketone, manufactured by IGM Resins BV), and Omnirad 1173 (2-hydroxy-2-methyl-1-phenylpropanone, manufactured by IGM Resins BV). Commercially available acylphosphine oxide-based photoinitiators include Omnirad 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, manufactured by IGM Resins BV) and Omnirad TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide, manufactured by IGM Resins BV). Examples of commercially available oxime ester photoinitiators include Irgacure OXE03 (BASF Japan).

[0065] In the pressure-sensitive adhesive composition, the content ratio of the photoinitiator is not particularly limited, and is, for example, preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, relative to the total mass M of 100 parts by mass, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and particularly preferably 1.5 parts by mass or less.

[0066] (polyfunctional monomer) The PSA composition may also contain a polyfunctional monomer in addition to the above-mentioned components. Examples of such polyfunctional monomers include compounds having two or more polymerizable double bonds in the molecule. The polyfunctional monomer has two or more polymerizable double bonds (e.g., radically polymerizable double bonds), preferably two or more but less than five, and more preferably two or more but less than four. When the PSA composition contains a polyfunctional monomer, it can react with the monofunctional monomer in the syrup to form, for example, a crosslinked polymer. That is, when the PSA composition contains a polyfunctional monomer, a polymer having a crosslinked structure due to the polyfunctional monomer can be contained in the PSA sheet.

[0067] Examples of polyfunctional monomers include bifunctional monomers (monomers having two polymerizable double bonds), such as polyethylene glycol diacrylate, polypropylene diacrylate, alkyl diacrylate, polytetramethylene glycol diacrylate, polypropylene glycol diacrylate, dioxane diacrylate, tricyclodecanol diacrylate, and fluorene diacrylate. Examples of polyfunctional monomers include trifunctional or higher functional monomers, such as alkoxylated trimethylolpropane triacrylate, alkoxylated glycerin triacrylate, caprolactone-modified isocyanurate triacrylate, pentaerythritol acrylate, alkoxylated pentaerythritol acrylate, (alkoxylated) pentaerythritol acrylate, (alkoxylated) ditrimethylolpropane acrylate, (alkoxylated) dipentaerythritol acrylate, and (ethoxylated) polyglycerin acrylate.

[0068] The polyfunctional monomer may have a bisphenol skeleton in one molecule, such as diacrylate of bisphenol A diglycidyl ether, diacrylate of propoxylated bisphenol A, and diacrylate of bisphenol F diglycidyl ether.

[0069] Commercially available polyfunctional monomers include, for example, "A-200" (polyethylene glycol #200 diacrylate), "A-400" (polyethylene glycol #400 diacrylate), and "A-600" (polyethylene glycol #600 diacrylate) from the NK Ester series, which are bifunctional polyethylene glycol acrylates manufactured by Shin-Nakamura Chemical Co., Ltd., the trifunctional monomer A-TMPT ((alkoxylated) trimethylolpropane acrylate), the trifunctional monomer M310 (trimethylolpropane PO-modified triacrylate) and the trifunctional monomer M321 (trimethylolpropane propylene oxide-modified triacrylate) manufactured by Toagosei Co., Ltd., the bifunctional monomer M211B (bisphenol A EO-modified diacrylate) and M240 (polyethylene glycol diacrylate), and the tetrafunctional monomer M-408 (ditrimethylolpropane tetraacrylate), all manufactured by Toagosei Co., Ltd. Other commercially available polyfunctional monomers include, for example, A-DOG, A-DCP, A-9300, and A-9200YN manufactured by Shin-Nakamura Chemical Co., Ltd., FA-731A manufactured by Hitachi Chemical Co., Ltd., and AOMA manufactured by Nippon Shokubai.

[0070] In the pressure-sensitive adhesive composition, the content of the polyfunctional monomer is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.15 parts by mass or more, and particularly preferably 0.2 parts by mass or more, relative to the total mass M of 100 parts by mass, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, and particularly preferably 1 part by mass or less.

[0071] The pressure-sensitive adhesive composition may contain one type of polyfunctional monomer alone or two or more types of polyfunctional monomers.

[0072] (Silane coupling agent) The pressure-sensitive adhesive composition may also contain a silane coupling agent, which can increase the adhesive strength to the adherend.

[0073] The type of silane coupling agent is not particularly limited, and a wide variety of known compounds can be used. Examples of silane coupling agents include γ-acryloxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyldialkoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltriakoxysilane, γ-methacryloxypropyltrialkoxysilane, γ-chloropropyltrialkoxysilane, γ-methacryloxypropyldialkoxysilane, γ-mercaptopropyltrialkoxysilane, tris(trimethoxysilylpropyl)isocyanurate, and vinyltrialkoxysilane. The silane coupling agent may also be an oligomer of various alkoxysiloxanes. All of these silane coupling agents are commercially available.

[0074] The content of the silane coupling agent in the pressure-sensitive adhesive composition is not particularly limited. The content of the silane coupling agent is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.15 parts by mass or more, and particularly preferably 0.2 parts by mass or more, relative to the total mass M of 100 parts by mass, and is preferably 3 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.8 parts by mass or less, and particularly preferably 0.5 parts by mass or less.

[0075] (Adhesive composition) The pressure-sensitive adhesive composition contains an acrylic polymer and a polycarbodiimide as essential components, and may also contain, as necessary, at least one selected from the group consisting of a tackifying resin, a polyfunctional monomer, a silane coupling agent, and a photoinitiator.

[0076] The hydroxyl value of the pressure-sensitive adhesive composition is preferably 30 mgKOH / g or more and 250 mgKOH / g or less, in which case the pressure-sensitive adhesive sheet of the present invention will have good adhesion to substrates such as touch sensors and will also tend to have increased durability.

[0077] The pressure-sensitive adhesive composition preferably has a hydroxyl value of 40 mgKOH / g or more, more preferably 50 mgKOH / g or more, even more preferably 60 mgKOH / g or more, particularly preferably 70 mgKOH / g or more, and preferably 200 mgKOH / g or less, more preferably 180 mgKOH / g or less, even more preferably 160 mgKOH / g or less, particularly preferably 140 mgKOH / g or more.

[0078] In the present invention, the hydroxyl value of the PSA composition can be measured in accordance with JIS K 0070. On the other hand, when the amount of the hydroxyl-containing acrylic monomer used in preparing the PSA composition is known, the hydroxyl value calculated based on that amount can be used as the hydroxyl value of the PSA composition. Also, when the amount of the hydroxyl-containing acrylic monomer or a unit thereof contained in the PSA composition is known, the hydroxyl value calculated based on that amount can be used as the hydroxyl value of the PSA composition.

[0079] The pressure-sensitive adhesive composition may contain other components to the extent that the effects of the present invention are not impaired. Examples of other components include solvents, plasticizers, antioxidants, metal corrosion inhibitors, and light stabilizers. Dyes or pigments may also be added for coloring purposes. The pressure-sensitive adhesive composition may not contain an ultraviolet absorber.

[0080] The PSA composition preferably does not substantially contain a solvent, that is, the PSA composition is preferably a solvent-free type.

[0081] The pressure-sensitive adhesive composition can be cured to form a pressure-sensitive adhesive sheet. For example, the pressure-sensitive adhesive composition can be cured by irradiating it with active energy rays such as ultraviolet rays, thereby facilitating its curing and forming it into a sheet, thereby forming the pressure-sensitive adhesive sheet. This pressure-sensitive adhesive sheet will be described below.

[0082] 2. Adhesive sheet The pressure-sensitive adhesive sheet of the present invention is formed by irradiating the pressure-sensitive adhesive composition with active energy rays such as ultraviolet rays to form a sheet. Therefore, the pressure-sensitive adhesive sheet can be said to be a pressure-sensitive adhesive material having a pressure-sensitive adhesive layer containing a cured product of the pressure-sensitive adhesive composition.

[0083] To form a pressure-sensitive adhesive sheet using a pressure-sensitive adhesive composition, it is necessary to cure the pressure-sensitive adhesive composition. The method for curing the pressure-sensitive adhesive composition is not particularly limited, and for example, a wide variety of known methods can be adopted. Specifically, the method can include a step of applying the pressure-sensitive adhesive composition to a substrate to form a coating film, and a step of irradiating the coating film with active energy rays to obtain a cured pressure-sensitive adhesive. This allows the pressure-sensitive adhesive to form a pressure-sensitive adhesive layer, thereby obtaining a pressure-sensitive adhesive sheet.

[0084] The PSA composition can be applied using a known coating device, such as a blade coater, air knife coater, roll coater, bar coater, gravure coater, microgravure coater, rod blade coater, lip coater, die coater, or curtain coater.

[0085] The substrate used for coating the pressure-sensitive adhesive composition is not particularly limited. For example, the pressure-sensitive adhesive composition can be coated onto various substrates such as resin substrates and glass substrates. The substrate may be a release sheet, as described below. In this case, the pressure-sensitive adhesive sheet with release sheet, as described below, is easily obtained. The pressure-sensitive adhesive composition can also be coated directly onto the member to be adhered. The thickness of the pressure-sensitive adhesive composition after coating is not particularly limited, and can be appropriately set depending on the desired thickness of the pressure-sensitive adhesive layer (or pressure-sensitive adhesive sheet). After forming the coating film, the coating film may be subjected to a heat treatment or a drying treatment, if necessary.

[0086] The step of irradiating the coating film with active energy rays can be, for example, a step similar to a known method. In this step, the photoinitiator in the pressure-sensitive adhesive composition generates radicals due to the active energy rays, and the polymerizable components in the pressure-sensitive adhesive composition initiate and progress a polymerization reaction due to the generated radicals, resulting in a polymerized and cured product. This allows the formation of a pressure-sensitive adhesive layer and improved adhesive strength.

[0087] Examples of active energy rays include ultraviolet rays, electron beams, visible light, X-rays, and ion beams, and can be appropriately selected depending on the photoinitiator contained in the pressure-sensitive adhesive composition. Among these, ultraviolet rays or electron beams are preferred from the viewpoint of versatility, and ultraviolet rays are particularly preferred. Examples of light sources that can be used for ultraviolet rays include chemical lamps, high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, carbon arcs, xenon arcs, and electrodeless ultraviolet lamps. The irradiation output of ultraviolet rays is such that the cumulative light amount is 100 to 10,000 mJ / cm. 2 It is preferable to set the value to 200 to 5000 mJ / cm 2 In the step of irradiating the coating film with active energy rays, the active energy rays may be irradiated in two stages.

[0088] The cured product formed as described above can be used as the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention. The pressure-sensitive adhesive layer may consist of only the cured product of the pressure-sensitive adhesive, or may contain other components in addition to the cured product of the pressure-sensitive adhesive.

[0089] The pressure-sensitive adhesive sheet of the present invention may include other layers as long as it includes the pressure-sensitive adhesive layer, or may be formed only with the pressure-sensitive adhesive layer. That is, the pressure-sensitive adhesive sheet preferably consists of only the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer has, for example, a single-layer structure.

[0090] The pressure-sensitive adhesive sheet of the present invention may also be a pressure-sensitive adhesive sheet provided with a substrate such as a release sheet on one or both sides. That is, the present invention also encompasses a pressure-sensitive adhesive sheet with a release sheet that includes a pressure-sensitive adhesive sheet and a release sheet.

[0091] Examples of the release sheet include a release laminate sheet having a release sheet substrate and a release agent layer provided on one side of the release sheet substrate, or a polyolefin film such as a polyethylene film or a polypropylene film as a low-polarity substrate. Paper or a polymer film is used as the release sheet substrate in the release laminate sheet. Examples of the release agent that constitutes the release agent layer include general-purpose addition-type or condensation-type silicone-based release agents and long-chain alkyl group-containing compounds. Commercially available release laminate sheets may also be used. Examples include a heavy-duty separator film, which is a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films, and a light-duty separator film, which is a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films.

[0092] The thickness of the pressure-sensitive adhesive sheet of the present invention is not particularly limited and can be, for example, 75 μm to 500 μm, preferably 100 μm or more, more preferably 400 μm or less, and even more preferably 300 μm or less. The pressure-sensitive adhesive sheet of the present invention can be made relatively thick by a simple manufacturing method, and thick pressure-sensitive adhesive sheets can be easily manufactured, particularly by ultraviolet curing.

[0093] The pressure-sensitive adhesive sheet of the present invention can be used in various applications for bonding adherends together, for example, for bonding optical components together, and is particularly preferably used in touch sensors, which have traditionally had durability issues.

[0094] When the metal vapor deposition film or metal nanowire surface constituting a touch sensor is coated with a film having an amide bond, a urethane bond, or a nurate structure, it deteriorates when exposed to ultraviolet light or in a high-temperature, high-humidity environment, resulting in deterioration of the touch sensor itself. In this regard, a pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition contains the above-mentioned components and therefore has excellent adhesion to films having urethane bonds or the like (polyurethane films). Furthermore, when the pressure-sensitive adhesive sheet and the touch sensor are bonded together, the phenomenon of air bubbles forming between the pressure-sensitive adhesive sheet and the touch sensor or peeling can be significantly suppressed compared to conventional cases, i.e., excellent durability can also be achieved.

[0095] The pressure-sensitive adhesive sheet of the present invention has particularly excellent adhesion to films having an amide bond, a urethane bond, or a nurate structure, and can also enhance the durability of such films. The pressure-sensitive adhesive sheet of the present invention is particularly suitable for films having a urethane bond. Examples of films having a urethane bond include films formed from urethane materials.

[0096] (Laminate) The pressure-sensitive adhesive sheet of the present invention can form a laminate together with an adherend. That is, the laminate comprises the pressure-sensitive adhesive sheet of the present invention and an adherend. In particular, the laminate preferably comprises the pressure-sensitive adhesive sheet of the present invention and a touch sensor. In such a laminate, the pressure-sensitive adhesive sheet is, for example, directly attached to the touch sensor.

[0097] In the laminate, the touch sensor can be, for example, a wide variety of known touch sensor films. For example, a film having an amide bond, a urethane bond, or a nurate structure may be formed on the surface of the touch sensor. As described above, the pressure-sensitive adhesive sheet of the present invention has high adhesion to these films and can impart excellent durability to the touch sensor. For example, the surface of the touch sensor can be coated with a urethane resin.

[0098] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification. [Example]

[0099] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0100] The following acrylic monomers were prepared for producing acrylic polymers used in the examples and comparative examples. 2EHA: 2-Ethylhexyl acrylate BA: Butyl acrylate CHMA: Cyclohexyl methacrylate 4HBA: 4-hydroxybutyl acrylate AA: Acrylic acid

[0101] In addition, the following "polyfunctional monomers," "silane coupling agents," "polycarbodiimides," and "photoinitiators" used in each example were prepared.

[0102] (polyfunctional monomer) A-200: Bifunctional monomer (polyethylene glycol #200 diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd., NK Ester A-200 (registered trademark))

[0103] (Silane coupling agent) KBM-9659 (Shin-Etsu Chemical Co., Ltd. "KBM-9659" (registered trademark), tris(trimethoxysilylpropyl) isocyanurate)

[0104] (Polycarbodiimide) The following polycarbodiimides having a weight-average molecular weight of 500 or more were prepared. V-02B: Polycarbodiimide (Nisshinbo Chemical, Carbodilite V-02B, carbodiimide equivalent weight 600) V-03: Polycarbodiimide (Nisshinbo Chemical, Carbodilite V-03, carbodiimide equivalent weight 216) V-05: Polycarbodiimide (Nisshinbo Chemical, Carbodilite V-05, carbodiimide equivalent weight 262)

[0105] (carbodiimide) The following carbodiimide compounds having a weight-average molecular weight of less than 500 were prepared. Stavaczol I: Bis(2,6-diisopropylphenyl)carbodiimide (manufactured by Rhein Chemie)

[0106] (photoinitiator) ESACURE ONE: IGM Resins BV

[0107] (Production Example 1: Production of acrylic tackifier a) A 2L flask equipped with a stirrer, nitrogen inlet tube, condenser, and thermometer was charged with 250 g of methyl methacrylate, 250 g of isobornyl methacrylate, 15 g of n-dodecyl mercaptan, 500 g of ethyl acetate, and 200 g of methyl ethyl ketone. The atmosphere was purged with nitrogen at a nitrogen flow rate of 300 ml / min for 60 minutes, after which the nitrogen flow rate was reduced to 100 ml / min and the temperature was raised to 70 °C in a water bath and then stopped. 2 g of AIBN was added and the mixture was allowed to react for 3 hours while controlling the heat generation. An additional 3 g of AIBN was then added and the mixture was allowed to react for 4 hours, after which it was cooled to 30 °C. Finally, the mixture was dried at 100 °C for 5 hours to remove the solvent, yielding an acrylic tackifier a (referred to as tackifying resin a in Table 1) with a weight average molecular weight of 8,000 and a glass transition temperature of 95 °C. The tackifier was previously dried at 100 °C for 5 hours to remove the solvent before use in each example.

[0108] Example 1 <Syrup production> A syrup containing an acrylic polymer was synthesized according to the acrylic syrup composition shown in Table 1. Specifically, 1,000 parts by mass of a monomer mixture consisting of BA and 4HBA (mass ratio 80:20) prepared in the amounts shown in Table 1 and 0.06 parts by mass of n-dodecyl mercaptan were added to a 2-L flask equipped with a stirrer, a nitrogen inlet tube, a condenser, and a thermometer. The mixture was then heated to 65°C in a water bath, 0.15 g of AIBN was added, and the reaction was allowed to proceed for 30 minutes while controlling the heat generation, and then cooled to room temperature. Additional monomers (2EHA and 4HBA) were added to the flask to achieve the aforementioned monomer ratio by mass, and the solids concentration was adjusted to 20%. In this manner, a syrup containing an acrylic polymer with a solids concentration of 20% by mass and a weight-average molecular weight of 900,000 was obtained.

[0109] <Production of Pressure-Sensitive Adhesive Composition> Next, a pressure-sensitive adhesive sheet was obtained from a pressure-sensitive adhesive composition prepared according to the blending conditions shown in Table 1. First, as shown in Table 1, 0.3 parts by mass of a polyfunctional monomer, 0.3 parts by mass of a silane coupling agent, 0.3 parts by mass of "Carbodilite V-02B" manufactured by Nisshinbo Chemical Co., Ltd. as a polycarbodiimide, and 0.3 parts by mass of a photoinitiator were added to 100 parts by mass of the total amount of syrup, and the mixture was stirred and degassed to obtain pressure-sensitive adhesive composition 1.

[0110] <Production of adhesive sheets> The obtained pressure-sensitive adhesive composition 1 was applied to a 100 μm thick polyester film (release sheet) coated with a silicone release agent to a thickness of 100 μm, and then laminated with a 75 μm thick polyester film (release sheet) coated with a silicone release agent. After that, the laminate was irradiated with a chemical lamp at an illuminance of 5 mW / cm. 2 , cumulative illuminance 750mJ / cm 2 and then irradiated with a high-pressure mercury lamp at an illuminance of 200 mW / cm 2 , cumulative illuminance 2000mJ / cm 2 A pressure-sensitive adhesive layer was formed by irradiating the material so as to obtain a pressure-sensitive adhesive sheet 1 having a thickness of 175 μm and provided with release sheets on both sides.

[0111] Example 2 <Syrup production> A syrup containing an acrylic polymer with a solid content of 20% by mass and a weight-average molecular weight of 900,000 was obtained in the same manner as in the production of the syrup of Example 1, except that the acrylic syrup composition was changed to the composition shown in Table 1.

[0112] <Production of Pressure-Sensitive Adhesive Composition> Pressure-sensitive adhesive composition 2 was obtained in the same manner as in the production of the pressure-sensitive adhesive composition of Example 1, except that the conditions for preparing the pressure-sensitive adhesive composition were changed to those shown in Table 1.

[0113] <Production of adhesive sheets> An adhesive sheet 2 was obtained in the same manner as in the production of the adhesive sheet of Example 1, except that adhesive composition 2 was used instead of adhesive composition 1.

[0114] Example 3 <Syrup production> A syrup containing an acrylic polymer with a solid content of 20% by mass and a weight-average molecular weight of 900,000 was obtained in the same manner as in the production of the syrup of Example 1, except that the acrylic syrup composition was changed to the composition shown in Table 1.

[0115] <Production of Pressure-Sensitive Adhesive Composition> Next, a pressure-sensitive adhesive sheet was obtained from a pressure-sensitive adhesive composition prepared according to the blending conditions shown in Table 1. First, as shown in Table 1, 3 parts by mass of tackifier resin a, 0.3 parts by mass of a polyfunctional monomer, 0.3 parts by mass of a silane coupling agent, 0.5 parts by mass of "Carbodilite V-05" manufactured by Nisshinbo Chemical Co., Ltd. as a polycarbodiimide, and 0.3 parts by mass of a photoinitiator were added to 100 parts by mass of the total amount of syrup, and the mixture was stirred and degassed to obtain pressure-sensitive adhesive composition 3.

[0116] <Production of adhesive sheets> An adhesive sheet 3 was obtained in the same manner as in the production of the adhesive sheet of Example 1, except that adhesive composition 3 was used instead of adhesive composition 1.

[0117] (Comparative Example 1) <Syrup production> A syrup containing an acrylic polymer with a solid content of 20% by mass and a weight-average molecular weight of 900,000 was obtained in the same manner as in the production of the syrup of Example 1, except that the acrylic syrup composition was changed to the composition shown in Table 1.

[0118] <Production of Pressure-Sensitive Adhesive Composition> A pressure-sensitive adhesive composition 1a (containing no polycarbodiimide) was obtained in the same manner as in the production of the pressure-sensitive adhesive composition of Example 3, except that the conditions for preparing the pressure-sensitive adhesive composition were changed to those shown in Table 1.

[0119] <Production of adhesive sheets> An adhesive sheet 1a was obtained in the same manner as in the production of the adhesive sheet of Example 1, except that adhesive composition 1a was used instead of adhesive composition 1.

[0120] (Comparative Example 2) <Syrup production> A syrup containing an acrylic polymer with a solid content of 20% by mass and a weight-average molecular weight of 900,000 was obtained in the same manner as in the production of the syrup in Example 1.

[0121] <Production of Pressure-Sensitive Adhesive Composition> Next, a pressure-sensitive adhesive sheet was obtained from a pressure-sensitive adhesive composition prepared according to the formulation conditions shown in Table 1. First, as shown in Table 1, 0.3 parts by mass of a polyfunctional monomer, 0.3 parts by mass of a silane coupling agent, 0.5 parts by mass of a carbodiimide, and 0.3 parts by mass of a photoinitiator were added to 100 parts by mass of a total amount of syrup, and the mixture was stirred and degassed to obtain pressure-sensitive adhesive composition 1b. This pressure-sensitive adhesive composition 1d did not contain a polycarbodiimide having a weight-average molecular weight of 500 or more, but contained a carbodiimide compound having a weight-average molecular weight of less than 500.

[0122] <Production of adhesive sheets> An adhesive sheet 1b was obtained in the same manner as in the production of the adhesive sheet of Example 1, except that adhesive composition 1b was used instead of adhesive composition 1.

[0123] (Comparative Example 3) <Syrup production> A syrup containing an acrylic polymer (containing carboxyl groups) with a solids concentration of 20% by mass and a weight-average molecular weight of 900,000 was obtained in the same manner as in the production of the syrup of Example 1, except that the acrylic syrup composition was changed to the composition shown in Table 1.

[0124] <Production of Pressure-Sensitive Adhesive Composition> A pressure-sensitive adhesive composition 1c was obtained in the same manner as in the production of the pressure-sensitive adhesive composition of Example 1, except that the conditions for preparing the pressure-sensitive adhesive composition were changed to those shown in Table 1.

[0125] <Production of adhesive sheets> An adhesive sheet 1c was obtained in the same manner as in the production of the adhesive sheet of Example 1, except that adhesive composition 1 was changed to adhesive composition 1c.

[0126] Evaluation method (Tg of acrylic tackifier) A Hitachi High-Tech Science DSC600 was used to measure the glass transition temperature of the tackifier. 5 mg of alumina was used as a reference, and approximately 5 mg of the solvent-removed tackifier resin was placed in a 5 mm diameter aluminum sample pan. The temperature was raised from 0 to 150°C at a rate of 10°C / min under a nitrogen flow rate of 50 ml / min. The inflection point where the specific heat changed was read as the glass transition temperature of the tackifier resin.

[0127] (Durability test) A urethane hard coating agent, "Z-876HL" manufactured by AICA, was applied to a 125 μm thick polyester film ("U403" manufactured by Toray) so that the thickness after drying would be 5 μm, and the film was formed by drying in a dryer at 80°C for 3 minutes. After that, a metal halide lamp was used to irradiate the film with a UV intensity of 100 mW / cm. 2 , the cumulative light intensity is 1000mJ / cm 2 The coating was irradiated with UV light so that the urethane hard-coat layer was formed. This resulted in a polyester film having a urethane hard-coat layer. Meanwhile, one release sheet (light separator) of the pressure-sensitive adhesive sheet prepared in each Example and Comparative Example was peeled off, and the exposed adhesive surface was attached to the urethane hard-coat surface of the polyester film having the urethane hard-coat layer formed thereon. Next, the other release sheet (heavy separator) was peeled off from the pressure-sensitive adhesive sheet, and a 1 mm thick, 76 mm long, and 52 mm thick glass sheet (manufactured by Matsunami Glass Industry Co., Ltd.) was attached to the exposed adhesive surface. This resulted in a laminate consisting of the glass sheet, the pressure-sensitive adhesive sheet, and the polyester film having a urethane hard-coat layer formed thereon. The laminate was then autoclaved at a temperature of 30°C and a pressure of 0.5 MPa for 30 minutes, and then left at atmospheric pressure and room temperature for 1 day to obtain a laminate for evaluation. This evaluation laminate was then left to stand for 500 hours in a thermo-hygrostat at a temperature of 85°C and a humidity of 85%, after which the condition of the evaluation laminate was observed and its durability was evaluated according to the following criteria. ≪Judgment criteria≫ ◯: No bubbles or peeling were observed in the pressure-sensitive adhesive sheet, the appearance was good, and the sheet had excellent durability. ×: Air bubbles or peeling was observed in the pressure-sensitive adhesive sheet, the appearance was poor, and the durability was poor.

[0128] Evaluation results Table 1 shows the acrylic syrup composition, glass transition temperature of the acrylic polymer, hydroxyl value (OHV) of the adhesive composition, preparation conditions of the adhesive composition, thickness of the obtained adhesive sheet, and measurement results of durability test in producing the adhesive sheet obtained in each Example and Comparative Example. Note that in Table 1, blank cells in the preparation conditions of the adhesive composition indicate that the raw material was not used.

[0129] As can be seen from Table 1, the pressure-sensitive adhesive sheets obtained in the Examples were excellent in durability. In contrast, the pressure-sensitive adhesive sheets obtained in Comparative Examples 1 and 2 were inferior in durability because they did not contain polycarbodiimide, and the pressure-sensitive adhesive sheet obtained in Comparative Example 3 was inferior in durability because it contained an acrylic polymer containing 10% by mass of acrylic monomer units having a carboxyl group.

[0130] From the above results, it was found that the adhesive sheets obtained in the examples have excellent adhesion to films formed from urethane materials and can also enhance the durability of films formed from urethane materials.

[0131] [Table 1]

Claims

1. An adhesive sheet for attaching a touch sensor, which is used to attach a touch sensor, Contains a cured product of the pressure-sensitive adhesive composition, The pressure-sensitive adhesive composition contains an acrylic polymer and a polycarbodiimide, The acrylic polymer is composed of acrylic monomer units having no carboxyl group, The pressure-sensitive adhesive sheet, wherein the polycarbodiimide has a carbodiimide group in the molecule and has a weight average molecular weight of 500 or more.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the surface of the touch sensor is coated with a film having an amide bond, a urethane bond, or a nurate structure.

3. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive composition is substantially free of solvent.

4. The pressure-sensitive adhesive composition according to claim 1 , wherein the acrylic polymer has a glass transition temperature of 0° C. or lower.

5. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive composition has a hydroxyl value of 30 mgKOH / g or more and 250 mgKOH / g or less.

6. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive composition further comprises a tackifier.

7. A laminate comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 6 and a touch sensor.

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