Adhesive compositions, adhesives, adhesive sheets and laminates

Abstract

An adhesive composition, adhesive, adhesive sheet, and laminate are provided that exhibit excellent step-following properties while suppressing optical inhomogeneity. The solution is an adhesive composition comprising: a (meth)acrylate polymer (A), an ionic compound (B), and an active energy line hardening component (C), wherein the aforementioned (meth)acrylate polymer (A) contains an ethyl carbonate-containing monomer having an ethyl carbonate structure as shown in formula (1) as a monomer unit constituting the polymer.

Description

Technical Field

[0001] This invention relates to an adhesive composition, adhesive, adhesive sheet, and laminate suitable for use in displays (showpieces), etc. Prior Technology

[0002] In recent years, various mobile electronic devices such as smartphones and tablets have been equipped with displays using display modules with liquid crystal elements, light-emitting diodes (LED elements), organic electroluminescent (organic EL) elements, etc. Most of these displays are touch panels.

[0003] In displays like the aforementioned, a protective panel is typically provided on the surface of the display module. With the trend towards thinner and lighter electronic devices, this protective panel has shifted from traditional glass panels to plastic panels such as acrylic sheets or polycarbonate sheets.

[0004] Here, a gap is provided between the protective panel and the display module so that the deformed protective panel will not collide with the display module even if it is deformed by external force.

[0005] However, when gaps, i.e. air layers, exist as described above, the light reflection loss caused by the difference in refractive index between the protective panel and the air layer, as well as the difference in refractive index between the air layer and the display module, increases, resulting in a decrease in the display's image quality.

[0006] Therefore, a method has been proposed to improve the image quality of a display by filling the gap between the protective panel and the display module with an adhesive layer. For example, Patent Document 1 discloses an adhesive layer for filling the gap between the protective panel and the display module, which has a shear storage modulus (G') of 1.0 × 10⁵ Pa or less at 25°C and 1 Hz, and a gel fraction of 40% or more. [Previous Technical Documents] [Patent Literature]

[0007] Patent Document 1: Japanese Patent Application Publication No. 2010-97070 Summary of the Invention

[0008] [The problem the invention aims to solve]

[0009] In Patent Document 1, step tracking is improved by reducing the storage modulus of the adhesive layer at room temperature. However, when the storage modulus at room temperature is reduced to such a low level as described above, the storage modulus at high temperatures is lower than required, causing problems under durable conditions. For example, bubbles are generated near the step when subjected to high temperature and high humidity conditions. In addition, conventional adhesive layers sometimes exhibit optical non-uniformity such as visible distortion near the step.

[0010] The present invention was made in view of this situation, and its object is to provide an adhesive composition, adhesive, adhesive sheet and laminate that have excellent step following properties and can suppress the generation of optical inhomogeneity. [Problem-solving methods]

[0011] To achieve the above objectives, firstly, the present invention provides an adhesive composition comprising: a (meth)acrylate polymer (A), an ionic compound (B), and an active energy line hardening component (C), wherein the (meth)acrylate polymer (A) contains an ethylene carbonate-containing monomer having the structure shown in the following formula (1) as a monomer unit constituting the polymer (Invention 1). [Chemistry 1]

[0012] In the aforementioned invention (Invention 1), the adhesive obtained by containing the above-mentioned components exhibits excellent cohesive strength even without a crosslinking agent, resulting in superior workability (e.g., workability when using adhesive sheets). Furthermore, along with this cohesive strength, it also exhibits excellent stress relaxation properties, and when hardened by active energy ray irradiation, its step-following performance from the initial stage to high temperature and humidity conditions (harsh durability conditions) becomes excellent. Moreover, the aforementioned excellent stress relaxation properties suppress optical inhomogeneities (optical distortion, etc.). Then, since the aforementioned adhesive composition does not require a crosslinking agent, an aging period is not needed when obtaining the adhesive, thus improving the productivity of adhesive sheets.

[0013] In the above invention (Invention 1), the above (meth)acrylate polymer (A), as the monomer unit constituting the polymer, preferably contains 0.5% by mass or more and 40% by mass or less of the above ethyl carbonate-containing monomer (Invention 2).

[0014] In the above inventions (Inventions 1 and 2), it is preferred that the above-mentioned ionic compound (B) is an alkali metal salt (Invention 3).

[0015] In the above inventions (Inventions 1 to 3), the content of the ionic compound (B) in the adhesive composition is preferably 0.1 parts by mass or more and 2 parts by mass or less relative to 100 parts by mass of the (meth)acrylate polymer (A) (Invention 4).

[0016] In the above inventions (Inventions 1 to 4), the content of the crosslinking agent in the adhesive composition is preferably 0.1 parts by weight or less relative to 100 parts by weight of the (meth)acrylate polymer (A) (Invention 5).

[0017] Second, the present invention provides an adhesive formed by crosslinking the above-mentioned adhesive compositions (Inventions 1-5) (Invention 6).

[0018] Third, the present invention provides an adhesive sheet having at least an adhesive layer, wherein the adhesive layer is formed from the adhesive (invention 6) (invention 7).

[0019] Fourth, the present invention provides an adhesive sheet having at least an adhesive layer. The adhesive constituting the adhesive layer is an active energy radiation-curable adhesive. The strain of the adhesive constituting the adhesive layer at 25°C after applying a stress of 7950 Pa for 1210 seconds is 30% to 1500%. The ratio of the strain of the cured adhesive formed by subjecting the adhesive constituting the adhesive layer to active energy radiation curing to 1210 seconds after applying a stress of 7950 Pa for 25°C to the cured adhesive is less than 1. The maximum relaxation modulus of the adhesive constituting the adhesive layer, measured according to JIS K7244-1 when the adhesive strain is 10%, is defined as the maximum relaxation modulus G(t)max (MPa). The maximum relaxation modulus G(t) is determined from the measured maximum relaxation modulus G(t). From the maximum time of 3757 seconds, the adhesive is subjected to a continuous strain of 10%. The minimum relaxation modulus value measured during this period is set as the minimum relaxation modulus G(t) min (MPa). The relaxation modulus variation value ΔlogG(t) calculated from the following formula (X) is 1.2 or more and 3 or less (Invention 8). ΔlogG(t)=logG(t) max-logG(t) min…(X)

[0020] In the above invention (Invention 8), the strain of the cured adhesive formed by subjecting the adhesive constituting the adhesive layer to active energy radiation curing is preferably 50% or more and 600% or less after 1210 seconds when a stress of 7950 Pa is applied to the cured adhesive at 25°C (Invention 9).

[0021] In the above inventions (Inventions 8 and 9), the cured adhesive formed by subjecting the adhesive constituting the adhesive layer to active energy radiation curing is defined as the maximum relaxation modulus G(t)max (MPa) measured when the cured adhesive is strained by 10% according to JIS K7244-1. The minimum relaxation modulus measured during the period from the time the maximum relaxation modulus G(t)max is measured until 3757 seconds later is defined as the minimum relaxation modulus G(t)min (MPa). The relaxation modulus variation ΔlogG(t) calculated from the above formula (X) is preferably 1.2 or more and 3 or less (Invention 10).

[0022] In the above inventions (Inventions 7-10), the adhesive sheet has two release sheets, and the adhesive layer is preferably held in contact with the release surfaces of the two release sheets (Invention 11).

[0023] Fifth, the present invention provides a laminate comprising: a display body constituting member, other display body constituting members, and a hardened adhesive layer for bonding the one display body constituting member and the other display body constituting members together, wherein the hardened adhesive layer is a hardened adhesive layer formed by hardening the adhesive layer of the adhesive sheet (Invention 7-11) with active energy rays (Invention 12).

[0024] In the above invention (Invention 12), it is preferable that at least one of the above-mentioned display body constituting member and the other display body constituting member has a step difference on the side surface that is adhered by the adhesive layer (Invention 13). [The effects of the invention]

[0025] The adhesive compositions, adhesives, adhesive sheets, and laminates of the present invention exhibit excellent step-following properties while suppressing optical inhomogeneities. Simple Explanation of the Diagram

[0026] [Figure 1] is a cross-sectional view of an adhesive sheet according to an embodiment of the present invention. [Figure 2] is a cross-sectional view of a laminate according to an embodiment of the present invention. Implementation

[0027] The following describes embodiments of the present invention. [Adhesive Composition] An adhesive composition of one embodiment of the present invention (hereinafter referred to as "adhesive composition P") preferably contains: a monomer unit constituting the polymer, a (meth)acrylate polymer (A) containing a monomer having an ethyl carbonate structure as shown in the following formula (1), and an ionic compound (B). [Chemistry 1] Furthermore, in this specification, the term (meth)acrylic acid refers to both acrylic acid and methacrylic acid. Other similar terms follow the same principle. Additionally, "polymer" also includes the concept of "copolymer."

[0028] Since the (meth)acrylate polymer (A) is composed of the aforementioned monomer containing ethyl carbonate, the adhesive composition P of this embodiment contains an ethyl carbonate structure as a side chain of the (meth)acrylate polymer (A). When the (meth)acrylate polymer (A) contains an ethyl carbonate structure in its side chain, the interaction between the side chains becomes stronger, and the glass transition temperature (Tg) of the (meth)acrylate polymer (A) becomes higher. As a result, the cohesive force of the obtained adhesive becomes stronger. Furthermore, the ethyl carbonate structure contains two carbonyl dipoles. Thus, the ethyl carbonate structure, as a side chain of the (meth)acrylate polymer (A), interacts with the ionic compound (B) to form a pseudo-crosslinking structure. With this crosslinking structure, the obtained adhesive can still exhibit good cohesive force even without a crosslinking agent, resulting in excellent workability (e.g., workability when using adhesive sheets). Furthermore, from the perspective of the polarity of the ethyl carbonate structure, the obtained adhesive exhibits higher adhesion, particularly to glass. On the other hand, when specific pressure (and heat) is applied to the adhesive, the aforementioned cross-linking structure relaxes, exhibiting excellent stress relaxation properties. For example, when the adherend has a gradient, it easily conforms to the shape of that gradient. Even after the specific pressure (and heat) is removed, it maintains a good conformity to the shape of the gradient, forming a pseudo-cross-linking structure again. In this case, since the stress in the adhesive is less likely to remain when conforming to the shape of the gradient, the force that the adhesive tries to return to its pre-contouring state is suppressed to a smaller extent, maintaining a good conformity to the shape of the gradient. In addition, the adhesive is hardened by irradiation with active energy rays (after adhesion to the adherend), further enhancing cohesion and increasing coating strength. Through these effects, the adhesive sheet obtained using this adhesive exhibits excellent gradient conformity from the initial stage to high temperature and humidity (severe durability conditions). Furthermore, the term "initial stage" here refers to removal immediately after application. Additionally, residual stress from conventional adhesives is significant near areas of step difference, etc. For example, even in cases of excellent step-following performance under initial high temperature and humidity conditions (in other words, no bubbles, bumps, or peeling occur near step difference), optical unevenness (optical distortion, etc.) occurs near step difference due to the distortion of the adhesive caused by the force of the adhesive attempting to return to its pre-following state. However, adhesive sheets obtained using the adhesive from the adhesive composition P of this embodiment exhibit excellent suppression of optical unevenness near step difference because the force of the adhesive attempting to return to its pre-following state is suppressed to a smaller level. For example, the image quality and appearance of the display can be improved.Furthermore, since the adhesive composition of this embodiment does not require a crosslinking agent, an aging period is not needed when obtaining the adhesive, thereby improving the productivity of the adhesive sheet. Moreover, the term "crosslinking" in this specification includes not only general crosslinking via covalent bonds, but also pseudo-crosslinking caused by interactions (including, but not limited to, those caused by coordination bonds, ionic bonds, intermolecular forces, etc.).

[0029] (1) Components of the adhesive composition (1-1) (Meth)acrylate polymer (A) As a monomer containing ethyl carbonate with the structure shown in formula (1) above, there are no particular limitations as long as it contains the ethyl carbonate structure and can undergo polymerization reaction with other monomers constituting (meth)acrylate polymer (A).

[0030] Preferred examples of monomers containing ethyl carbonate include (meth)acrylates having an organic group having an ethyl carbonate structure bonded to a (meth)acrylic acid oxy group. Examples of such (meth)acrylates include acrylates represented by the following formula (2). [Chemistry 2] , Or the methacrylate shown in formula (3) below. [Chemistry 3] Furthermore, in either formula (2) or formula (3), n represents an integer greater than or equal to 0. Among the (meth)acrylates represented by formulas (2) and (3) above, (meth)acrylates with n of 1 or more are preferred, and (meth)acrylates with n of 2 or more are preferred. With n of 1 or more, the ethyl carbonate group, which is a side chain of the (meth)acrylate polymer (A), becomes located further away from the main chain, and the probability of the ethyl carbonate structures in the obtained adhesive overlapping each other increases. As a result, the stacking interaction of the ethyl carbonate structures comes into play, making it easier to exhibit the following mechanical properties (strain, relaxation modulus variation, storage modulus) and adhesion. In addition, the interaction between the ethyl carbonate structure and the ionic compound (B) becomes more likely to occur, and it is easier to form a pseudo-crosslinking structure, resulting in higher cohesive strength. Through these effects, the obtained adhesive becomes one with better step-following properties. Furthermore, it exhibits excellent suppression of optical non-uniformity and superior operability. There is no particular limitation on the upper limit of n mentioned above; from the viewpoint of polymerizability, 10 or less is preferred, 6 or less is even better, especially 4 or less, and further preferably 3 or less. Among these, from the viewpoint of easily improving the mechanical properties (strain, relaxation modulus variation, storage modulus), adhesion, and step followability of the obtained adhesive, n=2 (meth)acrylate is preferred, especially n=2 methyl methacrylate (2-sideoxy-1,3-dioxolane-4-yl) from formula (3). Moreover, the monomer containing ethyl carbonate can be used alone or in combination of two or more.

[0031] As a monomer unit constituting the polymer, the (meth)acrylate polymer (A) preferably contains 0.5% by mass or more of the aforementioned ethyl carbonate-containing monomer, more preferably 1% by mass or more, particularly 5% by mass or more, and even more preferably 10% by mass or more. In this way, the stacking interaction of the ethyl carbonate structures becomes effective, making it easier to exhibit good mechanical properties (strain, relaxation modulus variation, storage modulus) and adhesion. Furthermore, the interaction between the ethyl carbonate structure and the ionic compound (B) becomes more readily apparent, making it easier to form a pseudo-crosslinking structure, resulting in higher cohesive strength. Through these effects, the obtained adhesive exhibits superior step-following properties. In addition, it exhibits excellent suppression of optical inhomogeneities and excellent workability. Moreover, from a polarity point of view, the adhesive strength of the adhesive, especially its adhesion to glass, becomes higher.

[0032] On the other hand, as a monomer unit constituting the polymer, the (meth)acrylate polymer (A) preferably contains 40% by mass or less of the aforementioned ethyl carbonate-containing monomer, more preferably 30% by mass or less, particularly preferably 25% by mass or less, and even more preferably 20% by mass or less. This makes it easier to satisfy the following mechanical properties (strain, relaxation modulus variation, storage modulus), resulting in superior step follower properties.

[0033] In this embodiment, the (meth)acrylate polymer (A) preferably contains an alkyl (meth)acrylate as a monomer unit constituting the polymer. This results in an adhesive exhibiting good adhesion. The alkyl group can be linear or branched.

[0034] From the viewpoint of adhesion, alkyl methacrylates with 1 to 20 carbon atoms in the alkyl group are preferred as (meth)acrylates. Examples of alkyl methacrylates with 1 to 20 carbon atoms in the alkyl group include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, n-decyl methacrylate, n-dodecyl methacrylate, myristyl methacrylate, palmitate methacrylate, stearyl methacrylate, etc.

[0035] Of the above, from the viewpoint of imparting good adhesion, alkyl (meth)acrylates with 2 to 12 carbon atoms in the alkyl group are preferred, especially alkyl (meth)acrylates with 4 to 10 carbon atoms in the alkyl group. Specifically, n-butyl (meth)acrylate is preferred, especially n-butyl acrylate. These can be used alone or in combination of two or more.

[0036] From the viewpoint of imparting good adhesion, the (meth)acrylate polymer (A), as a monomer unit constituting the polymer, preferably contains 50% by mass or more of alkyl (meth)acrylate, more preferably 60% by mass or more, particularly 70% by mass or more, and further preferably 80% by mass or more. Furthermore, from the viewpoint of ensuring the content of other monomers (especially monomers containing ethyl carbonate), it is preferable to contain 99.5% by mass or less of alkyl (meth)acrylate, more preferably 99% by mass or less, particularly 95% by mass or less, and further preferably 90% by mass or less.

[0037] The monomer constituting the (meth)acrylate polymer (A) is preferably a monomer containing reactive functional groups within its molecule. Monomers containing reactive functional groups facilitate the interaction between the (meth)acrylate polymer (A) and the ionic compound (B), making it easier to form a pseudo-crosslinking structure. As a result, the obtained adhesive exhibits higher cohesive strength and more readily satisfies the following mechanical properties (strain, relaxation modulus variation, storage modulus), thus exhibiting superior step-following properties.

[0038] Preferred examples of monomers containing reactive functional groups include monomers with an intramolecular hydroxyl group (hydroxyl-containing monomers), monomers with an intramolecular carboxyl group (carboxyl-containing monomers), and monomers with an intramolecular amino group (amino-containing monomers). Among these, monomers containing hydroxyl groups are preferred from the viewpoint of easily forming the aforementioned pseudo-crosslinking structure. One type of monomer containing reactive functional groups may be used alone, or two or more may be used in combination.

[0039] Examples of hydroxyl-containing monomers include, for instance, hydroxyalkyl methacrylates such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 3-hydroxybutyl methacrylate, and 4-hydroxybutyl methacrylate. Among these, 2-hydroxyethyl methacrylate and 4-hydroxybutyl methacrylate are preferred from the viewpoint of easily forming the aforementioned pseudo-crosslinking structure, especially 2-hydroxyethyl methacrylate and 4-hydroxybutyl methacrylate. These can be used alone or in combination of two or more.

[0040] Examples of carboxyl-containing monomers include vinyl unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. These can be used alone or in combination of two or more.

[0041] Examples of amine-containing monomers include (meth)acrylate aminoethyl ester and (meth)acrylate n-butylaminoethyl ester. These can be used alone or in combination of two or more.

[0042] As a monomer constituting the polymer, the (meth)acrylate polymer (A) preferably contains 0.1 to 10% by mass of monomers containing reactive functional groups, more preferably 0.4 to 8% by mass, particularly 0.8 to 6% by mass, and further preferably 1 to 3% by mass. By containing monomers containing reactive functional groups within the above range, the aforementioned pseudo-crosslinking structure is more easily formed. As a result, the resulting adhesive has higher cohesive strength and becomes easier to satisfy the following mechanical properties (strain, relaxation modulus variation, storage modulus), resulting in better step follower properties. In addition, it exhibits excellent suppression of optical non-uniformity and also excellent workability.

[0043] The (meth)acrylate polymer (A) in this embodiment may further contain other monomers as constituent monomers. Examples of such other monomers include, for instance, alicyclic (meth)acrylates such as dicyclopentane (meth)acrylate, adamantane (meth)acrylate, isoborneol (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate; alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; non-crosslinked acrylamides such as acrylamide and methacrylamide; non-crosslinked (meth)acrylates with tertiary amino groups such as N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate; vinyl acetate; and styrene. These monomers may be used alone or in combination of two or more.

[0044] The polymer (A) of this embodiment can be a random polymer or a block polymer. Furthermore, the (meth)acrylate polymer (A) can be obtained by polymerizing the aforementioned monomers using common methods. For example, it can be prepared by emulsion polymerization, solution polymerization, suspension polymerization, bulk polymerization, aqueous solution polymerization, etc. Among these methods, solution polymerization in an organic solvent is preferred from the viewpoint of stability during polymerization and ease of use.

[0045] The weight-average molecular weight of the (meth)acrylate polymer (A) is preferably 100,000 to 2,000,000, more preferably 300,000 to 1,500,000, especially 500,000 to 1,000,000, and further preferably 650,000 to 800,000. This makes the resulting adhesive more likely to meet the following mechanical properties (strain, relaxation modulus variation, storage modulus), resulting in superior step-following properties. Furthermore, it exhibits excellent suppression of optical non-uniformity and superior workability. Also, the weight-average molecular weight in this specification is a value converted to standard polystyrene, determined by gel permeation chromatography (GPC).

[0046] Furthermore, the adhesive composition P of this embodiment may contain one of the above-mentioned (meth)acrylate polymers (A), or it may contain two or more. Additionally, the adhesive composition P of this embodiment may contain the above-mentioned (meth)acrylate polymer (A) and also contain another (meth)acrylate polymer.

[0047] (1-2) Ionic compounds (B) The term "ionic compound" as used in this specification refers to a compound formed by electrostatic attraction primarily induced by cations and anions. The ionic compound (B) in this embodiment can be either a liquid (ionic liquid) or a solid (ionic solid) at room temperature.

[0048] Examples of ionic compounds (B) include alkali metal salts, alkaline earth metal salts, nitrogen-containing onium salts, sulfur-containing onium salts, and phosphorus-containing onium salts. Among these, alkali metal salts or alkaline earth metal salts are preferred from the viewpoint of easily forming the aforementioned pseudo-crosslinking structure with (meth)acrylate polymers (A), especially alkali metal salts. Furthermore, ionic compound (B) can be used alone or in combination of two or more.

[0049] Specific examples of alkali metal salts include potassium bis(fluorosulfonyl)imidin, lithium bis(fluorosulfonyl)imidin, potassium bis(fluoromethanesulfonyl)imidin, lithium bis(fluoromethanesulfonyl)imidin, potassium bis(trifluoromethanesulfonyl)imidin, and lithium bis(trifluoromethanesulfonyl)imidin. Among these, lithium bis(trifluoromethanesulfonyl)imidin is preferred from the viewpoint of easily forming the aforementioned pseudo-crosslinking structure.

[0050] The content of the ionic compound (B) in the adhesive composition is preferably 0.1 to 2 parts by weight, more preferably 0.2 to 1.5 parts by weight, and particularly preferably 0.3 to 1 part by weight, and further preferably 0.4 to 0.7 parts by weight, relative to 100 parts by weight of the (meth)acrylate polymer (A). By having the content of the ionic compound (B) within the above range, the degree of pseudo-crosslinking becomes appropriate. As a result, the obtained adhesive readily satisfies the following mechanical properties (strain, relaxation modulus variation, storage modulus), exhibiting superior step-following properties. Furthermore, it exhibits excellent suppression of optical non-uniformity and also excellent workability.

[0051] (1-3) Hardening components of active energy lines (C) An adhesive obtained from an adhesive composition P containing an active energy line-curing component (C) exhibits plasticity when specific pressure (and heat) is applied during adhesion to a substrate (before active energy ray curing). For example, when the substrate has a gradient, the adhesive readily conforms to the shape of that gradient. This results in excellent initial gradient conformability. Then, through curing caused by active energy ray irradiation after adhesion to the substrate, the active energy line-curing component (C) polymerizes with each other, presumably adhering to the pseudo-crosslinking structure of the (meth)acrylate polymer (A). The cured adhesive with this high-dimensional structure exhibits high cohesive strength and high coating strength, making it superior in gradient conformability under high temperature and humidity conditions (harsh durability conditions).

[0052] The active energy beam hardening component (C) is not particularly limited in terms of the component that can achieve the above-mentioned effect, as long as it is hardened by irradiation with active energy rays. It can be any of monomers, oligomers, or polymers, or a mixture thereof. Among them, polyfunctional acrylate monomers with excellent compatibility with (meth)acrylate polymers (A) are preferred examples.

[0053] Examples of multifunctional acrylate monomers include, for instance, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol adipic acid di(meth)acrylate, and neopentyl glycol hydroxypivalic acid di(meth)acrylate. diacrylate), dicyclopentyl di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, ethylene oxide-modified di(meth)acrylate phosphate, di(acryloxyethyl)triisocyanate, ethoxylated di(meth)acrylate, allylated cyclohexyl di(meth)acrylate, ethoxylated bisphenol A diacrylate, 9,9-bis[4-(2-acryloxyethoxy)phenyl]furan, etc., difunctional; trimethylolpropane tri(meth)acrylate, dinepentylenetetrol tri(meth)acrylate, propionic acid-modified dinepentylenetetrol tri(meth)acrylate, new Trifunctional monomers include pentylenetetroxide tri(meth)acrylate, ethoxylated triisocyanate tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, tris(acryloxyethyl)triisocyanate, and ε-caprolactone-modified tris(2-(meth)acryloxyethyl)triisocyanate; quadrufunctional monomers include diglycerol tetra(meth)acrylate and neopentylenetetroxide tetra(meth)acrylate; pentafunctional monomers include propionic acid-modified dinepentylenetetroxide penta(meth)acrylate; and hexafunctional monomers include dinepentylenetetroxide hexa(meth)acrylate and caprolactone-modified dinepentylenetetroxide hexa(meth)acrylate. These monomers can be used alone or in combination of two or more. Furthermore, from the viewpoint of compatibility with (meth)acrylate polymers (A), multifunctional acrylate monomers with a molecular weight of less than 1000 are preferred.

[0054] From the perspective of the step-following property of the obtained cured adhesive under high temperature and high humidity conditions, polyfunctional acrylate monomers containing a trimocyanate structure within the molecule are preferred. Among these polyfunctional acrylate monomers containing a trimocyanate structure within the molecule, those that have undergone ethoxylation are preferred, especially at least one of ethoxylated di(meth)acrylate and ethoxylated tri(meth)acrylate, and more preferably both ethoxylated di(meth)acrylate and ethoxylated tri(meth)acrylate.

[0055] As the active energy line curing component (C), an active energy ray curable acrylate oligomer can be used. Examples of such acrylate oligomers include polyester acrylates, epoxy acrylates, urethane acrylates, polyether acrylates, polybutadiene acrylates, and silicone acrylates.

[0056] The weight average molecular weight of the above-mentioned acrylate oligomers is preferably below 50,000, especially preferably between 1,000 and 50,000, and further preferably between 3,000 and 40,000. These acrylate oligomers can be used alone or in combination of two or more.

[0057] Furthermore, as the active energy line hardening component (C), an adduct acrylate polymer with a (meth)acrylic group introduced into the side chain can be used. Such an adduct acrylate polymer can be obtained by reacting a compound having a (meth)acrylic group and a group that reacts with the crosslinking functional group onto a portion of the crosslinking functional group of the copolymer using a copolymer of (meth)acrylate and a monomer having an intramolecular crosslinking functional group.

[0058] The weight average molecular weight of the above-mentioned acrylate polymers is preferably around 50,000 to 900,000, especially around 100,000 to 500,000.

[0059] The active energy line curing component (C) can be selected from the above-mentioned multifunctional acrylate monomers, acrylate oligomers and adduct acrylate polymers, or can be used in combination of two or more, or can be used in combination with other active energy line curing components.

[0060] From the viewpoint of improving initial step follow-through and enhancing the cohesive strength of the cured adhesive, the content of the active energy line curing component (C) in the adhesive composition P, resulting in superior step follow-through under high temperature and high humidity, is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and especially 3 parts by mass or more, relative to 100 parts by mass of the (meth)acrylate polymer (A). On the other hand, from the viewpoint of preventing phase separation between the active energy line curing component (C) and the (meth)acrylate polymer (A), the above-mentioned content is preferably 12 parts by mass or less, more preferably 8 parts by mass or less, and especially 6 parts by mass or less.

[0061] (1-4) Photopolymerization initiator (D) When using ultraviolet light as the active energy ray to harden the adhesive obtained from the adhesive composition P, it is preferable that the adhesive composition P further contains a photopolymerization initiator (D). By containing a photopolymerization initiator (D) in this way, the active energy line hardening component (C) can be polymerized efficiently, or the polymerization hardening time and the amount of active energy ray irradiation can be reduced.

[0062] Examples of photopolymerization initiators (D) include, for example, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, and 1-hydroxycyclohexyl. Phenylacetone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)one, benzophenone, p-phenyl diphenylone, 4,4'-diethylamino diphenylone, dichloro diphenylone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone These include thioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzil dimethyl ketal, acetophenone dimethyl ketal, p-dimethylaminobenzoate, oligomeric [2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]acetone], 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, etc. These can be used alone or in combination of two or more.

[0063] The content of photopolymerization initiator (D) in the adhesive composition P is preferably 0.1 to 30 parts by mass relative to 100 parts by mass of the active energy line curing component (C), particularly 1 to 20 parts by mass, and further preferably 5 to 12 parts by mass. In this way, the obtained adhesive readily satisfies the following mechanical properties (strain, relaxation modulus variation, storage modulus), becoming one with superior step-following properties.

[0064] (1-5) Various additives In the adhesive composition P, various additives commonly used in acrylic adhesives may be added as needed, such as crosslinking agents, silane coupling agents, rust inhibitors, UV absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, and refractive index modifiers. Furthermore, the polymerization solvents and diluents described below are not included in the additives constituting the adhesive composition P.

[0065] As mentioned above, since the adhesive composition P forms a pseudo-crosslinking structure, a crosslinking agent is unnecessary. Therefore, curing is not required in obtaining the adhesive. From this perspective, it is preferable that the adhesive composition P does not contain a crosslinking agent.

[0066] However, the adhesive composition P does not exclude the presence of a crosslinking agent. When the adhesive composition P contains a crosslinking agent, the content of the crosslinking agent is preferably 0.1 parts by weight or less relative to 100 parts by weight of the (meth)acrylate polymer (A), and more particularly preferably 0.01 parts by weight or less. Furthermore, the crosslinking agent referred to herein is a crosslinking agent that forms a covalent bond with the (meth)acrylate polymer (A), and examples include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and amine-based crosslinking agents.

[0067] (2) Preparation of adhesive composition The adhesive composition P can be prepared by mixing the obtained (meth)acrylate polymer (A) with an ionic compound (B) and an active energy line hardening component (C), and by adding a photopolymerization initiator (D), additives, etc. as needed.

[0068] (Meth)acrylate polymer (A) can be prepared by polymerizing a mixture of monomers constituting the polymer using a conventional free radical polymerization method. The polymerization of (meth)acrylate polymer (A) is preferably carried out by solution polymerization using a polymerization initiator as needed. However, the invention is not limited to this; polymerization can also be carried out in a solvent-free environment. Examples of polymerization solvents include, for instance, ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc., and two or more may be used in combination.

[0069] Examples of polymerization initiators include azo compounds and organic peroxides, and two or more can be used together. Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-formonitrile), 2,2'-azobis(2,4-dimethylpentanonitrile), 2,2'-azobis(2,4-dimethyl-4-methoxypentanonitrile), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanopentanoic acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane].

[0070] Examples of organic peroxides include, for instance, benzoyl peroxide, tributyl perbenzoate, cumene hydroperoxide, diisopropyl percarbonate, di-n-propyl percarbonate, di(2-ethoxyethyl) percarbonate, tributyl peroxyneodecanate, tributyl peroxynepentanoate, (3,5,5-trimethylhexyl) peroxide, dipropyl peroxide, and diacetyl peroxide.

[0071] Furthermore, by incorporating chain transfer agents such as 2-mercaptoethanol in the above polymerization steps, the weight-average molecular weight of the obtained polymer can be adjusted.

[0072] When obtaining (meth)acrylate polymer (A), an ionic compound (B), an active energy line hardening component (C), and, as needed, a photopolymerization initiator (D), a diluent, and additives are added to a solution of (meth)acrylate polymer (A) and thoroughly mixed to obtain a solvent-diluted adhesive composition P (coating solution). Furthermore, if any of the above components is used in solid form, or if precipitation occurs when mixed with other components in an undiluted state, this component can be pre-dissolved or diluted in a diluent before being mixed with other components.

[0073] As diluents, the following can be used: aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as dichloromethane and vinyl chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and ceroxox solvents such as ethyl ceroxox.

[0074] The concentration and viscosity of the coating solution prepared in this way can be appropriately selected according to the specific conditions, as long as they fall within the coatable range. For example, the adhesive composition P can be diluted to a concentration of 10-60% by mass. Furthermore, the addition of diluents is not necessary when obtaining the coating solution; as long as the adhesive composition P has a coatable viscosity, diluents may not be added. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent of (meth)acrylate polymer (A) is directly used as the diluent.

[0075] [Adhesive] The adhesive of one embodiment of the present invention is obtained from the adhesive composition P of the above embodiment, specifically, by crosslinking (pseudo-crosslinking) the adhesive composition P.

[0076] Crosslinking of the adhesive composition P can usually be achieved by heat treatment. Furthermore, this heat treatment can also serve as a drying process for the evaporation of diluents and other substances from the coating of the adhesive composition P applied to the desired object.

[0077] The optimal heating temperature for heat treatment is 50~150℃, and the optimal heating time is 10 seconds to 10 minutes.

[0078] When the adhesive composition P contains a crosslinking agent, it is desirable to provide a maturation period to complete the crosslinking reaction after the above-mentioned heat treatment. However, since the adhesive composition P of this embodiment does not contain a crosslinking agent, a maturation period is not necessary. This improves the productivity of the adhesive sheet.

[0079] [Adhesive sheet] An adhesive sheet according to one embodiment of the present invention has at least an adhesive layer, preferably an adhesive sheet formed by laminating a release sheet on one or both sides of the adhesive layer.

[0080] The adhesive sheet of this embodiment is preferably used for bonding one component to other components, especially when at least one of the components has a step difference on at least the surface of the adhesive layer. As such components, display body constituent components are preferably listed. Therefore, the adhesive sheet of this embodiment is preferably used for optical applications, but is not limited thereto.

[0081] In one embodiment of the present invention, the adhesive layer in the adhesive sheet is formed from the aforementioned adhesive. Preferably, the adhesive layer or the adhesive constituting the adhesive layer has the physical properties described below.

[0082] In other embodiments of the present invention, the adhesive sheet preferably has the following physical properties. In other words, the strain (pre-curing strain) of the adhesive constituting the adhesive layer at 25°C after applying a stress of 7950 Pa for 1210 seconds is preferably 30% or more and 1500% or less. Furthermore, relative to the pre-curing strain, the ratio of the strain (post-curing strain) of the cured adhesive formed by subjecting the adhesive constituting the adhesive layer to active energy ray curing to the cured adhesive at 25°C after applying a stress of 7950 Pa for 1210 seconds is preferably less than 1. Furthermore, the adhesive constituting the adhesive layer is defined as follows: the maximum relaxation modulus value measured when the adhesive is strained by 10% according to JIS K7244-1 is set as the maximum relaxation modulus G(t) max (MPa). From the time the maximum relaxation modulus G(t) max is measured until 3757 seconds later, the adhesive is continuously strained by 10%, and the minimum relaxation modulus value measured during this period is set as the minimum relaxation modulus G(t) min (MPa). The relaxation modulus variation value ΔlogG(t) calculated from the following formula (X) is preferably 1.2 or more and 3 or less. ΔlogG(t)=logG(t) max-logG(t) min…(X)

[0083] Furthermore, the details of the methods for determining the strain (%) and the relaxation modulus G(t) are shown in the experimental examples below. In addition, the phrase "when a stress of 7950 Pa is applied to the adhesive" refers to the time point at which the stress applied to the adhesive reaches 7950 Pa.

[0084] The adhesive sheet of this embodiment, by virtue of the aforementioned physical properties of the adhesive constituting the adhesive layer, makes the adhesive layer easy to deform. Furthermore, due to its excellent stress relaxation properties, it exhibits excellent step tracking performance from the initial stage to high temperature and humidity. In addition, it has excellent suppression of optical non-uniformity and also excellent operability.

[0085] Especially when the aforementioned strain is 30% or more, the adhesive layer is easily deformed due to moderate strain when external force is applied, resulting in excellent step follow-through both initially and after autoclaving. Furthermore, when the aforementioned strain is 120% or more, the stress relaxation percentage ΔlogG(t) tends to increase, making it easier to meet the desired range. From this perspective, a strain of 120% or more is preferred, 220% or more is even better, especially 320% or more, and further preferably 420% or more.

[0086] Furthermore, especially when the aforementioned strain is below 1500%, the adhesive exhibits high cohesiveness, and even under conditions of high temperature and high humidity, the step follow-through is excellent. In addition, cohesive fracture of the adhesive is less likely to occur, suppressing the formation of residues when the adhesive sheet is peeled from the substrate. Furthermore, the resulting adhesive sheet exhibits excellent workability. From this perspective, a strain of 1200% or less is preferred, especially below 1000%, and further preferably below 900%.

[0087] Furthermore, when the ratio of the aforementioned strain is less than 1, the cured adhesive layer exhibits high cohesiveness and adhesion, becoming an excellent performer in terms of step follow-through under high temperature and high humidity conditions. From this perspective, the aforementioned strain ratio is preferably 0.9 or less, more preferably 0.8 or less, especially preferably 0.7 or less, and further preferably 0.6 or less. From the viewpoint of preventing the cured adhesive layer from becoming too hard and the step follow-through under high temperature and high humidity conditions from deteriorating, the lower limit of the aforementioned strain ratio is preferably 0.1 or more, especially preferably 0.2 or more, and further preferably 0.3 or more.

[0088] Furthermore, when the aforementioned relaxation modulus variation value ΔlogG(t) is 1.2 or higher, it exhibits excellent stress relaxation properties. Therefore, after the adhesive sheet is attached to the step of the substrate, it is easy to relax the stress within the adhesive, especially the residual stress near the step. In this way, even under high temperature and high humidity conditions, it suppresses the occurrence of protrusion and peeling induced by the residual stress during step application, and exhibits excellent step following performance. From this point of view, the aforementioned relaxation modulus variation value ΔlogG(t) is preferably 1.4 or higher, especially 1.5 or higher, and further preferably 1.6 or higher.

[0089] Furthermore, when the aforementioned relaxation modulus variation value ΔlogG(t) is 3 or less, the adhesive becomes more likely to exhibit moderate stress relaxation. From this perspective, the aforementioned relaxation modulus variation value ΔlogG(t) is preferably 2.5 or less, especially 2.2 or less, and further preferably 1.9 or less.

[0090] The strain of the cured adhesive formed by applying a stress of 7950 Pa to the adhesive constituting the adhesive layer at 25°C for 1210 seconds after stress is applied is preferably 50% or more and 600% or less. Furthermore, the maximum relaxation modulus value measured when the cured adhesive is strained to 10% according to JIS K7244-1 is defined as the maximum relaxation modulus G(t)max (MPa). The minimum relaxation modulus value measured during the period from the measurement of the maximum relaxation modulus G(t)max to 3757 seconds after the measured minimum relaxation modulus G(t)min (MPa) is defined as the minimum relaxation modulus G(t)min (MPa). The relaxation modulus variation value ΔlogG(t) calculated from the above formula (X) is preferably 1.2 or more and 3 or less.

[0091] By virtue of the aforementioned physical properties of the cured adhesive, the cured adhesive layer readily exhibits excellent cohesiveness and adhesion, especially demonstrating superior step-following performance under harsh conditions of high temperature and high humidity. Furthermore, it also exhibits excellent suppression of optical inhomogeneities.

[0092] In particular, when the strain of the cured adhesive is 50% or more, it is easy to maintain good adhesion to the substrate (especially near the step difference), and its step-following performance remains excellent even under harsh high temperature and high humidity conditions. Furthermore, the stress relaxation rate variation ΔlogG(t) tends to increase, making it easier to meet the desired range. From this perspective, a strain of 120% or more for the cured adhesive is preferred, especially 180% or more, and further preferably 240% or more.

[0093] Furthermore, when the strain of the cured adhesive is 600% or less, the adhesive exhibits high cohesiveness, resulting in excellent step follow-through even under harsh high-temperature and high-humidity conditions. In addition, cohesive failure of the adhesive is less likely to occur, suppressing the formation of residues when the adhesive sheet is peeled off from the substrate. From this perspective, a strain of 500% or less for the cured adhesive is preferred, especially 400% or less, and further preferably 300% or less.

[0094] On the other hand, when the relaxation modulus variation ΔlogG(t) of the cured adhesive is 1.2 or higher, it exhibits excellent stress relaxation properties. Therefore, after the adhesive sheet is attached to the step of the substrate, it is easy to relax the stress within the adhesive, especially the residual stress near the step. In this way, even under high temperature and high humidity conditions, it suppresses the occurrence of bumps and peeling induced by residual stress during step application, and exhibits excellent step following properties. From this point of view, the relaxation modulus variation ΔlogG(t) of the cured adhesive is preferably 1.3 or higher, especially 1.4 or higher, and further preferably 1.5 or higher.

[0095] Furthermore, when the relaxation modulus variation ΔlogG(t) of the cured adhesive is 3 or less, the adhesive becomes more prone to exhibiting moderate stress relaxation. From this perspective, the relaxation modulus variation ΔlogG(t) is preferably 2.5 or less, especially 2 or less, and further preferably 1.8 or less.

[0096] The gel fraction of the adhesive constituting the adhesive layer is preferably between 0% and 60%. With this gel fraction within the aforementioned range, it becomes easier to adjust the strain and relaxation modulus variation ΔlogG(t) within the aforementioned range. From this perspective, a gel fraction of 1-40% is more preferred, especially 2-20%, further preferably 2.5-10%, and most preferably 3-6% or less. In particular, with a gel fraction of 10% or less, the adhesive can be considered pseudo-crosslinked, resulting in better initial step follow-through. Furthermore, the method for determining the gel fraction of the adhesive is shown in the following experimental example.

[0097] The gel fraction of the cured adhesive, formed by curing the adhesive constituting the adhesive layer with active energy rays, is preferably 10% or more, more preferably 20% or more, especially 30% or more, and further preferably 35% or more. This readily yields high cohesive strength and high coating strength, resulting in superior step follow-through under harsh conditions of high temperature and humidity. Furthermore, the gel fraction is preferably 90% or less, more preferably 75% or less, especially 65% ​​or less, and further preferably 55% or less. This makes it easier to meet the aforementioned strain requirements.

[0098] The storage modulus (G') of the adhesive constituting the adhesive layer at 25°C is preferably 0.01 MPa or higher, more preferably 0.04 MPa or higher, particularly preferably 0.06 MPa or higher, and even more preferably 0.08 MPa or higher. In this way, the obtained adhesive easily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the above-mentioned ranges, resulting in superior step follow-through under high temperature and high humidity conditions, while the adhesive sheet possessing this adhesive exhibits excellent operability. Furthermore, the following adhesive strength is easily satisfied. The test method for the storage modulus (G') is shown in the following test example.

[0099] On the other hand, the storage modulus (G') of the adhesive constituting the adhesive layer at 25°C is preferably below 1 MPa, more preferably below 0.5 MPa, especially below 0.3 MPa, and further preferably below 0.15 MPa. In this way, the obtained adhesive more easily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the aforementioned range, resulting in better initial step follow-through. Furthermore, it becomes easier to satisfy the following adhesion strength.

[0100] The storage modulus (G') of the adhesive constituting the adhesive layer at 50°C is preferably 0.01 MPa or higher, more preferably 0.02 MPa or higher, particularly preferably 0.03 MPa or higher, and even more preferably 0.04 MPa or higher. In this way, the obtained adhesive readily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the aforementioned range, resulting in superior step follow-through under high temperature and high humidity conditions. Furthermore, it readily satisfies the following adhesion strength.

[0101] On the other hand, the storage modulus (G') of the adhesive constituting the adhesive layer at 50°C is preferably below 1 MPa, more preferably below 0.5 MPa, especially below 0.3 MPa, and further preferably below 0.1 MPa. In this way, the obtained adhesive easily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the above range, resulting in excellent initial step followability, especially after lamination by hot pressing or the like. Furthermore, it becomes easier to satisfy the following adhesion strength.

[0102] The storage modulus (G') of the adhesive constituting the adhesive layer at 85°C is preferably 0.01 MPa or higher, particularly 0.015 MPa or higher, and even more preferably 0.02 MPa or higher. In this way, the obtained adhesive readily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the aforementioned range, resulting in superior step follow-through under high temperature and high humidity conditions. Furthermore, it readily satisfies the following adhesion strength.

[0103] On the other hand, the storage modulus (G') of the adhesive constituting the adhesive layer at 85°C is preferably below 1 MPa, more preferably below 0.5 MPa, particularly below 0.1 MPa, and further preferably below 0.03 MPa. In this way, the obtained adhesive readily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the aforementioned range, resulting in superior step follow-through under high temperature and high humidity conditions. Furthermore, it becomes easier to satisfy the following adhesion strength.

[0104] The storage modulus (G') of the cured adhesive formed by subjecting the adhesive constituting the above-mentioned adhesive layer to active energy ray curing is preferably 0.02 MPa or higher at 25°C, more preferably 0.08 MPa or higher, particularly preferably 0.1 MPa or higher, and even more preferably 0.12 MPa or higher. In this way, the cured adhesive readily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the above-mentioned ranges, resulting in superior step follow-through under high temperature and high humidity conditions. Furthermore, it readily satisfies the following adhesion strength.

[0105] On the other hand, the storage modulus (G') of the cured adhesive at 25°C is preferably below 2 MPa, more preferably below 1 MPa, especially below 0.6 MPa, and further preferably below 0.4 MPa. In this way, the cured adhesive becomes more likely to satisfy the above-mentioned strain and relaxation modulus variation value ΔlogG(t) within the above-mentioned range, and furthermore, it becomes more likely to satisfy the following adhesion.

[0106] The storage modulus (G') of the cured adhesive formed by subjecting the adhesive constituting the above-mentioned adhesive layer to active energy ray curing is preferably 0.02 MPa or higher at 50°C, particularly 0.03 MPa or higher, and even more preferably 0.04 MPa or higher. In this way, the cured adhesive readily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the above-mentioned ranges, resulting in superior step follow-through under high temperature and high humidity conditions. Furthermore, it readily satisfies the following adhesion strength.

[0107] On the other hand, the storage modulus (G') of the cured adhesive at 50°C is preferably below 2 MPa, more preferably below 1 MPa, especially below 0.5 MPa, and further preferably below 0.2 MPa. In this way, the cured adhesive becomes more likely to satisfy the above-mentioned strain and relaxation modulus variation value ΔlogG(t) within the above-mentioned range, and furthermore, it becomes more likely to satisfy the following adhesion.

[0108] The storage modulus (G') of the cured adhesive formed by subjecting the adhesive constituting the above-mentioned adhesive layer to active energy ray curing is preferably 0.01 MPa or higher at 85°C, particularly 0.02 MPa or higher, and even more preferably 0.03 MPa or higher. In this way, the cured adhesive readily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the aforementioned range, resulting in superior step follow-through under high temperature and high humidity conditions. Furthermore, it readily satisfies the following adhesion strength.

[0109] On the other hand, the storage modulus (G') of the cured adhesive at 85°C, as an upper limit, is preferably below 2 MPa, more preferably below 1 MPa, especially below 0.1 MPa, and further preferably below 0.06 MPa. In this way, the cured adhesive easily satisfies the aforementioned strain and relaxation modulus variation value ΔlogG(t) within the aforementioned range, becoming superior in step follow-through under high temperature and high humidity conditions. Furthermore, it becomes easier to satisfy the following adhesion strength.

[0110] The adhesion force of the adhesive sheet of this embodiment to soda-lime glass is preferably greater than 1 N / 25 mm, more preferably greater than 10 N / 25 mm, especially greater than 20 N / 25 mm, and further preferably greater than 24 N / 25 mm. Furthermore, the adhesion force of the adhesive sheet of this embodiment to alkali-free glass is preferably greater than 1 N / 25 mm, more preferably greater than 10 N / 25 mm, especially greater than 18 N / 25 mm, and further preferably greater than 22 N / 25 mm. When the lower limit of the adhesion force to soda-lime glass or alkali-free glass is as described above, it exhibits superior step follow-through under high temperature and high humidity conditions. On the other hand, there is no particular upper limit for the adhesion of the aforementioned soda-lime glass or alkali-free glass. Considering the need for reworkability, it is preferable to have a value of 100N / 25mm or less, even more preferable to have a value of 60N / 25mm or less, especially preferable to have a value of 40N / 25mm or less, and even more preferable to have a value of 30N / 25mm or less.

[0111] Furthermore, the aforementioned adhesion force basically refers to the adhesion force measured according to the 180-degree peel test method based on JIS Z0237:2009, and the specific test method is shown in the following test examples.

[0112] After the adhesive sheet of this embodiment is attached to soda-lime glass, the adhesion strength of the cured adhesive layer to the soda-lime glass after being cured by active energy rays is preferably greater than 1 N / 25 mm, more preferably greater than 10 N / 25 mm, especially more preferably greater than 20 N / 25 mm, and further preferably greater than 26 N / 25 mm. Furthermore, after the adhesive sheet of this embodiment is attached to alkali-free glass, the adhesion strength of the cured adhesive layer to the alkali-free glass after being cured by active energy rays is preferably greater than 1 N / 25 mm, more preferably greater than 10 N / 25 mm, especially more preferably greater than 20 N / 25 mm, and further preferably greater than 24 N / 25 mm. On the other hand, the upper limit of the adhesion force of the aforementioned soda-lime glass or alkali-free glass is preferably below 100 N / 25 mm, more preferably below 60 N / 25 mm, especially below 40 N / 25 mm, and further preferably below 30 N / 25 mm. When the lower and upper limits of the adhesion force of the cured adhesive layer to soda-lime glass or alkali-free glass are as described above, it results in superior step follow-through under high temperature and high humidity conditions.

[0113] The haze value of the adhesive layer in the adhesive sheet of this embodiment (measured according to JIS K7136:2000) is preferably 1% or less from the viewpoint of high transparency and suitability for optical applications, especially 0.8% or less, and further preferably 0.6% or less. The lower limit of this haze value is usually 0% or more, preferably 0.1% or more, more preferably 0.2% or more, and especially preferably 0.3% or more.

[0114] In this embodiment, the total light transmittance of the adhesive layer in the adhesive sheet (measured according to JIS K7361-1:1997) is preferably 80% or higher, more preferably 90% or higher, especially 95% or higher, and further preferably 99% or higher, from the viewpoint of good visibility of the display and suitability for optical applications. The upper limit of this total light transmittance is typically 100% or lower.

[0115] An adhesive or adhesive layer having the above-mentioned physical properties is preferably obtained according to the above-mentioned adhesive composition P, but is not limited thereto.

[0116] Here, a specific configuration of the adhesive sheet as an example of this embodiment is shown in FIG1. ​​As shown in FIG1, the adhesive sheet 1 of this embodiment is composed of two release sheets 12a and 12b, and an active energy ray-curable adhesive layer 11 sandwiched between the two release sheets 12a and 12b in contact with the release surfaces of the two release sheets 12a and 12b. Furthermore, the release surface of the release sheet referred to in this specification refers to the surface on the release sheet that has release properties, including either the surface to which a release treatment has been performed or the surface that still exhibits release properties even without a release treatment.

[0117] 1. Each component 1-1. Adhesive layer The adhesive layer 11 of the adhesive sheet 1 in this embodiment has the composition or physical properties described above.

[0118] In this embodiment, the thickness of the adhesive layer 11 (measured according to JIS K7130) is preferably 1 μm or more, more preferably 5 μm or more, especially 10 μm or more, and further preferably 20 μm or more. This makes it easier to achieve the aforementioned adhesive force, resulting in better step-following performance. Furthermore, the thickness of the adhesive layer 11 is preferably 500 μm or less, more preferably 200 μm or less, especially 100 μm or less, further preferably 50 μm or less, and most preferably 30 μm or less. This suppresses appearance defects such as indentations and dents in the adhesive layer 11. Furthermore, it makes it possible to achieve thinner laminates (such as displays) obtained using this adhesive sheet 1. Also, the adhesive layer 11 can be formed as a single layer or as a multilayer laminate.

[0119] 1-2. Peeling sheet Release tabs 12a and 12b protect the adhesive layer 11 until the adhesive sheet 1 is used, and are then removed when the adhesive sheet 1 (adhesive layer 11) is used. In the adhesive sheet 1 of this embodiment, one or both of the release tabs 12a and 12b are not necessary.

[0120] As release sheets 12a and 12b, for example, polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer film, ethylene-(meth)acrylate polymer film, ethylene-(meth)acrylate polymer film, polystyrene film, polycarbonate film, polyimide film, fluoropolymer film, etc. Furthermore, cross-linked films of these can also be used. Moreover, laminated films of these can also be used.

[0121] It is preferable to perform a stripping treatment on the stripping surfaces of the aforementioned stripping sheets 12a and 12b. Examples of stripping agents used in the stripping treatment include alkyd-based, silicone-based, fluorinated, unsaturated polyester-based, polyolefin-based, and wax-based stripping agents.

[0122] There are no particular restrictions on the thickness of the release strips 12a and 12b, which are usually around 20~200μm.

[0123] 2. Manufacturing of adhesive sheets As an example of manufacturing the adhesive sheet 1, a coating solution of the adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), and then subjected to heat treatment to crosslink the adhesive composition P, forming an adhesive layer 11. Then, the release surface of another release sheet 12b (or 12a) is laminated onto this adhesive layer 11. In this way, the adhesive sheet 1 is obtained. The conditions for the heat treatment are as described above. By using the adhesive composition P in the formation of the adhesive layer 11, the adhesive sheet 1 can be manufactured in a non-cure manner.

[0124] As another manufacturing example of the adhesive sheet 1, a coating solution of the adhesive composition P is applied to the release surface of the release sheet 12a on one side, and then subjected to heat treatment to crosslink the adhesive composition P, forming an adhesive layer, thus obtaining a release sheet 12a with an adhesive layer. Furthermore, a coating solution of the adhesive composition P is applied to the release surface of the release sheet 12b on the other side, and then subjected to heat treatment to crosslink the adhesive composition P, forming an adhesive layer, thus obtaining a release sheet 12b with an adhesive layer. Then, the release sheet 12a with an adhesive layer and the release sheet 12b with an adhesive layer are bonded together such that the two adhesive layers are in contact with each other, forming an adhesive layer 11. In this way, the adhesive sheet 1 is obtained. According to this manufacturing example, even if the adhesive layer 11 is thick, it can be manufactured stably.

[0125] As a method for applying the coating solution of the above-mentioned adhesive composition P, for example, bar coating, blade coating, roller coating, doctor blade coating, die coating, gravure coating, etc. can be used.

[0126] [Laminated body] One embodiment of the present invention provides a laminate comprising: a display body component, other display body components, and a cured adhesive layer for bonding these display body components together. The cured adhesive layer is formed by curing the adhesive layer of the aforementioned adhesive sheet using active energy rays. This laminate is a display body (display panel) or a component thereof.

[0127] At least one of the aforementioned display constituent components and other display constituent components preferably has a step difference on the surface to which it is bonded by the aforementioned adhesive layer. Furthermore, this step difference is preferably caused by a printed layer. Because the cured adhesive layer exhibits excellent step difference tracking under high temperature and humidity conditions (severe durability conditions), even when the laminate is placed under severe high temperature and humidity conditions (e.g., 85°C, 85%RH, 500 hours), it can suppress the occurrence of bubbles, bumps, peeling, etc., near the step difference. Furthermore, because the cured adhesive layer also exhibits excellent optical non-uniformity suppression, optical non-uniformity near the step difference is also suppressed.

[0128] Figure 2 shows a specific configuration of a laminate as an example of this embodiment. As shown in Figure 2, the laminate 2 of this embodiment is composed of a first display body component 21, a second display body component 22, and a cured adhesive layer 11' sandwiched between the first display body component 21 and the second display body component 22. Furthermore, in the laminate 2 of this embodiment, the surface of the first display body component 21 on the side of the cured adhesive layer 11' has a step difference; specifically, the step difference depends on the presence or absence of the printed layer 3.

[0129] As the laminate 2, it may be a component constituting part of a display body such as a liquid crystal display (LCD), a light-emitting diode display (LED), an organic electroluminescent display (OLED), or electronic paper, or it may be the display body itself. Furthermore, the display body may be a touch panel or a flexible display that can be repeatedly bent.

[0130] The cured adhesive layer 11' in the aforementioned laminate 2 is formed by curing the adhesive layer 11 of the aforementioned adhesive sheet 1 by irradiation with active energy rays. It is speculated that when the adhesive constituting the adhesive layer 11 is formed by crosslinking the adhesive composition P, the crosslinked structure composed of (meth)acrylate polymer (A) and ionic compound (B) in the adhesive constituting this cured adhesive layer 11' wraps around the polymerized active energy ray curing component (C) to form a high-dimensional structure.

[0131] The first display body component 21 and the second display body component 22 are not particularly limited as long as the adhesive layer 11' can be adhered to after hardening. In addition, the first display body component 21 and the second display body component 22 can be made of the same material or different materials.

[0132] The first display body component 21 is preferably a protective panel formed of a glass plate, a plastic plate, or a laminate including such a material. In this case, the printed layer 3 is usually formed as a frame on the side of the cured adhesive layer 11' in the first display body component 21.

[0133] The glass plates mentioned above are not particularly limited, and examples include chemically strengthened glass, alkali-free glass, quartz glass, soda-lime glass, barium-strontium glass, aluminosilicate glass, lead glass, borosilicate glass, and barium borosilicate glass. The thickness of the glass plates is not particularly limited, but is usually 0.1~5mm, preferably 0.2~2mm.

[0134] The aforementioned plastic sheet is not particularly limited; examples include acrylic sheets and polycarbonate sheets. The thickness of the plastic sheet is not particularly limited, but is typically 0.2 to 5 mm, preferably 0.4 to 3 mm, particularly preferably 0.6 to 2.5 mm, and even more preferably 0.8 to 2.1 mm.

[0135] Furthermore, various functional layers (transparent conductive film, metal layer, silicon oxide layer, hard coating, anti-glare layer, etc.) can be applied to one or both sides of the aforementioned glass or plastic sheet, and optical components can also be laminated. In addition, the transparent conductive film and metal layer can also be patterned.

[0136] The second display component 22 is preferably an optical component, a display module (e.g., a liquid crystal (LCD) module, a light-emitting diode (LED) module, an organic electroluminescent (OLED) module, etc.), an optical component that is part of a display module, or a laminate containing a display module that should be attached to the first display component 21.

[0137] Examples of the aforementioned optical components include, for instance, shatterproof films, polarizing plates (polarizing films), polarizing elements, retardation plates (retardation films), viewing angle compensation films, brightness enhancement films, contrast enhancement films, liquid crystal polymer films, diffusion films, semi-transparent reflective films, and transparent conductive films. Shatterproof films can be hard coatings formed on one side of a substrate film.

[0138] The material constituting the printed layer 3 is not particularly limited, and known printing materials can be used. The thickness of the printed layer 3, i.e., the lower limit of the step height, is preferably 3 μm or more, more preferably 5 μm or more, especially 7 μm or more, and ideally 10 μm or more. By using the lower limit as described above, the concealment of wiring and the like can be sufficiently ensured so that it is not visible from the observer's side. Furthermore, the upper limit is preferably thinner than the thickness of the cured adhesive layer 11', preferably 80 μm or less, more preferably 50 μm or less, especially 25 μm or less, and further preferably 20 μm or less. By using the upper limit as described above, the deterioration of the step followability of the cured adhesive layer 11' of the printed layer 3 can be prevented. Furthermore, the thinning of the obtained laminate 2 becomes possible.

[0139] As an example, in manufacturing the aforementioned laminate 2, the release tab 12a on one side of the adhesive sheet 1 is peeled off, and the adhesive layer 11 exposed on the adhesive sheet 1 is attached to the surface of the first display body component 21 on the side where the printed layer 3 exists. At this time, due to the excellent step-following properties of the adhesive layer 11, gaps and bumps are suppressed near the step differences caused by the printed layer 3. Furthermore, due to the excellent optical non-uniformity suppression properties of the adhesive layer 11, optical non-uniformity near the step differences is also suppressed.

[0140] Then, the release tab 12b on the other side is peeled off from the adhesive layer 11 of the adhesive sheet 1, and the adhesive layer 11 exposed on the adhesive sheet 1 is bonded to the second display body component 22. In addition, as another example, the bonding order of the first display body component 21 and the second display body component 22 can also be interchanged.

[0141] In the above-described bonding process, hot pressing can also be performed to bond the adhesive layer 11 to the first display component 21 and the second display component 22. Because the adhesive layer 11 has excellent step-following properties, even at this stage, the generation of bubbles, protrusions, etc., near the step can be suppressed. The hot pressing process can be performed using general methods; for example, it is preferable to perform the process at a temperature of 40–80°C, a pressure of 0.3–1 MPa, and for 5–60 minutes.

[0142] After the above bonding process, the adhesive layer 11 in the laminate is irradiated with active energy rays. Irradiation with these active energy rays causes the adhesive layer 11 to harden, becoming a hardened adhesive layer 11'. In this way, the laminate 2 described above can be obtained.

[0143] The irradiation of the adhesive layer 11 by energy rays is usually performed through either the first display body component 21 or the second display body component 22, preferably through the first display body component 21 which serves as a protective panel.

[0144] So-called active energy rays refer to electromagnetic waves or charged particle rays that possess energy quanta. Specifically, examples include ultraviolet rays and electron rays. Among active energy rays, ultraviolet rays, which are particularly easy to manipulate, are preferred.

[0145] Ultraviolet (UV) irradiation can be achieved using high-pressure mercury lamps, fusion lamps, xenon lamps, etc. The optimal UV irradiation intensity is approximately 50–1000 mW / cm², with 100–500 mW / cm² being particularly desirable. Furthermore, the optimal light intensity is 50–10000 mJ / cm², with 200–7000 mJ / cm² being even better, and especially 500–3000 mJ / cm². On the other hand, electron beam irradiation can be achieved using electron beam accelerators, with an optimal intensity of approximately 10–1000 krad.

[0146] The aforementioned laminate 2 exhibits excellent step-following properties after curing due to the adhesive layer 11'. Even when the laminate 2 is subjected to harsh conditions such as high temperature and high humidity (e.g., 85°C, 85%RH, 500 hours), issues such as bubbles, bumps, and peeling near the step are suppressed. Furthermore, the adhesive layer 11' also exhibits excellent optical non-uniformity suppression after curing, thus suppressing optical non-uniformity near the step.

[0147] The embodiments described above are for the purpose of facilitating understanding of the present invention, but are not intended to limit the present invention. Therefore, the elements disclosed in the above embodiments encompass all design changes and equivalents within the scope of the present invention.

[0148] For example, either or both of the release tabs 12a and 12b in the adhesive sheet 1 can be omitted. Alternatively, the required optical component laminations can be used to replace the release tabs 12a and / or 12b. Furthermore, the first display body component 21 may or may not have the printed layer 3 (step difference), or it may have a step difference other than the printed layer 3. Moreover, not only the first display body component 21, but the second display body component 22 may also have a step difference on the side of the cured adhesive layer 11'.

[0149] Furthermore, in this specification, when "X~Y" (where X and Y are arbitrary numbers) are mentioned, unless otherwise specified, "X or more and Y or less" includes both "preferably greater than X" and "preferably less than Y". Additionally, when "X or more" (where X is any number) is mentioned, unless otherwise specified, it also includes "preferably greater than X", and when "Y or less" (where Y is any number) is mentioned, unless otherwise specified, it also includes "preferably less than Y". [Example]

[0150] The present invention will be further described in detail below by way of examples, etc., but the scope of the present invention is not limited to these examples.

[0151] [Example 1] 1. Modulation of (meth)acrylate polymer (A) 84 parts by mass of n-butyl acrylate, 15 parts by mass of methyl methacrylate (2-sideoxy-1,3-dioxolane-4-yl) methacrylate (a monomer containing ethyl carbonate), and 1 part by mass of 4-hydroxybutyl acrylate were copolymerized by solution polymerization to prepare (meth)acrylate polymer (A). The molecular weight of this (meth)acrylate polymer (A) was determined by the following method, and the weight average molecular weight (Mw) was 750,000.

[0152] 2. Preparation of adhesive compositions 100 parts by weight of the (meth)acrylate polymer (A) obtained in step 1 above (solid content conversion value; the same applies below), 0.5 parts by weight of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) diluted with methyl ethyl ketone as ionic compound (B), 3 parts by weight of a mixture of ethoxyisocyanurate diacrylate and ethoxyisocyanurate triacrylate (manufactured by Dong-A Synthetic Co., Ltd., product name "M-315") as active energy line curing component (C), and 0.3 parts by weight of a mixture of diphenyl ketone and 1-hydroxycyclohexylphenyl ketone in a 1:1 mass ratio as photopolymerization initiator (D) are mixed together, stirred thoroughly, and diluted with methyl ethyl ketone to obtain a coating solution of adhesive composition.

[0153] 3. Fabrication of adhesive sheets The coating solution of the adhesive composition obtained in step 2 above was applied to the release-treated surface of a heavy-duty release sheet (manufactured by Lintec Corporation, product name "SP-PET382150"), which had been treated with a silicone-based release agent on one side of a polyethylene terephthalate film, using a blade coater. Then, the coating layer was heat-treated at 90°C for 1 minute to form an adhesive layer.

[0154] Next, the adhesive layer on the heavy-release release sheet obtained above is bonded to a light-release release sheet (manufactured by Lintec Corporation, product name "SP-PET381130") on which one side of the polyethylene terephthalate film has been treated with a silicone-based release agent, with the treated surface of the light-release release sheet in contact with the adhesive layer, to create an adhesive sheet composed of a heavy-release release sheet / adhesive layer (thickness: 25μm) / light-release release sheet.

[0155] Furthermore, the thickness of the adhesive layer is measured according to JIS K7130 using a constant pressure thickness measuring instrument (manufactured by Teclock Co., Ltd, product name "PG-02").

[0156] Here, the proportions (solid content conversion values) of the adhesive composition, where (meth)acrylate polymer (A) is taken as 100 parts by weight, are shown in Table 1. Furthermore, the details of the omitted symbols, etc., listed in Table 1 are explained below. [(Meth)acrylate polymer (A)] BA: n-Butyl acrylate CARBOM: Methyl methacrylate (2-sidek-1,3-dioxolane-4-yl) 4HBA: 4-Hydroxybutyl acrylate [Ionic compound (B)] Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) [Active Energy Line Hardening Component (C)] A mixture of ethoxyisocyanurate diacrylate and ethoxyisocyanurate triacrylate (manufactured by Dong-A Synthetic Co., Ltd., product name "M-315"). [Photopolymerization Initiator (D)] A mixture of diphenyl ketone and 1-hydroxycyclohexylphenyl ketone in a 1:1 mass ratio [Cross-linking agent] Trimethylolpropane modified xylene diisocyanate (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75").

[0157] [Example 2, Comparative Examples 1-2] Except for the changes in the amount of ionic compound (B), the amount of active energy line hardening component (C), and the amount of photopolymerization initiator (D) as shown in Table 1, the adhesive sheet was prepared in the same manner as in Example 1.

[0158] [Comparative Example 3] By mixing 100 parts by weight of the (meth)acrylate polymer (A) obtained in step 1 of Example 1 with 0.22 parts by weight of trimethylolpropane-modified xylene diisocyanate (manufactured by Soken Chemical & Engineering Co., Ltd, product name "TD-75") as a crosslinking agent, stirring thoroughly, and diluting with methyl ethyl ketone, a coating solution of the adhesive composition is obtained.

[0159] The obtained adhesive composition coating solution was applied using a blade coater to the release-treated surface of a heavy-duty release sheet (manufactured by Lintec Corporation, product name "SP-PET382150") that had been treated with a silicone-based release agent on one side of a polyethylene terephthalate film. The coating was then heat-treated at 90°C for 1 minute to form a coating layer.

[0160] Next, the coating layer on the obtained heavy-release release sheet is bonded to a light-release release sheet (manufactured by Lintec Corporation, product name "SP-PET381130"), on which one side of the polyethylene terephthalate film has been treated with a silicone-based release agent, with the treated surface of the light-release release sheet in contact with the coating layer. The bond is then cured for 7 days at 23°C and 50%RH to produce an adhesive sheet consisting of a heavy-release release sheet, an adhesive layer (thickness: 25μm), and a light-release release sheet.

[0161] [Comparative Example 4] 1. Modulation of (meth)acrylate polymer (A) 99 parts by weight of n-butyl acrylate and 1 part by weight of 4-hydroxybutyl acrylate were copolymerized by solution polymerization to prepare (meth)acrylate polymer (A). The molecular weight of this (meth)acrylate polymer (A) was determined by the following method, and the weight average molecular weight (Mw) was 750,000.

[0162] 2. Preparation of adhesive compositions By mixing 100 parts by mass of the (meth)acrylate polymer (A) obtained in step 1 above with 0.5 parts by mass of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) diluted with methyl ethyl ketone as an ionic compound (B), stirring thoroughly, and diluting with methyl ethyl ketone, a coating solution of an adhesive composition is obtained.

[0163] 3. Manufacturing of adhesive sheets Using the coating solution of the adhesive composition obtained in step 2 above, an adhesive sheet was prepared in the same manner as in Example 1.

[0164] [Comparative Example 5] By mixing 100 parts by weight of the (meth)acrylate polymer (A) obtained in step 1 of Comparative Example 4 with 0.22 parts by weight of trimethylolpropane-modified xylene diisocyanate (manufactured by Soken Chemical & Engineering Co., Ltd, product name "TD-75") as a crosslinking agent, stirring thoroughly, and diluting with methyl ethyl ketone, a coating solution of the adhesive composition was obtained.

[0165] Using the coating solution of the obtained adhesive composition, an adhesive sheet was prepared in the same manner as in Comparative Example 3.

[0166] [Comparative Example 6] A coating solution of an adhesive composition was obtained by mixing 100 parts by mass of the (meth)acrylate polymer (A) obtained in step 1 of Comparative Example 4, 0.5 parts by mass of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) diluted with methyl ethyl ketone as ionic compound (B), and 0.22 parts by mass of trimethylolpropane-modified xylene diisocyanate (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75") as a crosslinking agent, stirring thoroughly, and diluting with methyl ethyl ketone.

[0167] Using the coating solution of the obtained adhesive composition, an adhesive sheet was prepared in the same manner as in Comparative Example 3.

[0168] The weight-average molecular weight (Mw) mentioned above is the converted weight-average molecular weight of polystyrene determined by gel permeation chromatography (GPC) under the following conditions (GPC determination). <Measurement Conditions> GPC measuring device: Tosoh Corporation, HLC-8020 GPC tubing (passing through in the following order): Manufactured by Tosoh Corporation TSK guard column HXL-H TSK gel GMHXL (×2) TSK gel G2000HXL Determination solvent: tetrahydrofuran Measurement temperature: 40℃

[0169] [Experimental Example 1] (Determination of Gel Fraction) The adhesive sheet prepared in the examples and comparative examples was cut into 80mm × 80mm pieces. This adhesive layer was wrapped in a polyester sieve (sieve aperture size 200). The mass of this sieve was weighed using a precision balance. By deducting the mass of the sieve alone, the mass of the adhesive alone was calculated. This mass was taken as M1.

[0170] Next, the adhesive wrapped in the aforementioned polyester screen was immersed in ethyl acetate for 24 hours at room temperature (23°C). Afterward, the adhesive was removed and air-dried for 24 hours at 23°C and 50% relative humidity, followed by further drying in an oven at 80°C for 12 hours. The dried adhesive was weighed using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the screen. This mass was taken as M2. The gel fraction (%) is expressed as (M2 / M1) × 100. Thus, the gel fraction of the adhesive (before UV treatment) was derived. The results are shown in Table 2.

[0171] Furthermore, the adhesive layer of the adhesive sheet prepared in the embodiment was irradiated with active energy rays (ultraviolet; UV) under the following conditions through a light-peeling release sheet to harden the adhesive layer, thus forming a hardened adhesive layer. The gel fraction (after UV) was derived for the adhesive of this hardened adhesive layer in the same manner as described above. The results are shown in Table 2.

[0172] <Conditions of Irradiation by Active Energy Rays> Use a high-pressure mercury lamp Illuminance: 200 mW / cm², Light intensity: 1000 mJ / cm² The UV illuminance photometer used is the "UVPF-A1" manufactured by EYE GRAPHICS CO.,LTD.

[0173] [Experimental Example 2] (Determination of Storage Modulus) Multiple layers of adhesive layers from the adhesive sheets produced in the examples and comparative examples were stacked to form a laminate with a thickness of 0.8 mm. A cylinder with a punched hole diameter of 8 mm (height of 0.8 mm) was obtained from the laminated adhesive layers and used as a sample.

[0174] For the above samples, according to JIS K7244-1, a viscoelasticity measuring apparatus (manufactured by Anton Paar, product name "MCR302") was used to determine the dynamic viscoelasticity under the following conditions by torsional shear method: storage modulus (G') at 25℃, 50℃, and 85℃ (before UV; MPa). The results are shown in Table 2. Measurement frequency: 1Hz Measurement temperature range: -20℃ to 150℃ Heating rate: 3℃ / minute

[0175] Furthermore, for the adhesive sheet prepared in the examples, the adhesive was hardened by irradiating the sample with active energy rays (ultraviolet; UV) under the same conditions as in Test Example 1, thus obtaining a sample after active energy irradiation. The storage modulus (after UV irradiation; MPa) at 23°C was measured for the obtained sample after active energy irradiation, in the same manner as the sample before active energy irradiation. The results are shown in Table 2.

[0176] [Experimental Example 3] (Determination of Relaxation Modulus Variation) Multiple layers of adhesive layers were stacked on the adhesive sheets produced in the examples and comparative examples to form a stack with a thickness of 0.8 mm. A cylinder with a punched hole diameter of 8 mm (height of 0.8 mm) was obtained from the stack of adhesive layers and used as a sample.

[0177] For the above samples, according to JIS K7244-1, a viscoelasticity measuring apparatus (manufactured by Anton Paar, product name "MCR302") was used to measure the relaxation modulus G(t) (MPa) under the following conditions, with the adhesive subjected to a continuous strain of 10%. From the measurement results, the maximum relaxation modulus G(t)max (MPa) was derived, and the minimum relaxation modulus G(t)min (MPa) measured 3757 seconds after the measurement of the maximum relaxation modulus G(t)max was also derived. Measurement temperature: 25℃ Measurement points: 1000 points (logarithmic plot)

[0178] From the obtained maximum relaxation modulus G(t)max (MPa) and minimum relaxation modulus G(t)min (MPa), the relaxation modulus variation ΔlogG(t) (before UV) is calculated based on the following formula (X). The results are shown in Table 2. ΔlogG(t)=logG(t) max-logG(t) min…(X)

[0179] Furthermore, for the adhesive sheet prepared in the examples, the adhesive was irradiated with active energy rays (ultraviolet; UV) under the same conditions as in Test Example 1 to harden the sample, thus obtaining a sample after active energy irradiation. The relaxation modulus change value ΔlogG(t) (after UV irradiation) was calculated for the obtained sample after active energy irradiation, in the same manner as for the sample before active energy irradiation. The results are shown in Table 2.

[0180] [Experimental Example 4] (Determination of Dependent Variable) Multiple layers of adhesive layer were stacked on the adhesive sheets produced in the examples and comparative examples to form a laminate with a thickness of 0.2 mm. A cuboid with a hole of 15 mm × 15 mm (height 0.2 mm) was punched from the obtained laminate of adhesive layer and used as a sample.

[0181] For the above samples, according to JIS K7244-1, a viscoelasticity measuring apparatus (manufactured by Anton Paar, product name "MCR302") was used to continuously apply a certain stress to the samples under the following conditions, and the strain (before UV; %) was measured 1210 seconds after the stress was applied. The results are shown in Table 2. Measurement temperature: 25℃ Measurement points: 321 points Stress: 7950 Pa

[0182] Furthermore, for the adhesive sheet prepared in the examples, the sample was irradiated with active energy rays (ultraviolet; UV) under the same conditions as in Test Example 1 to harden the adhesive, thus obtaining a sample after active energy irradiation. The strain (after UV irradiation; %) of the obtained sample after active energy irradiation was measured in the same manner as the sample before active energy irradiation. The results are shown in Table 2.

[0183] Furthermore, the ratio of the strain after UV treatment (post-curing strain) to the strain before UV treatment obtained in the above measurements (pre-curing strain) was calculated (post-UV / pre-UV). The results are shown in Table 2.

[0184] [Experimental Example 5] (Determination of Haze Value) The adhesive layer of the adhesive sheet prepared in the examples and comparative examples was bonded to glass and used as the test sample. After background measurement of the glass, the haze value (%) of the test sample was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., product name "SH-7000") according to JIS K7136:2000. The results are shown in Table 2. Furthermore, the adhesive sheet prepared in the examples was irradiated with active energy rays under the same conditions as in Test Example 1 to harden the adhesive layer before the above measurements were performed.

[0185] [Experimental Example 6] (Determination of total light transmittance) The adhesive layer of the adhesive sheet prepared in the examples and comparative examples was bonded to glass and used as the test sample. After background measurement of the glass, the total light transmittance (%) of the test sample was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., product name "SH-7000") according to JIS K7361-1:1997. The results are shown in Table 2. Furthermore, the adhesive sheet prepared in the examples was irradiated with active energy rays under the same conditions as in Test Example 1 to harden the adhesive layer before the above measurements were performed.

[0186] [Experimental Example 7] (Determination of Adhesion) From the adhesive sheets produced in the examples and comparative examples, a light-release type release sheet was peeled off, and the exposed adhesive layer was bonded to the easy-bond layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET TA063", thickness: 100 μm) having an easy-bond layer, to obtain a laminate of a heavy-release type release sheet / adhesive layer / PET film. Furthermore, regarding Comparative Example 3, a light-release type release sheet was not used in the manufacture of the adhesive sheet; instead, an adhesive sheet consisting of a heavy-release type release sheet / adhesive layer (thickness: 25 μm) was produced, and an easy-bond layer of a PET film (manufactured by Toyobo Co., Ltd., product name "PET TA063", thickness: 100 μm) having an easy-bond layer was bonded to the exposed adhesive layer, to obtain a laminate of a heavy-release type release sheet / adhesive layer / PET film. The laminate obtained as described above was cut into pieces 25 mm wide and 100 mm long.

[0187] Under conditions of 23°C and 50%RH, the heavy-release peeling sheet was peeled off from the aforementioned laminate, and the exposed adhesive layer was attached to two types of substrates. The substrates were then pressurized for 20 minutes at 0.5 MPa and 50°C in an autoclave manufactured by Kurihara Corporation. Afterward, the substrates were left to stand for 24 hours at 23°C and 50%RH. The adhesion (before UV; N / 25 mm) when peeling the PET film and adhesive layer laminate from the substrates was measured using a tensile testing machine (Orientec Corporation, TENSILON) at a peeling speed of 300 mm / min and a peeling angle of 180 degrees. Conditions not described here were measured according to JIS Z0237:2009. The results are shown in Table 2. In the table, "CF" indicates cohesive failure of the adhesive layer. <Attached object> Sodium-calcium glass sheet (manufactured by Nippon Sheet Glass Co., Ltd., product name "Sodium-calcium glass", thickness: 1.1mm) Alkali-free glass sheet (manufactured by Nippon Sheet Glass Co., Ltd., product name "Eagle-X", thickness: 1.1mm)

[0188] Furthermore, for the adhesive sheet prepared in the examples, the adhesive layer was attached to the substrate in the same manner as described above. After hot pressing, it was placed at 23°C and 50%RH for 24 hours. Then, it was irradiated with active energy rays through a PET film under the same conditions as in Example 1 to harden the adhesive layer. The adhesion (after UV exposure; N / 25mm) of this hardened adhesive layer was measured in the same manner as described above. The results are shown in Table 2.

[0189] [Experimental Example 8] (Operational Assessment) When peeling off the light-peeling release sheet from the adhesive sheets produced in the examples and comparative examples, the operability (operability of the adhesive sheet) was evaluated according to the following criteria. The results are shown in Table 2. ◎: During peeling, the adhesive layer does not deform, string, or suffer any cohesive failure, making it easy to peel off the light-peeling release sheet. ○: During peeling, although the adhesive layer deforms, there is no stringing or cohesive damage, which is the degree to which the light-peeling release sheet can be peeled off. ×: During peeling, the adhesive layer undergoes significant deformation. Due to fiber pulling and cohesive damage, it is difficult to peel off the light-peeling release sheet.

[0190] [Experimental Example 9] (Evaluation of Step Followership) A glass plate (manufactured by NSG Precision, product name "Corning's EAGLE XG") was screen-printed with UV-curable ink (manufactured by Teikoku Printing Inks Mfg. Co., Ltd, product name "POS-911 ink") on a surface measuring 90mm x 50mm x 0.5mm. The ink was then cured by irradiation with ultraviolet light (80W / cm², two metal halide lamps, bulb height 15cm, conveyor belt speed 10-15m / min), creating a stepped glass plate with printing-induced variations (step heights: 5μm, 10μm, 15μm).

[0191] The light-release peeling sheet was peeled off from the adhesive sheets manufactured in the examples and comparative examples, and the exposed adhesive layer was bonded to the easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET TA063", thickness: 100 μm) with an easy-adhesion layer. Next, the heavy-release peeling sheet was removed to expose the adhesive layer, and lamination was performed on each stepped glass plate using a laminator (manufactured by Fujipura Co., Ltd., product name "LPD3214") so that the adhesive layer covered the entire frame-like printing. These were used as samples. At this stage, the step followability after lamination (immediately after application) was evaluated according to the following criteria. The results are shown in Table 2. <Step following property after lamination> A: Confirm that there are no bubbles, bumps, or peeling near the step difference. B: Although bubbles with a diameter of less than 0.2 mm were confirmed near the step difference, no bulging or peeling was found. C: Bubbles, protrusions, and peeling with a diameter exceeding 0.2 mm were confirmed near the step difference.

[0192] Subsequently, the samples were hot-pressed at 50℃ and 0.5MPa for 20 minutes, and then placed at atmospheric pressure, 23℃, and 50%RH for 24 hours. During this stage, the step followability after hot-pressing (initial step followability) was evaluated according to the following criteria. The results are shown in Table 2. <Step following property after hot pressing> A: Confirm that there are no bubbles, bumps, or peeling near the step difference. B: Although bubbles with a diameter of less than 0.2 mm were confirmed near the step difference, no bulging or peeling was found. C: Bubbles with a diameter exceeding 0.2 mm were confirmed near the step difference, indicating bulging and peeling.

[0193] Next, for the samples of the embodiments, the adhesive layer was hardened by irradiating the PET film with active energy rays under the same conditions as in Test Example 1. The samples of the embodiments were hardened after the adhesive layer was cured, while the samples of the comparative examples were stored for 96 hours and 500 hours (durability test) under high temperature and high humidity conditions of 85°C and 85%RH after the above-mentioned hot pressing treatment. After the durability test, the samples were removed at 23°C and 50%RH to visually confirm the hardened adhesive layer and the adhesive layer (especially near the step difference caused by the printing layer). The step difference followability after high temperature and high humidity conditions was evaluated according to the following criteria. The results are shown in Table 2. <Step following behavior under high temperature and high humidity conditions> A: Confirm that there are no bubbles, bumps, or peeling near the step difference. B: Although bubbles with a diameter of less than 0.2 mm were confirmed near the step difference, no bulging or peeling was found. C: Confirm that there are bubbles with a diameter greater than 0.2 mm near the step difference, or that there is bulging or peeling.

[0194] [Experimental Example 10] (Evaluation of Optical Inhomogeneity) On the surface of a glass plate (manufactured by NSG Precision, product name "Corning's EAGLEXG", 90mm x 50mm x 0.5mm thickness), a UV-curable ink (manufactured by Teikoku Printing Inks Mfg. Co., Ltd, product name "POS-911 ink") is screen-printed into a frame shape (90mm x 50mm, 5mm width). Then, the plate is irradiated with ultraviolet light (80W / cm², 2 metal halide lamps, lamp height 15cm, conveyor belt speed 10-15m / min) to harden the printed UV-curable ink, creating a stepped glass plate with a step difference (step height: 15μm) caused by printing.

[0195] The adhesive sheets prepared in the examples and comparative examples were used to peel off the light-peel release sheet and adhere the exposed adhesive layer to the easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET TA063", thickness: 100 μm). Next, the heavy-peel release sheet was removed to expose the adhesive layer, and lamination was performed on each stepped glass plate using a laminator (manufactured by Fujipura Co., Ltd., product name "LPD3214") so that the adhesive layer covered the entire frame-like printing. Afterwards, a hot-pressing treatment was performed for 20 minutes at 50°C and 0.5 MPa, followed by 24 hours of storage at normal pressure, 23°C, and 50% RH. In the comparative example, this was used as a sample. On the other hand, in the examples, the adhesive layer was hardened by irradiating the PET film with active energy rays under the same conditions as in Test Example 1. This was used as a sample.

[0196] For the above samples, the area near the step difference caused by the printing layer was visually confirmed, and the optical non-uniformity was evaluated according to the following criteria. The results are shown in Table 2. <Presence or absence of optical inhomogeneity> ○: No optical inhomogeneity was detected near the step difference. ×: Optical inhomogeneity was confirmed near the step difference.

[0197] Furthermore, regarding Comparative Example 4, the operability deteriorated because it was difficult to prepare the samples used for Test Examples 2, 3, 4 and 9, so Test Examples 2, 3, 4 and 9 were not conducted.

[0198] [Table 1] (Meth)acrylate polymer (A) Ionic compounds (B) Active energy lines Hardening component (C) Photopolymerization initiator (D) Crosslinking agent composition Mw Quality Quality Quality Quality Example 1 BA / CARBOM / 4HBA =84 / 15 / 1 750,000 0.5 3 0.3 0 Example 2 0.5 5 0.5 0 Comparative Example 1 0.5 0 0 0 Comparative Example 2 0 0 0 0 Comparative Example 3 0 0 0 0.22 Comparative Example 4 BA / 4HBA =99 / 1 750,000 0.5 0 0 0 Comparative Example 5 0 0 0 0.22 Comparative Example 6 0.5 0 0 0.22

[0199] [Table 2] gel fraction (%) Storage modulus G' (MPa) relaxation modulus Change value Δlog G(t) Dependent variables (%) Ratio of dependent variable Haze value Total light transmittance Adhesion (N / 25mm) Operability Step follower Optical inhomogeneity UV front UV after For sodium calcium glass plate For alkali-free glass plate After lamination After hot pressing After high temperature and high humidity conditions UV front UV after 25℃ 50℃ 85℃ 25℃ 50℃ 85℃ UV front UV after UV front UV after Post-UV / Pre-UV (%) (%) UV front UV after UV front UV after 85℃ / 85%RH, 96hr 85℃ / 85%RH, 500hr Example 1 3 38 0.11 0.05 0.02 0.13 0.05 0.03 1.68 1.59 886 297 0.3 0.4 ≥99 26 27 twenty three twenty four ◎ B A A A ○ Example 2 5 53 0.09 0.04 0.02 0.30 0.10 0.05 1.86 1.77 433 255 0.6 0.6 ≥99 twenty four 30 twenty three 25 ◎ B A A A ○ Comparative Example 1 1.4 - 0.11 0.04 0.02 - - - 1.44 - 198 - - 0.1 ≥99 twenty four - twenty one - ◎ C B A B ○ Comparative Example 2 0.9 - 0.11 0.05 0.02 - - - 1.43 - 302 - - 0.1 ≥99 1.4(CF) - 1.1(CF) - ○ C B C C ○ Comparative Example 3 50 - 0.13 0.06 0.02 - - - 1.15 - 102 - - 0.1 ≥99 16 - 18 - ◎ C C C C - Comparative Example 4 4 - - - - - - - - - - - - 0.1 ≥99 13(CF) - 11(CF) - × - - - - ○ Comparative Example 5 57 - 0.03 0.02 0.01 - - - 0.83 - 112 - - 0.1 ≥99 9.0 - 12 - ◎ A A C C × Comparative Example 6 60 - 0.05 0.03 0.02 - - - 0.87 - 109 - - 0.1 ≥99 3.4 - 5.6 - ◎ A A C C ×

[0200] As can be clearly seen from Table 2, the adhesive sheet manufactured in the examples exhibits excellent step follow-through after hot pressing (initial step follow-through) and after being subjected to high temperature and high humidity conditions (85°C, 85%RH, 500 hours), while also demonstrating excellent suppression of optical non-uniformity. Furthermore, the adhesive sheet manufactured in the examples possesses excellent optical properties, high adhesion, and excellent operability. [Industry Availability]

[0201] The adhesive sheet of the present invention can be applied, for example, to the bonding of a protective panel with a stepped design to a required display component.

[0202] 1: Adhesive sheet 11: Adhesive layer 12a, 12b: Peeling sheets 2: Laminated body 11': Hardened adhesive layer 21: First display body component 22: Second display body component 3: Printed layer

Claims

1. An adhesive composition comprising: a (meth)acrylate polymer (A), an ionic compound (B), and an active energy line curing component (C), wherein, The above-mentioned (meth)acrylate polymer (A) contains a monomer containing ethyl carbonate having the ethyl carbonate structure shown in the following formula (1) as a monomer unit constituting the polymer. The above-mentioned ethyl carbonate-containing monomer is a (meth)acrylate shown in the following formula (2) or the following formula (3), [Chemical 1], [Chemical 2] (where n is 1 or more and 10 or less), [Chemical 3] (where n is 1 or more and 10 or less).

2. The adhesive composition as described in claim 1, wherein, The above-mentioned (meth)acrylate polymer (A), as a monomer unit constituting the polymer, contains 0.5% by mass and 40% by mass of the above-mentioned monomer containing ethyl carbonate.

3. The adhesive composition as described in claim 1, wherein, The aforementioned ionic compound (B) is an alkali metal salt.

4. The adhesive composition as described in claim 1, wherein, The content of the ionic compound (B) in the adhesive composition is 0.1 parts by mass and 2 parts by mass or less relative to 100 parts by mass of the (meth)acrylate polymer (A).

5. The adhesive composition as described in claim 1, wherein, The adhesive composition described above contains a crosslinking agent, and the content of the crosslinking agent in the adhesive composition is 0.1 parts by mass or less relative to 100 parts by mass of the (meth)acrylate polymer (A).

6. An adhesive formed by crosslinking the adhesive composition described in claim 1.

7. An adhesive sheet having at least an adhesive layer formed of the adhesive described in claim 6.

8. An adhesive sheet having at least one adhesive layer, wherein the adhesive constituting the adhesive layer is an active energy radiation-curable adhesive, and the strain of the adhesive constituting the adhesive layer after 1210 seconds at 25°C when a stress of 7950 Pa is applied to the adhesive is 30% or more and 1500% or less, and the ratio of the strain of the cured adhesive formed by subjecting the adhesive constituting the adhesive layer to active energy radiation curing to 1210 seconds at 25°C when a stress of 7950 Pa is applied to the cured adhesive to 1210 seconds is less than 1, wherein the adhesive constituting the adhesive layer is formulated according to JIS. K7244-1 The maximum relaxation modulus value measured when the adhesive strain is 10% is set as the maximum relaxation modulus G(t)max (MPa). From the time the maximum relaxation modulus G(t)max is measured until 3757 seconds later, the adhesive is continuously strained by 10%. The minimum relaxation modulus value measured during this period is set as the minimum relaxation modulus G(t)min (MPa). The relaxation modulus variation value ΔlogG(t) calculated from the following formula (X) is 1.2 or more and 3 or less, ΔlogG(t)=logG(t)max-logG(t)min …(X).

9. The adhesive sheet as described in claim 8, wherein, The strain of the cured adhesive formed by subjecting the adhesive constituting the above adhesive layer to active energy radiation curing is more than 50% and less than 600% after 1210 seconds when a stress of 7950 Pa is applied to the cured adhesive at 25°C.

10. The adhesive sheet as described in claim 8, wherein, The cured adhesive formed by subjecting the adhesive constituting the above adhesive layer to active energy radiation curing is defined as the maximum relaxation modulus G(t)max (MPa) measured when the cured adhesive is strained by 10% according to JIS K7244-1. The minimum relaxation modulus measured during the period from the time the maximum relaxation modulus G(t)max is measured to 3757 seconds later is defined as the minimum relaxation modulus G(t)min (MPa). The relaxation modulus variation ΔlogG(t) calculated from the above formula (X) is 1.2 or more and 3 or less.

11. The adhesive sheet as described in any one of claims 7 to 10, wherein, The adhesive sheet has two release tabs, and the adhesive layer is clamped to the release tabs in such a way that it contacts the release surfaces of the two release tabs.

12. A laminate comprising: a display body constituting member, other display body constituting members, and a hardened adhesive layer for bonding the one display body constituting member and the other display body constituting members together, wherein the hardened adhesive layer is a hardened adhesive layer formed by subjecting the adhesive layer of the adhesive sheet described in any one of claims 7 to 10 to active energy radiation curing.

13. The stack as described in claim 12, wherein, At least one of the aforementioned display body constituent components and other display body constituent components has a step difference on the side surface to which it is adhered by the aforementioned adhesive layer.

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