Photocurable adhesives, adhesive sheets, laminates, and displays

Abstract

To provide an adhesive, an adhesive sheet, a laminate, and a display which are excellent in transparency and capable of combining heat resistance and moist heat resistance with flexibility and windability.SOLUTION: A photocurable adhesive contains a urethane prepolymer (X) and a polythiol (Y). The urethane prepolymer (X) contains all structural units derived from the following (x-1)-(x-3): (x-1) an alicyclic isocyanate and / or an aromatic isocyanate; (x-2) a polyether polyol; and (x-3) a monool having an alkenyl group or a (meth)acryloyl group in the molecule. The photocurable adhesive satisfies all of the following (1)-(3): (1) the adhesive has a storage modulus at -20°C and 1 Hz of 1×105-1×106 Pa; (2) the adhesive has a storage modulus at 20°C and 1 Hz of 5×104-5×105 Pa; and (3) the adhesive has a storage modulus at 60°C and 1 Hz of 1×104-2×105 Pa.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an adhesive, an adhesive sheet, and a laminate having an adhesive layer formed from the adhesive sheet, for forming a laminate comprising a light-transmitting substrate, an adhesive layer, and a polarizing plate. The laminate is used for displays. [Background technology]

[0002] Thin-film image display devices such as liquid crystal displays and organic EL displays typically have a laminated structure that includes image-forming layers such as liquid crystal layers and organic EL layers, and optical films and cover panels. Adhesives are commonly used to bond each layer that constitutes the image display device. For example, a transparent conductive film used in a touch panel is laminated to a support glass or support film via an adhesive layer. Similarly, a polarizing plate film used in an image device is attached to a liquid crystal module or organic EL module via an adhesive layer. In this way, each component of the image display device is attached and fixed by an adhesive layer.

[0003] Furthermore, while flat displays using glass substrates were the mainstream image display devices, in recent years, flexible displays such as foldable displays and rollable displays, which use flexible substrates such as plastic, have been developed. Compared to conventional flat displays using glass substrates, these flexible displays have various advantages, including superior lightness, thinness, flexibility, and design.

[0004] The aforementioned adhesive layer has traditionally required properties that prevent foaming and peeling in high-temperature and high-temperature / high-humidity environments. However, in recent years, further functionalization has become necessary, and in flexible displays, flexibility has become essential. Flexibility, for example, in foldable displays, refers to the ability to accommodate bending of the display (flexibility). Generally, flexibility requires the characteristic of not foaming, lifting, or peeling when repeatedly bent (dynamic flexibility).

[0005] On the other hand, the development of adhesive layers requires drying and curing processes during the manufacturing process, and in order to shorten the process and reduce costs, the development of solvent-free, photocurable adhesives is progressing. Furthermore, the thickness of the adhesive layer used in foldable displays is generally 50 to 200 μm, and photocurable adhesives that do not require a curing process are suitable for suppressing coating defects during roll winding after adhesive coating.

[0006] Patent Document 1 discloses an ultraviolet-curable adhesive containing an acrylic copolymer. Patent Document 2 discloses an adhesive comprising a cyclic polymerizable monomer or a urethane structure-containing monomer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-130399 [Patent Document 2] Japanese Patent Publication No. 2022-50677 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in recent years, in order to meet the demands for even greater durability in displays, the adhesives used require stricter durability than before. In particular, foldable displays require not only the ability to resist foaming, lifting, and peeling when repeatedly bent (dynamic flexibility), but also the ability to resist foaming, lifting, and peeling when held in a bent state for extended periods (static flexibility). Furthermore, rollable displays require suitability for winding up the display so that it can be used as a rollable display (windability). In terms of windability, it is necessary that the adhesive does not resist foaming, lifting, and peeling when held in a winded state for extended periods.

[0009] Furthermore, while these flexibility requirements were previously only necessary at room temperature, with the widespread adoption of displays, flexibility in low-temperature environments, such as those in extremely cold regions, and high-temperature environments, such as those in extremely hot regions or inside automobiles under direct sunlight, has become increasingly necessary.

[0010] In contrast, conventional adhesive sheets currently fail to meet practical requirements such as heat resistance and moisture resistance, as well as flexibility, including bendability and winding ability. Furthermore, flexibility requires dynamic bending, static bending, and winding depending on the display configuration. While it may be possible to satisfy these flexibility requirements individually, it is difficult to satisfy them simultaneously. In addition, it is currently not possible to satisfy dynamic bending, static bending, and winding requirements in high-temperature and high-temperature / high-humidity environments.

[0011] On the other hand, conventional photocurable adhesives require photoinitiators as an essential component, and the degradation of the adhesive layer over time due to residual photoinitiators is a problem. In the development of photocurable adhesives, it is becoming necessary to develop adhesives that do not contain photoinitiators.

[0012] The present invention aims to provide an adhesive, an adhesive sheet, a laminate, and further a display, which are excellent in transparency, can achieve all of heat resistance, heat and humidity resistance, flexibility, and winding property, do not require a drying process and a curing process, and do not deteriorate over time.

Means for Solving the Problems

[0013] As a result of intensive studies by the present inventors, it has been found that the problems of the present invention can be solved in the following embodiments, and the present invention has been completed. That is, an embodiment of the present invention is a photocurable adhesive comprising a urethane prepolymer (X) and a polythiol (Y), wherein the urethane prepolymer (X) is a urethane prepolymer containing all structural units derived from the following (x-1) to (x-3), and satisfies all of the following (1) to (3). That is, an embodiment of the present invention is solved by a photocurable adhesive characterized by comprising a urethane prepolymer (X) and a polythiol (Y), wherein the urethane prepolymer (X) is a urethane prepolymer containing all structural units derived from the following (x-1) to (x-3), and satisfying all of the following (1) to (3). (x-1) Alicyclic isocyanate and / or aromatic isocyanate (x-2) Polyether polyol (x-3) Monool having an alkenyl group or a (meth)acryloyl group in the molecule (1) The storage elastic modulus of the adhesive at -20°C and 1 Hz is 1×10 5 ~1×10 6 Pa (2) The storage elastic modulus of the adhesive at 20°C and 1 Hz is 5×10 4 ~5×10 5 Pa (3) The storage elastic modulus of the adhesive at 60°C and 1 Hz is 1×10 4 ~2×10 5 Pa

[0014] Moreover, an embodiment of the present invention is the above photocurable adhesive, wherein the ratio {(B) / (A)} of the equivalent number (A) of the alkenyl group or (meth)acryloyl group contained in the urethane prepolymer (X) to the equivalent number (B) of the thiol group contained in the polythiol is 1 to 5.

[0015] Furthermore, embodiments of the present invention are characterized by further containing a (meth)acrylic acid ester monomer (Z) having two or more (meth)acryloyl groups in its molecule, as described above for the photocurable adhesive.

[0016] Furthermore, an embodiment of the present invention is a photocurable adhesive characterized in that the urethane prepolymer (X) contains 10 to 25% by mass of (x-1) in 100% by mass of the urethane prepolymer (X).

[0017] Furthermore, an embodiment of the present invention is an adhesive sheet in which the adhesive layer, which is the cured product of the above-mentioned photocurable adhesive, is sandwiched between release films.

[0018] Furthermore, embodiments of the present invention include a light-transmitting substrate, an adhesive layer, and a polarizing plate, wherein the adhesive layer is a laminate which is a cured product of the above-mentioned photocurable adhesive.

[0019] Furthermore, an embodiment of the present invention is a display comprising the above-mentioned laminate and optical elements. [Effects of the Invention]

[0020] The present invention provides an adhesive, an adhesive sheet, and a laminate using the adhesive sheet that are highly transparent, heat-resistant, heat-resistant, flexible, and windable, and that do not require a drying or curing process and do not deteriorate over time. Furthermore, by using the adhesive sheet and laminate of the present invention, a display with excellent visibility and contrast can be provided. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic cross-sectional view partially showing the adhesive sheet of the present invention. [Figure 2] This is a schematic cross-sectional view partially showing a laminate, which is an example of using the adhesive sheet of the present invention. [Figure 3] This is a schematic cross-sectional view partially showing a display, which is an example of the use of the adhesive sheet of the present invention. [Modes for carrying out the invention]

[0022] The following describes, but is not limited to, examples of the configurations of the adhesive, adhesive sheet, laminate, and display of the present invention.

[0023] This specification defines the terms used herein. A urethane prepolymer is a copolymer obtained by copolymerizing an isocyanate with a compound having a hydroxyl group in its molecule through a urethane reaction. A polyol is a compound having two or more hydroxyl groups in its molecule. A monool is a compound having one hydroxyl group in its molecule. Furthermore, (meth)acrylic acid ester monomer includes acrylic acid ester monomer and methacrylic acid ester monomer, and is synonymous with (meth)acrylate. Furthermore, a photocurable adhesive is an adhesive that crosslinks and forms a coating film upon irradiation with X-rays, electron beams, ultraviolet light, visible light, etc. An adherend refers to the surface to which the adhesive sheet is attached. In this invention, sheet, film, and tape are synonymous. In this specification, (x-1) alicyclic isocyanates, aromatic isocyanates, (x-2) polyether polyols, (x-3) monools having an alkenyl group or (meth)acryloyl group in the molecule, (X-4) isocyanates other than (x-1), (x-5) polyols other than (x-2), (x-6) monools other than (x-3), urethane prepolymers (X), and (meth)acrylic acid ester monomers (Z) having two or more (meth)acryloyl groups in the molecule may be abbreviated as isocyanate (x-1), polyol (x-2), monool (x-3), isocyanate (x-4), polyol (x-5), monool (x-6), prepolymer (X), and monomer (Z), respectively. Unless otherwise noted, each of the components mentioned herein may be used individually or in combination of two or more.

[0024] In this specification, numerical ranges specified using "~" include the numbers before and after "~" as the lower and upper limits.

[0025] "Adhesive" The adhesive of the present invention contains a urethane prepolymer (X) and a polythiol (Y). The urethane prepolymer (X) is a urethane prepolymer containing all of the following (x-1) to (x-3), and is a photocurable adhesive characterized by satisfying all of the following (1) to (3). (x-1) Alicyclic isocyanate and / or aromatic isocyanate (x-2) Polyether polyol (x-3) Monool having an alkenyl group or a (meth)acryloyl group in the molecule (1) The storage modulus of the adhesive at -20°C and 1 Hz is 1×10 5 ~1×10 6 Pa (2) The storage modulus of the adhesive at 20°C and 1 Hz is 5×10 4 ~5×10 5 Pa (3) The storage modulus of the adhesive at 60°C and 1 Hz is 1×10 4 ~2×10 5 Pa

[0026] <Urethane prepolymer (X)> The urethane prepolymer (X) is a copolymer of a mixture containing all structural units derived from at least (x-1) to (x-3), and the mixture may contain structural units derived from (x-4) to (x-6) as necessary. (x-1) Alicyclic isocyanate and / or aromatic isocyanate (x-2) Polyether polyol (x-3) Monool having an alkenyl group or a (meth)acryloyl group in the molecule (x-4) Isocyanate other than (x-1) (x-5) Polyol other than (x-2) (x-6) Monool other than (x-3)

[0027] The urethane prepolymer (X) contains a monool having an alkenyl group or a (meth)acryloyl group as a component, thereby introducing an alkenyl group or a (meth)acryloyl group to the polymer main chain terminus. This allows for the formation of a three-dimensional crosslinked structure through an ene-thiol reaction with polythiol (Y).

[0028] [Isocyanate (x-1)] Isocyanates (x-1) are alicyclic isocyanates and aromatic isocyanates, specifically alicyclic isocyanates such as 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (also known as isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanate methyl)cyclohexane; Examples of aromatic isocyanates include 1,3-phenylenediisocyanate, 4,4'-diphenyldiisocyanate, 1,4-phenylenediisocyanate, 4,4'-diphenylmethanediisocyanate, 2,4'-diphenylmethanediisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 4,4'-toluidinediisocyanate, 2,4,6-triisocyanatetoluene, 1,3,5-triisocyanatebenzene, dianisidinediisocyanate, 4,4'-diphenyletherdiisocyanate, and 4,4',4"-triphenylmethanetriisocyanate. Of these isocyanates (x-1), 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI), 2,4'-diphenylmethanediisocyanate, and 2,4-tolidyleneisocyanate are more preferred from the viewpoint of cohesive force.

[0029] The isocyanate (x-1) is preferably present in an amount of 10 to 25% by weight, and more preferably 10 to 20% by weight, of 100% by weight of the urethane prepolymer (X). An amount of 10% by weight or more is preferable because it provides sufficient cohesive force, and an amount of 25% by weight or less is preferable because it provides sufficient flexibility.

[0030] [Isocyanate (x-4)] Isocyanates (x-4) are isocyanates other than alicyclic isocyanates and aromatic isocyanates, specifically aliphatic isocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate; Examples include aromatic aliphatic isocyanates such as ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylenediisocyanate, and 1,3-tetramethylxylylenediisocyanate.

[0031] Isocyanate (x-4) is used to adjust the cohesive strength and flexibility of the urethane prepolymer. Preferably, isocyanate (x-4) is present in an amount of 10% by weight or less per 100% by mass of the urethane prepolymer (X). When the content is 10% by mass or less, the cohesive strength and flexibility can be adjusted while maintaining durability.

[0032] [Polyol (x-2)] Polyol(x-2) is a polyether polyol, specifically a polymer and copolymer of alkylene oxide compounds such as tetrahydrofuran, ethylene oxide, propylene oxide, and butylene oxide; Examples include copolymers and copolymers obtained by ring-opening polymerization of alkylene oxide compounds using alcohols having two hydroxyl groups in their molecule, such as ethylene glycol, propylene glycol, and butylene glycol, or alcohols having three hydroxyl groups in their molecule, such as glycerin and trimethylolpropane, as starting materials. Of these polyols (X-2), polypropylene glycol, obtained by ring-opening polymerization of propylene oxide using an alcohol having two hydroxyl groups in its molecule as a starting material, is more preferable from the viewpoint of flexibility.

[0033] The weight-average molecular weight of polyol(x-2) is preferably 1,000 to 10,000, and more preferably 2,000 to 8,000. A weight-average molecular weight of 1,000 or more is preferable because it allows for sufficient flexibility, while a weight-average molecular weight of 10,000 or less is preferable because it allows for sufficient cohesive force. The weight-average molecular weight of polyol(x-2) is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0034] The polyol (x-2) is preferably present in an amount of 65 to 90% by weight, and more preferably 65 to 85% by weight, of 100% by weight of the urethane prepolymer (X). A content of 65% by weight or more is preferable because it allows for sufficient flexibility, and a content of 90% by weight or less is preferable because it allows for sufficient cohesive force.

[0035] [Polyol (x-5)] Polyol(x-5) refers to polyols other than polyol(x-2), and examples include polyester polyols, polycarbonate polyols, and polybutadiene polyols. Polyester polyols specifically include copolymers obtained by condensing an alcohol having a hydroxyl group in its molecule with a dibasic acid component, polymers and copolymers obtained by ring-opening polymerization of a cyclic ester compound using an alcohol having a hydroxyl group in its molecule as a starting material. Examples of alcohols having a hydroxyl group in their molecule include ethylene glycol, propylene glycol, dipropylene glycol, diethylene glycol, triethylene glycol, butylene glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolheptane, polyoxyethylene glycol, polyoxypropylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, octanediol, butylethylpentanediol, 2-ethyl-1,3-hexanediol, cyclohexanediol, bisphenol A, bisphenol F, glycerin, and trimethylolpropane. Examples of dibasic acid components include terephthalic acid, adipic acid, azelaic acid, sebatic acid, phthalic anhydride, isophthalic acid, and trimellitic acid. Examples of cyclic ester compounds include β-butyrolactone, β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, γ-caprolactone, γ-heptanolactone, and α-methyl-β-propiolactone.

[0036] The weight-average molecular weight of the polyol (x-5) is preferably 1,000 to 10,000, and more preferably 2,000 to 6,000. A weight-average molecular weight of 1,000 or more is preferable because it allows for sufficient flexibility, while a weight-average molecular weight of 10,000 or less is preferable because it allows for sufficient cohesive force.

[0037] Polyol (x-5) is used to adjust the cohesiveness and flexibility of the urethane prepolymer. Preferably, polyol (x-5) is present in an amount of 30% by weight or less per 100% by weight of the urethane prepolymer (X). An amount of 30% by weight or less allows for adjustment of cohesiveness and flexibility while maintaining durability.

[0038] [Monoall (x-3)] Monool(x-3) is a monool having an alkenyl group or a (meth)acryloyl group in its molecule. Here, the alkenyl group is a substituent selected from either a vinyl group or an allyl group. Examples of monools containing a vinyl group include 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, ethylene glycol monovinyl ether, and diethylene glycol monovinyl ether. Examples of monools containing an allyl group include 2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, ethylene glycol monoallyl ether, and diethylene glycol monoallyl ether. Examples of monools having a (meth)acryloyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and hydroxycyclohexyl (meth)acrylate. Of these monools (x-3), 4-hydroxyethyl vinyl ether, 2-hydroxyethyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoint of cohesive force, and 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are more preferred from the viewpoint of curability.

[0039] The monoall (x-3) is preferably present in an amount of 2 to 25% by weight, and more preferably 5 to 18% by weight, of 100% by weight of the urethane prepolymer (X). A content of 2% by weight or more is preferable because sufficient curability can be obtained, and a content of 25% by weight or less is preferable because sufficient flexibility can be obtained.

[0040] [Monoall (x-6)] Monools (x-6) are monools other than monools (x-3) and are monools that do not have an alkenyl group or a (meth)acryloyl group in their molecule. Specifically, examples include methanol, ethanol, propanol, butanol, isobutyl alcohol, tert-butyl alcohol, pentanol, isopentyl alcohol, neopentyl alcohol, hexanol, 2-methyl-1-pentanol, octanol, 2-ethylhexanol, 3,5,5-trimethyl-1-hexanol, decanol, undecanol, dodecanol, isooctadecanol, octadecenol, docosanol, 14-methylhexadecanol, cyclohexanol, methylcyclohexanol, etc.

[0041] Monoall (x-6) is used to adjust the curability and adhesion of the urethane prepolymer. Preferably, monoall (x-6) is present in an amount of 5% by weight or less per 100% by mass of the urethane prepolymer (X). A content of 5% by mass or less allows for adjustment of curability and adhesion while maintaining tackiness.

[0042] [Diamino compounds] The urethane prepolymer (X) of the present invention may further contain a diamino compound. By including a diamino compound, adhesion to the adherend can be improved. Specifically, these include aliphatic polyamines such as ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, triethylenetetramine, diethylenetriamine, triaminopropane, 2,2,4-trimethylhexamethylenediamine, 2-hydroxyethylethylenediamine, N-(2-hydroxyethyl)propylenediamine, (2-hydroxyethylpropylene)diamine, (di-2-hydroxyethylethylene)diamine, (di-2-hydroxyethylpropylene)diamine, (2-hydroxypropylethylene)diamine, (di-2-hydroxypropylethylene)diamine, piperazine, etc. Alicyclic polyamines such as isophorone diamine and dicyclohexylmethane-4,4'-diamine; Aromatic diamines such as phenylenediamine, xylylenediamine, 2,4-tolylenediamine, 2,6-tolylenediamine, diethyltoluenediamine, 3,3'-dichloro-4,4'-diaminodiphenylmethane, and 4,4'-bis-(sec-butyl)diphenylmethane; Other examples include dimer amines, which are obtained by converting the carboxyl group of a dimer acid to an amino group, and dendrimers having a primary or secondary amino group at the terminal end.

[0043] The diamino compound is preferably present in an amount of 2 to 5% by weight per 100% by weight of the urethane prepolymer (X). A content of 2% by weight or more improves cohesive strength, while a content of 5% by weight or less maintains coating suitability.

[0044] <Measurement of weight-average molecular weight (Mw) of urethane prepolymer (X)> Next, the Mw of the urethane prepolymer (X) will be explained. In this invention, the Mw of the urethane prepolymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). Specifically, it can be determined using the Shimadzu Corporation's GPC "LC-GPC system" as a weight-average molecular weight conversion value with polystyrene of known molecular weight as the standard substance. Equipment name: Shimadzu Corporation, LC-GPC system "Prominence" Columns: Four Tosoh GMHXL columns and one Tosoh HXL-H column were connected together. Mobile phase solvent: tetrahydrofuran Flow rate: 1.0ml / min Column temperature: 40℃

[0045] The weight-average molecular weight of the urethane prepolymer (X) is preferably 1,500 to 12,000, and more preferably 2,000 to 10,000. A molecular weight in the range of 1,500 to 12,000 further improves cohesive strength, moisture and heat resistance, and heat resistance.

[0046] <Polythiol (Y)> Polythiols (Y) are compounds that have two or more thiol groups in their molecule. Specifically, examples include aliphatic polythiols, aromatic polythiols, and esters of mercaptocarboxylic acids with polyhydric alcohols. Examples of aliphatic polythiols include 1,2-ethanedithiol, 1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, and 1,2,6-hexanetrithiol. Examples of aromatic polythiols include 4,6-diisopropylbenzene-1,3-bisthiol, benzene-1,3-bismethanethiol, and 1,3,5-benzenetrithiol. Examples of esters of mercaptocarboxylic acids with polyhydric alcohols include trimethylolpropanetris(3-mercaptopropionate), pentaerythritoltetrakis(3-mercaptopropionate), tetraethylene glycolbis(3-mercaptopropionate), and dipentaerythritolhexa(3-mercaptopropionate). Of these polythiols (Y), 1,6-hexanedithiol, trimethylolpropanetris (3-mercaptopropionate), and pentaerythritoltetrakis (3-mercaptopropionate) are preferred from the viewpoint of adhesion.

[0047] The polythiol (Y) preferably has a ratio {(B) / (A)} of 1 to 5 between the number of equivalents (A) of alkenyl groups or (meth)acryloyl groups contained in the urethane prepolymer (X) and the number of equivalents (B) of thiol groups contained in the polythiol. A ratio of 1 or more allows for sufficient curability and improved tackiness. A ratio of 5 or less is preferable because it suppresses the bleed-out of unreacted polythiol (Y) and allows for sufficient durability.

[0048] <Monomer (Z)> The adhesive of the present invention may contain, as a component of the adhesive, a (meth)acrylic acid ester monomer (Z) having two or more (meth)acryloyl groups in its molecule. By including monomer (Z), the cohesive force and flexibility of the adhesive can be adjusted. Furthermore, the viscosity of the adhesive can be reduced, improving its coating suitability.

[0049] Examples of monomers (Z) include polyfunctional (meth)acrylic acid ester monomers having an aliphatic skeleton, polyfunctional (meth)acrylic acid ester monomers having an alicyclic skeleton, polyfunctional (meth)acrylic acid ester monomers having an alkylene oxide skeleton, polyfunctional (meth)acrylic acid ester monomers having a bisphenol skeleton, and polyfunctional (meth)acrylic acid ester monomers having an isocyanuric acid skeleton. Here, polyfunctional means having two or more (meth)acryloyl groups in the molecule. Examples of polyfunctional (meth)acrylic acid ester monomers within molecules having an aliphatic skeleton include neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. Examples of polyfunctional (meth)acrylic acid ester monomers having an alicyclic skeleton include cyclohexane-1,4-dimethanol di(meth)acrylate, cyclohexane-1,3-dimethanol di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, and tricyclodecanedimethyl di(meth)acrylate. Polyfunctional (meth)acrylic acid ester monomers having an alkylene oxide skeleton include polyethylene glycol diacrylate (e.g., ARONIX M-240, manufactured by Toagosei Co., Ltd.; NK ester A-400, manufactured by Shin Nakamura Chemical Industry Co., Ltd.; NK ester A-600, manufactured by Shin Nakamura Chemical Industry Co., Ltd.; NK ester A-1000, manufactured by Shin Nakamura Chemical Industry Co., Ltd.), polyethylene glycol-modified triacrylate of trimethylolpropane (e.g., ARONIX M-350, ARONIX M-360, manufactured by Toagosei Co., Ltd.), polypropylene glycol diacrylate (e.g., ARONIX M-220, ARONIX M-225, ARONIX M-270, manufactured by Toagosei Co., Ltd.), polypropylene glycol-modified triacrylate of trimethylolpropane (e.g., ARONIX M-310, ARONIX M-321, manufactured by Toagosei Co., Ltd.), and polytetramethylene glycol diacrylate (e.g., NK ester Examples include A-PTMG65 (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.). Examples of polyfunctional (meth)acrylic acid ester monomers having a bisphenol skeleton include ethylene glycol-modified diacrylate of bisphenol F (e.g., ARONIX M-208, manufactured by Toagosei Co., Ltd.) and ethylene glycol-modified diacrylate of bisphenol A (e.g., ARONIX M-211B, manufactured by Toagosei Co., Ltd.). Examples of polyfunctional (meth)acrylic acid ester monomers having an isocyanuric acid skeleton include ethylene glycol-modified diacrylates of isocyanuric acid (e.g., ARONIX M-215, manufactured by Toagosei Co., Ltd.) and ethylene glycol-modified triacrylates of isocyanuric acid (e.g., ARONIX M-313, ARONIX M-315, manufactured by Toagosei Co., Ltd.). Of these monomers (Z), polyfunctional (meth)acrylic acid ester monomers having an alicyclic skeleton are preferred to improve cohesiveness, and polyfunctional (meth)acrylic acid ester monomers having an alkylene oxide skeleton are preferred to improve flexibility.

[0050] The monomer (Z) is preferably present in an amount of 5 to 40% by mass, and more preferably 10 to 30% by mass, relative to 100% by mass of the urethane prepolymer (X). If the monomer is 5% by mass or more, it is possible to adjust the cohesive force and flexibility of the adhesive, and if it is 40% by mass or less, the coating suitability of the adhesive can be maintained.

[0051] [Manufacturing of urethane prepolymer (X)] The urethane prepolymer (X) can be produced by polymerizing a mixture containing all of (x-1) to (x-3), and the mixture may optionally contain monomers (x-4) to (x-6). Polymerization can be carried out using known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization, but bulk polymerization is preferred. Preferred solvents for solution polymerization include, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is preferably between 60 and 120°C for boiling point reactions. The polymerization time is preferably around 3 to 8 hours.

[0052] Known catalysts can be used for the polymerization of the urethane prepolymer (X). Examples include tertiary amine compounds and organometallic compounds. Examples of tertiary amine compounds include triethylamine, triethylenediamine, N,N-dimethylbenzylamine, N-methylmorpholine, and diazabicycloundecene (also known as DBU). Examples of organometallic compounds include tin-based compounds and non-tin-based compounds. Examples of tin compounds include dibutyltin dichloride, dibutyltin oxide, dibutyltin dibromide, dibutyltin dimaleate, dibutyltin dilaurate (also known as DBTDL), dibutyltin diacetate, dibutyltin sulfide, tributyltin sulfide, tributyltin oxide, tributyltin acetate, triethyltin ethoxide, tributyltin ethoxide, dioctyltin oxide, tributyltin chloride, tributyltin trichloroacetate, dioctyltin dilaurylate (also known as DOTDL), and tin 2-ethylhexanoate. Examples of non-tin compounds include titanium-based compounds such as dibutyltitanium dichloride, tetrabutyltitanate, and butoxytitanium trichloride; lead-based compounds such as lead oleate, lead 2-ethylhexanoate, lead benzoate, and lead naphthenate; iron-based compounds such as iron 2-ethylhexanoate and iron acetylacetonate; cobalt-based compounds such as cobalt benzoate and cobalt 2-ethylhexanoate; zinc-based compounds such as zinc naphthenate and zinc 2-ethylhexanoate; and zirconium naphthenate. Among the catalysts mentioned above, dibutyltin dilaurate (also known as DBTDL), dioctyltin dilaurylate (also known as DOTDL), and tin 2-ethylhexanoate are preferred from the viewpoint of reactivity. The above catalysts can be used individually or in combination of two or more.

[0053] It is preferable to use 0.001 to 0.1% by mass of the catalyst, and more preferably 0.005 to 0.05% by mass, based on a total of 100 parts by mass of (x-1) to (x-3).

[0054] <Photopolymerization initiator> The adhesive of the present invention may further contain a photopolymerization initiator. The inclusion of a photopolymerization initiator can improve curability. Examples of photopolymerization initiators include 2-hydroxy-2-methyl-1-phenylpropan-1-one, hydroxycyclohexylphenyl ketone, methylphenylglyoxylate, benzyldimethylketal, Michla's ketone, 2-benzyl-2-dimethylamino-1-[4-(morpholino)phenyl]butanone-1, 2-chlorothioxanthone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, and 2-dimethylamino-2-(4-methylbenzyl)-1-[(4-morpholin-4- Examples include (phenyl)butan-1-one, 2-(O-benzoyloxime)-1-[4-(phenylthio)phenyl]-1,2-octanedione, 1-(O-acetyloxime)-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]ethanone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0055] The photopolymerization initiator is preferably used in an amount of 0.1 to 2.0 parts by mass, and more preferably 0.2 to 1.0 parts by mass, per 100 parts by mass of the total of the urethane prepolymer (X) and polythiol (Y).

[0056] <Organosilane compounds> The adhesive of the present invention may further contain an organic silane compound. The inclusion of an organic silane improves adhesion to the substrate. Organosilane compounds include, for example, alkoxysilane compounds having a (meth)acryloxy group, such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropyltrippropoxysilane, 3-(meth)acryloxypropyltributoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; Alkoxysilane compounds having a vinyl group, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane; Alkoxysilane compounds having an amino group, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltripropoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane; Alkoxysilane compounds having a mercapto group, such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltripropoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane; Alkoxysilane compounds having epoxy groups, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyltripropoxysilane, 3-glycidoxypropyltributoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; Tetraalkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane; Examples include 3-chloropropyltrimethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, styryltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate, 3-isocyanatetopropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, hexamethyldisilazane, and silicone resins having alkoxysilyl groups in the molecule.

[0057] The organosilane compound is preferably used in an amount of 0.01 to 2.0 parts by mass, and more preferably 0.05 to 1.0 parts by mass, per 100 parts by mass of the total of the urethane prepolymer (X) and polythiol (Y).

[0058] The adhesive of the present invention may contain various resins, oils, softeners, dyes, pigments, antioxidants, ultraviolet absorbers, weather stabilizers, plasticizers, fillers, anti-aging agents, and antistatic agents as optional components, as long as they can solve the problem.

[0059] <Storage modulus> The storage modulus of an adhesive is determined by viscoelasticity measurement at a frequency of 1 Hz. The storage modulus corresponds to the portion of elastic energy stored when a material deforms, and is an indicator of its hardness. In other words, a higher storage modulus value indicates a harder adhesive, while a lower value indicates a softer adhesive. Details of the measurement method are described in the Examples section.

[0060] The adhesive of the present invention has a storage modulus (hereinafter sometimes abbreviated as G'(-20)) of 1 × 10⁻¹⁰ at -20°C and 1 Hz. 5 ~1 × 10 6 Pa is 1 × 10 5 ~8×10 5 It is more preferable that it be Pa. G'(-20) is 1 × 10 5When the value is above Pa, rigidity in low-temperature environments improves, as do flexibility and winding properties. G'(-20) is 1 × 10 6 When the Pa level is below a certain level, adhesion improves, as do flexibility and winding properties.

[0061] Furthermore, the adhesive of the present invention has a storage modulus (hereinafter sometimes abbreviated as G'(20)) of 5 × 10 at 20°C and 1 Hz. 4 ~5×10 5 Pa is 5 × 10 4 ~2×10 5 It is more preferable that it be Pa. G'(20) is 5 × 10 4 When Pa is above, machinability improves. Also, G'(25) is 5×10 5 Adhesion improves when the Pa level is below a certain point.

[0062] Furthermore, the adhesive of the present invention has a storage modulus of elasticity (hereinafter sometimes abbreviated as G'(60)) of 1 × 10⁻¹⁰ at 60°C and 1 Hz. 4 ~2×10 5 Pa is 5 × 10 4 ~2×10 5 It is preferable that it be Pa. G'(60) is 1 × 10 4 When the Pa value is above Pa, rigidity in high-temperature environments improves, as do flexibility and winding properties. Also, when G'(60) is 2 × 10 5 When the pressure is below Pa, flexibility in high-temperature environments improves, resulting in improved bendability and winding properties.

[0063] The adhesive of the present invention, by having a storage modulus within a specific range, exhibits the flexibility required for foldable displays and the winding properties required for rollable displays.

[0064] <Adhesive strength> The adhesive of the present invention preferably has an adhesive strength of 10 N / 25 mm or more when measured after attaching a 50 μm thick adhesive layer obtained from the adhesive to glass and leaving it in a 23°C-50%RH environment for 24 hours. The adhesive strength can be measured by applying the adhesive to a first polyethylene terephthalate (PET) film that has been treated to release the adhesive, so that the thickness after application is 50 μm, curing it by light irradiation to form an adhesive layer, then laminating a second PET film that has been treated to release the adhesive to the surface of the adhesive layer opposite to the surface in contact with the first PET film that has been treated to release the adhesive, leaving it to stand in a 40°C environment for 7 days, and then producing an adhesive sheet (composition: treated PET film / adhesive layer / treated PET film) having an adhesive layer with a thickness of 50 μm, peeling off the second PET film that has been treated to release the adhesive to release the adhesive to release the adhesive to release the first PET film that has been treated to release the adhesive

[0065] "Adhesive sheet" The adhesive sheet of the present invention is an adhesive sheet used to form the adhesive layer in a laminate consisting of a light-transmitting substrate and an adhesive layer; that is, the adhesive sheet of the present invention is used to bond light-transmitting substrates. Figure 1 shows an example of a schematic cross-sectional view partially illustrating the adhesive sheet of the present invention. In Figure 1, 1 is the adhesive layer 1, and 2 is the release film.

[0066] As shown in Figure 1, the adhesive sheet of the present invention has a structure in which release films are formed on both sides of the adhesive layer, and the adhesive layer formed between the release films is an adhesive layer formed of a mixture of urethane prepolymer (X) and polythiol (Y).

[0067] <Release film> The release film is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of transparent plastic substrates include polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetylcellulose, polysulfone, polyarylate, and polycycloolefin. The plastic materials can be used individually or in combination of two or more.

[0068] As the release film, among the transparent plastic substrates mentioned above, a transparent plastic substrate with excellent heat resistance, that is, a transparent plastic substrate in which deformation is suppressed or prevented under harsh conditions such as high temperature and high temperature and humidity, can be suitably used. PET film or sheet is particularly suitable as the transparent plastic substrate.

[0069] The thickness of the transparent plastic substrate is not particularly limited, but is preferably 10 to 200 μm, and more preferably 25 to 150 μm.

[0070] The release film may be in the form of a single layer or a multi-layer structure. Furthermore, the surface of the transparent substrate may be subjected to appropriate surface treatments, such as physical treatments like corona discharge treatment or plasma treatment, or chemical treatments like primer treatment.

[0071] <Manufacturing of adhesive sheets> The adhesive sheet of the present invention can be manufactured according to a conventional method for manufacturing adhesive sheets. For example, it can be manufactured by applying a urethane prepolymer (X) and polythiol (Y) (hereinafter sometimes simply referred to as "adhesive") to the release surface of a release film so that the thickness after coating is predetermined, irradiating with light to form an adhesive layer, and then attaching the release film; or by applying the adhesive to the release surfaces of two release films so that the thickness after coating is predetermined, irradiating with light to form two adhesive layers, and then attaching each adhesive layer.

[0072] The aforementioned light irradiation is performed by irradiating with light of a specific wavelength that reacts with alkenyl groups or (meth)acryloyl groups, or light of a specific wavelength that acts on the added photopolymerization initiator. The amount of light irradiation can be set according to the formulation and thickness of the raw material composition, the type and amount of photopolymerization initiator added, for example, 500 to 1500 mJ / cm². 2 It can be done this way.

[0073] The thickness of the adhesive layer is not particularly limited, but is preferably 10 to 500 μm, and more preferably 50 to 200 μm. An adhesive layer thickness of 10 to 500 μm is preferable because it is easy to obtain sufficient cohesive force and can achieve a high level of balance between heat resistance, heat and humidity resistance, flexibility, and winding properties.

[0074] When applying the adhesive, conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, or spray coaters can be used.

[0075] The adhesive sheet may be cut to an appropriate width and wound into a roll, thereby having the form of an adhesive tape wound into a roll.

[0076] "Laminated structure" The laminate of the present invention comprises a light-transmitting substrate, an adhesive layer, and a polarizing plate, wherein the adhesive layer is formed using the adhesive sheet of the present invention.

[0077] The laminate of the present invention is formed from an adhesive sheet that is excellent in transparency, heat resistance, moisture resistance, flexibility, and windability, and therefore exhibits excellent transparency, heat resistance, moisture resistance, flexibility, and windability.

[0078] Figure 2 shows an example of a schematic cross-sectional view partially illustrating a laminate, which is an example of the use of the adhesive sheet of the present invention. In Figure 2, 3 is a light-transmitting substrate (cover panel), 1 is the adhesive layer 1, and 4 is a polarizing plate.

[0079] In the laminate shown in Figure 2, a light-transmitting substrate (cover panel) is attached to a polarizing plate via an adhesive layer made of the adhesive of the present invention. Thus, the adhesive sheet of the present invention can be used in a form in which a transparent adhesive layer formed from the adhesive is attached to a light-transmitting substrate (cover panel) and a polarizing plate.

[0080] The light-transmitting substrate (cover panel) is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of transparent plastic substrate materials include acrylic resins such as polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA), as well as plastic materials such as polycarbonate, polycycloolefin, and polyimide. The plastic materials can be used alone or in combination of two or more types.

[0081] As the light-transmitting substrate (cover panel), among the transparent plastic substrates mentioned above, a transparent plastic substrate with excellent heat resistance, that is, a transparent plastic substrate in which deformation is suppressed or prevented under harsh conditions such as high temperature and high humidity, can be suitably used. Polyethylene terephthalate (PET), polycycloolefin, and polyimide are particularly suitable as transparent plastic substrates.

[0082] The thickness of the light-transmitting substrate (cover panel) is not particularly limited, but is preferably 100 to 2000 μm, and more preferably 200 to 1000 μm.

[0083] "display" The display comprises the laminate of the present invention and optical elements. The optical elements are not particularly limited and include, for example, liquid crystal elements, organic EL elements, and the like.

[0084] The display of the present invention has a laminate that is excellent in transparency, heat resistance, moisture resistance, flexibility, and windability, and therefore exhibits excellent transparency, heat resistance, moisture resistance, flexibility, and windability.

[0085] Figure 3 shows an example of a schematic cross-sectional view partially illustrating a display, which is an example of the use of the adhesive sheet of the present invention. In Figure 3, 3 is a light-transmitting substrate (cover panel), 1 is adhesive layer 1, 4 is a polarizing plate, 5 is adhesive layer 2, 6 is a barrier layer such as silicon nitride, 7 is an organic EL layer, 8 is a support such as polyimide, and 9 is an organic EL cell. Note that the display configuration is not limited to Figure 3.

[0086] In the display shown in Figure 3, a light-transmitting substrate (cover panel) is attached to a polarizing plate via an adhesive layer (adhesive layer 1) made of the adhesive of the present invention, and further attached to an organic EL cell via an adhesive layer for the polarizing plate (adhesive layer 2). Thus, the adhesive sheet of the present invention can be used in a form in which a transparent adhesive layer formed from the adhesive is attached to a light-transmitting substrate (cover panel) and a polarizing plate, and the laminate is further attached to an organic EL via an adhesive layer for the polarizing plate. For example, in Figure 3, the adhesive of the present invention can be used in either adhesive layer 1 or adhesive layer 2. Generally, when comparing adhesive layer 1 and adhesive layer 2, the required quality for adhesive layer 1 is higher, and since the adhesive of the present invention has good adhesion and bonding properties to the substrate, it is preferable to use it for adhesive layer 1. In this case, the adhesive used to form adhesive layer 2 may be the adhesive of the present invention or a conventionally known adhesive.

[0087] There are no particular restrictions on the uses of the display, but examples include OLED TVs, OLED smartphones, OLED tablets, and OLED smartwatches. [Examples]

[0088] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In the examples, unless otherwise specified, "parts" refers to "parts by mass," "%" refers to "percentage by mass," and "RH" refers to relative humidity. Also, the amounts in the table are in parts by mass. A blank space in the table indicates that the ingredient was not included. The methods for measuring the weight-average molecular weight of the urethane prepolymer (X) and the storage modulus of the adhesive are as follows.

[0089] <Measurement of weight-average molecular weight> The weight-average molecular weight (Mw) of the urethane prepolymer (X) can be measured using the Shimadzu GPC "LC-GPC system," and the weight-average molecular weight (Mw) can be determined by conversion using polystyrene with a known molecular weight as the standard substance. Equipment name: Shimadzu Corporation, LC-GPC system "Prominence" Columns: Four Tosoh GMHXL columns and one Tosoh HXL-H column were connected together. Mobile phase solvent: tetrahydrofuran Flow rate: 1.0ml / min Column temperature: 40℃

[0090] [Method for measuring the storage modulus] The storage modulus can be determined by using a sample made by laminating a hardened adhesive to a thickness of approximately 1.0 mm, and performing viscoelastic measurements using TA Instrument-Waters LL.C.'s "Discovery HR-2 (DHR-2)" under the following conditions. From the measurement results, the storage modulus at -20°C, 20°C, and 60°C can be read. (Measurement conditions) Transformation mode: Twist Measurement frequency: 1Hz Heating rate: 10°C / min Jig shape: Parallel plate 8.0mmφ

[0091] <Example of Urethane Prepolymer (X) Manufacturing> (Urethane prepolymer (X-1)) In a four-necked flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 26.4 parts of isophorone diisocyanate (IPDI) and 60.0 parts of Sannix PP-1000 (bifunctional polypropylene glycol, Mn=1000, manufactured by Sanyo Chemical Industries, Ltd.) (PPG2-1000) were charged. The mixture was stirred under a nitrogen atmosphere and gradually heated to 95°C for 3 hours. Next, the temperature inside the four-necked flask was cooled to 85°C, and 13.6 parts of 2-hydroxyethyl acrylate were added dropwise over 30 minutes while maintaining the flask temperature at 85°C. The mixture was then reacted for 1 hour. After the reaction was complete, the flask was cooled to obtain urethane prepolymer (X-1). The weight-average molecular weight of the obtained urethane prepolymer was 3100.

[0092] (Urethane prepolymer (X-2~X-16, X'-1~X'-3) Except for changes to the composition and blending amounts (parts by mass) listed in Table 1, the urethane prepolymers (X-2 to X-16, X'-1 to X'-3) were manufactured using the same method as the urethane prepolymer (X-1).

[0093] Table 1 shows the weight-average molecular weight (Mw) of the obtained copolymers (X-1 to X-16, X'-1 to X'-3).

[0094] [Table 1]

[0095] The abbreviations used in the table are as follows: IPDI: Isophorone diisocyanate (alicyclic isocyanate) 2,4'-MDI: 2,4'-diphenylmethane diisocyanate (aromatic isocyanate) 2,4-TDI: 2,4-Tolylene diisocyanate (aromatic isocyanate) HDI: Hexamethylene diisocyanate (aliphatic isocyanate) 1,3-XDI: 1,3-Xylylene diisocyanate methyl acrylate (aromatic aliphatic isocyanate) PPG2-1000: Sannix PP-1000 (bifunctional polypropylene glycol, Mn=1000, manufactured by Sanyo Chemical Industries, Ltd.) PPG2-2000: Sannix PP-2000 (bifunctional polypropylene glycol, Mn=2000, manufactured by Sanyo Chemical Industries, Ltd.) PPG3-3000: ADEKA Polyether G-3000B (trifunctional polypropylene glycol, Mn=3000, manufactured by ADEKA Corporation) PPG3-6000: Preminol 7001K (trifunctional polypropylene glycol, Mn=6000, manufactured by Asahi Glass Co., Ltd.) PEG2-2000: PEG2000 (bifunctional polyethylene glycol, Mn=2000, manufactured by Sanyo Chemical Industries, Ltd.) PE2-1000: Kuraray Polyol P-1010 (Bifunctional polyester polyol, Mn=2000, manufactured by Kuraray Co., Ltd.) PC2-2000: Kuraray Polyol C-2090 (Bifunctional polycarbonate polyol, Mn=2000, manufactured by Kuraray Co., Ltd.) HEA: 2-hydroxyethyl acrylate (a monool containing an acryloyl group in the molecule) HBA: 4-hydroxybutyl acrylate (a monool containing an acryloyl group in the molecule) HBVE: Hydroxybutyl vinyl ether (a monool containing a vinyl group in the molecule) EHAOH: 2-Ethylhexanol (a monool that does not contain an alkenyl group or (meth)acryloyl group in the molecule) DOOH: 1-Dodecanol (a monool that does not contain an alkenyl group or (meth)acryloyl group in its molecule) IPDA: Isophorone diamine (diamino compound)

[0096] (Example 1) <Preparation of adhesive> To 100 parts of the non-volatile content of a urethane prepolymer (X-1), 15 parts of 1,6-hexanedithiol (Y-1) as a polythiol and 0.1 parts of 3-glycidoxypropyltrimethoxysilane (S-1) as an organosilane compound were mixed and stirred to obtain an adhesive.

[0097] <Manufacturing of adhesive sheets> The resulting adhesive was coated onto a 50 μm thick release film (polyethylene terephthalate (PET), "E7004", silicone-based release layer, manufactured by Toyobo Co., Ltd.) so that the thickness after coating was 50 μm, and then irradiated with light (wavelength: 365 nm, irradiation dose: 1000 mJ / cm²). 2 The material was cured using a solvent to form an adhesive layer. Next, one side of a 38 μm thick release film (polyethylene terephthalate, "SP-PET3811", silicone-based release layer, manufactured by Lintec Corporation) was laminated to this adhesive layer to obtain an adhesive sheet consisting of a "release sheet / adhesive layer / release sheet".

[0098] (Examples 2-18, Comparative Examples 1-4) As shown in Table 2, adhesives and adhesive sheets were obtained in the same manner as in Example 1, except that the type and amount (parts by mass) of the copolymer and curing agent were changed.

[0099] [Table 2]

[0100] The abbreviations used in the table are as follows: <Polythiol (Y)> Y-1: 1,6-Hexanedithiol Y-2: Trimethylolpropanetris(3-mercaptopropionate) Y-3: Pentaerythritol tetrakis(3-mercaptopropionate) <Monomer (Z)> Z-1: Cyclohexane-1,4-dimethanol diacrylate Z-2: ARONIX M-220 (Polypropylene glycol diacrylate, manufactured by Toagosei Co., Ltd.) Z-3: ARONIX M-310 (Trimethylolpropane polypropylene glycol modified triacrylate (manufactured by Toagosei Co., Ltd.)) <Organosilane compounds> S-1:3-Glycidoxypropyltrimethoxysilane

[0101] Measurement and evaluation of the physical properties of adhesive sheets. The adhesive sheets obtained were evaluated for their adhesive strength, transparency, heat resistance, humid heat resistance, dynamic bending resistance, static bending resistance, and winding properties. The results are shown in Tables 2 and 3.

[0102] <Preparation of test adhesive sheets> The 38 μm thick release film was peeled off the obtained adhesive sheet, and the exposed adhesive layer was laminated to a 50 μm thick PET film (Toray Industries, Inc., T60) at 23°C and 50% relative humidity using a laminator to prepare a test adhesive sheet consisting of PET film / adhesive layer / release film.

[0103] <Adhesive strength> A test adhesive sheet was cut to a size of 25 mm wide x 100 mm long to create test adhesive sheet 1 consisting of a PET film, an adhesive layer, and a release film. The release film of this test adhesive sheet 1 was peeled off, and it was attached to an alkali-free glass plate (EN-A1: manufactured by Asahi Glass Co., Ltd.) using a laminator at 23°C and a 50% RH atmosphere. After being left for 24 hours, the adhesive strength when the sample was peeled off the alkali-free glass was measured using a tensile testing machine (Orientec Co., Ltd. "Tensilon") in accordance with JIS Z 0237, under conditions of a peeling speed of 300 mm / min and a peeling angle of 180°.

[0104] <Transparency> A test adhesive sheet was cut to a size of 112 mm wide x 200 mm long (equivalent to a 9-inch display) to create test adhesive sheet 2, which consisted of a PET film, an adhesive layer, and a release film. The release film was peeled off the test adhesive sheet 2, and the exposed adhesive layer was laminated to an alkali-free glass plate (EN-A1: manufactured by Asahi Glass Co., Ltd.) at 25°C and 50% relative humidity, and the HAZE was measured. The HAZE was measured using a Turbidimeter NDH5000W manufactured by Nippon Denshoku Industries Co., Ltd. The evaluation criteria are as follows. [Evaluation Criteria] ○: HAZE is less than 1.0 (good). ×: HAZE is 1.0 or higher (defective).

[0105] <Heat resistance and moisture resistance> The release film was peeled off from a separately prepared test adhesive sheet 2, and the exposed adhesive layer was laminated to a polarizing plate (layer composition: triacetylcellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator at 25°C and 50% relative humidity to obtain a test laminate consisting of PET film / adhesive layer / polarizing plate. Next, as a heat resistance test, the laminate was left at 105°C for 500 hours, cooled at 25°C and 50% relative humidity, and then visually evaluated for bubble formation and lifting or peeling of the test laminate under the following conditions. Furthermore, as an evaluation of humidity and heat resistance, the above test laminate was left at 60°C and 95% relative humidity for 500 hours, cooled at 25°C and 50% relative humidity, and then visually evaluated for bubble formation and lifting or peeling of the adhesive sheet under the following conditions. Heat resistance and humidity and heat resistance were evaluated based on the following three evaluation criteria. [Evaluation Criteria] ◎: No bubbles, lifting, or peeling were observed at all, and there are absolutely no practical problems. ○: Although fewer than 5 instances of air bubbles, lifting, or peeling are observed, there are no practical problems. ×: Bubbles, lifting, and peeling were observed in 5 or more places, which poses a practical problem.

[0106] <Dynamic flexural resistance: flexural resistance [1], [2], [3]> The release film was peeled off from a separately prepared test adhesive sheet 2, and the exposed adhesive layer was laminated to a polarizing plate (layer composition: triacetylcellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator at 25°C and 50% relative humidity to obtain a test laminate consisting of PET film / adhesive layer / polarizing plate. The test laminate was then subjected to bending resistance tests at 25°C and 50% relative humidity [1] as a normal condition test [2], bending resistance at 85°C as a heat resistance test [3], and bending resistance at 60°C and 95% RH as a humid heat resistance test [3] using a bending test machine (manufactured by Yuasa System Equipment Co., Ltd.) with conditions set so that the inner diameter (diameter) when bent was 6 mm, and bending and 180° release constituted one cycle, repeated 300,000 times. Dynamic bending performance was evaluated by the appearance after the test from the following perspectives. Appearance: The presence or absence of air bubbles in the test laminate and the presence or absence of lifting or peeling of the adhesive layer were visually evaluated under the following conditions. [Evaluation Criteria] ◎: No bubbles, lifting, or peeling were observed at all, and there are absolutely no practical problems. ○: Although fewer than 5 instances of air bubbles, lifting, or peeling are observed, there are no practical problems. ×: Bubbles, lifting, and peeling were observed in 5 or more places, which poses a practical problem.

[0107] <Static bending resistance: Flexing resistance [1], [2], [3]> The release film was peeled off from a separately prepared test adhesive sheet 2, and the exposed adhesive layer was laminated to a polarizing plate (layer composition: triacetylcellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator at 25°C and 50% relative humidity to obtain a test laminate consisting of PET film / adhesive layer / polarizing plate. The test laminate was then subjected to the following tests: a normal condition test at 25°C and 50% relative humidity [1], a heat resistance test at 85°C [2], and a humid heat resistance test at 60°C and 95% RH [3], using a planar unloaded U-shaped stretch tester. The polarizing plate side of the test piece was facing inward, and it was held in a bent state with a bending radius of 3 mm and a bending angle of 180° for 240 hours. Static flexibility was evaluated by the appearance after the test from the following perspectives. Appearance: The presence or absence of air bubbles in the test laminate and the presence or absence of lifting or peeling of the adhesive layer were visually evaluated under the following conditions. [Evaluation Criteria] ◎: No bubbles, lifting, or peeling were observed at all, and there are absolutely no practical problems. ○: Although fewer than 5 instances of air bubbles, lifting, or peeling are observed, there are no practical problems. ×: Bubbles, lifting, and peeling were observed in 5 or more places, which poses a practical problem.

[0108] <Retractability> The release film was peeled off from a separately prepared test adhesive sheet 2, and the exposed adhesive layer was laminated to a polarizing plate (layer composition: triacetylcellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator in an atmosphere of 25°C and 50% relative humidity to obtain a test laminate consisting of PET film / adhesive layer / polarizing plate. Next, the test laminate was wound onto a metal rod with a radius of 3 mm, with the PET side of the test piece facing inward, in the direction of the long side, to form a roll, and then secured in three places with string. As a winding test, the rolled test laminate was held in an atmosphere of 25°C and 50% relative humidity for 240 hours. The winding performance was evaluated based on the appearance after the test from the following perspectives. Appearance: The presence or absence of air bubbles in the test laminate and the presence or absence of lifting or peeling of the adhesive layer were visually evaluated under the following conditions. [Evaluation Criteria] ◎: No bubbles, lifting, or peeling were observed at all, and there are absolutely no practical problems. ○: Although fewer than 5 instances of air bubbles, lifting, or peeling are observed, there are no practical problems. ×: Bubbles, lifting, and peeling were observed in 5 or more places, which poses a practical problem.

[0109] [Table 3]

[0110] Layer structure of test adhesive sheet and test laminate [A]; PET film / adhesive layer / glass [B]; PET film / adhesive layer / polarizing plate Test conditions Flexural resistance [1]; 25°C, 50% relative humidity atmosphere Flexural resistance [2]; 85°C atmosphere Flexural resistance [3]; 60°C, 95% relative humidity atmosphere

[0111] The results in Table 3 confirm that the adhesive sheets of Examples 1 to 18 exhibited excellent transparency, heat resistance, humidity resistance, flexibility, and windability. Therefore, laminates and displays using the adhesive sheets of the present invention exhibit superior transparency, heat resistance, humidity resistance, and flexibility. Furthermore, the displays of the present invention also demonstrated excellent visibility and contrast. On the other hand, the adhesive sheets of Comparative Examples 1 to 4 could not satisfy all of the above characteristics. [Explanation of Symbols]

[0112] 1 Adhesive layer 1 2. Release film 3. Light-transmitting substrate (cover panel) 4. Polarizing plate 5. Adhesive layer 2 6. Barrier layer 7 Organic EL layer 8 Support 9 OLED cells

Claims

1. The material comprises a urethane prepolymer (X), a polythiol (Y), and a (meth)acrylic acid ester monomer (Z) containing two or more (meth)acryloyl groups in its molecule. The product contains 5 to 20 parts by mass of polythiol (Y) and 5 to 15 parts by mass of (meth)acrylic acid ester monomer (Z) having two or more (meth)acryloyl groups in its molecule, per 100 parts by mass of urethane prepolymer (X). The urethane prepolymer (X) is a urethane polymer containing only structural units derived from (x-1), (x-2), and (x-3) below, or a urethane prepolymer containing only structural units derived from (x-1), (x-2), (x-3), and (x-4) below, and is characterized in that it contains 65 to 85% by mass of (x-2) in 100% by mass of the urethane prepolymer (X), and satisfies all of the following conditions (1) to (3). (x-1) Alicyclic isocyanates and / or aromatic isocyanates (x-2) Polypropylene glycol or polyethylene glycol with a weight-average molecular weight of 1000 to 6000 (x-3) Monools having an alkenyl group or (meth)acryloyl group in the molecule (x-4) Isocyanates other than alicyclic isocyanates and aromatic isocyanates (1) The storage modulus of the adhesive at -20°C and 1 Hz is 1 × 10 ５ ~1 x 10 ６ Pa (2) The storage modulus of the adhesive at 20°C and 1 Hz is 5 × 10 ４ ~5 x 10 ５ Pa (3) The storage modulus of the adhesive at 60°C and 1 Hz is 1 × 10 ４ ~2 x 10 ５ Pa

2. The photocurable adhesive according to claim 1, characterized in that the urethane prepolymer (X) contains 10 to 25% by mass of (x-1) in 100% by mass of the urethane prepolymer (X).

3. An adhesive sheet in which an adhesive layer, which is a cured product of the adhesive according to claim 1 or 2, is sandwiched between release films.

4. A laminate comprising a light-transmitting substrate, an adhesive layer, and a polarizing plate, wherein the adhesive layer is a cured product of the adhesive described in claim 1 or 2.

5. A display comprising the laminate and optical elements described in claim 4.

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