TW202344650A - Optical adhesive sheet - Google Patents

Abstract

The present invention provides an optical adhesive sheet suitable for a flexible device. An adhesive sheet 10 of the present invention is an optical adhesive sheet containing a base polymer and has a gel fraction of 85% or more and 95% or less. Among sol components of the base polymer in the adhesive sheet 10, the proportion of components having a molecular weight of 500,000 or less is 70% by mass or more. The base polymer is a polymer containing a monomer component of (meth)acrylic acid in an amount of 0.1% by mass or more and 10% by mass or less.

Description

Optical adhesive sheet

The invention relates to an optical adhesive sheet.

For example, a display panel has a multilayer structure including a pixel panel, a polarizing film, a touch panel, a cover film, and other components. In the manufacturing process of such a display panel, for example, an optically transparent adhesive sheet (optical adhesive sheet) is used to bond components included in the multilayer structure to each other.

On the other hand, for example, a display panel that can be bent repeatedly (folded) is developed for use in smartphones and tablet terminals. Specifically, the foldable display panel can repeatedly deform between a curved shape and a flat, non-curved shape. In this kind of foldable display panel, each component in the stacked structure is made to be foldable repeatedly, and a thinner optical adhesive sheet is used to join the components. An optical adhesive sheet for flexible devices such as foldable display panels is described in the following Patent Document 1, for example. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2018-111754

[Problem to be solved by the invention]

In areas where flexible devices undergo repeated deformation, optical adhesive sheets have traditionally been prone to peeling off from the adherend components. The reason is that a relatively large tensile stress will be generated in the deformed portion of the optical adhesive sheet in the repeatedly deformed portion of the flexible device. This tensile stress is repeatedly generated and is prone to cohesive failure.

In addition, optical adhesive sheets for flexible devices are required to be highly soft in order to have sufficient followability to the adherend when the device is deformed. However, the softer the previous optical adhesive sheets are, the more likely they are to be damaged by aggregation.

The present invention provides an optical adhesive sheet suitable for use in flexible devices. [Technical means to solve problems]

The present invention [1] includes an optical adhesive sheet, which contains a base polymer and has a gel fraction of 85% or more and 95% or less. The ratio of components with a molecular weight of 500,000 or less in the sol component of the base polymer is: 70 mass % or more, the above-mentioned base polymer is a polymer containing a (meth)acrylic acid monomer component of 0.1 mass % or more and 10 mass % or less.

The present invention [2] includes the optical adhesive sheet according to the above [1], wherein the proportion of components having a molecular weight of 100,000 or less in the sol component is 15 mass % or more.

The present invention [3] includes the optical adhesive sheet as described in the above [1] or [2], wherein the weight average molecular weight of the sol component of the above-mentioned base polymer is not less than 250,000 and not more than 450,000.

The present invention [4] includes the optical adhesive sheet according to any one of the above [1] to [3], wherein the total ratio of (meth)acrylic acid and hydroxyl-containing monomer in the above monomer components is 2 mass % More than 5% by mass or less.

The present invention [5] includes the optical adhesive sheet according to any one of the above [1] to [4], wherein the monomer component is a (meth)acrylic acid alkyl group having an alkyl group with a carbon number of 8 to 20. The ratio of the base ester is not less than 90% by mass and not more than 98% by mass. [Effects of the invention]

In the optical adhesive sheet of the present invention, as mentioned above, the gel fraction (mass ratio of gel components formed by cross-linking between base polymers) is 85% or more and 95% or less. A gel fraction of 85% or more is suitable for achieving higher cohesion in optical adhesive sheets (increased cohesion will help improve durability). A gel fraction of 95% or less is suitable for ensuring the softness of the optical adhesive sheet.

Furthermore, in the sol component of the base polymer in the optical adhesive sheet, the ratio of components having a molecular weight of 500,000 or less is 70 mass % or more as mentioned above. The sol component of the base polymer (the base polymer that is not incorporated into the gel component) contains a large amount of low molecular weight components (components with a shorter main chain) having a molecular weight of 500,000 or less. This means that a gel component is formed from a base polymer with a relatively large ratio of high molecular weight components (components with longer main chains) (the greater the ratio of low molecular weight components in the sol component, the lower the molecular weight of the gel component). The smaller the ratio of ingredients). The high molecular weight of the base polymer that forms the gel component helps to increase the degree of mutual entanglement of the base polymers in the gel component, and is therefore suitable for achieving high cohesion in optical adhesive sheets.

In addition, as mentioned above, the base polymer in the optical adhesive sheet is a polymer containing a monomer component of (meth)acrylic acid in an amount of not less than 0.1% by mass and not more than 10% by mass. (Meth)acrylic acid can form cross-linking points in the base polymer. The ratio of (meth)acrylic acid in the monomer component is 0.1% by mass or more, which helps to ensure the cross-linking points of the base polymer and achieve the above-mentioned high gel fraction. In addition, (meth)acrylic acid also helps to ensure the affinity of the surface of the optical adhesive sheet to glass in the base polymer and ensure the adhesion between the adhesive sheet and the glass. The ratio of (meth)acrylic acid (the glass transition temperature of the homopolymer is relatively high) in the monomer component is less than 10% by mass, which is suitable for lowering the glass transition temperature of the base polymer and ensuring the softness of the optical adhesive sheet.

As described above, the optical adhesive sheet of the present invention is suitable for ensuring softness and achieving high cohesion. This type of optical adhesive sheet is suitable for ensuring sufficient followability to the adherend and suppressing aggregation damage when the adherend to which the adhesive sheet is attached is deformed. Therefore, the optical adhesive sheet of the present invention is suitable for flexible device applications.

As shown in FIG. 1 , the adhesive sheet 10 as one embodiment of the optical adhesive sheet of the present invention has a sheet shape with a specific thickness and expands in a direction (surface direction) orthogonal to the thickness direction. The adhesive sheet 10 has an adhesive surface 11 and an adhesive surface 12 opposite to the adhesive surface 11 . FIG. 1 schematically shows a state where release liners L1 and L2 are bonded to the adhesive surfaces 11 and 12 of the adhesive sheet 10 . The release liner L1 is arranged on the adhesive surface 11 . The release liner L2 is arranged on the adhesive surface 12 . In addition, the adhesive sheet 10 is an optically transparent adhesive sheet arranged at a light-passing portion of the flexible device. An example of the flexible device is a flexible display panel. Examples of flexible display panels include foldable display panels and rollable display panels. For example, a flexible display panel has a multilayer structure including a pixel panel, a polarizing film, a touch panel, a cover film, and other components. The adhesive sheet 10 is used, for example, in the manufacturing process of a flexible display panel to join components included in the stacked structure to each other. The release liners L1 and L2 are respectively released at specific points when the adhesive sheet 10 is used.

The adhesive sheet 10 is formed from an adhesive composition. The adhesive composition includes a base polymer. That is, the adhesive sheet 10 contains a base polymer.

The gel fraction of the adhesive sheet 10 is 85% or more and 95% or less, the ratio R1 of components with a molecular weight of 500,000 or less in the sol component of the base polymer is 70 mass% or more, and the base polymer contains 0.1 mass% or more A polymer containing less than 10% by mass of (meth)acrylic acid monomer components. The "gel component" is an ethyl acetate-insoluble component, and the method for measuring the gel fraction is specifically described in the Examples below. The "sol component" is the tetrahydrofuran (THF) soluble component, and the "molecular weight" is the molecular weight based on the standard polystyrene measured by gel permeation chromatography (GPC). The measurement method of the ratio R1 is specifically as shown in the following examples. described. Moreover, "(meth)acrylic acid" means acrylic acid and/or methacrylic acid.

In the adhesive sheet 10, as mentioned above, the gel fraction (mass ratio of the gel component formed by cross-linking between base polymers) is 85% or more and 95% or less. A gel fraction of 85% or more is suitable for achieving higher cohesion in the adhesive sheet 10 (increased cohesion contributes to improved durability). A gel fraction of 95% or less is suitable for ensuring the softness of the adhesive sheet 10 .

Moreover, among the sol components of the base polymer in the adhesive sheet 10, the ratio R1 of components having a molecular weight of 500,000 or less is 70 mass % or more as mentioned above. The sol component of the base polymer (the base polymer that is not incorporated into the gel component) contains a large amount of low molecular weight components (components with a shorter main chain) having a molecular weight of 500,000 or less. This means that a gel component is formed from a base polymer with a relatively large ratio of high molecular weight components (components with longer main chains) (the greater the ratio of low molecular weight components in the sol component, the lower the molecular weight of the gel component). The smaller the ratio of ingredients). The high molecular weight of the base polymer forming the gel component helps to increase the degree of mutual entanglement of the base polymers in the gel component, and is therefore suitable for achieving high cohesive force in the adhesive sheet 10 .

In addition, as mentioned above, the base polymer in the adhesive sheet 10 is a polymer containing a monomer component of (meth)acrylic acid in an amount of not less than 0.1% by mass and not more than 10% by mass. (Meth)acrylic acid can form cross-linking points in the base polymer. The ratio of (meth)acrylic acid in the monomer component is 0.1% by mass or more, which helps to ensure the cross-linking points of the base polymer and achieve the above-mentioned high gel fraction. In addition, (meth)acrylic acid also helps to ensure the affinity of the surface of the adhesive sheet 10 to glass in the base polymer and ensure the close contact between the adhesive sheet 10 and the glass. If the ratio of (meth)acrylic acid (the glass transition temperature of the homopolymer is relatively high) in the monomer component is less than 10% by mass, it is suitable to lower the glass transition temperature of the base polymer and ensure the softness of the adhesive sheet 10 .

As described above, the adhesive sheet 10 is suitable for ensuring softness and achieving high cohesion. This adhesive sheet 10 is suitable for ensuring sufficient followability to the adherend and suppressing aggregation damage when the adherend to which the adhesive sheet is attached is deformed. Therefore, the adhesive sheet 10 is suitable for flexible device applications.

The gel fraction of the adhesive sheet 10 is preferably 87% or more, more preferably 89% or more, from the viewpoint of obtaining high cohesive force in the adhesive sheet 10 . From the viewpoint of ensuring the softness of the adhesive sheet 10, the gel fraction of the adhesive sheet 10 is preferably 93% or less, more preferably 91% or less. Examples of methods for adjusting the gel fraction include selection of the type of base polymer in the adhesive sheet 10, adjustment of the molecular weight, and adjustment of the blending amount. Selection of the type of base polymer involves adjusting the composition of the monomers forming the base polymer.

The above-mentioned ratio R1 of the base polymer in the adhesive sheet 10 is preferably 77 from the viewpoint of making the base polymer that forms the gel component in the adhesive sheet 10 highly molecular and thereby achieving higher cohesive force. mass% or more, more preferably 81 mass% or more. The upper limit of the ratio R1 is, for example, 85 mass%, 88 mass%, or 92 mass%. Examples of methods for adjusting the ratio R1 include selection of the type of base polymer in the adhesive sheet 10, adjustment of the molecular weight, and adjustment of the blending amount.

As for the ratio R2 of the components with a molecular weight of 100,000 or less in the sol component of the base polymer in the adhesive sheet 10, the base polymer forming the gel component in the adhesive sheet 10 becomes highly molecular and achieves higher aggregation. From the viewpoint of strength, 15 mass % or more is preferred, and 18 mass % or more is more preferred. The upper limit of the ratio R2 is, for example, 19% by mass, 22% by mass, or 25% by mass. The method for determining the ratio R2 is specifically described in the Examples below. Examples of methods for adjusting the ratio R1 include selection of the type of base polymer in the adhesive sheet 10, adjustment of the molecular weight, and adjustment of the blending amount.

The ratio of the ratio R2 to the ratio R1 (R2/R1) is preferably 0.2 or more, more preferably 0.22 or more, and more preferably 0.25 or less, from the viewpoint of ensuring the above-mentioned cohesive force in the adhesive sheet 10. More preferably, it is 0.23 or less.

The weight average molecular weight (Mw) of the sol component of the base polymer of the adhesive sheet 10 is preferably 250,000 or more, more preferably 300,000 or more, and is preferably 450,000 or less, more preferably 400,000 or less. Forming a cross-linked structure in the base polymer in the adhesive sheet 10 causes the base polymer to gel, which helps to improve the cohesion and durability of the adhesive sheet 10 . The fact that the Mw of the sol component of the base polymer is as small as mentioned above means that the gel component is formed from the base polymer with a relatively large ratio of high molecular weight components (components with longer main chains) (the lower the molecular weight of the sol component, the lower the Mw of the sol component. The smaller the low molecular weight components that form the gel component). The high molecular weight of the base polymer that forms the gel component helps to increase the degree of mutual entanglement of the base polymers in the gel component. Therefore, it is suitable for achieving high cohesion and durability in optical adhesive sheets. Methods for adjusting the weight average molecular weight of the sol component of the base polymer include, for example, selection of the type of base polymer, adjustment of the molecular weight distribution of the base polymer before cross-linking, selection of the cross-linking agent, and the amount of the prepared cross-linking agent. Preparation, and adjustment of time and temperature in the cross-linking reaction of the base polymer. The method for measuring the weight average molecular weight of the sol component of the base polymer is specifically described in the examples below.

The ratio of (meth)acrylic acid in the monomer component forming the base polymer is preferably 1 mass % or more, and more preferably 1.5 mass % from the viewpoint of achieving the above-mentioned high gel fraction in the adhesive sheet 10 % or more, more preferably 2 mass% or more, particularly preferably 2.5 mass% or more. The total ratio of (meth)acrylic acid and hydroxyl-containing monomers in the monomer components is preferably 2 mass % or more, and more preferably 2.5 from the viewpoint of achieving the above-mentioned high gel fraction in the adhesive sheet 10 Mass % or more, and more preferably 3 mass % or more (hydroxyl-containing monomers can form cross-linking points in the base polymer like alkyl (meth)acrylate).

The ratio of (meth)acrylic acid in the monomer component forming the base polymer is preferably 8 mass % or less from the viewpoint of lowering the glass transition temperature of the base polymer and ensuring the softness of the adhesive sheet 10 , and more preferably The content is preferably 6 mass% or less, more preferably 5 mass% or less, and particularly preferably 4 mass% or less. The total ratio of (meth)acrylic acid and hydroxyl-containing monomers in the monomer components is preferably 5 mass % or less from the viewpoint of lowering the glass transition temperature of the base polymer and ensuring the softness of the adhesive sheet 10 . More preferably, it is 4.5 mass % or less, and still more preferably, it is 4 mass % or less. Furthermore, the (meth)acrylic acid among the monomer components is preferably acrylic acid.

The glass transition temperature (Tg) of the base polymer is preferably 0°C or lower, more preferably -20°C or lower, and still more preferably -40°C from the viewpoint of ensuring sufficient softness in the adhesive sheet 10 below, and more preferably below -45°C. The glass transition temperature is, for example, -80°C or higher.

Regarding the glass transition temperature of the base polymer, the glass transition temperature (theoretical value) calculated based on the following Fox formula can be used. Fox's formula is a relationship between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of the homopolymer of the monomers constituting the polymer. In the following Fox formula, Tg represents the glass transition temperature (℃) of the polymer, Wi represents the weight fraction of the monomer i that constitutes the polymer, and Tgi represents the glass transition temperature of the homopolymer formed from the monomer i. (°C). Literature values can be used for the glass transition temperature of homopolymers. For example, in "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7: Introduction to Synthetic Resins for Coatings" (authored by Kyozo Kitaoka, Polymer Publishing Association , 1995) gives examples of the glass transition temperatures of various homopolymers. On the other hand, the glass transition temperature of the homopolymer of the monomer can also be determined by the method specifically described in Japanese Patent Application Laid-Open No. 2007-51271.

Fox formula 1/(273+Tg)=Σ[Wi/(273+Tgi)]

In the adhesive sheet 10, the base polymer is an adhesive component that exhibits adhesiveness. Examples of the base polymer include: acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate/ Vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. From the viewpoint of ensuring good transparency and adhesiveness of the adhesive sheet 10, an acrylic polymer is preferably used as the base polymer.

The acrylic polymer is a copolymer containing a monomer component of (meth)acrylate in a ratio of 50% by mass or more. "(Meth)acrylic" means acrylic acid and/or methacrylic acid.

As the (meth)acrylate, a (meth)acrylic acid alkyl ester is preferably used, and a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms is more preferably used. The alkyl (meth)acrylate may have a linear or branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group.

Examples of the (meth)acrylic acid alkyl ester having a linear or branched alkyl group include: (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid n-butyl ester Ester, isobutyl (meth)acrylate, second butyl (meth)acrylate, third butyl (meth)acrylate, amyl (meth)acrylate, isopentyl (meth)acrylate, (meth)acrylate Neopentyl acrylate, n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso(meth)acrylate Octyl ester, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, (meth)acrylate (Basic) dodecyl acrylate (i.e. lauryl (meth)acrylate), isotridecyl (meth)acrylate, myristyl (meth)acrylate, isotetradecyl (meth)acrylate Alkyl ester, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, (meth) Isostearyl acrylate, and nonadecyl (meth)acrylate.

Examples of the (meth)acrylic acid alkyl ester having an alicyclic alkyl group include: (meth)acrylic acid cycloalkyl ester, (meth)acrylic acid ester having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid ester having a bicyclic aliphatic hydrocarbon ring. (Meth)acrylate with more than three rings of aliphatic hydrocarbon ring. Examples of (meth)acrylic acid cycloalkyl esters include: (meth)acrylic acid cyclopentyl ester, (meth)acrylic acid cyclohexyl ester, (meth)acrylic acid cycloheptyl ester, and (meth)acrylic acid cycloalkyl ester. Octyl ester. Examples of the (meth)acrylate having a bicyclic aliphatic hydrocarbon ring include iso(meth)acrylate. Examples of the (meth)acrylate having an aliphatic hydrocarbon ring with three or more rings include: (meth)acrylic acid dicyclopentyl, (meth)acrylic acid dicyclopentoxyethyl, (meth)acrylic acid tricyclic Cyclopentyl ester, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate .

The ratio of alkyl (meth)acrylate in the monomer component is preferably 50 mass % or more, and more preferably 70 mass % from the viewpoint of appropriately expressing basic characteristics such as adhesiveness in the adhesive sheet 10 % or more, and more preferably 80 mass% or more. The above ratio is, for example, 99% by mass or less.

As the alkyl (meth)acrylate, from the viewpoint of balancing the softness and adhesive force required for an adhesive sheet for flexible device applications in the adhesive sheet 10, it is preferable to use an adhesive sheet having a carbon number of 8. At least one kind of (meth)acrylic acid alkyl esters having an alkyl group having 20 or less carbon atoms, more preferably at least one kind selected from the group consisting of (meth)acrylic acid alkyl esters having an alkyl group having 8 to 12 carbon atoms, and further Preferably, at least one selected from the group consisting of 2-ethylhexyl acrylate (2EHA) and lauryl acrylate (LA) can be used.

Regarding the ratio of alkyl (meth)acrylate having an alkyl group with a carbon number of 8 to 20 in the monomer component, from the viewpoint of ensuring the softness of the adhesive sheet 10, it is preferably 90 mass % or more, and more preferably Preferably, it is 93 mass % or more, and further more preferably, it is 96 mass % or more. Regarding the ratio of alkyl (meth)acrylate having an alkyl group with a carbon number of 8 to 20 in the monomer component, from the viewpoint of ensuring the adhesive force of the adhesive sheet 10, it is preferably 99 mass % or less, and more preferably Preferably, it is 98 mass % or less, More preferably, it is 97 mass % or less.

The monomer component may also include a copolymerizable monomer other than (meth)acrylic acid that can be copolymerized with alkyl (meth)acrylate. Examples of such copolymerizable monomers include monomers having a polar group (excluding a carboxyl group, the same applies below). Examples of the polar group-containing monomer include a hydroxyl group-containing monomer and a monomer having a nitrogen atom-containing ring. Monomers containing polar groups help to modify the acrylic polymer, such as introducing cross-linking points into the acrylic polymer and ensuring the cohesion of the acrylic polymer.

Examples of the hydroxyl-containing monomer include: (meth)acrylic acid 2-hydroxyethyl ester, (meth)acrylic acid 2-hydroxypropyl ester, (meth)acrylic acid 2-hydroxybutyl ester, (meth)acrylic acid 3 -Hydroxypropyl ester, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, ( 12-hydroxylauryl methacrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. As the hydroxyl-containing monomer, it is preferable to use at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.

The ratio of the hydroxyl-containing monomer in the monomer component is preferably 0.1 mass % or more, and more preferably 0.3 from the viewpoint of introducing a cross-linked structure into the acrylic polymer and ensuring the cohesion of the adhesive sheet 10 mass% or more, and more preferably 0.5 mass% or more. From the viewpoint of adjusting the polarity of the acrylic polymer (the compatibility of various additive components in the adhesive sheet 10 with the acrylic polymer), the above ratio is preferably 10 mass % or less, more preferably 5 mass % or less. .

Examples of the monomer having a nitrogen-containing ring include: N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinyl pyrimidine, N-vinyl piperazole, N-vinyl pyrrole, N-vinyl pyrrole, N-vinylimidazole, N-vinyl 㗁azole, N-(meth)acrylyl-2 -pyrrolidinone, N-(meth)acrylylpiperidine, N-(meth)acrylylpyrrolidine, N-vinyl𠰌line, N-vinyl-3-𠰌linone, N-ethylene Acetyl-2-caprolactamide, N-vinyl-1,3-㗁𠯤-2-one, N-vinyl-3,5-𠰌lindione, N-vinylpyrazole, N-vinyl Isothiazole, N-vinylthiazole, and N-vinylisothiazole. As the monomer having a nitrogen atom-containing ring, N-vinyl-2-pyrrolidone is preferably used.

The ratio of the monomer having a nitrogen-containing ring among the monomer components is preferably 0.1 mass % or more from the viewpoint of ensuring the cohesive force of the adhesive sheet 10 and ensuring the adhesive force of the adhesive sheet 10 to the adherend. , more preferably 0.5% by mass or more, further preferably 0.8% by mass or more. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (the compatibility of various additive components in the adhesive sheet 10 with the acrylic polymer), the above ratio is preferably 10 mass% or less, more preferably 5 mass% or less.

The monomer component may also include other copolymerizable monomers. Examples of other copolymerizable monomers include acid anhydride monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, and alkoxy group-containing monomers. monomers, and aromatic vinyl compounds. These other copolymerizable monomers may be used alone, or two or more types may be used in combination.

The base polymer has a cross-linked structure. An example of a method for introducing a cross-linked structure into a base polymer is as follows: a base polymer having a functional group capable of reacting with a cross-linking agent, and a cross-linking agent are blended into an adhesive composition, and the base polymer is polymerized. The reaction between the substance and the cross-linking agent in the adhesive sheet (first method); and the monomer component forming the base polymer contains a multi-functional monomer as a cross-linking agent, and the monomer component is polymerized to form a A base polymer having a branched structure (cross-linked structure) is introduced into the polymer chain (second method). These methods can also be used together.

Examples of the crosslinking agent used in the first method include compounds that react with functional groups (carboxyl group, hydroxyl group, etc.) contained in the base polymer. Examples of such cross-linking agents include isocyanate cross-linking agents, peroxide cross-linking agents, epoxy cross-linking agents, azoline cross-linking agents, aziridine cross-linking agents, and carbodiimide cross-linking agents. linking agent, and metal chelate cross-linking agent. The cross-linking agent may be used alone, or two or more types may be used in combination. As the cross-linking agent, in terms of its high reactivity with the hydroxyl and carboxyl groups in the base polymer and the ease of introducing a cross-linked structure, isocyanate cross-linking agents, peroxide cross-linking agents, and epoxy cross-linking agents are preferably used. Cross-linking agent.

Examples of the isocyanate cross-linking agent include toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and diphenylmethane diisocyanate. , hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate. Furthermore, examples of the isocyanate cross-linking agent include derivatives of these isocyanates. Examples of the isocyanate derivative include isocyanurate modified products and polyol modified products. Examples of commercially available isocyanate crosslinking agents include Coronate L (trimethylolpropane adduct of toluene diisocyanate, manufactured by Tosoh), Coronate HL (trimethylolpropane of hexamethylene diisocyanate). Adduct, manufactured by Tosoh), Coronate HX (isocyanurate form of hexamethylene diisocyanate, manufactured by Tosoh), Takenate D110N (trimethylolpropane adduct of xylylene diisocyanate, Mitsui Chemicals Manufactured by Mitsui Chemicals Co., Ltd.), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals Co., Ltd.).

Examples of peroxide cross-linking agents include dibenzoyl peroxide, di(2-ethylhexyl)peroxydicarbonate, di(4-tert-butylcyclohexyl)peroxydicarbonate, Di-second-butyl peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-hexyl peroxypivalate, and tert-butyl peroxypivalate.

Examples of the epoxy cross-linking agent include bisphenol A, epichlorohydrin-type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, and glyceryl triglycidyl ether. Ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl- m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminemethyl)cyclohexane.

As for the compounding amount of the cross-linking agent in the first method, from the viewpoint of ensuring the cohesion of the adhesive sheet 10, it is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, based on 100 parts by mass of the base polymer. More preferably, it is 0.1 part by mass or more. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the compounding amount of the cross-linking agent is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 100 parts by mass or less based on 100 parts by mass of the base polymer. 3 parts by mass or less.

In the above-mentioned second method, the monomer components (including polyfunctional monomers and other monomers used to introduce a cross-linked structure) can be polymerized in one go or in multiple stages. In the multi-stage polymerization method, first, the monofunctional monomers used to form the base polymer are polymerized (prepolymerization), thereby preparing a polymer containing part of the polymer (a mixture of polymers with a low degree of polymerization and unreacted monomers). Prepolymer composition. Next, after adding a polyfunctional monomer as a crosslinking agent to the prepolymer composition, a part of the polymer and the polyfunctional monomer are polymerized (main polymerization).

Examples of the polyfunctional monomer include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds in one molecule. As a polyfunctional monomer, a polyfunctional acrylate is preferable from the viewpoint that a crosslinked structure can be introduced by active energy ray polymerization (photopolymerization).

Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates having four or more functions.

Examples of the difunctional (meth)acrylate include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate. Tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerol di(meth)acrylate , neopentyl glycol di(meth)acrylate, stearic acid modified pentaerythritol di(meth)acrylate, dicyclopentenyl di(meth)acrylate, isocyanuric acid di(meth)acrylate ester, and alkylene oxide modified bisphenol di(meth)acrylate.

Examples of the trifunctional (meth)acrylate include: trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and isocyanuric acid tris(acryloyloxyethyl) ester.

Examples of the polyfunctional (meth)acrylate having four or more functions include di-trimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol monohydroxypenta(meth)acrylate. acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

As the polyfunctional (meth)acrylate, a polyfunctional (meth)acrylate having four or more functions is preferably used, and dipentaerythritol hexaacrylate is more preferably used.

As for the compounding amount of the polyfunctional monomer as the cross-linking agent in the second method among the monomer components, from the viewpoint of ensuring the cohesion of the adhesive sheet 10, it is, for example, 0.01 parts by mass relative to 100 parts by mass of the monofunctional monomer. Parts by mass or more, preferably 0.05 parts by mass or more. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the compounding amount of the polyfunctional monomer is, for example, 10 parts by mass or less, preferably 3 parts by mass or less, relative to 100 parts by mass of the monofunctional monomer.

The acrylic polymer can be formed by polymerizing the above-mentioned monomer components. Examples of the polymerization method include solution polymerization, solvent-free photopolymerization (for example, UV (Ultraviolet, ultraviolet) polymerization), block polymerization, and emulsion polymerization. As a solvent for solution polymerization, ethyl acetate and toluene can be used, for example. Moreover, as a polymerization initiator, for example, a thermal polymerization initiator and a photopolymerization initiator can be used. The polymerization initiator may be used alone, or two or more types may be used in combination. The usage amount of the polymerization initiator is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, further preferably 0.1 parts by mass or more, and more preferably 1 part by mass, based on 100 parts by mass of the monomer component. parts or less, more preferably 0.5 parts by mass or less, still more preferably 0.3 parts by mass or less.

Examples of the thermal polymerization initiator include azo polymerization initiators and peroxide polymerization initiators. Examples of the azo polymerization initiator include: 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis( 2-Methylpropionic acid) dimethyl ester, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane)bis Hydrochloride, 2,2'-Azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-Azobis(2-methyl propionamidine) disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride. Examples of the peroxide polymerization initiator include dibenzoyl peroxide, tert-butyl peroxymaleate, and lauryl peroxide.

Examples of the photopolymerization initiator include benzoin ether-based photopolymerization initiator, acetophenone-based photopolymerization initiator, α-ketool-based photopolymerization initiator, and aromatic sulfonyl chloride-based photopolymerization initiator. Initiator, photoactive oxime-based photopolymerization initiator, benzoin-based photopolymerization initiator, benzyl-based photopolymerization initiator, benzophenone-based photopolymerization initiator, ketal-based photopolymerization initiator , 9-oxysulfur𠮿 It is a photopolymerization initiator and a phosphine oxide-based photopolymerization initiator.

The weight average molecular weight of the base polymer is preferably 1.5 million or more, more preferably 1.6 million or more, further preferably 1.8 million or more, and still more preferably 2 million, from the viewpoint of ensuring the cohesion of the adhesive sheet 10 above. The weight average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

The adhesive sheet 10 may also contain oligomers. When an acrylic polymer is used as the base polymer, the oligomer is preferably an acrylic oligomer. The acrylic oligomer is a copolymer containing a monomer component of alkyl (meth)acrylate at a ratio of 50% by mass or more, and the weight average molecular weight is, for example, 2,000 or more and 8,000 or less. Oligomers with such molecular weights can be distinguished from the sol components of the base polymer in GPC because they are sufficiently smaller than the weight average molecular weight of the sol component of the base polymer.

The acrylic oligomer is preferably a hydrophobic oligomer having a glass transition temperature higher than that of the base polymer and having no polar group. From the viewpoint of ensuring the adhesion of the adhesive sheet 10 to the adherend, it is preferable that the adhesive sheet 10 contains such an oligomer. Examples of the polar group include a hydroxyl group and a carboxyl group. Regarding the glass transition temperature of the oligomer, the glass transition temperature (theoretical value) calculated based on the above-mentioned Fox formula can be used.

The acrylic oligomer is preferably a copolymer of a monomer component containing a (meth)acrylic acid alkyl ester having a chain alkyl group ((meth)acrylic acid chain alkyl ester), and Alkyl (meth)acrylate having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate). Specific examples of the (meth)acrylic acid alkyl esters include the (meth)acrylic acid alkyl esters described above regarding the base polymer.

As the (meth)acrylic acid chain alkyl ester, methyl methacrylate is preferred in that the glass transition temperature (Tg) is high and the compatibility with the acrylic polymer is excellent. As the alicyclic alkyl (meth)acrylate, from the viewpoint of achieving a high Tg of the acrylic oligomer, dicyclopentyl acrylate, dicyclopentyl methacrylate (DCPMA), and cyclohexyl acrylate are preferred. , and cyclohexyl methacrylate. That is, the acrylic oligomer is preferably a polymer of a monomer component selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. One or more of the group consisting of methyl methacrylate.

The ratio of alicyclic alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 10 mass% or more, more preferably 20 mass% or more, and still more preferably 30 mass% or more , preferably more than 35% by mass. The above ratio is preferably 90 mass% or less, more preferably 80 mass% or less, further preferably 70 mass% or less, particularly preferably 65 mass% or less. The ratio of the (meth)acrylic acid chain alkyl ester in the monomer component of the acrylic oligomer is preferably 90 mass% or less, more preferably 80 mass% or less, and still more preferably 70 mass% or less. The above-mentioned ratio is preferably 10 mass% or more, more preferably 20 mass% or more, and still more preferably 30 mass% or more. From the viewpoint of balancing the hydrophobicity and high Tg of the acrylic oligomer, the above composition regarding the monomer composition of the acrylic oligomer is preferred.

The acrylic oligomer is obtained by polymerizing the monomer component of the acrylic oligomer. Examples of the polymerization method include solution polymerization, active energy ray polymerization (for example, UV polymerization), block polymerization, and emulsion polymerization. In the polymerization of acrylic oligomers, a polymerization initiator may be used, and a chain transfer agent may be used to adjust the molecular weight.

From the viewpoint of expressing the function of the acrylic oligomer, the weight average molecular weight of the acrylic oligomer is preferably 2,000 or more, more preferably 3,000 or more, and still more preferably 4,000 or more. From the viewpoint of ensuring the mobility of the acrylic oligomer within the adhesive sheet 10 and distributing it in a high concentration on the adhesive surface, the weight average molecular weight of the acrylic oligomer is preferably 8,000 or less, more preferably 6,500 or less. , and more preferably 6,000 or less.

Regarding the content of the acrylic oligomer in the adhesive sheet 10, from the viewpoint of ensuring the adhesion of the adhesive sheet 10 to the adherend, it is preferably 0.1 parts by mass or more per 100 parts by mass of the base polymer, and more It is preferably 0.2 parts by mass or more, and more preferably 0.3 parts by mass or more. From the viewpoint of suppressing the increase in haze caused by the presence of acrylic oligomer in the adhesive sheet 10 and the increase in the elastic modulus at low temperature (for example, -20° C.), the acrylic oligomer in the adhesive sheet 10 The content of the substance is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less per 100 parts by mass of the base polymer.

The adhesive composition may contain a silane coupling agent. The content of the silane coupling agent in the adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and still more preferably 0.5 parts by mass or more based on 100 parts by mass of the base polymer. The above content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

The adhesive composition may also contain other ingredients if necessary. Examples of other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, ultraviolet absorbers, surfactants, and antistatic agents. Examples of the solvent include a polymerization solvent used if necessary when polymerizing an acrylic polymer, and a solvent added to a polymerization reaction solution after polymerization. As the solvent, for example, ethyl acetate and toluene can be used.

The adhesive sheet 10 can be produced, for example, by applying the adhesive composition to the release liner L1 (first release liner) to form a coating film, and then drying the coating film.

Examples of the release liner L1 include a flexible plastic film. Examples of the plastic film include polyethylene terephthalate film, polyethylene film, polypropylene film, and polyester film. The thickness of the release liner L1 is, for example, 3 μm or more, and may be, for example, 200 μm or less. The surface of the release liner L1 is preferably subjected to a release treatment.

Examples of coating methods for the adhesive composition include: roll coating, contact roll coating, gravure coating, reverse coating, roller brush coating, spray coating, dip roll coating, and rod coating. Coating, knife coating, air knife coating, curtain coating, die lip coating, and die nozzle coating. The drying temperature of the coating film is, for example, 50°C to 200°C. The drying time is, for example, 5 seconds to 20 minutes.

A release liner L2 (second release liner) may be further laminated on the adhesive sheet 10 on the release liner L1. The release liner L2 is preferably a flexible plastic film whose surface has been released. As the release liner L2, the plastic film described above with respect to the release liner L1 can be used.

In the above manner, the adhesive sheet 10 can be manufactured by covering and protecting the adhesive surfaces 11 and 12 with the release liners L1 and L2.

The thickness of the adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more, from the viewpoint of ensuring sufficient adhesion to the adherend and handleability. From the viewpoint of thinning the flexible device, the thickness of the adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, particularly preferably 50 μm or less.

The haze of the adhesive sheet 10 is preferably 3% or less, more preferably 2% or less, and more preferably 1% or less. The haze of the adhesive sheet 10 can be measured using a haze meter in accordance with JIS K7136 (2000). Examples of the haze meter include "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and "HM-150 type" manufactured by Murakami Color Technology Research Institute Co., Ltd.

The total light transmittance of the adhesive sheet 10 is preferably 60% or more, more preferably 80% or more, and further preferably 85% or more. The total light transmittance of the adhesive sheet 10 is, for example, 100% or less. The total light transmittance of the adhesive sheet 10 can be measured in accordance with JIS K 7375 (2008).

2A to 2C illustrate an example of how to use the adhesive sheet 10 .

In this method, first, as shown in FIG. 2A , the adhesive sheet 10 is bonded to one surface in the thickness direction H of the first member 21 (adherent). The first member 21 is, for example, one element in the multilayer structure of the flexible display panel. Examples of this element include a pixel panel, a polarizing film, a touch panel, and a cover film (the same applies to the second member 22 described below). Through this step, the adhesive sheet 10 for joining with another member (the second member 22 described below) is provided on the first member 21 .

Then, as shown in FIG. 2B , one side of the first member 21 in the thickness direction H is joined to the other side of the second member 22 in the thickness direction H through the adhesive sheet 10 on the first member 21 . The second member 22 is, for example, another element in the multilayer structure of the flexible display panel.

Then, as shown in FIG. 2C , the adhesive sheet 10 between the first member 21 and the second member 22 is aged. By aging, the cross-linking reaction of the base polymer proceeds in the adhesive sheet 10, thereby improving the bonding strength between the first member 21 and the second member 22. The aging temperature is, for example, 20°C to 160°C. The aging time ranges from 1 minute to 21 days, for example. When performing autoclave treatment (heating and pressure treatment) as aging, the temperature is, for example, 30°C to 80°C, the pressure is, for example, 0.1 to 0.8 MPa, and the treatment time is, for example, 15 minutes or more.

As mentioned above, the gel fraction of the adhesive sheet 10 is 85% or more and 95% or less, the ratio R1 of the components with a molecular weight of 500,000 or less in the sol component of the base polymer is 70 mass% or more, and the base polymer contains A polymer containing a monomer component of (meth)acrylic acid in an amount of not less than 0.1% by mass but not more than 10% by mass. This adhesive sheet 10 is suitable for use in flexible devices as described above. [Example]

Hereinafter, an Example is shown and this invention is demonstrated concretely. However, the present invention is not limited to the examples. In addition, the specific numerical values of the blending amount (content), physical property values, parameters, etc. described below can be replaced by the corresponding upper limits of the blending amount (content), physical property values, parameters, etc. described in the above "Embodiments" ( A value defined as "below" or "under") or a lower limit (a value defined as "above" or "exceeds").

[Example 1] <Preparation of acrylic polymer P1> In a reaction vessel equipped with a mixer, a thermometer, a reflux condenser, and a nitrogen introduction pipe, 59 parts by mass of 2-ethylhexyl acrylate (2EHA), 37.5 parts by mass of lauryl acrylate (LA), and 4-hydroxybutyl acrylate were placed. 0.5 parts by mass of ester (4HBA), 3 parts by mass of acrylic acid (AA), 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate-toluene mixed solvent ( A mixture of 95 mass% ethyl acetate and 5 mass% toluene (solid content concentration 60 mass%) was stirred at 55° C. for 6 hours in a nitrogen atmosphere (polymerization reaction). Thereby, a polymer solution containing acrylic polymer P1 was obtained. The monomer composition of acrylic polymer P1 is shown in Table 1 (the same applies to acrylic polymers P2 and P3 described below). The weight average molecular weight of acrylic polymer P1 is approximately 2.8 million. The total ratio of (meth)acrylic acid and hydroxyl-containing monomer (4HBA) in the monomer components (2EHA, LA, 4HBA, AA) of the acrylic polymer P1 was 3.5% by mass. The ratio of alkyl (meth)acrylate (2EHA, LA) having an alkyl group with a carbon number of 8 to 20 in the monomer component of the acrylic polymer P1 was 96.5% by mass.

<Preparation of acrylic oligomer M1> First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen introduction pipe, 58 parts by mass of dicyclopentyl methacrylate (DCPMA) and 39 parts by mass of methyl methacrylate (MMA) were placed as a chain. A mixture of 9 parts by mass of α-thioglycerol as a transfer agent, 0.3 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate as a solvent (solid content concentration 26% by mass), reacted at 70°C for 2 hours under a nitrogen atmosphere, and then reacted at 80°C for 3 hours (polymerization reaction). Next, the reaction solution was heated at 130° C. for 2 hours to volatilize and remove the ethyl acetate, chain transfer agent, and unreacted monomer. Thereby, a solid acrylic oligomer M1 (dry solid) which is a hydrophobic oligomer without a polar group is obtained. The weight average molecular weight Mw of the acrylic oligomer M1 is 2,500.

<Preparation of adhesive composition C1> To the polymer solution, 0.5 parts by mass of the acrylic oligomer M1 and the first cross-linking agent (product name "Nyper BMT-40SV") were added per 100 parts by mass of the acrylic polymer P1 in the polymer solution. Diphenyl peroxide, manufactured by Nippon Oils and Fats Co., Ltd.) 0.3 parts by mass, the second cross-linking agent (product name "Takenate D101E", manufactured by Mitsui Chemicals Co., Ltd.) 0.02 parts by mass, and the first silane coupling agent (product name "KBM- 403", manufactured by Shin-Etsu Chemical Industry Co., Ltd.) 1 part by mass and mixed to prepare adhesive composition C1.

＜Formation of adhesive layer＞ Next, the adhesive composition C1 is applied to the release-processed surface of the first release liner that has been subjected to silicone release treatment on one side to form a coating film. The first release liner is a polyethylene terephthalate (PET) film (product name "DIAFOIL MRF #75", thickness 75 μm, manufactured by Mitsubishi Chemical Co., Ltd.) with silicone release treatment on one side. Next, the coating film on the first release liner is bonded to the release-treated surface of the second release liner that has been subjected to silicone release treatment on one side. The second release liner is a PET film (product name "DIAFOIL MRF #75", thickness 75 μm, manufactured by Mitsubishi Chemical Co., Ltd.) that has been subjected to silicone release treatment on one side. Next, the coating film on the first release liner was dried by heating at 100°C for 1 minute and then at 150°C for 3 minutes to form a transparent adhesive layer with a thickness of 50 μm. In the above manner, the adhesive sheet (thickness 50 μm) of Example 1 with a release liner was produced.

[Comparative example 1] <Preparation of acrylic polymer P2> In a reaction vessel equipped with a mixer, a thermometer, a reflux condenser, and a nitrogen introduction pipe, 70 parts by mass of 2-ethylhexyl acrylate (2EHA), 8 parts by mass of lauryl acrylate (LA), and 4-hydroxybutyl acrylate 1 mass part of ester (4HBA), 20 mass parts of n-butyl acrylate (BA), 0.6 mass part of N-vinyl-2-pyrrolidone (NVP), 0.1 mass part of AIBN as a thermal polymerization initiator, and as A mixture of ethyl acetate as a solvent (solid content concentration: 47% by mass) was stirred at 56° C. for 6 hours in a nitrogen atmosphere (polymerization reaction). Thereby, a polymer solution containing acrylic polymer P2 was obtained. The weight average molecular weight of the acrylic polymer P2 is about 2 million. The total ratio of (meth)acrylic acid and hydroxyl-containing monomer (4HBA) in the monomer components (2EHA, LA, 4HBA, BA, NVP) of the acrylic polymer P2 is 1% by mass. The ratio of alkyl (meth)acrylate (2EHA, LA) having an alkyl group with a carbon number of 8 to 20 in the monomer component of the acrylic polymer P2 was 78 mass %.

<Preparation of adhesive composition C2> To the polymer solution, 0.5 parts by mass of the acrylic oligomer M1, 0.4 parts by mass of the first cross-linking agent (Nyper BMT-40SV), and 0.02 parts by mass of the third cross-linking agent (product name "Takenate D110N", trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals Co., Ltd.), and the second silane coupling agent (product name "A100" , acetyl acetyl group-containing silane coupling agent, manufactured by Soken Chemical Co., Ltd.) 0.2 parts by mass and mixed to prepare adhesive composition C2.

＜Formation of adhesive layer＞ Except that adhesive composition C2 was used instead of adhesive composition C1, the same operation was carried out as described in Example 1 above to form an adhesive layer with a thickness of 50 μm between release liners, and a comparison was made with release liners. Adhesive sheet of Example 1 (thickness 50 μm).

[Comparative example 2] <Preparation of acrylic polymer P3> In a reaction vessel equipped with a mixer, a thermometer, a reflux condenser, and a nitrogen introduction pipe, 100 parts by mass of n-butyl acrylate (BA), 0.1 parts by mass of 2-hydroxyethyl acrylate (2HEA), and 5 parts by mass of acrylic acid (AA) Parts by mass, 0.1 parts by mass of AIBN as a thermal polymerization initiator, and a mixture of ethyl acetate-toluene mixed solvent (ethyl acetate 95 mass%, toluene 5 mass%) (solid content concentration 30 mass%), in nitrogen The mixture was stirred at 55°C for 7 hours under the atmosphere (polymerization reaction). Thereby, a polymer solution containing acrylic polymer P3 was obtained. The weight average molecular weight of acrylic polymer P3 is approximately 1.6 million. The total ratio of (meth)acrylic acid and hydroxyl-containing monomer (2HEA) in the monomer components (BA, 2HEA, AA) of the acrylic polymer P3 was 4.9 mass %. The ratio of alkyl (meth)acrylate having an alkyl group having a carbon number of 8 to 20 in the monomer component of the acrylic polymer P3 is 0 mass %.

<Preparation of adhesive composition C3> To the polymer solution, a fourth cross-linking agent (product name "Coronate L", trimethylolpropane adduct of toluene diisocyanate) was added per 100 parts by mass of the acrylic polymer P3 in the polymer solution. , manufactured by Nippon Polyurethane Industry Co., Ltd.) and 0.05 parts by mass of the first silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Industry Co., Ltd.) were mixed to prepare adhesive composition C3.

＜Formation of adhesive layer＞ Except that adhesive composition C3 was used instead of adhesive composition C1, the same operation was carried out as described in Example 1 above to form an adhesive layer with a thickness of 50 μm between release liners, and comparison of preparation of release liners was carried out. Adhesive sheet of Example 2 (thickness 50 μm).

＜Weight average molecular weight＞ The weight average molecular weight (Mw) of each of the acrylic polymers P1 to P3 and the acrylic oligomer M1 was determined. Specifically, it is measured by gel permeation chromatography (GPC) under the following measurement conditions, and the Mw of the polymer or oligomer is determined in terms of polystyrene. In the measurement, a GPC measurement device (product name "Alliance", manufactured by Waters) was used. The sample solution is prepared as follows. First, a polymer or oligomer is used as a sample, a tetrahydrofuran (THF) solution (containing 10 mM phosphoric acid) with a sample concentration of 0.15% by mass is prepared, and the THF solution is left to stand for 20 hours. Then, the THF solution was filtered using a membrane filter with an average pore size of 0.45 μm to obtain a filtrate, which was used as a sample solution for molecular weight measurement.

[GPC measurement _{conditions ]} Column: _G7000H : 0.8 mL/min Sample injection volume: 100 μL Standard sample: Polystyrene (PS) Detector: Differential refractometer (RI)

＜Gel fraction＞ The gel fraction of each adhesive sheet of Example 1 and Comparative Examples 1 and 2 was measured. Specifically, it is as follows.

First, collect about 0.2 g of adhesive sample from the adhesive sheet (mass: W ₁ mg). Then, use a porous polytetrafluoroethylene membrane with an average pore size of 0.2 μm (size: 100 mm × 100 mm, mass: W ₂ mg) to wrap the adhesive sample in a bag shape to obtain a package. The mouth was tied with kite string (mass: W ₃ mg). As the porous polytetrafluoroethylene membrane, "NITOFLON NTF1122" manufactured by Nitto Denko Co., Ltd. (thickness 85 μm, average pore diameter 0.2 μm, porosity 75%) was used. Then, the package containing the adhesive sample was immersed in 50 mL of ethyl acetate, and left to stand in the ethyl acetate at 23°C for 5 days. Thereby, the sol component in the adhesive sample is dissolved out of the porous polytetrafluoroethylene membrane. Then, after the package was taken out from the ethyl acetate, the package was dried at 130° C. for 2 hours. Then, the package was left to cool for 20 minutes, and the mass of the package (W ₄ mg) was measured. Then, the gel fraction of the adhesive sheet was calculated by substituting the values of W ₁ to W ₄ into the following formula. The values are shown in Table 1.

Gel fraction (%) = [(W ₄ - W ₂ - W ₃ )/W ₁ ] × 100

＜Analysis of sol components＞ The molecular weight distribution of the sol component of the base polymer contained in each adhesive sheet of Example 1 and Comparative Examples 1 and 2 was measured. Specifically, it is as follows.

First, small pieces of the adhesive sheet of a specific size are cut out from the adhesive sheet. Next, a small piece of the adhesive sheet was immersed in a tetrahydrofuran (THF) solution containing phosphoric acid (phosphoric acid concentration: 10 mM), and left to stand in the THF solution at room temperature for 20 hours (immersion treatment). Thereby, the sol component in the small pieces of the adhesive sheet is dissolved in the THF solution (the sol component in the adhesive sheet includes the sol component of the base polymer). In addition, the size of the small pieces of the adhesive sheet and the size of the THF solution used in the immersion treatment were adjusted in consideration of the gel fraction of the small pieces of the adhesive sheet so that the amount of the sol component in the THF solution after the immersion treatment became about 0.2% by mass. quantity. Then, the THF solution containing the sol component was filtered using a membrane filter with an average pore size of 0.45 μm to obtain a filtrate, which was used as a sample solution for molecular weight measurement. Then, the molecular weight distribution of the sol component (soluble component) in the sample solution is measured by gel permeation chromatography (GPC), and the molecular weight distribution curve of the sol component is obtained. The measurement conditions are the same as the above-mentioned GPC measurement conditions. The weight average molecular weight (Mw) of the high molecular weight component derived from the acrylic polymer contained in the sol component (that is, the sol component of the acrylic polymer) is shown in Table 1. "Weight average molecular weight" is a value converted from standard polystyrene, and "molecular weight" is a value based on the calibration curve of standard polystyrene. Table 1 shows the ratio R1 of components with a molecular weight of 500,000 or less and the ratio R2 of components with a molecular weight of 100,000 or less in the sol component of the acrylic polymer. The ratio of the ratio R2 to the ratio R1 (R2/R1) is also shown in Table 1. The ratio R1 is the ratio of the integrated value of the region with a molecular weight of 500,000 or more to the total integrated value of the molecular weight distribution curve of the sol component. The ratio R2 is the ratio of the integrated value of the region with a molecular weight of 100,000 or more to the total integrated value of the molecular weight distribution curve of the sol component.

＜Adhesion＞ The adhesive force of each adhesive sheet of Example 1 and Comparative Examples 1 and 2 was investigated, specifically as follows.

First, test pieces were prepared for each adhesive sheet. In the preparation of the test piece, first, the adhesive sheet with the release liner was peeled off the second release liner, and a PET film (thickness 50 μm) was bonded to the exposed surface of the adhesive sheet thereby to obtain a laminated film (No. 1 release liner/adhesive sheet/PET film). During lamination, the adhesive sheet is press-bonded to the PET film by making a 2 kg roller reciprocate once. Next, a test piece (width 25 mm × length 100 mm) was cut out from the laminated film. Then, in an environment of 23°C and 50% relative humidity, the first release liner was peeled off from the adhesive sheet of the test piece, and the exposed surface of the adhesive sheet thus exposed was bonded to the alkali glass produced by the float method. The air surface of the plate (blue plate glass, thickness 1.35 mm, manufactured by Shonami Glass Co., Ltd.) was obtained to obtain a laminated body (alkali glass plate/adhesive sheet/PET film). The air surface refers to the exposed surface of the alkali glass plate when the alkali glass plate flows on the molten metal during the manufacturing process of the alkali glass plate (the opposite side to the surface that is in contact with the molten metal). During the lamination process, the test piece was pressed against the alkali glass plate by reciprocating the 2 kg roller once. Next, the laminated body was heat-processed at 80 degreeC for 5 hours. Then, the laminated body was left to cool for 30 minutes. Then, in an environment of 23°C and a relative humidity of 50%, a peeling test was performed on the test piece from an alkali glass plate, and the force required for peeling was measured and used as the adhesive force. In this measurement, a tensile testing machine (product name "Autograph AG-IS", manufactured by Shimadzu Corporation) was used. In this measurement, the peeling angle of the test piece relative to the adherend is set to 180°, the tensile speed of the test piece is set to 300 mm/min, and the peeling length is set to 50 mm (measurement conditions for peeling test). The measured adhesion force (N/25 mm) is shown in Table 1.

＜Bending Reliability Test＞ Regarding each adhesive sheet of Example 1 and Comparative Examples 1 and 2, a bending reliability test was performed as follows.

First, the second release liner is peeled off from the adhesive sheet with the release liner (first release liner/adhesive sheet/second release liner), and the exposed surface exposed thereby is subjected to plasma treatment. On the other hand, plasma treatment was also performed on both sides (the first side and the second side) of the polarizing film with a thickness of 31 μm. Also, for both sides of an ultra-thin glass (UTG) film (product name "Chemical Strengthened Glass Dinorex", manufactured by Nippon Electric Glass) with a thickness of 32 μm, and a polyethylene terephthalate (PET) film with a thickness of 125 μm The surface is also treated with plasma. In each plasma treatment, a plasma irradiation device (product name "AP-TO5", manufactured by Sekisui Industrial Co., Ltd.) was used, the voltage was set to 160 V, the frequency was set to 10 kHz, and the processing speed was set to 5000 mm/min. Then, the above-mentioned exposed surface of the adhesive sheet is bonded to the first surface of the polarizing film. This lamination is performed in an environment of 23°C by making a 2 kg roller reciprocate once to press-bond the adhesive sheet with the first release liner and the polarizing film (laminated in the following lamination process) The same applies to the conditions). Then, after peeling off the first release liner from the adhesive sheet with the polarizing film, the UTG film is bonded to the exposed surface of the adhesive sheet thus exposed. Then, the above-mentioned PET film was bonded to the second side of the polarizing film through a thin adhesive sheet with a thickness of 15 μm. Then, the adhesive layer side of the separately prepared cover film with an adhesive layer on one side is attached to the surface of the UTG film (the exposed surface opposite to the above-mentioned adhesive sheet). The cover film with an adhesive layer on one side includes a PET film with a thickness of 75 μm (corona-treated), and a specific acrylic adhesive with a thickness of 50 μm provided on one side of the PET film (corona-treated side). agent layer. In this way, a laminated structure consisting of a PET film (thickness 125 μm), a thin adhesive sheet (thickness 15 μm), a polarizing film (thickness 31 μm), an adhesive sheet (thickness 50 μm), and a UTG film (thickness 32 μm) was obtained. Laminated film.

Next, an evaluation sample was cut out from the laminated film prepared in this way. Specifically, a rectangular sample of 40 mm × 120 mm was cut out from the laminated film in such a way that the absorption axis direction of the polarizing film in the cut sample was parallel to the long side direction. Then, the sample was autoclaved at 35°C and 0.50 MPa for 15 minutes.

Next, a bending test was performed on this sample using a planar body unloaded U-shaped telescopic testing machine (manufactured by YUASA SYSTEM Co., Ltd.). In this test, for each of the two ends of the sample in the long side direction, a bending jig is installed within a range of 20 mm from the end edge of the sample, and the sample is fixed to the testing machine (60 mm from the center of the long side direction of the sample) The area is not fixed). In addition, this test is carried out in a constant temperature and humidity chamber with a temperature of 60°C and a relative humidity of 95%. The sample is repeatedly deformed at a bending speed of 60 rpm between the curved shape and the non-bent shape on the UTG film side. (Bend) 200,000 times. The bending shape in this test specifically refers to the shape in which the axial direction of the bending moment acting on the sample is orthogonal to the absorption axis direction of the polarizing film. In this bending form, the bending radius of the sample is set to 1.5 mm, and the bending angle is set to 180°. In addition, regarding the adhesion of the adhesive sheet (thickness 50 μm) to the adherend in this bending test, the case where there is no peeling between the adhesive sheet and its adherend (UTG film, polarizing film) is evaluated as "good" , the case where peeling occurs is evaluated as "poor". The evaluation results are shown in Table 1.

[Table 1] Table 1 Example 1 Comparative example 1 Comparative example 2 base polymer P1:2EHA(59)/LA(37.5)/4HBA(0.5)/AA(3) 100 - - P2:2EHA(70)/LA(8)/4HBA(1)/BA(20)/NVP(0.6) - 100 - P3:BA(100)/2HEA(0.1)/AA(5) - - 100 Oligomer M 1 :DCPMA(58)/MMA(39) 0.5 0.5 - Cross-linking agent dibenzoyl peroxide 0.3 0.4 - Takenate D101E 0.02 - - Takenate D110N - 0.02 - Coronate L - - 0.5 Silane coupling agent KBM-403 1 - 0.05 A100 - 0.2 - Thickness of adhesive sheet (nm) 50 50 50 gel fraction 89% 85% 81% Sol composition Weight average molecular weight (Mw) 308,000 319,000 454,000 Ratio R1 (wt%) of components with a molecular weight of less than 500,000 81.9 80.7 69.4 Ratio R2 (wt%) of components with a molecular weight of less than 100,000 18.2 19.8 14.3 R2/R1 0.22 0.25 0.21 Adhesion (N/25 mm) 18 14 twenty three Evaluation in bending reliability test good bad bad

10: Adhesive sheet (optical adhesive sheet) 11:Side 1 12:Side 2 21: 1st component 22: 2nd component H:Thickness direction L1: Release liner L2: Release liner

FIG. 1 is a schematic cross-sectional view of an embodiment of the optical adhesive sheet of the present invention. 2A to 2C illustrate an example of how to use the optical adhesive sheet of the present invention. Figure 2A shows the step of bonding the optical adhesive sheet to the first adherend. Figure 2B shows the step of joining the first adherend and the second adherend through the optical adhesive sheet. Figure 2C shows the curing step. .

10: Adhesive sheet (optical adhesive sheet)

11:Side 1

12:Side 2

H:Thickness direction

L1: Release liner

L2: Release liner

Claims (5)

An optical adhesive sheet containing a base polymer, and The gel fraction is above 85% and below 95%. The proportion of components with a molecular weight of less than 500,000 in the sol component of the above-mentioned base polymer is 70% by mass or more, The above-mentioned base polymer is a polymer containing a monomer component of (meth)acrylic acid in an amount of not less than 0.1% by mass and not more than 10% by mass. The optical adhesive sheet according to claim 1, wherein the proportion of components with a molecular weight of less than 100,000 in the above-mentioned sol component is 15% by mass or more. For example, the optical adhesive sheet of claim 1 or 2, wherein the weight average molecular weight of the above-mentioned sol component is not less than 250,000 and not more than 450,000. The optical adhesive sheet of claim 1 or 2, wherein the total ratio of (meth)acrylic acid and hydroxyl-containing monomer in the above monomer components is 2 mass% or more and 5 mass% or less. The optical adhesive sheet of claim 1 or 2, wherein the proportion of alkyl (meth)acrylate having an alkyl group with a carbon number of 8 to 20 in the above monomer component is 90 mass % or more and 98 mass % or less.