KR20230135083A - Optical adhesive sheet for foldable devices - Google Patents

Abstract

The optical adhesive sheet S as an optical adhesive sheet for a foldable device of the present invention has an adhesive layer (10). The adhesive layer 10 has a shear storage modulus of 20 to 50 kPa at 25°C. After the adhesive layer 10 is attached to an adherend, followed by heat and pressure treatment at 50°C, 0.5 MPa and 15 minutes, and then left to stand at 25°C for 72 hours, the adherend is subjected to a temperature of 25°C. It has a first adhesive force Xa. The adhesive layer 10 has a second adhesive force The first adhesive force Xa and the second adhesive force Xb satisfy 0.5≤Xb/Xa≤1.0.

Description

Optical adhesive sheet for foldable devices

The present invention relates to an optical adhesive sheet for foldable devices.

The display panel has a laminated structure including, for example, a pixel panel, a touch panel, a polarizer, and a cover film. In the manufacturing process of such a display panel, for example, a transparent adhesive sheet (optical adhesive sheet) is used to bond elements included in the laminated structure. Meanwhile, development of display panels that can be repeatedly bent (foldable) is in progress, for example, for smartphones and tablet terminals. In a foldable display panel, each element in the laminated structure is manufactured so that it can be repeatedly bent, and an optical adhesive sheet is used to bond the elements. An optical adhesive sheet for foldable devices such as a foldable display panel is described, for example, in Patent Document 1 below.

Japanese Patent Publication No. 2018-111754

Optical adhesive sheets in foldable devices are required to exhibit sufficient adhesion reliability to adherends. However, conventionally, peeling of the optical adhesive sheet from the adherend is likely to occur at the bent portion of the device. This is because when the device is bent, stress such as shear stress acts locally on the optical adhesive sheet at the bending point. Moreover, in conventional optical adhesive sheets, the change in adhesive force due to temperature change is relatively large, so the above-described peeling does not occur over a relatively wide temperature range (for example, including room temperature region and higher temperature region). Adhesion reliability is not obtained. The occurrence of the above-described peeling at the bending point causes malfunction of the device and is not desirable.

The present invention provides an optical adhesive sheet for foldable devices that is suitable for suppressing peeling from a bending adherend.

The present invention [1] is an optical adhesive sheet for a foldable device having an adhesive layer, wherein the adhesive layer has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C, and the adhesive layer has a shear storage modulus for an adherend. After sticking, subsequent heat and pressure treatment under conditions of 50°C, 0.5 MPa and 15 minutes, and subsequent standing at 25°C for 72 hours, the adhesive has a first adhesive force Xa at 25°C to the adherend, and the adhesive The layer has a second adhesive force It includes an optical adhesive sheet for a foldable device that satisfies Xb/Xa≤1.0.

As described above, the adhesive layer of the optical adhesive sheet of the present invention has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C. An adhesive layer having this level of flexibility secures the cohesive force necessary for bonding between adherends and relieves the stress acting locally on the adhesive layer at the bending point when the adherend to which the adhesive layer is bonded is bent. suitable for Therefore, the present optical adhesive sheet is suitable for suppressing peeling from the adherend to be bent.

As described above, the adhesive layer of the present optical adhesive sheet has a first adhesive force . A configuration in which the second adhesive force Xb is large such that the ratio (Xb/Xa) of the second adhesive force Xb to the first adhesive force Suitable for suppressing

In the present invention [2], the pressure-sensitive adhesive layer has a third adhesive force The optical adhesive sheet for a foldable device according to [1], wherein the third adhesive force Xc satisfies 0.5≤Xc/Xa≤0.8.

This configuration (a configuration in which the third adhesive force Xc is large such that the ratio of the third adhesive force Xc to the first adhesive force It is desirable to suppress

In the present invention [3], the minimum adhesive force that the adhesive layer has to the adherend in the temperature range of 25°C to 85°C after sticking to the adherend, the heat and pressure treatment, and the above standing is 10N. /25 mm or more, and includes the optical adhesive sheet for a foldable device according to [1] or [2] above.

Such a configuration is desirable for suppressing the above-mentioned peeling and for realizing good adhesion reliability over a room temperature range and a higher temperature range.

The present invention [4] includes the optical adhesive sheet for a foldable device according to [3], wherein the adhesive layer has the minimum adhesive force at 60°C or higher.

Such a configuration is desirable for realizing good adhesion reliability in the room temperature range.

In the present invention [5], the adhesive force of the adhesive layer to the adherend at 25°C after sticking to the adherend and standing for 2 minutes at 25°C is 0.5 N/25 mm or more and 12 N/25 mm. It includes the following optical adhesive sheet for a foldable device according to any one of [1] to [4] above.

The configuration in which the above-described adhesive force at 25°C is 0.5 N/25 mm or more ensures that the adhesive layer has the adhesive strength required for the work in the bonding operation of the optical adhesive sheet to the adherend, thereby ensuring good performance of the optical adhesive sheet to the adherend. It is suitable for realizing temporary fixation. The configuration in which the adhesive force at 25°C is 12 N/25 mm or less is suitable for ensuring light peelability of the adhesive layer and reworkability in the above bonding operation.

1 is a cross-sectional schematic diagram of one embodiment of the optical adhesive sheet of the present invention.
Figure 2 shows an example of a method of using the optical adhesive sheet of the present invention. FIG. 2A shows a process of bonding an optical adhesive sheet to a first adherend, FIG. 2B shows a process of bonding a first adherend and a second adherend through an optical adhesive sheet, and FIG. 2C shows an aging process.
Figure 3 is a graph showing the adhesive strength of each adhesive sheet of Example 1 and Comparative Example 1.

The adhesive sheet S as one embodiment of the optical adhesive sheet for a foldable device of the present invention is provided with an adhesive layer 10, as shown in FIG. 1 . The adhesive sheet S has a sheet shape of a predetermined thickness and extends in a direction perpendicular to the thickness direction (plane direction). In Fig. 1, release films L1 and L2 (release liners) are bonded to both sides of the adhesive sheet S. The release film L1 is disposed on one side of the adhesive sheet S in the thickness direction T. The release film L2 is disposed on the other side of the adhesive sheet S in the thickness direction T. The adhesive sheet S provided with a release film takes the form of a roll (not shown), for example.

This adhesive sheet S is a transparent adhesive sheet (optical adhesive sheet) disposed at a light passing location in the foldable device. Examples of foldable devices include foldable display panels. The foldable display panel has a stacked structure including, for example, a pixel panel, a touch panel, a polarizer, and a cover film. The adhesive sheet S is used, for example, to bond elements included in the laminated structure during the manufacturing process of a foldable display panel.

The adhesive layer 10 has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C, and the first adhesive force Xa and the second adhesive force Xb satisfy 0.5≤Xb/Xa≤1.0.

The shear storage modulus of the adhesive layer 10 is a storage modulus determined by dynamic viscoelasticity measurement described later regarding examples (the same applies to the shear storage modulus described later). The first adhesive force The second adhesive force The adherend is a polyimide film (the same applies to the adherend described later). The sticking of the adhesive layer 10 to the adherend is done by weighting a 2 kg roller in one reciprocation in an environment of 25°C (the same applies to the sticking described later). The heating and pressing treatment is a treatment carried out under the conditions of a temperature of 50°C, a pressure of 0.5 MPa, and a treatment time of 15 minutes, and is a treatment that is started within 3 minutes from the attachment of the adhesive layer 10 to the adherend (the heating and pressing treatment described later) The same goes for ). The adhesive force is the adhesive force as peel strength measured by a peel test under the conditions of a predetermined temperature, a peel angle of 180°, and a tensile speed of 300 mm/min (the same applies to the adhesive force described later).

As described above, the adhesive layer 10 in the adhesive sheet S has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C. The adhesive layer 10 with this level of flexibility secures the cohesive force necessary for bonding between adherends, and when the adherend to which the adhesive layer 10 is bonded is bent, the adhesive layer 10 is localized at the bending point. It is suitable for relieving the stress acting on it. Therefore, the adhesive sheet S is suitable for suppressing peeling from the adherend to be bent.

In addition, as described above, the adhesive layer 10 has a first adhesive force . A configuration in which the second adhesive force Xb is large such that the ratio (Xb/Xa) of the second adhesive force Xb to the first adhesive force Suitable for suppressing

As described above, the adhesive sheet S is suitable for suppressing peeling from the adherend to be bent. In addition, the configuration in which the adhesive layer 10 has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C is such that the adhesive layer ( 10) It is suitable for suppressing the adhesion of adhesive fragments. Therefore, this configuration is suitable for realizing good processing yield of the adhesive sheet S.

In the adhesive sheet S, from the viewpoint of obtaining stable adhesion reliability in the room temperature range and the temperature range higher than that, Xb/Xa is preferably 0.6 or more, more preferably 0.7 or more, and still more preferably 0.75 or more.

The first adhesive force Xa and the third adhesive force Xc of the adhesive layer 10 satisfy 0.5≤Xc/Xa≤0.8. The third adhesive force .

Such a configuration (a configuration in which the third adhesive force Xc is large such that From this viewpoint, Xc/Xa is more preferably 0.6 or more, further preferably 0.65 or more, and particularly preferably 0.68 or more.

The minimum adhesive force that the adhesive layer 10 has to the adherend in the temperature range of 25°C to 85°C after sticking to the adherend, subsequent heat and pressure treatment, and subsequent standing at 25°C for 72 hours. is preferably 10 N/25 mm or more, more preferably 11 N/25 mm or more, and even more preferably 12 N/25 mm or more. Such a configuration is desirable for suppressing the above-mentioned peeling and for realizing good adhesion reliability over a room temperature range and a higher temperature range.

The adhesive layer 10 has the minimum adhesive strength above 60°C. Such a configuration is desirable for realizing good adhesion reliability in the room temperature range.

The adhesive layer 10 preferably has an adhesive force at 25°C to an adherend after being left for 2 minutes at 25°C from the time it is attached to the adherend, and is preferably 0.5 N/25 mm or more and 12 N/25 mm or less. The configuration in which the above-described adhesive force (initial adhesive force) at 25°C is 0.5 N/25 mm or more ensures in the adhesive layer 10 the adhesive force required for the operation in the operation of bonding the adhesive sheet S to the adherend, It is suitable for realizing good temporary fixation of the adhesive sheet S. From this viewpoint, the initial adhesive force is more preferably 1 N/25 mm or more, further preferably 3 N/25 mm or more, and particularly preferably 5 N/25 mm or more. A configuration in which the initial adhesive force at 25°C is 12 N/25 mm or less is suitable for ensuring light peelability of the adhesive layer 10 and reworkability in the above bonding operation. From this viewpoint, the initial adhesive force is more preferably 10 N/25 mm or less, further preferably 9 N/25 mm or less, and particularly preferably 8 N/25 mm or less. Methods for adjusting the initial adhesive force include, for example, selection of the type of base polymer for the adhesive layer 10, adjustment of the molecular weight, and adjustment of the mixing amount. Selection of the type of base polymer includes selection of the type (configuration) of the main chain in the base polymer, and selection of the type and adjustment of the amount of functional groups (the same applies to selection of the type of base polymer, discussed later). ). Methods for adjusting the initial adhesive force include selection of the type of component other than the base polymer and adjustment of the compounding amount of the component. Examples of the component include crosslinking agents, silane coupling agents, and oligomers.

The first adhesive force Xa is preferably 15 N/25 mm or more, more preferably 17 N/25 mm or more, and even more preferably 19 N/25 mm or more. The first adhesive force Xa is preferably 30 N/25 mm or less, more preferably 25 N/25 mm or less, and even more preferably 23 N/25 mm or less. These configurations are preferable for ensuring the reliability of bonding between adherends by the optical adhesive sheet at around room temperature. Methods for adjusting the first adhesive force Examples include selection of the type of ring agent and oligomer and adjustment of the mixing amount. Each adjustment method of the second adhesive force Xb, the ratio of the second adhesive force Xb to the first adhesive force Xa (Xb/Xa), the third adhesive force Xc, and the ratio of the third adhesive force The same goes for . Additionally, the adhesive forces Xb, Xc, ratios Xb/Xa, and ratios Specifically, the higher the molecular weight and the elastic modulus, the more difficult it is for the adhesive forces Xb and

The second adhesive force Xb is preferably 7 N/25 mm or more, more preferably 9 N/25 mm or more, and even more preferably 10 N/25 mm or more. The second adhesive force Xb is preferably 30 N/25 mm or less, more preferably 25 N/25 mm or less, and even more preferably 23 N/25 mm or less. These configurations are preferable for ensuring the reliability of bonding between adherends by the optical adhesive sheet at around 60°C.

The third adhesive force Xc is preferably 7 N/25 mm or more, more preferably 9 N/25 mm or more, and even more preferably 10 N/25 mm or more. The third adhesive force Xc is preferably 25 N/25 mm or less, more preferably 22 N/25 mm or less, and even more preferably 20 N/25 mm or less. These configurations are preferable for ensuring the reliability of bonding between adherends by the optical adhesive sheet at around 85°C.

The shear storage modulus (first storage modulus Ma) of the adhesive layer 10 at 25°C is preferably 25 kPa or more, more preferably 30 kPa or more, and still more preferably is 33 kPa or more, particularly preferably 35 kPa or more. The first storage modulus Ma is preferably 50 kPa or less, more preferably 45 kPa or less, further preferably 43 kPa or less, and particularly preferably 40 kPa or less from the viewpoint of stress relaxation described above. Methods for adjusting the first storage modulus Ma of the pressure-sensitive adhesive layer 10 include, for example, selection of the type of base polymer for the pressure-sensitive adhesive layer 10, adjustment of the molecular weight and adjustment of the compounding amount, selection of the type of crosslinking agent, and Adjustment of the mixing amount may be mentioned. The second storage modulus Mb, the ratio of the second storage modulus Mb to the first storage modulus Ma (Mb/Ma), the latter third storage modulus Mc, and the third storage modulus Mc to the first storage modulus Ma. The same applies to each adjustment method of the ratio (Mc/Ma).

The shear storage modulus (second storage modulus Mb) of the adhesive layer 10 at 60°C is preferably 18 kPa or more from the viewpoint of securing the above-mentioned cohesive force required for bonding between adherends in a temperature range around 60°C. , more preferably 23 kPa or more, even more preferably 25 kPa or more. The second storage modulus Mb is preferably 45 kPa or less, more preferably 43 kPa or less, and still more preferably 40 kPa or less from the viewpoint of suppressing peeling from the adherend to be bent in a temperature range around 60°C. .

The ratio of the second storage modulus Mb to the first storage modulus Ma (Mb/Ma) preferably satisfies 0.6≤Mb/Ma≤1. Such a configuration is preferable from the viewpoint of stabilizing the adhesive properties in the temperature range from room temperature to around 60°C.

The shear storage modulus (third storage modulus Mc) of the adhesive layer 10 at 85°C is preferably 15 kPa or more from the viewpoint of securing the above-mentioned cohesive force required for bonding between adherends in a temperature range around 85°C. , more preferably 18 kPa or more, even more preferably 20 kPa or more. The third storage modulus Mc is preferably 45 kPa or less, more preferably 43 kPa or less, and still more preferably 40 kPa or less from the viewpoint of suppressing peeling from the adherend to be bent in a temperature range around 85°C. .

The ratio of the third storage modulus Mc to the first storage modulus Ma (Mc/Ma) preferably satisfies 0.5≤Mb/Ma≤0.8. Such a configuration is preferable from the viewpoint of stabilizing the adhesive properties in the temperature range from room temperature to around 85°C.

The adhesive layer 10 is a pressure-sensitive adhesive layer formed of an adhesive composition. The adhesive layer 10 has transparency (visible light transparency). The adhesive layer 10 includes at least a base polymer.

The base polymer is an adhesive component that develops adhesiveness in the adhesive layer 10. Base polymers include, for example, acrylic polymer, silicone polymer, polyester polymer, polyurethane polymer, polyamide polymer, polyvinyl ether polymer, vinyl acetate/vinyl chloride copolymer, modified polyolefin polymer, epoxy polymer, fluorine polymer, and rubber. Polymers may be mentioned. The base polymer may be used individually, or two or more types may be used together. From the viewpoint of ensuring good transparency and adhesion in the adhesive layer 10, an acrylic polymer is preferably used as the base polymer.

Acrylic polymer is a copolymer of a monomer component containing alkyl (meth)acrylate in a proportion of 50% by mass or more. “(meth)acrylic acid” means acrylic acid and/or methacrylic acid.

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

Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and (meth)acrylic acid. -Butyl, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethyl (meth)acrylate Hexyl, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, ( Dodecyl (meth)acrylate (i.e. lauryl acrylate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, Examples include heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid esters having a tricyclic or more aliphatic hydrocarbon ring. Acrylic acid ester can be mentioned. Examples of (meth)acrylic acid cycloalkyl esters include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. Examples of (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclofentanyl (meth)acrylate, and 1-acrylate. Examples include damantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

As the (meth)acrylic acid alkyl ester, preferably an acrylic acid alkyl ester having an alkyl group having 3 to 15 carbon atoms is used, and more preferably at least one selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate. One is used.

The proportion of alkyl (meth)acrylate in the monomer component is preferably 50% by mass or more, more preferably 60% by mass, from the viewpoint of appropriately expressing basic properties such as adhesiveness in the adhesive layer 10. or more, more preferably 70% by mass or more. The ratio is, for example, 99% by mass or less.

The monomer component may contain a copolymerizable monomer that can be copolymerized with an alkyl (meth)acrylate ester. Examples of copolymerizable monomers include monomers having a polar group. Examples of polar group-containing monomers include monomers having a nitrogen atom-containing ring, hydroxy group-containing monomers, and carboxyl group-containing monomers. The polar group-containing monomer is helpful in modifying the acrylic polymer, such as introducing crosslinking points into the acrylic polymer and securing the cohesion of the acrylic polymer.

Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, and N-vinylpipe. Razine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine , N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazine-2- ion, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, 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 atom-containing ring in the monomer component is preferably from the viewpoint of ensuring cohesion in the pressure-sensitive adhesive layer 10 and ensuring adhesion of the pressure-sensitive adhesive layer 10 to the adherend. It is 0.1 mass% or more, more preferably 0.3 mass% or more, and even more preferably 0.55 mass% or more. The ratio is preferably 30 mass from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and the polarity of the acrylic polymer (related to the compatibility of the various additive components and the acrylic polymer in the adhesive layer 10). % or less, more preferably 20 mass% or less.

Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and (meth)acrylic acid. ) 4-hydroxybutyl acrylic acid, 6-hydroxyhexyl (meth)acrylic acid, 8-hydroxyoctyl (meth)acrylic acid, 10-hydroxydecyl (meth)acrylic acid, 12-hydroxylauryl (meth)acrylic acid, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate can be mentioned. As the hydroxy group-containing monomer, 4-hydroxybutyl (meth)acrylate is preferably used, and 4-hydroxybutyl acrylate is more preferably used.

The ratio of the hydroxy group-containing monomer in the monomer component is preferably 0.1% by mass or more, more preferably 0.5% by mass, from the viewpoint of introducing a crosslinked structure to the acrylic polymer and ensuring cohesion in the pressure-sensitive adhesive layer 10. It is mass % or more, more preferably 0.8 mass % or more.

The ratio is preferably 20% by mass or less, more preferably 10% by mass, from the viewpoint of adjusting the polarity of the acrylic polymer (related to the compatibility of the acrylic polymer with various additive components in the adhesive layer 10). It is as follows.

Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

The ratio of the carboxyl group-containing monomer in the monomer component is from the viewpoint of introducing a cross-linked structure to the acrylic polymer, ensuring cohesion in the pressure-sensitive adhesive layer 10, and ensuring adhesion of the pressure-sensitive adhesive layer 10 to the adherend. Preferably it is 0.1 mass% or more, more preferably 0.5 mass% or more, and even more preferably 0.8 mass% or more. The ratio is preferably 30% by mass or less, more preferably 20% by mass or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend due to acid.

In order to prevent metal elements such as electrodes in a foldable device from being corroded by acid components, the adhesive layer 10 of the adhesive sheet S preferably has a low acid content. In addition, when the adhesive sheet S is used for adhering a polarizing plate, it is preferable that the adhesive layer 10 has a low acid content in order to suppress polyenization of the polyvinyl alcohol-based polarizer due to an acid component. In this acid-free adhesive sheet S, the content of organic acid monomers (for example, (meth)acrylic acid and carboxyl group-containing monomers) in the adhesive layer 10 is preferably 100 ppm or less, more preferably 70 ppm or less, More preferably, it is 50ppm or less. The organic acid monomer content of the adhesive layer 10 is determined by immersing the adhesive layer 10 in pure water and heating it at 100°C for 45 minutes, and quantifying the acid monomer extracted into the water using an ion chromatograph.

From an acid-free viewpoint, it is preferable that the base polymer in the pressure-sensitive adhesive layer 10 does not substantially contain an organic acid monomer as a monomer component. From the viewpoint of acid free, the proportion of organic acid monomer in the monomer component is preferably 0.5 mass% or less, more preferably 0.1 mass% or less, further preferably 0.05 mass%, and ideally 0 mass%. .

The monomer component may contain other copolymerizable monomers. Other copolymerizable monomers include, for example, acid anhydride monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds. These other copolymerizable monomers may be used individually, or two or more types may be used together.

The base polymer has a crosslinked structure in this embodiment. As a method of introducing a crosslinking structure to the base polymer, a base polymer having a functional group capable of reacting with the crosslinking agent and a crosslinking agent are blended into an adhesive composition, and the base polymer and the crosslinking agent are reacted in the adhesive layer 10 (first method), and A method of forming a base polymer in which a polyfunctional monomer is included in the monomer component forming the base polymer and a branched structure (crosslinked structure) is introduced into the polymer chain by polymerization of the monomer component is included. These methods may be used together.

Examples of the crosslinking agent used in the first method include compounds that react with functional groups (such as hydroxy groups and carboxyl groups) contained in the base polymer. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. The crosslinking agent may be used individually, or two or more types may be used together. As the cross-linking agent, an isocyanate cross-linking agent, a peroxide cross-linking agent, and an epoxy cross-linking agent are preferably used because the reactivity of the hydroxy group and carboxyl group in the base polymer is high, making it easy to introduce a cross-linking structure.

Isocyanate crosslinking agents include, for example, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, and tetramethylene diisocyanate. Examples include silylene diisocyanate, naphthalene diisocyanate, triphenylmethane trigasocyanate, and polymethylene polyphenylisocyanate. Additionally, examples of the isocyanate crosslinking agent include derivatives of these isocyanates. Examples of the isocyanate derivative include isocyanurate modified products and polyol modified products. Commercially available isocyanate crosslinking agents include, for example, Coronate L (trimethylolpropane adduct of tolylene diisocyanate, coating agent), Coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, coating agent), Coronate Examples include HX (isocyanurate form of hexamethylene diisocyanate, manufactured by Doso), and Takenate D110N (trimethylolpropane adduct form of xylylene diisocyanate, manufactured by Mitsui Chemicals).

As peroxide crosslinking agents, dibenzoyl peroxide, di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t -Butylperoxyneodecanoate, t-hexylperoxypivalate, and t-butylperoxypivalate.

As an epoxy crosslinking agent, bisphenol A, epichlorohydrin type epoxy resin, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycol. Sidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamineglycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3 -Bis(N,N-diglycidylaminomethyl)cyclohexane can be mentioned.

Isocyanate crosslinking agents (especially bifunctional isocyanate crosslinking agents) and peroxide crosslinking agents are preferable from the viewpoint of ensuring appropriate flexibility (and therefore flexibility) of the adhesive layer 10. An isocyanate crosslinking agent (particularly a trifunctional isocyanate crosslinking agent) is preferable from the viewpoint of ensuring the durability of the adhesive layer 10. In the base polymer, the bifunctional isocyanate crosslinking agent and the peroxide crosslinking agent form a more flexible two-dimensional crosslinking, whereas the trifunctional isocyanate crosslinking agent forms a stronger three-dimensional crosslinking. From the viewpoint of both durability and flexibility of the adhesive layer 10, combined use of a trifunctional isocyanate crosslinking agent, a peroxide crosslinking agent, and/or a bifunctional isocyanate crosslinking agent is preferable.

From the viewpoint of ensuring the cohesion of the adhesive layer 10, the amount of the crosslinking agent is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass, based on 100 parts by mass of the base polymer. That's it. From the viewpoint of ensuring good adhesion in the adhesive layer 10, the compounding amount of the crosslinking agent per 100 parts by mass of the base polymer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 3 parts by mass. It is below wealth.

In the second method, the monomer component (including a polyfunctional monomer for introducing a crosslinked structure and other monomers) may be polymerized at once or in multiple steps. In the multi-step polymerization method, first, monofunctional monomers to form a base polymer are polymerized (pre-polymerization), thereby preparing a prepolymer composition containing a partially polymerized product (a mixture of a low-polymerized polymer and unreacted monomers). Next, the polyfunctional monomer is added to the prepolymer composition, and then the partially polymerized product and the polyfunctional monomer are polymerized (main polymerization).

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

Examples of polyfunctional (meth)acrylate include bifunctional (meth)acrylate, trifunctional (meth)acrylate, and tetrafunctional or higher polyfunctional (meth)acrylate.

As bifunctional (meth)acrylate, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol dimethacrylate, 1 ,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, stearic acid modified pentaerythritol di. (meth)acrylate, dicyclopentenyl diacrylate, di(meth)acryloyl isocyanurate, and alkylene oxide-modified bisphenol di(meth)acrylate.

Examples of the trifunctional (meth)acrylate include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

Examples of tetrafunctional or higher polyfunctional (meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, Alkyl-modified dipentaerythritol pentaacrylate and dipentaerythritol hexa(meth)acrylate can be mentioned.

The molecular weight of the polyfunctional monomer is preferably 1500 or less, more preferably 1000 or less. In addition, the functional group equivalent weight (g/eq) of the polyfunctional monomer is preferably 50 or more, more preferably 70 or more, and even more preferably 80 or more. The functional group equivalent is preferably 500 or less, more preferably 300 or less, and even more preferably 200 or less. These structures are preferable from the viewpoint of appropriately adjusting viscoelasticity (for example, storage modulus G' and loss tangent tan δ) by introducing a crosslinked structure in the base polymer.

Acrylic polymer can be formed by polymerizing the monomer components described above. Examples of polymerization methods include solution polymerization, active energy ray polymerization (for example, UV polymerization), bulk polymerization, and emulsion polymerization. From the viewpoints of transparency, water resistance, and cost of the adhesive layer 10, solution polymerization and UV polymerization are preferred. As solvents for solution polymerization, for example, ethyl acetate and toluene are used. Additionally, as the polymerization initiator, for example, a thermal polymerization initiator and a photopolymerization initiator are used. The amount of the polymerization initiator used is, for example, 0.05 parts by mass or more, and for example, 1 part by mass or less, per 100 parts by mass of the monomer component.

Examples of thermal polymerization initiators 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, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2- (5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis(2-methylpropionamidine)disulfate, and 2,2'-azobis(N, N'-dimethyleneisobutylamidine)dihydrochloride can be mentioned. Examples of peroxide polymerization initiators include dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

Examples of the photopolymerization initiator include benzoin ether photopolymerization initiator, acetophenone photopolymerization initiator, α-ketol photopolymerization initiator, aromatic sulfonyl chloride photopolymerization initiator, photoactive oxime photopolymerization initiator, benzoin photopolymerization initiator, and benzyl photopolymerization initiator. , a benzophenone-based photopolymerization initiator, a ketal-based photopolymerization initiator, a thioxanthone-based photopolymerization initiator, and an acylphosphine oxide-based photopolymerization initiator.

In polymerization, a chain transfer agent and/or a polymerization inhibitor (polymerization retardant) may be used for purposes such as molecular weight adjustment. As chain transfer agents, α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolic acid, 2,3-dimercapto-1- Propanol, and α-methylstyrene dimer are included.

The molecular weight of the base polymer can be adjusted by adjusting the type and/or amount of the polymerization initiator. For example, in radical polymerization, the larger the amount of polymerization initiator, the higher the radical concentration in the reaction system, the higher the density of reaction initiation sites, and the lower the molecular weight of the base polymer formed. On the other hand, the smaller the amount of polymerization initiator, the lower the density of the reaction initiation point, so that the polymer chain is likely to be elongated, and the molecular weight of the base polymer formed tends to increase.

The weight average molecular weight of the acrylic polymer is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more from the viewpoint of ensuring cohesion in the adhesive layer 10. The weight average molecular weight is preferably 5,000,000 or less, more preferably 3,000,000 or less, and even more preferably 2,000,000 or less. The weight average molecular weight of the acrylic polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

The glass transition temperature (Tg) of the base polymer is preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. The glass transition temperature is, for example, -80°C or higher.

For the glass transition temperature (Tg) of the base polymer, the glass transition temperature (theoretical value) determined based on Fox's equation below can be used. Fox's equation is a relational expression 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 formula of Fox below, Tg represents the glass transition temperature (°C) of the polymer, Wi represents the weight fraction of monomer i constituting the polymer, and Tgi represents the glass transition temperature of the homopolymer formed from monomer i ( ℃). 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 Bunko 7 Introduction to Synthetic Resins for Paints” (Kyozo Kitaoka, Polymer Publishing Society, 1995), The glass transition temperatures of various homopolymers are illustrated. 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's expression 1/(273+Tg)=Σ[Wi/(273+Tgi)]

The adhesive composition may contain one or two or more types of oligomers in addition to the base polymer. When an acrylic polymer is used as the base polymer, an acrylic oligomer is preferably used as the oligomer. The acrylic oligomer is a copolymer of a monomer component containing an alkyl (meth)acrylate in a proportion of 50% by mass or more, and has a weight average molecular weight of, for example, 1,000 or more and 30,000 or less.

The glass transition temperature of the acrylic oligomer is preferably 60°C or higher, more preferably 80°C or higher, further preferably 100°C or higher, and particularly preferably 110°C or higher. The glass transition temperature of the acrylic oligomer is, for example, 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. By combining a low Tg acrylic polymer (base polymer) with a crosslinked structure and a high Tg acrylic oligomer, the adhesive strength of the pressure-sensitive adhesive layer 10, especially at high temperatures, can be increased. The glass transition temperature of the acrylic oligomer is calculated by Fox's equation above.

The acrylic oligomer having a glass transition temperature of 60°C or higher is preferably an alkyl (meth)acrylate ester (chain alkyl (meth)acrylate) having a chain alkyl group, and an alkyl (meth)acrylate ester (alicyclic alkyl) having an alicyclic alkyl group. It is a polymer of monomer components containing (meth)acrylate). Specific examples of these (meth)acrylic acid alkyl esters include the above-mentioned (meth)acrylic acid alkyl esters as monomer components of acrylic polymers.

As the chain alkyl (meth)acrylate, methyl methacrylate is preferable because it has a high glass transition temperature and is excellent in compatibility with the base polymer. As alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer is a polymer of a monomer component containing at least one member selected from the group consisting of dicyclofentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate. It is desirable.

The proportion of alicyclic alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 10% by weight or more, more preferably 20% by weight or more, and even more preferably 30% by weight or more. The ratio is preferably 90% by weight or less, more preferably 80% by weight or less, and even more preferably 70% by weight or less. The proportion of linear alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 90% by weight or less, more preferably 80% by weight or less, and even more preferably 70% by weight or less. The ratio is preferably 10% by weight or more, more preferably 20% by weight or more, and even more preferably 30% by weight or more.

The weight average molecular weight of the acrylic oligomer is preferably 1000 or more, more preferably 1500 or more, and even more preferably 2000 or more. The molecular weight is preferably 30,000 or less, more preferably 10,000 or less, and even more preferably 8,000 or less. This molecular weight range of the acrylic oligomer is desirable to ensure the adhesion and adhesion retention of the adhesive layer 10.

Acrylic oligomer is obtained by polymerizing the monomer component of the acrylic oligomer. Examples of polymerization methods include solution polymerization, active energy ray polymerization (for example, UV polymerization), bulk polymerization, and emulsion polymerization. In the polymerization of acrylic oligomers, a polymerization initiator may be used, or a chain transfer agent may be used for the purpose of adjusting the molecular weight.

In order to sufficiently increase the adhesive strength of the adhesive layer 10, the content of the acrylic oligomer in the adhesive layer 10 is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, based on 100 parts by mass of the base polymer. , more preferably 1 part by mass or more. On the other hand, from the viewpoint of ensuring transparency of the adhesive layer 10, the content of acrylic oligomer in the adhesive layer 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass, based on 100 parts by mass of the base polymer. It is 3 parts by mass or less, more preferably 3 parts by mass or less. In the adhesive layer 10, when the content of the acrylic oligomer is too large, haze tends to increase and transparency decreases due to a decrease in compatibility of the acrylic oligomer.

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, based on 100 parts by mass of the base polymer. The copper content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

The adhesive composition may contain other components as needed. Other components include, for example, tackifiers, plasticizers, softeners, anti-deterioration agents, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, and antistatic agents.

The adhesive sheet S can be manufactured, for example, by applying the above-described adhesive composition onto release film L1 (first release film) to form a coating film, and then drying the coating film.

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

Application methods of the adhesive composition include, for example, roll coat, kiss roll coat, gravure coat, reverse coat, roll brush, spray coat, dip roll coat, bar coat, knife coat, air knife coat, curtain coat, lip coat, and A die coat is included. The drying temperature of the coating film is, for example, 50°C to 200°C. Drying time is, for example, 5 seconds to 20 minutes.

You may further laminate a release film L2 (second release film) on the adhesive layer 10 on the first release film L1. The second release film is a flexible plastic film that has been subjected to a surface release treatment, and can be used the same way as that described above for the first release film.

As described above, the adhesive sheet S whose adhesive surface is covered and protected by the release films L1 and L2 can be manufactured. The release films L1 and L2 are peeled from the adhesive sheet S as needed when using the adhesive sheet S.

The thickness of the adhesive layer 10 is preferably 10 μm or more, more preferably 15 μm or more from the viewpoint of ensuring sufficient adhesion to the adherend. From the viewpoint of handling properties of the adhesive sheet S, the thickness of the adhesive layer 10 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, and particularly preferably 50 μm or less.

The haze of the adhesive layer 10 is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. The haze of the adhesive layer 10 can be measured using a haze meter based on JIS K 7136 (2000). Examples of the haze meter include "NDH2000" manufactured by Nippon Denshoku Kogyo Co., Ltd., and "HM-150 Type" manufactured by Murakami Shikisai Kijutsu Kenkyujo Co., Ltd.

The total light transmittance of the adhesive layer 10 is preferably 60% or more, more preferably 80% or more, and even more preferably 85% or more. The total light transmittance of the adhesive layer 10 is, for example, 100% or less. The total light transmittance of the adhesive layer 10 can be measured based on JIS K 7375 (2008).

2A to 2C show an example of a method of using the adhesive sheet S.

In this method, first, as shown in FIG. 2A, the adhesive sheet S is bonded to one side of the first member 21 (adhered body) in the thickness direction T. The first member 21 is, for example, an element of the laminated structure of a flexible panel. Examples of the element include a pixel panel, a touch panel, a polarizing plate, and a cover film (the same applies to the second member 22 described later). Through this process, an adhesive layer 10 for bonding to other members is provided on the first member 21.

In this process, when a bonding defect (for example, misalignment of the adhesive sheet S on the first member 21) occurs, the adhesive sheet S is peeled from the first member 21. After that, the bonding operation using the replacement adhesive sheet S is performed again.

Next, as shown in FIG. 2B, through the adhesive layer 10 on the first member 21, one side in the thickness direction T of the first member 21 and the thickness direction T of the second member 22 Join the other side. The second member 22 is, for example, another element in the laminated structure of the flexible panel.

Next, as shown in FIG. 2C, the adhesive layer 10 between the first member 21 and the second member 22 is aged. Due to aging, the crosslinking reaction of the base polymer progresses in the adhesive layer 10, and the bonding force between the first member 21 and the second member 22 increases. The aging temperature is, for example, 20°C to 160°C. Aging time is, for example, from 1 minute to 21 days. In the case of 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 described above, the adhesive sheet S used as described above in the manufacturing process of a foldable device has the adhesive layer 10 having a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C, and also has a first adhesive force. Xa and the second adhesive force Xb satisfy 0.5≤Xb/Xa≤1. As described above, this adhesive sheet S is suitable for suppressing peeling from the adherend to be bent.

Example

The present invention will be described in detail below by way of examples. The present invention is not limited to the examples. In addition, the specific values of the mixing amount (content), physical property values, parameters, etc. described below are the corresponding mixing amounts (content), physical property values, parameters, etc. It can be replaced with the upper limit (a value defined as “less than” or “less than”) or the lower limit (a value defined as “above” or “above”).

<Preparation example 1 of acrylic oligomer>

In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas introduction tube, 95 parts by mass of cyclohexyl methacrylate (CHMA), 5 parts by mass of acrylic acid (AA), and α-methylstyrenedimer as a chain transfer agent. A mixture containing 10 parts by weight of toluene as a solvent and 120 parts by weight of toluene as a solvent was stirred at room temperature for 1 hour under a nitrogen atmosphere. Thereafter, 10 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added to the mixture to prepare a reaction solution, and the reaction was performed at 85°C for 5 hours in a nitrogen atmosphere (first acrylic formation of oligomers). As a result, an oligomer solution (solid content concentration of 50% by mass) containing the first acrylic oligomer was obtained. The weight average molecular weight of the first acrylic oligomer was 4300. Additionally, the glass transition temperature (Tg) of the first acrylic oligomer was 84°C.

<Preparation example 2 of acrylic oligomer>

In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas introduction tube, 60 parts by mass of dicyclopentanyl methacrylate (DCPMA), 40 parts by mass of methyl methacrylate (MMA), and α- as a chain transfer agent. A mixture containing 3.5 parts by mass of thioglycerol and 100 parts by mass of toluene as a solvent was stirred at 70°C for 1 hour under a nitrogen atmosphere. Thereafter, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added to the mixture to prepare a reaction solution, and incubated at 70°C for 1 hour under a nitrogen atmosphere, and then at 80°C. It was reacted for 2 hours (formation of the second acrylic oligomer). Thereafter, the reaction solution was heated to 130°C to volatilize and remove toluene, chain transfer agent, and unreacted monomer. As a result, a solid acrylic oligomer (second acrylic oligomer) was obtained. The weight average molecular weight of the second acrylic oligomer was 5100. The glass transition temperature (Tg) of the second acrylic oligomer was 130°C.

[Example 1]

<Preparation of acrylic base polymer>

In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas introduction tube, 70 parts by mass of 2-ethylhexyl acrylate (2EHA), 20 parts by mass of n-butyl acrylate (BA), and lauryl acrylate ( LA) 8 parts by mass, 1 part by mass of 4-hydroxybutyl acrylate (4HBA), 0.6 parts by mass of N-vinyl-2-pyrrolidone (NVP), and 2,2'-azobisiso as a thermal polymerization initiator. A mixture (solid content concentration: 47% by mass) containing 0.1 parts by mass of butyronitrile (AIBN) and ethyl acetate as a solvent was stirred at 56°C for 6 hours under a nitrogen atmosphere (polymerization reaction). As a result, a polymer solution containing an acrylic base polymer was obtained. The weight average molecular weight of the acrylic base polymer in this polymer solution was about 2 million.

<Preparation of adhesive composition>

In the polymer solution, per 100 parts by mass of solid content of the polymer solution, 1.5 parts by mass of the first acrylic oligomer, 0.26 parts by mass of the first crosslinking agent (brand name "Niper BMT-40SV", dibenzoyl peroxide, manufactured by Nippon Yushi), and the second. Add and mix 0.02 parts by mass of a crosslinking agent (brand name "Coronate L", trimethylolpropane/tolylene diisocyanate trimer adduct, coating agent) and 0.3 parts by mass of a silane coupling agent (brand name "KBM403", manufactured by Shin-Etsu Chemical Co., Ltd.). Thus, adhesive composition C1 was prepared.

<Formation of adhesive layer>

Next, adhesive composition C1 was applied on the peeling surface of the first peeling film, one side of which was subjected to silicone peeling treatment, to form a coating film. The first release film is a polyethylene terephthalate (PET) film (brand name “Diafoil MRF#75”, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) on which one side has undergone a silicone release treatment. Next, the peeling-treated side of the second peeling film, one of which had undergone silicone peeling treatment, was bonded to the coating film on the first peeling film. The second release film is a PET film (brand name “Diafoil MRF#75”, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) on which one side has undergone a silicone release treatment. Next, the coating film on the first release film 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. As described above, the adhesive sheet of Example 1 having a transparent adhesive layer (thickness 50 μm) was produced. The monomer composition of the acrylic base polymer and the adhesive layer composition in the pressure-sensitive adhesive sheet of Example 1 are shown in Table 1 in units by mass (the same applies to the examples and comparative examples described later).

[Examples 2 to 4]

Each of the adhesive sheets of Examples 2 to 4 was produced in the same manner as the adhesive sheet of Example 1, except that the monomer composition was changed as shown in Table 1 in the preparation of the acrylic base polymer.

[Example 5, 6]

Each of the adhesive sheets of Examples 5 and 6 was prepared in the same manner as the adhesive sheet of Example 1, except that the thickness of the adhesive layer formed was 25 μm (Example 5) or 100 μm (Example 6) instead of 50 μm. Produced.

[Comparative Example 1]

56 parts by mass of 2-ethylhexyl acrylate (2EHA), 34 parts by mass of lauryl acrylate (LA), 7 parts by mass of 4-hydroxybutyl acrylate (4HBA), and N-vinyl-2-pyrrolidone (NVP) ) A mixture containing 2 parts by mass and 0.015 parts by mass of a photopolymerization initiator (trade name “Omnirad 184” manufactured by IGM Resins) was irradiated with ultraviolet rays (polymerization reaction) to obtain a prepolymer composition (polymerization rate of about 10%) (prepolymer composition) (contains monomer components that have not undergone polymerization).

Next, 100 parts by mass of the prepolymer composition, 0.08 parts by mass of 1,6-hexanediol diacrylate (HDDA), 1 part by mass of the second acrylic oligomer, and a silane coupling agent (product name "KBM403", Shinetsu Chemical Co., Ltd. 0.3 parts by mass of the mixture was mixed to prepare photocurable adhesive composition C2.

Next, adhesive composition C2 was applied on the peeling surface of the first peeling film, one side of which was subjected to silicone peeling treatment, to form a coating film. The first release film is a polyethylene terephthalate (PET) film (brand name “Diafoil MRF#75”, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) on which one side has undergone a silicone release treatment. Next, the peeling-treated side of the second peeling film, one of which had undergone silicone peeling treatment, was bonded to the coating film on the first peeling film. The second release film is a PET film (brand name “Diafoil MRF#75”, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) on which one side has undergone a silicone release treatment. Next, the coating film was irradiated with ultraviolet rays through the second peeling film to cure the coating film with ultraviolet rays. For ultraviolet irradiation, a black light was used. The irradiation intensity of ultraviolet rays was set to 5 mW/cm2. As described above, the adhesive sheet (thickness 50 μm) of Comparative Example 1 was produced.

[Comparative Example 2]

The pressure-sensitive adhesive sheet of Comparative Example 2 was produced in the same manner as the pressure-sensitive adhesive sheet of Comparative Example 1, except that the monomer composition was changed as shown in Table 1 in the preparation of the acrylic base polymer.

[Comparative Example 3]

The pressure-sensitive adhesive sheet of Comparative Example 3 was produced in the same manner as the pressure-sensitive adhesive sheet of Example 1, except that the monomer composition was changed as shown in Table 1 in the preparation of the acrylic base polymer.

<Adhesion>

The adhesive strength of each adhesive sheet in Examples 1 to 6 and Comparative Examples 1 to 3 was examined by a peel test.

First, for each adhesive sheet, the required number of test pieces were produced for the peeling test before autoclave treatment and for the peeling test after autoclave treatment, which will be described later. In producing the test piece, first, the second release film was peeled from the adhesive sheet, and a PET film (thickness of 25 μm) was bonded to the exposed surface of the adhesive layer thus exposed to obtain a laminate. Next, a test piece (width 25 mm x length 100 mm) was cut from this laminate. Next, the first release film was peeled from the adhesive layer of the test piece, and the exposed surface thereby exposed was plasma treated. Meanwhile, a polyimide film (brand name “GV200D”, thickness 80 μm, manufactured by SKC Kolon PI) as the adherend was also plasma treated. In each plasma treatment, a plasma irradiation device (brand name "AP-TO5", manufactured by Sekisui Kogyo 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 exposed surface of the adhesive layer of the test piece and the plasma-treated surface of the polyimide film were bonded. In this bonding, the test piece was pressed against the adherend by rotating a 2 kg roller once in an environment of 25°C.

[Peeling test before autoclave treatment]

From the above-described bonding, a peeling test was performed in which the test piece was peeled from the polyimide film after standing at 25°C for 2 minutes, and the peeling strength was measured as adhesive force. For this measurement, a tensile tester (brand name “Autograph AGS-J”, manufactured by Shimadzu Seisakusho) was used. In this measurement, the measurement temperature was 25°C, the peeling angle of the test piece with respect to the adherend was 180°, the tensile speed of the test piece was 300 mm/min, and the peeling length was 50 mm (measurement of peel test) condition). The measured adhesive force is shown in Table 1 as initial adhesive force (N/25 mm).

[Peeling test after autoclave treatment]

Within 3 minutes from the above-described bonding, autoclave treatment (heating and pressing treatment) of the test piece provided with the adherend was started. In the autoclave treatment, the temperature was 50°C, the pressure was 0.5 MPa, and the treatment time was 15 minutes. Then, after autoclave treatment, after standing at 25°C for 72 hours, a peeling test under the above measurement conditions (measurement temperature 25°C) was performed, similar to the peeling test before autoclave treatment, and the adhesive force was measured. The measured adhesive force is shown in Table 1 as adhesive force Xa (N/25 mm). Meanwhile, the above-mentioned autoclave treatment and peeling test were performed on the test pieces in the same manner, except that the measurement temperature in the peeling test was replaced with a predetermined temperature (60°C, 70°C, 85°C), and the adhesive force was measured. Adhesion Xb (N/25 mm) at 60°C, Xd (N/25 mm) at 70°C, /Xa), the ratio of Xd to Xa (Xd/Xa), and the ratio of Xc to Xa (Xc/Xa) are shown in Table 1. In addition, the measurement results of the peeling test after autoclave treatment are shown in the graph in FIG. 3. In the graph, at each measurement temperature, the bar on the left represents the adhesive force of the adhesive sheet of Comparative Example 1, and the bar on the right represents the adhesive force of the adhesive sheet of Example 1.

<Storage modulus, loss tangent, and glass transition temperature>

The dynamic viscoelasticity of the adhesive layer of each adhesive sheet of Examples 1 to 6 and Comparative Examples 1 to 3 was measured. The sample for measurement was prepared as follows. First, a plurality of adhesive layer pieces were bonded to produce an adhesive sheet with a thickness of approximately 1.5 mm. Next, this sheet was punched to obtain a cylindrical pellet (diameter 7.9 mm) as a measurement sample. Then, the sample for measurement was fixed to a jig of a parallel plate with a diameter of 7.9 mm using a dynamic viscoelasticity measuring device (brand name "Advanced Rheometric Expansion System (ARES)", manufactured by Rheometric Scientific), and then dynamic viscoelasticity measurement was performed. In this measurement, the measurement mode was set to torsion mode, the measurement temperature range was -50°C to 150°C, the temperature increase rate was 5°C/min, and the frequency was 1 Hz. From the measurement results, the storage modulus G' (shear storage modulus) and loss tangent tan δ at each temperature (shown in Table 1) were read. The storage elastic modulus Ma (kPa) at 25°C, the storage elastic modulus Mb (kPa) at 60°C, the storage elastic modulus Mc (kPa) at 85°C, and the ratio of the storage elastic modulus Mb to the storage elastic modulus Ma (Mb/Ma), , the ratio (Mc/Ma) of the storage elastic modulus Mc to the storage elastic modulus Ma is shown in Table 1. In addition, the temperature at which the loss tangent tan δ was maximized was set as the glass transition temperature of the adhesive sheet. The glass transition temperature (°C) is also shown in Table 1.

<Haze and total light transmittance>

The haze and total light transmittance of the adhesive layer of each adhesive sheet of Examples 1 to 6 and Comparative Examples 1 to 3 were examined as follows. First, a sample for haze measurement was produced. Specifically, after peeling the second release film from the adhesive sheet, the adhesive layer side of the sheet (first release film, adhesive layer) is covered with alkali-free glass (thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.4%, (manufactured by Matsunami Glass Co., Ltd.), and the first release film was peeled from the adhesive layer on the glass. In this way, a sample for measurement was produced. Next, each of the haze and total light transmittance of the adhesive layer in the sample were measured using a haze measuring device (brand name "HM-150", manufactured by Murakami Shikisai Kijutsu Kenkyujo Co., Ltd.). In this measurement, the measurement sample was installed in the device so that light was exposed to the measurement sample from the alkali-free glass side. In addition, in this measurement, the measurement results obtained by measuring only alkali-free glass under the same conditions were used as a baseline. The haze and total light transmittance of the adhesive layer obtained in this way are shown in Table 1.

<Bending test>

Each of the adhesive sheets in Examples 1 to 6 and Comparative Examples 1 to 3 was tested for adhesion to a bent adherend (the degree to which peeling from the adherend is suppressed). Specifically, it is as follows.

First, a laminate sample was produced for each adhesive sheet. In the production of the laminate sample, first, the second release film was peeled from the adhesive sheet, and the exposed surface (first exposed surface) thereby exposed was plasma treated. Meanwhile, the exposed surface of the polarizer (having a laminated structure of a polarizer with a thickness of 51 μm and an adhesive layer with a thickness of 15 μm) provided with an adhesive layer of a polarizing plate with a thickness of 66 μm as the first adherend was also plasma treated. In each plasma treatment, a plasma irradiation device (brand name "AP-TO5", manufactured by Sekisui Kogyo 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 (described later). The same applies to plasma treatment). Then, the first exposed surface of the adhesive sheet and the plasma-treated surface of the polarizing plate were bonded. In this bonding, the polarizing plate and the adhesive sheet were pressed together in an environment of 25°C by rotating a 2 kg roller once. Next, the first release film was peeled from the adhesive sheet on the polarizing plate, and the exposed surface (second exposed surface) thereby exposed was plasma treated. Meanwhile, a polyimide film (brand name “GV200D”, thickness 80 μm, manufactured by SKC Kolon PI) as the second adherend was also plasma treated. Then, the second exposed surface of the adhesive sheet and the plasma-treated surface of the polyimide film were bonded. In this bonding, the polyimide film and the adhesive sheet were pressed together by reciprocating a 2 kg roller once in an environment of 25°C. Next, a plasma-treated PET film with a thickness of 125 μm was bonded to the pressure-sensitive adhesive layer surface of the polarizing plate provided with the pressure-sensitive adhesive layer by reciprocating a 2-kg roller once. As described above, a laminate sample was produced. The laminate sample has a laminated structure of a PET film, an adhesive layer, a polarizing plate, an adhesive sheet (an adhesive sheet according to any of the examples or comparative examples), and a polyimide film.

Next, the laminate sample was cut into a rectangle of 35 mm x 100 mm so that the absorption axis direction of the polarizing plate was parallel to the long side direction. Next, the laminate sample was autoclaved (heated and pressed) under the conditions of 50°C, 0.5 MPa, and 15 minutes. Next, a bending test was performed on the laminate sample that had undergone the autoclave treatment using a planar unloaded U-shaped stretch tester (manufactured by Yuasa System Kiki). In this test, a bending jig was installed in a range of 20 mm from the edge of the sample end for each end portion in the long side direction of the laminate sample, and the laminate sample was fixed to the tester (long side of the laminate sample) The central 60 mm area of the direction is in an unfixed state). In addition, in this test, the copper sample was held in a bent form with a bending radius of 1.3 mm and a bending angle of 180° so that the PET film side of the laminate sample was inside, and the copper sample in this state was stored at a temperature of 25°C. and maintained for 240 hours in a constant temperature and humidity chamber with a relative humidity of 95% (first bending test).

The laminate sample after this first bending test was observed with the naked eye to confirm the presence or absence of peeling between the polyimide film and the polarizing plate in the bent portion. In all of the samples where peeling was confirmed, peeling (voids) occurred from the end portion in the short side direction of the laminate sample. For the laminate samples in which peeling was confirmed, the length (mm) of the void portion in the short side direction of the sample was measured. Regarding the adhesiveness of the adhesive sheet to the adherend to be bent (the extent to which peeling from the adherend is suppressed), cases where the gap length is less than 2 mm are evaluated as "excellent", and the gap length is evaluated as "excellent". If it was 2 mm or more, it was evaluated as "defective" (in this evaluation, when peeling (voids) extending over the entire length of the short side direction of the laminate sample was confirmed, the length of the voids was 35 mm, and if no peeling was confirmed, the gap length was set to 0 mm). The evaluation results are shown in Table 1.

Additionally, a bending test was conducted in the same manner as the first bending test except that the holding temperature in the constant temperature and humidity bath was 85°C instead of 25°C (second bending test). After that, the laminate sample after the second bending test was observed with the naked eye, and the presence or absence of peeling between the polyimide film and the polarizing plate in the bent portion was confirmed. Then, the adhesiveness of the adhesive sheet to the adherend to be bent was evaluated using the same standards as those in the first bending test. The evaluation results are shown in Table 1.

The above-described embodiments are examples of the present invention, and the present invention should not be construed as limited by the embodiments. Modifications of the present invention apparent to those skilled in the art are included in the following claims.

The optical adhesive sheet for a foldable device of the present invention can be used, for example, in the manufacturing process of a foldable display panel, for bonding elements included in the laminated structure of the panel.

S: Adhesive sheet (optical adhesive sheet for foldable devices)
T: Thickness direction
10: Adhesive layer
L1, L2: Release film
21: first member
22: Second member

Claims (5)

It is an optical adhesive sheet for a foldable device having an adhesive layer,
The adhesive layer has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C,
After the adhesive layer is attached to an adherend, followed by heat and pressure treatment at 50°C, 0.5 MPa and 15 minutes, and then left to stand at 25°C for 72 hours, the adhesive layer is applied to the adherend at 25°C. It has a first adhesive force Xa,
The adhesive layer has a second adhesive force
An optical adhesive sheet for a foldable device, wherein the first adhesive force Xa and the second adhesive force Xb satisfy 0.5≤Xb/Xa≤1.0. According to paragraph 1,
The adhesive layer has a third adhesive force
An optical adhesive sheet for a foldable device, wherein the first adhesive force Xa and the third adhesive force Xc satisfy 0.5≤Xc/Xa≤0.8. According to paragraph 1,
The minimum adhesive force that the adhesive layer has to the adherend in a temperature range of 25°C to 85°C after sticking to the adherend, the heating and pressing treatment, and the standing is 10N/25mm or more. Optical adhesive sheet for devices. According to paragraph 3,
An optical adhesive sheet for a foldable device, wherein the adhesive layer has the minimum adhesive force at 60°C or higher. According to paragraph 1,
Optics for a foldable device, wherein the adhesive layer has an adhesive force at 25°C to the adherend after being left for 2 minutes at 25°C from the time it is attached to the adherend, and is 0.5 N/25 mm or more and 12 N/25 mm or less. Adhesive sheet.