WO2022163638A1

WO2022163638A1 - Optical adhesive sheet for foldable device

Info

Publication number: WO2022163638A1
Application number: PCT/JP2022/002619
Authority: WO
Inventors: 拓也永田; 翔寳田; 美菜子野田
Original assignee: 日東電工株式会社
Priority date: 2021-01-29
Filing date: 2022-01-25
Publication date: 2022-08-04
Also published as: KR20230135083A; TW202244214A; CN116802246A; JP2022116860A

Abstract

An optical adhesive sheet S that serves as optical adhesive sheet for a foldable device according to the present invention has an adhesive agent layer (10). The adhesive agent layer (10) has a shear storage modulus of 20-50 kPa at 25°C. After being adhered to an adherend, then being subjected to heating and pressurizing processing for 15 minutes at 0.5 MPa and 50°C, and then being allowed to stand for 72 hours at 25°C, the adhesive agent layer (10) has a first adhesive strength Xa to the adherend at 25°C. After being adhered to the adherend, then being subjected to the heating and pressurizing processing and then being allowed to stand as previously described, the adhesive agent layer (10) has a second adhesive strength Xb to the adherend at 60°C. The first adhesive strength Xa and the second adhesive strength Xb satisfy the expression 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.

A display panel has a laminated structure including, for example, a pixel panel, a touch panel, a polarizing plate and a cover film. In the manufacturing process of such a display panel, for example, a transparent adhesive sheet (optical adhesive sheet) is used for bonding elements included in the laminated structure. On the other hand, for smartphones and tablet terminals, for example, display panels that can be repeatedly folded (foldable) are being developed. In a foldable display panel, each element in the laminated structure is manufactured to be repeatedly foldable, and an optical adhesive sheet is used for bonding between such elements. Optical adhesive sheets for foldable devices such as foldable display panels are described, for example, in Patent Document 1 below.

JP 2018-111754 A

The optical adhesive sheet in the foldable device is required to exhibit sufficient adhesion reliability to the adherend. However, conventionally, the optical pressure-sensitive adhesive sheet tends to peel off from the adherend at the bending 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 portion. Moreover, since the conventional optical adhesive sheet has a relatively large change in adhesive strength due to temperature changes, it is possible to achieve adhesion that does not cause the peeling described above over a relatively wide temperature range (for example, including a room temperature range and a higher temperature range). Unreliable. Occurrence of the above-described peeling at the bent portion causes malfunction of the device, which is not preferable.

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

The present invention [1] is an optical pressure-sensitive adhesive sheet for a foldable device having a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C, and the pressure-sensitive adhesive layer , Attachment to the adherend, subsequent heat and pressure treatment under conditions of 50 ° C., 0.5 MPa and 15 minutes, and then standing at 25 ° C. for 72 hours, to the adherend It has a first adhesive force Xa at 25 ° C., and the adhesive layer has a second adhesive force at 60 ° C. to the adherend after being attached to the adherend, the heat and pressure treatment, and the standing. An optical pressure-sensitive adhesive sheet for a foldable device having a force Xb, wherein the first pressure-sensitive adhesive strength Xa and the second pressure-sensitive adhesive strength Xb satisfy 0.5≦Xb/Xa≦1.0.

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 as described above. The pressure-sensitive adhesive layer having this degree of softness secures the cohesive force necessary for bonding between adherends, and when the adherend to which the pressure-sensitive adhesive layer is attached is folded, the adhesive layer is tacky at the bending portion. It is suitable for relieving stress acting locally on the agent layer. Therefore, the present optical pressure-sensitive adhesive sheet is suitable for suppressing peeling from a folded adherend.

As described above, the adhesive layer of the present optical adhesive sheet has the first adhesive force Xa (adhesive force within the normal temperature range) and the second adhesive force Xb (adhesive force within the temperature range higher than normal temperature) of 0. . satisfies 5≤Xb/Xa≤1; The ratio of the second adhesive force Xb to the first adhesive force Xa (Xb/Xa) is 0.5 or more, and the second adhesive force Xb is large to the extent that the adhesion is stable in the normal temperature range and the higher temperature range. Suitable for securing force and suppressing the aforementioned peeling.

In the present invention [2], the pressure-sensitive adhesive layer has a third adhesive force Xc to the adherend at 85° C. after being adhered to the adherend, the heating and pressurizing treatment, and the standing still. and the first adhesive force Xa and the third adhesive force Xc satisfy 0.5≦Xc/Xa≦0.8.

Such a configuration (a configuration in which the third adhesive force Xc is large to the extent that the ratio of the third adhesive force Xc to the first adhesive force Xa is 0.5 or more) is stable in the normal temperature range and the higher temperature range. It is preferable to secure the adhesive strength and suppress the above-described peeling.

In the present invention [3], the pressure-sensitive adhesive layer is applied to the adherend at a temperature range of 25 ° C. or higher and 85 ° C. or lower after being attached to the adherend, the heat and pressure treatment, and the standing. The optical adhesive sheet for foldable devices according to the above [1] or [2], which has a minimum adhesive strength of 10 N/25 mm or more.

Such a configuration is preferable for suppressing the above-described peeling and for achieving good adhesion reliability over normal temperature range and higher temperature range.

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

Such a configuration is preferable for achieving good adhesion reliability in the normal temperature range.

In the present invention [5], the pressure-sensitive adhesive layer has an adhesive strength of 0.5 N/ The optical pressure-sensitive adhesive sheet for a foldable device according to any one of [1] to [4] above, which is 25 mm or more and 12 N/25 mm or less.

The configuration in which the above adhesive strength at 25°C is 0.5 N/25 mm or more ensures that the adhesive layer has the adhesive strength necessary for the work in laminating the optical adhesive sheet to the adherend. It is suitable for achieving good temporary fixation of the optical adhesive sheet to the body. The configuration in which the adhesive strength at 25° C. is 12 N/25 mm or less is suitable for ensuring easy releasability of the adhesive layer and ensuring reworkability in the laminating operation.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram of one Embodiment of the optical adhesive sheet of this invention. An example of how to use the optical pressure-sensitive adhesive sheet of the present invention is shown. FIG. 2A shows the step of bonding the optical adhesive sheet to the first adherend, and FIG. 2B shows the step of bonding the first adherend and the second adherend via the optical adhesive sheet. 2C represents the aging process. 4 is a graph showing the adhesive strength of each adhesive sheet of Example 1 and Comparative Example 1. FIG.

A pressure-sensitive adhesive sheet S as an embodiment of the optical pressure-sensitive adhesive sheet for foldable devices of the present invention includes a pressure-sensitive adhesive layer 10 as shown in FIG. The adhesive sheet S has a sheet shape with a predetermined thickness and extends in a direction (surface direction) perpendicular to the thickness direction. In FIG. 1, release films L1 and L2 (release liners) are adhered to both sides of an adhesive sheet S. As shown in FIG. The release film L1 is arranged on one surface of the adhesive sheet S in the thickness direction T. As shown in FIG. The release film L2 is arranged on the other surface of the adhesive sheet S in the thickness direction T. As shown in FIG. The adhesive sheet S with a release film is, for example, in the form of a roll (not shown).

Such an adhesive sheet S is a transparent adhesive sheet (optical adhesive sheet) that is placed at a light passage location in a foldable device. Foldable devices include, for example, foldable display panels. A foldable display panel has a laminated structure including, for example, a pixel panel, a touch panel, a polarizing plate and a cover film. The adhesive sheet S is used, for example, in the process of manufacturing a foldable display panel to bond elements included in the laminated structure.

The pressure-sensitive adhesive layer 10 has a shear storage elastic 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 elastic modulus of the pressure-sensitive adhesive layer 10 is the storage elastic modulus obtained by the dynamic viscoelasticity measurement described later with regard to Examples (the same applies to the shear storage elastic modulus described later). The first adhesive force Xa is 25 to the adherend after the pressure-sensitive adhesive layer 10 is attached to the adherend, heated and pressurized, and then allowed to stand at 25° C. for 72 hours. It is the adhesive strength that it has at °C. The second adhesive force Xb was 60 to the adherend after the adhesive layer 10 was attached to the adherend, heat-pressed after that, and left still at 25°C for 72 hours. It is the adhesive strength that it has at °C. The adherend is a polyimide film (the same applies to the adherend described later). The pressure-sensitive adhesive layer 10 is applied to the adherend by reciprocating a 2 kg roller once under an environment of 25° C. (the same applies to the application described below). The heating and pressurizing treatment is a treatment performed under the conditions of a temperature of 50° C., a pressure of 0.5 MPa, and a treatment time of 15 minutes, and is started within 3 minutes after the adhesive layer 10 is attached to the adherend. treatment (the same applies to the heating and pressurizing treatment described later). The adhesive strength is adhesive strength 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 adhesive strength described later).

The adhesive layer 10 in the adhesive sheet S has a shear storage elastic modulus of 20 kPa or more and 50 kPa or less at 25°C, as described above. The pressure-sensitive adhesive layer 10 having this degree of softness ensures the cohesive force necessary for bonding between adherends, and when the adherend to which the pressure-sensitive adhesive layer 10 is attached is folded, Suitable for relieving stress acting locally on the pressure-sensitive adhesive layer 10 . Therefore, the adhesive sheet S is suitable for suppressing peeling from a folded adherend.

In addition, as described above, the pressure-sensitive adhesive layer 10 has a first adhesive force Xa (adhesive force within the normal temperature region) and a second adhesive force Xb (adhesive force within a temperature region higher than normal temperature) of 0.5. ≦Xb/Xa≦1 is satisfied. The ratio of the second adhesive force Xb to the first adhesive force Xa (Xb/Xa) is 0.5 or more, and the second adhesive force Xb is large to the extent that the adhesion is stable in the normal temperature range and the higher temperature range. Suitable for securing force and suppressing the aforementioned peeling.

As described above, the adhesive sheet S is suitable for suppressing peeling from an adherend that is folded. In addition, the configuration in which the pressure-sensitive adhesive layer 10 has a shear storage elastic modulus of 20 kPa or more and 50 kPa or less at 25° C. is such that when the pressure-sensitive adhesive sheet S is cut in the manufacturing process, a cutting means such as a Thomson blade is used to cut the pressure-sensitive adhesive layer 10. Suitable for suppressing adhesion of adhesive pieces. Therefore, this configuration is suitable for realizing a good processing yield of the pressure-sensitive adhesive sheet S.

In the pressure-sensitive adhesive sheet S, from the viewpoint of obtaining stable adhesion reliability in a normal temperature range and a higher temperature range, Xb/Xa is preferably 0.6 or more, more preferably 0.7 or more, and still more preferably 0.7. 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 Xc was 85 to the adherend after the adhesive layer 10 was attached to the adherend, heat-pressed after that, and left still at 25°C for 72 hours. It is the adhesive strength that it has at °C.

Such a configuration (a configuration in which the third adhesive force Xc is large to the extent that Xc/Xa is 0.5 or more) secures a stable adhesive force and prevents the above-described peeling in the normal temperature range and the higher temperature range. preferred to suppress. From this point of view, Xc/Xa is more preferably 0.6 or more, still more preferably 0.65 or more, and particularly preferably 0.68 or more.

After the pressure-sensitive adhesive layer 10 is attached to an adherend, heat-pressed after that, and then allowed to stand at 25°C for 72 hours, the adherend is exposed to a temperature of 25°C or higher and 85°C or lower. The minimum adhesive strength to have in the range is preferably 10 N/25 mm or more, more preferably 11 N/25 mm or more, even more preferably 12 N/25 mm or more. Such a configuration is preferable for suppressing the above-described peeling and for achieving good adhesion reliability over normal temperature range and higher temperature range.

The adhesive layer 10 has the above minimum adhesive strength at 60°C or higher. Such a configuration is preferable for achieving good adhesion reliability in the normal temperature range.

The pressure-sensitive adhesive layer 10 preferably has an adhesive force of 0.5 N/25 mm or more and 12 N/25 mm to the adherend at 25° C. after standing at 25° C. for 2 minutes after being attached to the adherend. It is below. The configuration in which the adhesive strength (initial adhesive strength) at 25° C. is 0.5 N/25 mm or more provides the adhesive layer 10 with the adhesive strength necessary for the work in laminating the adhesive sheet S to the adherend. It is suitable for ensuring good temporary fixation of the adhesive sheet S to the adherend. From this point of view, the initial adhesive strength is more preferably 1 N/25 mm or more, still more preferably 3 N/25 mm or more, and particularly preferably 5 N/25 mm or more. The configuration in which the initial adhesive strength at 25° C. is 12 N/25 mm or less is suitable for ensuring easy releasability of the adhesive layer 10 and ensuring reworkability in the laminating operation. From this point of view, the initial adhesive strength is more preferably 10 N/25 mm or less, still more preferably 9 N/25 mm or less, and particularly preferably 8 N/25 mm or less. Methods for adjusting the initial adhesive strength include, for example, selection of the type of base polymer for the adhesive layer 10, adjustment of the molecular weight, and adjustment of the compounding amount. Selection of the type of base polymer includes selection of the type (structure) of the main chain in the base polymer, and selection of the type and adjustment of the amount of functional groups (the selection of the type of base polymer described later also includes similar). Methods for adjusting the initial adhesive strength include selection of the types of components other than the base polymer and adjustment of the blending amounts of the components. Such components include crosslinkers, 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, still 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, still more preferably 23 N/25 mm or less. These configurations are preferable for ensuring the reliability of bonding between adherends by the optical pressure-sensitive adhesive sheet near room temperature. As a method for adjusting the first adhesive force Xa, for example, selection of the type of base polymer for the adhesive layer 10, adjustment of the molecular weight, adjustment of the blending amount, and components other than the base polymer (for example, a cross-linking agent, silane coupling agent, and oligomer), and adjustment of the blending amount. 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 Xc to the first adhesive force Xa (Xc/Xa ) is the same for each adjustment method. In addition, the adhesive strengths Xb and Xc, the ratio Xb/Xa, and the ratio Xc/Xa in the relatively high temperature region can also be adjusted by adjusting the molecular weight of the base polymer and the elastic modulus of the adhesive layer 10. . Specifically, the higher the molecular weight and the elastic modulus, the more difficult it is for the adhesive strengths Xb and Xc to drop from the first adhesive strength Xa in the normal temperature range (that is, the ratio Xb/Xa and the ratio Xc/Xa are less likely to decrease). .

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

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

The shear storage modulus (first storage modulus Ma) of the pressure-sensitive adhesive layer 10 at 25° C. is preferably 25 kPa or more, more preferably 30 kPa or more, and still more preferably 33 kPa or more, from the viewpoint of ensuring the cohesive force described above. , particularly preferably 35 kPa or more. The first storage elastic modulus Ma is preferably 50 kPa or less, more preferably 45 kPa or less, even more 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 break 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, adjustment of the compounding amount, and type of cross-linking agent. and adjustment of the blending amount. A second storage modulus Mb described later, a ratio (Mb/Ma) of the second storage modulus Mb to the first storage modulus Ma, a third storage modulus Mc described later, and a third storage modulus to the first storage modulus Ma The same applies to each adjustment method of the ratio (Mc/Ma) of the storage elastic modulus Mc.

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

The ratio (Mb/Ma) of the second storage modulus Mb to the first storage modulus 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 pressure-sensitive adhesive layer 10 at 85°C is preferable from the viewpoint of ensuring the cohesive force necessary for bonding between adherends in a temperature range around 85°C. is 15 kPa or more, more preferably 18 kPa or more, and still more preferably 20 kPa or more. The third storage elastic modulus Mc is preferably 45 kPa or less, more preferably 43 kPa or less, and even more preferably 40 kPa or less from the viewpoint of suppressing peeling from the adherend that is bent in a temperature range around 85°C.

The ratio (Mc/Ma) of the third storage modulus Mc to the first storage modulus 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 from an adhesive composition. The adhesive layer 10 has transparency (visible light transmittance). The adhesive layer 10 contains at least a base polymer.

The base polymer is an adhesive component that makes the adhesive layer 10 exhibit adhesiveness. Base polymers include, for example, 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. The base polymer may be used alone or in combination of two or more. From the viewpoint of ensuring good transparency and adhesiveness in the adhesive layer 10, an acrylic polymer is preferably used as the base polymer.

The acrylic polymer is a copolymer of monomer components containing 50% by mass or more of (meth)acrylic acid alkyl ester. "(Meth)acrylic acid" means acrylic acid and/or methacrylic acid.

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms is preferably 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, and isobutyl (meth)acrylate. , s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, (meth)acrylate Heptyl acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, (meth) ) isodecyl acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate (that is, lauryl acrylate), isotridecyl (meth) acrylate, tetradecyl (meth) acrylate, isotetradecyl (meth) acrylate, (meth) Pentadecyl acrylate, cetyl (meth)acrylate, 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 tricyclic (Meth)acrylic acid esters having the above aliphatic hydrocarbon ring can be mentioned. Cycloalkyl (meth)acrylates include, for example, 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 a tricyclic or higher aliphatic hydrocarbon ring include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, and tricyclopentanyl (meth)acrylate. , 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

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

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

The monomer component may contain a copolymerizable monomer that can be copolymerized with the (meth)acrylic acid alkyl ester. Examples of copolymerizable monomers include monomers having a polar group. Polar group-containing monomers include, for example, nitrogen atom-containing ring-containing monomers, hydroxy group-containing monomers, and carboxy group-containing monomers. The polar group-containing monomer is useful for modifying the acrylic polymer, such as introducing cross-linking points into the acrylic polymer and securing the cohesive strength 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, N-vinylpiperazine, 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-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N -vinylthiazole, and N-vinylisothiazole. N-vinyl-2-pyrrolidone is preferably used as the monomer having a nitrogen atom-containing ring.

The ratio of the monomer having a nitrogen atom-containing ring in the monomer component is preferably 0.1 mass from the viewpoint of ensuring the cohesive force of the adhesive layer 10 and ensuring the adhesive strength of the adhesive layer 10 to the adherend. % or more, more preferably 0.3 mass % or more, and still more preferably 0.55 mass % or more. The same ratio is preferably 30% by mass from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (related to compatibility between various additive components and the acrylic polymer in the adhesive layer 10). Below, more preferably 20% by 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, ( 4-hydroxybutyl meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. 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, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive strength in the pressure-sensitive adhesive layer 10. It is at least 0.8% by mass, more preferably at least 0.8% by mass.
The same ratio is preferably 20% by mass or less, more preferably 10% by mass or less, from the viewpoint of adjusting the polarity of the acrylic polymer (related to compatibility between various additive components and the acrylic polymer in the pressure-sensitive adhesive layer 10). .

Carboxy group-containing monomers include, for example, 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 preferable from the viewpoint of introducing a crosslinked structure into the acrylic polymer, ensuring cohesive force in the adhesive layer 10, and ensuring adhesion to the adherend in the adhesive layer 10. is 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 0.8% by mass or more. The same ratio is preferably 30% by mass or less, more preferably 20% by mass or less, from the viewpoints of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of acid corrosion of the adherend.

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 small acid content. Further, when the adhesive sheet S is used for bonding polarizing plates, the adhesive layer 10 preferably has a small acid content in order to suppress polyene formation of the polyvinyl alcohol-based polarizer due to the acid component. In such an acid-free pressure-sensitive adhesive sheet S, the content of organic acid monomers (for example, (meth)acrylic acid and carboxyl group-containing monomers) in the pressure-sensitive adhesive layer 10 is preferably 100 ppm or less, more preferably 70 ppm or less, and further It is preferably 50 ppm or less. The organic acid monomer content of the adhesive layer 10 is obtained by quantifying the acid monomer extracted into water by immersing the adhesive layer 10 in pure water and heating at 100° C. for 45 minutes by ion chromatography. is required by

From the viewpoint of acid-free, 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 ratio of the organic acid monomer in the monomer component is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and still more preferably 0.05% by mass. is 0% by 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. be done. These other copolymerizable monomers may be used alone, or two or more of them may be used in combination.

The base polymer has a crosslinked structure in this embodiment. As a method for introducing a crosslinked structure into the base polymer, the base polymer having a functional group capable of reacting with the crosslinker and the crosslinker are blended in the adhesive composition, and the base polymer and the crosslinker are mixed in the adhesive layer 10. A reaction method (first method), and a base polymer in which a polyfunctional monomer is included in the monomer components forming the base polymer, and a branched structure (crosslinked structure) is introduced into the polymer chain by polymerization of the monomer components. Methods of forming are included. These methods may be used in combination.

Examples of the cross-linking agent used in the first method include compounds that react with functional groups (hydroxy groups, carboxy groups, etc.) contained in the base polymer. Such crosslinkers include, for example, isocyanate crosslinkers, peroxide crosslinkers, epoxy crosslinkers, oxazoline crosslinkers, aziridine crosslinkers, carbodiimide crosslinkers, and metal chelate crosslinkers. The cross-linking agents may be used alone, or two or more of them may be used in combination. 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 they are highly reactive with the hydroxy groups and carboxy groups in the base polymer and facilitate the introduction of a cross-linked structure. be done.

Examples of isocyanate cross-linking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, isocyanates, and polymethylene polyphenyl isocyanates. The isocyanate cross-linking agent also includes derivatives of these isocyanates. Examples of the isocyanate derivative include isocyanurate-modified products and polyol-modified products. Commercially available isocyanate cross-linking agents include, for example, Coronate L (trimethylolpropane adduct of tolylene diisocyanate, manufactured by Tosoh), Coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh), Coronate HX (hexa isocyanurate of methylene diisocyanate, manufactured by Tosoh), and Takenate D110N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals).

Peroxide crosslinking agents include dibenzoyl peroxide, di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t- butyl peroxyneodecanoate, t-hexyl peroxypivalate, and t-butyl peroxypivalate.

Examples of epoxy cross-linking agents include bisphenol A, epichlorohydrin type epoxy resin, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether. , diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

An isocyanate cross-linking agent (especially a bifunctional isocyanate cross-linking agent) and a peroxide cross-linking agent are preferable from the viewpoint of ensuring appropriate flexibility (thus flexibility) of the pressure-sensitive adhesive layer 10 . An isocyanate cross-linking agent (especially a trifunctional isocyanate cross-linking agent) is preferable from the viewpoint of ensuring the durability of the pressure-sensitive adhesive layer 10 . In the base polymer, difunctional isocyanate and peroxide crosslinkers form softer two-dimensional crosslinks, while trifunctional isocyanate crosslinkers form stronger three-dimensional crosslinks. From the viewpoint of achieving both durability and flexibility of the pressure-sensitive adhesive layer 10, it is preferable to use a trifunctional isocyanate cross-linking agent together with a peroxide cross-linking agent and/or a bifunctional isocyanate cross-linking agent.

From the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive layer 10, the amount of the cross-linking agent is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.05 parts by mass or more with respect to 100 parts by mass of the base polymer. is 0.07 parts by mass or more. From the viewpoint of ensuring good tackiness in the pressure-sensitive adhesive layer 10, the amount of the cross-linking agent blended with respect to 100 parts by mass of the base polymer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 3 parts by mass or less. is.

In the second method, the monomer components (including the polyfunctional monomer for introducing the crosslinked structure and other monomers) may be polymerized at once or in multiple stages. In the multi-stage polymerization method, first, a monofunctional monomer for forming the base polymer is polymerized (prepolymerization), thereby containing a partially polymerized product (a mixture of a polymerized product with a low degree of polymerization and an unreacted monomer). A prepolymer composition is prepared. Next, after adding a polyfunctional monomer to the prepolymer composition, the partial polymer and the polyfunctional monomer are polymerized (main polymerization).

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

Polyfunctional (meth)acrylates include bifunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

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

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

Tetrafunctional or higher polyfunctional (meth)acrylates include, for example, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, and alkyl-modified dipentaerythritol pentaacrylate. , and dipentaerythritol hexa(meth)acrylate.

The molecular weight of the polyfunctional monomer is preferably 1500 or less, more preferably 1000 or less. Also, the functional group equivalent (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 weight is preferably 500 or less, more preferably 300 or less, still more preferably 200 or less. These configurations are preferable from the viewpoint of appropriately adjusting viscoelasticity (for example, storage elastic modulus G' and loss tangent tan ?) by introducing a crosslinked structure in the base polymer.

The acrylic polymer can be formed by polymerizing the above monomer components. Polymerization methods include, for example, solution polymerization, active energy ray polymerization (eg, UV polymerization), bulk polymerization, and emulsion polymerization. Solution polymerization and UV polymerization are preferred from the viewpoints of transparency, water resistance, and cost of the pressure-sensitive adhesive layer 10 . Ethyl acetate and toluene, for example, are used as solvents for solution polymerization. Moreover, as a polymerization initiator, for example, a thermal polymerization initiator and a photopolymerization initiator are used. The amount of the polymerization initiator to be used is, for example, 0.05 parts by mass or more and, for example, 1 part by mass or less with respect to 100 parts by mass of the monomer component.

Thermal polymerization initiators include, for example, azo polymerization initiators and peroxide polymerization initiators. Examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionate)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'-dimethyleneisobutyramidine) dihydrochloride mentioned. Peroxide polymerization initiators include, for example, dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

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

In polymerization, a chain transfer agent and/or a polymerization inhibitor (polymerization retarder) may be used for the purpose of molecular weight adjustment. Chain transfer agents include α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and α-methylstyrene. Dimers 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 the polymerization initiator, the higher the radical concentration in the reaction system, the higher the density of reaction initiation points, and the smaller the molecular weight of the base polymer formed. On the other hand, the smaller the amount of the polymerization initiator, the lower the density of the reaction initiation points, the easier it is for the polymer chain to extend, and the greater the molecular weight of the base polymer formed.

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 securing the cohesive force in the pressure-sensitive adhesive layer 10 . The weight average molecular weight is preferably 5,000,000 or less, more preferably 3,000,000 or less, and still more preferably 2,000,000 or less. The weight average molecular weight of the acrylic polymer is calculated by measuring by gel permeation chromatography (GPC) and converting to 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) obtained based on the following Fox formula can be used. The Fox equation is a relational expression between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of a homopolymer of monomers constituting the polymer. In the Fox formula below, Tg represents the glass transition temperature (° C.) of the polymer, Wi represents the weight fraction of the monomer i constituting the polymer, and Tgi represents the glass transition of the homopolymer formed from the monomer i. Indicates temperature (°C). Literature values can be used for the glass transition temperature of homopolymers. For example, "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Bunko 7 Introduction to Synthetic Resins for Paints" (Kyozo Kitaoka, Kobunshi Publications, 1995) , which lists the glass transition temperatures of various homopolymers. On the other hand, the glass transition temperature of a homopolymer of a monomer can also be determined by the method specifically described in JP-A-2007-51271.

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

The adhesive composition may contain one or more oligomers in addition to the base polymer. When an acrylic polymer is used as the base polymer, preferably an acrylic oligomer is used as the oligomer. The acrylic oligomer is a copolymer of monomer components containing 50% by mass or more of (meth)acrylic acid alkyl ester, 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, even more 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, more preferably 160° C. or lower. The combined use of a low-Tg acrylic polymer (base polymer) introduced with a cross-linked structure and a high-Tg acrylic oligomer can increase the adhesive strength of the pressure-sensitive adhesive layer 10, especially at high temperatures. The glass transition temperature of the acrylic oligomer is calculated by the above Fox formula.

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

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

The proportion of the 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 same 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 chain 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 still more preferably 30% by weight or more.

The weight average molecular weight of the acrylic oligomer is preferably 1,000 or more, more preferably 1,500 or more, and even more preferably 2,000 or more. The molecular weight is preferably 30,000 or less, more preferably 10,000 or less, still more preferably 8,000 or less. Such a molecular weight range of the acrylic oligomer is preferable for ensuring the adhesive strength and adhesive holding power of the pressure-sensitive adhesive layer 10 .

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

The content of the acrylic oligomer in the pressure-sensitive adhesive layer 10 is preferably 0.5 parts by mass or more, more preferably 0.5 parts by mass or more, with respect to 100 parts by mass of the base polymer, in order to sufficiently increase the adhesive strength of the pressure-sensitive adhesive layer 10 . It is 8 parts by mass or more, more preferably 1 part by mass or more. On the other hand, from the viewpoint of ensuring the transparency of the adhesive layer 10, the content of the acrylic oligomer in the adhesive layer 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass with respect to 100 parts by mass of the base polymer. 3 parts by mass or less, more preferably 3 parts by mass or less. In the pressure-sensitive adhesive layer 10, when the content of the acrylic oligomer is too large, the haze tends to increase and the transparency tends to decrease due to the 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 pressure-sensitive adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, relative to 100 parts by mass of the base polymer. The 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 necessary. Other ingredients include, for example, tackifiers, plasticizers, softeners, antidegradants, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents.

The adhesive sheet S can be produced, for example, by coating the adhesive composition described above on the 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 release film is, for example, 3 μm or more and, for example, 200 μm or less. The surface of the release film is preferably release-treated.

Examples of methods for applying the adhesive composition include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, and lip coating. , and die coats. 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 film L2 (second release film) may be further laminated on the adhesive layer 10 on the first release film L1. The second release film is a flexible plastic film subjected to surface release treatment, and the same film as described above for the first release film can be used.

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 off from the adhesive sheet S when the adhesive sheet S is used.

The thickness of the pressure-sensitive 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 handleability of the adhesive sheet S, the thickness of the adhesive layer 10 is preferably 300 μm or less, more preferably 200 μm or less, still more 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 more preferably 1% or less. The haze of the pressure-sensitive adhesive layer 10 can be measured using a haze meter according to 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 Research Laboratory.

The total light transmittance of the adhesive layer 10 is preferably 60% or higher, more preferably 80% or higher, and even more preferably 85% or higher. 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 according to JIS K 7375 (2008).

2A to 2C show an example of how to use the adhesive sheet S.

In this method, first, as shown in FIG. 2A, an adhesive sheet S is attached to one surface of the first member 21 (adherend) in the thickness direction T. The first member 21 is, for example, one element in the laminated structure of the flexible panel. Examples of such elements 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 step, the pressure-sensitive adhesive layer 10 for bonding with another member is provided on the first member 21 .

In this process, if a bonding failure (for example, positional deviation of the adhesive sheet S on the first member 21) occurs, the adhesive sheet S is peeled off from the first member 21. After that, the lamination work is redone with a substitute adhesive sheet S.

Next, as shown in FIG. 2B, through the pressure-sensitive adhesive layer 10 on the first member 21, the thickness direction T one side of the first member 21 and the thickness direction T other side of the second member 22 Join with. 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. Aging promotes the cross-linking reaction of the base polymer in the pressure-sensitive adhesive layer 10 and increases 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 is, for example, 1 minute to 21 days. When autoclave treatment (heat and pressure treatment) is performed 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 longer.

In the pressure-sensitive adhesive sheet S used in the manufacturing process of the foldable device as described above, the pressure-sensitive adhesive layer 10 has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25° C. and the first The adhesive force Xa and the second adhesive force Xb satisfy 0.5≦Xb/Xa≦1. Such a pressure-sensitive adhesive sheet S is suitable for suppressing peeling from a folded adherend, as described above.

The present invention will be specifically described below with reference to examples. The invention is not limited to the examples. In addition, the specific numerical values such as the compounding amount (content), physical property values, parameters, etc. described below are the corresponding compounding amounts ( content), physical properties, parameters, etc., upper limits (values defined as “less than” or “less than”) or lower limits (values defined as “greater than” or “greater than”).

<Preparation Example 1 of Acrylic Oligomer>
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 95 parts by mass of cyclohexyl methacrylate (CHMA), 5 parts by mass of acrylic acid (AA), and α- A mixture containing 10 parts by weight of methylstyrene dimer and 120 parts by weight of toluene as a solvent was stirred at room temperature for 1 hour under a nitrogen atmosphere. After that, 10 parts by mass of 2,2′-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator is added to the mixture to prepare a reaction solution, which is reacted at 85° C. for 5 hours under a nitrogen atmosphere. (formation of the first acrylic oligomer). As a result, an oligomer solution (solid concentration: 50% by mass) containing the first acrylic oligomer was obtained. The weight average molecular weight of the first acrylic oligomer was 4,300. Also, the glass transition temperature (Tg) of the first acrylic oligomer was 84°C.

<Preparation Example 2 of Acrylic Oligomer>
60 parts by mass of dicyclopentanyl methacrylate (DCPMA), 40 parts by mass of methyl methacrylate (MMA), and a chain transfer agent A mixture containing 3.5 parts by mass of α-thioglycerol as a solvent 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 is added to the mixture to prepare a reaction solution, which is placed under a nitrogen atmosphere at 70° C. for 1 hour. and then reacted at 80° C. 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 monomers. As a result, a solid acrylic oligomer (second acrylic oligomer) was obtained. The weight average molecular weight of the second acrylic oligomer was 5,100. The glass transition temperature (Tg) of the second acrylic oligomer was 130°C.

[Example 1]
<Preparation of acrylic base polymer>
70 parts by mass of 2-ethylhexyl acrylate (2EHA), 20 parts by mass of n-butyl acrylate (BA), and lauryl acrylate were placed in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube. (LA) 8 parts by mass, 4-hydroxybutyl acrylate (4HBA) 1 part by mass, N-vinyl-2-pyrrolidone (NVP) 0.6 parts by mass, and 2,2′- as a thermal polymerization initiator A mixture containing 0.1 part by mass of azobisisobutyronitrile (AIBN) and ethyl acetate as a solvent (solid concentration: 47% by mass) was stirred under a nitrogen atmosphere at 56°C for 6 hours (polymerization reaction ). This gave a polymer solution containing an acrylic base polymer. The weight average molecular weight of the acrylic base polymer in this polymer solution was about 2 million.

<Preparation of adhesive composition>
To the polymer solution, 1.5 parts by mass of the first acrylic oligomer per 100 parts by mass of the solid content of the polymer solution, and 0 of the first cross-linking agent (trade name "Niper BMT-40SV", dibenzoyl peroxide, manufactured by NOF) .26 parts by mass, 0.02 parts by mass of a second cross-linking agent (trade name "Coronate L", trimethylolpropane / tolylene diisocyanate trimer adduct, manufactured by Tosoh), and a silane coupling agent (trade name "KBM403 , manufactured by Shin-Etsu Chemical Co., Ltd.) was added and mixed to prepare an adhesive composition C1.

<Formation of adhesive layer>
Next, the pressure-sensitive adhesive composition C1 was applied onto the release-treated surface of the first release film, one surface of which had been subjected to silicone release treatment, to form a coating film. The first release film is a polyethylene terephthalate (PET) film (trade name “Diafoil MRF #75”, thickness 75 μm, manufactured by Mitsubishi Chemical Co., Ltd.) with one side subjected to silicone release treatment. Next, the release-treated surface of the second release film having one surface subjected to silicone release treatment was attached to the coating film on the first release film. The second release film is a PET film (trade name: "Diafoil MRF#75", thickness: 75 µm, manufactured by Mitsubishi Chemical Co., Ltd.) with one side subjected to silicone release treatment. Next, the coating film on the first release film was dried by heating at 100° C. for 1 minute and then heating at 150° C. for 3 minutes to form a transparent adhesive layer with a thickness of 50 μm. As described above, a pressure-sensitive adhesive sheet of Example 1 having a transparent pressure-sensitive adhesive layer (thickness: 50 µm) was produced. The monomer composition of the acrylic base polymer and the pressure-sensitive adhesive layer composition in the pressure-sensitive adhesive sheet of Example 1 are shown in Table 1 in units of parts by mass (the same applies to Examples and Comparative Examples described later).

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

[Examples 5 and 6]
Each 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 to be formed was changed from 50 μm to 25 μm (Example 5) or 100 μm (Example 6). An adhesive sheet was produced.

[Comparative Example 1]
56 parts by weight of 2-ethylhexyl acrylate (2EHA), 34 parts by weight of lauryl acrylate (LA), 7 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 2 parts by weight of N-vinyl-2-pyrrolidone (NVP) A mixture containing 0.015 parts by mass of a photopolymerization initiator (trade name “Omnirad 184” manufactured by IGM Resins) was irradiated with ultraviolet rays (polymerization reaction), and a prepolymer composition (polymerization rate is about 10% ) was obtained (the prepolymer composition contains a monomer component that has not undergone a polymerization reaction).

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 (trade name "KBM403", Shin-Etsu Chemical Co., Ltd.) was mixed with 0.3 parts by mass to prepare a photocurable pressure-sensitive adhesive composition C2.

Next, the pressure-sensitive adhesive composition C2 was applied onto the release-treated surface of the first release film, one surface of which had been subjected to silicone release treatment, to form a coating film. The first release film is a polyethylene terephthalate (PET) film (trade name “Diafoil MRF #75”, thickness 75 μm, manufactured by Mitsubishi Chemical Co., Ltd.) with one side subjected to silicone release treatment. Next, the release-treated surface of the second release film having one surface subjected to silicone release treatment was attached to the coating film on the first release film. The second release film is a PET film (trade name: "Diafoil MRF#75", thickness: 75 µm, manufactured by Mitsubishi Chemical Co., Ltd.) with one side subjected to silicone release treatment. Next, the coating film was irradiated with ultraviolet rays through the second release film to cure the coating film with ultraviolet rays. A black light was used for ultraviolet irradiation. The irradiation intensity of ultraviolet rays was set to 5 mW/cm ² . As described above, a pressure-sensitive adhesive sheet (thickness: 50 μm) of Comparative Example 1 was produced.

[Comparative Example 2]
A pressure-sensitive adhesive sheet of Comparative Example 2 was prepared 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]
A pressure-sensitive adhesive sheet of Comparative Example 3 was prepared 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.

<Adhesive force>
The adhesive strength of each adhesive sheet in Examples 1-6 and Comparative Examples 1-3 was examined by a peel test.

First, for each pressure-sensitive adhesive sheet, the required number of test pieces were prepared for the peel test before autoclaving and the peel test after autoclaving, which will be described later. In preparing the test piece, first, the second release film was peeled off from the pressure-sensitive adhesive sheet, and a PET film (thickness: 25 µm) was adhered to the exposed surface of the pressure-sensitive adhesive layer to obtain a laminate. Next, a test piece (width 25 mm×length 100 mm) was cut out from this laminate. Next, the first release film was peeled off from the pressure-sensitive adhesive layer of the test piece, and the exposed surface thereby exposed was plasma-treated. On the other hand, a polyimide film (trade name “GV200D”, thickness 80 μm, manufactured by SKC Kolon PI) as an adherend was also plasma-treated. In each plasma treatment, a plasma irradiation apparatus (trade name “AP-TO5”, manufactured by Sekisui Kogyo Co., Ltd.) was used, the voltage was 160 V, the frequency was 10 kHz, and the treatment speed was 5000 mm/min. Then, the exposed surface of the pressure-sensitive adhesive layer of the test piece and the plasma-treated surface of the polyimide film were bonded together. In this bonding, the test piece was press-bonded to the adherend by reciprocating a 2-kg roller one time in an environment of 25°C.

[Peeling test before autoclave treatment]
A peeling test was performed by peeling the test piece from the polyimide film after standing at 25° C. for 2 minutes from the above-described bonding, and the peel strength was measured as the adhesive strength. A tensile tester (trade name “Autograph AGS-J” manufactured by Shimadzu Corporation) was used for this measurement. In this measurement, the measurement temperature was 25° C., the peel angle of the test piece to the adherend was 180°, the tensile speed of the test piece was 300 mm/min, and the peel length was 50 mm (measurement conditions of the peel test). . Table 1 shows the measured adhesive strength as the initial adhesive strength (N/25 mm).

[Peeling test after autoclave treatment]
Autoclave treatment (heating and pressure treatment) of the adherend-attached test piece was started within 3 minutes from the above bonding. In the autoclave treatment, the temperature was 50° C., the pressure was 0.5 MPa, and the treatment time was 15 minutes. Then, after standing at 25 ° C. for 72 hours after autoclave treatment, the peel test (measurement temperature 25 ° C.) under the above measurement conditions was performed in the same manner as the above peel test before autoclave treatment, and the adhesive strength was measured. did. Table 1 shows the measured adhesive strength as adhesive strength Xa (N/25 mm). On the other hand, the test pieces were subjected to the above autoclave treatment and peel test in the same manner, except that the measurement temperature in the peel test was changed to a predetermined temperature (60°C, 70°C, 85°C) to measure the adhesive force. Adhesive force Xb (N/25mm) at 60°C, adhesive force Xd (N/25mm) at 70°C, adhesive force Xc (N/25mm) at 85°C, and the ratio of Xb to Xa (Xb/ Xa), the ratio of Xd to Xa (Xd/Xa), and the ratio of Xc to Xa (Xc/Xa) are shown in Table 1. Further, the measurement results of the peel test after autoclave treatment are shown in the graph of FIG. In the graph, the left bar represents the adhesive strength of the adhesive sheet of Comparative Example 1, and the right bar represents the adhesive strength of the adhesive sheet of Example 1 at each measurement temperature.

<Storage modulus, loss tangent, and glass transition temperature>
Dynamic viscoelasticity measurement was performed on the adhesive layer of each adhesive sheet of Examples 1 to 6 and Comparative Examples 1 to 3. A sample for measurement was prepared as follows. First, a pressure-sensitive adhesive sheet having a thickness of about 1.5 mm was produced by laminating a plurality of pressure-sensitive adhesive layer pieces. Next, this sheet was punched out to obtain cylindrical pellets (diameter 7.9 mm) as samples for measurement. Then, the measurement sample was fixed to a parallel plate jig with a diameter of 7.9 mm using a dynamic viscoelasticity measuring device (trade name "Advanced Rheometric Expansion System (ARES)", manufactured by Rheometric Scientific). Dynamic viscoelasticity measurements were performed. In this measurement, the measurement mode was the 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 elastic modulus G' (shear storage elastic modulus) and the loss tangent tan δ at each temperature (shown in Table 1) were read. The storage modulus Ma (kPa) at 25°C, the storage modulus Mb (kPa) at 60°C, the storage modulus Mc (kPa) at 85°C, and the ratio of the storage modulus Mb to the storage modulus Ma (Mb /Ma) and the ratio of storage modulus Mc to storage modulus Ma (Mc/Ma) are shown in Table 1. Further, the temperature at which the loss tangent tan δ becomes maximum was defined 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 adhesive layer of each adhesive sheet of Examples 1-6 and Comparative Examples 1-3 was examined for haze and total light transmittance as follows. First, a sample for haze measurement was produced. Specifically, after peeling off the second release film from the adhesive sheet, the adhesive layer side of the same sheet (first release film, adhesive layer) is covered with non-alkali glass (thickness 0.8 to 1.0 mm, total thickness). Light transmittance 92%, haze 0.4%, manufactured by Matsunami Glass Co., Ltd.), and the first release film was peeled off from the adhesive layer on the glass. Thus, a sample for measurement was produced. Next, using a haze measuring device (trade name “HM-150”, manufactured by Murakami Color Research Laboratory), the haze and total light transmittance of the pressure-sensitive adhesive layer of each sample were measured. In this measurement, the measurement sample was placed in the apparatus so that light was applied to the measurement sample from the alkali-free glass side. In addition, in this measurement, the measurement result obtained by measuring only the alkali-free glass under the same conditions was used as a baseline. Table 1 shows the haze and total light transmittance of the pressure-sensitive adhesive layer thus obtained.

<Bending test>
The adhesive sheets of Examples 1 to 6 and Comparative Examples 1 to 3 were examined for adhesion to a folded adherend (degree of suppression of peeling from the adherend). Specifically, it is as follows.

First, a laminate sample was produced for each adhesive sheet. In preparing the laminate sample, first, the second release film was peeled off from the pressure-sensitive adhesive sheet, and the exposed surface (first exposed surface) thereby exposed was plasma-treated. On the other hand, the exposed surface of the polarizing plate of the 66 μm thick polarizing plate with an adhesive layer (having a laminated structure of a 51 μm thick polarizing plate and a 15 μm thick adhesive layer) as the first adherend was also , plasma treated. In each plasma treatment, a plasma irradiation apparatus (trade name “AP-TO5”, manufactured by Sekisui Kogyo Co., Ltd.) was used, the voltage was 160 V, the frequency was 10 kHz, and the treatment speed was 5000 mm / min (in the plasma treatment described later is also the same). Then, the first exposed surface of the adhesive sheet and the plasma-treated surface of the polarizing plate were bonded together. In this bonding, the polarizing plate and the adhesive sheet were pressure-bonded by reciprocating a 2-kg roller once in an environment of 25°C. Next, the first release film was peeled off from the adhesive sheet on the polarizing plate, and the exposed surface (second exposed surface) thereby exposed was plasma-treated. On the other hand, a polyimide film (trade name “GV200D”, thickness 80 μm, manufactured by SKC Kolon PI) as a 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 together. In this bonding, the polyimide film and the adhesive sheet were press-bonded by reciprocating a 2-kg roller once in an environment of 25°C. Next, a plasma-treated PET film having a thickness of 125 μm was attached to the adhesive layer surface of the polarizing plate with an adhesive layer by reciprocating a 2 kg roller once. A laminate sample was produced as described above. The laminate sample has a laminate configuration of a PET film, an adhesive layer, a polarizing plate, an adhesive sheet (an adhesive sheet according to any of 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 pressurized) under 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 body no-load U-shaped stretching tester (manufactured by Yuasa System Co., Ltd.). In this test, a bending jig was attached to each of both ends of the laminate sample in the long side direction in a range of 20 mm from the sample edge, and the laminate sample was fixed to the test machine (long side of the laminate sample The central 60 mm region of the direction is in an unfixed state). In this test, the laminate 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 surface of the laminate sample was on the inside. It was held for 240 hours in a thermo-hygrostat at a temperature of 25° C. and a relative humidity of 95% (first bending test).

The laminate sample after such a first bending test was visually observed to confirm the presence or absence of peeling between the polyimide film and the polarizing plate at the bending portion. In all of the samples in which peeling was confirmed, peeling (void) occurred from the end portion in the short side direction of the laminate sample. For the laminated body samples in which peeling was confirmed, the length (mm) of the gap in the short side direction of the sample was measured. Then, regarding the adhesiveness of the adhesive sheet to the adherend to be folded (the extent to which peeling from the adherend is suppressed), the case where the void length is less than 2 mm was evaluated as "excellent", and the void When the length was 2 mm or more, it was evaluated as "defective" (in this evaluation, if peeling (void) extending over the entire length of the short side direction of the laminate sample was confirmed, the length of the void was 35 mm, and when no peeling was observed, the void length was set to 0 mm). Table 1 shows the evaluation results.

In addition, a bending test was performed in the same manner as the first bending test, except that the holding temperature in the constant temperature and humidity chamber was changed from 25°C to 85°C (second bending test). After that, the laminate sample after the second bending test was visually observed to confirm the presence or absence of peeling between the polyimide film and the polarizing plate at the bending portion. Then, the adhesiveness of the pressure-sensitive adhesive sheet to the bendable adherend was evaluated according to the same criteria as in the first bending test. Table 1 shows the evaluation results.

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

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

S Adhesive sheet (optical adhesive sheet for foldable devices)
T thickness direction 10 adhesive layers L1, L2 release film 21 first member 22 second member

Claims

An optical adhesive sheet for a foldable device having an adhesive layer,
The pressure-sensitive adhesive layer has a shear storage modulus of 20 kPa or more and 50 kPa or less at 25°C,
After the pressure-sensitive adhesive layer is attached to the adherend, heat-pressed under conditions of 50 ° C., 0.5 MPa and 15 minutes, and then allowed to stand at 25 ° C. for 72 hours, the Having a first adhesive force Xa at 25 ° C. to the adherend,
The pressure-sensitive adhesive layer has a second adhesive force Xb to the adherend at 60° C. after being attached to the adherend, the heating and pressurizing treatment, and the standing, and
The optical adhesive sheet for foldable devices, wherein the first adhesive force Xa and the second adhesive force Xb satisfy 0.5≦Xb/Xa≦1.0.
The pressure-sensitive adhesive layer has a third adhesive force Xc to the adherend at 85 ° C. after being attached to the adherend, the heating and pressurizing treatment, and the standing, and
2. The optical pressure-sensitive adhesive sheet for a foldable device according to claim 1, wherein said first pressure-sensitive adhesive strength Xa and said third pressure-sensitive adhesive strength Xc satisfy 0.5≦Xc/Xa≦0.8.
The pressure-sensitive adhesive layer has a minimum adhesive strength of 10 N to the adherend within a temperature range of 25° C. or higher and 85° C. or lower after being attached to the adherend, heat-pressed, and allowed to stand. The optical pressure-sensitive adhesive sheet for a foldable device according to claim 1, which has a thickness of at least /25 mm.
The optical adhesive sheet for foldable devices according to claim 3, wherein the adhesive layer has the minimum adhesive strength at 60°C or higher.
The pressure-sensitive adhesive layer has an adhesive strength of 0.5 N/25 mm or more and 12 N/25 mm or less to the adherend at 25 ° C. after standing at 25 ° C. for 2 minutes after sticking to the adherend. The optical pressure-sensitive adhesive sheet for a foldable device according to claim 1.