JP7327701B1 - Double-sided adhesive sheet and laminate for image display device - Google Patents

Abstract

[Problem] To provide a substrate-less double-sided pressure-sensitive adhesive sheet that has excellent visibility even when applied to optical applications and can suppress wrinkles and air bubbles even when applied to flexible displays. The double-sided adhesive sheet is a substrate-less double-sided adhesive sheet in which a first release sheet 1, an adhesive layer 3, and a second release sheet 2 are laminated in this order. , the reflection intensity Wa in the wavelength range of 0.1 to 0.3 mm is 1 to 26, and the reflection intensity Wd in the wavelength range of 3 to 10 mm is 0.3 to 8. The adhesive layer 3 is (i) an adhesive layer containing a (meth)acrylic copolymer (a) having a weight average molecular weight of 1,000,000 to 1,800,000, and an adhesive composition containing the (meth)acrylic copolymer (a). (ii) a storage modulus of 1 × 10 to 8 × 10 Pa at 23 ° C., and (iii) a glass transition temperature by DSC of -70 ° C. ≤ Tg ≤ -35°C. [Selection drawing] Fig. 1

Description

TECHNICAL FIELD The present disclosure relates to a double-sided pressure-sensitive adhesive sheet and a laminate for image display devices.

Adhesive sheets can be joined to adherends by a simple means of sticking, so they are often used in electronic devices such as personal computers and smartphones that require joining of various members, and various proposals have been made. For example, in Patent Document 1, an acrylic polymer containing a monomer having a Tg of −10° C. or more when forming a homopolymer as an essential monomer component, and a shear storage modulus at 23° C. of 0.5° C. is used. It has an acrylic pressure-sensitive adhesive layer of 8×10 ⁵ to 5.0×10 ⁵ Pa, and has a moisture content of 0.65% by weight or more after storage for 120 hours in an environment of 60° C. and 95% RH. An optical pressure-sensitive adhesive sheet is disclosed. Further, in Patent Documents 2 and 3, an ethylenically unsaturated monomer (A1) having an alkyl group with an SP value of 8 or more and less than 9.00 is 20 to 90% by weight and an SP value of 9.00 or more and 15 or less An acrylic copolymer (A) obtained by radically polymerizing 10 to 80% by weight of an ethylenically unsaturated monomer (A2) having a polar group of, a polyisocyanate curing agent (B) and a silane coupling agent (C) is disclosed. Furthermore, in Patent Document 4, 5% by mass or more of the structural unit (A) derived from a (meth)acrylic acid alkyl ester having an alkyl group having 12 or more carbon atoms and an alkyl group having 1 to 8 carbon atoms ( 5% by mass or more of the structural unit (B) derived from a meth)acrylic acid alkyl ester, and 2% by mass or more and 30% by mass or less of the structural unit (C) derived from a monomer having a hydroxyl group, and the structural unit ( A), a pressure-sensitive adhesive composition containing a (meth)acrylic polymer in which the total content of structural units (B) and structural units (C) is 80% by mass or more is disclosed. Further, in Patent Document 5, the acid value is 2.5 mgKOH / g or less, and the structural unit derived from a monomer having a hydroxyl group is contained in the range of 0.01 to 1% by mass with respect to all structural units ( A pressure-sensitive adhesive composition comprising a meth)acrylic copolymer, a tolylene diisocyanate compound in the range of 5 to 30 parts by mass with respect to 100 parts by mass of the (meth)acrylic copolymer, and an imidazole compound is disclosed. ing. Furthermore, in Patent Document 6, a (meth)acrylic polymer having a carboxy group and 0.005 to 2.5 parts by mass of an alicyclic epoxy-modified silicone per 100 parts by mass of the (meth)acrylic polymer are added. Disclosed is an adhesive composition comprising: Further, in Patent Document 7, the gel fraction immediately after the formation of the adhesive layer is 40% or more and 80% or less, and the gel after storage for 7 days under the conditions of 23 ° C. and 55% RH from the formation of the adhesive layer A pressure-sensitive adhesive composition having a fraction of 60% or more and 85% or less is disclosed. In Patent Document 8, when the exposed surface of the release film is measured for the reflection intensity (Wb) in the wavelength range of 0.3 to 1.0 mm using a wave scanning device, the reflection intensity (Wb) is 10.0. In Patent Document 9, the thickness of the film substrate is 38 μm or less, and the exposed surface of the release film is reflected in the wavelength range of 0.3 to 1.0 mm using a wave scanning device. When the strength (Wb) is measured, the reflection strength (Wb) is 10 or more, and the pressure-sensitive adhesive layer is disclosed as a laminated sheet containing at least a structure derived from a (meth)acrylic copolymer and a chelate cross-linking agent. there is

WO2011/111575 JP 2013-127012 A Chinese Patent Application Publication No. 104231981 JP 2014-74122 A JP 2016-188309 A JP 2016-79266 A Japanese Unexamined Patent Application Publication No. 2018-2961 JP-A-2020-83908 Japanese Patent Application Laid-Open No. 2020-83910

As described above, adhesive layers are frequently used in electronic devices because they can bond adherends together by a simple method. However, the adhesive layer cannot be said to have high resistance to repeated bending. For example, when it is applied to foldable displays, which have rapidly become popular in recent years, there is a problem that wrinkles and air bubbles are likely to occur over time. be. The occurrence of such wrinkles and air bubbles not only lowers the adhesion but also lowers the visibility of the surface protective film, which is particularly serious in the case of optical member applications such as displays.

The market demands substrate-less double-sided pressure-sensitive adhesive sheets due to the needs for productivity, versatility, and lightness, thinness, and miniaturization of various electronic devices. In addition, even when applied to applications requiring flexibility such as foldable displays, there is a demand for an adhesive layer with excellent visibility that can suppress the generation of wrinkles and air bubbles over time. In particular, there is a demand for development of an adhesive layer capable of suppressing the generation of wrinkles and air bubbles over a range from low temperature (0°C) to high temperature (40°C).

In addition, although the problems of the adhesive layer used for display applications have been described above, similar problems may arise in general applications where visibility is desired to be improved.

The present disclosure has been made in view of the above problems, and has excellent visibility even when applied to optical applications, and a substrate-less double-sided pressure-sensitive adhesive sheet that can suppress wrinkles and air bubbles even when applied to flexible display applications. The task is to provide

The present disclosure provides the following double-sided pressure-sensitive adhesive sheet and laminate for image display device.
[1]: A double-sided pressure-sensitive adhesive sheet for substrate-less flexible display applications, in which a first release sheet, an adhesive layer, and a second release sheet are laminated in this order,
A glass substrate is attached to the surface of the adhesive layer exposed by peeling off the first release sheet, and the glass substrate is placed on a blank sheet of paper, and then the surface of the adhesive layer exposed by peeling off the second release sheet is removed. When measured with a wave scan device,
The reflection intensity Wa in the wavelength range of 0.1 to 0.3 mm is 1 to 26, and the reflection intensity Wd in the wavelength range of 3 to 10 mm is 0.3 to 8,
The adhesive layer is
(i) cross-linking an adhesive layer containing a (meth)acrylic copolymer (a) having a weight average molecular weight of 1,000,000 to 1,800,000, and an adhesive composition containing the (meth)acrylic copolymer (a); is either one of the adhesive layers,
(ii) a storage modulus at 23° C. of 1×10 ³ to 8×10 ⁴ Pa;
(iii) A double-sided pressure-sensitive adhesive sheet having a glass transition temperature of -70°C ≤ Tg ≤ -35°C by DSC.
[2]: A glass substrate is attached to the surface of the adhesive layer exposed by peeling off the first release sheet, and after placing the glass substrate on a blank sheet of paper, the adhesive exposed by peeling off the second release sheet When measuring the surface of the layer with a wave scan device,
The double-sided pressure-sensitive adhesive sheet according to [1], which has a reflection intensity Wc of 1 to 12 in a wavelength range of 1 to 3 mm and a reflection intensity We of 1 to 12 in a wavelength range of 10 to 30 mm.
[3]: The (meth)acrylic copolymer (a) comprises a structural unit derived from a chain or branched (meth)acrylic acid alkyl ester monomer having 1 to 6 carbon atoms in the alkyl group, and an alkyl The double-sided pressure-sensitive adhesive sheet according to [1] or [2], which has a structural unit derived from a chain or branched (meth)acrylic acid alkyl ester monomer having 7 to 12 carbon atoms in the group.
[4]: The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the (meth)acrylic copolymer (a) has a molecular weight distribution Mw/Mn of less than 5.
[5]: A laminate for an image display device in which adherends are bonded via the adhesive layer of the double-sided adhesive sheet of any one of [1] to [4].

According to the present disclosure, it is possible to provide a substrate-less double-sided pressure-sensitive adhesive sheet that has excellent visibility even when applied to optical applications and can suppress wrinkles and air bubbles even when applied to flexible display applications. .

Schematic cross-sectional view showing an example of a double-sided pressure-sensitive adhesive sheet according to an embodiment. Sectional drawing for demonstrating the measuring method by a wave scanning device of the adhesion layer surface.

The present disclosure will be described in detail below. It goes without saying that other embodiments are also included in the scope of the present disclosure as long as they match the gist of the present disclosure. In addition, the numerical range specified using "to" in this specification includes the numerical values described before and after "to" as the range of lower and upper values. Also, "film", "sheet" and "tape" are synonymous and are not distinguished by thickness or shape. (Meth)acrylic means at least one of acrylic and methacrylic, and (meth)acrylic acid alkyl ester means at least one of acrylic acid alkyl ester and methacrylic acid alkyl ester. In addition, unless otherwise noted, each of the various components may be independently used alone or in combination of two or more. Numerical values in this specification refer to values obtained by the method described in Examples described later.

1. Double-sided pressure-sensitive adhesive sheet The double-sided pressure-sensitive adhesive sheet of the present disclosure (hereinafter also referred to as the present pressure-sensitive adhesive sheet) is a substrate-less sheet in which a first release sheet, an adhesive layer and a second release sheet are laminated in this order. The pressure-sensitive adhesive sheet can be applied to bonding various adherends. Since the pressure-sensitive adhesive sheet has excellent visibility, it is particularly suitable for optical applications. In addition, since the pressure-sensitive adhesive sheet can suppress wrinkles and air bubbles, it is suitable for use in flexible displays. In particular, it is suitable for use as a foldable display because it is excellent in repeated folding durability.

FIG. 1 shows a schematic cross-sectional view showing an example of the substrate-less double-sided pressure-sensitive adhesive sheet according to this embodiment. The double-sided pressure-sensitive adhesive sheet 10 is a substrate-less sheet in which the pressure-sensitive adhesive layer 3 is sandwiched between the first release sheet 1 and the second release sheet 2 . From the viewpoint of peeling balance, as shown in FIG. It is preferable that the release sheet 1 and the second release sheet 2 have a visor w (have a non-formation region w of the adhesive layer 3).

The unevenness of the surface of the adhesive layer 3, for example, the degree of undulation, waviness, and orange peel can be confirmed by a wave scanning device. The reflection intensity Wa in the wavelength range of 0.1 to 0.3 mm obtained by a wave scanning device is an index of fine structure visible from a short distance of about 40 cm, and usually takes a value of 0 to 80. Among these, it is said that the reflection intensity Wa is preferably in the range of 0 to 1 in order to prevent a decrease in luster and cloudiness. The reflection intensity Wd in the wavelength range of 3 to 10 mm obtained by a wave scanning device is an index of fine structure visible from a medium distance of about 3 m, and usually takes a value of 0 to 50. Among these, it is said that the reflection intensity Wd is preferably in the range of 8 to 30 in order to prevent a decrease in adhesive strength due to a decrease in smoothness.

The reflection intensities Wa and Wd and the reflection intensities Wc and Wd described later were measured by peeling off the first release sheet 1 and attaching the exposed surface 31 of the adhesive layer 3 to the glass substrate 4 as shown in FIG. After placing the glass substrate 4 on the white paper 5, the surface 32 of the adhesive layer 3 exposed by peeling off the second release sheet 2 is measured with a wave scanning device.

As a result of extensive studies by the present inventors on substrate-less double-sided pressure-sensitive adhesive sheets, the combination of the reflection intensity Wa of the surface 32 of the pressure-sensitive adhesive layer 3 of 1 to 26 and the reflection intensity Wd of 0.3 to 8 can be used for optical applications. It was found that a substrate-less double-sided pressure-sensitive adhesive sheet can be obtained that has excellent visibility even when applied to a flexible display and can suppress the generation of air bubbles and wrinkles even when applied to a flexible display. The reason for this is speculative, but the combination of the small undulations Wa within the above range and the relatively large undulations Wd within the above range made it possible to improve the adhesion to the adherend. According to

The value of Wa can be adjusted mainly by the coating process. Specifically, it can be adjusted by adjusting the solid content concentration when the pressure-sensitive adhesive composition is applied in the form of a sheet. Wa tends to decrease as the solid content concentration decreases (Wa tends to increase as the solid content concentration increases). Moreover, the value of Wa can be adjusted by the coating speed of the pressure-sensitive adhesive composition. Wa tends to increase as the coating speed increases. Also, the value of Wa can be adjusted by the drying conditions (temperature, time, air volume, etc.) during coating of the pressure-sensitive adhesive composition for forming the sheet. Wa tends to increase as the drying temperature increases. Moreover, Wa tends to increase as the drying time increases. Moreover, Wa fluctuates by adjusting the amount of drying air. Furthermore, Wa may be adjusted according to the aging conditions (time and temperature) after the sheet is formed. Wa can also be adjusted by the film thickness, and Wa tends to increase as the film thickness decreases.

As a method for adjusting Wd, the same method as that for Wa described above can be used. In particular, Wd tends to increase as the drying temperature increases (Wd tends to decrease as the drying temperature decreases). Wd tends to increase as the drying time increases.

Wa is more preferably in the range of 3-24, more preferably in the range of 4-23, and particularly preferably in the range of 7-19. Wd is more preferably in the range of 0.5-5, more preferably in the range of 0.8-5, and particularly preferably in the range of 1-4.

From the viewpoint of improving the visibility, in addition to satisfying the specific range of Wa and the specific range of Wd, the surface 32 of the adhesive layer 3 shown in FIG. It is preferable that the reflection intensity Wc of 1-3 mm is 1-12 and the reflection intensity We of the wavelength range 10-30 mm is 1-12. Wc is an index of fine structure visible from short to medium distances of about 40 cm to 3 m. By combining Wc with Wa and Wd within the above specific ranges, the haze reduction effect is more excellent. By combining Wa, Wd, and Wc within the specific ranges with We within the above ranges, the effect of reducing the difference in luminance between brightness and darkness is more excellent. Note that We is an index of a fine structure that can be visually recognized from a long distance of 3 m or longer.

As a method for adjusting Wc, the same method as that for Wa described above can be used. Among them, the method of adjusting the solid content concentration and/or adjusting the film thickness is preferable. Wc tends to increase as the solid content concentration increases (Wc tends to decrease as the solid content concentration decreases).
Moreover, as a method of adjusting We, the same method as the above Wa can be used. Among them, a method of adjusting the aging conditions (time and temperature) after sheet formation is preferable. We tends to increase as the aging temperature increases (We tends to decrease as the aging temperature decreases).

A more preferred range for Wc is 2-11, and a more preferred range is 2-7. A more preferable range of We is 1-9, and a more preferable range is 1-7.

From the viewpoint of tack, the reflection intensity Wb in the wavelength range of 0.3-1.0 mm is preferably in the range of 2-30. The tackiness referred to here is an index of stickiness determined by the J. Dow method according to JIS Z-0237:2022. Wb is more preferably 6-30, more preferably 9-25. A method of adjusting the coating speed is suitable for adjusting Wb. Wb tends to increase as the coating speed increases (Wb tends to decrease as the coating speed decreases).

From the viewpoint of improving productivity, the pressure-sensitive adhesive sheet is preferably produced in the form of a roll sheet in which a long double-sided pressure-sensitive adhesive sheet is wound around a core. For example, a roll sheet can be obtained by winding a long double-sided pressure-sensitive adhesive sheet around a cylindrical core having an outer diameter (diameter) of about 100 to 1000 mm. The width of the double-sided adhesive sheet is, for example, 100 to 3000 mm, and the winding length of the adhesive sheet is, for example, 10 to 3000 m. In the case of a roll sheet, the pressure-sensitive adhesive sheet is unwound, cut and/or punched at the time of shipment or use. Then, after peeling off the first release sheet 1, the exposed adhesive layer 3 is attached to the adherend, and then the second release sheet 2 is peeled off, whereby the exposed adhesive layer 3 is attached to another adherend. Stick it on your body. Through such steps, the adherends are bonded together.

2. Adhesive Layer The present adhesive layer is a layer formed from an adhesive composition. The pressure-sensitive adhesive composition is a cross-linking pressure-sensitive adhesive or non-cross-linking pressure-sensitive adhesive, and may be emulsion type, solvent type or non-solvent type.

The adhesive layer has Wa in the specific range and Wd in the specific range, and satisfies (i) to (iii) below.
(i) an adhesive layer containing a (meth)acrylic copolymer (a) having a weight-average molecular weight of 1,000,000 to 1,800,000 (adhesive layer made of a non-crosslinked adhesive), or a (meth)acrylic copolymer (a) ) is a pressure-sensitive adhesive layer obtained by cross-linking a pressure-sensitive adhesive composition containing (a pressure-sensitive adhesive layer obtained by cross-linking a cross-linkable pressure-sensitive adhesive).
(ii) a storage modulus at 23° C. of 1×10 ³ to 8×10 ⁴ Pa;
(iii) The glass transition temperature by DSC is -70°C ≤ Tg ≤ -35°C.

According to this pressure-sensitive adhesive layer, deformation of the pressure-sensitive adhesive layer can be effectively suppressed, for example, at the stage of the roll-shaped double-sided pressure-sensitive adhesive sheet (first release sheet/adhesive layer/second release sheet). In addition, according to the present adhesive layer, it can withstand repeated flexing, and exhibits an excellent recovery rate when returning from the flexed state to the original state. The effect of suppressing air bubbles and wrinkles over time is not only excellent at room temperature (23° C.), but also air bubbles and wrinkles can be suppressed in a range from low temperature (0° C.) to high temperature (40° C.).

A more preferable range of storage elastic modulus at 23°C is 3×10 ³ to 7×10 ⁴ Pa, and a further preferable range is 1×10 ⁴ to 5×10 ⁴ Pa. In particular, by using an adhesive layer whose storage elastic modulus satisfies the above (ii), it is believed that the uneven portions of the adhesive layer absorb the displacement that causes air bubbles and wrinkles, thereby suppressing the generation of air bubbles and wrinkles. Therefore, it is particularly suitable for use in flexible displays such as foldable displays.

The adhesive layer satisfying the above (i) is, in other words, the adhesive layer containing (meth)acrylic copolymer (a) as an adhesive resin, or crosslinked (meth)acrylic copolymer (a ). The cross-linking may be cross-linking between the (meth)acrylic copolymers (a) or cross-linking between the (meth)acrylic copolymer (a) and the curing agent. From the viewpoint of obtaining an adhesive layer having both adhesive strength and cohesive strength, an adhesive layer having a crosslinked structure between the (meth)acrylic copolymer (a) and the curing agent is suitable. In addition to Wa and Wd within the specific ranges, the adhesive layer is a combination of (ii) and (iii) above (i) containing the (meth)acrylic copolymer component, thereby improving adhesiveness and flexibility. In addition, excellent transparency is obtained.

Furthermore, when the glass transition temperature by DSC is -70 ° C. ≤ Tg ≤ -35 ° C. (iii), the adhesion layer combining Wa and Wd in the above specific ranges with the above (i) and (ii) provides excellent Flexibility can be brought out. As a result, it is possible to obtain an adhesive layer that can suppress wrinkles and air bubbles even when applied to flexible displays. A more preferable range is -65°C ≤ Tg (DSC) ≤ -50°C, and a further preferable range is -65°C ≤ Tg (DSC) ≤ -55°C.

The adhesive layer preferably has a storage elastic modulus of 2×10 ³ to 1.5×10 ⁵ Pa at 0° C. and a frequency of 1 Hz, from the viewpoint of air bubbles and wrinkles when folded under low temperature (0° C.) conditions. ⁴ to 1.4×10 ⁵ Pa is more preferred, and 1.2×10 ⁴ to 9×10 ⁴ Pa is even more preferred.

In addition, the adhesive layer preferably has a storage elastic modulus of 8×10 ² to 7×10 ⁴ Pa at 40° C. and a frequency of 1 Hz, from the viewpoint of air bubbles and wrinkles when folded under high temperature (40° C.) conditions. ³ to 5.5×10 ⁴ Pa is more preferable, and 8×10 ³ to 5×10 ⁴ Pa is even more preferable.

The thickness Ta of the adhesive layer is arbitrary. The thickness Ta of the adhesive layer is preferably about 5 to 150 μm from the viewpoint of maintaining good light transmittance, flexibility and surface structure while exhibiting adhesive strength. A more preferable range for the thickness Ta of the adhesive layer is 15 to 120 μm, and a more preferable range is 25 to 100 μm. The thickness Ta of the adhesive layer can be obtained by the method described later in Examples.

The adhesive strength of the adhesive layer can be arbitrarily designed according to the application. The adhesive strength of the adhesive layer can be controlled by the composition of the adhesive resin constituting the adhesive composition described below, the Tg of the adhesive resin, the amount of the curing agent in the adhesive composition, and the like. By using a (meth)acrylic copolymer (a) obtained by using a highly polar (meth)acrylic monomer ((meth)acrylic monomer) derived from a carboxy group-containing monomer as a monomer, adhesive strength is improved can be enhanced. The lower the Tg of the adhesive resin, the higher the adhesive force tends to be. Furthermore, there is a tendency that the smaller the amount of the curing agent in the adhesive composition, the higher the adhesive strength.

The adhesive layer is a sea-island microphase composed of a continuous phase containing soft segments and a dispersed phase containing hard segments, from the viewpoint of effectively preventing cohesive failure and effectively suppressing dents in double-sided pressure-sensitive adhesive sheets. It may be a layer having a separation structure. The adhesive layer preferably has a structure in which a dispersed phase containing hard segments is dispersed in a matrix forming a continuous phase containing soft segments. A microphase separation structure can be confirmed by an atomic force microscope (AFM), TEM, SPM, or the like. By forming a microphase-separated structure, it is possible to provide an adhesive layer that imparts excellent stretchability and can effectively suppress the occurrence of cracks.

The gel fraction of the adhesive layer is preferably 70 to 90% from the viewpoint of air bubbles and wrinkles during folding. The gel fraction can be obtained by the method described in Examples below. The gel fraction is more preferably 75-90%, even more preferably 75-85%.

2-1. Adhesive Resin As the adhesive resin, as described above, a (meth)acrylic copolymer (a) having a weight average molecular weight (Mw) of 1,000,000 to 1,800,000 is used. By using the (meth)acrylic copolymer (a) within the above range, not only excellent strength but also excellent punching workability can be obtained. The lower limit of Mw of the (meth)acrylic copolymer (a) is more preferably 1,100,000. Moreover, the upper limit of the Mw is more preferably 1.7 million, still more preferably 1.5 million, and particularly preferably 1.3 million. In addition, from the viewpoint of suppressing air bubbles and wrinkles over time during folding in a region from low temperature (0 ° C.) to high temperature (40 ° C.), the (meth)acrylic copolymer (a) has a molecular weight distribution Mw / Mn of 5. It is preferably less than More preferably from 2 to 4.5, still more preferably from 2.5 to 4.

The (meth)acrylic copolymer (a) preferably contains a (meth)acrylic acid ester as a monomer. Preferred examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl ester monomers. When forming a crosslinked adhesive layer, a (meth)acrylic copolymer obtained by copolymerizing a functional group-containing monomer and a (meth)acrylic acid ester is preferable.

The alkyl group of the (meth)acrylic acid alkyl ester may be linear or branched. The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms. Specific examples of (meth) acrylic acid alkyl esters include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, ( isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, (meth)acrylic acid Octyl, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, (meth)acrylic undecyl acid, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, (meth)acrylic acid octadecyl, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and lauryl (meth)acrylate.

The (meth)acrylic copolymer (a) is a structural unit derived from a chain or branched (meth)acrylic acid alkyl ester monomer (a-1) having an alkyl group having 1 to 6 carbon atoms, and It preferably has a structural unit derived from a chain or branched (meth)acrylic acid alkyl ester monomer (a-2) in which the alkyl group has 7 to 12 carbon atoms. By containing one or more structural units derived from a chain or branched (meth)acrylic acid alkyl ester monomer having 1 to 6 carbon atoms in the alkyl group, interaction with the adherend interface is achieved in a short contact time. The action is easily expressed, and the adhesion can be enhanced. In addition, by including one or more types of structural units derived from chain or branched (meth)acrylic acid alkyl ester monomers having 7 to 12 carbon atoms in the alkyl group, the adhesion to the adherend interface during a long contact time It spreads easily and can enhance adhesion.

As a more preferred form of the (meth)acrylic copolymer (a), one type of structural unit derived from a chain or branched (meth)acrylic acid alkyl ester monomer having 1 to 4 carbon atoms in the alkyl group A combination of the above and one or more structural units derived from a chain or branched (meth)acrylic acid alkyl ester monomer having an alkyl group having 8 to 12 carbon atoms may be mentioned. Preferred combinations include methyl (meth)acrylate and n-butyl (meth)acrylate as (a-1), and 2-ethylhexyl (meth)acrylate and dodecyl (meth)acrylate as (a-2). can be exemplified.

The (meth)acrylic copolymer (a) 100% by mass, the structural unit derived from the (meth)acrylic acid alkyl ester containing a linear or branched alkyl group is preferably 10 to 100% by mass, and 20 to 100% by mass. 90% by mass is more preferable, and 30 to 80% by mass is even more preferable.

As a monomer used for the (meth)acrylic copolymer (a), a (meth)acrylic acid alkyl ester monomer (a-3) having a cyclic alkyl group is also suitably used. Examples of such monomers include cyclohexyl (meth)acrylate, 4-n-butylcyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. . Among these, cyclohexyl (meth)acrylate and isobornyl (meth)acrylate are particularly preferable from the viewpoint of flexibility and adhesive strength.

The ratio (a-2) / (a-1) of the monomer (a-2) to the monomer (a-1) is more effective for air bubbles and wrinkles during folding under low temperature, normal temperature, and high temperature conditions. 0.9 to 20 is preferable, 1 to 20 is more preferable, 3 to 20 is still more preferable, and 4 to 20 is particularly preferable from the viewpoint of exerting to.

Among the monomers (a-2), the combined use of a chain or branched (meth)acrylic acid alkyl ester having 12 carbon atoms in the alkyl group and the monomer (a-1) is effective from the viewpoint of the recovery rate. preferred. Further, from the viewpoint of the recovery rate, a chain or branched (meth)acrylic acid alkyl ester monomer (a-1) having an alkyl group having 1 to 6 carbon atoms and an alkyl group having a carbon number of In addition to the combined use of 8 to 12 chain or branched (meth)acrylic acid alkyl ester monomers (a-2), combined use of the monomer (a-3) is preferred.

Examples of functional group-containing monomers include carboxy group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, and amino group-containing monomers. Containing a functional group-containing monomer improves the cohesive strength of the adhesive, resulting in a tough adhesive layer.

Carboxy group-containing monomers include, for example, (meth)acrylic acid, β-carboxyethyl (meth)acrylate, p-carboxybenzyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, Acids include crotonic acid, citraconic acid and isocrotonic acid. Among these, (meth)acrylic acid is preferable from the viewpoint of cohesive strength and adhesive strength.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, (meth) ) 4-hydroxybutyl acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and ( meth)acrylic acid (4-hydroxymethylcyclohexyl)methyl ester. Among these, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are more preferable from the viewpoint of cohesive strength and adhesive strength.

Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and 6-methyl-3,4-(meth)acrylate. Epoxycyclohexylmethyl may be mentioned.

Examples of amino group-containing monomers include (meth)acrylates such as monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, monomethylaminopropyl (meth)acrylate, and monoethylaminopropyl (meth)acrylate. ) acrylic acid monoalkylamino esters.

From the viewpoint of tack, the Tg (DSC) of the (meth)acrylic copolymer (a) is preferably −70° C.<Tg<−35° C. More preferably -65 to -40°C, more preferably -65 to -50°C.

The total amount of structural units derived from functional group-containing monomers is preferably 1 to 20% by mass with respect to 100% by mass of the (meth)acrylic copolymer (a). By setting it within the above range, the cohesive force can be adjusted by the reaction with the curing agent, and the flexibility and recovery rate can be enhanced.
The (meth)acrylic copolymer (a) preferably contains 1 to 10% by mass of structural units derived from a carboxy group-containing monomer relative to 100% by mass. By being within the above range, both the cohesive strength and relaxation properties of the adhesive layer can be achieved. Further, the structural unit derived from the hydroxyl group-containing monomer is preferably 1 to 10% by mass with respect to 100% by mass of the (meth)acrylic copolymer (a). By being within the above range, both adhesion and heat resistance of the adhesive layer can be achieved.

The (meth)acrylic copolymer (a) may contain structural units derived from other monomers copolymerizable with the above-mentioned monomers. Other monomers include, for example, monomers having an alkyleneoxy group and other vinyl monomers. Further, methoxyethyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, vinyl acetate, vinyl crotonate, styrene, acrylonitrile, and acrylamide can be exemplified. The structural unit derived from the other monomer is preferably 0.1 to 20% by mass in 100% by mass of the (meth)acrylic copolymer (a).

The (meth)acrylic copolymer (a) is obtained by polymerizing a monomer mixture. At the time of polymerization, a polymerization initiator is used as necessary. The content of the polymerization initiator is, for example, 0.01 to 10 parts by mass with respect to 100 parts by mass of the monomer mixture. The polymerization method is not limited. For example, it can be polymerized by solution polymerization, bulk polymerization, emulsion polymerization and suspension polymerization. Examples of solvents used in solution polymerization include acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is, for example, 60 to 120° C., and the polymerization time is about 2 to 12 hours.

The adhesive resin may contain other resins than the (meth)acrylic copolymer (a) within the scope of the present disclosure. Examples of other resins include rubber-based resins, silicone-based resins, urethane-based resins, polyamide resins, polyimide resins, polyester resins, and fluorine resins. These resins may be used alone or in combination of two or more.

2-2. Curing Agent The adhesive composition may contain a curing agent as described above. Examples of curing agents include isocyanate compounds, epoxy compounds, aziridine compounds, carbodiimide compounds, metal chelates, and the like. The curing agent may be a low-molecular-weight compound or a high-molecular-weight compound. When the functional group is a hydroxy group or a carboxy group, isocyanate compounds and epoxy compounds are preferred, and among these, isocyanate compounds are preferred from the viewpoint of achieving both high cohesion and adhesion.

Among isocyanate curing agents, aromatic-containing isocyanates are more preferred. A better recovery rate can be obtained by using a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (a) and an aromatic-containing isocyanate curing agent. From the viewpoint of compatibility between the (meth)acrylic copolymer (a) and the curing agent, an isocyanate curing agent (b) having an aromatic ring such as an aromatic polyisocyanate or an araliphatic polyisocyanate is preferred.

An isocyanate compound is an isocyanate having two or more isocyanate groups. Isocyanate compounds are preferably isocyanate monomers such as aromatic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates and alicyclic polyisocyanates, and burettes, nurates and adducts thereof.

Aromatic polyisocyanates are, for example, 1,3-phenylene diisocyanate, 4,4'-diphenyldiisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6- tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanatotoluene, 1,3,5-triisocyanatobenzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4',4 ''-triphenylmethane triisocyanate.

Aliphatic polyisocyanates include, for example, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate and 2,4,4-trimethylhexamethylene diisocyanate.

Aroaliphatic polyisocyanates are, for example, ω,ω′-diisocyanate-1,3-dimethylbenzene, ω,ω′-diisocyanate-1,4-dimethylbenzene, ω,ω′-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate and 1,3-tetramethylxylylene diisocyanate.

Alicyclic polyisocyanates include, for example, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4 -cyclohexanediisocyanate, methyl-2,4-cyclohexanediisocyanate, methyl-2,6-cyclohexanediisocyanate, 4,4'-methylenebis(cyclohexylisocyanate), 1,4-bis(isocyanatomethyl)cyclohexane.

The burette body is a self-condensed product having a burette bond formed by self-condensation of an isocyanate monomer. The burette body includes, for example, a burette body of hexamethylene diisocyanate.

The nurate compound is a trimer of isocyanate monomers. Examples thereof include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, a trimer of tolylene diisocyanate, and the like.

The adduct is a bifunctional or higher isocyanate compound obtained by reacting an isocyanate monomer and a bifunctional or higher low-molecular-weight active hydrogen-containing compound. Adducts include, for example, a compound obtained by reacting trimethylolpropane and hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane and tolylene diisocyanate, a compound obtained by reacting trimethylolpropane and xylylene diisocyanate, trimethylol A compound obtained by reacting propane with isophorone diisocyanate and a compound obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate can be mentioned.

The isocyanate compound is preferably a trifunctional isocyanate compound from the viewpoint of forming a sufficient crosslinked structure. The isocyanate compound is more preferably an adduct or a nurate which is a reaction product of an isocyanate monomer and a trifunctional low-molecular-weight active hydrogen-containing compound. Isocyanate compounds include trimethylolpropane adduct of hexamethylene diisocyanate, nurate of hexamethylene diisocyanate, trimethylolpropane adduct of tolylene diisocyanate, nurate of tolylene diisocyanate, trimethylolpropane adduct of isophorone diisocyanate, and isophorone diisocyanate. A nurate compound is preferred, and a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, and a trimethylolpropane adduct of isophorone diisocyanate are more preferred.

Epoxy compounds include, for example, glycerol diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'- diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidylaminophenylmethane.

Aziridine compounds include, for example, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, 4, 4'-bis(ethyleneiminocarbonylamino)diphenylmethane is mentioned.

The carbodiimide compound is preferably a high-molecular-weight polycarbodiimide produced by a decarboxylation condensation reaction of a diisocyanate compound in the presence of a carbodiimidation catalyst. Carbodilite series manufactured by Nisshinbo Co., Ltd. is preferable as the commercial product of the high-molecular-weight polycarbodiimide. Among them, Carbodilite V-03, 07 and 09 are preferable because of their excellent compatibility with organic solvents.

Metal chelates are preferably coordination compounds of polyvalent metals such as, for example, aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium, with acetylacetone or ethyl acetoacetate. Examples of metal chelates include aluminum ethylacetoacetate/diisopropylate, aluminum trisacetylacetonate, aluminum bisethylacetoacetate/monoacetylacetonate, and aluminum alkylacetoacetate/diisopropylate.

The curing agent is preferably contained in an amount of 0.001 to 1 part by mass, more preferably 0.01 to 0.1 part by mass, based on 100 parts by mass of the (meth)acrylic copolymer (a). When the content is 0.001 part by mass or more, the cohesive force is further improved, and when the content is 1 part by mass or less, cohesive force and flexibility are easily compatible, which is preferable.

2-3. Polymerization Initiator The polymerization initiator is preferably a radical polymerization initiator. Peroxides and azo compounds are suitable as radical polymerization initiators. 2,2'-azobisbutyronitrile such as 2,2'-azobisisobutyronitrile (abbreviation: AIBN), 2,2'-azobis(2-methylbutyronitrile); 2,2′-azobisvaleronitrile such as ,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis(2,4-dimethylvaleronitrile); - 2,2'-azobispropionitrile such as azobis(2-hydroxymethylpropionitrile); 1,1'-azobis-1-alkanes such as 1,1'-azobis(cyclohexane-1-carbonitrile) Nitriles may be mentioned. Peroxides are, for example, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, 2,5- Dialkyl peroxides such as di(t-butylperoxy)hexyne-3; t-butylperoxybenzoate, t-butylperoxyacetate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane Peroxy esters; ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl-4,4-bis(t-butylperoxy ) peroxyketals such as barate; hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylcyclohexane-2,5-dihydroperoxide; benzoyl peroxide, decanoyl peroxide, diacyl peroxides such as lauroyl peroxide and 2,4-dichlorobenzoyl peroxide; and peroxydicarbonates such as bis(t-butylcyclohexyl)peroxydicarbonate.

2-4. Hard segment If necessary, the adhesive composition may contain a hard segment to form a sea-island microphase-separated structure in the adhesive layer. The hard segment has a higher Tg than the soft segment and consists of non-crosslinked bead-like particles. Examples of bead-like particles include (meth)acrylic resins, polystyrene resins, polyethylene resins, epoxy resins, and silicone resins. A resin having excellent compatibility with the adhesive resin is preferred. From this point of view, it is preferable to use the same kind of resin. From the viewpoint of compatibility, it is preferable to combine the (meth)acrylic copolymer (a) as the soft segment with the (meth)acrylic resin as the hard segment.

2-5. Other Additives The present pressure-sensitive adhesive composition may further contain solvents, tackifiers, silane coupling agents, fillers, colorants, antioxidants, antistatic agents, ultraviolet absorbers, etc., as necessary. good.

Examples of solvents include esters such as ethyl acetate, propyl acetate and butyl acetate, and ketones such as acetone, methyl ethyl ketone and cyclohexanone. In addition, aromatic hydrocarbons such as toluene, xylene, benzene, solvent naphtha, cyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, trimethylcyclohexane, ethylcyclohexane, diethylcyclohexane, decahydronaphthalene, bicycloheptane, tricyclodecane, hexahydro Aliphatic hydrocarbons such as indenecyclohexane, cyclooctane, α-pinene, terpinolene, and limonene. Solvents may be used alone or in combination.

Tackifiers include adhesive compounds having a weight-average molecular weight of 10,000 or less. For example, rosin resin, polymerized rosin resin, rosin ester resin, polymerized rosin ester resin, terpene resin, terpene phenol resin, coumarone resin, coumarone indene resin, styrene resin, xylene resin, phenol resins, petroleum-based resins, and the like. Among these, rosin-based resins, polymerized rosin-based resins, rosin ester-based resins, and polymerized rosin ester-based resins are preferred because they have good compatibility with the (meth)acrylic copolymer (a) and can further improve adhesive performance. Rosin ester-based resins and polymerized rosin ester-based resins are more preferred. The tackifying resin is preferably used in an amount of 0.01 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (a). A high adhesive strength can be obtained by using 0.01 to 10 parts by mass of the tackifying resin.

Silane coupling agents include, for example, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropyltripropoxysilane, 3-(meth)acryloxysilane alkoxysilane compounds having a (meth)acryloxy group, such as roxypropyltributoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane;
alkoxysilane compounds having a vinyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane;
3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltripropoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)- 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl) -Alkoxysilane compounds having an amino group such as 3-aminopropylmethyldiethoxysilane and N-phenyl-3-aminopropyltrimethoxysilane;
Alkoxysilane compounds having a mercapto group such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltripropoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane;
3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyltripropoxysilane, 3-glycidoxypropyltributoxysilane, 3-glycidoxypropylmethyldimethoxysilane, Alkoxysilane compounds having an epoxy group such as 3-glycidoxypropylmethyldiethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane;
Tetraalkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane;
3-chloropropyltrimethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, styryltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate, 3-isocyanatopropyltrimethoxysilane, 3-isocyanatopropyl Examples include triethoxysilane, hexamethyldisilazane, and silicone resins having alkoxysilyl groups in the molecule.

The silane coupling agent is preferably used in an amount of 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (a).

Optical properties and mechanical properties can be adjusted by adding fillers. Examples of fillers include inorganic white pigments such as silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, and titanium dioxide.

3. First Release Sheet and Second Release Sheet The adhesive layer is sandwiched between the first release sheet and the second release sheet. Wa to We of the adhesive layer are also affected by the release sheet of the adhesive layer, particularly the release layer of the second release sheet.
The release force of the first release sheet 1 and the second release sheet 2 can be adjusted by release treatment of the sticking surface of each release sheet to the adhesive layer. For example, the release force can be adjusted by the type of release agent. Also, the release force can be adjusted by the amount of the release agent applied. Furthermore, it can be adjusted by the surface roughness of the release layer. It can also be adjusted by the adhesive composition forming the adhesive layer. If you want to increase the peeling force, it is effective to smooth the surface roughness, increase the amount of release agent applied, etc. If you want to weaken the peeling force, you can adjust the reverse .

The first release sheet and the second release sheet can be arbitrarily selected, and the same release sheet may be used. From the viewpoint of handling, it is preferable that the first release sheet is a light release sheet and the second release sheet is a heavy release sheet. It is preferable that the thickness Tl of the light release sheet is 25 to 100 μm and the thickness of the heavy release sheet is 50 to 188 μm, and that Tl<Th. Moreover, when it is set as an adhesive sheet roll, it is preferable to provide a light release sheet on the outer side of the roll.

The peel force Pl when the first release sheet is peeled from the adhesive layer at a peel angle of 180 ° and a peel speed of 300 mm / min in an environment of 23 ° C. and a relative humidity of 50% can be adjusted as appropriate, but the adhesive layer may lift or partially peel. From the viewpoint of effectively suppressing tunneling phenomena such as the above, it is preferable to set it to 0.02 to 0.30 N/25 mm. In addition, from the viewpoint of effectively suppressing the phenomenon of tearing between the adhesive layer and the second release sheet, after peeling the first release sheet from the adhesive layer, the second release sheet is further removed from the adhesive layer at 23 ° C. and relative humidity. In a 50% environment, the peel force Ph when peeled at a peel angle of 180° and a peel speed of 300 mm / min is in a relationship with the peel force Pl. It is preferable to set it to 10 to 0.80 N/25 mm.

Examples of the first release sheet and the second release sheet include polyethylene sheet, polypropylene sheet, polybutene sheet, polybutadiene sheet, polymethylpentene sheet, polyvinyl chloride sheet, vinyl chloride copolymer sheet, polyethylene terephthalate sheet, and polyethylene naphthalate. Sheet, polybutylene terephthalate sheet, polyurethane sheet, ethylene vinyl acetate sheet, ionomer resin sheet, ethylene/(meth)acrylic acid copolymer sheet, ethylene/(meth)acrylate copolymer sheet, polystyrene sheet, polycarbonate sheet, A polyimide sheet and a fluororesin sheet can be exemplified. The first release sheet may be a single layer or a laminate.

In addition to using a sheet having releasability for the first release sheet 1 and/or the second release sheet 2 itself, releasability may be imparted by coating a release agent on the joint surface with the adhesive layer 3. good. As the release agent, for example, there is a method of applying an alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, or wax-based release agent. The release force can be adjusted by changing the type of release agent.

The release layer is preferably formed by applying a release agent composition onto a release substrate. The release agent can contain a solvent when applied to form the release layer. Examples of solvents include, but are not limited to, hydrocarbon solvents such as normal hexane, cyclohexane, and normal heptane; aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate and methyl acetate; ketone solvents; and organic solvents such as alcohol solvents such as methanol, ethanol and butanol.

A micro gravure coater, a gravure coater, and the like are available as methods for applying the release agent. The release agent is applied in a solid content of 0.1 to 2.0 g/m ² , preferably 0.5 to 1.2 g/m ² , and cured to form a release layer. .

As the curing method, heat curing is preferred in order to facilitate curing. Although the curing temperature is not particularly limited, 80 to 130°C is preferable. When the temperature is 80° C. or higher, long-time heating is not required for sufficient curing, and productivity is enhanced. In addition, when the temperature is less than 130° C., it is possible to reduce the generation of wrinkles due to heat in the base material or the release base material. The thickness of the release layer is not particularly limited. For example, it is about 0.1 to 2 μm.

4. Production of double-sided pressure-sensitive adhesive sheet The double-sided pressure-sensitive adhesive sheet of the present disclosure can be produced by a known method. For example, a step of applying the adhesive composition on the second release sheet to form a film and curing to form an adhesive layer, and attaching the first release sheet to one exposed surface of the adhesive layer, Adhesive sheets can be manufactured. A roll sheet is obtained by winding the obtained double-sided pressure-sensitive adhesive sheet into a roll.

Coating can be performed by, for example, a micro gravure coater, gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, rod blade coater, knife coater, spray coater, die coater, or curtain coater. When the adhesive composition contains a solvent, the solvent is removed by a drying step after coating. Curing is performed, for example, by aging. In the case of a photocurable pressure-sensitive adhesive composition, it is cured by irradiation with UV or the like.

A double-sided pressure-sensitive adhesive sheet roll can be obtained by winding the double-sided pressure-sensitive adhesive sheet around a winding core after manufacturing the double-sided pressure-sensitive adhesive sheet or while manufacturing the double-sided pressure-sensitive adhesive sheet. The winding length can be designed according to the application. From the viewpoint of increasing productivity, the length is preferably 50 m or more, more preferably 100 m or more. The winding length is preferably 2500 m or less from the viewpoint of production yield.

In addition, the adhesive layer is applied to the release surfaces of the first release sheet and the second release sheet so that the thickness after drying becomes a predetermined thickness, and after forming two adhesive layers, each adhesive layer You may manufacture by the method of sticking.

5. Laminate for Image Display Device In the laminate for image display device of the present disclosure, adherends are bonded to each other via the adhesive layer of the double-sided pressure-sensitive adhesive sheet. This laminate for image display devices is formed using a substrate-less double-sided pressure-sensitive adhesive sheet that can suppress wrinkles and air bubbles even when applied to flexible displays. and other optical elements. A flexible display is a bendable display, such as an organic electroluminescence (organic EL) display, an electrophoretic display (electronic paper), a liquid crystal display using a plastic substrate (film) as a substrate, and a foldable folder. A bull display can be exemplified.

The adhesive layer formed from this adhesive sheet is suitable for bonding flexible members (adherends) to each other. For example, liquid crystal polymer sheet, luminescent polymer sheet, sheet liquid crystal module, organic EL module (organic EL sheet), electronic paper module, transparent conductive sheet, metal mesh sheet, sheet sensor, cover sheet, barrier film, polarizing film, polarized light It is suitable for adhering members of any combination of a layer, a retardation film, a viewing angle compensation film, a brightness enhancement film, a contrast enhancement film, a diffusion film, a transflective film, and an electrode film.

The present disclosure will be described in more detail below based on examples. However, the present disclosure is not limited by these. Unless otherwise specified, "part" in the examples indicates "mass part" and "%" indicates "% by mass". A blank column in the table indicates that it was not blended.

(a) Measurement method Numerical values obtained in the present examples are values obtained by the following methods.
a-1. Tg of (meth)acrylic copolymer (a)
The Tg of the adhesive resin was measured by a robot DSC (differential scanning calorimeter, "RDC220" manufactured by Seiko Instruments Inc.). About 2 mg of the sample is placed in an aluminum pan, weighed, set in a differential scanning calorimeter, held at 100 ° C. for 5 minutes with the same type of aluminum pan without a sample as a reference, and then -120 ° C. using liquid nitrogen. quenched to Thereafter, the temperature was raised at a rate of temperature increase of 5°C/min, and the Tg (°C) of the adhesive resin was determined from the obtained DSC chart.

a-2. Tg of adhesive layer
The first release sheet and the second release sheet were peeled off from the double-sided pressure-sensitive adhesive sheet of each example and comparative example produced by the method described later, 2 mg of the pressure-sensitive adhesive layer was placed in an aluminum pan, weighed and set in a differential scanning calorimeter, and the sample As a reference, the same type of aluminum pan without any gas was kept at 100° C. for 5 minutes and then rapidly cooled to −120° C. using liquid nitrogen. Thereafter, the temperature was raised at a rate of temperature increase of 5°C/min, and the Tg (°C) of the adhesive resin was determined from the obtained DSC chart.

a-3. Weight Average Molecular Weight Mw and Molecular Weight Dispersity Mw/Mn of Adhesive Resin
Mw was measured using GPC "LC-GPC System" manufactured by Shimadzu Corporation, and Mw and molecular weight distribution Mw/Mn were obtained by converting polystyrene having a known molecular weight as a standard substance.
Apparatus name: LC-GPC system "Prominence" manufactured by Shimadzu Corporation
Column: 4 GMHXL manufactured by Tosoh Corporation and 1 HXL-H manufactured by Tosoh Corporation were connected.
Mobile phase solvent: Tetrahydrofuran Flow rate: 1.0 mL/min Column temperature: 40°C

a-4. Double-sided adhesive sheet thickness Tt, adhesive layer thickness Ta, first release sheet thickness Tl, second release sheet thickness Th
Determine 10 points that are equally spaced from the end of the width direction of the double-sided adhesive sheet (first release sheet/adhesive layer/second release sheet) to the other end, measure the thickness of the 10 points, and calculate the average value. Tt. The end portion refers to the end portion of the region where the first release sheet/adhesive layer/second release sheet are laminated. Next, the first release sheet was peeled off from the double-sided pressure-sensitive adhesive sheet, and the thickness of the peeled first release sheet was measured at 10 locations corresponding to the same positions as above. Let the average value be Tl. After that, the second release sheet was further peeled off from the adhesive layer, and the thickness of the peeled second release sheet was measured at 10 locations corresponding to the same positions as above. Let the average value be Th. The thickness Ta of the adhesive layer was obtained from Tt-Tl-Th.
In Reference Example 1 described later, the thickness Tt of the single-sided PSA sheet was measured in the same manner as the double-sided PSA sheet, the thickness Tl of the release sheet was measured in the same manner as the first release sheet, and the adhesive layer was optionally removed from the base film. The thickness Th of the base film was measured in the same manner as in the case of the second release sheet.

a-5. Measurement of the reflection intensity Wa to We of the adhesive layer Peel off the first release sheet of the double-sided adhesive sheet cut to 20 mm in width and 200 mm in length, and place a 200 mm wide, 120 mm long, and 1.1 mm thick A glass plate (blue plate glass, manufactured by Kawamura Kyuzo Shoten Co., Ltd.) was attached, and the glass plate was placed on thick white drawing paper (P156J, manufactured by Jointex Co., Ltd.) to obtain a measurement sample. The surface of the adhesive layer exposed by peeling off the second release sheet of the measurement sample is scanned in the length direction by 150 mm or more using a wave scan device (wave-scan 3dual, manufactured by BYK Gardner). ~We were measured.
In Reference Example 1, the film substrate was placed on the glass plate having a thickness of 1 mm, and the glass plate was placed on the white drawing paper (thick) to obtain the measurement sample. It was measured in the same manner as in Example 1.

a-6. Measurement of Solid Content The mass (W0) of the aluminum cup was weighed with a precision balance. Next, about 1 g of the sample solution was placed in an aluminum cup, and the mass (W1) of the sample in the aluminum cup was measured using a precision balance. After heating the sample in the aluminum cup in an oven at 150° C. for 2 hours, it was taken out from the oven and returned to room temperature. The residual mass (W2) of the sample in the aluminum cup after heating was measured with a precision balance. Then, the solid content was calculated by the formula (W2-W0)/(W1-W0)×100(%).

a-7. Storage Modulus Two sets of double-sided PSA sheets were prepared by removing the first release sheet, and the adhesive layers were laminated together using a laminator to prepare a laminate of second release sheet/adhesive layer/second release sheet. The second release sheet on one side of the laminate was peeled off, and the adhesive layers were successively adhered to each other to form an adhesive layer laminate having a thickness of 1 mm. Using a rheometer (DHR-2, manufactured by TA Instruments Co., Ltd.), a strain of 0.1%, a frequency of 1 Hz, and a heating rate of 10°C from -70°C to 200°C were applied to this laminate. The storage elastic modulus G' was measured under the condition of /min. From the data obtained, the measured values were read at temperatures of 0°C, 23°C, and 40°C.

a-8. Measurement of gel fraction The double-sided adhesive sheet was cut into a size of 30 mm × 100 mm, the first release sheet was peeled off, and the exposed adhesive layer was attached to a weighed 300-mesh stainless steel wire mesh (mass W0). A sample was obtained by peeling off the release sheet. The mass obtained by weighing this sample was defined as W1. The sample was then allowed to stand in ethyl acetate for 24 hours and then dried at 100° C. for 1 hour. After that, the weighed mass was taken as W2. The gel fraction was calculated from the following formula.
Gel fraction (%) = {(W2-W0)/(W1-W0)} x 100

(b) Production example of (meth)acrylic copolymer (a) b-1. (Meth) acrylic copolymer (R1)
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen inlet tube (hereinafter simply referred to as "reaction vessel") was charged with 80 parts of ethyl acetate (EtAc) and butyl acrylate (BA). 30 parts, 2-ethylhexyl acrylate (2EHA) 35 parts, isobornyl acrylate (IBXA) 30 parts, 4-hydroxybutyl acrylate (4HBA) 5 parts, 2,2'-azobisisobutyronitrile as an initiator (Hereinafter, simply referred to as "AIBN".) 0.1 part was charged, and the atmosphere in the reaction vessel was replaced with nitrogen gas. After that, the reaction was started by heating to 65° C. while stirring in a nitrogen atmosphere. After that, the reaction solution was reacted at 65° C. for 4 hours. After completion of the reaction, the reaction mixture was cooled and diluted with ethyl acetate (EtAc) to obtain a (meth)acrylic copolymer (R1) solution having a solid content of 50%. The resulting copolymer (R1) had an Mw of 1,000,000 and a Tg of -39°C.

(Meth)acrylic copolymers (R2 to R7) were produced in the same manner as the production of the (meth)acrylic copolymer (R1) except that the composition and amount (parts by mass) shown in Table 1 were changed. .

Abbreviations in the table are as follows.
(Chained or branched (meth)acrylic acid alkyl ester monomer)
MA: methyl acrylate (1 carbon number of alkyl group)
BA: n-butyl acrylate (alkyl group has 4 carbon atoms)
2EHA: 2-ethylhexyl acrylate (alkyl group with 8 carbon atoms)
2EHMA: 2-ethylhexyl methacrylate (alkyl group has 8 carbon atoms)
DOA: dodecyl acrylate (alkyl group has 12 carbon atoms)
(Other monomers)
IBXA: isobornyl acrylate CHA: cyclohexyl acrylate AA: 4HBA acrylic acid: 4-hydroxybutyl acrylate

(c) Preparation of adhesive composition c-1. Production of adhesive composition C1 (Meth) acrylic copolymer (R1 (solid content 100 parts, xylylene diisocyanate (XDI) (Takenate D-110N, manufactured by Mitsui Chemicals, Inc.) as a curing agent 0.1 part , 0.1 part of a silane coupling agent (KBM-303, manufactured by Shin-Etsu Silicone Co., Ltd.) as an additive, and ethyl acetate (EtAc) so that the solid content is 25%. C1 was obtained.

c-2. Production of pressure-sensitive adhesive compositions C2 to C11 The pressure-sensitive adhesive composition was prepared in the same manner as for pressure-sensitive adhesive composition C1, except that the types of (meth)acrylic copolymer, curing agent, and additive were changed as shown in Table 2. C2-C11 were obtained. As for C3, the solid content was appropriately adjusted according to the examples described later.

Abbreviations in the table are as follows.
(curing agent)
XDI: xylylene diisocyanate (Takenate D-110N, manufactured by Mitsui Chemicals)
TDI: toluene diisocyanate (Cosmonate T100, manufactured by Mitsui Fine Chemicals, Inc.)
HDI: hexamethylene diisocyanate (trimethylolpropane adduct) (Takenate D-160N, manufactured by Mitsui Chemicals)
EP: Epoxy curing agent (E-5XM, manufactured by Soken Chemical Co., Ltd.)
SC: Silane coupling agent (KBM-303, manufactured by Shin-Etsu Silicone Co., Ltd.)
TF: Tackifier (D-125, manufactured by Arakawa Chemical Industries, Ltd.)

(d) Production example of double-sided pressure-sensitive adhesive sheet d-1. Example 1
On the release layer of the second release sheet (heavy release polyethylene terephthalate separator) having a thickness of 75 μm and a width of 30 cm, the adhesive composition C1 is applied so that the thickness of the adhesive layer after drying is 50 μm and the width is 20 cm. It was coated at a speed of 10 m/min using a die coater and dried in a hot air oven at 120°C for 2 minutes to form an adhesive layer. Next, a release layer of a first release sheet (light release polyethylene terephthalate separator) having a thickness of 50 μm and a width of 30 cm was adhered to the adhesive layer to prepare a double-sided adhesive sheet. The obtained double-sided pressure-sensitive adhesive sheet was wound up to a length of 50 m under a tension of 50 N while taking care not to wrinkle an ABS core having a diameter of 3 inches to prepare a roll-shaped double-sided pressure-sensitive adhesive sheet. The produced roll-shaped double-sided pressure-sensitive adhesive sheet was aged for one week at a temperature of 40° C. and a relative humidity of 50%. After that, it was unwound from the outer winding side of the roll, starting from the 5 m unwound position, further unwound 50 cm in the longitudinal direction, and cut out to obtain an outer-wound double-faced PSA sheet of 30 cm in width x 50 cm in the longitudinal direction.
Separately, starting from the position 5 m from the end of the double-sided adhesive sheet on the inner winding side (rolling core side) of the roll, cut up to 50 cm in the longitudinal direction toward the outer winding side, and cut both sides of the inner winding of 30 cm in width x 50 cm in the longitudinal direction. A sticky sheet was obtained.

d-2. Examples 2-35, Comparative Examples 1-6
Double-sided pressure-sensitive adhesive sheets according to Examples 2-35 and Comparative Examples 1-6 were obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive compositions and coating conditions were changed to those shown in Tables 3-5.

d-3. Reference example 1
On the release layer of a release film (manufactured by Toray Advanced Film Co., Ltd., BX8A) with a thickness of 75 μm and a width of 30 cm, the pressure-sensitive adhesive composition C9 is applied using a die coater so that the thickness after drying becomes 50 μm and the width becomes 20 cm. An adhesive layer was formed by coating at a speed of 10 m/min and drying for 2 minutes in a hot air oven at 120°C. Next, a film substrate (U403, manufactured by Toray Industries, Inc.) having a thickness of 23 μm and a width of 30 cm was adhered to the adhesive layer to prepare a single-sided adhesive sheet. The obtained single-sided pressure-sensitive adhesive sheet with a substrate was wound up to a length of 50 m under a tension of 50 N while taking care not to wrinkle an ABS core having a diameter of 3 inches to prepare a roll-shaped single-sided pressure-sensitive adhesive sheet. The produced roll-shaped single-sided pressure-sensitive adhesive sheet was aged for one week under conditions of a temperature of 40° C. and a relative humidity of 50%. Thereafter, in the same manner as in Example 1, an outer-wound single-sided PSA sheet and an inner-wound single-sided PSA sheet were obtained.

(e) Evaluation of double-sided pressure-sensitive adhesive sheets, etc. The double-sided pressure-sensitive adhesive sheets of Examples and Comparative Examples and the single-sided pressure-sensitive adhesive sheets of Reference Examples were evaluated as follows. The results are shown in Tables 3-5. In the examples and comparative examples, the first release sheet is a so-called light release sheet, and the second release sheet is a so-called heavy release sheet.
e-1. Evaluation of Visibility The double-faced pressure-sensitive adhesive sheet of each example and comparative example was cut into a size of 80 mm×40 mm, the first release sheet was peeled off, and the cut sheet was attached to a glass plate. Further, the second release sheet was peeled off and attached to an organic EL module (REC001602A-W manufactured by Teidek Co., Ltd.) to form a display. The display displayed white characters (a total of 32 characters consisting of uppercase letters A to P and lowercase letters a to p) on a black background, and was placed on a horizontal table. The observer observed the display light from three angles, 30°, 45°, and 90° from the horizontal. An observer visually compared and evaluated the distortion of the image displayed on the display and the blurring of the outline before and after the double-sided pressure-sensitive adhesive sheet was attached.
For Reference Example 1, the release sheet was peeled off, the module was attached to an organic EL module (REC001602A-W manufactured by Teidek Co., Ltd.), and a glass plate was placed on the base film to form a display in the same manner as in Example 1. evaluated with
The evaluation criteria were as follows. 3 or more is good, and 2 is practical.
5: Distortion and contour bleeding are not observed under any angle conditions.
4: Slight distortion and/or outline bleeding is observed at any one angle condition.
3: Slight distortion and/or contour bleeding is observed at any two angle conditions.
2: Distortion and/or blurring of the contour is slightly observed under all angle conditions, but there is no practical problem.
1: Under any one or more angle conditions, distortion and/or contour bleeding is seen beyond the range of "slightly", and many characters are difficult to distinguish.
In the above description, "slightly" means that 2 characters or less out of 32 characters are difficult to distinguish due to distortion and blurred contours.

e-2. Evaluation of air bubbles and wrinkles (roll) Cut out four 10 cm squares from arbitrary portions of the double-sided pressure-sensitive adhesive sheet of each example, comparative example, and reference example, and visually check for the presence or absence of air bubbles and wrinkles derived from roll storage. Observed.
Evaluation criteria are as follows. 3 or more is good, and 2 is practical.
5: No bubbles and wrinkles of 1 mm or more are observed on all four double-sided pressure-sensitive adhesive sheets.
4: No bubbles and wrinkles of 1 mm or more are observed in the 3 double-sided pressure-sensitive adhesive sheets.
3: No bubbles and wrinkles of 1 mm or more are observed on the two double-sided pressure-sensitive adhesive sheets.
2: No air bubbles and wrinkles of 1 mm or more are observed in one double-sided pressure-sensitive adhesive sheet.
1: Bubbles and wrinkles of 1 mm or more are observed in all double-sided pressure-sensitive adhesive sheets.

e-3. Evaluation of Air Bubbles and Wrinkles (Folding) The first release sheet was peeled off from the double-sided pressure-sensitive adhesive sheet of each example and comparative example, and the exposed pressure-sensitive adhesive layer was laminated on a polyimide film.
Then, the second release sheet was peeled off from the adhesive layer, and the exposed adhesive layer was laminated to an easily adhesive PET film. The laminate was placed in an autoclave and held at 50°C for 20 minutes. Next, the laminate was taken out and allowed to stand at 25° C. and 50% RH for 30 minutes, and then cut into a size of 70 mm in width and 100 mm in length. got
Next, the laminate for test was folded in a planar body no-load twist tester (manufactured by Yuasa System Co., Ltd.) in an atmosphere of 23° C. and 50% RH, and then returned to the state before folding. 10,000 cycles were repeated. The test was conducted with N=5, and the appearance after the test was visually evaluated. For Reference Example 1, evaluation was performed in the same manner as in Example 1, except that the release sheet was peeled off to obtain an adhesive layer with a film substrate, and the exposed adhesive layer was laminated to a polyimide film. Evaluation criteria are as follows.
No air bubbles or wrinkles are seen in all 5:5 samples.
Bubbles and/or wrinkles were seen in the 4:1 sample.
Bubbles and/or wrinkles were seen in the 3:2 samples.
Bubbles and/or wrinkles were seen in the 2:3 samples.
Bubbles and/or wrinkles were seen in the 1:4 samples or all samples.
Bubbles and wrinkles (folding) were evaluated in the same manner except that the temperature was changed from 23°C to 0°C and 40°C. The evaluation criteria are the same as for 23°C.

Double-faced PSA sheets that do not satisfy both the reflection intensity Wa of 1 to 26 and the reflection intensity Wd of 0.3 to 8 have problems of reduced visibility, air bubbles, and wrinkles, as shown in Comparative Examples 1 to 4. was confirmed. In addition, the double-sided pressure-sensitive adhesive sheets that satisfy both companies with a reflection intensity Wa of 1 to 26 and a reflection intensity Wd of 0.3 to 8, but whose adhesive layer does not satisfy the above (i) to (iii) are shown in Comparative Examples 5 and 6. As shown in , problems were confirmed in air bubbles and wrinkles (folding). On the other hand, the double-sided pressure-sensitive adhesive sheet that satisfies both the reflection intensity Wa of 1 to 26 and the reflection intensity Wd of 0.3 to 8, and the adhesive layer satisfies the above (i) to (iii) is the first embodiment. As shown in 1 to 35, visibility was excellent, and wrinkles and air bubbles could be suppressed.

1: First release sheet 2: Second release sheet 3: Adhesive layer 4: Glass substrate 5: White paper 10: Double-sided adhesive sheets 31, 32: Surface

Claims (5)

A double-sided pressure-sensitive adhesive sheet for substrate-less flexible display applications, in which a first release sheet, an adhesive layer, and a second release sheet are laminated in this order,
A glass substrate is attached to the surface of the adhesive layer exposed by peeling off the first release sheet, and the glass substrate is placed on a blank sheet of paper, and then the surface of the adhesive layer exposed by peeling off the second release sheet is removed. When measured with a wave scan device,
The reflection intensity Wa in the wavelength range of 0.1 to 0.3 mm is 1 to 26, and the reflection intensity Wd in the wavelength range of 3 to 10 mm is 0.3 to 8,
The adhesive layer is
(i) cross-linking an adhesive layer containing a (meth)acrylic copolymer (a) having a weight average molecular weight of 1,000,000 to 1,800,000, and an adhesive composition containing the (meth)acrylic copolymer (a); is either one of the adhesive layers,
(ii) a storage modulus at 23° C. of 1×10 ³ to 8×10 ⁴ Pa;
(iii) A double-sided pressure-sensitive adhesive sheet having a glass transition temperature of -70°C ≤ Tg ≤ -35°C by DSC. A glass substrate is attached to the surface of the adhesive layer exposed by peeling off the first release sheet, and the glass substrate is placed on a blank sheet of paper, and then the surface of the adhesive layer exposed by peeling off the second release sheet is removed. When measured with a wave scan device,
2. The double-sided pressure-sensitive adhesive sheet according to claim 1, which has a reflection intensity Wc of 1-12 in the wavelength range of 1-3 mm and a reflection intensity We of 1-12 in the wavelength range of 10-30 mm. The (meth)acrylic copolymer (a) is a structural unit derived from a chain or branched (meth)acrylic acid alkyl ester monomer having an alkyl group having 1 to 6 carbon atoms, and an alkyl group having a carbon number of 2. The double-sided pressure-sensitive adhesive sheet according to claim 1, which has 7 to 12 chain or branched (meth)acrylic acid alkyl ester monomer-derived structural units. 2. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the (meth)acrylic copolymer (a) has a molecular weight distribution Mw/Mn of less than 5. 5. A laminate for an image display device, wherein adherends are joined via the adhesive layer of the double-sided adhesive sheet according to any one of claims 1 to 4.

Images