KR20120065472A - Adhesive composition for optical use - Google Patents

Abstract

PURPOSE: An adhesive composition for optics, an adhesive using thereof, and an adhesive film including thereof are provided to maintain coatability and adhesion and to manufacture thick adhesive film. CONSTITUTION: An adhesive composition for optics comprises 100 parts by weight of acrylate monomer, 50-120 parts by weight of urethane acrylate oligomer which includes ether group in a main chain, 70-150 parts by weight of unsaturated monomer which includes carboxy group, 0.1-20 parts by weight of free radical photo-initiator, 2.5-100 parts by weight of acrylate resin syrup. The acrylate-based monomer has 1 - 6 functionalities. The unsaturated monomer which includes carboxy group is from a group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid, and fumaric acid. The adhesive is manufactured by solidifying the adhesive composition. The adhesive film comprises a transparent base film and an adhesive formed in one side of the transparent base film.

Description

Optical adhesive composition {ADHESIVE COMPOSITION FOR OPTICAL USE}

The present invention relates to a pressure-sensitive adhesive composition for optics having a uniform thickness and excellent surface appearance while less hardening shrinkage occurs while maintaining the properties of the pressure-sensitive adhesive itself.

In general, a liquid crystal display device (LCD) includes a liquid crystal cell and a polarizing plate including liquid crystal, and an appropriate adhesive layer or an adhesive layer for bonding them should be used.

The pressure-sensitive adhesive layer (film) may be classified into a thin film type adhesive layer and a thick film type adhesive layer depending on the use of a solvent.

The double thick-film adhesive layer is generally prepared by photopolymerizing a composition containing an acrylate oligomer or a urethane acrylate oligomer.

However, the composition containing the acrylate oligomer has a problem that the curing process is too slow at the time of photopolymerization and the processability is low, and the composition containing the urethane acrylate oligomer has a fast curing process at the time of photopolymerization, but the physical properties of the adhesive layer such as adhesive force are lowered. There is a problem.

In addition, photopolymerization using a composition containing an oligomer having an acrylic functional group such as an acrylate oligomer and a urethane acrylate oligomer has a problem that the thickness of the pressure-sensitive adhesive layer is increased due to hardening shrinkage and the surface appearance is not good. .

The present invention is to provide a pressure-sensitive adhesive composition having a uniform thickness and excellent surface appearance due to less curing shrinkage during photopolymerization while maintaining the physical properties of the pressure-sensitive adhesive composition such as adhesion, coating properties.

The present inventors made an effort to achieve the above object. As a result, the ether group of the urethane acrylate oligomer provides flexibility of the adhesive to maintain an appropriate storage modulus, and improves the adhesive strength due to the strong polarity of the unsaturated monomer containing a carboxyl group, thereby reducing the occurrence of shrinkage during photocuring. In addition, it was found that high adhesion can be maintained to complete the present invention.

Therefore, the pressure-sensitive adhesive composition of the present invention is 100 parts by weight of the acrylate monomer, 50 to 120 parts by weight of the urethane acrylate oligomer containing an ether group in the main chain, 2.5 to 100 parts by weight of acrylate resin syrup, unsaturated monomer containing a carboxyl group 70 to 150 Parts by weight, and 0.1 to 20 parts by weight of free radical photoinitiator.

The acrylate monomer may be 1 to 6 functional.

The unsaturated monomer containing the carboxyl group may be at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid and fumaric acid.

Moreover, the adhesive of this invention is what hardened | cured the said adhesive composition.

In addition, the adhesive film of the present invention is a transparent substrate film; It includes the pressure-sensitive adhesive formed on one surface of the transparent base film.

The pressure-sensitive adhesive may be 25 to 1000㎛.

The pressure-sensitive adhesive composition of the present invention not only maintains coating properties and adhesive strengths equivalent to those of the related art, but also has less hardening shrinkage, so that the thickness is uniform and the surface appearance is excellent.

In addition, since the pressure-sensitive adhesive composition of the present invention does not contain a separate solvent, it is possible to manufacture a thick-film pressure-sensitive adhesive film.

The present invention relates to a pressure-sensitive adhesive composition for optics having a uniform thickness and excellent surface appearance while less hardening shrinkage occurs while maintaining the properties of the pressure-sensitive adhesive itself.

Hereinafter, the present invention will be described in detail.

The pressure-sensitive adhesive composition of the present invention comprises an acrylate monomer, a urethane acrylate oligomer comprising an ether group in the main chain, an acrylate resin syrup, an unsaturated monomer comprising a carboxyl group, a carboxylate and a free radical photoinitiator.

The acrylate monomer serves to provide viscoelasticity of the film including the pressure-sensitive adhesive composition and at the same time maintain an easy viscosity for coating the pressure-sensitive adhesive composition.

As the acrylate monomer, 1 to 6 functional acrylic monomers may be used, and specific examples thereof include ethyl acrylate, methyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, butyl acrylate and isobutyl acrylate. , Allyl methacrylate, 2-ethoxyethyl (meth) acrylate, isodecyl (meth) acrylate, 2-dodecylthioethyl methacrylate, octyl acrylate, isooctyl acrylate, 2-methoxyethyl acryl Rate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, isooctyl (meth) acrylate, isodecyl (meth) acrylate, stearyl (meth) Acrylate, tetraperfuryl (meth) acrylate, phenoxyethyl (meth) acrylate, octadecyl methacrylate, isobornyl (meth) acrylate, tetrahydrofuryl a A monofunctional monomer such as a relay agent, one know acryloyl morpholine; 1,3-butanedioldi (meth) acrylate, 1,4-butanedioldi (meth) acrylate, 1,6-hexanedioldi (meth) acrylate, ethylene glycoldi (meth) acrylate, bisphenol A-ethylene Glycol diacrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, dipropylene glycol di (meth) Acrylate, tripropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dicyclopentanyldi (meth) acrylate, caprolactone modified dicyclopentenyldi (meth) acrylate, ethylene oxide modified phosphoric acid Di (meth) acrylate, bis (2-hydroxyethyl) isocyanurate di (meth) acrylate, di (acryloxyethyl) isocyanurate, allylated cyclohexyldi (meth) acrylate Difunctional monomers such as hydrate, dimethylol dicyclopentanediacrylate, ethylene oxide modified hexahydrophthalic acid diacrylate, tricyclodecane dimethanol acrylate, neopentyl glycol modified trimethylolpropane diacrylate, adamantane diacrylate ; Trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol tri (meth) acrylate, propionic acid modified dipentaerythritol tri (meth) acrylate, propylene oxide modified trimethylolpropane Trifunctional monomers such as tri (meth) acrylate, tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, tris (acryloxyethyl) isocyanurate, and glycerol tri (meth) acrylate ; Tetrafunctional monomers such as diglycerin tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate; Pentafunctional monomers such as propionic acid-modified dipentaerythritol penta (meth) acrylate; Six functional monomers, such as dipentaerythritol hexa (meth) acrylate and caprolactone modified dipentaerythritol hexa (meth) acrylate, etc. are mentioned, These can be used individually or in mixture of 2 or more types.

The urethane acrylate oligomer including ether group in the main chain serves to maintain the viscoelasticity and storage modulus by providing flexibility of the film including the pressure-sensitive adhesive composition.

Polyethers consist primarily of polymeric diols or polyols and hydroxy acid components, and polyols suitable for use include polyether diols, hydrocarbon diols, polycarbonate diols, polyacrylate polyols (hydroxy functional acrylic polymers), polycaprolactone Diols and the like. These polyols can be used individually or in combination of 2 or more.

The method of polymerizing each structural unit of the polyol is not particularly limited, but arbitrary polymerization, block polymerization or graft polymerization may be used.

The polyether diol is obtained by ring-opening copolymerization of polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, two or more ion-polymerized cyclic compounds, and the like. Can lose.

The ion-polymerized cyclic compound may be, for example, ethylene oxide, propylene oxide, butene-1-oxide, isobutene oxide, 3,3'-bischloromethyloxetane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, dioxane, trioxane, tetraoxane, cyclohexene oxide, styrene oxide, epichlorohydrin, glycidyl methacrylate, allyl glycidyl ether, allyl glycidyl carbonate, butadiene monoxide Cyclic ethers such as isoprene monoxide, vinyl oxetane, vinyltetrahydrofuran, vinyl cyclohexene oxide, phenyl glycidyl ether, butyl glycidyl ether and glycidylbenzoate and the like.

Specific examples of the polyether diol obtained by ring-opening copolymerization of two or more forms of such ion-polymerized cyclic compounds include tetrahydrofuran and propylene oxide; Tetrahydrofuran and 2-methyltetrahydrofuran; Tetrahydrofuran and 3-methyltetrahydrofuran; Tetrahydrofuran and ethylene oxide; Propylene oxide and ethylene oxide; And copolymers obtained by the combination of ethylene oxide and butene-1-oxide, tertiary copolymers obtained by the combination of tetrahydrofuran, ethylene oxide and butene-1-oxide.

In addition, one of the ion-copolymerized cyclic compounds described above and cyclic imines such as ethylene imine; cyclic lactones such as β-propiolactone and glycolic acid lactide; Or polyether diol obtained by ring-opening copolymerization of dimethylcyclopolysiloxane can also be used. The ring-opening copolymer of such ion-polymerized cyclic compounds may be random copolymers or block copolymers.

The urethane acrylate oligomer comprising an ether group in such a main chain may contain 50 to 120 parts by weight, preferably 75 to 100 parts by weight, based on 100 parts by weight of the acrylate monomer. If the content is less than 50 parts by weight, the viscosity of the pressure-sensitive adhesive composition is low, there is a difficulty in coating, and if it exceeds 120 parts by weight, the viscosity is increased to lower the flowability of the composition, there is a fear that the processability is lowered.

The acrylate resin syrup is a resin syrup in which an acrylic monomer and a polyacrylate, which is a polymer thereof, are dissolved. The acrylate resin syrup serves to exhibit an easy storage modulus in the handling and adhesion process of the adhesive film.

The acrylic monomers include acrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethyl hexyl acrylate, and the like.

The polyacrylate is a polymer such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethyl hexyl acrylate, and most preferably, 2-ethyl hexyl acrylate (2-EHA). .

Such acrylate resin syrup may contain 2.5 to 100 parts by weight, preferably 10 to 75 parts by weight, based on 100 parts by weight of the acrylate monomer. If the content is less than 2.5 parts by weight, the elasticity is high, there is a problem that the handling of the adhesive film is difficult, when it exceeds 100 parts by weight there is a problem that the curing does not proceed sufficiently in the photopolymerization process.

The unsaturated monomer containing a carboxyl group photopolymerizes with the urethane acrylate oligomer containing an ether group in a principal chain, and improves adhesive force.

As the unsaturated monomer including the carboxyl group, at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid and fumaric acid may be used.

The unsaturated monomer containing such a carboxyl group may contain 70 to 150 parts by weight, preferably 80 to 120 parts by weight, more preferably 95 to 105 parts by weight, based on 100 parts by weight of the acrylate monomer. If the content is less than 70 parts by weight, there is a risk that the adhesive strength is lowered, if the content exceeds 150 parts by weight, the viscosity of the pressure-sensitive adhesive composition is low, there is a problem that the film formation by coating is difficult.

The free radical photoinitiator plays a role of sufficiently advancing the internal and surface hardening of the pressure-sensitive adhesive, and the type is not particularly limited as long as it is known in the art.

Specific examples of the free radical photoinitiator include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, acetophenone, hydroxydimethylacetophenone, Dimethylaminoacetophenone, dimethoxy-2-phenylacetophenone, 3-methylacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 4-chronolo Cetophenone, 4,4-dimethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 4-hydroxycyclophenylketone, 1-hydroxycyclohexylphenylketone, 2-methyl -1- [4- (methylthio) phenyl] -2-morpholino-propane-1-one, 4- (2-hydroxyethoxy) phenyl-2- (hydroxy-2-propyl) ketone, benzo Phenone, p-phenylbenzophenone, 4,4-diaminobenzophenone, 4,4'-diethylaminobenzophenone, dichlorobenzophenone, anthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-t -Butyl anthra Paddy, 2-aminoanthraquinone, 2-methyl thioxanthone, 2-ethyl thioxanthone, 2-chlorothioxanthone, 2,4-dimethyl thioxanthone, 2,4-diethyl thioxanthone, benzyldimethyl Ketal, diphenyl ketone benzyl dimethyl ketal, acetophenone dimethyl ketal, p-dimethylaminobenzoic acid ester, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, fluorene, triphenylamine, carbazole and the like. have. Moreover, as a commercially available product, brand names Darocure 1173, Igacure 184, Igacure 907 (Ciba company), etc. can also be used. These can be used individually or in combination of 2 or more types.

The free radical photoinitiator may be used in an appropriate range in consideration of the emission characteristics, the intensity, the content of each component, etc., respectively, preferably 0.1 to 20 parts by weight, more preferably 0.1 to 10 parts by weight. .

The adhesive composition of the present invention can be cured to form an adhesive. In addition, transparent substrate film; An adhesive film may be formed by including the adhesive formed on one surface of the transparent base film. The pressure-sensitive adhesive may have a thickness of 25 to 1000㎛.

The transparent base film is not particularly proposed to be excellent in transparency, mechanical strength, thermal stability, moisture shielding, isotropy, and the like.

The curing is used in the art, but is not particularly limited, photocuring using ultraviolet light is generally.

When curing using ultraviolet rays, the light source has a light emission distribution having a wavelength of 400 nm or less, preferably 150 to 400 nm, more preferably 200 to 380 nm. For example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultra high pressure mercury lamp, and a chemical lamp , Black light lamps, microwave-excited mercury lamps and metal halide lamps.

The intensity of the light irradiation can be appropriately adjusted according to the required physical properties of the pressure-sensitive adhesive, the amount of accumulated light useful for the activity of the free radical photoinitiator is preferably 10 to 5000mJ / ㎠, more preferably 200 to 800mJ / ㎠. It is preferable to have an appropriate curing reaction time within the above range, and do not cause a decrease in cohesion, yellowing or deterioration of the support of the cured product produced by heat radiated from the lamp and exotherm during the polymerization reaction.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

[Example]

Example 1

(1) pressure-sensitive adhesive composition

100 parts by weight of 2-ethylhexyl acrylate as an acrylate monomer, 100 parts by weight of atresin UN-6301 (Negami Chemical Co., Ltd.) as a urethane acrylate oligomer containing an ether group in the main chain, and SY-1063 (Nega US Chemical Co.) 33.89 parts by weight, 100 parts by weight of acrylic acid and 1.69 parts by weight of a free radical photoinitiator (Darocure-1173, Ciba) with an unsaturated monomer containing a carboxyl group were prepared to prepare an adhesive composition.

(2) Preparation of adhesive film

The pressure-sensitive adhesive composition prepared in (1) was applied on a transparent base film coated with a silicone release agent to have a thickness of 300 μm, and completely cured by irradiating ultraviolet rays at a speed of 4 m / min (600 mJ / cm 2) to form an adhesive.

Example 2-8 and Comparative Example 1-9

The same procedure as in Example 1, except that the composition of each component was used as shown in Table 1 below.

division
(Parts by weight) Urethane acrylate oligomer Acrylate resin syrup Acrylate monomer Unsaturated monomers containing carboxyl groups Photopolymerization
Initiator A-1 A-2 A-3 B-1 B-2 C-1 C-2 Example 1 100 - - 33.89 100 - 100 - 1.69 Example 2 52.5 - - 33.89 100 - 100 - 1.69 Example 3 122.5 - - 3.5 100 - 100 - 1.69 Example 4 100 - - 97.5 100 - 100 - 1.69 Example 5 100 - - 33.89 100 - 100 - 1.69 Example 6 100 - - 33.89 100 - 72.5 - 1.69 Example 7 100 - - 33.89 100 - 147.5 - 1.69 Example 8 100 - - 33.89 100 - - 100 1.69 Comparative Example 1 47.5 - - 33.89 100 - 100 - 1.69 Comparative Example 2 127.5 - - 33.89 100 - 100 - 1.69 Comparative Example 3 100 - - One 100 - 100 - 1.69 Comparative Example 4 100 - - 110 100 - 100 - 1.69 Comparative Example 5 100 - - 33.89 100 - 67.5 - 1.69 Comparative Example 6 100 - - 33.89 100 - 152.5 - 1.69 Comparative Example 7 - 100 - 33.89 100 - 100 - 1.69 Comparative Example 8 - - 100 33.89 100 - 100 - 1.69 Comparative Example 9 100 - - 33.89 100 100 - - 1.69 A-1: Urethane acrylate oligomer containing an ether group (Atresin UN-6301, Negami Chemical Co., Ltd.)
A-2: urethane acrylate oligomer containing ester group (ATS resin KY-101, Negami Chemical Co., Ltd.)
A-3: urethane acrylate oligomer (carbonate resin UN-9000PEP, Negami Chemical Co., Ltd.) containing a carbonate group
Acrylate resin syrup: trade name SY-1063, Negami Chemical Co., Ltd.
B-1: 2-ethylhexyl acrylate
B-2: Hydropropylacrylate
C-1: acrylic acid
C-2: carboxyethyl acrylate
Free radical photoinitiator: Darocure-1173, Ciba

Test Example

Physical properties of the pressure-sensitive adhesive composition and pressure-sensitive adhesive film prepared in Examples and Comparative Examples were measured by the following method, and the results are shown in Table 2 below.

1.Adhesion (N / 25mm)

After peeling the base film coated with the release agent laminated on the adhesive film, the base film was not laminated. The adhesive sheet was cut into a size of 25 mm × 250 mm using a super cutter, bonded to glass, fixed to an autograph, and then peeled by 180 ° PEEL at a speed of 300 m / min.

2. Adhesive failure shape

When evaluating the adhesion, the shape of the glass surface was reported, and the results were evaluated based on the following criteria.

<Evaluation Criteria>

(Double-circle): A very clean state in which no adhesive remains on the glass surface.

○: A slight amount of adhesive remains on the glass surface, but it is in a clean state.

X: A state in which many adhesives and foreign substances remain on the glass surface (agglomeration fracture).

3. Storage modulus

The storage modulus of the prepared pressure-sensitive adhesive film was prepared using a cylindrical test piece having a diameter of 25 mm and a thickness of 1 mm, and then measured using a torsional shear method.

Measuring instrument: dynamic viscoelasticity measuring device (MCR300, PSICA)

Frequency: 1 Hz

Measuring temperature: 23 ℃

4. Hardening shrinkage

The prepared pressure-sensitive adhesive composition was coated to have a thickness of 300 μm, and then cured by ultraviolet irradiation at a speed of 600 mJ / cm 2 using an ultraviolet irradiator. The hardened coating layer surface was visually observed, and the results were evaluated based on the following criteria.

<Evaluation Criteria>

(Double-circle): Hardening shrinkage does not occur at all. The surface is uniform and clean.

(Circle): Hardening shrinkage generate | occur | produces but there is no problem in appearance. The surface is generally uniform and clean.

X: Problems with appearance due to curing shrinkage. Uneven surface and contamination (hardening of hardening).

5. coatability

After coating the prepared adhesive composition to form an adhesive layer, the surface of the hardened coating layer was visually observed and the result was evaluated based on the following criteria.

<Evaluation Criteria>

(Circle): There is no coatability problem. Clean surface.

X: There exists a coatability problem. Surface contamination occurs (curing incomplete).

division Adhesion (N / 25mm) Adhesive failure phenomenon Storage modulus (Pa) Hardening shrinkage Coatability Example 1 11.7 ◎ 1.07 × 10 ⁵ ◎ ○ Example 2 9.8 ◎ 3.51 × 10 ⁵ ◎ ○ Example 3 10.6 ◎ 6.12 × 10 ⁵ ◎ ○ Example 4 13.2 ◎ 9.51 × 10 ⁵ ◎ ○ Example 5 8.6 ◎ 7.50 × 10 ⁴ ◎ ○ Example 6 6.4 ◎ 2.06 × 10 ⁴ ◎ ○ Example 7 15.7 ◎ 7.46 × 10 ⁵ ◎ ○ Example 8 13.0 ◎ 6.50 × 10 ⁴ ◎ ○ Comparative Example 1 - - - × × Comparative Example 2 - - - ○ × Comparative Example 3 12.1 X 7.23 × 10 ⁶ ○ ○ Comparative Example 4 - - - ○ × Comparative Example 5 2.1 ◎ 6.26 × 10 ⁵ ◎ ○ Comparative Example 6 - - - × × Comparative Example 7 1.8 ○ 1.88 × 10 ⁵ ◎ ○ Comparative Example 8 5.2 X 4.32 × 10 ⁶ ◎ ○ Comparative Example 9 0.8 ◎ 1.47 × 10 ⁵ ◎ ○

As shown in the above table, the composition of Examples 1 to 9 containing urethane acrylate oligomer, acrylate resin syrup, acrylate monomer, unsaturated monomer including carboxyl group and free radical photoinitiator in the main chain, and containing a certain amount of adhesion, coating While maintaining the physical properties of the pressure-sensitive adhesive composition, such as high storage modulus during photopolymerization and less hardening shrinkage, it was confirmed that the thickness is uniform and the surface appearance is excellent.

On the contrary, Comparative Examples 1 to 6, which contained components outside the content range of the present invention, did not reach a certain standard, resulting in poor coatability or poor adhesion failure or adhesive strength due to high storage modulus. In particular, Comparative Examples 1, 2, 4, and 6 could not measure the adhesive strength, adhesion failure and storage modulus because the viscosity did not meet a certain standard.

Comparative Examples 7 and 8 containing the urethane acrylate oligomer including ester group and carbonate group showed adhesive breakdown due to a decrease in adhesive force and a high storage modulus. Moreover, the comparative example 9 which does not contain the unsaturated monomer containing a carboxyl group showed low adhesive force.

Claims (6)

100 parts by weight of acrylate monomer, 50 to 120 parts by weight of urethane acrylate oligomer containing ether group in the main chain, 2.5 to 100 parts by weight of acrylate resin syrup, 70 to 150 parts by weight of unsaturated monomer including carboxyl group, and free radical photoinitiator 0.1 Optical pressure-sensitive adhesive composition comprising 20 to 20 parts by weight.
The optical pressure-sensitive adhesive composition of claim 1, wherein the acrylate monomer is 1 to 6 functional.
The optical pressure-sensitive adhesive composition of claim 1, wherein the unsaturated monomer containing a carboxyl group is at least one member selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid, and fumaric acid.
The adhesive which hardened the adhesive composition of any one of Claims 1-3.
Transparent substrate film;
Adhesive film comprising the pressure-sensitive adhesive of claim 4 formed on one surface of the transparent base film.
The pressure-sensitive adhesive film of claim 5, wherein the pressure-sensitive adhesive has a thickness of 25 to 1000 μm.