KR20200117874A - Adhesive sheet for image display device - Google Patents

Abstract

The present invention provides an adhesive sheet for an image display device and an adhesive sheet laminate for an image display device capable of preventing cracking or peeling from occurring in a cover film when the cover film or the like is attached to an image display device. The present invention relates to an adhesive sheet for an image display device which contains an adhesive layer comprising a crosslinked product of an adhesive composition which contains a (meth)acrylic acid ester copolymer as a main component, an isocyanate crosslinking agent, and a rosin ester tackifier resin, and based on 100 parts by weight of the (meth)acrylic acid ester copolymer, contains 1 to 40 parts by weight of the rosin ester tackifier resin, wherein the adhesive layer has a maximum tanδ at 1 Hz of -20°C or less, and the adhesive layer has a storage elastic modulus of 1.0 × 10^5 Pa or less at 1 Hz and 25°C.

Description

Adhesive sheet for image display devices {ADHESIVE SHEET FOR IMAGE DISPLAY DEVICE}

The present invention relates to an adhesive sheet for an image display device and an adhesive sheet laminate for an image display device.

In recent years, in order to bond and laminate a cover film, an electrode film, a casing, and the like constituting a touch panel display used in a smart phone or the like, for example, a pressure-sensitive adhesive sheet as described in Patent Document 1 is used.

Japanese Patent Application Publication No. 2012-025808

However, in recent years, image display devices such as touch panel displays have a curved surface or a curved surface, and may be repeatedly bent and used, so that a cover film, which is a constituent member, needs to be adhered to follow a curved surface or the like. have. However, when the cover film is affixed to such a curved surface, there is a concern that cracks and peeling may occur in the cover film, and improvement has been desired. The present invention has been made in order to solve the above problem, and when a cover film or the like is attached to an image display device, a pressure-sensitive adhesive sheet for an image display device and an image display device capable of preventing cracking or peeling from occurring in the cover film It is an object of the present invention to provide an adhesive sheet laminate for use.

Item 1. A (meth)acrylic acid ester copolymer as a main component, and

An isocyanate crosslinking agent,

It contains rosin ester tackifying resin,

An adhesive sheet for an image display device comprising an adhesive layer containing 1 to 40 parts by weight of the rosin ester tackifier resin and a crosslinked product of the adhesive composition based on 100 parts by weight of the (meth)acrylic acid ester copolymer as,

The adhesive layer has a maximum tan δ at 1 Hz of -20°C or less,

The adhesive sheet for an image display device, wherein the adhesive layer has a storage modulus of 1.0 × 10 ⁵ Pa or less at 1 Hz and 25°C.

Item 2. The pressure-sensitive adhesive sheet for an image display device according to item 1, wherein the storage modulus at 1 Hz and -20°C is 1.0 × 10 ⁵ Pa or less.

Item 3. The pressure-sensitive adhesive sheet for an image display device according to item 1 or 2, wherein the thickness is 5 to 100 µm.

Item 4. An adhesive sheet laminate for an image display device, comprising a base sheet for peeling attached to at least one surface of the pressure-sensitive adhesive sheet for an image display device according to any one of items 1 to 3.

According to the pressure-sensitive adhesive sheet according to the present invention, when a cover film is attached to an image display device, it is possible to prevent cracking or peeling from occurring in the cover film.

1 is a cross-sectional view of an adhesive sheet laminate according to an embodiment of the present invention.
2 is a cross-sectional view of a test piece for a bending test.
3 is a diagram showing a method of a bending test.

Hereinafter, an embodiment of the pressure-sensitive adhesive sheet according to the present invention will be described. This pressure-sensitive adhesive sheet is a pressure-sensitive adhesive sheet for attaching a cover film, an electrode film, a casing, and the like constituting an image display device such as a touch panel display. Used. This adhesive sheet is obtained by crosslinking an adhesive composition containing a (meth)acrylic acid ester copolymer as a main component, an isocyanate crosslinking agent, and a rosin ester tackifier resin. Hereinafter, it demonstrates in detail.

<1. (Meth)acrylic acid ester copolymer>

The (meth)acrylic acid ester polymer preferably contains an alkyl (meth)acrylate having 2 to 20 carbon atoms in the alkyl group and a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer) as a monomer unit. Thereby, desirable adhesiveness can be expressed.

The (meth)acrylate alkyl ester having 2 to 20 carbon atoms in the alkyl group is preferably a homopolymer having a glass transition temperature (Tg) of -40°C or less (hereinafter, referred to as "specific acrylate"). By containing such a specific acrylate as a constituent monomer unit, it becomes easy to set the maximum value of tan δ of the pressure-sensitive adhesive sheet according to the present embodiment in the range described later.

Specific acrylates include, for example, n-butyl acrylate (Tg -55°C), n-octyl acrylate (Tg -65°C), isooctyl acrylate (Tg -58°C), 2-ethylhexyl acrylate (Tg- 70 ℃), isononyl acrylate (Tg -58 ℃), isodecyl acrylate (Tg -60 ℃), isodecyl methacrylate (Tg -41 ℃), n-lauryl methacrylate (Tg -65 ℃) , It is preferable to use tridecyl acrylate (Tg -55°C), tridecyl methacrylate (Tg -40°C) and the like. Among them, from the viewpoint of more effectively reducing the storage modulus, as a specific acrylate, it is more preferable that the homopolymer has a Tg of -45°C or less, and particularly preferably -50°C or less. Specifically, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. These may be used alone or in combination of two or more. In addition, the alkyl group in the C2-C20 alkyl (meth)acrylate of the alkyl group means a linear, branched or cyclic alkyl group.

The (meth)acrylic acid ester polymer preferably contains 60% by mass or more of a specific acrylate as a monomer unit, more preferably 80% by mass or more, and particularly preferably 90% by mass or more. By containing 60 mass% or more of said specific acrylate, it becomes easier to set the maximum value of tan delta of the adhesive sheet concerning this embodiment in the range mentioned later.

In addition, the (meth)acrylic acid ester polymer preferably contains 99.9% by mass or less, more preferably 99% by mass or less, and particularly preferably 98% by mass or less, as a monomer unit. . By containing 99.9 mass% or less of the said specific acrylate, a preferable amount of other monomer components (especially reactive functional group-containing monomers) can be introduced into the (meth)acrylic acid ester polymer.

The (meth)acrylic acid ester polymer, by containing a reactive functional group-containing monomer as a monomer unit, reacts with a crosslinking agent to be described later through a reactive functional group derived from the reactive functional group-containing monomer, thereby forming a crosslinked structure (three-dimensional network structure). Thus, an adhesive sheet having a desired cohesive force is obtained.

As the reactive functional group-containing monomer contained in the (meth)acrylic acid ester polymer as a monomer unit, a monomer having a hydroxyl group in the molecule (a hydroxyl group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer), and the like are preferable. Among these, a hydroxyl group-containing monomer is particularly preferred. In many cases, the hydroxyl group-containing monomer has a glass transition temperature (Tg) of 0°C or less, and it is easy to set the maximum tan δ of the pressure-sensitive adhesive sheet according to the present embodiment in the range described later.

As a hydroxyl-containing monomer, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, And (meth)acrylate hydroxyalkyl esters such as 3-hydroxybutyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate. Among them, in terms of the glass transition temperature (Tg), the reactivity of the hydroxyl group in the resulting (meth)acrylic acid ester polymer with the crosslinking agent, and the copolymerization with other monomers, 2-hydroxyethyl acrylate and 2-hydroxy acrylate. It is preferably at least one of propyl, 3-hydroxypropyl acrylic acid, and 4-hydroxybutyl acrylic acid. These may be used alone or in combination of two or more.

The hydroxyl value of the (meth)acrylic acid ester copolymer is not particularly limited, but when the pressure-sensitive adhesive sheet is repeatedly bent in a state in which it is in close contact with an adherend, from the viewpoint of suppressing peeling from the adherend, the lower limit is preferable. Preferably, 5 mgKOH/g or more, more preferably 10 mgKOH/g or more may be mentioned. On the other hand, about the upper limit, Preferably it is 100 mgKOH/g or less, More preferably, it is 90 mgKOH/g or less.

As a monomer unit, the (meth)acrylic acid ester polymer preferably contains 0.1% by mass or more of the reactive functional group-containing monomer, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more. In addition, as a monomer unit, the (meth)acrylic acid ester polymer preferably contains 30% by mass or less of the reactive functional group-containing monomer, more preferably 20% by mass or less, and particularly preferably 8% by mass or less. Do.

However, the (meth)acrylic acid ester polymer according to the present embodiment does not contain a carboxy group-containing monomer, particularly acrylic acid, as a monomer unit. Since the carboxyl group is an acid component, it does not contain a carboxy group-containing monomer, so that a problem occurs due to an acid on the adhesive sheet to be affixed, for example, a transparent conductive film such as tin-doped indium oxide (ITO), a metal film, Even when a metal mesh or the like is present, such problems (corrosion, change in resistance value, etc.) caused by acid can be suppressed.

The polymerization mode of the (meth)acrylic acid ester polymer may be a random copolymer or a block copolymer.

The lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer is preferably 200,000 or more, more preferably 300,000 or more, and particularly preferably 400,000 or more. If the lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer is more than the above, problems such as leaching of the adhesive are suppressed when processing the adhesive sheet. In addition, the weight average molecular weight in this specification is a value in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method.

Moreover, the upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer is preferably 1 million or less, more preferably 900,000 or less, and particularly preferably 800,000 or less. When the upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer is below the above, the adhesive force and storage modulus of the obtained pressure-sensitive adhesive sheet with an adherend tend to fall within the preferable ranges described later.

In addition, in the pressure-sensitive adhesive according to the present embodiment, the (meth)acrylic acid ester polymer may be used singly or in combination of two or more of those described above.

<2. Isocyanate crosslinking agent>

When the adhesive composition according to the present embodiment is heated, the isocyanate crosslinking agent crosslinks the (meth)acrylic acid ester polymer to form a three-dimensional network structure. Thereby, the cohesive force of the obtained adhesive sheet is improved.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane. Reaction products with alicyclic polyisocyanates such as diisocyanates, etc., and their biuret body, isocyanurate body, and further, low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, castor oil, etc. Inductor bodies, etc. are mentioned. Among them, from the viewpoint of reactivity with a hydroxyl group, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate are preferred.

The content of the isocyanate crosslinking agent in the adhesive composition is preferably 0.01 parts by mass or more, particularly preferably 0.05 parts by mass or more, and further preferably 0.1 parts by mass or more with respect to 100 parts by weight of the (meth)acrylic acid ester polymer. . Further, the content is preferably 10 parts by mass or less, particularly preferably 8 parts by mass or less, and further preferably 5 parts by mass or less.

<3. Rosin Ester Tackifying Resin>

The rosin ester tackifying resin according to the present embodiment is a gum rosin containing resin acids such as abietic acid, palustric acid, neoabietic acid, pimaric acid, isopimaric acid, and dihydroabietic acid as a main component. , Rosin-based tackifying resins such as wood rosin and tall oil rosin, and rosin-ester-based tackifying resins which are esters of various alcohols.

The content of the rosin ester tackifying resin in the adhesive composition is preferably 1 to 40 parts by weight, more preferably 1.5 to 35 parts by weight, and more preferably 2 to 30 parts by weight based on 100 parts by weight of the (meth)acrylic acid ester polymer. It is more preferable that it is a weight part. When the content is 1 part by weight or more, the bending resistance when the cover film is attached to the image display device by the pressure-sensitive adhesive sheet is improved. On the other hand, by making the content into 40 parts by weight or less, white cloudiness of the pressure-sensitive adhesive sheet can be suppressed.

<4. Additive>

In the adhesive composition, if necessary, various additives commonly used in acrylic adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index adjusters, etc., are added. can do. In addition, it is assumed that the polymerization solvent and the diluted solvent described later are not included in the additive constituting the adhesive composition.

<5. Properties of the adhesive sheet>

<5-1. Adhesive sheet thickness>

It is preferable that it is 5-100 micrometers, and, as for the thickness of an adhesive sheet, it is more preferable that it is 10-50 micrometers. This is because there is a possibility that the cover film is easily peeled off when the thickness is less than 5 µm. On the other hand, when the thickness exceeds 100 µm, when the cover film is pressed, since the cover film is settled, there is a fear that the pencil hardness may decrease.

<5-2. Storage modulus and tanδ>

The pressure-sensitive adhesive sheet according to the present embodiment has a maximum tan δ (glass transition temperature) of -20°C or less at 1 Hz, and a storage modulus of 1.0 × 10 ⁵ Pa or less at 1 Hz and 25°C. The lower the maximum value of tan δ is, the lower the storage elastic modulus, and the pressure-sensitive adhesive sheet becomes flexible. Therefore, the maximum value of tan δ at 1 Hz of the pressure-sensitive adhesive sheet is preferably -30°C or less, and more preferably -50°C or less. The storage modulus of the pressure-sensitive adhesive sheet at 1 Hz and 25°C is preferably lower, preferably 1.0 × 10 ⁵ Pa or less, more preferably 8.0 × 10 ⁴ Pa or less, and furthermore 5.0 × 10 ⁴ Pa or less. It is preferable, and it is particularly preferable that it is 3.0 × 10 ⁴ Pa or less. In addition, in order to maintain the flexibility even at low temperatures, the storage modulus of the pressure-sensitive adhesive sheet at 1 Hz and -20°C is preferably 1.0 × 10 ⁵ Pa or less, more preferably 7.0 × 10 ⁴ Pa or less, and 5.5 × It is particularly preferably 10 ⁴ Pa or less.

In addition, the maximum value of tan δ can be measured using, for example, "Discovery HR-3" manufactured by TA Instruments, and the storage modulus can be measured by a method conforming to JIS K7244-6. .

<6. Manufacturing method of adhesive sheet>

Although it does not specifically limit, the manufacturing method of the adhesive sheet concerning this embodiment, For example, it can implement as follows.

First, a (meth)acrylic acid ester polymer, an isocyanate-based crosslinking agent, and a rosin ester-based tackifier resin are mixed, and the above-described additives are added as necessary.

The (meth)acrylic acid ester polymer can be produced by polymerizing a mixture of monomers constituting the polymer by a conventional radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer is preferably carried out by a solution polymerization method using a polymerization initiator as necessary. As a polymerization solvent, ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc. are mentioned, for example, and two or more types may be used together.

Examples of the polymerization initiator include an azo compound and an organic peroxide, and two or more types may be used in combination. As an azo compound, for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane1- Carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl2,2' -Azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2' -Azobis[2-(2-imidazolin-2-yl)propane] etc. are mentioned.

Examples of the organic peroxide include benzoyl peroxide, t-butylperbenzoate, cumene hydroperoxide, diisopropylperoxydicarbonate, di-n-propylperoxydicarbonate, and di(2-ethoxyethyl)peroxydi Carbonate, t-butylperoxyneodecanoate, t-butylperoxypivalate, (3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, diacetyl peroxide, and the like.

In addition, in the polymerization step, by blending a chain transfer agent such as 2-mercaptoethanol, the weight average molecular weight of the obtained polymer can be adjusted.

When the (meth)acrylic acid ester polymer is obtained, to the solution of the (meth)acrylic acid ester polymer, an isocyanate-based crosslinking agent, a rosin ester-based tackifying resin, and an additive and a diluting solvent are added as desired, and sufficiently mixed to the solvent. Thus, the diluted adhesive composition (coating solution) is obtained.

In addition, in any of the above components, when a solid substance is used, or when precipitation occurs when mixed with other components in an undiluted state, the component is dissolved or diluted in a pre-diluted solvent alone. After making it, you may mix with other components.

Examples of the diluting solvent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride and ethylene chloride, methanol, ethanol, propanol, butanol, 1- Alcohols such as methoxy-2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, cellosolve solvents such as ethyl cellosolve Etc. are used.

The concentration and viscosity of the coating solution thus prepared may be within a range in which coating is possible, and may be appropriately selected according to the situation. For example, it can be diluted so that the concentration of the adhesive composition becomes 10-60 mass %. In addition, when obtaining a coating solution, addition of a diluting solvent etc. is not a necessary condition, and it is not necessary to add a diluting solvent as long as the adhesive composition has a coatable viscosity, etc. In this case, the adhesive composition becomes a coating solution using the polymerization solvent of the (meth)acrylic acid ester polymer as a diluting solvent.

Crosslinking of the above-described adhesive composition can be usually performed by heat treatment. In addition, this heat treatment can also serve as a drying treatment when volatilizing a diluted solvent or the like from the coating film of the adhesive composition applied to a desired object.

It is preferable that it is 50-150 degreeC, and, as for the heating temperature of a heat treatment, it is more preferable that it is 70-120 degreeC. Moreover, it is preferable that it is 10 seconds-10 minutes, and, as for a heating time, it is more preferable that it is 50 seconds-2 minutes.

After the heat treatment, if necessary, a curing period of about 1 to 2 weeks may be formed at room temperature (eg, 23° C., 50% RH). When this curing period is required, an adhesive sheet is formed after the curing period has elapsed. On the other hand, when the curing period is unnecessary, after the heat treatment is completed, an adhesive sheet is formed.

By the above heat treatment (and curing), the (meth)acrylic acid ester polymer is sufficiently crosslinked through an isocyanate crosslinking agent to form a crosslinked structure, and a pressure-sensitive adhesive sheet is obtained.

<7. Adhesive Sheet Laminate>

Next, the adhesive sheet laminate according to the present embodiment will be described. As shown in FIG. 1, the adhesive sheet laminate according to the present embodiment includes a first release sheet 1, an adhesive layer 2 laminated on the first release sheet 1, and this adhesive layer ( 2) It has the 2nd release sheet 3 arrange|positioned on it. The first and second release sheets 1 and 3 are known release sheets and have a release surface on at least one of them.

This adhesive sheet laminate can be manufactured as follows, for example. First, the 1st peeling sheet 1 is fed out from the feeding roll which wound up the 1st peeling sheet 1. And the pressure-sensitive adhesive layer 2 is formed by applying the coating liquid of the pressure-sensitive adhesive composition described above to the release surface of the first release sheet 1, performing heat treatment, and thermally crosslinking the pressure-sensitive adhesive composition. This adhesive layer 2 corresponds to the adhesive sheet of the present invention. Then, the 2nd release sheet 3 is affixed so that this adhesive layer 2 may be covered. At this time, the release surface of the second release sheet 3 is brought into contact with the adhesive layer 2. In this way, an adhesive sheet laminate as shown in Fig. 1 is formed.

<8. Cover film＞

The cover film attached to the image display device through the above-described adhesive sheet is not particularly limited, and a known one can be adopted. There are various methods for attaching the above-described adhesive sheet to a cover film. For example, after peeling the 1st or 2nd peeling sheet of the above-mentioned adhesive sheet laminated body, it can attach to a cover film by transferring the exposed adhesive layer to a cover film. Alternatively, a pressure-sensitive adhesive layer (adhesive sheet) can be formed by applying the coating liquid of the pressure-sensitive adhesive composition described above to one surface of the cover film, performing heat treatment, and thermally crosslinking the pressure-sensitive adhesive composition.

<9. Features>

Since the pressure-sensitive adhesive sheet according to the present invention has a low storage modulus and contains a rosin ester-based pressure-sensitive adhesive resin, when the cover film on which this pressure-sensitive adhesive sheet is formed is attached along an image display device having a bent portion, it is covered due to bending. The stress acting on the film can be relieved by the adhesive sheet. Therefore, when the cover film is bent, it is possible to prevent occurrence of cracks or peeling including cracks.

Example

Next, an embodiment of the present invention will be described. However, the present invention is not limited to the following examples.

<1. Preparation of Examples and Comparative Examples>

PSA sheets according to Examples 1 to 7 and Comparative Examples 1 to 4 were prepared. Moreover, the cover film was affixed to the target film with each adhesive sheet, and the laminated body as shown in FIG. 2 was produced. The cover film and the target film are as follows.

(1) Cover film: An acrylic resin film that does not crack with R = 3.0 mm in a 100 µm-thick bending test

(2) Target film: 30 µm thick polyimide resin film

In addition, the target film assumed an image display device that is a target for attaching a cover film.

Compositions of the pressure-sensitive adhesives according to Examples 1 to 7 and Comparative Examples 1 to 4 are as follows. Coronate L-55E constituting the isocyanate-based crosslinking agent is manufactured by Tosoh Corporation, BXX8515 is manufactured by Toyo Ink, and Duranate TPA-100 is manufactured by Asahi Kasei. In addition, fine crystal ME-GH constituting the rosin ester tackifier resin is manufactured by Arakawa Chemical Industries, Ltd.. About the acrylic acid ester copolymer, a weight average molecular weight and a hydroxyl value are shown.

The physical properties of the pressure-sensitive adhesive sheets according to Examples 1 to 7 and Comparative Examples 1 to 4 are as follows.

The storage elastic modulus and loss tangent tan δ of the pressure-sensitive adhesive sheet were measured using "Discovery HR-3" manufactured by T-A Instruments. The measurement conditions are as follows.

(Measuring conditions)

Measurement mode: shear mode

Deformation: 0.1%

Measurement frequency: 1 Hz

Measurement temperature: -60 ∼ 25 ℃ (heating 5 ℃/min)

Measurement sample: The adhesive layer of each adhesive sheet was superimposed, and the total thickness was about 1 mm.

Moreover, about each adhesive sheet, the total light transmittance and haze ratio were measured by the glass/adhesive sheet/PET film lamination structure. The total light transmittance was measured according to JIS K7136-1 and the haze according to JIS K7136, and the results are as shown in Table 3.

Moreover, about the laminated body shown in FIG. 2 using each adhesive sheet, a bending test was performed. For the flexural test, a no-load U-shaped tester shown in FIG. 3 was used. This testing machine has two movable plates that can be rotated, and the rotating shafts are arranged adjacent to each other so that the rotating shafts of the movable plates are parallel. And the laminated body which is a sample piece was arrange|positioned on the movable plate of the horizontal state shown in FIG. 3(a). At this time, the laminate was disposed so that the cover film surface of the laminate was in contact with the movable plate. Subsequently, as shown in Fig. 3(b), the sample piece was bent in a U-shape by turning both movable plates 90 degrees. Such bending was repeated at room temperature at a test speed of 0.85 sec/circuit. Then, after the test, it was confirmed whether or not cracks occurred in the cover film of the sample piece, and the bending resistance was evaluated based on the following criteria (1) to (3). The test was carried out so that the bending diameter R of the sample piece was 2.5 mm and 3.0 mm, and as a result, it was tested whether it corresponds to any of the following (1) to (3).

(1) R = 2.5 mm, no cracks occurred at more than 100,000 bending times (R = 2.5 mm no crack),

(2) R = 2.5 mm, cracks occurred at less than 100,000 bending times, but no cracks occurred at R = 3.0 mm and more than 100,000 bending times (R = 3.0 mm no crack),

(3) R = 3.0 mm, cracks occurred at less than 100,000 bends (R = 3.0 mm cracks)

According to Table 3, in Examples 1 to 7, R = 2.5 mm or 3.0 mm, no cracks occurred in the cover film at more than 100,000 bending times, but Comparative Examples 1 to 4 had R = 3.0 mm, bending frequency 100,000 times. Cracks occurred below. In Example 6, cracks were generated when R = 2.5 mm and the number of bendings was less than 100,000, but this is considered to be the reason that the content of the rosin ester tackifier resin was small.

In Comparative Examples 1 to 4, since the storage elastic modulus at 25°C is high, it is considered that the bending resistance is low. In addition, in Comparative Example 2, since the storage elastic modulus was high as described above, even if the rosin ester-based tackifying resin was contained, the bending resistance was considered to be low.

1: 1st peeling sheet
2: adhesive sheet (adhesive layer)
3: 2nd peeling sheet

Claims (4)

(Meth)acrylic acid ester copolymer as a main component, and
An isocyanate crosslinking agent,
It contains rosin ester tackifying resin,
An adhesive sheet for an image display device comprising an adhesive layer containing 1 to 40 parts by weight of the rosin ester tackifier resin and a crosslinked product of the adhesive composition based on 100 parts by weight of the (meth)acrylic acid ester copolymer as,
The adhesive layer has a maximum tan δ at 1 Hz of -20°C or less,
The adhesive sheet for an image display device, wherein the adhesive layer has a storage modulus of 1.0 × 10 ⁵ Pa or less at 1 Hz and 25°C. The method of claim 1,
The pressure-sensitive adhesive sheet for an image display device, wherein the storage modulus at 1 Hz and -20°C is 1.0×10 ⁵ Pa or less. The method of claim 1,
A pressure-sensitive adhesive sheet for an image display device having a thickness of 5 to 100 µm. A pressure-sensitive adhesive sheet laminate for an image display device, comprising a base sheet for peeling, which is attached to at least one surface of the pressure-sensitive adhesive sheet for an image display device according to claim 1.

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