TWI818157B - Adhesive sheet for image display devices and adhesive sheet laminate for image display devices - 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, which can prevent the cover film from cracking or peeling when a cover film or the like is installed on the image display device. The present invention is an adhesive sheet for an image display device, which is provided with an adhesive layer containing a cross-linked product of an adhesive composition containing (meth)acrylate copolymer and an isocyanate-based cross-linking agent as main components. , and a rosin ester-based adhesive-imparting resin, containing 1 to 40 parts by weight of the aforementioned rosin ester-based adhesive-imparting resin relative to 100 parts by weight of the aforementioned (meth)acrylate copolymer, and the aforementioned adhesive layer has a tan delta of 1 Hz. The maximum value is below -20°C, and the storage elastic modulus of the aforementioned adhesive layer at 1Hz and 25°C is below 1.0×10 ⁵ Pa.

Description

Adhesive sheet for image display devices and adhesive sheet laminate for image display devices

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

In recent years, in order to laminate and laminate cover films, electrode films, frames, and the like constituting touch panel displays used in smartphones and the like, the adhesive sheet described in Patent Document 1, for example, is used. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2012-025808

[Problem to be solved by the invention]

On the other hand, in recent years, some image display devices such as touch panel displays have curved or curved surfaces, and some are even used with repeated bending. Therefore, the cover film and other components of the image display device must also follow the curved surface, etc. And be attached. However, if a cover film is attached to such a curved surface, there is a risk that the cover film will crack or peel off, so it is desired to improve this situation. The present invention is made to solve the above problems, and aims to provide an adhesive sheet for an image display device and an adhesive sheet laminate for an image display device that can prevent the cover film from cracking when a cover film or the like is mounted on an image display device. or peeling. [Means used to solve problems]

Plan 1. An adhesive sheet for an image display device, having an adhesive layer including a cross-linked product of an adhesive composition containing (meth)acrylate copolymer and an isocyanate-based cross-linking agent as main components. and a rosin ester-based adhesive-imparting resin, which contains 1 to 40 parts by weight of the aforementioned rosin ester-based adhesive-imparting resin relative to 100 parts by weight of the aforementioned (meth)acrylate copolymer; and the aforementioned adhesive layer has a tan δ of 1 Hz. The maximum value is below -20°C; the storage elastic modulus of the aforementioned adhesive layer at 1Hz and 25°C is below 1.0×10 ⁵ Pa.

Option 2. The adhesive sheet for image display devices as described in Option 1 has a storage elastic modulus of 1.0×10 ⁵ Pa or less at 1 Hz and -20°C.

Option 3. The adhesive sheet for an image display device as described in Option 1 or 2, with a thickness of 5 μm to 100 μm.

Embodiment 4. An adhesive sheet laminate for an image display device, which is provided with a base material sheet for peeling off, and the base material sheet for peeling off is mounted on the image display device according to any one of Embodiments 1 to 3. Use at least one side of the adhesive sheet. [Invention effect]

According to the adhesive sheet of the present invention, the cover film can be prevented from cracking or peeling when the cover film is attached to an image display device.

Hereinafter, one embodiment of the adhesive sheet of the present invention will be described. The adhesive sheet is used to install cover films, electrode films, frames, etc. that constitute image display devices such as touch panel displays. It is especially suitable for installing cover films on displays with curved or buckled surfaces. The adhesive sheet is formed by cross-linking an adhesive composition containing (meth)acrylate copolymer, an isocyanate-based cross-linking agent, and a rosin ester-based adhesive-imparting resin as main components. This is explained in detail below.

[1.(Meth)acrylate copolymer] The (meth)acrylate polymer is preferably an alkyl (meth)acrylate having an alkyl group and a carbon number of 2 to 20, or a monomer having a reactive functional group in the molecule (a monomer containing a reactive functional group). ) as a single unit. In this way, better adhesion can be demonstrated.

The (meth)acrylic acid alkyl ester having an alkyl group having 2 to 20 carbon atoms is preferably a homopolymer having a glass transition temperature (Tg) of -40°C or lower (hereinafter sometimes 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 adhesive sheet of this embodiment to the following range.

As the specific acrylate, it is preferable to use, for example, n-butyl acrylate (Tg: -55°C), n-octyl acrylate (Tg: -65°C), isooctyl acrylate (Tg: -58°C), 2-ethyl acrylate Hexyl acrylate (Tg is -70℃), isononyl acrylate (Tg is -58℃), isodecyl acrylate (Tg is -60℃), isodecyl methacrylate (Tg is -41℃), methanol n-lauryl acrylate (Tg is -65°C), tridecyl acrylate (Tg is -55°C), tridecyl methacrylate (-40°C), etc. Among these, from the viewpoint of reducing the storage elastic modulus more effectively, the specific acrylate is more preferably an acrylate having a homopolymer 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 acrylic esters can be used individually or in combination of 2 or more types. Furthermore, the alkyl group in the alkyl (meth)acrylate having an alkyl group carbon number of 2 to 20 means a linear, branched chain or cyclic alkyl group.

The (meth)acrylate polymer preferably contains 60% by mass or more of the specific acrylate as a monomer unit, more preferably 80% by mass or more, and even more preferably 90% by mass or more. By containing 60 mass % or more of the above-mentioned specific acrylate, it becomes easy to set the maximum value of tan δ of the adhesive sheet of this embodiment to the following range.

In addition, the (meth)acrylate polymer preferably contains 99.9% by mass or less of the specific acrylate as a monomer unit, more preferably 99% by mass or less, and particularly preferably 98% by mass or less. By containing 99.9% by mass or less of the above-mentioned specific acrylate, an appropriate amount of other monomer components (especially monomers containing reactive functional groups) can be introduced into the (meth)acrylate polymer.

The (meth)acrylate polymer contains a reactive functional group-containing monomer as a monomer unit and reacts with the following cross-linking agent via the reactive functional group derived from the reactive functional group-containing monomer. , thereby forming a cross-linked structure (three-dimensional network structure), and obtaining an adhesive sheet with the required cohesive force.

The reactive functional group-containing monomer contained in the (meth)acrylate polymer as a monomer unit is preferably a monomer having a hydroxyl group in the molecule (hydroxyl-containing monomer) or a monomer having an amine group in the molecule. monomers (amine-containing monomers), etc. Among these monomers, hydroxyl-containing monomers are particularly preferred. The glass transition temperature (Tg) of the hydroxyl-containing monomer is often 0° C. or lower, and it is easy to set the maximum value of tan δ of the adhesive sheet of this embodiment to the following range.

Examples of the hydroxyl-containing monomer include: (meth)acrylic acid 2-hydroxyethyl ester, (meth)acrylic acid 2-hydroxypropyl ester, (meth)acrylic acid 3-hydroxypropyl ester, (meth)acrylic acid 2 -Hydroxyalkyl (meth)acrylate such as hydroxybutyl ester, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc. Among them, acrylic acid is preferred in terms of glass transition temperature (Tg), reactivity of the hydroxyl group in the obtained (meth)acrylate polymer with the cross-linking agent, and copolymerizability with other monomers. At least one of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate and 4-hydroxybutyl acrylate. These can be used individually or in combination of 2 or more types.

The hydroxyl value of the (meth)acrylate copolymer is not particularly limited. When the adhesive sheet and the adherend are in close contact with each other and the adhesive sheet is repeatedly buckled, from the viewpoint of suppressing peeling from the adherend, The lower limit is preferably 5 mgKOH/g or more, and more preferably 10 mgKOH/g or more. On the other hand, the upper limit is preferably 100 mgKOH/g or less, more preferably 90 mgKOH/g or less.

The (meth)acrylate polymer preferably contains 0.1% by mass or more of a reactive functional group-containing monomer as a monomer unit, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. In addition, the (meth)acrylate polymer preferably contains 30% by mass or less of a reactive functional group-containing monomer as a monomer unit, more preferably 20% by mass or less, and even more preferably 8% by mass or less.

However, the (meth)acrylate polymer of this embodiment does not contain a carboxyl group-containing monomer, especially acrylic acid, as a monomer unit. Since carboxyl groups are acid components, by not containing carboxyl group-containing monomers, it is possible to prevent acid-induced defects in the objects to which the adhesive sheet is attached, such as transparent conductive films or metal films containing tin-doped indium oxide (ITO). , metal mesh, etc., it can suppress defects (corrosion, resistance value changes, etc.) caused by acid in these attached objects.

The polymerization mode of the (meth)acrylate polymer can be a random copolymer or a block copolymer.

The lower limit of the weight average molecular weight of the (meth)acrylate polymer is preferably 200,000 or more, more preferably 300,000 or more, and particularly preferably 400,000 or more. If the lower limit value of the weight average molecular weight of the (meth)acrylate polymer is equal to or higher than the above value, problems such as adhesive bleeding during processing of the adhesive sheet can be suppressed. Furthermore, the weight average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) and converted to standard polystyrene.

In addition, the upper limit of the weight average molecular weight of the (meth)acrylate polymer is preferably 1 million or less, more preferably 900,000 or less, and particularly preferably 800,000 or less. If the upper limit of the weight average molecular weight of the (meth)acrylate polymer is equal to or less than the above-mentioned value, the adhesive force and storage elastic modulus of the obtained adhesive sheet and adherend will be easily within the following appropriate ranges.

Furthermore, in the adhesive agent of this embodiment, one of the above-mentioned (meth)acrylate polymers may be used alone, or two or more types may be used in combination.

[2. Isocyanate cross-linking agent] When the adhesive composition of this embodiment is heated, the isocyanate cross-linking agent cross-links the (meth)acrylate polymer to form a three-dimensional network structure. Thereby, the cohesiveness of the obtained adhesive sheet is improved.

The isocyanate cross-linking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as 1,6-hexamethylene diisocyanate, and isophorone diisocyanate. , alicyclic polyisocyanates such as hydrogenated diphenylmethane diisocyanate, etc., and biuret bodies, isocycyanurate bodies of these polyisocyanates, and as combinations with ethylene glycol, propylene glycol, neopentyl glycol, triglyceride Adducts of reactants of low molecular weight active hydrogen-containing compounds such as hydroxymethylpropane and castor oil. Among them, from the viewpoint of reactivity with hydroxyl groups, aromatic polyisocyanates modified with trimethylolpropane are preferred, especially toluene diisocyanate modified with trimethylolpropane and trimethylolpropane-modified toluene diisocyanate. Modified xylylene diisocyanate.

The content of the isocyanate cross-linking agent in the adhesive composition is preferably 0.01 part by mass or more, particularly preferably 0.05 part by mass or more, and more preferably 0.1 part by mass or more based on 100 parts by weight of the (meth)acrylate polymer. . In addition, the content is preferably 10 parts by mass or less, particularly preferably 8 parts by mass or less, and more preferably 5 parts by mass or less.

[3. Rosin ester-based adhesive-imparting resin] The rosin ester adhesive-imparting resin of this embodiment is composed of abietic acid, palustric acid, neorosin acid, pimaric acid, isopimaric acid, and dehydroabietic acid. Rosin ester-based tackifying resins are rosin-based tackifying resins such as gum rosin, wood rosin, tall oil rosin and other rosin-based tackifying resins whose main components are resin acids and esters of various alcohols.

The content of the rosin ester-based tackifying resin in the adhesive composition is preferably 1 to 40 parts by weight, more preferably 1.5 to 35 parts by weight based on 100 parts by weight of the (meth)acrylate polymer. , and more preferably 2 to 30 parts by weight. If the content is 1 part by weight or more, the buckling resistance of the cover film when mounted on an image display device through an adhesive sheet is improved. On the other hand, by setting the content to 40 parts by weight or less, white turbidity of the adhesive sheet can be suppressed.

[4.Additives] In the adhesive composition, various additives commonly used in acrylic adhesives may be added as necessary, such as silane coupling agents, ultraviolet absorbers, antistatic agents, adhesion-imparting agents, antioxidants, light stabilizers, softeners, and fillers. agents, refractive index adjusters, etc. In addition, the following polymerization solvent and dilution solvent are regarded as substances not included in the additives constituting the adhesive composition.

[5. Physical properties of the adhesive sheet] [5-1. Thickness of adhesive sheet] The thickness of the adhesive sheet is preferably 5 μm to 100 μm, more preferably 10 μm to 50 μm. The reason is that if the thickness is less than 5 μm, the cover film may peel off easily. On the other hand, if the thickness exceeds 100 μm, the cover film may sink in when the cover film is pressed, so the pencil hardness may decrease.

[5-2. Storage elastic modulus and tan δ] The maximum value of tan δ (glass transition temperature) of the adhesive sheet of this embodiment at 1 Hz is -20°C or less, and the storage elastic modulus at 1 Hz and 25° C. is 1.0× Below 10 ⁵ Pa. The lower the maximum value of tan δ, the lower the storage elastic modulus becomes, and the softer the adhesive sheet becomes. Therefore, the maximum value of tan δ of the adhesive sheet at 1 Hz is preferably -30°C or lower, and more preferably -50°C or lower. The storage elastic modulus of the adhesive sheet at 1Hz and 25°C is preferably lower, preferably 1.0×10 ⁵ Pa or less, more preferably 8.0×10 ⁴ Pa or less, and even more preferably 5.0×10 ⁴ Pa or less, especially Preferably, it is 3.0×10 ⁴ Pa or less. In addition, in order to maintain flexibility at low temperatures, the storage elastic modulus of the adhesive sheet at 1Hz and -20°C is preferably 1.0×10 ⁵ Pa or less, more preferably 7.0×10 ⁴ Pa or less, and particularly preferably 5.5×10 Below ⁴ Pa.

In addition, the maximum value of tanδ can be measured using "Discovery HR-3" manufactured by TA Instruments, for example, and the storage elastic modulus can be measured by a method based on JIS K7244-6.

[6. Manufacturing method of adhesive sheet] The manufacturing method of the adhesive sheet of this embodiment is not specifically limited, For example, it can be carried out by the following method.

First, a (meth)acrylate polymer, an isocyanate cross-linking agent, and a rosin ester-based tackifying resin are mixed, and the above-mentioned additives are added as necessary.

(Meth)acrylate polymers can be produced by polymerizing a mixture of monomers constituting the polymer using a common radical polymerization method. The polymerization of the (meth)acrylate polymer is preferably carried out by a solution polymerization method using a polymerization initiator as necessary. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, and the like, and two or more types may be used in combination.

Examples of the polymerization initiator include azo compounds, organic peroxides, and the like, and two or more types may be used in combination. Examples of azo compounds include: 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane) Alkane 1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxypentane) nitrile), 2,2'-azobis(2-methylpropionic acid dimethyl ester), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2 -hydroxymethylpropionitrile), 2,2'-azobis[2-(2-imidazolin-2-yl)propane], etc.

Examples of organic peroxides include: benzoyl peroxide, tert-butyl peroxybenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, Di(2-ethoxyethyl) peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, 3,5,5-trimethylhexyl peroxide, Dipropyl peroxide, diethyl peroxide, etc.

Furthermore, in the above-mentioned polymerization step, the weight average molecular weight of the obtained polymer can be adjusted by formulating a chain transfer agent such as 2-mercaptoethanol.

After obtaining the (meth)acrylate polymer, add an isocyanate cross-linking agent, a rosin ester-based adhesive resin, and optional additives and diluting solvents to the solution of the (meth)acrylate polymer, and Mix thoroughly to obtain a solvent-diluted adhesive composition (coating solution).

Furthermore, when any of the above components is used in solid form or when it is mixed with other components in an undiluted state and precipitates, the component can be separately pre-dissolved or diluted in a diluted solution. Solvent before mixing with other ingredients.

As the dilution solvent, for example, aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as carbon dichloride and ethylene chloride, methanol, ethanol, and propanol can be used. , butanol, 1-methoxy-2-propanol and other alcohols, acetone, methyl ethyl ketone, 2-pentanone, isophorone, cyclohexanone and other ketones, ethyl acetate, butyl acetate and other esters, Cellosolve solvents such as ethyl cellosolve, etc.

The concentration and viscosity of the coating solution thus prepared only need to be within a range that enables coating, and can be appropriately selected depending on the situation. For example, the concentration of the adhesive composition can be diluted to 10 mass% to 60 mass%. Furthermore, when obtaining the coating solution, it is not necessary to add a diluting solvent. If the adhesive composition has a viscosity that enables coating, the diluting solvent does not need to be added. In this case, the adhesive composition is a coating solution in which the polymerization solvent of the (meth)acrylate polymer is directly used as the diluting solvent.

The above-mentioned cross-linking of the adhesive composition can usually be performed by heat treatment. Furthermore, the heat treatment may be performed incidentally by a drying treatment performed to volatilize a dilute solvent or the like from the coating film of the adhesive composition applied to the desired object.

The heating temperature of the heat treatment is preferably 50°C to 150°C, more preferably 70°C to 120°C. In addition, the heating time is preferably from 10 seconds to 10 minutes, for example, and more preferably from 50 seconds to 2 minutes.

After the heat treatment, a curing period of about 1 to 2 weeks can also be set at normal temperature (such as 23°C and 50%RH) as needed. When this curing period is required, the adhesive sheet will be formed after the curing period. On the other hand, when there is no need for a curing period, an adhesive sheet will be formed after the heat treatment is completed.

Through the above-mentioned heat treatment (and aging), the (meth)acrylate polymer is fully cross-linked through the isocyanate-based cross-linking agent to form a cross-linked structure, and an adhesive sheet is obtained.

[7. Adhesive sheet laminate] Next, the adhesive sheet laminate of this embodiment will be described. As shown in FIG. 1 , the adhesive sheet laminate of this embodiment includes a first release sheet 1 , an adhesive layer 2 laminated on the first release sheet 1 , and a second release sheet 3 arranged on the adhesive layer 2 . The first release sheet 1 and the second release sheet 3 are known release sheets and have a release surface on at least one side.

The adhesive sheet laminate can be produced in the following manner, for example. First, the first release sheet 1 is pulled out from the take-out roller around which the first release sheet 1 is wound. Then, the above-mentioned coating liquid of the adhesive composition is applied to the release surface of the first release sheet 1, and heat treatment is performed to thermally cross-link the adhesive composition, thereby forming the adhesive layer 2. The adhesive layer 2 corresponds to the adhesive sheet of the present invention. Thereafter, the second release sheet 3 is attached so as to cover the adhesive layer 2 . At this time, the peeling surface of the second peeling sheet 3 is brought into contact with the adhesive layer 2 . In this way, the adhesive sheet laminate shown in Figure 1 is formed.

[8. Covering film] The cover film attached to the image display device via the above-mentioned adhesive sheet is not particularly limited, and a known cover film can be used. There are many ways to install the above adhesive sheet on the cover film. For example, the adhesive layer can be attached to the cover film by peeling off the first release sheet or the second release sheet of the adhesive sheet laminate and then transferring the exposed adhesive layer to the cover film. Alternatively, the adhesive layer (adhesive sheet) may be formed by applying the above-mentioned coating liquid of the adhesive composition on one side of the cover film and performing heat treatment to thermally cross-link the adhesive composition.

[9.Features] Since the adhesive sheet of the present invention has a low storage elastic modulus and contains a rosin ester-based adhesive resin, when a cover film provided with the adhesive sheet is attached along an image display device having a curved portion, the adhesive sheet can The stress exerted on the covering film due to buckling is relaxed. Therefore, it is possible to prevent cracking or peeling including cracks from occurring when the cover film flexes. [Example]

Next, embodiments 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] Adhesive sheets of Examples 1 to 7 and Comparative Examples 1 to 4 were prepared. Furthermore, the cover film was attached to the target film using each adhesive sheet, and a laminated body as shown in FIG. 2 was produced. Covering films and target films are as follows. (1) Covering film: an acrylic resin film with a thickness of 100 μm and no cracks when R=3.0mm in the buckling test (2) Target film: Polyimide resin film with a thickness of 30 μm Furthermore, the target film is assumed to be an image display device to which the cover film is attached.

The compositions of the adhesives of Examples 1 to 7 and Comparative Examples 1 to 4 are as follows. Coronate L-55E constituting the isocyanate cross-linking agent is manufactured by Tosoh Corporation, BXX8515 is manufactured by Toyo Ink Corporation, and Duranate TPA-100 is manufactured by Asahi Kasei Corporation. In addition, Pinecrystal ME-GH constituting the rosin ester-based adhesive-imparting resin is manufactured by Arakawa Chemical Industry Co., Ltd. For acrylate copolymers, the weight average molecular weight and hydroxyl value are disclosed. [Table 1] Acrylate copolymer Isocyanate cross-linking agent Rosin ester-based adhesion-imparting resin Example 1 Weight average molecular weight: 400,000 Hydroxyl value: 10mgKOH/g to 20mgKOH/g 100 parts by weight Coronate L-55E 0.13 parts by weight Pinecrystal ME-GH 5 parts by weight Example 2 Weight average molecular weight: 400,000 Hydroxyl value: 10mgKOH/g to 20mgKOH/g 100 parts by weight Coronate L-55E 0.13 parts by weight Pinecrystal ME-GH 10 parts by weight Example 3 Weight average molecular weight: 400,000 Hydroxyl value: 10mgKOH/g to 20mgKOH/g 100 parts by weight Coronate L-55E 0.13 parts by weight Pinecrystal ME-GH 20 parts by weight Example 4 Weight average molecular weight: 400,000 Hydroxyl value: 10mgKOH/g to 20mgKOH/g 100 parts by weight Coronate L-55E 0.13 parts by weight Pinecrystal ME-GH 5 parts by weight Example 5 Weight average molecular weight: 400,000 Hydroxyl value: 10mgKOH/g to 20mgKOH/g 100 parts by weight Coronate L-55E 0.13 parts by weight Pinecrystal ME-GH 5 parts by weight Example 6 Weight average molecular weight: 400,000 Hydroxyl value: 10mgKOH/g to 20mgKOH/g 100 parts by weight Coronate L-55E 0.13 parts by weight Pinecrystal ME-GH 2 parts by weight Example 7 Weight average molecular weight: 400,000 Hydroxyl value: 10mgKOH/g to 20mgKOH/g 100 parts by weight Coronate L-55E 0.13 parts by weight Pinecrystal ME-GH 30 parts by weight Comparative example 1 Weight average molecular weight: 650,000 Hydroxyl value: 30mgKOH/g to 40mgKOH/g 100 parts by weight BXX8515 0.2 parts by weight - Comparative example 2 Weight average molecular weight: 650,000 Hydroxyl value: 30mgKOH/g to 40mgKOH/g 100 parts by weight BXX8515 0.2 parts by weight Pinecrystal ME-GH 5 parts by weight Comparative example 3 Weight average molecular weight: 800,000 Hydroxyl value: 20mgKOH/g to 30mgKOH/g 100 parts by weight BXX8515 0.2 parts by weight - Comparative example 4 Weight average molecular weight: 900,000 Hydroxyl value: 20mgKOH/g to 30mgKOH/g 100 parts by weight Duranate TPA-100 0.2 parts by weight -

The physical property values of the adhesive sheets of Examples 1 to 7 and Comparative Examples 1 to 4 are as follows.

The storage elastic modulus and loss tangent tan δ of the adhesive sheet were measured using "Discovery HR-3" manufactured by TA Instruments. The measurement conditions are as follows. (Measurement conditions) Measurement mode: Cut mode Deformation rate: 0.1% Measuring frequency: 1Hz Measuring temperature: -60℃ to 25℃ (heating at 5℃/min) Measurement sample: The adhesive layers of each adhesive sheet are stacked so that the total thickness becomes approximately 1 mm and measured.

[Table 2] Thickness(μm) Storage elastic modulus at 25℃ (Pa) -20℃ storage elastic modulus (Pa) 25℃tanδ -20℃tanδ Maximum value of tanδ(℃) Example 1 10 2.4×10 ⁴ 5.2×10 ⁴ 0.36 0.45 -55 Example 2 10 2.3×10 ⁴ 4.6×10 ⁴ 0.32 0.45 -55 Example 3 10 2.2×10 ⁴ 4.2×10 ⁴ 0.30 0.44 -55 Example 4 5 2.4×10 ⁴ 5.2×10 ⁴ 0.36 0.45 -55 Example 5 100 2.4×10 ⁴ 5.2×10 ⁴ 0.36 0.45 -55 Example 6 10 2.5×10 ⁴ 5.4×10 ⁴ 0.36 0.45 -55 Example 7 10 2.1×10 ⁴ 4.0×10 ⁴ 0.25 0.44 -55 Comparative example 1 10 1.1×10 ⁵ 1.9×10 ⁵ 0.38 1.1 -15 Comparative example 2 10 1.1×10 ⁵ 1.7×10 ⁵ 0.4 1.15 -17 Comparative example 3 10 1.9×10 ⁵ 2.1×10 ⁵ 0.38 0.9 -5 Comparative example 4 10 2.2×10 ⁵ 3.4×10 ⁵ 0.49 0.82 -1.1

In addition, for each adhesive sheet, the total light transmittance and haze rate were measured using a laminated structure of glass/adhesive sheet/PET film. The total light transmittance was measured in accordance with JIS K7136-1 and the haze was measured in accordance with JIS K7136. The results are shown in Table 3.

Furthermore, a buckling test was performed on the laminated body shown in FIG. 2 using each adhesive sheet. The buckling test system uses the unloaded U-shaped testing machine shown in Figure 3. This testing machine has two rotatable movable plates, and the rotation axes of the movable plates are arranged close to each other so that they become parallel. Then, the laminated body as the sample piece was placed on the movable plate in the horizontal state shown in (a) of FIG. 3 . At this time, the laminated body is arranged so that the film surface of the laminated body is in contact with the movable plate. Then, as shown in (b) of FIG. 3 , the sample piece is bent into a U shape by rotating the two movable plates 90 degrees. This buckling is repeated at a test speed of 0.85 seconds/time at normal temperature. Then, after the test, it was confirmed whether cracks occurred in the covering film of the sample piece, and the buckling resistance was evaluated based on the following standards (1) to (3). The test is carried out so that the buckling radius R of the sample piece becomes 2.5 mm and 3.0 mm, and the test result is tested to see whether the result is one of the following (1) to (3). (1) No cracks occurred under the condition of R=2.5mm and the number of buckling times is more than 100,000 times (R=2.5mm, no cracks); (2) Under the conditions of R=2.5mm and the number of buckling times does not reach 100,000 times Cracks occurred under the condition of R=3.0mm and the number of buckling times was more than 100,000 times, but no cracks occurred (R=3.0mm, no cracks); (3) When R=3.0mm and the number of buckling times did not reach 100,000 times Cracks occurred under the conditions (R=3.0mm, cracks occurred) [Table 3] Total light transmittance (%) Haze(%) Buckling test Example 1 90.6 0.7 (1)R=2.5mm, no cracks Example 2 90.6 0.7 (1)R=2.5mm, no cracks Example 3 90.4 0.8 (1)R=2.5mm, no cracks Example 4 90.5 0.7 (1)R=2.5mm, no cracks Example 5 90.2 0.7 (1)R=2.5mm, no cracks Example 6 90.6 0.7 (2)R=3.0mm, no cracks Example 7 90.2 1.1 (1)R=2.5mm, no cracks Comparative example 1 90.6 0.7 (3)R=3.0mm, cracks occur Comparative example 2 90.6 0.7 (3)R=3.0mm, cracks occur Comparative example 3 90.6 0.7 (3)R=3.0mm, cracks occur Comparative example 4 90.6 0.7 (3)R=3.0mm, cracks occur

According to Table 3, Examples 1 to 7 did not produce cracks in the covering film under the conditions of R = 2.5 mm or 3.0 mm and the number of buckling times of more than 100,000 times, while Comparative Examples 1 to 4 did not produce cracks in the covering film under the conditions of R = 3.0 mm and flexion times of more than 100,000 times. Cracks occurred under the condition that the number of buckling times did not reach 100,000 times. In Example 6, cracks occurred under the conditions of R = 2.5 mm and the number of buckling times less than 100,000 times. However, it is believed that the reason for this is that the content of the rosin ester-based adhesive-imparting resin is small.

It is considered that Comparative Examples 1 to 4 have low buckling resistance due to their high storage elastic modulus at 25°C. Furthermore, it is considered that Comparative Example 2 has low flexural resistance even if it contains a rosin ester-based tackifier-imparting resin because the storage elastic modulus is high as described above.

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

[Fig. 1] is a cross-sectional view of an adhesive sheet laminate according to an embodiment of the present invention. [Figure 2] is a cross-sectional view of the test piece used for the buckling test. [Fig. 3] is a diagram showing the buckling test method.

1: 1st peeling piece

2: Adhesive sheet (adhesive layer)

3: 2nd peeling piece

Claims (4)

An adhesive sheet for an image display device, having an adhesive layer including a cross-linked product of an adhesive composition containing: (meth)acrylate copolymer as a main component, an isocyanate-based cross-linking agent, and Rosin ester-based adhesive imparting resin; containing 1 to 40 parts by weight of the aforementioned rosin ester-based adhesive imparting resin relative to 100 parts by weight of the aforementioned (meth)acrylate copolymer; relative to the aforementioned (meth)acrylic ester copolymer 100 parts by weight of the material, the content of the aforementioned isocyanate cross-linking agent is from 0.01 to 0.13 parts by weight; the weight average molecular weight of the aforementioned (meth)acrylate copolymer is from 200,000 to 400,000; the aforementioned (methyl) ) The hydroxyl value of the acrylate copolymer is 5 mgKOH/g or more and 20 mgKOH/g or less; the maximum value of tan δ of the aforementioned adhesive layer at 1Hz is less than -20°C; the storage elastic modulus of the aforementioned adhesive layer at 1Hz and 25°C is 1.0 ×10 ⁵ Pa or less. For example, the adhesive sheet for image display devices described in claim 1 has a storage elastic modulus of 1.0×10 ⁵ Pa or less at 1 Hz and -20°C. The adhesive sheet for an image display device as described in claim 1 has a thickness of 5 μm to 100 μm. An adhesive sheet laminated body for an image display device, which is provided with a base material sheet for peeling off, and the base material sheet for peeling off is attached to at least one side of the adhesive sheet for an image display device according to claim 1.

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