TRANSPARENT PRESSURE-SENSITIVE ADHESIVE SHEET, IMAGE DISPLAY

APPARATUS COMPRISING THE SAME, AND THE PRODUCTION METHODS

FOR MAKING THE IMAGE DISPLAY APPARATUS

TECHNICAL FIELD

The present disclosure relates to a transparent pressure-sensitive adhesive sheet and an image display apparatus comprising the same.

BACKGROUND There has recently been spreading of a method in which the gap between an image display screen and a surface protective layer or touch panel or the gap between a surface protective layer and a touch panel in an image display apparatus is replaced by a transparent material whose refractive index is closer to that of the image display screen, than the refractive index of air, thereby enhancing transparency and preventing lowering of brightness or contrast of the image display apparatus. Examples of the transparent material include transparent polymer materials such as a transparent resin sheet, a pressure-sensitive adhesive, and a curing adhesive (e.g., silicone gel).

Japanese Unexamined Patent Publication (kokai) No. 09-197387 describes a method for producing a liquid crystal display apparatus in which a visible side of a liquid crystal display panel and a transparent protective plate are adhered through a transparent resin sheet as a transparent polymer material in a state where a volatile liquid is allowed to exist between the transparent resin sheet and either or both of the liquid crystal display panel and the transparent protective plate through a transparent resin sheet made of a polymer containing a plasticizer. Japanese Unexamined Patent Publication (Kokai) No. 06-59253 describes a method for producing a liquid crystal display apparatus in which a reaction-curable silicone gel composed of a colorless and transparent elastic resin as a transparent polymer material. The colorless and transparent elastic resin is injected in a liquid form and then cured thereby fixing the crystal display panel with the glass plate. Japanese Unexamined Patent Publication (Kokai) No. 03-204616 describes a liquid crystal display in which a transparent polymer material is filled between a liquid crystal display device and a protective plate. A material obtained by dissolving an unsaturated polyester in a polymerizable monomer is used as the transparent polymer material, and this material is injected in a gap between the liquid crystal display device and the protective plate, and then solidified.

Japanese Unexamined Patent Publication (Kokai) No. 2007-31506 describes a pressure-sensitive adhesive composition for an optical member, comprising 100 parts by mass of a (meth)acrylic polymer (A) containing, as a copolymerization component, 0.01 to 5 parts by mass of a hydroxyl group-containing (meth)acrylate represented by the formula: CH ₂ =CR ¹ COOR ² (wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents a C _4-12 hydroxylalkyl group having at least one hydroxyl group) based on 100 parts by mass of an alkyl (meth)acrylate, and 0.02 to 2 parts by mass of a peroxide.

SUMMARY

As the transparent material, there can be mentioned an adhesive, a silicone gel, a pressure-sensitive adhesive, etc. However, the adhesive involves a process of handling liquids and thus it has a problem that the manufacturing process may become complicated.

Also, because the silicone gel has a weak adhesive strength, a long-term reliability becomes a problem. In contrast, a pressure-sensitive adhesive can solve these problems, and thus is effective in a structure where an image display apparatus and a protective layer cover are directly attached. However, with conventional acrylic pressure-sensitive adhesives containing an acrylic acid alkyl ester and an acrylic acid, unevenness may occur in the display apparatus when the application thickness of the pressure-sensitive adhesive becomes thin. Also, under high temperature and high humidityconditions, there can be a risk of blister formation and detachment of the pressure-sensitive adhesive.

Solutions for inhibition of uneven display are desired when (i) the application thickness of the pressure-sensitive adhesive is 10 μm or less, (ii) the surface protective layer of the image display apparatus has an uneven shape, (iii) the pressure-sensitive adhesive sheet is applied to the surface of uneven shape or (iv) the pressure-sensitive adhesive sheet is applied to an image display unit screen having an uneven shape (for example, a polarizer). In addition to inhibition of uneven display, it is required to provide a transparent pressure-sensitive adhesive sheet, which enables prevention of blister formation or detachment of the sheet at the interface with a surface protective layer, an image display unit screen or a touch panel in an image display apparatus (sometimes referred to as "adherent", hereinafter) even when allowed to stand in a high-temperature and high-humidity environment, and also does not cause whitening.

According to one aspect of the present disclosure, there is provided a method of producing an image display apparatus comprising the steps of: (1) preparing a transparent pressure-sensitive adhesive sheet having 1.0 x 10 ⁴ Pa or less and 1.0 x 10 ³ Pa or more of a storage elastic modulus at 1 Hz and 8O ⁰ C, wherein the sheet comprises (A) an alicyclic hydrocarbon resin, (B) an amorphous saturated polyolefm resin, (C) an acrylic group-containing resin, and (D) an initiator that triggers the reaction of the resins, and wherein, based on the amount of 100 parts by mass of (A) component, the amount of (B) component is 10-200 parts by mass, the amount of (C) component is 10-200 parts by mass, and the amount of (D) component is 0.1-20 parts by mass;

(2) attaching the pressure-sensitive adhesive sheet to a surface protective layer or a touch panel;

(3) attaching the opposite side of the pressure-sensitive adhesive sheet to which a surface protective layer or a touch panel is attached, to the image display unit screen; and

(4) curing the pressure-sensitive adhesive.

According to another aspect of the present disclosure, there is provided a transparent pressure-sensitive adhesive sheet for attaching a surface protective layer or a touch panel to an image display unit screen or for attaching a surface protective layer to a touch panel, in the image display apparatus. The transparent pressure-sensitive adhesive sheet has 1.0 x 10 ⁴ Pa or less and 1.0 x 10 ³ Pa or more of a storage elastic modulus at 1 Hz and 80 ⁰ C. The transparent pressure-sensitive adhesive sheet comprises (A) an alicyclic hydrocarbon resin, (B) a saturated polyolefm resin, (C) an acrylic group-containing resin, and (D) an initiator that triggers the reaction of the resins, and wherein, based on the amount of 100 parts by mass of (A) component, the amount of (B) component is 10-200 parts by mass, the amount of (C) component is 10-200 parts by mass, and the amount of (D) component is 0.1-20 parts by mass.

According to further aspect of the present disclosure, there is provided an image display apparatus comprising an image display unit, the above-mentioned transparent pressure-sensitive adhesive sheet, and a surface protective layer.

Herein, "storage elastic modulus" means the storage elastic modulus measured by the viscoelastic measurement within a temperature range from -6O ⁰ C to 200 ⁰ C at 5°C/min of a temperature increasing rate under 1 Hz of a shear mode. The application temperature (usually 40-80 ⁰ C) in the step of attaching the opposite side of the pressure-sensitive adhesive sheet to which a surface protective layer and/or a touch panel is attached, to the image display unit screen is important. By using the methods provided herein, the produced image display apparatus

1) has substantially no unevenness of display on said display screen, 2) has substantially no blister formation in the interface, when attached to a surface protective layer, an image display unit screen or a touch panel even in a high-temperature and high-humidity environment, and 3) can also inhibit the detachment of the pressure-sensitive adhesive sheet attached between a surface protective layer or a touch panel and an image display unit screen.

In other words, by using the transparent pressure-sensitive adhesive sheet provided as another aspect of the present disclosure, there will be substantially no unevenness of display when it is used in attaching a surface protective layer or a touch panel to an image display unit screen, or in attaching a surface protective layer to a touch panel, in the image display apparatus. In particular, the generation of unevenness of display can be prevented, even when the transparent pressure-sensitive adhesive sheet is applied to a surface protective layer having uneven shape, or when it is applied to an image display unit screen having an uneven shape (for example, a polarizer). Also, the transparent pressure-sensitive adhesive sheet has substantially no blister formation in the interface, when it is attached to a surface protective layer, an image display unit screen or a touch panel in the image display apparatus, even in a high-temperature and high-humidity environment. Furthermore, detachment after attaching a surface protective layer or a touch panel to an image display unit screen or after attaching a surface protective layer to a touch panel, in the image display apparatus can be inhibited.

Furthermore, because the transparent pressure-sensitive adhesive (PSA) sheet has a low water-absorbing property, it can prevent whitening in the image display apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 A cross-sectional view showing one embodiment of an image display device comprising the laminate of the present disclosure. Fig. 2 A cross-sectional view showing another embodiment of an image display apparatus comprising the laminate of the present disclosure.

Fig. 3 A cross-sectional view showing still another embodiment of an image display apparatus comprising the laminate of the present disclosure. Fig. 4 A cross-sectional view showing yet still another embodiment of an image display apparatus comprising the laminate of the present disclosure.

DETAILED DESCRIPTION

Turning now to the components of the transparent PSA sheet, component (A) is an alicyclic hydrocarbon resin. It is a resin that has excellent water-absorbing property and compatible with an amorphous saturated polyolefm resin (such as a polyisobutylene resin) and which can control the storage elastic modulus of a pre-curing composition at room temperature. Specifically, there can be mentioned a petroleum resin, a terpene resin, a rosin resin that are known as a tackifier, and a hydrogenated resin thereof, and a modified resin that is copolymerized with an aromatic resin.

Alicyclic hydrocarbon resins include, specifically, a terpene resin (Clearon P, M and K series etc.), a rosin and a rosin ester resin (Foral AX, Foral 105, Pensel A, Estergum H, Superester A series etc.), a disproportionated rosin and a disproportionated rosin ester resin (Pine Crystal series, etc.), a hydrogenated dicyclopentadiene-based resin (Escorez 5300 and 5400 series, Eastotac H series etc.) that are hydrogenated resins of the C5-based petroleum resins obtained by copolymerizing C5 fractions such as pentene, isoprene, piperine and 1,3-pentadiene formed by the thermal decomposition of petroleum naphtha, partially hydrogenated aromatic modified dicyclopentadiene-based resins (Escorez 5600 series etc.), a hydrogenated resin (Alcon P or M series) of C9-based petroleum resins obtained by copolymerizing C9 fractions such as indene, vinyltoluene, α- or β-methylstyrene formed by thermal decomposition of petroleum naphtha, a hydrogenated resin (I-Marv series) of the copolymerized petroleum resin of the above-mentioned C5 and C9 fractions, and the like. Among these polymers, a hydrogenated resin is preferred in terms of securing a low water-absorbing property and transparency. Examples of a hydrogenated resin include, for example, from a partially hydrogenated resin to a completely hydrogenated resin, that is different in the rate of hydrogenation, and either can be used. However, from the viewpoint of securing a water-absorbing property, compatibility with a binder polymer and transparency, a completely hydrogenated one is preferred.

The alicyclic hydrocarbon resin has a softening point (ring and ball softening point). Depending on the pressure-sensitive adhesive property, operating temperature, and ease of production of the composition, one having any ring and ball softening point can be used. Generally, one having a ring and ball softening point in the range of about

50-200 ⁰ C, or about 70-150 ⁰ C may be used.

The weight-average molecular weight of the alicyclic hydrocarbon resin may usually be in the range of about 200-5,000, and specifically one in the range of about 500-3,000 may be suitable. Within these ranges, the storage elastic modulus at the attaching temperature can be lowered, and the compatibility with amorphous polyolefϊns can be secured.

In the transparent pressure-sensitive adhesive sheet of the present disclosure, the alicyclic hydrocarbon resin may be blended with an amorphous saturated polyolefϊn at various ratios. Generally, it is preferred that the saturated polyolefm may be blended at the lower limit of 10 parts by mass or 20 parts by mass and the upper limit of 200 parts by mass or 150 parts by mass relative to 100 parts by mass of the alicyclic hydrocarbon resin. The second component (B), which is an amorphous polyolefm, is a polyolefϊn that has practically no carbon-carbon double or triple bonds. Among the carbon-carbon bonds contained in the saturated polyolefm, 90% or more is a single bond. Examples of a saturated polyolefϊn include polyisobutylene, a poly α-olefϊn, an ethylene propylene copolymer, an ethylene α-olefϊn copolymer, a propylene α-olefϊn copolymer, a hydrogenated polybutadiene, and a block copolymer thereof with styrene and the like.

They may be used alone or in combination with two or more. An amorphous polymer refers to a polymer that has an extremely low crystallinity or that can not enter into the crystalline state. In an amorphous polymer, its glass transition temperature can be measured but not its melting point. When an amorphous polymer is used, there is no reduction in the transparency due to crystallization.

Furthermore, in more detail, as the amorphous saturated polyolefϊn, a block copolymer (hereinafter referred to as "block copolymer") having a saturated polyolefϊn block and an aromatic vinyl monomer block is preferred. This block copolymer has a first block comprising a polyolefϊn having substantially no carbon-carbon double or triple bonds and a second block comprising an aromatic vinyl monomer. Among the carbon-carbon bonds contained in the saturated polyolefm block, 90% or more is the single bond. Examples of an aromatic vinyl monomer include styrene, p-methylstyrene, α-methylstyrene, indene and the like. They may be used alone or in combination with two or more. Examples of a block copolymer include, for example, a styrene-ethylene-propylene-styrene block copolymer, a styrene-ethylene-propylene block copolymer, a styrene-ethylene-butylene-styrene block copolymer and the like.

Among them, saturated polyisobutylene is preferred. Polyisobutylene is a resin that has a polyisobutylene skeleton. Such a polyisobutylene resin can be prepared by polymerizing isoprene alone, and isoprene and n-butene, or isoprene or butadiene in the presence of a Lewis acid catalyst such as aluminum chloride and boron trifluoride. Specifically, such a polyisobutylene resin is known under the trade name of Vistanex (Exxon Chemical Co.), Hycar (Goodrich), Oppanol (BASF), JSR butyl (Japan Butyl Co., Ltd.), and the like. Such an amorphous saturated polyolefm for use in the present disclosure is highly compatible with (A) an alicyclic hydrocarbon resin, and thus can form a transparent film. Because a saturated polyolefin has a low surface energy, it may easily spread on the adherent when used as a pressure-sensitive adhesive, and voids in the interface may not be generated easily. Furthermore, because it has a low water-absorbing property, it is suitable as a base resin for sheet materials.

An amorphous saturated polyolefin has a weight-average molecular weight (molecular weight in terms of polystyrene by GPC) of about 10,000 or more and 2,000,000 or less, and specifically about 100,000 or more and 1,000,000 or less. Within this range, fluidity can be secured and sufficient thermal resistance can be maintained. The third component (C), which is a curable resin, increases the fluidity of the composition before curing and wettability to the adherent and also follows the uneven surface thereby inhibiting the generation of unevenness in liquid crystal. Furthermore, curing can enhance the retentive strength. It is also possible to control physical properties after curing to the desired physical properties by the additive amount and the type thereof.

The curable resin (C) may be any of a thermosetting resin and a radiation (light)-curable resin. Examples of curable resins (liquid monomers and/or oligomers) include those referred to in the industry as curable acrylic compounds. In one aspect, they are selected from acrylated urethanes, acrylated epoxy, aminoplast derivatives having α,β -unsaturated carbonyl groups, ethylenic unsaturated compounds, isocyanurate derivatives having at least one acrylate group, isocyanates having at least one acrylate group, and mixtures thereof.

A curable acrylic compound generally has a (meth) acryloyl group in the molecule, and has a molecular weight of 70-700, and in an embodiment 80-600. Generally, an acrylic acid ester or a methacrylic acid ester is included. Examples of photocurable acrylic compounds include the following materials described in the next two paragraphs.

Examples of mono functional acrylic monomers include (meth)acrylates that include linear alkyl groups such as lauryl (meth)acrylate, cetyl (meth)acrylate (n-C16) where "n" means "normal" type and "C 16" denotes 16 atoms of carbon, stearyl (meth)acrylate (n-C18), aralkyl (meth)acrylate (n-C20) and behenyl (meth)acrylate (n-C22), and (meth)acrylates that include branched alkyl groups such as 2-ethylhexyl

(meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isododecyl (meth)acrylate, isotridecyl (meth)acrylate, isomyristyl (meth)acrylate, isocetyl (meth)acrylate (iso-C16), isostearyl (meth)acrylate (iso-C18) and 2-octyldodecanyl (meth)acrylate (iso-C20). There can also be mentioned alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate and dicyclopentanyl (meth)acrylate. There can also be mentioned substituted acrylamide such as N, N-dimethyl acrylamide, N, N-diethyl acrylamide, acryloyl morpholine, N, N-dimethylaminopropyl acrylamide, isopropyl acrylamide, t-butyl acrylamide and t-octyl acrylamide. Examples of polyfunctional monomers include hexanediol (meth)acrylate, neopentyl di(meth)acrylate, nonandiol di(meth)acrylate, decanediol di(meth)acrylate, dodecandiol di(meth)acrylate, cyclohexane dimethanol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, hydrogenated polybutadiene di(meth)acrylate, hydrogenated isoprene di(meth)acrylate, trimetilolpropane tri(meth)acrylate, and the like. There can also be used acrylates that are polyhydric alcohols for use in acryl monomers that have been oligomerized by the urethane bond. Mixtures thereof can also be used. Generally, among the above use embodiments, (meth)acrylate resins having a long chain or alicyclic skeleton of 9 carbons or more are preferred. Generally, photocurable resins having a (meth)acryloyl group or a glycidyl group that have a relatively high polarity and thus are not very compatible with saturated olefins having a very low polarity, but these compounds can be compatible with mixtures of an alicyclic hydrocarbon resin (A) and a saturated polyolefm (B).

In the pressure-sensitive adhesive sheet of the present disclosure, (C) a curable resin may be blended with (A) an alicyclic hydrocarbon resin and (B) an amorphous saturated polyolefm at various ratios. Generally, relative to 100 parts by mass of (A) component and 10-200 parts by mass of (B) component, the amount of (C) component may be in the range of 10-200 parts by mass, and more preferably 50-150 parts by mass.

By using in these ranges, sufficient cohesiveness can be obtained, and a composition that is small in shrinkage during curing and that cannot be easily peeled, can be obtained. Specific examples of radiation (light) polymerization initiators include, as a radical polymerization initiator, benzophenone,

2-methyl- 1 - [4-(methy lthio)phenyl] ] -2-morpholinopropane- 1 -one, camphorquinone, benzoin, benzoin methylether, benzoin-n-propylether, benzoin-n-butylether, benzyl, p-methylbenzophenone, diacetyl, eosine, thionine, Michler's ketone of the general formula ((CH3)2NC6H ₄ ) ₂ CO, acetophenone, 2-chlorothioxanthone, anthraquinone, chloroanthraquinone, 2-methylanthraquinone, (α-hydroxyisobutylphenone, p-isopropyl-α-hydroxyisobutylphenone, α,α'-dichloro-4-phenoxyacetophenone, 1 -hydroxy- 1 -cyclohexyl acetophenone, 2,2-dimethoxy-2-phenylacetophenone, methylbenzoin formate, dichlorothioxanthone, diisopropylthioxanthone, phenyldisulfido-2-nitrosofluorene, butyloine, anisoinethylether, tetramethylthiuram disulfide, 2,2-dimethoxy- 1 ,2-diphenylethane- 1 -one, 1 -hydroxy-cyclohexyl-phenyl-ketone,

2-hydroxy-2-methyl- 1 -phenyl-propane- 1 -one,

1 - [4-(2-hydroxyethoxy)-phenyl] -2-hydroxy-2-methyl- 1 -propane- 1 -one,

2-hydroxy- 1 - {4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl} -2-methyl-propane- 1 - one, 2-methyl- l-(4-methylthiophenyl)-2-morpholinopropane-l -one,

2-benzyl-2-dimethylamino- 1 -(4-morpholinophenyl)-butanone- 1 ,2-(dimethylamino)-2-[(4- methylphenyl)methy 1] - 1 - [4-(4-morpholinyl)phenyl] - 1 -butanone, 2,4,6-trimethylbenzoyl-diphenyl-phosphoinoxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide and the like.

Specific examples of thermal polymerization initiators include, as a radical polymerization initiator, organic peroxides such as iso-butyryl peroxide, cumyl peroxyneodecanoate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, cumyl peroxyneohexanoate, di(2-ethoxyethyl)peroxydicarbonate, di(methoxyisopropyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, t-butyl peroxyneodecanoate, t-hexyl peroxyneohexanoate, t-butyryl peroxy neohexanoate, t-butyryl peroxypivalate, lauroyl peroxide, cumyl peroxyoctate and benzoyl peroxide. There can also be mentioned azo compounds such as

2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2-methylvaleronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2-methylpropionate) and 4,4'-azobis(4-cyanovaleric acid). (D) A radiation (light) polymerization initiator may be contained at an amount of

0.1-20 parts by mass and in some embodiment 0.5-5 parts by mass. Within this range, acrylic monomers can preferably be polymerized and the storage stability of the resin compositions can be secured.

By using the above-mentioned monomer components in the above-mentioned composition, the obtained pressure-sensitive adhesive sheet can attain a sufficient follow-up property at the time of attaching before curing, and has a sufficient retention after curing. In general, the term "follow-up property" describes a situation where the PSA sheet has sufficiently high fluidity such that there is substantially no void and separation between the surface protective layer and the PSA sheet, even if the surface protective layer is uneven. By using a transparent pressure-sensitive adhesive sheet having such a sufficient follow-up property, even when a transparent pressure-sensitive adhesive sheet is to be applied on an image display unit screen provided with a surface protective layer having an uneven shape or a layer having an uneven shape (for example, a polarizer), the unevenness can be absorbed, resulting in the eliminating uneven display in the image display apparatus. Also, even when there is variation in the thickness of the sheet per se, it can be attached without gaps on the surface of the adherent because it has sufficient flexibility, and can prevent the generation of uneven display in the image display apparatus.

Thus, the follow-up property of the pressure-sensitive adhesive sheet can be expressed in terms of storage elastic modulus of the resin composition. If the storage elastic modulus of the resin composition at 8O ⁰ C and 1 Hz is 1.0 x 10 ⁴ Pa or less, uneven display can be prevented even when the pressure-sensitive adhesive sheet is applied to an adherent having a surface of uneven shape having about 10 μm. Furthermore, if the storage elastic modulus of the resin composition at 8O ⁰ C and 1 Hz is 1.0 x 10 ⁴ Pa or less, uneven display can be reduced even when the pressure-sensitive adhesive sheet is applied to an adherent having an uneven shape having greater height difference or more complicated shape.

And if the storage elastic modulus of the resin composition at 8O ⁰ C and 1 Hz is 1.0 x 10 ³ Pa or more, the resin composition does not flow-out at application and can be used without any inconvenience. The storage elastic modulus of a resin composition can be adjusted by suitably changing the kinds of A, B and C components, molecular weight, and ratios of the components.

Furthermore, by imparting a low water-absorbing property, whitening in the image display apparatus can be prevented. The extent of prevention of whitening (transparency) can be indicated by the haze value. The haze value is measured by the following environmental test in accordance with JIS K 7136. Firstly, the transparent pressure-sensitive adhesive sheet is attached to a transparent adherent (for example, the surface protective layer of the image display apparatus) to form a laminate, the resulting laminate is allowed to stand under conditions at a temperature of 6O ⁰ C and relative humidity (RH) of 90% for three days, and then the haze value of the laminate is measured after three days. It can be judged that whitening has not occurred, if the haze value of the laminate obtained by attaching the transparent pressure-sensitive adhesive sheet to the surface protective layer of the image display apparatus is 2% or less.

In addition, the pressure-sensitive adhesive sheet has a transparency such that a laminate obtained by attaching the sheet to a transparent adherent (for example, the surface protective layer of an image display apparatus) has 90% or higher total light transmittance in the spectrum of visible light wavelength (JIS K 7361). In addition to the above-mentioned components, the pressure-sensitive adhesive sheet may contain other components such as filler, an antioxidant and a silane coupling agent.

The thickness of the pressure-sensitive adhesive sheet is not particularly limited, as long as it is large enough to bring about no problem in the attaching to an image display apparatus (in an image display apparatus, when laminating a surface protective layer or a touch panel to the display surface of an image display unit, or laminating a surface protective layer to a touch panel). For example, the thickness of the pressure-sensitive adhesive sheet may be from 0.025 to 1 mm. When the thickness of the transparent pressure-sensitive adhesive sheet is increased, the adhesive force to an adherent (for example, a polymer film such as PMMA or a glass plate) becomes high.

Then, an image display apparatus including the above-described pressure-sensitive adhesive sheet is described below by referring to Figs. 1 to 4. The image display apparatus comprises an image display unit, a transparent pressure-sensitive adhesive sheet and a surface protective layer. With regard to the transparent pressure-sensitive adhesive sheet included in the image display apparatus, the internal residual stress in the transparent pressure-sensitive adhesive sheet is relieved.

The image display unit is not particularly limited, and examples thereof include an image display unit such as reflection- or backlight-type liquid crystal display unit, plasma display unit, electroluminescent (EL) display and electronic paper. On the display surface of the image display unit, an additional layer (which may be either one layer or multiple layers), for example, a polarizing plate (which sometimes has an irregularly shaped surface), may be provided. Also, a below-described touch panel may be present on the display surface of the image display unit. The surface protective layer is a layer disposed as the outermost surface, when disposed on an image display apparatus. The surface protective layer may be composed only of a polymer film, a glass plate or the like, or may be composed of a plurality of layers together with other layers. The surface protective layer is not particularly limited as long as it is a film conventionally used as a protective film or the like of an image display apparatus, and may be, for example, an acrylic resin film such as polymethyl methacrylate (PMMA), a polycarbonate resin film or a glass plate. The thickness of the film or glass plate is not limited but is usually from 0.1 to 5 mm. In the case where the surface protective layer is a laminate composed of a plurality of layers, a layer for imparting functions or properties such as abrasion resistance, scratch resistance, antifouling property, antireflection property and antistatic property may be provided on the viewer side of the image display apparatus. The layer for imparting abrasion resistance and scratch resistance can be formed by coating a curable resin composition capable of forming a hard coat, and curing the coating. For example, a coating material comprising a partial condensation reaction product of a silane mixture containing an alkyl trialkoxy silane as the main component and colloidal silica is coated and then cured under heating to form a cured film, or a coating material containing a polyfunctional acrylate as the main component is coated and the coating film is irradiated with an ultraviolet light, whereby a cured film can be formed. Also, in order to ensure an antifouling property, a resin layer containing an organic silicon compound or a fluorine-based compound may be formed. Furthermore, for obtaining an antistatic property, a resin layer containing a surfactant or electrically conductive fine particles may be formed. The layer for imparting such functions or properties is preferably a film not inhibiting the transparency of the surface protective layer and is preferably as thin as possible within a range where the function can be fulfilled. The thickness of the layer for imparting functions or characteristics is not limited but is usually from 0.05 to 10 μm. Also, in the case where the surface protective layer is a laminate composed of a plurality of layers, an additional layer such as a printing layer, a hard coat layer and a vapor-deposition layer may be included on the transparent pressure-sensitive adhesive sheet side to cover the all or a partial region of the surface protective layer. In the case where such an additional layer is formed in a partial region of the surface protective layer, the surface protective layer comes to have an irregularly shaped surface. The thickness of the surface protective layer is, including such an additional layer, usually from 0.1 to

6 mm in total. Incidentally, when the additional layer is a printing layer or a vapor-deposition layer used as a light-shielding layer described later, the thickness of the layer is usually 10 μm or less. In other embodiments, the thickness of the layer is generally 100 μm or less, or 50 μm or less. Fig. 1 is a cross-sectional view showing one embodiment of an image display device comprising the transparent pressure-sensitive adhesive sheet described above. The image display device 10 has a structure where a transparent pressure-sensitive adhesive sheet 3 and a surface protective layer 4 are stacked in this order on the display surface of an image display unit 1. The surface protective layer 4 is composed of a continuous layer 5 and a light-shielding layer 6 provided in a partial region on the bottom surface (on the transparent pressure-sensitive adhesive sheet 3 side) of the continuous layer 5 and has an unevenly shaped surface. The light-shielding layer 6 is formed by coating a coating solution of a curable resin composition, in which a colorant is mixed, on a predetermined region of the continuous layer 5 by a proper method such as screen printing, and curing the coating by a proper curing method such as UV irradiation. The transparent pressure-sensitive adhesive sheet 3 is laminated to the unevenly shaped surface side of the surface protective layer 4. The transparent pressure-sensitive adhesive sheet 3 has flexibility and therefore, even if the surface protective layer 4 is unevenly shaped and furthermore, a layer having an uneven surface shape (for example, a polarizing plate) is provided on the display surface of the image display unit, the internal residual stress of the sheet itself is relieved, so that the image display device can be prevented from display unevenness. Also, the transparent pressure-sensitive adhesive sheet 3 has sufficiently high adhesive force and hydrophilicity and therefore, even under a high-temperature high-humidity environment, foaming or detachment is not generated at the interface between the display surface of the image display unit 1 and the transparent pressure-sensitive adhesive sheet 3 and the interface between the transparent pressure-sensitive adhesive sheet 3 and the surface protective layer 4, and whitening does not occur either. The image display device 10 can be obtained, for example, by laminating the above-described laminate 2 comprising a surface protective layer 4 and a transparent pressure-sensitive adhesive sheet 3 to the display surface of the image display unit 1. Fig. 2 is a cross-sectional view showing another embodiment of an image display device comprising the transparent pressure-sensitive adhesive sheet described above. In Fig. 2, the image display device 20 has a structure where a transparent pressure-sensitive adhesive sheet 3 and a surface protective layer 4 are stacked in this order on a touch panel 7 which is present on the display surface of an image display unit 1. The structure of the laminate 2 where a transparent pressure-sensitive adhesive sheet 3 and a surface protective layer 4 are stacked in this order is the same as that described in Fig. 1. The touch panel 7 is disposed on the display surface of the image display unit 1, and the displayed image of the image display device 20 can be viewed through the touch panel. The touch panel 7 is transparent and has such a construction as that a transparent electrically conductive layer is disposed on the back surface of each of two transparent plates made of glass or polyethylene terephthalate (PET) and the transparent electrically conductive layers of these transparent plates are disposed to face each other with a small gap in a non-contact state. When an operator of the touch panel presses with a finger or a pen the pertinent position on the surface of one transparent plate, the transparent electrically conductive layer on the back surface of one transparent plate is put into contact with the transparent electrically conductive layer of another transparent plate to produce a state allowing for electrical conduction only at the pertinent position. This position at which electrical conduction is allowed is electrically detected by a sensor, whereby the position on the touch panel pressed by the operator can be specified. Such a touch panel-type display is being used in PC (personal computer), a cellular phone or a mobile terminal such as PDA. The transparent pressure-sensitive adhesive sheet 3 has flexibility and therefore, even if the surface protective layer 4 is irregularly shaped, the internal residual stress of the sheet itself is relieved, so that the image display device can be prevented from display unevenness. Also, the transparent pressure-sensitive adhesive sheet 3 has sufficiently high adhesive force and hydrophilicity and therefore, even under a high-temperature high-humidity environment, foaming or detachment is not generated at the interface between the touch panel 7 and the transparent pressure-sensitive adhesive sheet 3 and the interface between the transparent pressure-sensitive adhesive sheet 3 and the surface protective layer 4, and whitening does not occur either. The image display device 20 can be obtained, for example, by laminating the above-described laminate 2 comprising a surface protective layer 4 and a transparent pressure-sensitive adhesive sheet 3 to the touch panel 7 present on the display surface of the image display unit 1.

Fig. 3 is a cross-sectional view showing still another embodiment of an image display device comprising the transparent pressure-sensitive adhesive sheet described above. In Fig. 3, the image display device 30 has a structure where a transparent pressure-sensitive adhesive sheet 3, a touch panel 7, a transparent pressure-sensitive adhesive sheet 3' and a surface protective layer 4 are stacked in this order on the display surface of an image display unit 1. The structure of the laminate where a transparent pressure-sensitive adhesive sheet 3' and a surface protective layer 4 are stacked in this order is the same as that described in Fig. 1. The transparent pressure-sensitive adhesive sheet 3 and the transparent pressure-sensitive adhesive sheet 3' may comprise the same copolymer or may comprise different copolymers. The transparent pressure-sensitive adhesive sheets 3 and 3' have flexibility and therefore, even if the surface protective layer 4 is irregularly shaped and furthermore, a layer having an irregular surface shape (for example, a polarizing plate) is provided on the display surface of the image display unit, the internal residual stress of each sheet itself is relieved, so that the image display device can be prevented from display unevenness. Also, the transparent pressure-sensitive adhesive sheets 3 and 3' have sufficiently high adhesive force and hydrophilicity and therefore, even under a high-temperature high-humidity environment, foaming or detachment is not generated at each interface, for example, between the display surface of the image display unit 1 and the transparent pressure-sensitive adhesive sheet 3 or between the transparent pressure-sensitive adhesive sheet 3' and the surface protective layer 4, and whitening does not occur either. The image display device 30 can be obtained, for example, by laminating the above-described laminate 2 comprising a surface protective layer 4, a transparent pressure-sensitive adhesive sheet 3', a touch panel 7 and a transparent pressure-sensitive adhesive sheet 3 to the display surface of the image display unit 1.

Fig. 4 is a cross-sectional view showing yet still another embodiment of an image display device comprising the transparent pressure-sensitive adhesive sheet described above. In Fig. 4, the image display device 40 has a structure where a transparent pressure-sensitive adhesive sheet 3, a touch panel 7 and a surface protective layer 4 are stacked in this order on an image display unit 1. The surface protective layer 4 has, similarly to that of Fig. 1, a light-shielding layer 6 in a partial region, giving an unevenly shaped surface. The transparent pressure-sensitive adhesive sheet 3 is present on the unevenly shaped surface side of the surface protective layer 4 through the touch panel 7. The transparent pressure-sensitive adhesive sheet 3 has flexibility and therefore, even if a layer having an uneven surface shape (for example, a polarizing plate) is provided on the display surface of the image display unit, the internal residual stress of the sheet itself is relieved, so that the image display device can be prevented from display unevenness. Also, the transparent pressure-sensitive adhesive sheet 3 has sufficiently high adhesive force and hydrophilicity and therefore, even under a high-temperature high-humidity environment, foaming or detachment is not generated at the interface between the display surface of the image display unit 1 and the transparent pressure-sensitive adhesive sheet 3 and the interface between the transparent pressure-sensitive adhesive sheet 3 and the touch panel 7, and whitening does not occur either. The image display device 40 can be obtained, for example, by laminating the above-described laminate 2 comprising a surface protective layer 4, a touch panel 7 and a transparent pressure-sensitive adhesive sheet 3 to the display surface of the image display unit 1.

According to still another aspect of the present disclosure, an electronic device comprising the above-described image display device is provided. The electronic device is not particularly limited and includes a cellular phone, a personal digital assistance

(PDA), a portable video game machine, an electronic reading terminal, a car navigation system, a portable music player, a watch or clock, a television (TV), a video camera, a video player, a digital camera, a global positioning system (GPS) device, and a personal computer (PC).

EXAMPLES

The present disclosure is described in greater detail below by referring to Examples, but the present disclosure is not limited to these Examples.

Sample Preparation Method

Example 1

100 parts by mass of a hydrogenated DCPD-based resin (manufactured by Exxon Mobil Corporation, Escorez 5340)as an alicyclic hydrocarbon resin, 17 parts by mass of a saturated polyisobutylene resin (manufactured by BASF, Oppanol BlOO) as a amorphous saturated polyolefm resin, 50 parts by mass of a UV curable acrylate resin (manufactured by Shin-nakamura Chemical Corporation, DCP) as an acrylic group-containing resin, and 0.8 part by weight of a photoinitiator (manufactured by Ciba Specialty Chemicals K.K., TPO)as an initiator were dissolved in toluene to prepare a 25% by weight solution. This solution was coated on a release-treated PET film and dried in a 100 ⁰ C oven for 30 minutes. The obtained pressure-sensitive adhesive-attached film was laminated with a release-treated PET film with a thickness of 25 μm to prepare a release liner-attached pressure-sensitive adhesive sheet. A transparent film with the thickness of the pressure-sensitive adhesive of 25 μm was obtained. Example 2

The same as Working Example 1 except that 100 parts by mass of a hydrogenated DCPD-based resin (manufactured by Exxon Mobil Corporation, Escorez 5340)as an alicyclic hydrocarbon resin, 25 parts by mass of one type of saturated polyisobutylene resin (manufactured by BASF, Oppanol B50) and 8 parts by mass of the other type of saturated polyisobutylene resin (manufactured by BASF, Oppanol B 15) as a amorphous saturated polyolefm resin, 33 parts by mass of a UV curable acrylate resin (manufactured by Shin-nakamura Chemical Corporation, DCP) as an acrylic group-containing resin, and 0.8 part by weight of a photoinitiator (manufactured by Ciba Specialty Chemicals K.K., TPO)as an initiator were used. Example 3

The same as Working Example 1 except that 100 parts by mass of a hydrogenated DCPD-based resin (manufactured by Exxon Mobil Corporation, Escorez 5340)as an alicyclic hydrocarbon resin,40 parts by mass of one type of Hydrogenated polybutadiene (manufactured by Kuraray Co. Ltd., LIR200) and 20 parts by mass of Poly alpaha olefine copolymer (manufactured by SUMITOMO CHEMICAL Co., Ltd,Xl 102P) as a amorphous saturated polyolefm resin, 40 parts by mass of hydrogenated polybutadiene urethane modified diacrylate (manufactured by Nippon soda Corporation, TEAIlOOO) as an acrylic group-containing resin, and 1 part by weight of a photoinitiator (manufactured by Ciba Specialty Chemicals K.K., TPO)as an initiator were used. Example 4

The same as Working Example 1 except that 100 parts by mass of a hydrogenated DCPD-based resin (manufactured by Exxon Mobil Corporation, Escorez 5340)as an alicyclic hydrocarbon resin,40 parts by mass of a saturated polyisobutylene resin (manufactured by BASF, Oppanol B50) as a amorphous saturated polyolefm resin, 60 parts by mass of hydrogenated polybutadiene diacrylate (manufactured by Osaka Yuki Kogyo, SPBDA-S30 ) as an acrylic group-containing resin, and 1.3 part by weight of a photoinitiator (manufactured by Ciba Specialty Chemicals K.K., TPO)as an initiator were used. Example 5

The same as Working Example 1 except that 100 parts by mass of a hydrogenated DCPD-based resin (manufactured by Exxon Mobil Corporation, Escorez 5340)as an alicyclic hydrocarbon resin, 100 parts by mass of a saturated polyisobutylene resin (manufactured by BASF,

Oppanol B30) as a amorphous saturated polyolefm resin, 50 parts by mass of tricyclodecane dimethanol diacrylate(manufactured by Shin-nakamura Chemical Corporation, A-DCP) as an acrylic group-containing resin, and 1 part by weight of a photoinitiator (manufactured by Ciba Specialty Chemicals K.K., TPO)as an initiator were used.

Comparative Example 1

87.5 parts by mass of isooctyl acrylate, 4 parts by mass of acrylic acid, and 0.04 part by weight of Irgacure 651 (2, 2-dimethoxy-2-phenylacetophenone) as a photopolymerization initiator were mixed well in a glass container, and after dissolved oxygen was replaced with nitrogen, a UV light was irradiated with a low pressure mercury lamp for a few minutes for partial polymerization to obtain a viscous liquid with a viscosity of about 1500 cP. To the composition obtained, 8.5 parts by mass of 2-hydroxy ethyl acrylate, 0.1 part by weight of HDDA (1, 6-hexanediol acrylate) as a crosslinking agent, and 0.1 part by weight of an additional polymerization initiator (Irgacure 651) were added and mixed well. After the mixture was defoamed under vacuum, it was applied on a release-treated polyester film with a thickness of 50 μm to be a thickness of 50 μm. In order to remove the oxygen that inhibits polymerization, the above film was further coated, and irradiated from the both sides with a low pressure mercury lamp for about 4 minutes to obtain a pressure-sensitive adhesive sheet. Comparative Example 2

The same as Comparative Example 1 except that 87.5 parts by mass of an isooctyl acrylate , 12.5 parts by mass of acrylic acid and no 2-hydroxyethyl acrylate were added. Comparative Example 3

The same as Working Example 1 except that 100 parts by mass of a hydrogenated DCPD-based resin (manufactured by Exxon Mobil Corporation, Escorez 5340), 33.4 parts by mass of a polyisobutylene resin (manufactured by BASF, Oppanol BlOO), and 33.4 parts by mass of a UV curable acrylate resin (manufactured by Shin-nakamura Chemical Corporation, DCP) were used.

Evaluation Method Unevenness Test

After separating the release film on one surface of the pressure-sensitive adhesive sheet for evaluation, the sheet was attached to a glass plate (manufactured by Corning, #1737) with a thickness of 0.7 mm by using a roller so as to prevent air from entering the interface, and the protruded portion was removed using a cutter. Separately, a commercially available cellular phone (913SH, manufactured by Sharp Corporation) after removing the entire protective cover therefrom was processed such that the liquid crystal module became the outermost surface. Subsequently, the release film of the pressure-sensitive adhesive sheet attached on the glass plate was removed, and the adhesive surface of the pressure-sensitive adhesive sheet was put into contact with the liquid crystal module and then press-bonded by a rubber roller. The obtained laminate of glass plate/pressure-sensitive adhesive sheet/liquid crystal module was placed in an autoclave and treated at 4O ⁰ C under 0.5 MPa for 15 minutes. For Example 1, Example 2, Example 3, Example 4, Example 5, Comparative Example 1, Comparative Example 2 and Comparative Example 3, a UV light (manufactured by Fusion K.K., F300S (H valve was used), 50 mJ x 20 times) was irradiated from the glass plate side. Thereafter, the power source of the cellular phone was turned on to display a white screen, and unevenness was confirmed with an eye. The results are shown in Table 1. In the unevenness test results shown in Table 1, "3" indicates that "unevenness was not observed", and "2" indicates that "slight unevenness was observed " and "1" indicates that "strong unevenness was observed to cause a problem in practice".

Reliability Test (Detachment/Foaming/Whitening)

After separating the release film on one surface of the pressure-sensitive adhesive sheet for evaluation, the sheet was attached to a glass plate (manufactured by Corning, #1737) with a thickness of 0.7 mm by using a roller so as to prevent air from entering the interface, and the protruded portion was removed using a cutter. Separately, a polarizing plate with a pressure-sensitive adhesive (produced by Sanritz Corporation) was laminated to a 0.55 mm-thick float glass (50x80 mm) in the same manner by using a rubber roller. The release film of the pressure-sensitive adhesive sheet attached on the glass plate was removed, and the adhesive surface of the pressure-sensitive adhesive sheet was put into contact with the polarizer and then press-bonded by a rubber roller. The obtained laminate of glass plate/pressure-sensitive adhesive sheet/polarizing plate/glass was placed in an autoclave and treated at 4O ⁰ C under 0.5 MPa for 15 minutes. For Example 1, Example 2,

Example 3, Example 4, Example 5, Comparative Example 1, [Comparative Example 2 and Comparative Example 3, a UV light (manufactured by Fusion K.K., F300S (H valve was used), 50 mJ x 20 times) was irradiated from the glass plate side. The laminate was allowed to stand at room temperature for 12 hours and then placed in a thermo-hygrostat at 60 ⁰ C and 90% RH. After 3 days, the laminate was taken out, and the presence or absence of foaming or detachment was confirmed with an eye. The results are shown in Table 1.

Evaluation Results

Table 1 - Test Results

K) K)

Unevenness test evaluation: 3: no unevenness, 2: slight unevenness, 1 : strong unevenness

BlOO, B50, B30, B15: Polyisobutylene (manufactured by BASF)

LIR200: Hydrogenated polybutadiene (manufactured by Kuraray Co. Ltd.)

Xl 102P: Poly alpaha define copolymer (manufactured by SUMITOMO CHEMICAL Co., Ltd)

5340: Alicyclic hydrocarbon (tackifier) (manufactured by Exxon Chemical Co. Ltd.)

KBM-502: γ-Methacryloxypropylmethyl diethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.)

TPO: Photopolymerization initiator (manufactured by Ciba Specialty Chemicals K.K.)

IOA: Isooctyl acrylate (manufactured by 3M)

AA: Acrylic acid (manufactured by Toa Gosei)

HEA: 2-hydroxyethyl acrylate (manufactured by Osaka Yuki Kogyo)

HDDA: 1 , 6-hexanediol diacrylate (manufactured by Shin-nakamura Chemical Corporation)

DCP: tricyclodecane dimethanol dimethacrylate(manufactured by Shin-nakamura Chemical Corporation)

A-DCP: tricyclodecane dimethanol diacrylate(manufactured by Shin-nakamura Chemical Corporation)

TEAIlOOO: hydrogenated polybutadiene urethane modified diacrylate (manufactured by Nippon soda Corporation)

SPBDA-S30: hydrogenated polybutadiene diacrylate (manufactured by Osaka Yuki Kogyo)

IRGACURE651 : Light polymerization initiator (manufactured by Exxon Chemical Co. Ltd.)

Measurement of Visco elasticity

The viscoelasticity was evaluated by using a dynamic viscoelasticity measuring apparatus, ARES, manufactured by TA Instruments Inc. in a shear mode (1 Hz). A stack obtained by stacking 16 sheets of the transparent pressure-sensitive adhesive sheet having removed therefrom the release films was punched by a punching edge of 7.9 mm in diameter and used as a test piece. The measurement was performed by elevating the temperature from -60 to 200 ⁰ C at a rate of 5°C/min. The values of viscoelasticity at 25 ⁰ C are shown in Table 1.