JP2005179481A - Laminate sheet and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a member which, while employing the advantage of an adhesive sheet method that is hard to give rise to reflection loss, parallax and image blurring, is hard to generate the foaming or peeling in the adhesion interface with a panel even under heat or humidity. <P>SOLUTION: Under a rigid layer (1) consisting of a transparent polymer, a transparent adaptation layer (2) consisting of an acrylic adhesive layer, whose gel fraction is 80-98% and whose sol fraction has a weight average mol.wt. of 100,000-500,000, is attached to form a laminate sheet. The laminate sheet is arranged with close adhesion on the view side of a liquid crystal display panel to compose a liquid crystal display device. This enables to obtain a touch input type liquid crystal display layer excellent in durability and retaining good appearance for a long period of time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laminated sheet suitable for a touch input type display panel and a liquid crystal display device on which the laminated sheet is arranged.

  In a pen-input type liquid crystal display device, a liquid crystal display panel and a protective plate are used to prevent the liquid crystal display panel from being bent and disturbed by a pressing force applied through a protective plate arranged on the viewing side of the liquid crystal display panel. A method of providing a gap of about 0.5 to 2 mm between the two was employed. However, in this method, there is a problem that the visibility is lowered due to the reflection of light at the interface between the liquid crystal display panel and the protective plate, and parallax and image blur tend to occur.

In view of the above, a technique has been proposed in which a liquid crystal display panel and a protective plate are brought into close contact with each other via a buffering adhesive sheet to suppress the occurrence of reflection loss, parallax, and image blur. However, the conventional pressure-sensitive adhesive sheet has a problem of poor durability because foaming or peeling (floating) occurs at the adhesive interface with the panel under heating or humidification.
JP-A-8-327975 Japanese Patent Laid-Open No. 9-6256

  An object of the present invention is to develop a member that does not easily cause foaming or peeling at an adhesive interface with a panel even under heating or humidification while taking advantage of an adhesive sheet system that is less likely to cause reflection loss, parallax, and image blur.

  In the present invention, a transparent relaxation layer made of an acrylic adhesive layer having a gel fraction of 80 to 98% and a sol weight average molecular weight of 100,000 to 500,000 is adhered to the lower side of a rigid layer made of a transparent polymer. And a liquid crystal display device in which the laminated sheet is disposed in close contact with the viewing side of the liquid crystal display panel via the relaxation layer side.

  According to the laminated sheet of the present invention, it is possible to prevent a gap from being interposed between the liquid crystal display panel and the protective plate, and it is difficult to cause a decrease in visibility due to interface reflected light, parallax or image blur, and the protective plate has excellent buffering properties. Display distortion due to bending of the liquid crystal display panel at the time of touch input with a pen etc. through the touch panel is less likely to occur, and it has excellent adhesion and adhesion, such as foaming and floating at the adhesive interface with the display panel even under heating and humidification It is possible to obtain a touch-input type liquid crystal display layer that is less likely to peel off, has excellent durability, and maintains a good appearance for a long time.

  The laminated sheet according to the present invention has a transparent relaxation comprising an acrylic adhesive layer having a gel fraction of 80 to 98% and a weight average molecular weight of sol of 100,000 to 500,000 below the rigid layer made of a transparent polymer. The layers are in close contact. An example thereof is shown in FIG. 1 is a rigid layer and 2 is a relaxation layer. The figure shows a liquid crystal display device of a touch input type in which a laminated sheet is arranged on the viewing side of the liquid crystal display panel 4.

The rigid layer functions as a protective plate, and is formed of a transparent polymer for the purpose of suppressing deformation due to pressing force at the time of touch input via a pen or the like with its strength or rigidity. If the rigid layer sinks and deforms excessively at the time of touch input, display disturbance is likely to occur. The rigid layer has a dynamic storage elastic modulus G ′ (1 Hz, shear) at 20 ° C. of 5 × 10 ⁸ Pa or more, especially 10 ⁹ to 10 ¹² Pa, in view of preventing the occurrence of display disturbance due to the subduction deformation. In particular, it is preferably 2 × 10 ^{9 to} 5 × 10 ¹⁰ Pa.

  Polymers that can be preferably used for forming the rigid layer are those having a light transmittance of 70% or more, in particular 80% or more, in particular 85% or more. Those having excellent mechanical strength and good heat resistance are more preferred. Incidentally, examples of polymers for forming the rigid layer include polyester resins such as polyethylene naphthalate resins and polyethylene terephthalate resins (PET), (meth) acrylic resins and polycarbonate resins, triacetyl cellulose resins and norbornene resins. And epoxy resins, polyimide resins, polyetherimide resins, polyamide resins, polysulfone resins, polyphenylene sulfide resins, polyethersulfone resins, polystyrene resins, and the like. In particular, PET and epoxy resins are preferable from the viewpoint of transparency, heat resistance, mechanical strength, and the like. The (meth) acrylic means acryl or methacryl (hereinafter the same).

  The rigid layer can be formed as a film, sheet, plate, or the like made of one or more transparent polymers, and may be formed by an appropriate method such as a casting method or an extrusion method. The thickness is generally 100 μm to 2 mm, in particular 120 μm to 1.5 mm, in particular 150 μm to 1 mm. The rigid layer may be composed of a single layer or may be composed of two or more composite layers.

  The rigid layer may be provided with the surface treatment layer 3 on the upper side thereof as shown in the figure, that is, on the side that becomes the viewing side of the liquid crystal display device. The surface treatment layer is, for example, a touch input type liquid crystal display device such as an antireflection layer, an antireflection layer, an antireflection layer, a hard coating layer, an antistatic layer or a contamination prevention layer that exhibits both functions. Can be formed to exhibit various known functions, and one or more of these functional layers can be provided.

Incidentally wherein the antireflection layer is for the purpose of antireflection of outdoor daylight on the laminated sheet surface, for example, SiO ₂ or ZrO _2, Al ₂ O ₃ and _{Y 2 O 3, TiO 2,} MgF 2 and BaF _2, CaF ₂ and LaF _2, LiF and NaF, such as inorganic oxides and inorganic halides SrF _2, or monolayers or superposition of their interference thin film comprising a composite, etc., etc., an anti-reflection in accordance with conventional It can be formed as a film.

  The anti-reflection layer is intended to prevent the external light from being regularly reflected on the surface of the laminated sheet and obstructing the visibility of the light transmitted through the laminated sheet, such as display light. For example, a sandblasting method, an embossing method, etc. It can be formed as an anti-glare layer according to the prior art, such as a method of forming a coating film with transparent fine particles, or a method of forming a coating film containing transparent fine particles, or the like, in which a fine concavo-convex structure is provided on the surface of the laminated sheet. The reflection preventing layer may also serve as a diffusion layer that diffuses the light transmitted through the laminated sheet and expands the viewing angle.

  Examples of the transparent fine particles for forming fine irregularities include inorganic fine particles composed of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide, and the like having an average particle diameter of 0.5 to 50 μm. , Organic fine particles composed of crosslinked or non-crosslinked polymer particles, and the like, and one kind or two or more kinds can be used. In the case of forming a surface fine concavo-convex structure, the amount of transparent fine particles used is 2 to 50 parts by weight, especially 3 to 35 parts by weight, per 100 parts by weight of a binder resin such as an ultraviolet curable silicone resin that forms a coating film. 5 to 25 parts by weight is particularly preferable.

  The antireflection antireflection layer exhibits an antireflection function and an antireflection function. For example, the antireflection layer is superimposed on the antireflection layer, or the above-described coating containing transparent fine particles is antireflection. It can be formed by a method of manufacturing as a coherent interference thin film.

  The hard coat layer is intended to prevent scratches on the surface of the laminated sheet. For example, an unsaturated polyester resin, an unsaturated (meth) acrylic resin, an unsaturated polyurethane resin, a polyamide resin, or a silicone resin. It can be formed as a cured film of an appropriate curable resin such as ultraviolet ray, electron beam curable type, or thermosetting type such as epoxy resin.

  A hard hard coat layer excellent in slipperiness is preferable, and a layer having a surface hardness of 2H or more, especially 3 to 8H, particularly 4 to 6H is preferable from the point of touch input, particularly pen input. If the surface hardness is less than 2H, the scratch resistance at the time of pen input may be insufficient. Further, in terms of slipperiness with respect to pen input, the dynamic friction coefficient at the time of pen input is preferably 0.02 to 0.30, especially 0.05 to 0.25, and particularly preferably 0.07 to 0.20. If the coefficient is less than 0.02, the pen may slide too much, and if it exceeds 0.30, the sliding may be poor and the pen movement may become too heavy, resulting in poor writing.

  The hard coat layer is preferably located on the upper side (surface side) of the antireflection layer or the antireflection layer, and the thickness is 30 μm or less, especially 0.1 to 25 μm, especially 0, in view of hardness and durability. .2 to 20 μm is common. The hard coat layer can also be formed to contain a transparent fine particle or the like to serve as a reflection preventing layer.

  The antistatic layer is intended to prevent dust adhering due to electrification, and can be formed, for example, as a transparent conductive film. Moreover, it can also form as an antistatic layer which doubles as a reflection preventing layer by using a conductive material for transparent fine particles. The contamination prevention layer is intended to prevent contamination due to adhesion of fingerprints and the like, and can be formed as a coating film made of, for example, a polyfluorinated alkyl ether compound.

  The transparent conductive film is, for example, gold, silver, copper, aluminum, nickel, tin, titanium, iron, alloys thereof, indium oxide, tin oxide, titanium oxide, cadmium oxide, a mixture or a composite thereof, etc. It can be formed as a thin film made of a metal oxide made of, another metal compound made of copper iodide or the like. The thin film can be formed by, for example, vacuum deposition, sputtering, ion plating, spray pyrolysis, chemical plating, electroplating, or a combination thereof.

  When the antireflection layer is located on the surface of the laminated sheet, particularly, the antistatic layer and / or antifouling layer is preferably provided on the upper side (surface side). When providing both an antistatic layer and a pollution prevention layer, the system which provides a pollution prevention layer above an antistatic layer is common.

  The surface treatment layer can be directly attached to the surface of the rigid layer 1 as shown in the drawing method by the coating method or the thin film forming method, or can be attached to a separate support substrate such as a transparent film. The material can be adhered to the surface of the rigid layer 1 through an appropriate transparent adhesive layer such as an adhesive layer.

  The relaxation layer has a gel fraction of 80 to 98 for the purpose of preventing display disturbance due to relaxation of pressing force at the time of touch input via a pen or the like, and improving pen writing quality by appropriate elastic deformation at the time of input. %, And a transparent acrylic adhesive layer having a sol weight average molecular weight of 100,000 to 500,000. Accordingly, the display panel and the rigid layer can be closely adhered to and integrated with each other via the adhesive force of the relaxation layer.

  If the gel fraction is less than 80%, the cohesive force of the adhesive layer is insufficient and foaming is likely to occur at high temperature or high temperature and humidity, and if it exceeds 98%, tackiness disappears and adhesion to the adherend is insufficient. . If the weight average molecular weight of the sol is less than 100,000, the pressure-sensitive adhesive layer in the vicinity of the adhesive interface is insufficiently agglomerated and foaming is likely to occur at high temperature or high temperature and high humidity. Insufficient adhesion.

  In the above, the gel fraction was determined by immersing 1 g of acrylic adhesive layer (sample) in 100 g of ethyl acetate and leaving it at room temperature for 2 weeks, followed by filtration through a 0.2 μm microfilter to obtain the soluble content (sol content). After removing and drying the remaining amount, the weight of the solvent-insoluble component is measured, and the weight percent of the solvent-insoluble component in the sample can be calculated.

  The weight average molecular weight of the sol can be obtained from a curve obtained by obtaining a molecular weight distribution curve of a soluble component obtained as the filtrate by gel permeation chromatography (GPC). The measurement conditions of the molecular weight distribution curve by the GPC method are a sample concentration of 1 mg / ml, a sample introduction amount of 500 mg, a column temperature of 40 ° C., and a flow rate of 1.0 ml / min.

A preferable relaxation layer has a light transmittance of 70% or more, especially 80% or more, particularly 85% or more, and a storage elastic modulus G (shear) by dynamic viscoelasticity of 10 ⁶ Pa or less, especially 7 × 10 ^5. 10 ² Pa, especially 5 × 10 ⁵ to 2 × 10 ² Pa. The storage elastic modulus G is a value at 25 ° C. obtained from a temperature dispersion profile of G at −50 to 100 ° C. at a frequency of 1 Hz. The temperature dispersion profile can be known with a dynamic viscoelasticity measuring apparatus (for example, ARES manufactured by Rheometric Co., Ltd.).

When the G is more than 10 ⁶ Pa, there are cases where the writing quality at the time of pen input and the prevention of cracking of the glass cell substrate against impact are poor. Also, if it is less than 10 ² Pa, the display may be disturbed at the time of pen input, and the edge portion may protrude during cutting processing such as punching of a laminated sheet, resulting in poor workability or handling. .

  The relaxation layer can be formed as a pressure-sensitive adhesive layer such as a film or sheet made of one or more acrylic pressure-sensitive adhesives, and has a thickness of 0.1 to 2 mm, especially 0.2 to 1.8 mm. In particular, 0.3 to 1.5 mm is preferable. If the thickness is less than 0.1 mm, the display may be disturbed during input, the writing quality of pen input may be deteriorated, and the glass cell substrate may be broken by impact, and if it exceeds 2 mm, the image may be degraded due to parallax.

  The acrylic pressure-sensitive adhesive layer forming the relaxation layer is preferably made of an acrylic polymer containing a (meth) acrylic acid alkyl ester as a component from the viewpoint of transparency and durability.

  Examples of the (meth) acrylic acid alkyl ester used for the formation of the acrylic polymer include ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, isoamyl group, hexyl group, heptyl group, cyclohexyl group, and 2 Examples thereof include those having a linear or branched alkyl group such as an ethylhexyl group, an isooctyl group, an isononyl group, a decyl group or a dodecyl group, and particularly an alkyl group having 1 to 18 carbon atoms.

  (Meth) acrylic acid alkyl ester can be used singly or in combination of two or more, and when two or more are used, the alkyl group should be used in combination with an average of 2 to 14 carbon atoms. Is preferred. The acrylic polymer may be a polymer based only on (meth) acrylic acid alkyl ester.

  Acrylic polymer is a copolymer that is used in combination with a modifying monomer for the purpose of improving adhesion by introducing functional groups and polar groups, and improving cohesion and heat resistance by controlling the glass transition temperature. Also good. One or more modifying monomers can be used. The copolymerization ratio of the modifying monomer in the acrylic polymer is preferably 30% by weight or less, especially 1 to 25% by weight, particularly 5 to 15% by weight.

  Examples of the modifying monomer include monoethylenic monomers copolymerizable with (meth) acrylic acid alkyl ester. Specific examples thereof include (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, carboxyl group-containing monomers such as crotonic acid, maleic anhydride and itaconic anhydride. And an acid anhydride monomer such as, and a caprolactone adduct of (meth) acrylic acid.

  Also sulfonic acids such as styrene sulfonic acid, allyl sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, (meth) acrylamide propane sulfonic acid, sulfopropyl (meth) acrylate and (meth) acryloyloxynaphthalene sulfonic acid. A group-containing monomer and a phosphate group-containing monomer such as 2-hydroxyethylacryloyl phosphate are also examples of the modifying monomer.

  Further, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate Hydroxyl group-containing monomers such as 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate and (4-hydroxymethylcyclohexyl) -methyl acrylate are also examples of the modifying monomer.

  Furthermore, (N-substituted) amides such as (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-butyl (meth) acrylamide, N-methylol (meth) acrylamide, and N-methylolpropane (meth) acrylamide. Monomers, alkylaminoalkyl (meth) acrylate monomers such as aminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, and t-butylaminoethyl (meth) acrylate are also modifying monomers. As an example.

  In addition, (meth) acrylic acid alkoxyalkyl monomers such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate, N- (meth) acryloyloxymethylene succinimide and N- (meth) acryloyl-6-oxyhexa Succinimide monomers such as methylene succinimide and N- (meth) acryloyl-8-oxyoctamethylene succinimide are also examples of the modifying monomer.

  Also vinyl acetate, vinyl propionate, N-vinyl pyrrolidone, methyl vinyl pyrrolidone, vinyl pyridine, vinyl piperidone, vinyl pyrimidine, vinyl piperazine, vinyl pyrazine, vinyl pyrrole, vinyl imidazole, vinyl oxazole, vinyl morpholine, N-vinyl carboxylic acid amides Examples of the modifying monomer include vinyl monomers such as styrene, α-methylstyrene and N-vinylcaprolactam, and cyano (meth) acrylate monomers such as (meth) acrylonitrile.

  Furthermore, epoxy group-containing acrylic monomers such as glycidyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxyethylene glycol (meth) acrylate and methoxypolypropylene glycol (meth) acrylate Such as glycol acrylic ester monomers such as tetrahydrofurfuryl (meth) acrylate, fluorine (meth) acrylate, silicone (meth) acrylate and (meth) acrylate ester monomers such as 2-methoxyethyl (meth) acrylate, etc. An example of a quality monomer is given.

  In addition, the acrylic polymer has one or more cross-linking agents (internal crosslinking) as necessary for the purpose of increasing the shear strength when the cohesive force is improved by crosslinking treatment to form a relaxation layer. It may be formed using an agent. As the cross-linking agent, a polyfunctional (meth) acrylate having a plurality of, especially 2 to 8, (meth) acryloyl groups in the molecule can be preferably used.

  Incidentally, specific examples of the polyfunctional (meth) acrylate include hexanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate and neopentyl glycol di (meta). ) Acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, and the like.

  The amount of the cross-linking agent used is 0.01 to 10 parts by weight per 100 parts by weight of the (meth) acrylic acid alkyl ester, from the viewpoint of preventing the generation of bubbles and the prevention of blistering at the adhesive interface with the display panel. 0.03 to 5 parts by weight, particularly 0.05 to 3 parts by weight is preferable. A relaxed layer with a small amount of use and a low degree of cross-linking tends to generate bubbles at the adhesion interface, and a relaxed layer with a large amount of use and a high degree of cross-linking has a low adhesive force and tends to swell.

  The acrylic polymer is prepared by using a known appropriate method such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, a photopolymerization method, etc. on one monomer or a mixture of two or more monomers. Can be applied. In the preparation, one or more kinds of polymerization initiators can be used as necessary. As the polymerization initiator, appropriate ones such as a photopolymerization initiator and a thermal polymerization initiator are used according to the polymerization method. Can be used.

  A preferable acrylic pressure-sensitive adhesive from the point of forming the relaxation layer having the above thickness is a composition capable of photopolymerization. The preferred photopolymerization method is such that, first, a heating type or light irradiation type polymerization initiator is dissolved in the raw material monomer of the pressure-sensitive adhesive, and the polymerization rate is, for example, 1 to 30%, especially 3 to 20%, especially by heat or light. Partial polymerization is carried out to about 5 to 15% to syrup the reaction system to obtain a viscosity advantageous for coating.

  Next, a photopolymerization initiator and an optional cross-linking agent are added to the syrup, and the syrup is coated on a rigid layer and irradiated with light, and the syrup is polymerized to form a relaxation layer. By doing so, a laminated sheet is obtained. Using a support base material treated with a release agent in place of the rigid layer, after forming a relaxation layer on the support layer according to the above, it is possible to obtain a laminated sheet even if the relaxation layer is transferred onto the rigid layer. it can.

  In the above, the polymerization treatment by light irradiation is carried out in an air-blocking state such as a replacement atmosphere with an inert gas such as nitrogen gas or a light-transmitting film covering the pressure-sensitive adhesive layer. This is preferable from the standpoint of property development.

As the irradiation light for the polymerization treatment, ultraviolet rays, in particular, electromagnetic radiation having a wavelength of 180 to 460 nm can be preferably used from the viewpoint of processing efficiency, etc., but the polymerization treatment is performed even with light having a longer wavelength or shorter wavelength. Can do. As the ultraviolet ray generation source, for example, an appropriate irradiation device such as a mercury arc, a carbon arc, a (low pressure, medium pressure, high pressure) mercury lamp, a metal halide lamp, or a black light can be used. The irradiation amount can be appropriately determined according to the preliminary polymerization situation, but is usually about 400 to 4000 mJ / cm ² .

From the point of efficiently forming an adhesive layer (relaxation layer) showing the gel fraction and polymerization average molecular weight described above, the illuminance is 0.1 to 10 mW / cm ² , especially 0.5 to 8 mW / cm ² , especially 1 to 1. A method of photopolymerization with a low illuminance ultraviolet ray of about 5 mW / cm ² is preferable, and a low illuminance light source such as a black light is preferably used as the ultraviolet ray generation source.

  Examples of the photopolymerization initiator include 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone, α-hydroxy-α, α′-dimethylacetophenone, methoxyacetophenone, and 2,2- Acetophenone compounds such as dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-methyl-1- [4- (methylthio) -phenyl] -2-morpholinopropane-1 can give.

  Also, benzoin ether compounds such as benzoin ethyl ether, benzoin isopropyl ether and anisoin methyl ether, α-ketol compounds such as 2-methyl-2-hydroxypropiophenone, ketal compounds such as benzyldimethyl ketal, 2- Aromatic sulfonyl chloride compounds such as naphthalenesulfonyl chloride, photoactive oxime compounds such as 1-phenone-1,1-propanedione-2- (o-ethoxycarbonyl) oxime, benzophenone and benzoylbenzoic acid, 3,3 ′ Examples of photopolymerization initiators include benzophenone compounds such as -dimethyl-4-methoxybenzophenone.

  The photopolymerization initiator is used in an amount of 100% by weight from the viewpoint of reducing the remaining amount of unreacted monomer that is likely to cause bubbles at the bonding interface and reducing the remaining amount of initiator that is likely to cause yellowing. 0.005-3 parts by weight per part, especially 0.01-1 part by weight, especially 0.05-0.5 part by weight are preferred.

  Examples of the thermal polymerization initiator described above include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate and di (2-ethoxyethyl). ) Organic peroxidation such as peroxydicarbonate, t-butylperoxyneodecanoate, t-butylperoxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide Things are given.

  Also, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane 1-carbonitrile), 2,2′-azobis (2 , 4-dimethylvaleronitrile), 2,2′-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl-2,2′-azobis (2-methylpropionate), 4,4′- Azo series such as azobis (4-cyanovaleric acid), 2,2′-azobis (2-hydroxymethylpropionitrile), 2,2′-azobis [2- (2-imidazolin-2-yl) propane] Compounds and the like are also examples of thermal polymerization initiators.

  The amount of the thermal polymerization initiator used is 100% by weight of the monomer from the viewpoint of reducing the remaining amount of unreacted monomer that tends to cause bubbles at the adhesive interface and reducing the remaining amount of initiator that tends to cause yellowing. 0.005 to 5 parts by weight per part, especially 0.01 to 4 parts by weight, especially 0.05 to 3 parts by weight are preferred.

  The acrylic pressure-sensitive adhesive may be composed of a solution or suspension containing an acrylic polymer prepared in advance using the above-described thermal polymerization initiator or the like. The pressure-sensitive adhesive is of a type that contains one or two or more photopolymerization initiators or intermolecular crosslinking agents as necessary, and is crosslinked with light such as ultraviolet rays or electron beams, or heat. Also good.

  The acrylic pressure-sensitive adhesive layer can be obtained, for example, as a coating dried film such as a solution of such a polymer, or a film obtained by subjecting the dried film to a crosslinking treatment as necessary. Therefore, a laminated sheet can be formed by providing such an acrylic pressure-sensitive adhesive layer on the rigid layer according to the photopolymerization described above.

  The cohesive force of the pressure-sensitive adhesive layer (relaxation layer) can be increased even when the acrylic polymer is subjected to the crosslinking treatment method via the intermolecular crosslinking agent. As the intermolecular crosslinking agent, an appropriate one can be used depending on the type of functional group involved in intermolecular crosslinking in the acrylic polymer, and there is no particular limitation. Therefore, any known material can be used.

  Incidentally, examples of intermolecular crosslinking agents include polyfunctional isocyanate-based crosslinking agents such as tolylene diisocyanate, trimethylol propane tolylene diisocyanate, and diphenylmethane triisocyanate, polyethylene glycol diglycidyl ether, diglycidyl ether, and trimethylol propane triglycidyl ether. Such epoxy-based crosslinking agents, other melamine-based crosslinking agents, metal salt-based crosslinking agents, metal chelate-based crosslinking agents, amino resin-based crosslinking agents, and the like.

  The compounding amount of the intermolecular crosslinking agent can be appropriately determined according to the functional group content in the acrylic polymer. In general, from the viewpoint of achievement of the gel fraction described above, the amount is 0.01 to 20 parts by weight, especially 0.1 to 15 parts by weight, especially 0.2 to 10 parts by weight per 100 parts by weight of the acrylic polymer. .

  The relaxation layer made of an acrylic adhesive layer has a color purity improver exhibiting neon light (570 to 590 nm) absorption characteristics and pigments and dyes for the purpose of liquid crystal color correction, as long as transparency is not impaired. Pigments, tackifiers and antioxidants, anti-aging agents and UV absorbers, plasticizers and silane coupling agents, natural and synthetic resins and rubbers, acrylic oligomers, glass fibers and glass beads, etc. One or two or more of these appropriate additives can be blended. The relaxation layer can also have a light diffusing property by containing a light diffusing material such as transparent fine particles or an inorganic filler.

  As described above, a laminated sheet can be prepared by forming an acrylic adhesive layer on a rigid layer. For the application of the adhesive at that time, for example, a roll coating method, a casting method, a curtain coating method or a casting method is used. Appropriate development methods such as law can be adopted. The relaxation layer in the laminated sheet may be a single layer or a multilayer.

  It is preferable that the release layer of the laminated sheet is temporarily covered with a release film for the purpose of preventing adhesion of foreign substances and the like until it is put to practical use. Note that the rigid layer of the laminated sheet may exhibit ultraviolet absorbing ability for the purpose of improving the weather resistance of the relaxation layer. The ultraviolet absorbing ability can be imparted by an appropriate method such as a method of blending an ultraviolet absorber in the layer. As the ultraviolet absorber, for example, one or more appropriate compounds such as a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, and a nickel complex salt compound can be used.

  The laminated sheet can be preferably used in a touch input type, particularly a pen input type liquid crystal display device. In that case, as shown in the figure, the laminated sheet is disposed in close contact with the viewing side of the liquid crystal display panel with the relaxation layer 2 side as the liquid crystal display panel 4 side, and thus the rigid layer 1 as the upper side.

  The touch input type liquid crystal display device to which the laminated sheet is applied may be composed of a liquid crystal display panel by an appropriate method such as an electromagnetic induction method or a resistance thin film method, and any of the known touch input type liquid crystal display panels may be used. Also a laminated sheet can be applied. Incidentally, the liquid crystal display panel 4 shown in the figure is formed by disposing polarizing plates 41 and 43 on both sides of the liquid crystal cell 42.

  In a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer, an ultraviolet irradiation device and a stirring device, 100 parts of 2-ethylhexyl acrylate (parts by weight, the same applies hereinafter), 8 parts of acrylic acid, 2,2-dimethoxy-2- 0.1 part of phenylacetophenone (initiator) was added and pre-polymerized by ultraviolet irradiation to obtain a syrup composed of an acrylic polymer / monomer mixture having a polymerization rate of 10% by weight.

Next, 100 parts of the syrup is mixed with 0.2 part of trimethylpropane triacrylate (crosslinking agent) and 0.15 part of the initiator, and the resultant is thickened on a rigid layer made of a transparent PET film having a thickness of 350 μm. After coating with a thickness of 600 μm, the upper surface is coated with a PET-based transparent separator and irradiated with ultraviolet light with an illuminance of ² mW / cm ² from the upper surface using a black light to form a transparent relaxation layer, A surface-treated film (N5SPB, manufactured by Kimoto Co., Ltd.) having an anti-glare hard coat applied to the surface of a PET film having a thickness of 125 μm is adhered to the exposed surface of the rigid layer via a transparent adhesive layer having a thickness of 35 μm. Obtained.

  Next, a polarizing plate with a transparent adhesive layer (manufactured by Nitto Denko Corporation, TEG-DU) is bonded to a 14-inch liquid crystal display cell (manufactured by Toshiba Matsushita Display Co., Ltd.) via the adhesive layer, and the laminate is applied to the polarizing plate surface. After adhering the sheet through the relaxing layer from which the separator was peeled off, the sheet was held in an autoclave at 50 ° C. and 5 atm for 20 minutes to obtain a liquid crystal display device.

  A liquid crystal display device was obtained in the same manner as in Example 1 except that the amount of trimethylpropanetriacrylate was changed to 0.1 part.

  A liquid crystal display device was obtained in the same manner as in Example 1 except that 17 parts of hydroxybutyl acrylate was used instead of 8 parts of acrylic acid.

  A liquid crystal display device was obtained in the same manner as in Example 1 except that 100 parts of isononyl acrylate was used instead of 100 parts of 2-ethylhexyl acrylate.

Comparative Example 1
A liquid crystal display device was obtained in the same manner as in Example 1 except that a metal halide lamp was used instead of the black light, and the photopolymerization treatment was performed by irradiating ultraviolet rays with an illuminance of 20 mW / cm ² .

Comparative Example 2
A liquid crystal display device was obtained in the same manner as in Comparative Example 1 except that the amount of trimethylolpropane triacrylate was 0.3 parts.

Hiei example 3
A liquid crystal display device was obtained in the same manner as in Example 1 except that the amount of trimethylolpropane triacrylate was changed to 0.5 part.

Evaluation Test Gel Fraction 1 g of acrylic adhesive layer that forms a relaxation layer is accurately weighed, immersed in 100 g of ethyl acetate and allowed to stand at room temperature for 2 weeks, and then 0.2 μm Teflon (registered trademark) microfilter. The soluble component was removed by filtration, and the remaining amount was dried and then its weight was measured to calculate the weight percent of the solvent-insoluble component.

Weight average molecular weight of sol (sol molecular weight)
The molecular weight weight distribution curve of the soluble component (sol component) obtained as the filtrate by the GPC method was determined, and the weight average molecular weight of the sol component was determined from the curve. The measurement conditions for the distribution curve were a sample concentration of 1 mg / ml, a sample introduction amount of 500 mg, a column temperature of 40 ° C., and a flow rate of 1.0 ml / min.

Storage elastic modulus Using a dynamic viscoelasticity measuring device (Ares, manufactured by Rheometric Co., Ltd.), a temperature dispersion profile at −50 to 100 ° C. is obtained for an acrylic adhesive layer forming a relaxation layer under the condition of a frequency of 1 Hz, and 25 ° C. The storage elastic modulus was determined.

Durability The liquid crystal display devices obtained in Examples and Comparative Examples were 80 ° C. (high temperature) or 60 ° C., 90% R.D. Leave in an atmosphere of H (high temperature and high humidity) for 500 hours, and visually check the interface between the polarizing plate and the relaxing layer of the display panel, and the presence or absence of foaming and foaming at each interface between the rigid layer and the relaxing layer. Observed and evaluated according to the following criteria.
○: When peeling or foaming is not recognized ×: When peeling or / and foaming occurs

The results are shown in the following table.
Mild layer durability
Gel fraction (%) Sol molecular weight storage elastic modulus (Pa)
Example 1 95 350,000 5.9 × 10 ⁴ ○
Example 2 83 310,000 5.2 × 10 ⁴ ○
Example 3 97 135,000 6.4 × 10 ⁴ ○
Example 4 92 470,000 4.5 × 10 ⁴ ○
Comparative Example 1 71 950,000 4.0 × 10 ⁴ ×
Comparative Example 2 93 92,000 4.9 × 10 ⁴ ×
Comparative Example 3 99.5 120,000 1.2 × 10 ⁵ ×

From the table, the liquid crystal display devices of the examples can withstand the harsh conditions and do not peel off or foam even when placed in a high temperature or high humidity atmosphere, and have excellent durability and good visibility for a long time. I know that However, in the liquid crystal display device of the comparative example, it can be seen that the relaxation layer does not satisfy the conditions of the gel fraction or / and the weight average molecular weight of the sol, so that peeling or foaming occurs and the durability is poor.

Cross-sectional side view of laminated sheet and its application example

Explanation of symbols

1: Rigid layer 2: Relaxation layer 3: Surface treatment layer 4: Liquid crystal display panel


Patent applicant Nitto Denko Corporation
Agent Tsutomu Fujimoto

Claims (4)

  Lamination formed by adhering a transparent relaxation layer made of an acrylic adhesive layer having a gel fraction of 80 to 98% and a weight average molecular weight of 100,000 to 500,000 under a rigid layer made of a transparent polymer. Sheet. According to claim 1, comprising at least one of the upper antireflection layer or glare prevention layer of the rigid layer, relaxation layer is obtained by photopolymerization by ultraviolet illuminance 0.1 to 10 MW / cm ² an acrylic pressure-sensitive adhesive A laminated sheet.   The liquid crystal display device formed by closely_contact | adhering the lamination sheet of Claim 1 or 2 to the visual recognition side of a liquid crystal display panel through the relaxation layer side. 4. The liquid crystal display device according to claim 3, wherein the liquid crystal display panel is of a pen input type.

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