JPH1054908A - Polarizing plate with reflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent peeling or color change in a high temp. environment for a long period by laminating a polarizing plate having a cellulose acetate film as a protective layer with an adhesive layer to a reflector having through holes. SOLUTION: The polarizer of this polarizing plate contains uniaxially oriented polyvinylalcohol(PVA)-iodine complex or PVAdichroic dye as a dichroic material. Cellulose acetate films are laminated as protective layers on both surfaces of the polarizer. This polarizing plate is laminated with an adhesive layer to a reflector having through holes. The adhesive layer consists of an acryl copolymer. The holes formed in the reflector are preferably circular or square since the opening process of the holes is easy. The aperture area of one hole is preferably about 1 to 100μm<2> and more preferably about 5 to 50μm<2> . If the area is <1μm<2> , the gas produced by decomposition of the polarizing plate is hardly permeated, and if the area exceeds 100μm<2> , the through holes can be visually observed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate with a reflector used in a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art Heretofore, reflection type liquid crystal display devices have been widely used for calculators, watches, inexpensive word processors, and the like. The reflection type liquid crystal display device has a structure of a polarizing plate / a liquid crystal display cell / a polarizing plate / a reflecting plate (hereinafter, symbol / means lamination) in order from an observation surface, and a reflecting plate is provided inside the liquid crystal display cell. The laminated polarizing plates are used as electronic components in an assembly process.

As the reflection plate, a metal having a high reflectance such as aluminum or silver is selected. Such a metal deposition film, a metal foil or a metal foil laminated with a polyethylene terephthalate (hereinafter referred to as PET) film is used. In particular, metal foil is often used because of its excellent reflectance and durability. However, since these reflectors generally have no air permeability, when they are bonded to a polarizing plate via an adhesive, volatile components accumulate between the reflector and the polarizing plate in a long-term high-temperature environment. As a result, problems such as peeling at the interface and discoloration of the pressure-sensitive adhesive occurred.

[0004] In order to solve the above problems, a method of suppressing the decomposition of the cellulose film of the polarizing plate is considered as one means. For example, as a method for suppressing the decomposition of the cellulosic film of the polarizing plate, Japanese Patent Application Laid-Open No.
In Japanese Patent Publication No. 4 (1994), a method in which a basic compound, a peroxide decomposer, a radical chain inhibitor, and a metal deactivator are contained in a cellulose film on the surface of a polarizing plate or an adhesive between the polarizing plate and the reflector is proposed. Have been.

[0005] However, these chemicals have a consumption time individually, and when all of them are consumed, decomposition of a cellulose film or the like is started, a volatile component is generated, and a result of discoloration and peeling of the adhesive is obtained. Disappears. Further, when a basic compound such as an amine is added to the pressure-sensitive adhesive layer, the performance of the crosslinking agent used in the pressure-sensitive adhesive layer is often adversely affected.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a polarizing plate with a reflector which does not peel or discolor under long-term high-temperature environments.

[0007]

A polarizing plate with a reflector according to the present invention is a polarizing plate with a reflector used for a reflection type liquid crystal display device, wherein the polarizing plate having a cellulose acetate film as a protective layer and a through-hole are provided. And a reflection plate having the following.

In the present invention, a polarizing plate is an electronic component which functions as a polarizing plate together with a liquid crystal display cell in manufacturing a normal reflection type liquid crystal display panel. And the dichroic substance among the components of the polarizer is a uniaxially stretched polyvinyl alcohol (hereinafter, referred to as PVA) -iodine complex or a PVA-dichroic dye. On both surfaces of the polarizer, a cellulose acetate-based film is laminated as a protective layer. As the cellulose acetate film, a cellulose triacetate film is mainly used.

The reflector is not particularly limited as long as it is a material that effectively reflects visible light. For example, aluminum, silver,
A foil or a vapor-deposited film of titanium, nickel, platinum or the like can be used, but aluminum is preferably used in view of workability and economy. Further, a thermoplastic film such as PET may be laminated on the metal foil.

The shape of the through hole provided in the reflection plate is not particularly limited, and any shape such as a circle, a rectangle, and a triangle can be selected. A circle and a square are preferable from the viewpoint of easy opening processing.

Regarding the size of the through hole,
Opening area is 1 to 100 μm^TwoIt is preferred that
More preferably 5 to 50 μm^TwoIt is. 1 μm^TwoLess than
Indicates that gas generated due to decomposition of the polarizing plate is hard to escape.
0 μm ^TwoAbove, the size of the through hole can be visually observed
Would.

The number (density) per unit area of through-holes formed in the reflector is preferably 5 to 100 per cm ² , more preferably 5 to 50 / cm ² . If the density of the through-holes is less than 5 / cm ² , it is difficult for gas to escape from between the polarizing plate and the reflecting plate.
If the number exceeds the number of pieces / cm ² , the reflectance is reduced, and a group of through holes can be visually confirmed.

As a method of forming a through-hole in the reflector, an ordinary known method is applied. For example, using a large number of needles,
Needling method, embossing roll opening method by metal roll, die cutting method by punching die, laser beam drilling method, method of drilling by neutron irradiation,
Method of drilling by performing corona discharge treatment, in the case of metal foil,
There is a method of using a photoresist to regularly corrode a specific location of a metal foil.

When the polarizing plate and the reflecting plate having through holes are bonded via the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer is not particularly limited, but is usually formed of an acrylic copolymer. Agent layers are often used.

The pressure-sensitive adhesive comprising an acrylic copolymer mainly contains an alkyl (meth) acrylate having an alkyl group of 4 to 12 carbon atoms, and contains at least one of the alkyl (meth) acrylates in an amount of 50% by weight or more. It is a copolymer of this with a copolymerizable vinyl monomer. When the number of carbon atoms of the alkyl group is less than 4 or more than 12, the glass transition temperature is high, and the obtained acrylic pressure-sensitive adhesive cannot have sufficient tackiness.

Examples of the alkyl (meth) acrylate having 4 to 12 carbon atoms in the alkyl group include butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and isooctyl. (Meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate and the like are used, and at least one of these is used.

The vinyl monomer copolymerized with an alkyl (meth) acrylate having 4 to 12 carbon atoms in the alkyl group may be used as a monomer for controlling the polarity of an adhesive comprising the alkyl (meth) acrylate copolymer. Or a vinyl monomer used to impart cohesive force to the pressure-sensitive adhesive by crosslinking, for example, containing a carboxylic acid such as (meth) acrylic acid, itaconic acid, crotonic acid, (anhydrous) maleic acid, fumaric acid; Hydroxyl-containing vinyl monomers such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and N-methylolacrylamide; amino-containing vinyl monomers such as (meth) acrylamide; glycidyl (meth) ) Vinyl monomers containing epoxy groups such as acrylates, Vinyl monomers having a high glass transition point, such as ethyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, vinyl acetate, styrene, N-vinylpyrrolidone, and acrylonitrile; Examples thereof include monomers having a low glass transition point such as furyl acrylate and polyethylene glycol acrylate, and at least one of them is used.

The polymerization method of the acrylic copolymer includes:
Conventionally known methods are employed, and solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization and the like are performed. The polymerization initiation method is not particularly limited, and any of radical polymerization, ionic polymerization, ultraviolet polymerization, radiation polymerization, etc. may be used, but usually, radical polymerization such as benzoyl peroxide, azobisisobutyronitrile, etc. An initiator is employed, and a chain transfer agent such as lauryl mercaptan is used as a molecular weight regulator. Further, the acrylic copolymer includes a general random copolymer, a graft copolymer, and a block copolymer, and may be a mixture of at least two or more of these.

A pressure-sensitive adhesive composed of an acrylic copolymer is often mixed with a crosslinking agent before coating in order to improve the cohesive force of the pressure-sensitive adhesive layer. As the cross-linking agent, a substance that is chemically bonded to an active hydrogen atom incorporated in the copolymer is mainly selected, and examples thereof include a polyfunctional organic compound, an organometallic compound, and an organometallic salt. used.

More specifically, polyfunctional isocyanate compounds such as toluene diisocyanate, trimethylolpropane adduct of tolylene diisocyanate, adduct of hexamethylene diisocyanate, triphenylmethane triisocyanate and polymethylene polyphenyl isocyanate; N'-hexamethylene-1,
6-bis (1-aziridinecarboxamide), N,
Bifunctional or higher functional aziridine compounds such as N'-diphenylmethane-4,4'-bis (1-aziridinecarboxamide), trimethylolpropane-tri-β-aziridinylpropionate; N, N, N ', N Epoxy resins such as'-tetraglycidyl-m-xylenediamine; epoxy compounds such as ethylene glycol diglycidyl ether; alkyl etherified melamine resins; amino resins; acetylacetone and acetoacetic acid of polyvalent metals such as aluminum, tin, zinc, and titanium Coordination compounds of esters; metal chelates and the like.

The pressure-sensitive adhesive composition comprising an acrylic copolymer may contain, in addition to the crosslinking agent, an ultraviolet absorber, an antioxidant,
Various additives such as a tackifier and a viscosity modifier may be blended.

The method for producing the polarizing plate with a reflector is not particularly limited, but can be achieved by a usual method. That is, the pressure-sensitive adhesive composition comprising the acrylic copolymer is uniformly applied to a release sheet (for example, release paper), and if necessary, heated and dried to obtain a release sheet / pressure-sensitive adhesive layer. A release sheet having the following structure is produced, and this is bonded to one side of a polarizing plate and a reflection plate, respectively. The release sheet / pressure-sensitive adhesive layer / polarization plate, and release sheet / pressure-sensitive adhesive layer / reflection plate Two types of structures are produced. Thereafter, on the back of the former polarizing plate, the latter release sheet is peeled off, and both are bonded to each other, and the release sheet / adhesive layer / polarizing plate / adhesive layer /
A polarizing plate with a reflecting plate having a structure of a reflecting plate is obtained.

In the above-mentioned polarizing plate with a reflecting plate, the pressure-sensitive adhesive layers on both sides of the polarizing plate need not have the same composition at all, and there is no problem even if they are different compositions according to the purpose.

[0024]

In the polarizing plate with a reflecting plate of the present invention, a large number of fine through-holes are provided in a reflecting plate having a good reflectivity, so that the polarizing plate / adhesive layer / reflecting plate structure can be used for a long time at a high temperature. Even when exposed to the environment described above, the generated gas is scattered from the through holes of the reflection plate, and discoloration and peeling of the pressure-sensitive adhesive layer do not occur.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to explain the present invention in more detail, examples and comparative examples will be given below. Example 1 (1) Preparation of adhesive An n-butyl acrylate 9 was added to 100 parts by weight of ethyl acetate.
4.8 parts by weight, 5 parts by weight of acrylic acid and 0.2 parts by weight of 2-hydroxyethyl methacrylate are mixed, and in the presence of nitrogen gas, 0.3 parts by weight of benzoyl peroxide is used at 70 ° C. for 8 hours. The solution was polymerized.

The resultant acrylic copolymer has a weight average molecular weight of 1,000,000, a weight average molecular weight (M _w) and number average molecular weight (M _n) and the ratio of (M _w / M _n) of 4.9 met Was. Next, toluene was added to the above solution to make the solid content 18% by weight.
2 parts by weight (trimethylolpropane adduct of tolylene diisocyanate, manufactured by Nippon Polyurethane Co.)
An acrylic pressure-sensitive adhesive composition was prepared.

(2) Preparation of Polarizing Plate with Pressure-Sensitive Adhesive Layer The acrylic pressure-sensitive adhesive composition prepared in (1) was uniformly applied to a PET film that had been subjected to silicone release treatment.
The resultant was dried by heating at 5 ° C. for 5 minutes to prepare a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer thickness of 25 μm, and this was laminated on a commercially available polarizing plate having TAC as a protective layer to prepare a polarizing plate with a pressure-sensitive adhesive layer. .

(3) Reflective sheet pressure-sensitive adhesive sheet having through holes
The acrylic pressure-sensitive adhesive composition prepared in (1) was uniformly applied to the prepared PET release film, and dried by heating at 100 ° C. for 5 minutes to prepare a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 25 μm. . Next, a circular through-hole (a through-hole area of 5 μm ² , a through-hole density of 10 /
cm ² ) was opened, and the above-mentioned pressure-sensitive adhesive sheets were laminated to prepare a reflective sheet pressure-sensitive adhesive sheet with through holes.

(4) Production of polarizing plate with reflection plate The reflection plate adhesive sheet with through holes produced in (3) is
Laminating the surface of the polarizing plate with the pressure-sensitive adhesive layer prepared in (2), on which the pressure-sensitive adhesive layer is not laminated, using a desktop laminator,
A polarizing plate with a reflecting plate was produced.

(5) Evaluation of Polarizing Plate with Reflector A polarizing plate with a reflector was cut into a rectangle of 150 mm × 75 mm, and the PET release film was peeled off.
The layers were laminated at a bonding pressure of g / cm ² and placed in an autoclave at 50 ° C. and 5 atm for 10 minutes to complete the lamination. Thereafter, the substrate was left at a temperature of 90 ° C., a temperature of 80 ° C., and a relative humidity of 90% for 500 hours to perform a long-term durability test at high temperature and high temperature and high humidity. In the performance evaluation, discoloration and peeling of the pressure-sensitive adhesive layer between the aluminum foil and the polarizing plate were visually observed, and are shown in Table 1.

[0031]

[Table 1]

Example 2 The specification of the through hole of the aluminum foil was such that the through hole area was 50 μm.
^2. A polarizing plate with a reflector was prepared in the same manner as in Example 1 except that the through-hole density was 50 holes / cm ² , and a long-term durability test at high temperature and high temperature and high humidity was performed. It was shown to.

Comparative Example 1 A polarizing plate with a reflector was prepared and subjected to a high-temperature and high-temperature and high-humidity long-term durability test in the same manner as in Example 1 except that no through-hole was formed in the aluminum foil. Are shown in Table 1.

[0034]

Since the polarizing plate with a reflector according to the present invention is configured as described above, the adhesive layer does not discolor or peel even if left for a long time in a high-temperature and high-temperature and high-humidity environment. Therefore, a reflective liquid crystal display panel obtained by using the same exhibits excellent durability.

[0035]

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a structure in which a polarizing plate with a reflector according to one embodiment of the present invention is mounted on a lower structure of a liquid crystal display cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass plate (of a liquid crystal display cell) 2 Adhesive layer 3 Polarizing plate 4 Adhesive layer 5 Aluminum foil 6 Through-hole

Claims (1)

[Claims] 1. A polarizing plate with a reflecting plate used in a reflection type liquid crystal display device, wherein a polarizing plate having a cellulose acetate film as a protective layer and a reflecting plate having through holes are bonded via an adhesive layer. A polarizing plate with a reflecting plate, characterized in that: