JPH10186131A - Elliptic polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of foaming and peeling in high-temperature, high-humidity environment and to prevent optical performance from deteriorating by providing sides which shift within a specific range in parallel to respective main surfaces between a polarizing plate end side and a phase difference plate end side after a durability test under specific conditions. SOLUTION: The polarizing plate 1 and phase difference plate 3 are stuck together across an adhesive layer 2 formed of an acryl-based adhesive, and the other surface of the phase difference plate 3 is stuck on a glass plate 5 for a liquid crystal cell across an adhesive layer 4. This laminate is thermally processed to cause the polarizing plate 1 and phase difference plate 3 deform owing to heat and the shrinkage of the polarizing plate 1 is large, so the adhesive layer 2 also deforms. The polarizing plate 1 is different in shrinkage behavior between an absorption axis direction and its orthogonal direction. For example, when the laminate is exposed at 90 deg.C for 24 hours, a polarizing plate end side 1a and a phase plate end side 3a constituting the same end side of the elliptic polarizing plate 6 shift in parallel to the respective main surfaces. At least one side having a shift (x) of 100 to 450μm is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an elliptically polarizing plate used as a component of a liquid crystal display. More specifically, the present invention relates to an elliptically polarizing plate which does not cause foaming and peeling even under a high temperature or high temperature and high humidity environment and does not deteriorate optical characteristics.

[0002]

2. Description of the Related Art Recently, a liquid crystal display (LCD) has been developed.
With the increasing use of such devices in vehicles and outdoors, and the diversification of usage environments, the elliptically polarizing plates used as components of liquid crystal displays are required to have high durability. I have. In particular, when an elliptically polarizing plate is mounted on a liquid crystal display, heat treatment is involved, so that when the elliptically polarizing plate is bonded to a liquid crystal cell in a high-temperature or high-temperature, high-humidity environment, there is no foaming or peeling, and the optical characteristics also deteriorate. Not required.

Hitherto, a method of thermally annealing a polarizing plate has been proposed as a means for improving the durability of an elliptically polarizing plate, but there is a problem that the optical performance of the polarizing plate is reduced. As another method, a method of improving the performance of an adhesive used when a polarizing plate and a liquid crystal cell or the like are bonded to each other has been proposed. As the means, for example, a method of improving the balance of durability by adjusting a cohesive force based on a shift speed when a shear stress is applied to the acrylic adhesive layer has been proposed (Japanese Patent Laid-Open No. 7-30179).
2). However, even with this method, when the obtained elliptically polarizing plate is actually evaluated, the balance of durability cannot be said to be sufficient. It is conceivable that the cause is that it does not correspond to the physical properties at high temperature.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to not only prevent foaming or peeling under a high temperature or high temperature and high humidity environment, but also to improve optical performance. Another object of the present invention is to provide an elliptically polarizing plate that does not decrease.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an elliptically polarizing plate comprising a polarizing plate and a retardation plate bonded together via an acrylic pressure-sensitive adhesive layer. Provided is an elliptically polarizing plate characterized by having at least one side having a deviation of 100 to 450 μm in a direction parallel to each main surface with respect to an edge of a retardation plate.

As shown in FIG. 1, the elliptically polarizing plate is obtained by laminating a polarizing plate 1 and a retardation plate 3 via an adhesive layer 2 made of an acrylic adhesive or the like. The other surface is bonded to a liquid crystal cell glass plate 5 via an adhesive layer 4. When such a laminate is subjected to heat treatment, the polarizing plate 1 and the retardation plate 3 are deformed by heat, and particularly, the shrinkage of the polarizing plate 1 is large, so that the pressure-sensitive adhesive layer 2 is also deformed.
In particular, the polarizing plate 1 has a different shrinkage behavior between the absorption axis direction and the direction perpendicular thereto. For example, when the laminate is exposed at 90 ° C. for 24 hours, the polarizing plate edge 1 constituting the same edge of the elliptically polarizing plate 6 is exposed.
a and the edge 3a of the retardation plate are displaced in a direction parallel to each main surface. The magnitude x of this deviation can be an index of the durability of the elliptically polarizing plate 6.

When x is less than 100 μm, peeling is likely to occur when the substrate is then placed in a severe environment of high temperature or high temperature and high humidity, and before and after being placed in such a severe environment. Then, the change in the phase difference becomes large. On the other hand, when x exceeds 450 μm, the change in retardation is small, but foaming is likely to occur. When the balance between the appearance characteristics and the optical characteristics is considered, the range of x is 15
It is preferable that 0 <x <400.

According to the present invention, there is provided at least one side having a deviation of 100 to 450 μm in a direction parallel to each principal surface of the edge of the polarizing plate and the edge of the retardation plate after exposure at 90 ° C. for 24 hours. Although it is a feature, two or more sides or all sides that satisfy the above conditions may be used. For example, when the elliptically polarizing plate is cut into a rectangular shape, the two opposite sides are symmetrical, so that generally the two opposite sides have almost the same deviation, and x is almost equal. Therefore, it is sufficient that at least one side satisfies the above condition, and of course, all four sides may satisfy the above condition. Although the case where the elliptically polarizing plate is rectangular has been described as an example, the shape is not limited to a rectangle.

The polarizing plate in the present invention means an electronic component functioning as a polarizing plate together with a liquid crystal cell. To be specific, it is a general polarizing plate mass-produced today.
Among the constituent components of the polarizer, the dichroic substance is a uniaxially stretched polyvinyl alcohol-iodine complex or a PVA dichroic dye, and a cellulose triacetate film or a methyl (meth) acrylate resin as a protective layer on both surfaces of the polarizer. Films are laminated.

The retardation plate in the present invention compensates and eliminates coloring in a liquid crystal display caused by birefringence of liquid crystal by utilizing its own birefringence. It is not particularly limited as long as it has. For example, the one generally used today is a uniaxial thermoplastic resin film having excellent transparency and stretchability such as polycarbonate, polysulfone, polyvinyl alcohol, polystyrene, polyamide, polyarylate, and polyethylene terephthalate. It has been subjected to a stretching treatment.

As the acrylic pressure-sensitive adhesive in the present invention,
Examples of the pressure-sensitive adhesive include an acrylic polymer having a (meth) acrylic acid alkyl ester as a main component and a polar monomer component copolymerized therewith.

The alkyl (meth) acrylate is an alkyl acrylate or an alkyl methacrylate, and is not particularly limited. Examples thereof include ethyl (meth) acrylate and (meth) acrylic acid. Isopropyl, n-butyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
Examples thereof include isooctyl (meth) acrylate, n-octyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, and lauryl (meth) acrylate.

The polar monomer copolymerized with the alkyl (meth) acrylate is, for example, a carboxyl group-containing monomer such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, and fumaric acid; Hydroxyl-containing monomers such as (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polyoxypropylene (meth) acrylate, and caprolactone-modified (meth) acrylate; N-vinylpyrrolidone;
Nitrogen-containing monomers such as vinylcaprolactam, acroylmorpholine, (meth) acrylamide, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and dimethylaminopropyl (meth) acrylate; and epoxy group-containing such as glycidyl (meth) acrylate And monomers.

The above-mentioned polar monomer acts as a cross-linking point when the above-mentioned acrylic polymer is cross-linked using a cross-linking agent. The amount of the polar monomer is preferably about 0.5 to 20% by weight based on all the monomers constituting the acrylic polymer.

The crosslinking agent is not particularly restricted but includes, for example, polyisocyanate compounds such as aliphatic diisocyanates, aromatic diisocyanates and aromatic triisocyanates, butyl etherified styrene melamine and trimethylol melamine. Melamine compounds, polyethylene glycol, glycol compounds such as trimethylolpropane, hexamethylenediamine, polyamine compounds such as diethylenetriamine,
In addition, phenol resin compounds, epoxy resin compounds, urea resin compounds, polyaldehyde compounds and the like are used.

The amount of the crosslinking agent is preferably about 0.3 to 10 parts by weight based on 100 parts by weight of the acrylic polymer.

The acrylic pressure-sensitive adhesive layer in the present invention preferably has a gel fraction of 50 to 90% by weight. When the gel fraction is less than 50% by weight, foaming easily occurs in the adhesive layer, and
If it exceeds 0% by weight, peeling tends to occur in the adhesive layer. Here, the gel fraction is a ratio of insoluble in tetrahydrofuran (hereinafter, referred to as “THF”) in the pressure-sensitive adhesive expressed as a percentage by weight, and is determined by the following equation. (Gel fraction (% by weight)) = (weight insoluble in THF (g)) × 100 / (collected weight of adhesive (g))

The thickness of the pressure-sensitive adhesive layer in the present invention is 20 to 3
5 μm is preferred. When the thickness is less than 20 μm, the stress relaxation property is insufficient, peeling is liable to occur, and a decrease in optical characteristics under a high temperature or high temperature and high humidity environment is inevitable. On the other hand, if the thickness exceeds 35 μm, foaming is likely to occur, which is not preferable. A more preferable thickness satisfying these balances is 25 μm to 30 μm.

[0019]

Embodiments of the present invention will be described below.

[Preparation of acrylic pressure-sensitive adhesive (1)] 94.8 parts by weight of butyl acrylate, 5 parts by weight of acrylic acid,
0.2 parts by weight of hydroxyethyl methacrylate was copolymerized in the presence of 0.3 parts by weight of benzoyl peroxide using ethyl acetate as a solvent to give a weight average molecular weight (Mw) of 120.
10,000, the ratio of the weight average molecular weight to the number average molecular weight (Mn) (Mw
(Mn) of 3.9 was obtained as an ethyl acetate solution of an acrylic polymer. Toluene was added to the obtained ethyl acetate solution of the acrylic polymer to dilute it, thereby obtaining a 13% by weight toluene solution of the acrylic polymer.

[Preparation of Acrylic Adhesive (2)] 94 parts by weight of butyl acrylate, 6 parts by weight of acrylic acid, 0.03 parts by weight of azobisisobutyronitrile (AIBN) and 0.0015 parts by weight of dodecyl mercaptan In the presence, 100 parts by weight of ethyl acetate was copolymerized to give an acrylic polymer ethyl acetate having a weight average molecular weight (Mw) of 1,290,000 and a ratio of weight average molecular weight to number average molecular weight (Mw / Mn) of 2.6. A solution was obtained. Toluene was added to the obtained ethyl acetate solution of the acrylic polymer to dilute it, thereby obtaining a 13% by weight toluene solution of the acrylic polymer.

Example 1 (Preparation of Materials Used) Polarizing plate: Commercially available polarizing plate (product name: HC2-8218RE)
(Manufactured by Sanritz Co., Ltd.). Retardation plate: A 60 μm-thick retardation plate prepared by uniaxially stretching a polycarbonate resin film was prepared. Adhesive: A mixture obtained by adding 1.2 parts by weight of an isocyanate cross-linking agent (product name: Coronate L (manufactured by Nippon Polyurethane Industries, Ltd.)) to the prepared acrylic adhesive (1) was used.

(Preparation of Elliptically Polarizing Plate) The pressure-sensitive adhesive obtained as described above was applied to a silicone release-treated PET film so that the average thickness after drying was 27 μm, and dried in an oven at 110 ° C. for 5 minutes. After that, it was bonded to a polarizing plate to obtain a polarizing plate adhesive sheet. Further, the above-mentioned pressure-sensitive adhesive was treated in the same manner as in the production of the polarizing plate pressure-sensitive adhesive sheet, and bonded to a phase difference plate to obtain a phase difference plate pressure-sensitive adhesive sheet. Next, the release PET film of the polarizing plate pressure-sensitive adhesive sheet is peeled off, and the absorption axis of the polarizing plate and the slow axis of the phase difference plate form 45 ° on the surface of the retardation plate where the pressure-sensitive adhesive is not applied. They were bonded using a laminator to form an elliptically polarizing plate.

[Example 2] An elliptically polarizing plate was prepared in the same manner as in Example 1 except that 2.0 parts by weight of Coronate L was added to the prepared acrylic pressure-sensitive adhesive (2). Produced.

Comparative Example 1 An elliptically polarizing plate was prepared in the same manner as in Example 1, except that 0.3 parts by weight of Coronate L was added to the prepared acrylic pressure-sensitive adhesive (1). Produced.

Comparative Example 2 An elliptically polarizing plate was prepared in the same manner as in Example 1, except that 3.0 parts by weight of Coronate L was added to the prepared acrylic pressure-sensitive adhesive (1). Produced.

Comparative Example 3 An elliptically polarizing plate was prepared in the same manner as in Example 1, except that 0.5 parts by weight of Coronate L was added to the prepared acrylic pressure-sensitive adhesive (2). Produced.

Comparative Example 4 An elliptically polarizing plate was prepared in the same manner as in Example 1 except that the prepared acrylic pressure-sensitive adhesive (2) to which 5.0 parts by weight of Coronate L was added was used as the pressure-sensitive adhesive. Produced.

[Evaluation Test] The elliptically polarizing plates obtained in the above Examples and Comparative Examples were cut into 11.3 inch squares, the release PET on the surface of the retardation plate was peeled off, and the liquid crystal was exposed through the exposed adhesive layer. The laminate was bonded to a cell glass plate with a laminator at a lamination pressure of 3 kg / cm ² . After performing an autoclave treatment at 50 ° C., 5 atm, and 10 min for these laminates, a durability test was performed for 500 hours under high-temperature and high-temperature and high-humidity conditions of 90 ° C. and 60 ° C. × 95% RH.
Changes in appearance (foaming and peeling) were visually evaluated. Also,
Regarding the optical characteristics, the change in the phase difference value before the autoclave treatment and after 500 hours of the durability test was evaluated for 10 points at the position of 10 mm in the peripheral portion of the elliptically polarizing plate. Here, the phase difference value refers to a spectral value in a state where the polarizing plate of the elliptically polarizing plate faces the incident light side and the absorption axes of the two polarizing plates on the incident light side coincide between the crossed Nicols. The transmittance is measured, and the wavelength at the longest wavelength side where the transmittance shows a minimum is set.

Table 1 shows the gel fraction of the pressure-sensitive adhesive, the magnitude x of the deviation of the edge of the polarizing plate and the edge of the retardation plate in the main surface direction, the appearance characteristics, and the evaluation of the optical characteristics in each of Examples and Comparative Examples. The results are shown.

[0031]

[Table 1]

[0032]

As described above, according to the present invention, under the conditions of high temperature, high temperature and high humidity, a balance between the elastic modulus at a high temperature and an appropriate stress relaxation property is obtained. An elliptically polarizing plate that does not impair the appearance and does not cause a decrease in optical characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a laminate in which an elliptically polarizing plate is bonded to a glass plate for a liquid crystal cell.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Polarizer 1a Polarizer edge 2 Adhesive layer 3 Retardation plate 3a Retardation plate edge 4 Adhesive layer 5 Glass plate for liquid crystal cell

Claims (1)

[Claims] 1. An elliptically polarizing plate comprising a polarizing plate and a retardation plate bonded together via an acrylic pressure-sensitive adhesive layer, wherein 90
The degree of deviation in the direction parallel to each principal surface between the edge of the polarizing plate and the edge of the retardation plate after exposure at 24 ° C. for 24 hours is 100 to 45.
An elliptically polarizing plate having at least one side having a length of 0 μm.