JPH1039135A - Protecting method for phase difference plate surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent foaming or peeling during a durability test against a high temp. and high humidity by subjecting the surface of a phase difference plate to corona discharge treatment to obtain a specified range of wetting index, applying a fatty acid ester on the surface, and sticking a surface protective tape containing no fatty acid ester in an adhesive layer to the plate surface. SOLUTION: After the surface of a phase difference plate is treated with corona discharge to obtain 50 to 70dyn/cm wetting index, a fatty acid ester is applied to obtain about 45dyn/cm wetting index to protect the high polarity surface obtd. by the corona discharge treatment. Then, a surface protective tape having no fatty acid ester in the adhesive layer is stuck to the treated surface. Thereby, the fatty acid ester tightly adheres to the adhesive layer of the surface protective tape so that when the surface protective tape is removed by peeling, the fatty acid ester can be effectively removed. Therefore, the high polarity surface by the corona discharge treatment can be reproduced again, and adhesion strength to an adhesive layer of a polarizing plate can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for protecting a surface of a retardation plate used for a liquid crystal display or the like.

[0002]

2. Description of the Related Art In recent years, the use of liquid crystal displays in automobiles or outdoors where the temperature is high or the temperature and humidity are increasing, and the use environment is diversified. Under such an environment, when the foaming and peeling occur in the adhesive layer of the elliptically polarizing plate formed by laminating a retardation plate and a polarizing plate via an adhesive layer, which are bonded to a liquid crystal cell such as glass,
The display on the liquid crystal display may be fuzzy or even impossible to display. Therefore, the pressure-sensitive adhesive layer of the elliptically polarizing plate has been required to have high durability without foaming or peeling. As means for improving the durability of the pressure-sensitive adhesive layer of the elliptically polarizing plate, JP-A-4-347802 discloses a method in which a polarizing plate-side surface of a retardation plate is subjected to a corona discharge treatment and then a polarizing plate pressure-sensitive adhesive layer is adhered to the surface. Although disclosed in the gazette, the method disclosed in the gazette has a limitation that the polarizer must be laminated immediately after the corona discharge treatment. However, before the retardation plate is laminated with the polarizing plate, an adhesive layer and release paper are provided in this order on the opposite side of the surface to be laminated with the polarizing plate, and the surface laminated with the polarizing plate is protected from dust and dirt. It is often stored with a surface protection tape attached to it. If this storage is carried out for a long period of time, the adhesion of the pressure-sensitive adhesive of the surface protection tape becomes difficult to peel off at the time of use, or the effect of corona discharge treatment is reduced due to surface contamination by bleeding material from the pressure-sensitive adhesive. There was something.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to allow a tape to be easily peeled off even if stored for a long period of time with a surface protection tape attached. A polarizing plate is attached to the elliptically polarizing plate,
It is an object of the present invention to provide a method for protecting the surface of a retardation plate which can provide an adhesive sheet for a retardation plate which is less likely to foam and peel even when exposed to a liquid crystal cell made of glass or the like under high temperature or high temperature and high humidity.

[0004]

In order to achieve the above object, a method for protecting the surface of a retardation plate according to the present invention comprises the steps of: providing at least one surface of the retardation plate with a corona discharge so that the wetting index is 50 to 70 dyn / cm; After the treatment, a fatty acid ester is applied to the surface, and a surface protection tape containing no fatty acid ester in the adhesive layer is attached to the surface.

The retardation plate in the present invention compensates and eliminates coloring in a liquid crystal display due to birefringence of liquid crystal by utilizing its own birefringence. The retardation plate is made of polycarbonate, polysulfone, polyvinyl alcohol, It is obtained by subjecting a thermoplastic resin film such as polystyrene, polyamide, polyethylene terephthalate and the like having excellent transparency and stretchability to a uniaxial stretching treatment.

The corona discharge treatment may be performed on at least the surface of the retardation plate to which the polarizing plate is attached.
The wetting index by a wetting indicator specified in 6768 is 50 to 70 dyn / cm. If it is less than 50 dyn / cm, peeling is likely to occur at the interface between the retardation plate and the adhesive layer on the polarizing plate side in a durability test when an elliptically polarizing plate is used, and if it exceeds 70 dyn / cm, wrinkles will occur on the film during corona treatment. Or deterioration of the film may occur. It is preferably 55 to 70 dyn / cm.

The fatty acid ester is an ester obtained by a condensation reaction between a fatty acid and an alcohol. The fatty acid preferably has 10 or more carbon atoms, may have an unsaturated bond in the molecule, and may have an isocyanate group. Or a functional group such as an epoxy group. On the other hand, alcohols include monohydric alcohols having 1 to 18 carbon atoms,
Examples include polyhydric alcohols such as ethylene glycol and glycerin.

[0008] The amount of the fatty acid ester applied is desirably determined so that the wettability index of the surface after application is 45 dyn / cm or less. As a method for applying the fatty acid ester, any conventionally known means is used.In particular, after applying a surface protection tape containing the fatty acid ester in the pressure-sensitive adhesive layer, it is bleeding on the surface by peeling off. It is preferable because a trace amount of fatty acid ester can be transferred and applied to the surface of the retardation plate.

[0009] The surface after the fatty acid ester is applied is scratched, dusty,
As for the surface protection tape for protecting from dust, etc., it is only necessary that the fatty acid ester is not contained in the pressure-sensitive adhesive layer, and if the surface protection function of the retardation plate is satisfied, a special limitation is applied. However, those having a polyolefin-based base material are advantageous in terms of cost and disposal, and two-layer extruded ethylene-vinyl acetate copolymer or polyethylene-based pressure-sensitive adhesive, Examples thereof include those coated with an acrylic pressure-sensitive adhesive or a rubber-based pressure-sensitive adhesive.
After the fatty acid ester is applied, the surface of the pressure-sensitive adhesive layer may be subjected to a treatment such as corona discharge again before the surface protective tape containing no fatty acid ester is applied.

The constitution of the present invention is as described above. The retardation plate protected by the surface protective tape is peeled off in the next step and laminated with the adhesive layer of the polarizing plate to form an elliptically polarizing plate. Configure. The polarizing plate is not particularly limited as long as it is a film that transmits only light having a polarization plane in a certain direction, but usually, an iodine-based polarizing film composed of a polyvinyl alcohol-iodine complex, and a polyvinyl alcohol-dichroic dye. A polarizer such as a dye-based polarizing film is used in which a protective layer made of a film having a small optical anisotropy such as triacetyl cellulose or polymethyl methacrylate and having excellent transparency is laminated. The elliptically polarizing plate obtained in this manner is adhered to a glass plate such as a liquid crystal cell by an adhesive layer laminated on the other surface of the retardation plate, and constitutes a liquid crystal display for practical use.

The kind of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer formed on the polarizing plate or the pressure-sensitive adhesive layer formed on the other surface of the retardation plate is not particularly limited. In consideration of the durability in the above, an acrylic pressure-sensitive adhesive is preferable, and its layer thickness is about 10 to 35 μm.

[0012]

According to the method for protecting the surface of a retardation plate of the present invention, a fatty acid ester is applied to the surface of a retardation plate subjected to a corona discharge treatment so as to have a wetting index of 50 to 70 dyn / cm with a wetting index of about 45 dyn / cm. By applying as much as possible, the highly polar surface by the corona discharge treatment is protected. Then
By attaching a surface protection tape containing no fatty acid ester in the pressure-sensitive adhesive layer, the fatty acid ester adheres to the pressure-sensitive adhesive layer of the surface protection tape, and the fatty acid ester is also effective when the surface protection tape is peeled off. Therefore, it is considered that the highly polar surface by the corona discharge treatment can be reproduced. This ensures a sufficient adhesive force with the polarizing plate pressure-sensitive adhesive layer, suppresses foaming and peeling in a durability test, and has a low affinity between the fatty acid ester and the surface of the retardation plate. It is considered that light peeling can be achieved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments. Preparation of adhesive for polarizing plate and retardation plate 94.8 parts by weight of butyl acrylate, 5 parts by weight of acrylic acid, 0.2 parts by weight of 2-hydroxyethyl methacrylate 0.3 parts by weight of benzoyl peroxide as a polymerization initiator Was thermally copolymerized in ethyl acetate by using
A polymer solution having a weight average molecular weight of 10,000 and a ratio of the number average molecular weight to the number average molecular weight of 4.9 was obtained. Toluene was added thereto to form a solution having a solid content of 18% by weight, and a polyisocyanate crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd .:
2 parts by weight of trade name “Coronate L”) were blended to form an adhesive.

A polarizing plate comprising a polyvinyl alcohol-iodine complex having a thickness of 24 μm
A polarizing plate having a 75 μm-thick cellulose triacetate film laminated on both sides of an iodine-based polarizing film was prepared. Polarizing plate pressure-sensitive adhesive sheet The above-mentioned acrylic pressure-sensitive adhesive solution was applied to one surface of a polarizing plate so that the layer thickness after drying was 25 μm, dried, and then a release paper film was temporarily attached to obtain a polarizing plate pressure-sensitive adhesive sheet. . Thickness 60 obtained by uniaxially stretching a retardation plate polysulfone resin film
A μm retardation plate was prepared. Surface protection tape containing no fatty acid ester (1) Surface protection tape made of polyethylene and laminated with an ethylene-vinyl acetate copolymer pressure-sensitive adhesive layer containing no fatty acid ester (trade name, manufactured by Sekisui Chemical Co., Ltd.) "Protect tape # 625C") was prepared. Fatty acid ester-containing surface protective tape (2) 5 parts by weight of fatty acid octyl ester (trade name "ADEKASIZER D-32") based on 100 parts by weight of the pressure-sensitive adhesive of the surface protective tape (1). Was prepared by laminating a pressure-sensitive adhesive layer obtained by blending with a polyethylene substrate.

(Example 1) A surface protective tape (2) was adhered to the surface of a retardation plate having a wettability index of 68 dyn / cm by a corona discharge treatment and a wettability index of 5 dyn / cm at 30 ° C.
After leaving this tape for 2 days, the tape (2) was peeled off, and the surface wetting index was 39 dyn / cm. Next, the surface protective tape (1) is adhered to this surface, and the acrylic pressure-sensitive adhesive solution is applied to the other surface so that the layer thickness after drying is 25 μm, and after drying, a release film is temporarily attached. Thus, an adhesive sheet for a retardation plate was obtained.

(Example 2) In the same manner as in Example 1, a surface protective tape (2) was adhered, and the tape (2) was peeled off from the retardation plate left at 30 ° C for 5 days. Upon treatment, the wetting index was 70 dyn / cm. Thereafter, a pressure-sensitive adhesive sheet for a retardation plate was obtained in the same manner as in Example 1.

(Comparative Example 1) A surface protective tape (1) was adhered to the surface of the retardation plate subjected to corona discharge treatment under the same conditions as in Example 1, and the layer thickness after drying the acrylic adhesive solution on the other surface was reduced. It was applied so as to have a thickness of 25 μm, dried, and then a release film was temporarily attached to obtain an adhesive sheet for a retardation plate.

Preparation of Evaluation Test Specimens The adhesive sheet of the retardation plate was cut into a strip having a width of 25 mm to obtain a test piece for measuring a peeling force. The surface protective tape (1) of the pressure-sensitive adhesive sheet obtained in Examples 1 and 2 and Comparative Example 1 was peeled off the release film of the pressure-sensitive adhesive sheet, and the stretching axis of the retardation film and the Z-axis of the polarizing sheet were removed. Is 4
The elliptically polarizing plate pressure-sensitive adhesive sheet was laminated by intersecting at 5 degrees. Next, the Z axis of the polarizing plate is set at 45 degrees with each side so that
It was cut into a rectangle of 0 mm x 75 mm to obtain a test piece for durability measurement.

Evaluation test The test piece for measuring durability was cured for 4 days at room temperature after application of the adhesive, and then subjected to evaluation. 1. Peeling force measurement test: 180 degree peeling force was measured at a tensile speed of 300 mm / min by a Shopper tester. 2. High-temperature durability test: The release film was removed from the elliptically polarizing plate pressure-sensitive adhesive sheet and laminated on a liquid crystal display glass at a pressure of 3 kg / cm ² in a 90 ° C. gear oven.
After being exposed for 00 hours, the mixture was allowed to cool, and the pressure-sensitive adhesive layer was visually observed to evaluate the presence or absence of foaming or peeling, coloring, and the presence or absence of abnormal appearance. 3. High-temperature and high-humidity durability test: An environmental tester maintained at 60 ° C. × 95% RH was used in place of the 90 ° C. gear oven. Was performed in the same manner as described above. Table 1 shows the evaluation results.

[0020]

[Table 1]

[0021]

According to the present invention, the tape can be easily peeled off even when stored for a long period of time with the surface protective tape attached, and a polarizing plate can be attached to this to form an elliptically polarizing plate, which can be applied to a liquid crystal cell such as glass. Provided is a method for producing a pressure-sensitive adhesive sheet which is hardly foamed or peeled off even when the bonded product is exposed to high temperature or high temperature and high humidity.

Claims (1)

[Claims] At least one surface of a retardation plate is subjected to a corona discharge treatment so that a wetting index is 50 to 70 dyn / cm, and then a fatty acid ester is applied to the surface.
A method for protecting the surface of a retardation plate, characterized in that a surface protective tape containing no fatty acid ester in an adhesive layer is attached to the surface.