JPH0430120A - Surface protective film for liquid crystal display panel - Google Patents

Abstract

PURPOSE:To obtain a surface protective film for liquid crystal display panel which need not be peeled off in the case of inspection by forming the surface protective film of specified two layers respectively having the visible light beam transmittivity and surface smoothness of specified values. CONSTITUTION:The protective film 1 is constituted of two layers, such as an optical isotropic base material film layer 11 whose visible light beam transmittivity is >=75% and an optical isotropic adhesive resin layer 12 whose surface smoothness is <=0.1mm. When this film 1, which has high visible light beam transmittivity and flexibility and which is soft and excellent in mechanical characteristic, is stuck to the polarizing plate of the liquid crystal display panel by press-bonding, it is unnecessary to peel off the protective film in the case of performing optical evaluation of displaying ability, hue and contrast, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a protective film for protecting the surface of a polarizing plate of a liquid crystal display panel by pasting it over the polarizing plate.

(In this specification, the terms film, sheet, and plate are used, but there is no special distinction between them.) As is well known in the art, a liquid crystal cell It has a structure in which liquid crystal is sealed inside. A liquid crystal display panel is produced by laminating a polarizing plate on at least one side (usually both sides) of this liquid crystal cell. The stacking of polarizing plates on liquid crystal cells is
Usually, this is done by pressing a polarizing plate with an adhesive layer onto a liquid crystal cell.

Note that a polarizing plate that can also be used as a liquid crystal cell substrate has also been proposed.

In any case, the outermost layer of the liquid crystal display panel is formed of a polarizing plate, and a commonly used polarizing plate is one in which cellulose triacetate films are laminated as protective plates on both sides of a polarizing element film.

However, this cellulose triacetate film has poor scratch resistance and water resistance, so after installing the polarizing plate on the liquid crystal cell, immediately cover it with a protective film.
This is to prevent damage to the polarizing plate during subsequent processes and distribution processes. Installing a protective film also helps prevent dust from adhering.

This protective film is peeled off and removed only when the liquid crystal display panel is actually used.

As the above-mentioned protective film, a thermocompression type film such as a polyethylene film or an ethylene-vinyl acetate copolymer film, and a pressure sensitive adhesive type film such as a polyester film with a weak adhesive layer are used.

PROBLEMS TO BE SOLVED BY THE INVENTION It is customary for manufactured liquid crystal display panels to be inspected at appropriate times to evaluate display ability, hue, contrast, and the like. However, the above-mentioned conventional protective film is a hindrance to inspections that involve such optical evaluation, so the protective film must be peeled off before the inspection, and a new protective film is reapplied once the inspection is complete. things are done.

The reason why the protective film is reapplied with a new one is because the protective film does not have reattachability, or even if it can be reattached, the beauty will be lost if it is reattached.

Peeling off and reapplying the protective film for the above-mentioned inspection requires two steps, which must be a major hindrance in this field where cost reduction is pursued to the utmost. Since it is recognized that protective films are originally like this, no particular measures have been taken at present to improve them.

In view of this situation, the present invention was made for the purpose of providing a surface protection film that does not require peeling during inspection.

Means for Solving the Problems The surface protection film for a liquid crystal display panel of the present invention is a protective film for protecting the surface of the polarizing plate (2) by pasting it over the polarizing plate (2) of the liquid crystal display panel. film(
1), wherein the protective film (1) has a layer structure of an optically isotropic base film layer (Ill/optical isotropic adhesive resin layer (12)) and has a visible light transmittance of 75% or more. And,
and the smoothness of the surface of the optically isotropic adhesive resin layer (12) is 0.
It is characterized by being composed of an optically isotropic laminated film having a volume of 1 μl or less.

The present invention will be explained in detail below.

As shown in Figure 3 below, the 1Li Yu5 liquid crystal display panel has liquid crystal cells (
It is produced by laminating a polarizing plate (2) on at least one side (usually both sides) of 3). Incidentally, the polarizing plate (2) can also serve as a liquid crystal cell substrate.

Among these, the liquid crystal cell (3) has a transparent electrode (3) made of ITO.
2) are arranged facing each other with a spacer (33) in between, and a liquid crystal (34) is sealed in the gap between them. Although an alignment film and the like are also provided, the details are omitted.

Polarizing plate (2) is made of vinyl alcohol polymer/iodine, vinyl alcohol polymer/dichroic dye, vinyl alcohol polymer/polyene, polyvinyl halide/polyene. It consists of a protective plate (22) such as a cellulose triacetate film or a cellulose butyrate acetate film laminated on both sides of a polarizing element film (21) made of a polyacrylonitrile/polyene type or the like. As the protective plate (22), in addition to cellulose triacetate film and cellulose butyrate acetate film, polycarbonate film, polymethyl methacrylate film, polyvinyl chloride film, ethylene-vinyl alcohol copolymer film, polyamide film, polystyrene film, etc. Although it is said to be used, it is actually limited to cellulose triacetate films and cellulose butyrate acetate films, particularly cellulose triacetate films.

A protective film (1) is pasted on top of this polarizing plate (2), but in the present invention, as this protective film (1), a light isotropic base film layer (111/light isotropic An optically isotropic laminated film having a layer structure of an adhesive resin layer (12) is used.

Here, as the optically isotropic base film layer (11), a film having the necessary mechanical strength, such as a hard polyvinyl chloride film, a polyvinylidene chloride film, a polycarbonate film, a polystyrene film, a polyester film, a polysulfone film, a polyester film, etc. -4-
Methylpentene film, polyphenylene oxide film, polyether sulfone film, polyarylene ester film, polyvinyl alcohol film,
Ethylene-vinyl alcohol copolymer film, cellulose polymer film, etc. are used. Since this base film layer (11) needs to have optical isotropy, the retardation value is 30n+ or less, especially 20n
+m or less film with visible light transmittance of 75%
Use the above. The base film layer (11) having such optical isotropy can be obtained by forming a film by a casting method, but the retardation value and visible light transmittance satisfy the above conditions. If so, other molding methods such as extrusion can also be used.

The thickness of the optically isotropic base film layer (11) is 5 to 200μ
Kindergarten level is appropriate.

The optically isotropic adhesive resin layer (12) is a polarizing plate (2).
A layer that has adhesion to, for example, polyester,
Heat-sensitive adhesive resin layer of acrylic, polyolefin, polyamide, etc. Pressure-sensitive adhesive resin layer of acrylic, polyester, urethane, polyether, rubber, etc.: saturated polyester resin, polyurethane resin, polybutadiene A partially crosslinked or incompletely crosslinked film formed by blending a curing agent with a resin having a functional group such as a polyol, a polyolefin polyol, or a functional group-containing acrylic copolymer: For example, 20% by weight of a plasticizer is added to polyvinyl chloride. % or above Soft polyvinyl chloride film: Saturated polyester resin film: Acrylic copolymer film: Butyl rubber, urethane rubber, butadiene rubber (polybutadiene rubber, styrene-butadiene rubber, styrene-butadiene-styrene block copolymer, etc.) ), films obtained by forming synthetic rubbers such as styrene-isoprene-styrene rubber; films obtained by forming films from polyolefin resins such as low molecular weight polyethylene, acidic polypropylene, and chlorinated polypropylene: Examples include films obtained by forming ethylene copolymers such as ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, and ethylene-acrylic acid ester copolymers.

In order to ensure adhesion to the polarizing plate (2), the surface of the protective film (optical isotropic adhesive resin layer (12)) must have a smoothness of 0.1 μm or less. The surface smoothness is defined as the smoothness specified in JIS B-0601, 1970.

When reworkability is required, the optically isotropic adhesive resin layer (12) is selected to have peelability, and when permanent adhesion is required, strong adhesive strength or adhesive strength is selected. Choose what you want. The thickness of the optically isotropic adhesive resin layer (12) is often set to about 1 to 50 μm.

This optically isotropic adhesive resin layer (12) is also required to have optical isotropy like the optically isotropic base film layer (Ill).

Care should be taken to ensure that the retardation value and visible light transmittance of the entire protective film (11) made of the optically isotropic laminated film having the above-mentioned layer structure are 30n1 or less and 75% or less, respectively.

As described above, the protective film (1) of the present invention has a photoisotropic base film layer (ill)/a photoisotropic adhesive resin layer (12
), but since it is usually handled in a rolled state, when using a sticky material as the optically isotropic adhesive resin layer (12), the optically isotropic adhesive resin layer (12) is The side of the optically isotropic base film layer (11) in contact with the adhesive resin layer (12) is back-treated with a release agent such as a silicone release agent, a fluororesin release agent, or a compound having a long-chain alkyl group. Alternatively, a releasable sheet (13) is further provided on the optically isotropic adhesive resin layer (12).

Here, the releasable sheet (13) is a paper or plastic film whose surface has been treated with a silicone release agent or other release agent, a film or sheet that itself has releasability, or a blend of a release agent. Molded films or sheets, plastic films or sheets obtained by graft polymerization of organopolysiloxane and polyolefin resin, etc. are used. Peelable sheet (1
The thickness of 3) is often about 12 to 250 μm.

Function The protective film (1) of the present invention has a layer structure of an optically isotropic base film layer (11)/a optically isotropic adhesive resin layer (12).

In use, place the optically isotropic adhesive resin layer (12) side of this protective film (1) on the polarizing plate (2) of the liquid crystal display panel.
) on the surface. (Optical isotropic adhesive resin layer (12)
When the side is covered with a releasable sheet (13), this releasable sheet (13) is peeled off and removed prior to pasting, and if necessary, pasting is performed by thermocompression bonding.)Display ability, hue When conducting tests for evaluating contrast, etc., in the present invention, there is no need to peel off the protective film (1) attached to the polarizing plate (2) of the liquid crystal display panel; These tests can be carried out with the device in place.

If the protective film (1) is required to have reworkability, the protective film (1) is peeled off and removed before the liquid crystal display panel is actually used. On the other hand, when good workability is not required, a protective film (1
) is used for actual use with permanent adhesive.

Example Next, the present invention will be further explained with reference to Examples.

"1 part" below refers to parts by weight.

Example 1 Film 1 FIG. 2 is a sectional view showing an example of the surface protection film (11) of the present invention.

(11) is a polycarbonate film as an example of an optically isotropic base film layer, and was manufactured by a casting method. The retardation value is 5 parts m, the visible light transmittance is 90%, and the thickness is 30 μm.

(13) is a releasable sheet, which is made of a polyester film having a thickness of 50 μm and subjected to a release treatment using silicone.

(12) is an optically isotropic adhesive resin layer, in which a polyolefin polyol (Epol, hydroxyl group content 0.90 seq. manufactured by Idemitsu Petrochemical Co., Ltd. /g, viscosity 75000cps/'
30°C) 100 parts, IP solvent (aliphatic hydrocarbon solvent manufactured by Mitsui Petrochemical Industries, Ltd.) 50 parts, hydrogenated MD
It was formed by casting a solution consisting of 3 parts of I (diphenylmethane diisocyanate) type curing agent and drying at 80° C. for 5 minutes. The thickness was 20 μm, and the surface smoothness of the lower surface (the surface on the releasable sheet (13) side) at the time of film formation was 0.032 μm.

The above-mentioned optically isotropic substrate is placed on the optically isotropic adhesive resin layer (12) side of the thus obtained laminated film consisting of the optically isotropic adhesive resin layer (12)/releasable sheet (13). The film layer (111) is laminated and pressed, and the optically isotropic base film layer (111) is laminated and pressed.
1) / Optical isotropic adhesive resin layer (12) / Peelable sheet (
The releasable sheet (13) shown in FIG.
A protective film (11) with 13) was obtained.

The retardation value of the entire protective film (1) excluding the peelable sheet (13) is 6n■, and the visible light transmittance is 87.
%, and the thickness was 50 μm.

This protective film (1) is not only soft and flexible, but also has good mechanical properties.

This protective film (1) is adhered to a polarizing plate (2) of a liquid crystal display panel by pressure bonding after peeling off the releasable sheet (13).

Figure 3 is a sectional view showing an example of a liquid crystal display panel to which the surface protection film (11) of the present invention is attached.

(3) is a liquid crystal cell, which has a structure in which two substrates (31) with transparent electrodes (32) are placed facing each other with a spacer (33) interposed therebetween, and a liquid crystal (34) is sealed in the gap between them.

(2) is a polarizing plate, for example, a 35 μm thick polarizing film (21) made of polyvinyl alcohol/iodine is coated on both sides with a 5 μm thick cellulose triacetate film.
It consists of a 0μ protective plate (22) laminated using an acrylic resin pressure-sensitive adhesive. (23) is the pressure sensitive adhesive layer.

(1) is the surface protection film mentioned earlier, and the polarizing plate (
2)/Liquid crystal cell (3)/Polarizing plate (2) It is attached by pressure bonding onto the polarizing plate (2) of a liquid crystal display panel having the following structure.

After the surface protection film (1) has been applied, the outermost layer is formed of an optically isotropic adhesive resin layer (12), so it has good damage resistance, water resistance, and dust resistance, and is optically isotropic. Therefore, evaluation of optical performance such as display ability, hue, and contrast can be performed without peeling off this surface protection film (11).

Since this surface protection film (1) has a strong adhesion to the polarizing plate (2), it can be permanently adhered as is when the liquid crystal display panel is actually used. However, there is no problem even if it is peeled off and removed.

Example 2 FIG. 1 is a sectional view showing an example of the surface protection film (1) of the present invention.

Silicone was coated on one side of the optically isotropic base film layer (ill) of Example 1 at a rate of 0.5 g/n and fixed by heating to perform back side treatment.

The above-mentioned back-treated light, etc. was applied to the optical isotropic adhesive resin layer (12) side of the laminated film consisting of the optical isotropic adhesive resin layer (12)/releasable sheet (13) of Example 1. At the same time as the orthogonal base film layer (11) was laminated and pressed, the releasable sheet (13) was peeled off and wound up.

The surface protection film shown in Figure 1 obtained in this way (
1) was preferable as in Example 1.

Example 3 (Ill is a polyarylate film as an example of an optically isotropic base film layer, which was produced by a casting method from a solution with a concentration of 20% by weight using methylene chloride as a solvent.The retardation value is 5 ns, visible light transmittance is 92%, and thickness is 20 μm.

(13) is the same releasable sheet as in Example 1.

(12) is an optically isotropic adhesive resin layer, in which the copolymerization ratio of butyl allylate/2-ethylhexyl acrylate/acrylic acid is Formed by casting a solution consisting of 30 parts of an acrylic copolymer with a ratio of 50/47/3, 1 ffl of tolylene diisocyanate-trimethylolpropane adduct and 70 parts of ethyl acetate, and drying at 60 to 90°C for 3 minutes. The thickness was 20 μm, and the surface smoothness of the lower surface (surface on the peelable sheet (13) side) during film formation was 0.
．． It was 024μ garden. be.

The light of the thus obtained laminated film consisting of the optically isotropic adhesive resin layer (12)/peelable sheet (13), the above-mentioned light etc. on the isotropic adhesive resin layer (12) side. A second layer having a layer structure of optically isotropic base film layer (1)/optical isotropic adhesive resin layer (12)/peelable sheet (13) is formed by laminating and press-bonding the optically isotropic base film layer (11). A protective film (1) with a releasable sheet (13) shown in the figure was obtained.

The retardage value of the entire protective film (1) excluding the removable sheet (13) is 5 nm, and the visible light transmittance is 8.
9%, and the thickness was 40μ.

This protective film (1) is not only soft and flexible, but also has good mechanical properties.

This protective film (1) is adhered to a polarizing plate (2) of a liquid crystal display panel by pressure bonding after peeling off the releasable sheet (13). Evaluation of optical performance can be performed without peeling off the attached surface protection film (1).

Since this surface protection film (1) has a strong adhesion to the polarizing plate (2), when the liquid crystal display panel is actually used, it can be permanently bonded as is. However, there is no problem even if it is peeled off and removed.

Effects of the Invention The surface protective film of the present invention does not require peeling off the protective film when performing optical evaluations of the display ability, hue, contrast, etc. of a liquid crystal display panel, so it is not necessary to peel off the protective film as required in the conventional method. You can omit the right-handling and re-attachment operations at all. Therefore, the process is greatly simplified and manufacturing costs can be reduced.

Further, in the present invention, since the outermost layer after the surface protection film (1) is attached is formed of the optically isotropic base film layer (11), it has good damage resistance, water resistance, and dust resistance.
The desired surface protection effect is achieved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the surface protection film (1) of the present invention. FIG. 2 is a sectional view showing an example of the surface protection film (1) of the present invention. FIG. 3 is a sectional view showing an example of a liquid crystal display panel to which the surface protection film (1) of the present invention is attached. (1) -...Protective film, (11)... Optically isotropic base film layer, (12)...
- Optically isotropic adhesive resin layer, (13)--peelable film, +2)--polarizing plate. +211-... Polarizing element film, (22)... Protective plate, (23)... Pressure-sensitive adhesive layer, +3) -... Liquid crystal cell, (31)-... Substrate, (32)...・Transparent electrode, (33)...Spacer, (34)...Liquid crystal

Claims (1)

[Claims] 1. A protective film (1) for protecting the surface of the polarizing plate (2) of a liquid crystal display panel by pasting it on top of the polarizing plate (2), the protective film (1) The optically isotropic adhesive resin layer has a layer structure of isotropic base film layer (11)/optical isotropic adhesive resin layer (12), and has a visible light transmittance of 75% or more. (12) A surface protective film for a liquid crystal display panel, comprising an optically isotropic laminated film having a surface smoothness of 0.1 μm or less.