JPH0432805A - Surface protective film of liquid crystal display panel - Google Patents

Abstract

PURPOSE:To eliminate the need for peeling at the time of inspection by constituting the protective film of three layers consisting of a scratching resistant optically isotropic material layer/optically isotropic base material film/optically isotropic stickable resin layer and specifying the visible ray transmittance thereof. CONSTITUTION:The protective film 1 is stuck from above a polarizing plate 2. The laminated films having the three-layered constitution consisting of the scratching resistant optically isotropic material layer 13/optically isotropic base material film 11/optically isotropic stickable resin layer 12 are used as the protective film 1. In addition, the visible ray transmittance is specified to >=75%. The need for peeling the protective film 1 is eliminated at the time of making optical evaluation of the display capacity, hue, contrast, etc., of a liquid crystal display panel. The process thereof is simplified and the cost is reduced.

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 conventional protective film mentioned above is a hindrance to inspections that involve such optical evaluation, so it is necessary to peel off the protective film before the inspection and reapply a new protective film after the inspection. will be held.

The reason why the protective film is reapplied with a new protective film 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 f
l), wherein the protective film (1) comprises a scratch-resistant optically isotropic material layer (13)/a optically isotropic substrate film layer (
11)/optically isotropic adhesive resin layer (12), and has a visible light transmittance of 75% or more.

The present invention will be explained in detail below.

As shown in Figure 3 below, the liquid crystal display panel consists of liquid crystal cells (
3) by laminating a polarizing plate (2) on at least one side (usually both N sides). Note that the polarizing plate (2) can also serve as a liquid crystal cell substrate.

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.

1. Exit 21 The polarizing plate (2) is made of vinyl alcohol polymer/iodine type, vinyl alcohol polymer/dichroic dye type, vinyl alcohol polymer/polyene type, polyhalogenated vinyl/polyene type, 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 polyacrylonitrile/polyene or the like. As the protective plate (22), cellulose triacetate film, cellulose butyrate acetate film, polycarbonate film, polymethyl methacrylate film, polyvinyl chloride film, ethylene-vinyl alcohol copolymer film, polyamide film, polystyrene film, etc. However, it is actually limited to cellulose triacetate films and cellulose butyrate acetate films, particularly cellulose triacetate films.

A protective film (TI) is pasted on top of the polarizing plate (2), but in the present invention, this protective film (1) is made of a scratch-resistant optically isotropic material. Layer (131/Photoisotropic base film layer (111/Photoisotropic adhesive resin layer (1)
A laminated film having the layer structure of 2) 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, polyarylate film, polyvinyl alcohol film, ethylene-vinyl alcohol copolymer film, cellulose polymer film, etc. are used. This base film layer (
Since 11) needs to have optical isotropy, a film with a retardation value of 30 nm or less, particularly 20 nm or less, and a visible light transmittance of 75% or more is used. A base film layer having such optical isotropy (
11) can be obtained by forming a film by a casting method, but other molding methods such as extrusion can also be used as long as the retardation value and visible light transmittance satisfy the above conditions.

The thickness of the optically isotropic base film layer (11) is 5 to 200μ
-The 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 or incompletely crosslinked film formed by blending a curing agent with a resin having a functional group such as a polyol, polyolefin polyol, or functional group-containing acrylic copolymer: For example, 20% by weight of a plasticizer is added to polyvinyl chloride. % or more of 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, atactic polypropylene, and chlorinated polypropylene: ethylene - Films obtained by forming ethylene copolymers such as vinyl acetate copolymers, ethylene-acrylic acid copolymers, and ethylene-acrylic acid ester copolymers are included.

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 microns. Like layer (11), it is required to have optical isotropy.

The scratch-resistant optically isotropic material layer (13) includes a thermosetting resin cured material layer (phenoxyether type crosslinkable resin, epoxy resin, acrylic resin, melamine resin,
Phenolic resin, urethane resin, rubber resin part,
Examples include an ultraviolet curable resin layer (phosphazene resin, acrylic resin, etc.), an inorganic layer (silicon dioxide layer, etc.).

The scratch-resistant optically isotropic material layer (13) is also required to have a retardation value of 30 nm or less and a visible light transmittance of 75% or more (particularly 80% or more).

The thickness of the scratch-resistant optically isotropic material layer (13) is 0.
The amount is often about 5 to 50μ.

The retardation value and visible light transmittance of the entire protective film m having the above layer structure were also 30n, respectively.
Care should be taken to keep it below m and below 75%.

As described above, the protective film (1) of the present invention has a layer structure of a scratch-resistant optically isotropic material layer (131/optical isotropic base film layer (111)/optical isotropic adhesive adhesive layer (12)). However, since it is usually handled in a rolled state, when a material with adhesiveness is used as the optically isotropic adhesive resin layer (12), the optically isotropic adhesive property is increased during one winding. a scratch-resistant optically isotropic material layer (1) in contact with the resin layer (12);
3) 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 so that it has releasability to the optically isotropic adhesive resin layer (12). Alternatively, a releasable sheet (14) is further provided on the optically isotropic adhesive resin layer (12).

Here, the releasable sheet (14) may be 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 41 is often about 12 to 250 μm.

Function The protective film (1) of the present invention has a scratch-resistant optically isotropic material layer f131/optical isotropic base film layer (111/
It has a layer structure of an optically isotropic adhesive adhesive resin layer (12).

The brittleness and lack of flexibility of the scratch-resistant optically isotropic material layer (13) are covered by the optically isotropic substrate film layer (11), and the lack of surface properties of the optically isotropic substrate film layer (11) is covered by the optically isotropic substrate film layer (11). It is covered with a scratchable optically isotropic material layer (13), making the whole film suitable as a protective film.

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.
). (Optical isotropic adhesive resin layer (12)
When the side is covered with a releasable sheet (14), this removable sheet f141 is peeled off and removed prior to pasting, and if necessary, pasting is performed by thermocompression bonding.)Display Capacity 2 Hue, Contrast When conducting tests for evaluation of the You can perform these tests as is.

If the protective film (1) is required to have reworkability, the protective film fl) 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 fi
1 is used for actual use with it permanently attached.

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

Hereinafter, "parts" refer to parts by weight.

Example 1 Film (1) Figure 2 is a sectional view showing an example of the surface protection film (1) 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 5nffl, the visible light transmittance is 90%, and the thickness is 30 μm.

(13) is a cured acrylic resin layer as an example of a scratch-resistant optically isotropic material layer. -508 (viscosity 7.5 cps, resin content 40% by weight,
The solvent composition (weight ratio: Impropatol/butyl acetate/ethyl cellosolve = 40/40/20) solution was applied to a thickness of approximately 0.2 mm using a bar coater, and dried at 50 to 60°C for 2 minutes. After that, by ultraviolet lamp! 20
It was formed by irradiating ultraviolet light under the conditions of W/Cm, 1 lamp, and 3 seconds. The thickness of this scratch-resistant optically isotropic material layer (13) is 7 μm, and the surface hardness is 2H.
It is.

The scratch-resistant optically isotropic material layer (1
The retardation value of the entire laminated film consisting of 31/optically isotropic base film layer (11) was 5 Hm, the visible light transmittance was 87%, and the thickness was 37 μm.

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

(12) is an optically isotropic adhesive resin layer, and a polyolefin polyol (Epol, hydroxyl group content 0.90 meq. /g, viscosity 75000cps/3
0°C) 100 parts, IP solvent (aliphatic hydrocarbon solvent manufactured by Mitsui Petrochemical Industries, Ltd.) 50 parts, hydrogenated MDI
It was formed by casting a solution consisting of 3 parts of a (diphenylmethane diisocyanate) type curing agent and drying it at 80° C. for 5 minutes. The thickness is 20 μm.

The thus obtained laminated film consisting of the optically isotropic adhesive resin layer (12)/releasable sheet (14) and the scratch-resistant optically isotropic material layer (131/photoisotropic group) obtained above. A laminated film consisting of a material film layer (11) is laminated and pressure bonded so that the optically isotropic adhesive resin layer (12) side of the former is opposed to the optically isotropic base film layer (11) side of the latter. and scratch-resistant optically isotropic material layer (13) / optically isotropic base film layer (11) / optically isotropic adhesive resin layer (12)
) / Peelable sheet (14) A protective film (11) with a peelable sheet (14) shown in FIG.
I got it.

The retardation value of the entire protective film (1) excluding the peelable sheet (14) is 6na+, and the visible light transmittance is 8.
6%, and the thickness was 57 μm.

This protective film (11) is not only soft and flexible, but also has good mechanical properties.

This protective film (1) is adhered to the polarizing plate (2) of the liquid crystal display panel by pressure bonding after peeling off the releasable sheet (14).

FIG. 3, part 5 of L1111, 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.

(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 polarizer film (21) made of polyvinyl alcohol/iodine is coated on both sides with a 5 μm thick cellulose triacetate film.
It consists of a 0 μm protective plate (22) laminated using an acrylic resin pressure sensitive adhesive. f231 is its 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 adhered 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 made of a scratch-resistant optically isotropic material layer (13), so it has excellent 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 (fl).

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 2 100 parts of urethane acrylate (Violex T-2060) manufactured by Showa Kobunshi Co., Ltd. and 3 parts of a curing agent were dissolved in ethyl acetate so that the resin concentration was 70%, and the peelability of Example 1 was improved. It was cast onto a sheet (14) and dried at 80° C. for 5 minutes to form an optically isotropic adhesive resin layer (12).

The thus obtained laminated film consisting of the optically isotropic adhesive resin layer (12)/peelable sheet (14) and Example 1
A laminated film consisting of the scratch-resistant optically isotropic material layer (13)/optical isotropic base film layer (11) obtained in
Laminated so that the former optically isotropic adhesive resin layer (12) side and the latter optically isotropic base film layer (11) side are opposed to each other,
The scratch-resistant optically isotropic material layer (13)/optical isotropic base film layer (111 parts, optically isotropic adhesive adhesive resin layer (111 parts)
Protective film (1) with a releasable sheet (14) shown in FIG.
) was obtained.

The surface protection film shown in Figure 2 obtained in this way (
1) was equivalent to or more preferable than Example 1.

When the liquid crystal display panel is actually used, this surface protection film fl) may be peeled off or may be permanently attached.

Example 3 FIG. 1 is a sectional view showing an example of the surface protection film (1) of the present invention.

Silicone was applied to the surface of the scratch-resistant optically isotropic material layer (13) of the laminated film consisting of the scratch-resistant optically isotropic material layer (13) and the optically isotropic base film layer (11) of Example 1. Back surface treatment was carried out by coating at a rate of 5 g/rn' and fixing with heat.

A laminated film consisting of the optically isotropic adhesive resin layer (12)/releasable sheet (14) of Example 2 and the above-mentioned back-treated scratch-resistant optically isotropic material layer (13)/photoisotropic group A laminated film consisting of a material film layer (11) is laminated and pressure bonded so that the optically isotropic adhesive resin layer (12) side of the former is opposed to the optically isotropic base film layer (11) side of the latter. At the same time, the releasable sheet (14) was peeled off and wound up.

The surface protection film shown in Figure 1 obtained in this way (
1) was preferable as in Example 2.

Example 4 (11) is a polyarylate film as an example of an optically isotropic base film layer, which was produced by a casting method from a 20% by weight solution using methylene chloride as a solvent. The retardation value is 5n+m, the visible light transmittance is 92%, and the thickness is 20 μm.

(13) is a cured phosphazene resin layer as an example of a scratch-resistant optically isotropic material layer, and on the optically isotropic base film layer (11) described above, a phosphazene resin layer manufactured by Shoko Petrochemical Co., Ltd. A solvent solution of resin ppz with a concentration of 30% by weight was applied using a No. 20 wire bar and heated at 70°C for 2 hours.
After drying for 1 minute, use an ultraviolet lamp at 120W/am for 1 hour.
It was formed by irradiating ultraviolet light for 3 seconds.

The thickness of this scratch-resistant optically isotropic material layer (13) is 5
μ■, surface hardness is 2H.

The scratch-resistant optically isotropic material layer (1
The retardation value of the entire laminated film consisting of 3)/optically isotropic base film layer (11) was 5 Hm, the visible light transmittance was 90%, and the thickness was 25 μm.

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

(12) is a photoisotropic adhesive resin layer, which has a copolymerization ratio of butyl allylate/2-ethylhexyl acrylate/acrylic acid on the HM-treated surface of the above-mentioned releasable sheet (14). A solution consisting of 30 parts of acrylic copolymer, 1 part of tolylene diisocyanate-trimethylolpropane adduct and 70 parts of ethyl acetate in a weight ratio of 50/47/3 is cast and dried at 60 to 90°C for 3 minutes. It was formed by The thickness is 20 μm.

The thus obtained laminated film consisting of the optically isotropic adhesive resin layer (12)/releasable sheet (14) and the scratch-resistant optically isotropic material layer (13) obtained above/light etc. A laminated film consisting of the photoisotropic base film layer m) is laminated and pressure bonded so that the optically isotropic adhesive resin layer (12) side of the former is opposed to the optically isotropic base film layer (11) side of the latter. death,
The releasable sheet (14) shown in FIG. ) was obtained.

The retardation value of the entire protective film (1) excluding the releasable sheet (14) was 5nIIl, the visible light transmittance was 87%, and the thickness was 45 μm.

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

This protective film (1) is adhered to the polarizing plate (2) of the liquid crystal display panel by pressure bonding after peeling off the releasable sheet (14). 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), 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.

Effects of the Invention The surface protection film of the present invention does not require peeling off the protective film when performing optical evaluations of display ability, hue, contrast, etc. of a liquid crystal display panel, so it does not require peeling of the protective film as in conventional methods. The reattachment operation can be completely omitted. Therefore, the process is greatly simplified and manufacturing costs can be reduced.

In addition, in the present invention, the outermost layer after adhering the surface protection film (1) is formed of a scratch-resistant optically isotropic material layer (13), so it has excellent damage resistance, water resistance, and dust resistance. Therefore, it has a much superior surface protection effect compared to conventional surface protection films.

[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)... Scratch-resistant optically isotropic material layer, (14)... Peelable film, (2)... Polarizing plate, (21)... ...Polarizing element film, (22)...Protection 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) having a It has a layer structure of scratchable optically isotropic material layer (13) / optically isotropic base film layer (11) / optically isotropic adhesive resin layer (12) and has a visible light transmittance of 75% or more. A surface protection film for a liquid crystal display panel, characterized by the following.