JP2002019040A - Protective film for protecting surface of optical member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface protective film capable of holding an antistatic performance even at a high humidity. SOLUTION: In the protective film 1 comprising a layer 13 exhibiting antistatic properties to protect a surface of an optical member 2 by being laminated on the member 2, a polymer layer 14 having a water absorbing ratio of 5% or less is provided on the layer 13 exhibiting the antistatic properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface protective film, particularly a protective film for protecting the surface of an optical member such as a polarizing plate or a wave plate.

[0002]

2. Description of the Related Art In general, a surface protective film is bonded to an object to be protected via an adhesive formed on the surface protective film in order to prevent the object to be protected from being scratched or contaminated. For example, a panel of a liquid crystal display is formed by attaching an optical member such as a polarizing plate or a wavelength plate to a liquid crystal cell via an adhesive. These optical members to be bonded to the liquid crystal cell have a surface protective film bonded thereto via an adhesive to protect them from scratches, dirt, and the like. Then, the surface protection film is peeled off and removed when the surface protection becomes unnecessary by bonding the optical member to a liquid crystal cell or the like.

[0003] The properties generally required for such a surface protective film include (1) that it is not easily peeled off from the object to be protected even when subjected to environmental changes such as temperature and humidity or a slight impact; (3) that the adhesive of the surface protective film does not remain on the surface to be protected when the film is protected, and (3) that the adhesive can be easily peeled off by machine or hand.

Further, in the case of a film for protecting the surface of an optical member which is a component of a liquid crystal display, it is necessary to have an antistatic property. This is for the following reason.
After bonding the optical member protected by the surface protection film to the liquid crystal panel, static electricity is generated when the surface protection film is peeled off from the optical member. When a voltage is applied to the liquid crystal without removing the static electricity, the alignment of the liquid crystal molecules is lost or the panel is damaged. In order to prevent such a problem, the surface protective film is provided with an antistatic property by providing a layer having an antistatic property (hereinafter, also referred to as an "antistatic layer"). Since the pressure-sensitive adhesive is formed on one surface of the surface protection film, the antistatic layer may be formed on the other surface, that is, the outermost surface after the optical member is attached to the liquid crystal panel. Many.

[0005]

However, since the antistatic layer generally has low water resistance, the antistatic property is deteriorated by the influence of humidity, or the antistatic layer itself falls off the surface protective film to prevent the antistatic. In some cases, it did not exhibit its properties.
Therefore, an object of the present invention is to provide a surface protective film that can maintain antistatic performance even under high humidity.

[0006]

Means for Solving the Problems In order to achieve the object, a surface protective film of the present invention comprises a protective film having an antistatic layer which is bonded to the surface of an optical member to protect the surface. And a polymer layer having a water absorption of 5% or less, preferably 2% or less, provided on the layer exhibiting antistatic properties.

Since the polymer layer having a low water absorption is provided on the antistatic layer as described above, even if the antistatic layer is made of a material having low water resistance, it is possible to prevent water from entering the antistatic layer. Therefore, the antistatic property of the surface protective film is maintained. The effect of the present invention is particularly remarkable when the layer exhibiting antistatic properties, that is, the antistatic layer is made of a material mainly containing a surfactant such as a quaternary ammonium salt. Surfactants such as quaternary ammonium salts are excellent in antistatic properties but high in water absorption.

It is preferable that the polymer layer is made of at least one selected from a urethane acrylate polymer and a polymer having a long-chain alkyl. This is because these polymers not only have low water absorption, but also often have good adhesion to the surfactant constituting the main component of the antistatic layer.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG.
The surface protective film 1 according to the embodiment of the present invention includes a protective substrate 1
1, an adhesive layer 12 formed by forming an adhesive on one surface of a protective substrate 11, an antistatic layer 13 formed on the other surface, and a low water absorption rate formed on the antistatic layer 13. And a polymer layer 14. The surface protection film 1 is bonded to the optical member 2 via the adhesive layer 12 so that the protection substrate 11 can be peeled off from the optical member 2 together with the adhesive layer 12 when unnecessary. An adhesive layer 21 made of another adhesive is formed on the surface on the opposite side of the optical member 2 so as to be attached to the liquid crystal cell, and is adhered to an unexpected place before the adhesive layer 21 is attached to the liquid crystal cell. It is covered with a release film (not shown) so as not to be removed.

As the protective substrate 11, a thin sheet or film material can be used as in the prior art, and is not particularly limited. Generally, from the viewpoint of inspectability and manageability of optical members by seeing through, for example, polyester resin, cellulose resin, acetate resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin Examples thereof include films and rubber sheets made of transparent polymers such as resin and acrylic resin, and laminates thereof. The thickness of the protective substrate is also not limited, but from the viewpoint of strength and the like, is generally 500 μm or less, particularly 5 to 300 μm, particularly 10 to 200 μm.
μm. For the adhesive layers 12 and 21, an acrylic adhesive based on an acrylic polymer is generally used from the viewpoints of transparency, weather resistance, heat resistance and the like.

The above acrylic polymer can be adjusted by applying an appropriate polymerization method such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization or the like to a mixture of component monomers. The acrylic polymer that can be preferably used in the present invention has a weight average molecular weight of 100,000 or more, especially 200,000 or more, and particularly 300,000 to 2,000,000 in terms of heat resistance and adhesive properties.

The surface protective film can be manufactured by forming an adhesive layer on a protective substrate. For example, a base polymer or the like as a main component is dissolved or dispersed in a solvent such as toluene or ethyl acetate to prepare an acrylic pressure-sensitive adhesive liquid of about 10 to 40% by weight, which is appropriately developed by casting or coating. Examples of the method include a method of directly forming the pressure-sensitive adhesive layer on the protective substrate by a means, and a method of once forming an adhesive layer on a release film and transferring it to the protective substrate. The surface of the protective substrate on which the adhesive layer is provided may be subjected to an appropriate surface treatment such as a corona treatment for the purpose of improving the adhesion to the adhesive layer.

If necessary, the pressure-sensitive adhesive layer may contain, for example, natural or synthetic resins,
An additive such as an antioxidant may be blended. In addition, the adhesive layer may be provided on the protective substrate with different compositions or types superimposed. The thickness of the adhesive layer can be determined according to the adhesive strength, the surface roughness of the optical member, and the like.
m, especially 5 to 200 μm, especially 10 to 100 μm.

In the present invention, the pressure-sensitive adhesive layer preferably has a pressure-sensitive adhesive strength to an optical member of 400 gf / 5 based on a 180 degree peel at a peeling speed of 20 m / min at normal temperature.
0 mm or less, especially 50 to 350 gf / 50 mm, especially 10 to 3
It is a layer adjusted to 00 gf / 50 mm.

The optical member to be protected by the surface protective film includes, for example, a polarizing plate, a wave plate, an elliptically polarizing plate, a reflective polarizing plate, a semi-transmissive polarizing plate, a reflective elliptically polarizing plate, and a semi-transmissive plate. Examples thereof include those used for forming a liquid crystal panel such as an elliptically polarizing plate, and the type is not particularly limited. Accordingly, a wave plate having an appropriate purpose such as a phase difference of 波長 wavelength or 波長 wavelength or viewing angle compensation is also used as the wavelength plate. When the optical member is a laminate such as an elliptically polarizing plate, the lamination may be performed via an adhesive layer.

Specific examples of the polarizing plate include iodine and / or two-color hydrophilic polymer films such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and an ethylene / vinyl acetate copolymer-based partially saponified film. And a stretched film obtained by adsorbing a coloring dye, and a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product. Further, the polarizing plate may have a transparent protective layer on one side or both sides of the polarizing film.

On the other hand, the reflection type polarizing plate is provided with a reflection layer on the polarizing plate, and is used for forming a reflection type liquid crystal panel or the like for displaying by reflecting incident light from the viewing side (display side). In addition, there is no need to incorporate a light source such as a backlight, so that the liquid crystal panel has an advantage of being easily thinned.
The reflective polarizing plate can be formed, for example, by providing a reflective layer made of metal or the like on one side of the polarizing plate via a transparent protective layer or the like.

As a specific example of the reflective polarizing plate, for example, a reflective protective layer made of a reflective metal such as aluminum or a vapor-deposited film on one side of a matte-treated transparent protective layer can be mentioned. Further, there may be mentioned, for example, those in which fine particles are contained in the transparent protective layer to form a fine uneven structure on the surface, and a reflective layer having a fine uneven structure is provided thereon. The reflective layer is
When the reflective surface is used in a state where it is covered with a transparent protective layer or a polarizing plate, it is possible to prevent a decrease in reflectance due to oxidation, and thus to maintain the initial reflectance for a long period of time, or to provide a separate protective layer. It is preferable in such points.

The reflective layer having the above-described fine uneven structure imparts non-directionality and anti-glare properties by diffusing incident light by irregular reflection.
There is an advantage that unevenness in brightness can be suppressed. In addition, the transparent protective layer containing fine particles is diffused when the incident light and the reflected light are transmitted through the transparent protective layer, so that the uneven brightness can be further suppressed. The reflective layer having a fine uneven structure reflecting the fine uneven structure on the surface of the transparent protective layer is provided with a metal directly on the surface of the transparent protective layer by means of a vapor deposition method such as vacuum deposition, ion plating, sputtering, or a plating method. It can be obtained by:

As a material of the transparent protective layer in the above-mentioned polarizing plate, a polymer excellent in transparency, mechanical strength, heat stability, moisture shielding property and the like is preferable. Examples thereof include a cellulose resin, a polyester resin, an acetate resin, a polyether sulfone resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, an acrylic resin, or an acrylic resin.
Examples thereof include thermosetting or ultraviolet curable resins such as urethane, acrylic urethane, epoxy, and silicone.

The transparent protective layer can be formed by an appropriate method such as applying a polymer or laminating a film. Its thickness is generally below 500 μm, in particular between 1 and 300 μm, in particular between 5 and 200 μm. The fine particles to be contained in the transparent protective layer having a fine surface irregularity structure include, for example, inorganic particles having an average particle diameter of 0.5 to 50 μm such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide. Organic fine particles or organic fine particles made of a crosslinked or uncrosslinked polymer or the like are used. This fine surface uneven structure can also function as an anti-glare layer.

On the other hand, as a specific example of the above-mentioned wave plate,
Polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyallate, birefringent film formed by stretching a film such as polyamide, liquid crystal polymer alignment film, liquid crystal polymer alignment layer by film There are things that you support. The wave plate preferably has a retardation according to the purpose of use such as compensation for coloring due to birefringence of the liquid crystal layer and compensation for a viewing angle such as expansion of a viewing angle, and an inclined alignment film in which a refractive index in a thickness direction is controlled. It may be. Further, two or more types of wave plates may be laminated to control optical characteristics such as a phase difference.

The above-mentioned obliquely oriented film is, for example, a method in which a heat-shrinkable film is adhered to a polymer film and the polymer film is stretched and / or shrunk under the action of the heat-induced shrinkage force, or a method in which a liquid crystal polymer is obliquely oriented. Can be obtained. The optical member is made of a laminate such as a laminate of the above-mentioned elliptically polarizing plate, reflection type polarizing plate, and wave plate.
It may be composed of a layer or a laminate of three or more layers. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining a transflective polarizing plate and a wavelength plate may be used.

In the case of laminating two or three or more layers, they may be laminated separately in the course of manufacturing a liquid crystal panel or the like.
An optical material obtained by previously laminating the optical material is excellent in quality stability, assembling workability, and the like, so that the efficiency of manufacturing a liquid crystal panel or the like can be improved. The pressure-sensitive adhesive layer 21 can be formed with a normal pressure-sensitive adhesive. Above all, low moisture absorption rate and heat resistance to obtain high quality and durable liquid crystal panel to prevent foaming phenomenon and peeling phenomenon due to moisture absorption, deterioration of optical characteristics due to thermal expansion difference etc. and warpage of liquid crystal cell An adhesive layer having excellent properties is preferred.

When the adhesive layer provided on the optical member is exposed on the surface, it is preferable to temporarily cover with the release film as described above in order to prevent contamination and the like until the adhesive layer is used. . The release film is formed by providing a release layer using an appropriate release agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide on the same sheet material or film material as the above-described protective base material. Can be. Each layer in the optical member and the adhesive layer is treated with an ultraviolet absorbent such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex salt compound to form an ultraviolet ray. It can also have absorption capacity.

The antistatic layer 13 is formed by mixing a plastic with an antistatic agent such as a surfactant, conductive carbon, or metal powder and molding the plastic on the protective substrate 11. Method of applying conductive resin, protective substrate 11
A conductive material such as a metal or a conductive metal oxide may be applied, deposited, or plated. The lower the surface resistance of the antistatic layer 13 is, the more preferable it is, and it is usually 10 ¹⁴ Ω / □ or less, especially 10 ¹⁰ Ω / □.
The following are preferred.

Examples of the surfactant include anionic or amphoteric compounds such as carboxylic acid compounds, sulfonic acid compounds and phosphate salts, and cationic compounds such as amine compounds and quaternary ammonium salts. And nonionic compounds such as fatty acid polyhydric alcohol ester compounds and polyoxyethylene adducts, and high molecular compounds such as polyacrylic acid derivatives. Examples of the conductive resin include those obtained by dispersing a conductive filler such as a tin-antimony filler and an indium oxide filler in the resin.

The conductive substance to be applied, deposited or plated includes tin oxide, indium oxide, cadmium oxide,
Titanium oxide, metal indium, metal tin, gold, silver, platinum,
Examples include palladium, copper, aluminum, nickel, chromium, titanium, iron, cobalt, copper iodide, and alloys or mixtures thereof. Examples of the type of vapor deposition or plating include vacuum vapor deposition, sputtering, ion plating, chemical vapor deposition, spray pyrolysis, chemical plating, and electroplating.

Next, examples of the polymer of the polymer layer provided on the antistatic layer include polymers having a long-chain alkyl group or a fluoroalkyl group. Examples of the polymer include a hydroxyl group-containing polymer such as perfluoroalkyl carbamate and perfluoroalkyl acrylate. Copolymer, copolymer of long chain alkyl acrylate, copolymer of long chain alkyl vinyl ester, copolymer of long chain alkyl vinyl ether, copolymer of long chain alkyl acrylamide, copolymer of long chain alkyl allyl ester It is.

[0030]

EXAMPLES-Example 1-100 parts of isononyl acrylate (parts by weight, the same applies hereinafter) and 1 part of hydroxyethyl acrylate in ethyl acetate with 0.3 part of benzoyl peroxide as an initiator in about 60 parts
A polymer solution was obtained by performing a polymerization reaction at 8 ° C. for 8 hours. This acrylic polymer solution has a solid content of 1
An adhesive syrup was prepared by adding 3 parts of an isocyanate-based crosslinking agent (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) per 00 parts.

Separately, a protective base material made of a 38 μm-thick polyester film (T-100G film manufactured by Mitsubishi Gas Chemical Co., Ltd.) having an antistatic layer mainly composed of a quaternary ammonium salt on one surface was prepared. A 3% toluene solution of a long-chain alkyl polymer obtained by reacting polyvinyl butyral and octadecyl isocyanate was applied on the surface of the antistatic layer so that the thickness after drying was 0.3 μm. Thereafter, the pressure-sensitive adhesive syrup was dried on the surface opposite to the long-chain alkyl polymer layer of the protective substrate to a thickness of 30 μm.
m and dried to produce a surface protective film.

Example 2 On the surface of the antistatic layer shown in Example 1, 100 parts of a urethane acrylate monomer (Unidec V-4011 manufactured by Dainippon Ink Co., Ltd.) and UV were used instead of the long-chain alkyl polymer.
A solution containing 2 parts of an initiator (Irgacure 184 manufactured by Ciba Specialty Chemicals) was dried to a thickness of 0.5.
μm, and a urethane acrylate polymer layer was formed by irradiation with a high-pressure mercury lamp. In other respects, a surface protective film was manufactured in the same manner as in Example 1.

Comparative Example 1 A surface protective film was produced in the same manner as in Example 1, except that the long-chain alkyl polymer layer was not formed on the surface of the antistatic layer. Comparative Example 2 Instead of the long-chain alkyl polymer, a 10% aqueous solution of polyvinyl alcohol was applied on the surface of the antistatic layer shown in Example 1 so that the thickness after drying became 1.5 μm. In other respects, a surface protective film was manufactured in the same manner as in Example 1.

[Evaluation of Water Resistance of Surface Protective Film] Each of the prepared surface protective films was bonded to a polarizing plate. Thereafter, the protective film was immersed in warm water of 40 ° C., and the surface of the protective film was subjected to a load of 3.92 using steel wool # 0000.
N, speed 100 m / min. Rubbed 5 times. Then, the surface resistivity of the rubbed portion was measured in an atmosphere of 23 ° C./58% RH. Table 1 shows the measurement results. The lower the surface resistivity, the more the antistatic performance is maintained closer to the level at the time of manufacturing. The water absorption was 50 mm x 50 mm x 25 μm
The adhesive bulk was dried in a vacuum dryer at 50 ° C. and 0 mmHg for 1 day, weighed, and then dried at 50 ° C. and 90% RH.
Was calculated by measuring the weight after humidification for one day.

[0035]

[Table 1] Note: The polymer layer refers to the polymer layer formed on the antistatic layer. However, it is not formed in Comparative Example 1.

As can be seen from Table 1, the surface protective films of Examples 1 and 2 in which a polymer layer having a water absorption of 5% or less was formed on the antistatic layer were compared with those in which no polymer layer was formed. The antistatic performance was maintained higher than in Example 1 or Comparative Example 2 in which the polymer layer was formed but the water absorption was much more than 5%.

[0037]

According to the present invention, since the antistatic performance of the surface protective film is maintained at a high level, static electricity is less likely to be generated on the protected object after peeling. Therefore, the surface of the protected object can be protected well until immediately before use.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which a surface protection film of an embodiment is attached to an optical member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Surface protective film 11 Protective substrate 12 Adhesive layer 13 Antistatic layer 14 Polymer layer 2 Optical member 21 Adhesive layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 5/72 G02B 1/10 Z (72) Inventor Yuji Shiki 1-1-1 Shimohozumi, Ibaraki-shi, Osaka No. 2 Nitto Denko Corporation (72) Inventor Masamori Mamoru 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA02 BA05 BA06 BB23 BB26 BB27 BB28 BB33 BB36 BB67 BC22 2K009 BB14 BB24 BB28 CC24 CC35 CC47 DD01 EE03 4F100 AK01B AK01K AK21 AK25B AK25K AK41 BA03 BA07 CA18A GB41 JB06B JG03 JG03A JL13C 5C058 AA06 DA15 5G435 AA08 AA09 AA32 BB12 FF12 GG05

Claims (5)

[Claims] 1. A protective film having an antistatic layer which is bonded to the surface of an optical member to protect the surface, wherein a polymer layer having a water absorption of 5% or less is provided on the antistatic layer. A protective film, which is provided. 2. The protective film according to claim 1, wherein the layer exhibiting antistatic properties is made of a material mainly containing a surfactant such as a quaternary ammonium salt. 3. The protective film according to claim 1, wherein the polymer layer comprises at least one selected from a urethane acrylate polymer and a polymer having a long-chain alkyl. 4. The optical member according to claim 1, wherein the optical member is any one of various polarizing plates such as a reflective polarizing plate, a semi-transmissive polarizing plate, and a polarization separating polarizing plate, a wave plate, and a laminate thereof. A protective film as described in Crab. 5. A liquid crystal display, wherein a laminate of the protective film according to claim 1 and the optical member is disposed on one side of a liquid crystal cell.