JPH08271734A - Front side protective sheet for front side polarizing plate and sticking method of front side protective sheet to polarizing film side - Google Patents

Abstract

PURPOSE: To provide a front side protective sheet for front side polarizing plate easy in sticking to a polarizing base film with an aq. solution of a vinyl alcoholic polymer in spite of using a biaxially oriented polyester film as a base material. CONSTITUTION: The front side protective sheet 1 is composed of a laminated sheet provided with a water anchor coating layer 1b on one side of the biaxially oriented polyester film 1a. The aq. solution of vinyl alcoholic polymer is applied as an adhesive on the water anchor coating layer 1b of the front side protective sheet 1 to be stuck to the polarizing base film 2 side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front side protective sheet which is a constituent member of a front side polarizing plate of a liquid crystal display panel. The present invention also relates to a method for attaching the front side protective sheet to the polarizing film side.

[0002]

2. Description of the Related Art As is well known, a liquid crystal display panel has a basic structure of front side polarizing plate / liquid crystal cell / rear side polarizing plate when the incident light side is the front side and the opposite side is the rear side. A phase plate is often interposed between the front-side polarizing plate and the liquid crystal cell. Here, the liquid crystal cell has a configuration in which liquid crystal is sealed between two electrode substrates on which transparent electrodes (and an alignment film) are formed.

The polarizing plates on the front surface side and the rear surface side have a construction in which protective sheets are laminated and adhered on both sides of the polarizing element film in order to protect the polarizing element film. That is, one liquid crystal display panel uses two polarizing plates, and each of the two polarizing plates uses two protective sheets.

As a protective sheet for a polarizing plate, a cellulose triacetate sheet is actually used in most cases, but it has been proposed to use other polymer sheets.

For example, Japanese Patent Application Laid-Open No. 6-888907 filed by the applicant of the present invention discloses a polarizing plate having a layer structure of a vinyl alcohol polymer layer having optical isotropy / active energy ray curable cured material layer. A manufacturing protective sheet is shown. In this case, the surface of the vinyl alcohol polymer layer is adhered to the polarizing element film. The protective sheet attached to the other surface of the polarizing element film is said to be preferably a moisture-permeable sheet such as cellulose triacetate.

[0006] Similarly, Japanese Patent Laid-Open No. Hei 6 (1994)-
No. 888908 discloses a polarizing plate in which an active energy ray-curable cured product layer is provided on either surface of a laminated sheet having a layer structure of an optically isotropic vinyl alcohol polymer layer / an optically isotropic base material layer. A manufacturing protective sheet is shown.

Further, Japanese Patent Application Laid-Open No. 7-
No. 26103 discloses a sheet made of a polymer alloy obtained by graft-modifying a vinyl alcohol polymer with an ethylenically unsaturated monomer or a composition of the polymer alloy and an aqueous crosslinking agent, for protecting a polarizing element film or a retardation element film. It has been shown to be used as a sheet. Similarly, Japanese Patent Application Laid-Open No. 7-24978, which is also filed by the applicant of the present invention, discloses a sheet made of the above polymer alloy or a composition of the polymer alloy and an aqueous crosslinking agent.
It is shown that a sheet provided with a coating layer having a low moisture permeability having a moisture permeability lower than that of the sheet is used as a protective sheet for a polarizing element film or a retardation element film.

In addition to the above four applications, the present applicant has filed a number of applications for optical sheets that can also be used for protecting a polarizing film.

In the four publications cited above, in the description of the prior art, as the conventionally proposed protective sheet, polycarbonate, polymethylmethacrylate, polyvinylchloride, ethylene-vinylalcohol copolymer is used. Coalesce, polystyrene, acrylic resin, polyester,
Polyolefin, polyamide, nitrocellulose, poly-4-methylpentene, polyacrylonitrile, phenoxy resin, polyphenylene oxide, epoxy resin,
Vinyl resin, polysulfone, polyether sulfone,
It is introduced that there are sheets or layers such as polyarylene esters.

[0010]

[Problems to be Solved by the Invention] As described above,
A cellulose triacetate sheet is widely used as a protective sheet for producing a polarizing plate. This is because the cellulose triacetate sheet has excellent optical properties and can be adhered to a polarizing film (usually using a polyvinyl alcohol-iodine type) with an aqueous adhesive having water as a solvent. Is.

However, the cellulose triacetate sheet is disadvantageous in that a chlorine-based solvent (methylene chloride) which may cause environmental pollution must be used in forming the film, and the cellulose triacetate sheet has a relatively high cost. It is desirable to reduce In addition, the cellulose triacetate sheet is not necessarily satisfactory in adhesive strength with a water-based adhesive when laminating and adhering to the polarizing film side, and therefore, the surface of the cellulose triacetate sheet is treated to improve adhesion (for example, alkali treatment). However, the cost of the cellulose triacetate sheet is unavoidably increased. Further, when the electrode substrate of the liquid crystal cell is a plastic substrate, the cellulose triacetate sheet tends to absorb moisture when the polarizing plate is attached to the electrode substrate, so that the liquid crystal display panel may curl.

In the description of the prior arts of the four publications cited above, various protective sheets introduced as being proposed even before the inventions of these publications are compared with the cellulose triacetate sheet. If so, the basic suitability as a protective sheet is insufficient.

On the other hand, the protective sheets according to the inventions of the above-cited four publications themselves can be replaced with a cellulose triacetate sheet because of various devises, but the demands of the market are becoming more and more severe. In order to respond, there is still room for improvement in terms of moisture resistance and cost.

By the way, as a protective sheet for a polarizing plate,
A light isotropic sheet that does not have birefringence is used,
The front side protective sheet of the front side polarizing plate does not need to be optically isotropic.

Therefore, the present inventors have examined the use of an inexpensive biaxially stretched polyester film (which is anisotropic) as the front side protective sheet of the front side polarizing plate.
If it becomes possible to use the biaxially stretched polyester film, one of the four protective sheets required for one liquid crystal display panel can be substituted, and the cost can be reduced accordingly. Further, since moisture resistance is imparted to the front side polarizing plate, the liquid crystal display panel does not curl even when the electrode substrate of the liquid crystal cell is a plastic substrate.

However, since the biaxially stretched polyester film is a typical hydrophobic resin film, it cannot be bonded to a polarizing film (polyvinyl alcohol-iodine system) which is a hydrophilic film by a water-based adhesive as a single film. Extremely difficult. Even if the adhesive can be adhered, water, which is a solvent of the water-based adhesive, is difficult to escape, or the adhesive operation does not proceed smoothly.

Under such a background, the present invention uses the biaxially stretched polyester film as a base material, but the front surface side is easy to adhere to the polarizing film by the aqueous solution of the vinyl alcohol polymer. An object of the present invention is to provide a front protective sheet for a polarizing plate and a method for sticking the front protective sheet to the polarizing film side.

[0018]

In the following, when assembling a liquid crystal display panel, polarizing plates arranged on the front side and the rear side of a liquid crystal cell are named front side polarizing plate and rear side polarizing plate, respectively. The protective members disposed on the front surface side and the rear surface side of the polarizing element film (2), which is a constituent member of the polarizing plate, are named front surface side protective sheet (1) and rear surface side protective sheet (3), respectively. Further, in the following, “water-based” means that water is used as a main solvent, and an organic solvent may be used in combination with water as long as the purpose is not impaired.

In the front side protective sheet of the front side polarizing plate of the liquid crystal display panel of the present invention, the front side protective sheet (1) has a water-based anchor coating layer (1b) on one side of the biaxially stretched polyester film (1a). It is characterized by comprising a laminated sheet provided.

The method of sticking the front side protective sheet of the front side polarizing plate of the liquid crystal display panel of the present invention to the polarizing element film side is the same as that of the above water side anchor coating layer (1) of the front side protective sheet (1).
It is characterized in that an aqueous solution of a vinyl alcohol-based polymer is applied onto b) as an adhesive to adhere it to the polarizing film (2) side.

The present invention will be described in detail below.

The front side protective sheet (1) is a biaxially stretched polyester film (1a) / water-based anchor coating layer (1b).
A laminated sheet having the layer structure of.

The biaxially stretched polyester film (1a) may be of any thickness as long as it has good transparency, but it is usually 20 to 200 μm, preferably 30.
A thickness of -100 μm is preferred. When the thickness is too thick, the visibility from an oblique direction when used as a liquid crystal display panel is impaired, and also the transparency is reduced, and when the thickness is too thin, the flatness (shape retention or self-supporting property) is impaired. There is a risk.

The water-based anchor coating layer (1b) is an anchor coating agent such as polyester resin, polyurethane resin, isocyanate resin, epoxy resin, melamine resin, phenol resin, polyamine resin, polyimine resin, etc. Among them, a layer formed of an aqueous solution or an aqueous dispersion type is used. A mixture of these resins, for example, a water-based anchor coating agent made of a mixture of polyester resin and urethane resin is also suitably used.

The thickness of the water-based anchor coating layer (1b) is usually 0.1 to 5 μm, preferably 0.2 to 4 μm, more preferably 0.3 to 3 μm. When the thickness is less than this range, the operation of adhering to the polarizing film side by the adhesive composed of an aqueous solution of a vinyl alcohol polymer does not proceed smoothly, while when the thickness is extremely thick, moisture absorption from the side or It becomes negative in terms of transparency.

Front side protection sheet (1) having the above structure
The one side of the biaxially stretched polyester film (1a) is coated with a water-based anchor coating agent, dried, and further cured or heat-treated or aged at a relatively low temperature for a long time to form a water-based anchor coating layer (1b). It is manufactured by forming.

After thus obtaining the front side protective sheet (1), an aqueous solution of a vinyl alcohol polymer is applied as an adhesive onto the aqueous anchor coating layer (1b) of the front side protective sheet (1). Then, it is attached to the side of the polarizing film (2).
At this time, the polarizing film (2) is a single film polarizing film (2).
Or the polarizing element film (2) already attached to the rear surface side protection sheet (3). Generally, the polarizing element film is applied to one of the front side protective sheet (1) and the rear side protective sheet (3) by applying an aqueous solution of a vinyl alcohol polymer by dropping or the like.
While stacking (2), squeeze with a pair of rolls and then dry
Subsequently, the other protective sheet is coated with an aqueous solution of a vinyl alcohol-based polymer by a means such as dripping, and the polarizing element film (2) of the protective sheet / polarizing element film (2) laminate prepared above.
A method is employed in which the sides are overlapped and squeezed by a pair of rolls before being dried. In addition, while applying an aqueous solution of a vinyl alcohol-based polymer to each of the front side protective sheet (1) and the rear side protective sheet (3) by a means such as dripping, the protective sheet (1) and the rear side protective sheet (3) are both applied between them. A method in which the polarizing element film (2) is sandwiched and squeezed by a pair of rolls and then dried is also used.

As an aqueous solution of a vinyl alcohol polymer used as an adhesive, an aqueous solution of a vinyl alcohol polymer having various degrees of polymerization and saponification such as polyvinyl alcohol, copolymer modified polyvinyl alcohol and graft modified polyvinyl alcohol is used. It may be used and may contain a crosslinking agent. However, an aqueous solution of unmodified polyvinyl alcohol is usually sufficient.

At this time, the polymer concentration of the aqueous solution of vinyl alcohol polymer is set to an appropriate value (for example, 1 to 20% by weight) in consideration of adhesiveness, smooth coating property and the like.

As mentioned above, the front side protective sheet (1)
Consists of a laminated sheet having a layer structure of biaxially stretched polyester film (1a) / water-based anchor coating layer (1b). On the other side of the biaxially stretched polyester film (1a),
The functional layer (1d) can be provided directly or through the anchor coating layer (1c). The anchor coating layer (1c) at this time is not limited to a water-based anchor coating layer, and can be formed using a solvent-based anchor coating agent.

The purpose of installing the functional layer (1d) is to prevent glare, scratches,
This is for drawing and focusing. The functional layer (1d) is composed of a thermosetting resin cured product layer, an active energy ray curable resin cured product layer, an inorganic layer and the like.

As the rear side protective sheet (3) for the front side polarizing plate, for example, any sheet having optical isotropy as described in the section of the prior art can be used. Particularly preferable as the rear surface side protective sheet (3) is a water vapor transmission rate (based on JIS Z0208, temperature 40 ° C., relative humidity 9
100% / m ² · 24hr or more, especially 200
An optically isotropic sheet having a g / m ² · 24 hr or more, further 400 g / m ² · 24 hr or more, an example of which is a cellulose triacetate sheet (including a corona discharge-treated or alkali-treated surface).

The front side polarizing plate may be of a type in which the rear side protective sheet (3) is not provided. That is, the installation of the rear side protective sheet (3) is omitted, and the front side protective sheet
The surface of the laminated body of (1) / polarizer film (2) on the polarizer film (2) side is
It may be of a type of being laminated on an electrode substrate or a phase plate via an adhesive layer.

[0034]

[Function] Front side protective sheet of front side polarizing plate of the present invention (1)
Consists of a biaxially stretched polyester film (1a) with a water-based anchor coating layer (1b) on one side, so a biaxially stretched polyester film is used as the base material for the front side protective sheet (1) of the front side polarizing plate. Despite the use of, it is easy to adhere the polarizing film (2) with an aqueous solution of a vinyl alcohol polymer.

This is the water-based anchor coating layer
When an aqueous solution of a vinyl alcohol polymer is applied as an adhesive on (1b) and is adhered to the polarizing film (2) side, the adhesive and the water-based anchor coating layer (1b) have good compatibility. This is because excess water in the adhesive is partially absorbed by the water-based anchor coating layer (1b), and as a result, the water-based anchor coating layer (1b) is smoothly and firmly bonded.

Then, in this way, the front side protective sheet (1)
The fact that the biaxially stretched polyester film (1a) can be used as the base material of the above contributes to a significant reduction in the cost of the polarizing plate and can meet the strong demand of the market.

Further, the use of the biaxially stretched polyester film (1a) imparts moisture resistance to the front side polarizing plate, so that the liquid crystal display panel curls even when the electrode substrate of the liquid crystal cell is a plastic substrate. There is no fear.

[0038]

EXAMPLES The present invention will be further described with reference to examples. Hereinafter, "parts" are expressed on a weight basis.

Example 1 FIG. 1 shows a front side protective sheet (1) of the front side polarizing plate of the present invention.
It is explanatory drawing which showed an example of typically.

As the water-based anchor coating agent, a water-based anchor coating agent composed of a mixture of polyester resin and urethane resin (“WA manufactured by Takamatsu Oil & Fat Co., Ltd.
C-10 ") was prepared.

On one side of a biaxially stretched polyester film (1a) having a thickness of 50 μm, the above water-based anchor coating agent was applied, dried at a temperature of 70 to 100 ° C. for 1 minute, and then cured at a temperature of 120 ° C. for 5 minutes. , Thickness 1μ
An m 2 aqueous anchor coating layer (1b) was formed.

As a result, a front side protective sheet (1) comprising a laminated sheet having a biaxially oriented polyester film (1a) / water-based anchor coating layer (1b) was obtained. While dropping an aqueous solution of polyvinyl alcohol having a degree of polymerization of 1000 and a degree of saponification of 98.5 mol% on the side of 1b) at a concentration of 12% by weight,
Commercially available polyvinyl alcohol-iodine based polarizing film (2)
Was squeezed by a pair of rolls, and then dried at a temperature of 60 ° C.

A front side protective sheet (3) obtained by separately preparing a commercially available alkali-treated cellulose triacetate sheet having a thickness of 80 μm was dropped onto one side of the same aqueous polyvinyl alcohol solution as above. The laminated body of 1) / polarizer film (2) was overlapped with the polarizer film (2) side, squeezed by a pair of rolls, and subsequently dried at a temperature of 60 ° C. As a result, the front side protective sheet (1) / polarizing film
A polarizing plate on the front surface side having a layer structure of (2) / protective sheet on the rear surface side (3) was obtained.

The obtained front-side polarizing plate was extremely beautiful, and the adhesion between the front-side protective sheet (1) and the polarizing film (2) could not be peeled off. The rear-side protective sheet (3) The adhesion between the film and the polarizing film (2) was also good because the alkali-treated cellulose triacetate was used.

Example 2 FIG. 2 is a front side protective sheet (1) of the front side polarizing plate of the present invention.
It is explanatory drawing which showed another example typically.

On the other surface of the biaxially stretched polyester film (1a), a thin film having fine irregularities for preventing glare, scratches, drawing or focusing by an ultraviolet curable resin via an anchor coating layer (1c) in advance. Example 1 was repeated except that the functional layer (1d) was prepared. As a result, a front-side polarizing plate having the same preferable properties as in Example 1 with further added functionality was obtained.

Example 3 On one side of the biaxially stretched polyester film (1a), an aqueous anchor coating agent (however, "Byron" manufactured by Toyobo Co., Ltd. was used) was applied, dried and cured to give an aqueous system having a thickness of 2 μm. Anchor coating layer (1b) was formed. Also in this case, the front side protective sheet (1) having the same properties as in Example 1 was obtained.

[0048]

The front side protective sheet (1) of the front side polarizing plate of the present invention comprises a laminated sheet in which the water-based anchor coating layer (1b) is provided on one surface of the biaxially stretched polyester film (1a). Biaxially stretched polyester film
Despite the use of (1a), it is easy to adhere to the polarizing film (2) with an adhesive composed of a polyvinyl alcohol-based aqueous solution, and the adhesive strength becomes strong. .

Then, in this way, the front side protective sheet (1)
Despite the use of biaxially stretched polyester film (1a) as the base material, it is possible to obtain a front-side polarizing plate with excellent quality, which makes it possible to significantly reduce the cost of the polarizing plate and meet the strong market demand. I can respond.

Further, the use of the biaxially stretched polyester film (1a) imparts moisture resistance to the front side polarizing plate, so that the liquid crystal display panel curls even when the electrode substrate of the liquid crystal cell is a plastic substrate. There is no fear.

[Brief description of drawings]

FIG. 1 is a front side protective sheet (1) for a front side polarizing plate of the present invention.
It is explanatory drawing which showed an example of typically.

FIG. 2 is a front side protective sheet (1) of the front side polarizing plate of the present invention.
It is explanatory drawing which showed another example typically.

[Explanation of symbols]

 (1) ... Front side protective sheet, (1a) ... Biaxially oriented polyester film, (1b) ... Water-based anchor coating layer, (1c) ... Anchor coating layer, (1d) ... Functional layer, (2) ... Polarizer Membrane, (3) ... Rear side protective sheet

Continued Front Page (72) Inventor Mizuko Hayashi Fujimori Kogyo Co., Ltd. 1-4-16 Nihonbashi Bakurocho, Chuo-ku, Tokyo

Claims (5)

[Claims] 1. When assembling a liquid crystal display panel, polarizing plates arranged on the front side and the rear side of a liquid crystal cell are named front side polarizing plate and rear side polarizing plate, respectively, and a polarizing plate which is a constituent member of the front side polarizing plate. When the protective members disposed on the front side and the rear side of the film (2) are named front side protective sheet (1) and rear side protective sheet (3), respectively, the front side protective sheet (1) is A front side protective sheet for a front side polarizing plate of a liquid crystal display panel, comprising a laminated sheet in which an aqueous anchor coating layer (1b) is provided on one surface of an axially stretched polyester film (1a). 2. The front side protective sheet according to claim 1, wherein the functional layer (1d) is provided on the other surface of the biaxially stretched polyester film (1a) directly or via an anchor coating layer (1c). 3. The front side protective sheet according to claim 2, wherein the functional layer (1d) is a layer for antiglare, scratch prevention, drawing or light collection. 4. The front side protective sheet according to claim 1, wherein the front side polarizing plate is of a type in which the rear side protective sheet (3) is not provided. 5. A water-based anchor coating layer (1b) of the front side protective sheet (1) according to claim 1, wherein an aqueous solution of a vinyl alcohol polymer is applied as an adhesive to bond the polarizing film (2) side. A method for adhering a front side protective sheet of a front side polarizing plate of a liquid crystal display panel to a polarizing element film side, comprising: