JP2002122735A - Film for polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film for a polarizing plate which makes a liquid crystal display free from light leaking over a long period of time. SOLUTION: The film is a cellulose ester film, produced by casting a dope prepared by dissolving a cellulose ester in an organic solvent from a casting die on a casting base and has <=0.2% shrinkage percentage, after a heat treatment at 80 deg.C for 24 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate film used as an optical compensation film or the like of a polarizing plate, and more particularly to a polarizing plate film capable of preventing frame-shaped light leakage.

[0002]

2. Description of the Related Art In general, a liquid crystal display device is constituted by laminating a polarizing plate on a liquid crystal cell with an adhesive layer. The liquid crystal cell has a liquid crystal compound layer and a liquid crystal compound layer. , And an electrode layer for applying a voltage to the liquid crystal compound layer provided inside the glass plate.

[0003] The polarizing plate is, for example, a polarizer, an optical compensation film having a protective function laminated on one surface (the surface on the liquid crystal cell side) of the polarizer, and a polarizing plate protective film laminated on the other surface. And a membrane. This optical compensation film has a function of removing coloring of the liquid crystal screen, and generally, a support, an adhesion layer laminated on one surface of the support,
It is composed of an orientation providing layer and an optical compensation layer, and a back layer laminated on the other surface.

[0004] As a support of this optical compensation film,
Cellulose ester films are used because they have good transparency, high mechanical strength, and small dimensional fluctuations due to changes in humidity and heat (good dimensional stability). This cellulose ester film is manufactured by a solution casting method, for example, by a manufacturing apparatus as shown in FIG.

In FIG. 3, reference numeral 20 denotes a casting step of casting a dope on a support, 30 denotes a stretching step of stretching the film formed in the casting step 20 by a tenter, and 40 denotes a step of drying the stretched film. This is a drying step. Casting process 20
Is provided with a casting die 21.
A dope in which a cellulose ester is dissolved in a solvent is cast on a casting support 22 provided below. In the stretching drying step 30, a tenter 31 is provided to stretch and dry the film in the width direction. In the drying step 40, a transport roll 41 is provided and a drying air 42
Is used to dry the film being transported by the transport roll 41. Reference numeral 50 denotes a winding section for winding the completed film. In some cases, a step of applying an undercoat layer such as an adhesion layer and a back layer may be provided between the stretching drying step 30 and the drying step 40.

[0006]

However, in recent years, TF
As the size of the screen of the liquid crystal display device for T has increased, the quality of the display screen has been regarded as important. One of the quality items is light leakage due to aging. For example, there is a picture-like light leak seen after performing a forced thermotest.
This light leakage may be caused by a shift in the alignment axis of a polarizing plate film (a support for an optical compensation film, a polarizing plate protective film, etc.) used for a polarizing plate of a liquid crystal display device, an increase in retardation, and the like. I understand. However, no effective method for preventing these problems has been found, and a technology for preventing light leakage has been demanded.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a polarizing plate film in which a liquid crystal display device does not leak light for a long period of time.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the occurrence of light leakage due to the aging of a polarizing plate film, and have found that there is a relationship between the shrinkage of the film and the sound wave propagation velocity in the plane of the film. The present invention was completed by finding out a range in which the occurrence of light leakage was small and which can be used practically.

That is, the polarizing plate film according to the first invention is a cellulose ester film formed by casting a dope obtained by dissolving a cellulose ester in an organic solvent from a casting die onto a casting support, The shrinkage ratio after heat treatment at 80 ° C. for 24 hours is 0.2% or less.

The film for polarizing plate according to the second invention is a cellulose ester film formed by casting a dope in which a cellulose ester is dissolved in an organic solvent from a casting die onto a casting support, 2k in-plane acoustic wave propagation velocity
m / s or more.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the film for polarizing plate of the present invention, the shrinkage after heat treatment at 80 ° C. for 24 hours is 0.2% or less, preferably 0.15% or less. The shrinkage rate depends on the casting direction of the cellulose ester film (M
There are a shrinkage rate in D) and a shrinkage rate in the width direction (TD), and both of these must be satisfied.

The shrinkage is greatly affected by the amount of residual solvent in the cellulose ester film, and it is preferable that the amount of residual solvent be 0.8% by weight or less. By setting the amount of the residual solvent to 0.8% by weight or less, the shrinkage is reduced to 0.1%.
It can be less than 2%.

Further, in the polarizing plate film of the present invention, the in-plane sound wave propagation speed is 2 km / s or more, preferably 2.3 km / s or more. The in-plane acoustic wave propagation speed is determined by the casting direction (MD) of the cellulose ester film.
And the propagation speed in the width direction (TD), both of which must be satisfied. What is used for this in-plane sound wave propagation velocity is a longitudinal wave. The propagation speed of this longitudinal wave has a positive correlation with the Young's modulus, and the Young's modulus increases as the propagation speed increases.

[0014] Light leakage can be effectively prevented if at least one of the above-mentioned shrinkage ratio and in-plane sound wave propagation velocity is satisfied, but it is preferable that both are satisfied at the same time. That is, the shrinkage after heat treatment at 80 ° C. for 24 hours is 0.2% or less, and the in-plane acoustic wave propagation velocity is 2 km /
By setting s or more, light leakage can be more effectively prevented.

Representative examples of the cellulose ester include lower fatty acid esters of cellulose (eg, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate). Lower fatty acids are
It means a fatty acid having 6 or less carbon atoms. Cellulose acetate includes triacetyl cellulose (TAC) and cellulose diacetate (DAC).

As the solvent, chlorides of lower aliphatic hydrocarbons and lower aliphatic alcohols are generally used. Examples of chlorides of lower aliphatic hydrocarbons include methylene chloride. Examples of lower aliphatic alcohols include methanol, ethanol, n-propyl alcohol, isopropyl alcohol and n-butanol.
Examples of other solvents include acetone, which is substantially free of halogenated hydrocarbons, and ketones having 4 to 12 carbon atoms include, for example, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone, and methylcyclohexanone. Examples of the ester having 3 to 12 atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, pentyl acetate, 2-ethoxy-ethyl acetate, and the like. Examples of the alcohols from to 6 include methanol, ethanol, propanol, iso-propanol, 1-butanol, t
-Butanol, 2-methyl-2-butanol, 2-methoxyethanol, 2-butoxyethanol and the like. Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, and 1,4. -Dioxane, 1,3-dioxolan, tetrahydrofuran, anisole, phenetole and the like, and the cyclic hydrocarbons having 5 to 8 carbon atoms include cyclopentane, cyclohexane, cycloheptane and cyclooctane.

In the present invention, a plasticizer can be added to the dope. Examples of the plasticizer include phosphate esters, such as triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, and tributyl phosphate.Phthalate esters include diethyl phthalate. , Dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, etc., glycolate esters such as triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. Are preferably used alone or in combination.

An ultraviolet absorbent can be added to the dope of the present invention. Examples of the ultraviolet absorber include benzophenone-based, salicylate-based, and benzotriazole-based compounds. Examples of the benzophenone-based ultraviolet absorber include 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2-hydroxy-4-methoxybenzophenone and 2-hydroxy-4-n-dodecyloxybenzophenone. Examples of the salicylate-based ultraviolet absorber include 4-t-butylphenyl salicylate. Examples of the benzotriazole-based ultraviolet absorber include 2- (hydroxy-5-t-octylphenyl) benzotriazole and 2- (2′-hydroxy-
5′-methylphenyl) benzotriazole and 2-
(2'-hydroxy-3,5'-di-t-butylphenyl) -5-chlorobenzotriazole. Examples of other ultraviolet absorbers include [2,2'-thiobis (4-t-octylphenolate)] n-butylamine nickel II.

The film for a polarizing plate of the present invention is a polarizing plate protective film provided on both sides or one surface of a polarizer of a polarizing plate, a support of an optical compensation film also serving as a protective film, and an optical layer laminated on the polarizing plate protective film. It can be used as a support for a compensation film. That is, the polarizing plate has a mode in which a polarizing plate protective film is laminated on both surfaces of a polarizer, and a mode in which a polarizing plate protective film is laminated on one of the polarizers and an optical compensation film also serving as a protective film is laminated on the other. A mode in which an optical compensation film serving also as a protective film is laminated on both surfaces of the polarizer, a mode in which a polarizing plate protective film is laminated on both surfaces of the polarizer, and an optical compensation film is further laminated on the polarizer protective film, and the like. .

An embodiment of a polarizing plate using the polarizing plate film according to the present invention will be described with reference to the drawings.

FIG. 1 is a partial sectional view showing a layer structure of an optical compensation film used for a polarizing plate, and FIG. 2 is a partial sectional view showing a layer structure of a display panel of a liquid crystal display device.

In FIG. 1, an optical compensation film 1 is provided with a support 2 using a polarizing plate film according to the present invention. On one surface of the support 2, an adhesion layer 3 as an undercoat layer, An orientation providing layer 4 and an optical compensation layer 5 are laminated in this order, and a back layer 6 as an undercoat layer is provided on the other surface.
Are laminated.

Then, as shown in FIG. 2, the optical compensation film 1 is laminated on one surface of the polarizer 7, and the other surface of the polarizer 7 is laminated with a protective film 8 for the polarizing plate. The display panel is manufactured by bonding the polarizing plate 9 to both surfaces of the glass plate 10.

[0024]

EXAMPLES Examples 1 to 4 and Comparative Example 1 <Optical Compensation Film> An optical compensation film as shown in FIG. 1 was produced. First, a dope was prepared by dissolving 23 parts by weight of triacetyl cellulose and 12 parts by weight of triphenyl phosphate (plasticizer) in a solvent consisting of 80 parts by weight of methylene chloride, 15 parts by weight of methanol, and 5 parts by weight of butanol. The film was cast on a casting support, and the triacetylcellulose film peeled off from the casting support was stretched and dried. Subsequently, an adhesion layer and a back layer as shown below were applied on both sides. Then, the film having the three-layer structure was dried at an arbitrary temperature for 15 minutes in each of Examples and Comparative Examples. At this time, the casting direction (MD) and the width direction (T
The stretching ratio of D) was arbitrarily changed in each of Examples and Comparative Examples.

An orientation-imparting layer and an optical compensation layer as shown below are applied to the laminated film comprising the support, the adhesion layer, and the back layer comprising the triacetyl cellulose film. Irradiation was performed to crosslink and harden to produce an optical compensation film.

<Adhesion Layer> Gelatin 200 mg / m²  Solvent 25cc / m²  (Acetone: methanol: methylene chloride = 5: 3: 2)

<Back layer> Diacetyl cellulose 200 mg / m²  0.01 μm silica 10 mg / m²  Solvent 25cc / m²  (Acetone: methanol: methylene chloride = 5: 3: 2)

<Orientation-imparting layer> Polyvinyl alcohol 500 mg / m²  Solvent (water) 20cc / m²

<Optical compensation layer> Discotic liquid crystal 2 g / m²  UV curing initiator 0.01 g / m²  Solvent (methyl ethyl ketone) 5cc / m²

[Simulated Display Panel] Using the optical compensation film as described above, a simulated display panel as shown in FIG. 2 was produced.

That is, an optical compensation film is laminated on one surface of a polarizer, and a polarizing plate protective film is provided on the other surface to produce two polarizing plates having a diagonal length of 15 inches.
This polarizing plate was adhered to both sides of a glass plate so as to form a cross Nicol, thereby producing a simulated display panel.

<Polarizer> A polyvinyl alcohol film was immersed in an iodine solution, stretched and dried to produce a polarizer.

<Polarizing Plate Protective Film> Fuji Tack (manufactured by Fuji Photo Film Co., Ltd.) was used.

<Glass plate> Soda glass (1.1 mm thick)

[Comparison of Examples and Comparative Examples] The shrinkage and in-plane acoustic wave propagation velocity of the three-layer laminated film after heat treatment at 80 ° C. for 2 hours were measured. Film) was measured.
Further, light leakage of the simulated display panel was evaluated. Table 1 shows the results.

[0036]

[Table 1]

[Shrinkage ratio] Holes of 6 mmφ are opened at intervals of 100 mm, and the original size (L1) of the interval is set to the minimum scale 1/1000.
mm, and then heat-treated at 80 ° C. and 5% RH for 2 hours, and then the dimension (L2) of the hole interval was measured. From these, the shrinkage was determined by the following equation. Shrinkage = {(L1-L2) / L1} × 100

[Surface acoustic wave propagation velocity] Two oscillators (a transmitting oscillator and a receiving oscillator) are brought into contact with each other at an interval of 150 mm, and a longitudinal wave (ultrasonic pulse) is generated from the transmitting oscillator. The time until the wave was received (T [μs]) was measured. SST-110 (Nomura Trading Co., Ltd.) was used as a measuring device. From this time, the propagation velocity (C [km / s]) was determined by the following equation. C = 150 / T

[Evaluation of Light Leakage] First, the simulation display panel was
Heat treatment was performed at 0 ° C. and 95% for 17 hours. Then, after being left at room temperature for 24 hours, it was placed on a sharks-ten and the light leakage unevenness in the screen was visually observed. The evaluation is as follows. ：: No light leakage ：: Slight light leakage at four edges △: Clear light leakage at four edges ×: Light leakage to near film center

From the above results, it has been confirmed that light leakage can be prevented if one of the contraction rate and the sound wave propagation velocity is satisfied. In addition, it was confirmed that light leakage can be more effectively prevented in the example (Examples 1 and 2) that satisfies both the contraction rate and the sound wave propagation velocity than in the example (Examples 2 and 3) that satisfies only one of them. Was done. Furthermore, even when both are satisfied, the example in which the contraction rate is small and the sound wave propagation speed is large (Example 1) is larger than the example in which the contraction rate is large and the sound wave propagation velocity is small (Example 2). It was confirmed that light leakage could be effectively prevented.

[0041]

The present invention is configured as described above.
Light leakage can be prevented from occurring on the screen of the liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a layer configuration of an optical compensation film using a polarizing plate film according to the present invention.

FIG. 2 is a partial cross-sectional view showing a layer configuration of a display panel using the polarizing plate film according to the present invention.

FIG. 3 is a schematic diagram of a production apparatus for producing a cellulose ester film by a solution casting method. DESCRIPTION OF SYMBOLS 1 ... Optical compensation film 2 ... Support 3 ... Adhesion layer 4 ... Orientation providing layer 5 ... Optical compensation layer 6 ... Back layer 7 ... Polarizer 8 ... Polarizer protective layer 9 ... Polarizer 10 ... Glass plate 20 ... Casting process 30: stretching drying step 40: drying step 50: winding section

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // B29K 1:00 B29K 1:00 B29L 7:00 B29L 7:00 C08L 1:10 C08L 1:10 F Terms (reference) 2H049 BA02 BA06 BB03 BB13 BB49 BC01 BC09 BC10 BC22 2H091 FA08X FA08Z FA11X FA11Z FB02 FC07 FC23 FC29 FD10 LA03 4F071 AA09 AF49Y AF61Y AH16 BA02 BB02 BC02 4F205 AA01 AC07 AG02 GC07 GE07

Claims (5)

[Claims] 1. A cellulose ester film formed by casting a dope obtained by dissolving a cellulose ester in an organic solvent from a casting die onto a casting support.
A film for a polarizing plate, wherein the shrinkage after heat treatment for 0.2 hour is 0.2% or less. 2. The polarizing plate film according to claim 1, wherein the amount of the residual solvent in the cellulose ester film is 0.8% by weight or less. 3. A cellulose ester film formed by casting a dope in which a cellulose ester is dissolved in an organic solvent from a casting die onto a casting support, and having an in-plane acoustic wave propagation speed of 2 km / s or more. A film for a polarizing plate, comprising: 4. A cellulose ester film formed by casting a dope obtained by dissolving a cellulose ester in an organic solvent from a casting die onto a casting support.
A film for a polarizing plate, wherein a shrinkage ratio after heat treatment for a time is 0.2% or less and an in-plane acoustic wave propagation velocity is 2 km / s or more. 5. The protective film for a polarizing plate according to claim 1, wherein at least one optical compensation layer is laminated.