JP2001114914A - Optical film, preparation method therefor, deflector plate and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film which has sufficient visual angle properties and is extremely hard to be affected by the outer environment, a preparation method therefor, a deflector plate (deflector film) thereof and a liq. crystal display therefrom. SOLUTION: This optical film is characterized in that the retardation value (Rt) in the thickness direction which is defined by formula (1): Rt value = (Nx+Ny)/2-Nz}×d is in the range of 50<=Rt<=300 nm when measured at 23 deg.C and 55% RH. Furthermore, the difference between the Rt value at 23 deg.C/20% RH and the Rt value at 23 deg.C/80% RH is <=40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical film, a method for manufacturing an optical film, a polarizing plate film, and a liquid crystal display.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device has a low voltage and low power consumption, can be directly connected to an IC circuit, and in particular, can be made thin, so that a liquid crystal display device such as a word processor or a personal computer can be used. Widely used as a device. This liquid crystal display device has a basic configuration in which, for example, polarizing plates are provided on both sides of a liquid crystal cell.

In such a liquid crystal display device, from the viewpoint of contrast and the like, a liquid crystal display device using a twisted nematic (TN) having a twist angle of 90 degrees is replaced with a super twisted nematic (STN) having a twist angle of 160 degrees or more. Has been shifted to a liquid crystal display device using the same.

However, a liquid crystal display device using STN is
Since the birefringence of the liquid crystal is used, there is a problem that a normally white background in a liquid crystal display device using TN is colored blue or yellow in a white background. Is narrow,
There is a problem that colorization is difficult.

In order to solve this problem, that is, to compensate for the birefringence, a technique using a retardation plate below an upper polarizing plate has been proposed. According to this technique, the problem of coloring is solved, but the viewing angle is hardly improved.

In order to solve this problem, a technique has been proposed in which a birefringent film having a refractive index in the thickness direction larger than the refractive index in the direction perpendicular to the birefringent optical axis is manufactured and used as a retardation plate. Was. Further, a technique has been proposed in which films each having a positive and negative intrinsic birefringence value are used one by one, or a laminated film is used as a retardation plate.

Further, as disclosed in JP-A-7-218724, at least one of the protective films of the polarizer is made of a plastic made of triacetyl cellulose having an in-plane retardation value of 30 to 70 nm when measured with light having a wavelength of 590 nm. A polarizing plate that is a film has been proposed.

[0008] By these proposed techniques, the change in contrast due to the viewing angle is reduced, and the viewing angle characteristics are improved.

[0009] By the way, the demand for improvement of the biggest problem in a liquid crystal display device, which is a low voltage, low power consumption, and a large feature not found in other display devices, which is not found in other display devices, that is, a problem with a narrow viewing angle, is increasing. On the other hand, further research is underway.

As one of such research and development, a liquid crystal of a type different from the TN or STN type has been proposed. That is, the liquid crystal cell of the TN or STN type is a type in which the liquid crystal molecules are parallel to the alignment plate when the voltage is turned off and the liquid crystal molecules are aligned perpendicular to the alignment plate when the voltage is turned on. A type in which molecules are perpendicular to the alignment plate and parallel when the voltage is turned on, for example, a so-called vertical alignment type using negative liquid crystal having negative dielectric anisotropy has been developed.

[0011] This vertical alignment (VA)
Since the liquid crystal display device is a vertical alignment mode liquid crystal cell in which liquid crystal molecules are perpendicular to the alignment plate when voltage is turned off and liquid crystal molecules are aligned in parallel with the alignment plate when voltage is turned on, black is firmly displayed as black. High contrast, TN and S
Compared with the TN type, the viewing angle can be made relatively wide. However, with the recent increase in the size of the liquid crystal screen, there is an increasing demand for further widening the viewing angle.

In order to solve this problem, application of a retardation film as described in the following patent documents has been examined for a VA liquid crystal display device. For example, JP-A-11-
Japanese Patent No. 95208 discloses a technique using a retardation film having an in-plane retardation value of 0 to 100 nm and a retardation in the thickness direction of 100 nm or more. Japanese Patent Application Laid-Open No. 11-183724 discloses an in-plane retardation. A method using a retardation film having a thickness of 0 to 30 nm, a thickness direction retardation of 100 to 600 nm, a variation of 1 m square of 5 nm or less, and an absolute value of the slow axis angle of 30 degrees or less has been proposed. . With these technologies, the viewing angle was certainly widened.

However, as the present inventors continue their research, these retardation films aimed at expanding the viewing angle have a problem that the basic performance greatly changes depending on the change of the storage environment. It turns out.

That is, when the equilibrium water content of the film is high under high humidity, the retardation in the thickness direction is reduced, and the effect of widening the viewing angle is reduced.

In addition, the rate of exposure to harmful light such as ultraviolet rays increases due to the increase in the size of the liquid crystal screen and the opportunity for outdoor use, thereby deteriorating the liquid crystal. Also, there is a problem that the effect of widening the viewing angle is impaired when both are used.

Further, in a severe environment such as high temperature and high humidity, the flatness of the retardation film is deteriorated, and the molecular orientation in the film is disturbed, which also causes a loss of the viewing angle expanding effect.

On the other hand, the retardation film is generally stored in a roll shape after the film is formed until it is shipped as a product. A phenomenon called blocking, in which the front and back surfaces of the film are in close contact, may occur. As a result, not only the surface quality of the film is deteriorated, but also the variation of the retardation value within a unit area is increased, which causes the quality at the time of product shipment to be greatly reduced.

There has been a demand for an optical film, a polarizing plate film, and a liquid crystal display device having the same, which have alleviated the above problems.

[0019]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical film having a sufficient viewing angle characteristic and being extremely insensitive to the external environment, a method for producing the optical film,
It is to provide a polarizing plate film and a liquid crystal display device.

[0020]

The above objects of the present invention have been attained by the following items 1 to 19.

1. The retardation value (Rt) in the thickness direction defined by the following general formula (1) is 23 ° C., 55% R
In H, 50 ≦ Rt ≦ 300 nm and 2
An optical film, wherein the difference in Rt value between 3 ° C., 20% RH and 23 ° C., 80% RH is 40 or less.

General formula (1) Rt value = ((Nx + Ny) / 2−Nz) × d (where Nx is the refractive index of the film in a direction parallel to the film forming direction, and Ny is perpendicular to the film forming direction. Nz represents the refractive index of the film in the thickness direction, and d represents the thickness (nm) of the film. ] 2. In the general formula (1), the Rt value at 23 ° C. and 55% RH is 50 ≦ Rt ≦ 300 nm, and the equilibrium water content at 23 ° C. and 55% RH is 6% or less. Optical film.

3. In the general formula (1), 23 ° C.
Rt value at 55% RH is 50 ≦ Rt ≦ 300 nm
And an optical film containing a plasticizer.

4. In the general formula (1), 23 ° C.
Rt value at 55% RH is 50 ≦ Rt ≦ 300 nm
And a transmittance at 380 nm of 60% or less.

[5] In the general formula (1), 23 ° C.
Rt value at 55% RH is 50 ≦ Rt ≦ 300 nm
And a fluctuation width of the Rt value within 1 m square is 5 nm or less.

6. In the general formula (1), 23 ° C.
Rt value at 55% RH is 50 ≦ Rt ≦ 300 nm
And an optical film characterized by containing a matting agent.

7. When the retardation value (Ro) in the in-plane direction of the film defined by the following general formula (2) is | R
o | ≦ 30 nm, and the angle of the slow axis of the film is | slow axis angle | ≦ 30 °.
7. The optical film according to any one of claims 6 to 6.

General formula (2) Ro value = (Nx-Ny) × d [wherein Nx, Ny and d are each the same as in the general formula (1).
Is synonymous with ] 8. 8. The optical film according to any one of the above items 1 to 7, wherein a lower fatty acid ester of cellulose is contained as a main component of the film.

9. The optical film according to any one of the above items 1 to 8, wherein the film has a thickness of 75 to 250 µm.

10. 10. The optical film according to any one of 1 to 9, wherein the film is formed by uniaxial stretching.

[11] The optical film according to any one of the above items 1 to 10, which is a polarizing plate protective film for a liquid crystal display.

12. In producing the optical film according to any one of the above 1 to 11, when casting the optical film on a belt or a drum, when peeling the optical film from the belt or the drum A method for producing an optical film, wherein the difference obtained by subtracting the amount of residual solvent at the time of winding after forming the optical film from the amount of residual solvent is 10% or more.

13. In producing the optical film according to any one of the above items 1 to 11, when casting the optical film on a belt or a drum, the optical film is peeled off from the belt or the drum to form a roll. A state of (amount of residual solvent in the optical film) ≧ 10% is maintained for at least one minute immediately after peeling until the film is wound.

14. In producing the optical film according to any one of the above items 1 to 11, when casting the optical film on a belt or a drum, the amount of residual solvent when peeling off from the belt or the drum is 10%. ~ 120
%. A method for producing an optical film, wherein the method is adjusted to%.

15. In producing the optical film according to any one of the items 1 to 11, in the drying step after the film is formed, the optical film is peeled off from a belt or a drum and wound up into a roll. Wherein the highest temperature is maintained below the glass transition temperature of the optical film.

16. 12. The optical film according to any one of 1 to 11, wherein the optical film is used for a vertical alignment type liquid crystal display device.

17. 12. A polarizing plate film having a polarizing plate on the optical film according to any one of the above items 1 to 11, wherein an equilibrium water content in the optical film is 6% or less.

18. 18. A liquid crystal display device comprising a polarizing plate and a liquid crystal cell, wherein the polarizing plate film described in 17 is provided on at least one surface of the liquid crystal cell.

19. 12. A liquid crystal display device comprising a polarizing plate and a liquid crystal cell, wherein the liquid crystal cell has at least one type of vertical alignment type liquid crystal, and the polarizing plate is any one of the optical devices according to any one of the above items 1 to 11. A liquid crystal display device characterized by being a film.

Hereinafter, the present invention will be described in detail.

The present inventors have disclosed a VA (vertical alignment) type liquid crystal display device as disclosed in JP-A-11-1.
Even if a film with controlled in-plane retardation, retardation in the thickness direction, and slow axis as described in JP-A-83724 is used, a change in the production environment during production, a change in the use environment of the optical film, It has been found that undesirable phenomena such as a reduction in the effect of expanding the viewing angle or an increase in the fluctuation of the viewing angle occur due to a change in the storage state or the like.

The control of retardation or slow axis, which has been conventionally studied, is not enough to make full use of the liquid crystal's original basic performance. 4 retardations in the thickness direction
By developing films that are below 0,
The object of the present invention has been achieved.

First, the retardation value (Rt value) according to the present invention is 50 to 300 at 23 ° C. and 55% RH.
A method for producing a film adjusted to nm is described.
The film will be described with reference to a cellulose ester film having a lower fatty acid ester of cellulose as a main component, particularly acetyl cellulose as a main component, but is not limited thereto.

The above-mentioned cellulose ester film having acetyl cellulose as a main component is dissolved in an organic solvent such as methylene chloride, ethanol, acetone and methanol to form a dope. The concentration of acetylcellulose in the dope is about 10 to 35 wt%. Incidentally, a plasticizer such as a phthalic acid ester or a phosphoric acid ester may be added to the acetyl cellulose in an amount of 3 to 20% by mass. Further, if necessary, additives such as an ultraviolet absorber and a lubricant may be added. Then, the obtained dope is cast on a support to form a film.

As a method of forming the optical film of the present invention, it is preferable to form the film by a uniaxial stretching method from the viewpoint of increasing the Rt value, and the film can be formed by a band method or a drum method. Next, the film thus obtained is peeled off from a support such as a band or a drum. afterwards,
It is transported through a drying zone under tension and dried.

At this time, the amount of residual solvent when the film is peeled off from the belt (band) or drum is preferably adjusted to 10 to 120%. In a range less than 10%, the orientation of the molecules constituting the film is not sufficiently performed,
The Rt value is not sufficiently below the desired value and
%, The film is not sufficiently dried, and the film is not sufficiently peeled off, which is insufficient for practical use. Further, the amount of the residual solvent is more preferably 15 to 100%, particularly preferably 20 to 100%.
~ 80%.

The amount of residual solvent in the film according to the present invention is represented by the following equation.

Residual solvent content = mass of residual volatiles / mass of film after heat treatment × 100% The mass of residual volatiles is calculated from the mass of the film before heat treatment to the mass of film after heat treatment when the film is heat-treated at 115 ° C. for 1 hour. This is a value obtained by subtracting the film weight.

When the tension at the time of peeling the film and the tension at the time of transporting through the drying zone are increased, the Rt value decreases, and as the tension decreases, the Rt value increases. The preferable peel tension is 5 to 40 kg / m, more preferably 10 to 30 k.
g / m, more preferably 10 to 25 kg / m.
Further, the transport tension in the drying zone is preferably 5 to 2
0 kg / m, more preferably 8 to 17 kg / m, further preferably 11 to 15 kg / m.

In the present invention, in the drying step after peeling the film from the belt or drum, it is preferable to dry the film while stretching it by a pin tenter method or a clip tenter method. In this case, the Rt value increases as the stretching ratio increases, and decreases as the stretching ratio decreases. The preferred stretching ratio is 2 to 50%, more preferably 5 to 40%, and still more preferably 10 to 30%.

In order to make the molecular orientation of the molecules constituting the film sufficiently and to adjust the retardation value (Rt) within the above-mentioned range, it is necessary to maintain a state in which the residual solvent is relatively large for a certain period of time. There is. For this purpose, when the film is cast on a belt or a drum, after the film is peeled off from the belt or the drum and before it is wound into a roll, (the amount of residual solvent) ≧ 10% It is preferable that the state is maintained for 1 minute or more immediately after the peeling, more preferably 3 minutes or more, particularly preferably 5 minutes or more.

In order to increase the Rt value, it is preferable that the residual solvent after film formation and winding is small. Therefore, it is preferable that the residual amount of the solvent at the time of winding after film formation is reduced by 10% or more than the residual amount of the solvent at the time of peeling, more preferably 15% or more, particularly preferably. 2
That is, it is reduced by 0% or more.

In the process of forming the film, the drying step in which the film is peeled off from a belt or a drum and wound up in a roll shape, the highest temperature set in the drying step is equal to or lower than the glass transition temperature of the film. It is preferably adjusted to. In the range higher than the glass transition temperature, the molecular orientation of the film is disturbed, which not only causes a decrease in the Rt value, but also significantly deteriorates the surface quality of the film.

The temperature set in the drying step described above is preferably Tg (representing a glass transition temperature) to (Tg-70 ° C.), and more preferably Tg to 70 ° C.
(Tg-50 ° C.), and particularly preferably Tg to (Tg
g-30 ° C).

The retardation value (Rt value) in the thickness direction of the optical film of the present invention is a positive value of 23 ° C. and 55% RH.
Is 50 to 300 nm, preferably 70 to 2 nm.
It is 50 nm, particularly preferably 85 to 200 nm.

Further, the optical film of the present invention has a temperature of 23 ° C.
The difference between the Rt value at 20% RH and the Rt value at 23 ° C. and 80% RH is 40 or less, preferably 30 or less, more preferably 20 or less, and particularly preferably 0.

In the present invention, “at 23 ° C. and 55% RH” means that a measurement sample cut into a 35 mm square is 2
This means that the sample is left under the conditions of 3 ° C. and 55% RH for 8 hours and then measured under the same conditions.

The in-plane retardation value (Ro) of the optical film of the present invention is -30 to 30 nm,
The angle of the slow axis is preferably in the range of -30 to 30 °. Beyond these ranges, the isotropy of the film deteriorates, and the effect of widening the viewing angle decreases. More preferably, | Ro | ≦ 15 and | slow axis angle | ≦ 15.

Further, in the optical film of the present invention, the fluctuation width of the retardation value (Rt) in a square of 1 m is 5n.
m or less is preferable for stably exhibiting viewing angle characteristics. In the present invention, the fluctuation width of the retardation value (Rt) within 1 m square is 5 nm or less when 1 m from a film wound into a roll after film formation.
It indicates that the fluctuation range of the retardation value (Rt) when the retardation value (Rt) of a sample arbitrarily cut out in a square is measured at 100 points is 5 nm or less.

For the measurement of the retardation value and the slow axis angle according to the present invention, an automatic birefringence meter KOBRA-21AD was used.
H (manufactured by Oji Scientific Instruments) with a wavelength of 590 n
m, a three-dimensional refractive index measurement is performed, and the refractive indices Nx, N
It is obtained by obtaining y and Nz.

The optical film of the present invention has a thickness of 75
~ 250 μm is preferred. If the film thickness is smaller than 75 μm, the desired value of Rt cannot be obtained. If the film thickness is larger than 250 μm, problems occur in surface quality and handleability. More preferably 80 to 220 μm, even more preferably 85 to 1 μm.
85 μm.

Various polymers can be used as the film material according to the present invention, and are not particularly limited.
Polyester film, polyethylene film, polypropylene film, cellophane, cellulose diacetate film, cellulose acetate propionate film, cellulose acetate butyrate film, cellulose acetate phthalate film, cellulose triacetate, and cellulose esters such as cellulose nitrate or derivatives thereof Film, polyvinylidene chloride film, polyvinyl alcohol film, ethylene vinyl alcohol film, syndiotactic polystyrene film, polycarbonate film, norbornene resin film, polymethylpentene film, polyetherketone film, polyethersulfone film, polysulfone film , Polyetherketone Films, polyamide films,
Examples thereof include a fluororesin film, a nylon film, a polymethyl methacrylate film, an acrylic film and a polyarylate-based film. Among the above descriptions, a film material mainly containing a lower fatty acid ester of polycarbonate or cellulose (for example, cellulose triacetate) Etc.) are preferred.

When cellulose triacetate is used as the film material, the polymerization degree is particularly preferably from 250 to 400.
Cellulose triacetate having an amount of bound acetic acid of 54 to 62.5% is preferable, and an amount of bound acetic acid of 58 to 62.5% is more preferable because of strong base strength. As the cellulose triacetate, either cellulose triacetate synthesized from cotton linter or cellulose triacetate synthesized from wood pulp can be used alone or in combination. It is preferable to use a large amount of cellulose triacetate synthesized from a cotton linter having good releasability from a belt or a drum because productivity is high and thus it is preferable. When the proportion of cellulose triacetate synthesized from cotton linter is 60% by mass or more, the effect of releasability becomes remarkable, preferably 60% by mass or more, more preferably 85% by mass or more, particularly preferably used alone. It is to be.

It is preferable to incorporate a plasticizer into the film according to the present invention. The plasticizer that can be used is not particularly limited, but in the case of a phosphate ester system, phthalic acid such as triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For acid ester type, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, etc., and for glycolate type, triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl It is preferable to use glycolate, methylphthalylethyl glycolate, butylphthalylbutylglycolate alone or in combination. There. If necessary, two or more types of plasticizers may be used in combination. When used in a cellulose ester, the use ratio of a phosphate ester-based plasticizer is 50% or less, which causes hydrolysis of the cellulose ester film. It is preferable because it is difficult to obtain and has excellent durability. It is more preferable that the ratio of the phosphate plasticizer is smaller, and it is particularly preferable to use only the phthalate or glycolate plasticizer.

It is preferable to use an ultraviolet absorber in the film according to the present invention. The ultraviolet absorber is excellent in the ability to absorb ultraviolet light having a wavelength of 380 nm or less from the viewpoint of preventing deterioration of the liquid crystal and has good liquid crystal display properties. 400n wavelength from the point
Those that absorb as little as possible visible light of m or more are preferably used. In particular, the transmittance at a wavelength of 380 nm is 60
%, Preferably 40% or less, more preferably 20% or less.

Examples of the ultraviolet absorber include oxybenzophenone compounds, benzotriazole compounds, salicylate compounds, benzophenone compounds,
Examples thereof include a cyanoacrylate compound and a nickel complex salt compound, but the present invention is not limited thereto.

In the present invention, one of these ultraviolet absorbers
It is preferable to use at least two kinds of UV absorbers, and two or more different UV absorbers may be contained.

As a method of adding the ultraviolet absorber, the ultraviolet absorber may be dissolved in an organic solvent such as alcohol, methylene chloride or dioxolane and then added to the dope, or may be directly added to the dope composition. Those that do not dissolve in an organic solvent, such as inorganic powder, are dispersed in an organic solvent and a cellulose ester using a dissolver or a sand mill, and then added to the dope.

The amount of the ultraviolet absorber used in the present invention is 0.1% by mass to 2.5% by mass, preferably 0.5% by mass to 2% by mass based on the cellulose ester.
0 mass%, more preferably 0.8 mass% to 2.0 mass%
It is.

It is preferable to add fine particles such as silicon oxide as a matting agent to the film according to the present invention. Fine particles such as silicon oxide are preferably surface-treated with an organic substance because the haze of the film can be reduced. Preferred organic substances for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes and the like. The larger the average diameter of the fine particles, the greater the matting effect, and the smaller the average diameter, the better the transparency. Therefore, the average primary particle diameter of the preferred fine particles is 5 to 50 n.
m is more preferably 7 to 14 nm. AEROSIL20 manufactured by Aerosil Co., Ltd. is used as the fine particles of silicon oxide.
0, 300, R972, R974, R202, R81
2, OX50, TT600, etc., preferably AEROSILR972, R974, R202, R81
2 and the like.

In producing the film according to the present invention,
Embossing can be performed on both sides of the film to prevent blocking during winding. Embossing can be performed to any height depending on the purpose, but in the present invention, it is preferably 5 μm or more in order to volatilize the residual solvent after winding. More preferably, it is 10 μm or more.

In addition, after being wound up in a roll shape, the product is usually packaged until it is shipped, in order to protect the product from dirt and adhesion of dust due to static electricity. The packaging material is not particularly limited as long as the above purpose can be achieved, but is preferably a material which does not prevent the evaporation of the residual solvent from the film. Specific examples include polyethylene, polyester, polypropylene, nylon, polystyrene, paper, various nonwoven fabrics, and the like. Fibers in the form of mesh cloth are more preferably used.

In the present invention, a vertical alignment (VA) type liquid crystal display device is a liquid crystal of a vertical alignment mode in which the liquid crystal molecules are oriented perpendicular to the alignment plate when the voltage is turned off and parallel to the alignment plate when the voltage is turned on. Refers to a liquid crystal display device using cells.

As the polarizer on which the optical film of the present invention is provided on the surface, conventionally known polarizers can be used.
For example, a film made of a hydrophilic polymer such as polyvinyl alcohol is treated with a dichroic dye such as iodine and stretched, or a film obtained by treating a plastic film such as vinyl chloride and orienting a polyene is used. Used. And a polarizing plate is comprised as what laminated | stacked the said polarizing plate protective film on at least one surface side of the polarizer.

In the present invention, in order to suppress the fluctuation of the retardation value (Rt) due to humidity and to obtain good viewing angle characteristics, the optical film of the present invention and the polarizing plate film (the polarizing plate) of the present invention are required. The equilibrium water content of the optical film after lamination is preferably 6% or less, more preferably 5% or less, 4% or less, 3% or less, 2% or less, and 1% or less. Particularly preferably, it is substantially zero. In the present invention, “substantially zero” means 0.5% or less.

[0076]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

Example 1 << Preparation of Sample 1 >> (Dope Composition I) 50 parts of cellulose triacetate synthesized from cotton linter (degree of acetylation: 61.0%) Cellulose triacetate synthesized from wood pulp (degree of acetylation: 61.%) 0 parts) 50 parts Tinuvin 326 (UV absorber 1 manufactured by Ciba Specialty Chemicals) 0.5 parts Tinuvin 328 (UV absorber 2 manufactured by Ciba Specialty Chemicals) 0.5 part Triphenyl phosphate (plasticizer A) 12 parts Fine particles Silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd .: 0.016 μm, matting agent 1) 18 parts Methylene chloride 460 parts Ethanol 40 parts The above composition is charged into a closed container, and completely dissolved while being heated and stirred at 80 ° C. under pressure. I let it. Next, the dope was filtered, cooled and kept at 31 ° C., and was uniformly cast on a rotating endless stainless steel band having a length of 6 m (effective length 5.5 m) stretched between two drums. 5 solvent
When the solvent was evaporated to 0%, the film was peeled off from the stainless steel band at a peeling tension of 17 kg / m, dried while being transported by a number of rolls at a transporting tension of 13 kg / m, and dried to a thickness of 160 μm to form cellulose triacetate (TAC). Film sample 1 was obtained. At this time, the amount of the residual solvent 5 minutes after peeling was 40%, and the amount of the residual solvent upon winding after film formation was 5%. The maximum temperature in the final drying zone was 100 ° C. When the glass transition temperature of the film sample 1 was measured, it was Tg = 120 ° C.

<< Measurement of Glass Transition Temperature >> The glass transition temperature was measured using the sample before the alkali saponification treatment described above. The measurement of the glass transition temperature was performed based on the method described in JIS K7121.

This film sample 1 was subjected to a 2.5N-
Alkaline treatment with sodium hydroxide aqueous solution for 60 seconds, 3
After washing with water for a minute, a saponified layer was formed to obtain an alkali-treated film. Next, a polyvinyl alcohol film having a thickness of 120 μm is coated with an aqueous solution 100 containing 1 part of iodine and 4 parts of boric acid.
Then, the film was dipped at 50 ° C. and stretched 4 times to form a polarizing film.
A polarizing plate was prepared by laminating the alkali-treated film on both sides of this polarizing film using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive, and providing polarizing plates on both sides of a VA liquid crystal cell. Obtained. The equilibrium water content of the alkali-treated film at the time of producing the polarizing plate was 3
%Met.

<< Preparation of Film Samples 2 to 11 and Liquid Crystal Display Samples 2 to 11 >> In the above-described film sample 1, an ultraviolet absorber, a plasticizer, a matting agent, an amount of residual solvent at the time of peeling, a film thickness of the film, etc. Was changed as shown in Table 1, except that film samples 2 to 11 were prepared in the same manner.
Next, Liquid Crystal Display Samples 2 to 11 were manufactured in the same manner as in the preparation of Liquid Crystal Display Sample 1.

With respect to the obtained film samples 1 to 11,
As shown in the following (1) and (2), the measurement of the retardation value (Rt, Ro), the angle of the slow axis, and the measurement of the transmittance were performed.

(1) Retardation value (Rt, Ro)
The sample before alkali saponification treatment was measured using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments).
Under the respective environments of 3 ° C., 20% RH and 23 ° C., 80% RH, a three-dimensional refractive index was measured at a wavelength of 590 nm, and a slow axis angle and refractive indices Nx, Ny, Nz were obtained. The retardation value Rt in the thickness direction and the retardation value Ro in the in-plane direction were calculated according to the following general formulas (1) and (2).

General formula (1) Rt value = ((Nx + Ny) / 2−Nz) × d General formula (2) Ro value = (Nx−Ny) × d In the formula, Nx is parallel to the film forming direction of the film. Ny represents the refractive index of the film in a direction perpendicular to the film forming direction, Nz represents the refractive index of the film in the thickness direction, and d represents the thickness (nm) of the film.

The retardation at 23 ° C. and 20%
t1, 23 ° C., 55% retardation at Rt2,
The retardation at 23 ° C. and 80% is defined as Rt3.
Further, the retardation value in the in-plane direction of the film is defined as Ro. The obtained results are shown in the column of film properties in Table 1.

(2) Measurement of Transmittance at 380 nm Using a spectrophotometer U-3400 (manufactured by Hitachi, Ltd.), the film samples 1 to 11 before alkali saponification were measured for light transmittance at a wavelength of 380 nm. Table 1 shows the obtained results.

Next, regarding the liquid crystal display devices 1 to 11,
The viewing angle characteristics were measured and evaluated as shown below.
Shown in

<< Evaluation of Viewing Angle Characteristics and Differences in Viewing Angle Characteristics >> A VG3 manufactured by AMT Corporation was added to the obtained liquid crystal display device sample.
White display with 65N video pattern generator,
LCD-700 manufactured by Otsuka Electronics Co., Ltd. performs black display and 8-gradation gray display, and adjusts the contrast ratio at the time of white / black display.
At 0, the measurement was performed in the range of 60 degrees vertically and horizontally. An angle indicating a contrast ratio ≧ 10 was defined as a viewing angle. 23 ° C, 5
The viewing angle characteristics under 5% RH conditions were measured.
The viewing angle characteristic difference between 80 ° C. and 80% RH and 23 ° C. and 20% RH was measured. The obtained results are shown in Table 2,
It is shown in the column of viewing angle characteristic difference.

Regarding the viewing angle characteristics, the following rank evaluation was performed.

◎: Very wide viewing angle and very good ○: Wide and good viewing angle 視野: Slightly wide viewing angle ×: Narrow viewing angle XX: Very narrow viewing angle Regarding the angular characteristic difference, the following rank evaluation was performed.

A: Very good with no difference in viewing angle characteristics due to changes in humidity conditions B: Very small and good difference in viewing angle characteristics due to changes in humidity conditions Δ: Little difference in viewing angle characteristics due to change in humidity conditions ×: The viewing angle characteristic difference due to the change in humidity condition is large. XX: The viewing angle characteristic difference due to the change in humidity condition is extremely large, and the results are shown in Tables 1 and 2.

[0091]

[Table 1]

[0092]

[Table 2]

Tables 1 and 2 show that the optical film of the present invention
The liquid crystal display device of the present invention, the optical film of the present invention, each optical film not only shows excellent viewing angle characteristics,
It is clear that there is little change and extremely stable even when the external environment changes under high humidity conditions or low humidity conditions.

Example 2 The light resistance, heat resistance and moisture resistance of the liquid crystal display devices 1 to 4 of the present invention and the comparative liquid crystal display device 11 produced in Example 1 were evaluated as follows. Incidentally, the equilibrium water content of the alkali saponified film at the time of producing the polarizing plate was adjusted as shown in Table 3.

<< Measurement of Equilibrium Moisture Content >> The equilibrium moisture content was measured by a Karl Fischer moisture meter. In the present invention, the water content was calculated by the following equation after heating at 120 ° C. for 45 minutes using a trace moisture measuring device CA-06 and a moisture vaporizer VA-06 (manufactured by Mitsubishi Chemical Corporation).

Water content (%) = residual moisture mass / film mass after heat treatment × 100 << Evaluation of light fastness >> Regarding the liquid crystal display devices 1 to 4 of the present invention and the comparative liquid crystal display device 11, the xenon long life weather was used. The sample was left for 500 hours at 60 ° C. at an illuminance of 70,000 lux with a meter, and the difference in viewing angle characteristics before and after the standing was measured, and the following rank evaluation was performed.

Regarding the viewing angle characteristic difference, the following rank evaluation was performed.

◎: no difference in viewing angle characteristics before and after xenon lamp irradiation, very good ○: very small difference in viewing angle characteristics before and after xenon lamp irradiation △: viewing angle before and after xenon lamp irradiation A slight difference in characteristics is observed. ×: Large difference in viewing angle characteristics before and after irradiation with xenon lamp. XX: Very large difference in viewing angle characteristics before and after irradiation with xenon lamp. << Evaluation of heat resistance and moisture resistance >> obtained. The obtained liquid crystal display device sample was allowed to stand for 1000 hours under the conditions of 80 ° C. and 90% RH. The evaluation of the viewing angle characteristics before and after the standing was evaluated by the following ranks.

◎: no difference in viewing angle characteristics under high temperature and high humidity conditions,
Very good ○: Very small difference in viewing angle characteristics under high temperature and high humidity conditions △: Small difference in viewing angle characteristics under high temperature and high humidity conditions ×: High temperature and high humidity conditions XX: Very large difference in viewing angle characteristics under high temperature and high humidity conditions << Method for evaluating dispersion of retardation value (Rt) >> Liquid crystal display device samples 1 to 1 of the present invention 4. Comparative liquid crystal display device 1
For each of the film samples 1 to 4 used for the production of No. 1 and the comparative film sample 11, after forming each of the films, a sample arbitrarily cut out from a film wound into a roll in a size of 1 m square. Using any 100
Rt values were measured at various locations. The difference between the maximum value and the minimum value of the obtained data was defined as the fluctuation width of the Rt value.

Table 3 shows the obtained results.

[0101]

[Table 3]

From Table 3, it can be seen that the liquid crystal display devices 1 to 4 of the present invention produced using an optical film having an equilibrium water content of 6% or less.
It is clear that is excellent in light resistance, heat resistance and moisture resistance as compared with the comparative liquid crystal display device 11 manufactured using an optical film having an equilibrium water content of 9%.

Example 3 << Preparation of Samples 12 to 16 >> The amount of the residual solvent at the time of peeling, the amount of the residual solvent at the time of winding, the amount of the residual solvent after 5 minutes of the peeling, Liquid crystal display samples 12 to 16 were prepared in the same manner except that the final drying zone temperature and the water content of the optical film during the production of the polarizing plate were changed as shown in Table 4. For these, the viewing angle characteristics were evaluated in the same manner as in Example 1. Table 5 shows the obtained results.

[0104]

[Table 4]

[0105]

[Table 5]

Tables 4 and 5 show that the liquid crystal display device of the present invention exhibits excellent viewing angle characteristics and a small difference in viewing angle characteristics due to changes in humidity conditions as compared with the comparative liquid crystal display device. The thing is clear.

[0107]

According to the present invention, it is possible to provide an optical film which has sufficient viewing angle characteristics and is hardly affected by an external environment, a method for manufacturing the optical film, a polarizing plate film and a liquid crystal display device. done.

Continued on the front page F-term (reference) 2H049 BA02 BB33 BC03 BC09 BC22 2H091 FA08X FA08Z FA11X FA11Z FC08 GA16 KA02 LA04 LA06 LA19 4F071 AA09 AA15 AA20 AA21 AA22 AA25 AA28 AA29 AA43 AA50 AA51 BC26 BCBA

Claims (19)

[Claims] 1. A retardation value (Rt) in a thickness direction defined by the following general formula (1): 23 ° C., 55% RH
In the formula, 50 ≦ Rt ≦ 300 nm and 23
An optical film, wherein a difference between Rt values at 20 ° C. and 20% RH and at 23 ° C. and 80% RH is 40 or less. General formula (1) Rt value = ((Nx + Ny) / 2−Nz) × d [where Nx is the refractive index of the film in a direction parallel to the film forming direction, and Ny is the direction perpendicular to the film forming direction. Nz represents the refractive index of the film in the thickness direction, and d represents the thickness (nm) of the film. ] 2. In the general formula (1), at 23 ° C., 5 ° C.
An optical film, wherein the Rt value at 5% RH is 50 ≦ Rt ≦ 300 nm, and the equilibrium water content at 23 ° C. and 55% RH is 6% or less. 3. In the general formula (1), at 23.degree.
An optical film having an Rt value at 5% RH of 50 ≦ Rt ≦ 300 nm and containing a plasticizer. 4. In the general formula (1), at 23.degree.
An optical film, wherein the Rt value at 5% RH is 50 ≦ Rt ≦ 300 nm, and the transmittance at 380 nm is 60% or less. 5. In the general formula (1), at 23 ° C., 5
An optical film, wherein the Rt value at 5% RH is 50 ≦ Rt ≦ 300 nm, and the fluctuation width of the Rt value within 1 m square is 5 nm or less. 6. In the general formula (1), at 23 ° C., 5
An optical film, characterized in that the Rt value at 5% RH is 50 ≦ Rt ≦ 300 nm and contains a matting agent. 7. The in-plane retardation value (Ro) defined by the following general formula (2) is | Ro
| ≦ 30 nm, and the angle of the slow axis of the film is | slow axis angle | ≦ 30 °.
7. The optical film according to any one of claims 6 to 6. General formula (2) Ro value = (Nx−Ny) × d [wherein, Nx, Ny and d are each the general formula (1)
Is synonymous with ] 8. The film according to claim 1, wherein a lower fatty acid ester of cellulose is contained as a main component of the film.
8. The optical film according to any one of items 7 to 7. 9. The optical film according to claim 1, wherein the film has a thickness of 75 to 250 μm. 10. The optical film according to claim 1, wherein the film is formed by uniaxial stretching. 11. The optical film according to claim 1, wherein the optical film is a polarizing plate protective film for a liquid crystal display. 12. The method for producing the optical film according to claim 1, wherein the optical film is cast from the belt or the drum when the optical film is cast on a belt or a drum. A method for producing an optical film, wherein a difference obtained by subtracting an amount of residual solvent at the time of winding after forming the optical film from an amount of residual solvent at the time of peeling the film is 10% or more. 13. In producing the optical film according to any one of claims 1 to 11, when casting the optical film on a belt or drum, the optical film is removed from the belt or drum. A method for producing an optical film, wherein a state of (amount of residual solvent in the optical film) ≧ 10% is maintained for 1 minute or more from immediately after the peeling until the film is wound into a roll. . 14. In producing the optical film according to any one of claims 1 to 11, when casting the optical film on a belt or a drum, when the optical film is peeled off from the belt or the drum. 10% to 120
%. A method for producing an optical film, wherein the method is adjusted to%. 15. In producing the optical film according to any one of claims 1 to 11, drying after the film is formed until the optical film is separated from a belt or a drum and wound up into a roll. In the process, the highest temperature of the drying step is maintained at or below the glass transition temperature of the optical film. 16. The optical film according to claim 1, which is used for a vertical alignment type liquid crystal display device. 17. The polarizing plate film having a polarizing plate on the optical film according to claim 1, wherein an equilibrium water content in the optical film is 6% or less. Polarizing plate film. 18. A liquid crystal display device comprising a polarizing plate and a liquid crystal cell, wherein the polarizing plate film according to claim 17 is provided on at least one side of the liquid crystal cell. 19. A liquid crystal display device comprising a polarizing plate and a liquid crystal cell, wherein the liquid crystal cell has at least one vertical alignment type liquid crystal, and the polarizing plate is any one of claims 1 to 11. A liquid crystal display device, which is the optical film according to claim 1.