JPH11305038A - Birefringent film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a birefringent film which has small variances in phase difference value and also has phase difference compensation effect and field angle expansion effect. SOLUTION: This film is obtained by giving a shrinkage force to a drawn film having a 0.30 wt.% or less difference in the presence amount of a solvent or plasticizer, among blocks obtained by dividing the film equally into three along the width. A superior Z-alignment coefficient is given by equally distributing the thickness-directional alignment of the film. The variance in phase difference value is made small and the superior phase difference compensation effect and field angle expansion effect are imparted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a birefringent film used for an electro-optical display device represented by a liquid crystal display device.

2. Description of the Related Art In recent years, a liquid crystal display device having a feature of being capable of providing a large screen and being lightweight and thin has been increasingly used as a display element in a portable personal computer, word processor, monitor and the like.

A conventional liquid crystal display device employs a method of controlling light by using an optical anisotropy of a liquid crystal material to generate an alignment upon application of an electric field. However, simply using this method is not sufficient. On the other hand, the liquid crystal display device has a problem that the display becomes colored due to birefringence by liquid crystal molecules and the display is colored.

As a method of avoiding this phenomenon and compensating for birefringence of liquid crystal molecules, a retardation compensation film composed of a stretched polymer film is interposed between a liquid crystal cell and a polarizing plate.
Methods have been proposed to prevent coloration of the display, and most commercially available STN-type displays are produced with this construction.

[0004] However, the STN type display having the above structure has a problem that a display color is inverted or a display light amount is reduced depending on an angle at which the screen is viewed, so that a large number of persons view the same display screen at a time. Was difficult.

[0005] In order to solve this problem, there has been proposed a method of widening the viewing angle by using a field expansion film.
Examples of such a field-of-view expanding film include a so-called microlens sheet provided with fine lens-shaped depressions, and a birefringent film in which a group of molecules oriented in a plane direction and a group of molecules oriented in a thickness direction are mixed. JP-A-5-157
911) and the like.

In the birefringent film, the refractive index in the film is defined as a refractive index nx in the direction of the orthogonal axis, and a refractive index n perpendicular thereto.
y, if the refractive index in the thickness direction is nz, then nx> ny,
(Nx-nz) / (nx-ny) = Nz (Nz: Z orientation coefficient), where 0 <Nz <1. Theoretically, birefringence phase difference due to liquid crystal molecules is compensated. However, it has an effect of widening an angle generally called a viewing angle, which allows an observer to observe the display with good contrast.

As a method for producing the above birefringent film,
The extruded thermoplastic resin is sliced to obtain a sheet in which molecules are arranged in the thickness direction, and the sheet is stretched. Alternatively, a production method has been proposed in which a shrinkable film is attached to both surfaces to impart a shrink force in a direction perpendicular to the stretching direction (Japanese Patent Application Laid-Open No. 5-157911).

However, the former method has a major problem in its productivity, so that an inexpensive birefringent film cannot be obtained. In addition, the latter method has no problem as in the former, but has a contraction force. When the temperature at the time of application is low or when the time for applying the contraction force is short, the orientation in the thickness direction may not be sufficient and the visual field enlarging effect may not be exhibited. However, there is a problem in that the phase difference value in the product surface varies, and color unevenness occurs on the display.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in view of the above circumstances, and has a birefringent film having a small variation in retardation value and having an excellent phase difference compensating effect and a wide viewing angle effect. I will provide a.

[0010]

A birefringent film according to the present invention is a birefringent film obtained by applying a shrinkage force under predetermined conditions to a stretched film produced by a predetermined method. The difference between the total amount of the solvent or the plasticizer in each block obtained by dividing the stretched film before the stretching into approximately three equal parts in the thickness direction is 0.30% by weight or less.

First, the stretched film is prepared by dissolving a mixture of a thermoplastic resin and a plasticizer or a thermoplastic resin in a solvent,
A film is obtained by casting this solution, and the obtained film is obtained by uniaxially stretching.

The thermoplastic resin is not particularly limited as long as it has been conventionally used for a birefringent film. For example, a cellulose resin, a vinyl chloride resin,
Thermoplastic resins such as polycarbonate-based resins, acrylonitrile-based resins, olefin-based resins, polysulfone-based resins, and polyethersulfone-based resins are exemplified.

[0013] A plasticizer is added to the above-mentioned thermoplastic resin, if necessary. The plasticizer is not particularly limited as long as it has been conventionally used in the production of a birefringent film. A phthalic acid plasticizer, a phosphoric acid plasticizer, an adipic acid plasticizer, a citric acid plasticizer, a glycolic acid plasticizer, and the like can be applied. Particularly, phthalic acid plasticizers such as diethyl phthalate and dibutyl phthalate can be used. It is suitable.
Further, two or more kinds of these plasticizers may be mixed and applied.

A mixture of the above-mentioned thermoplastic resin and the above-mentioned plasticizer or the above-mentioned thermoplastic resin is dissolved in a solvent capable of dissolving them, and the resulting solution is smoothed using a general-purpose means such as a die coater or a comma coater. It is uniformly cast on a metal belt or film having the same and then dried to evaporate a solvent or a plasticizer component to a certain level to obtain a smooth thermoplastic resin film. Then, the thermoplastic resin film is uniaxially stretched by a general-purpose stretching means at a temperature near the glass transition point of the thermoplastic resin to obtain the stretched film.

[0015] Here, only by drying performed when obtaining the thermoplastic resin film, the total amount of the solvent or the plasticizer increases in the thermoplastic resin film from the surface layer portion to the center portion, Due to the non-uniformity of the total amount of the solvent or the plasticizer, the thermoplastic resin film has a difference in elastic modulus in its thickness direction (the central portion of the thermoplastic resin film has a low elastic modulus. While
The surface layer of the thermoplastic resin film has a high elastic modulus).

When such a stretched film having a difference in elastic modulus in the thickness direction is shrunk by a shrinkable film described later, the resulting birefringent film has a uniform thickness in the thickness direction due to the difference in elasticity. In some cases, a proper orientation cannot be provided, and the Z orientation coefficient may not show a sufficient numerical value.

Therefore, in the present invention, the difference between the total amount of the solvent or the plasticizer in the thickness direction of the stretched film before the application of the shrinkage force is set to a certain value or less, more specifically, the stretched film before the application of the shrinkage force. The total amount of the solvent or plasticizer between the blocks obtained by dividing approximately three in the thickness direction, that is, the total amount of the solvent when no plasticizer is contained, and the solvent and the plasticizer when the plasticizer is contained. 0.30
% By weight, preferably 0.20% by weight or less, and after making the elastic modulus in the thickness direction of the stretched film substantially uniform, a contraction force in a predetermined direction is applied to the stretched film.

A method for reducing the difference in the total amount of the solvent or plasticizer between the blocks obtained by dividing the stretched film into approximately three equal parts in the thickness direction to 0.30% by weight or less is as follows.
Although not particularly limited, for example, a method of irradiating electromagnetic waves such as far infrared rays and microwaves may be used.

Next, a shrinkable film is adhered to one or both sides of the stretched film in which the difference in the total amount of the solvent or plasticizer in the thickness direction is not more than a certain value as described above, and this shrinkable film is stretched by the stretching method. The film is shrunk in a direction perpendicular to the direction, and a contraction force is applied to the stretched film in a direction perpendicular to the stretching direction to obtain a birefringent film.

The shrinkable film is not particularly limited as long as it shrinks in a predetermined direction within a predetermined temperature range. Examples of the shrinkable film include a polycarbonate resin, a polyester resin, a polystyrene resin, and a polyethylene resin.
Examples include a uniaxially stretched film and a biaxially stretched film made of a polypropylene resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, and the like.

The method of attaching the above-mentioned shrinkable film to one or both sides of the above-mentioned stretched film employs a general-purpose means, such as a method utilizing the adhesive force of the stretched film or the shrinkable film itself, and a method of peeling off an adhesive or the like. Any suitable bonding means may be used.

Thereafter, the stretched film having the shrinkable film adhered to one or both sides is heated to shrink the shrinkable film, thereby applying a shrink force acting on the stretched film in a direction perpendicular to the stretching direction. By shrinking this, a birefringent film in which a group of molecules oriented in a plane direction and a group of molecules oriented in a thickness direction are mixed can be obtained.

The difference in the total amount of the solvent or plasticizer between the blocks obtained by substantially equal division in the thickness direction is 0.3
The stretched film having 0% by weight or less has a substantially uniform elastic modulus in the thickness direction, and can apply the shrinkage force applied to the stretched film substantially uniformly in the thickness direction.

Accordingly, the obtained birefringent film has a uniform orientation in the thickness direction, has an excellent Z-orientation coefficient, is excellent in phase difference compensation effect and viewing angle widening effect, and has a variation in in-plane retardation value. Less is. Also, the application of shrinkage force to the stretched film can be performed in a short time and at a low temperature.

[0025]

EXAMPLES (Preparation of Stretched Film) 100 parts by weight of polysulfone resin (trade name "Udel P-3500" manufactured by Teijin Amoco Engineering Plastics Co., Ltd.) and 3 parts by weight of dibutyl phthalate in anisole at a concentration of 40% by weight. It was cast on a chrome-plated smooth steel belt so that the wet thickness was 200 μm, dried at 180 ° C. for 10 minutes, and wound up to obtain a polysulfone resin film. Then, the length of the obtained polysulfone resin film is set to 1.
The film was uniaxially stretched so as to be 5 times. In addition, the thickness of the obtained stretched film was 60 μm. Then, the obtained stretched film is not irradiated with far infrared rays,
Both were illuminated for 0 or 20 minutes.

A portion of each of the stretched film not irradiated with the far infrared ray and the stretched film irradiated with the far infrared ray is sampled, divided into three equal parts in the thickness direction, and dissolved in methylene chloride. Manufacturing G
Using C-14A), the amounts of the remaining anisole and dibutyl phthalate were measured, and the total amount of the remaining anisole and dibutyl phthalate was shown in Table 1.

[0027]

[Table 1]

(Preparation of shrinkable film) Polycarbonate resin (trade name "PANLITE C-1" manufactured by Teijin Chemicals Ltd.)
Prepare a pellet of 400), dissolve it in methylene chloride, form a film by a casting method, uniaxially stretch the obtained film by a tenter stretching machine, and shrink in only a certain direction at about 150 ° C. I got An acrylic pressure-sensitive adhesive was layered on one surface of the shrinkable film to a thickness of 30 μm.

(Examples 1 to 6) The above-mentioned shrinkable film was laminated and integrated on one surface of the stretched film irradiated with far-infrared rays via an acrylic pressure-sensitive adhesive layered on one surface thereof to obtain a laminate. When laminating the shrinkable film on one side of the stretched film, the stretching direction of the stretched film and the shrinking direction of the shrinkable film were set to be orthogonal to each other.

Next, the laminate is kept in a furnace maintained at the temperature shown in Table 2 for the time shown in Table 2 so that the shrinkable film is shrunk in a certain direction. A birefringent film was obtained by applying a shrinking force in a direction perpendicular to the direction.

The Z-orientation coefficient and the in-plane variation of the retardation value of the obtained birefringent film were measured by the following methods, and the results are shown in Table 2.

(Measurement of Z-Orientation Coefficient) The Z-orientation coefficient of the obtained birefringent film was measured using an automatic birefringence meter (trade name “KOBRA-21ADH” manufactured by Oji Scientific Instruments).

(Variation in retardation value) An arbitrary portion of the obtained birefringent film was cut into a square of 50 cm, and an automatic birefringence meter (trade name “KOBRA-21ADH” manufactured by Oji Scientific Instruments) was used.
)), The in-plane retardation value was measured, and the difference between the maximum value and the minimum value was measured as a variation in the retardation value.

[0034]

[Table 2]

(Comparative Examples 1 to 5) A laminate was obtained by laminating and integrating the above-mentioned shrinkable film on one surface of the stretched film which was not irradiated with the far-infrared ray via an acrylic adhesive having one surface thereof layered. . When laminating the shrinkable film on one side of the stretched film, the stretching direction of the stretched film and the shrinking direction of the shrinkable film were set to be orthogonal to each other.

Next, the laminate is kept in a furnace maintained at the temperature shown in Table 3 for the time shown in Table 3 to cause the shrinkable film to shrink in a certain direction and to be stretched into a stretched film in the stretching direction. A birefringent film was obtained by applying a shrinking force in a direction perpendicular to the direction.

The Z-orientation coefficient and in-plane variation of the retardation value of the obtained birefringent film were measured in the same manner as in Example 1. The results are shown in Table 3.

[0038]

[Table 3]

[0039]

The birefringent film of the present invention shrinks to a stretched film in which the difference in the amount of the solvent or plasticizer between the blocks obtained by substantially equally dividing in the thickness direction is 0.30% by weight or less. Since it is obtained by applying a force, the orientation in the thickness direction of the film is uniformly distributed, has an excellent Z-orientation coefficient, has a small variation in retardation value, and has an excellent retardation compensation effect. And a viewing angle expanding effect.

Claims (1)

[Claims] A film is obtained by dissolving a mixture of a thermoplastic resin and a plasticizer or a thermoplastic resin in a solvent, casting the solution, and uniaxially stretching the obtained film. A plane obtained by attaching a shrinkable film to one or both sides, shrinking the shrinkable film in a direction perpendicular to the stretching direction, and applying a shrinking force to the stretched film in a direction orthogonal to the stretching direction. In a birefringent film in which a molecule group oriented in the direction and a molecule group oriented in the thickness direction are mixed, the stretched film before imparting a contraction force in a direction perpendicular to the stretching direction is substantially three or more in the thickness direction. A birefringent film, wherein the difference in the total amount of the solvent or plasticizer between the blocks obtained by division is 0.30% by weight or less.