JP2000241628A - Phase difference film and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase difference film of large width having optical performance applicable of a large-sized liquid crystal display device and capable of taking multiple pieces, and to be advantageous in cost. SOLUTION: This phase difference film formed by drawing a thermoplastic resin film has shift of a retardation phase axis to the drawing direction in the cross direction within ±0.7 degree, and/or its dispersion of retardation in the width direction is 10 nm or less and the film width is 700 mm or more. This manufacturing method includes a drawing process of drawing at a temperature set higher than drawing temperature by 2 deg.C or more where the difference between the maximum value and the minimum value of retardation in the width direction of the phase difference film is minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a retardation film and a method for producing the same, and more particularly, to a retardation film used as a retardation compensation film in a large-sized liquid crystal display device and the like, and a method for producing the same.

[0002]

Hitherto, a retardation film has been used as an anti-glare material for a CRT of a television, or as a material for preventing coloring of a liquid crystal display element and improving contrast. In recent years, the light and thin characteristics of this retardation film have been evaluated, and the development of large-sized liquid crystal display devices has been actively promoted. ing. Further, from the viewpoint of productivity, a retardation film having a wide width is expected.

On the other hand, strict uniformity is required to maintain the compensation state of the liquid crystal cell uniformly in the display plane. However, when attempting to produce a wide retardation film using conventional techniques, variations in the physical properties of the film before stretching, stretching conditions, and the like become large, causing unstable color compensation and uneven local contrast. There was a problem such as doing. For this reason, the quality is not stable not only between manufacturing lots but also within a manufacturing lot, and a practically wide retardation film has not been obtained. In particular, since the variation in the width direction is large, even in a single retardation film cut out according to the size of the liquid crystal display element, there is a problem that optical characteristics are partially different and uniform screen display cannot be performed. The problem that the optical characteristics differ between the obtained retardation films has become remarkable.

Accordingly, the present inventor has proposed a relatively wide retardation film which has sufficient characteristics which can be used for a large-sized liquid crystal display device and the like, and which is capable of sorting a large number of pieces and which is advantageous in cost. As a result of intensive studies on the method for producing the same, the present invention has been achieved.

[0005]

The gist of the retardation film according to the present invention is a retardation film having a width of 700 mm or more formed by stretching a thermoplastic resin film. The deviation of the slow axis from the stretching direction is within ± 0.7 degrees over the entire width of the film.

Another feature of the retardation film according to the present invention is that the deviation of the slow axis with respect to the stretching direction formed by stretching the thermoplastic resin film is ± 0.7 degrees over the entire width of the film. And the difference between the maximum value and the minimum value of the retardation in the width direction is 10
nm or less.

[0007] The gist of the method for producing a retardation film according to the present invention is a method for producing a retardation film having a film width of 700 mm or more. A stretching step of stretching at a temperature 2 ° C. or more higher than the stretching temperature at which the difference between the maximum value and the minimum value of the dating is minimized, wherein the deviation of the slow axis with respect to the stretching direction is ± 0.7 over the entire width of the film.
To produce a film that is within a degree.

Another feature of the method for producing a retardation film according to the present invention is that the film width is 700 m.
m or more, wherein the thermoplastic resin film is stretched at a temperature 2 ° C. or more higher than the stretching temperature at which the difference between the maximum value and the minimum value of the retardation in the width direction of the film is minimized. And then passing the film through a temperature control zone in which a temperature distribution is formed in association with the variation of the retardation in the width direction of the film, wherein the deviation of the slow axis with respect to the stretching direction is ± 0. 7 degrees or less, and the difference between the maximum value and the minimum value of the retardation in the width direction is 10 mn.
The following is to produce a film.

Further, a step of selectively heating a portion having a large retardation at a high temperature by a plurality of heat sources arranged in a heating furnace, while observing a variation in retardation in the width direction of the thermoplastic resin film. Is to include.

[0010]

Next, embodiments of the retardation film according to the present invention will be described in detail. The retardation film according to the present invention is manufactured by, for example, forming a film using a thermoplastic resin as a material, followed by a stretching step and an annealing step.

The thermoplastic resin which can be used in the present invention is variously selected from the viewpoints of light transmittance, heat resistance, optical homogeneity, optical compatibility with a liquid crystal cell, workability, and the like. Basically, there is no limitation as long as it conforms to these characteristics. For example, polycarbonate resin, cellulose resin, polyarylate resin, vinyl chloride resin, acrylonitrile resin, styrene resin, polyphenylene oxide resin, polysulfone resin, polyester resin, polyolefin resin,
A polyamide resin or the like can be used. Further, a liquid crystalline polymer can be applied. Among them, the polycarbonate resin is a material having a high intrinsic birefringence and excellent stretchability, and can be used particularly in the present invention.

The method for forming the thermoplastic resin film is not particularly limited, and a melt extrusion method, a calendering method, or the like may be used, but a solution casting method is preferably used.

Generally, when a deformation stress is applied in the film forming process,
As the molecular orientation advances, the birefringence of the film increases. Since the variation in the birefringence increases with the increase in the birefringence, the film before stretching preferably has the lowest possible birefringence. From this viewpoint, the solution casting method can form a film with a relatively small stress in a low viscosity state, so that a film having a small birefringence can be formed as compared with other film forming methods.

In the stretching step of the formed thermoplastic resin film, various stretching methods known to those skilled in the art can be applied, for example, a transverse uniaxial stretching method using a tenter, a rolling stretching method using a calender. And a longitudinal uniaxial stretching method of stretching between rolls having different speeds. Among these, the longitudinal uniaxial stretching method in which stretching is performed between rolls can be preferably used because simple equipment can be used and stretching with good productivity can be performed.

In general, the degree of uniformity of the retardation film obtained by stretching with respect to the optical properties depends on the degree of uniformity of the film before stretching and the uniformity of the stretching conditions, and has a synergistic effect. That is, the orientation unevenness and thickness unevenness of the film before stretching are as follows.
The expansion due to the tension applied in the stretching step, and the unevenness in the tension during the stretching causes a new alignment unevenness, thereby increasing the non-uniformity of the optical properties of the formed retardation film.

In the stretching step, the shift of the slow axis with respect to the stretching direction of the resin film must be minimized.
For this reason, it is necessary that stress in a direction other than the stretching direction of the film is not applied to the film.

In the stretching step, the temperature in the furnace is set higher than the optimum temperature in the furnace to minimize the difference between the maximum value and the minimum value of the retardation in the width direction, thereby reducing the shift of the slow axis. can do.

Here, the retardation is the product of the film thickness and the birefringence. This variation in retardation is affected by uneven thickness and birefringence.Thus, the uniformity of the temperature distribution and the uniformity of the tension in the film forming process and the stretching process are improved, and the unevenness of the thickness is improved. It is necessary to eliminate the occurrence of unevenness and the variation of the birefringence. The thickness unevenness refers to a thickness variation, and particularly affects a variation in retardation due to a thickness variation in a width direction. Further, the variation in the birefringence directly affects the numerical value of the retardation.

The temperature control is performed in the stretching step and / or the annealing step. Specifically, the temperature is controlled by adjusting the heat source. Although the heat source is not particularly limited, it can be preferably used from the viewpoint of forming an appropriate temperature distribution in the width direction, such as an infrared panel heater and a hot air generator. Among them, the small infrared panel heater is particularly preferable because it can be divided so as to obtain an appropriate temperature distribution in the width direction. These heat sources may be installed in a furnace for stretching or in a heating furnace provided independently of the stretching furnace.

The uniformity of the tension is adjusted by adjusting the tension in the stretching step, for example, by increasing the precision of the parallelism between the stretching rolls.

In the present invention, “retardation” and “slow axis” are measured on a film that has been subjected to the above-mentioned stretching step or annealing step as needed or constantly, and the results are reflected in the manufacturing step while reflecting the results in the manufacturing process. The production of such a retardation film is performed. These measurements are performed by a polarizing microscope, a spectrophotometer, a birefringence meter or the like based on a standard method. Specifically, 10 cm over the entire width of the retardation film
The measurement is performed at the pitch, and the average value and the variation of the measured values are obtained.
The variation of the retardation is represented by the difference between the maximum value and the minimum value in the width direction, and the variation of the slow axis is represented by the difference between the maximum value and the minimum value of the deviation angle from the film stretching direction.

The variation in the slow axis of the retardation film of the present invention measured as described above is, specifically, ± 0.
Within 7 degrees, especially within ± 0.5 degrees. If the dispersion of the slow axis is larger than ± 0.7 degrees, the color compensation becomes insufficient or the viewing angle improvement effect cannot be sufficiently obtained in each of the above-mentioned applications, and the contrast unevenness due to a local change in retardation. This is not preferable because of problems such as the occurrence of

The difference between the maximum value and the minimum value in the width direction of the retardation of the retardation film according to the present invention is 1
It is preferably 0 nm or less, more preferably 6 nm or less.
If the difference between the maximum value and the minimum value of the retardation is larger than 10 nm, the color compensation becomes insufficient. For example, a monochrome liquid crystal display element is partially colored. Also, it is difficult to express a clear color over the entire screen with a color liquid crystal display element. Furthermore, in the case of cutting out a small number of pieces of retardation film in the width direction, one having a different average retardation value is obtained, and there is a problem that the quality is not constant.

In order to make the dispersion of the retardation, which is the above index, within the above range, the temperature in the furnace in which the thermoplastic resin film is stretched in the production process of the retardation film is adjusted to the maximum retardation in the width direction of the film. It is preferable that the temperature be 2 ° C. or more higher than the stretching temperature at which the difference between the value and the minimum value becomes the minimum. Specifically, the difference between the maximum value and the minimum value of the retardation in the width direction of the film is measured in the heating step, the minimum stretching temperature is specified, and the furnace temperature is set to 2 ° C. or more from the stretching temperature. When set, the dispersion of the retardation becomes smaller and more stable.

The stretching temperature at which the difference between the maximum value and the minimum value of the retardation in the width direction of the film becomes the minimum is 2 degrees or more.
When the temperature in the furnace is not less than ℃, the stress applied to the film at the time of stretching is reduced due to an increase in the furnace temperature in the stretching process, and at the same time the variation is also reduced. Can be obtained within ± 0.7 degrees, particularly ± 0.5 degrees.

Specifically, the furnace temperature to be raised from the stretching temperature is from 2 ° C. to about 20 ° C. from the stretching temperature, and specifically, to a temperature at which the properties of the thermoplastic resin film used in the present invention are not lost. It is possible to raise.

However, it is not enough to set the in-furnace temperature for stretching as described above to a temperature higher than the stretching temperature at which the difference between the maximum value and the minimum value of the retardation in the width direction of the film is at least 2 ° C. or more. In some cases, the variation in the retardation in the width direction may be 10 nm or more.

Therefore, a retardation film in which the shift of the slow axis with respect to the stretching direction is within ± 0.7 ° over the entire width of the film and the difference between the maximum value and the minimum value of the retardation in the width direction is 10 nm or less. In order to obtain, the temperature in the furnace for performing stretching to a temperature 2 ° C. or more higher than the stretching temperature at which the difference between the maximum value and the minimum value of the retardation in the width direction of the film is minimized, and further after the stretching step In the annealing step, the film is preferably passed through a temperature control zone which has a temperature distribution linked to the variation of the retardation in the width direction of the film. In this temperature control zone, it is possible to minimize variations in retardation by passing through a temperature control zone such as selectively heating a large retardation portion or selectively cooling a small retardation portion. It is. The means for interlocking with the fluctuation of the retardation is not limited, either automatically or manually.

By increasing the stretching temperature by 2 ° C. or more as described above, the variation of the slow axis with respect to the stretching direction can be reduced by ±
0.7 degrees or less, and by providing a temperature control zone in which a temperature distribution is formed in conjunction with the variation of retardation by a temperature control zone arranged in a stretching furnace or another annealing furnace. As a result, a retardation film in which the difference between the maximum value and the minimum value of the retardation in the width direction is 10 nm or less as a result of low retardation in a heated portion and high retardation in a cooled portion. Becomes possible.

In the case of heating, a heat source arranged in a drawing furnace or an annealing furnace is provided with, for example, a plurality or rows of infrared panel heaters in the width direction in the latter half of the drawing furnace. Is changed by the measured value of. In the case of cooling, specifically, a cooling plate capable of controlling the temperature in the width direction of the film is disposed in a stretching furnace or an annealing furnace, and a temperature distribution is formed in conjunction with the retardation distribution.

The retardation film produced as described above further improves the adhesiveness of the film surface.
For example, surface treatment such as corona treatment, plasma treatment, and coupling treatment may be performed.

The retardation film according to the present invention obtained as described above is a retardation film suitable for the purpose of preventing coloration of the liquid crystal display element, increasing the contrast, and improving the viewing angle. , 700 mm or more, preferably 1000 mm or more. Accordingly, it is possible to obtain a retardation film corresponding to an increase in the size of the apparatus, and it is possible to reduce the cost by increasing the number of film cuts in the width direction.

In addition, the present invention does not depart from the gist of the present invention, and the raw material of the retardation film, the film forming method, the stretching method,
The characteristics and the like of the retardation film can be implemented in various modified and modified forms based on the knowledge of those skilled in the art.

[0034]

EXAMPLES Examples of the present invention will be described in detail below, but are not limited thereto.

[0035]

Example 1 Using methylene chloride as a solvent, polycarbonate (manufactured by Teijin Chemicals Limited, product number Panlite C-140) was used.
A 15% solution of (1) was prepared, and the solution was cast to a width of 130.
A 0 mm film was formed. In order to reduce variations in thickness, particularly variations in the width direction, attention was paid particularly to the drying temperature and the flow of air in film formation. Result, average thickness 6
A film having a thickness of 6 μm and a variation in the width direction of 1.5 μm was obtained. The end of the film is cut off, the width is set to 1200 mm, the average temperature in the furnace for stretching is determined, and the optimum stretching temperature at which the variation in retardation in the width direction is minimized is determined. Go 1000mm wide
Was obtained. At this time, the average temperature in the furnace of the stretching section was 156 ° C.

When the displacement of the slow axis with respect to the stretching direction of the obtained retardation film was measured at a pitch of 10 cm in the width direction, +0.2, +0.4, +0.3, +0.1, -0.
2, -0.4, -0.5, -0.6, -0.4, -0.
2 degrees, and the range of displacement of the slow axis with respect to the stretching direction is +
0.4 to -0.6 degrees.

[0037]

Example 2 An infrared panel heater divided into 10 sections in the width direction was placed in a furnace of a stretching machine, and 160, 16 in order from the end.
0, 170, 175, 180, 180, 175, 17
A retardation film was manufactured under the same conditions as in the first example except that the temperature was set to 0, 160, and 160 ° C. When the retardation of the obtained retardation film was measured at a pitch of 10 cm in the width direction, 421, 423, 424, 42
5, 427, 427, 425, 424, 422, 423
nm, and the dispersion of the retardation was 6 nm. Further, when the displacement of the slow axis with respect to the stretching direction of this retardation film was measured at a pitch of 10 cm in the width direction, it was found that +0.3, +0.4, +0.3, +0.1, -0.0.
2, -0.4, -0.5, -0.6, -0.5, -0.
2 degrees, and the range of displacement of the slow axis with respect to the stretching direction is +
0.4 to -0.6 degrees. From this retardation film 2
When cut out like a 5 × 20 cm chip and used for an STN type liquid crystal display device, complete black and white display was obtained in any of the display devices.

[0038]

Comparative Example 1 A retardation film was produced in the same manner as in the first example, except that the stretching was performed at the optimum stretching temperature at which the variation in retardation in the width direction was minimized. At this time, the average temperature in the furnace of the stretching section was 154 ° C. The retardation of the obtained retardation film was measured at a pitch of 10 cm in the width direction.
7, 425, 426, 426, 425, 422, 42
4, 424 nm, and the variation in retardation was 7 nm. Also, when the displacement of the slow axis with respect to the stretching direction of this retardation film was measured at a pitch of 10 cm in the width direction, it was found that +0.4, +0.6, +0.3, +0.1,
-0.2, -0.5, -0.7, -0.8, -0.9,
−0.5 degrees, and the range of the shift of the slow axis with respect to the stretching direction was +0.6 to −0.9 degrees.

[0039]

According to the wide retardation film of the present invention, the deviation of the slow axis with respect to the stretching direction in the width direction is ± 10%.
Since it is within 0.7 degrees, sufficient color compensation and high contrast can be secured over the entire screen even in a large liquid crystal display device, and a large number of cutouts in the width direction are used for the liquid crystal display device. In each case, the effect of obtaining the same color tone and contrast can be obtained.

Further, according to the method for producing a retardation film according to the present invention, even if the film has a wide width of 700 mm or more, the deviation of the slow axis with respect to the stretching direction in the width direction is ±.
It is possible to obtain a uniform film having a retardation of 0.7 nm or less and a variation in retardation in the width direction of 10 nm or less. The retardation film according to the present invention can be suitably used for a large-sized optical device such as a liquid crystal display element, and can provide a wide-width retardation film that can be sorted in the width direction and is advantageous in cost. More specifically, it can contribute to the purpose of achromatism in a liquid crystal display device, and further to the improvement of the viewing angle, the improvement of the brightness of a polarizing plate, and the like.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI theme coat ゛ (reference) B29L 11:00 F term (reference) 2H049 BA06 BB42 BC03 BC22 4F071 AA09 AA22 AA24 AA34 AA48 AA50 AA51 AA64 AH12 BB07 BC01 BC17 4F210 AA00 AA28 AE01 AG01 AR06 QA03 QC02 QD13 QD16 QG01 QG18 QW09

Claims (5)

[Claims] 1. A retardation film formed by stretching a thermoplastic resin film and having a width of 700 mm or more, wherein a shift of a slow axis with respect to a stretching direction is within ± 0.7 degrees over the entire width of the film. A retardation film characterized by the following. 2. A retardation film formed by stretching a thermoplastic resin film and having a width of 700 mm or more, wherein a shift of a slow axis with respect to a stretching direction is within ± 0.7 degrees over the entire width of the film, A retardation film wherein the difference between the maximum value and the minimum value of the retardation in the width direction is 10 nm or less. 3. A method for producing a retardation film having a film width of 700 mm or more, wherein a stretching temperature at which a difference between a maximum value and a minimum value of retardation in a width direction of the thermoplastic resin film is minimized. A retardation film comprising a stretching step of stretching at a temperature higher than 2 ° C. or more, wherein a shift of the slow axis in the stretching direction is within ± 0.7 ° over the entire width of the film. Production method. 4. A method for producing a retardation film having a film width of 700 mm or more, wherein a stretching temperature at which a difference between a maximum value and a minimum value of retardation in the width direction of the thermoplastic resin film is minimized. Stretching at a temperature higher than 2 ° C. or higher, and thereafter, passing the film through a temperature control zone in which a temperature distribution is formed in association with a change in retardation in the width direction of the film, wherein the slow axis of the film in the stretching direction The deviation is ± 0.
A method for producing a retardation film, comprising producing a film having a thickness of 7 degrees or less and a difference between a maximum value and a minimum value of retardation in a width direction of the film is 10 mn or less. 5. A step of selectively heating a portion having a large retardation at a high temperature by a plurality of heat sources disposed in a heating furnace while observing a variation in retardation in a width direction of the thermoplastic resin film. The method for producing a retardation film according to claim 4, comprising: