JPH09218307A - Production of phase difference film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control fluctuation in the retardation and to obtain uniform retardation by measuring the phase difference obtd. in the production process and sending the obtd. data by the measurement to a stretching process with fast response for feedback. SOLUTION: A transparent thermoplastic resin film having >70% transmittance for light such as polycarbonate is stretched in one direction along the longitudinal direction in a stretching zone between a feeding roll and a stretching roll, and then the phase difference on plural points in the width direction of the thermoplastic resin film after passed over the stretching roll is measured. The phase difference is represented by the retardation for 590nm wavelength. The phase difference data on plural points obtd. by the measurement are compared with preliminarily designed phase difference data corresponding to the length of the stretching zone. Based on the information of comparison, the stretching length to by corrected is calculated and the geometric relation between the feeding roll and the tension roll is changed to correct the stretching zone length so that the phase difference data measured all over the width of the stretched thermoplastic resin film is controlled within a specified range.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a retardation film.

[0002]

2. Description of the Related Art A retardation film made of a thermoplastic resin film or sheet having optical transparency and birefringence is widely used as an antiglare material and as a retardation compensator in an F-STN type liquid crystal display device. ing. A retardation plate made of a thermoplastic resin film utilizes birefringence caused by a difference in refractive index between a stretching direction and a direction orthogonal to the stretching direction due to molecular orientation by stretching the polymer film.

As a method for producing a retardation film of this type, a method for producing a thermoplastic resin film such as a cellulose resin, a polyvinyl chloride resin, a polycarbonate resin, an acrylonitrile resin, a polystyrene resin or a polyolefin resin by uniaxial stretching is already known. It is known that a material having a high intrinsic birefringence can be imparted with birefringence by uniaxial stretching.

The retardation film is used for compensating the retardation of the liquid crystal display cell in the F-STN type liquid crystal display device. The retardation compensation performance, which is one of the optical characteristics, is called the retardation value, and is represented by the product of the birefringence value and the film thickness, and the required value varies depending on the purpose. As a prior art relating to a method for producing a retardation film, JP-A-2-89007 discloses an alignment parameter of 0.01 by a solvent casting method with relatively little alignment.
By using the following polymer film and uniaxially stretching under a uniform temperature of conditions selected from the range of glass transition temperature Tg to Tg + 30 ° C by tenter stretching, retardation variation of retardation value within 1.0% is standard deviation. Manufacturing a plate is disclosed.

The retardation film as the retardation compensator is
Various improvements are desired with the expansion of applications of liquid crystal display devices, and it is expected to be used for the purpose of removing coloring and improving contrast of black and white liquid crystal displays. However, when a commonly available thermoplastic resin film is stretched by a known method such as transverse uniaxial stretching by a tenter method or longitudinal uniaxial stretching performed at a peripheral speed difference between rolls, the problem of uneven coloring and uneven contrast remains, and it is still sufficient. The performance is not satisfactory.

The above-mentioned conventional longitudinal uniaxial stretching is carried out in the stretching section of the feed roll and the tension roll, but both rolls are fixed in parallel. Therefore, due to the thickness deviation in the width direction of the thermoplastic resin film before stretching and the temperature deviation peculiar to the equipment at the time of stretching, it is inevitable that retardation unevenness occurs in the obtained retardation film, which is a nonstandard product. The production efficiency was lowered due to the occurrence of. Further, uneven thickness in the lengthwise direction of the thermoplastic resin film before stretching and fluctuation of the temperature of the thermoplastic resin film during stretching also promote the occurrence of retardation unevenness of the obtained retardation film.

Conventionally, the factors for the unevenness in phase difference have been adjusted mainly by the stretching temperature. However, for example, even if the stretching temperature is adjusted by setting a temperature gradient or spot adjustment, the thermoplastic resin is stretched. It was extremely difficult to finely adjust the unevenness of the film thickness and the adjusted stretching temperature individually, and the response speed was very slow. As a result of diligent study of the above problems, the present inventor has made the stretching section length of the conventionally fixed feed roll and tension roll variable, and changes its position based on the phase difference data measured in the process. As a result, it has been found that the response speed is extremely fast and the retardation in the width direction of the obtained thermoplastic resin film can be uniformly controlled, and the present invention has been completed.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and its object is to:
By measuring the data of the retardation obtained in the process, by feeding back the measured data to the stretching process at a fast response speed, the variation of the retardation value is controlled, and a high quality retardation film having a uniform retardation value is obtained. It is to provide a manufacturing method.

[0009]

MEANS FOR SOLVING THE PROBLEMS The present invention comprises means for longitudinally uniaxially stretching a thermoplastic resin film in a stretching section between a feed roll and a tension roll, and a width direction of the thermoplastic resin film passing through the tension roll. Means for measuring the phase difference of a plurality of points, comparing the measurement data of the phase difference of the plurality of points with the setting data of the phase difference provided corresponding to the stretching section length,
Means for calculating a modified stretch length based on the comparison information,
A gist of a method for producing a retardation film is characterized by having means for changing a positional relationship between a feed roll and a tension roll for realizing the modified stretched section length.

The thermoplastic resin film used in the production method of the present invention is not particularly limited as long as it is a substantially transparent film having a light transmittance of 70% or more. For example, polycarbonate, polysulfone, Examples thereof include polyarylate, polyether sulfone, polyphenyl sulfide, polyphenylene oxide, polyallyl sulfone, polyamide imide, polyimide, polystyrene, polyolefin, polyacrylonitrile and cellulose.

A retardation value of 590 nm is used for the retardation. Further, the means for measuring the phase difference at the plurality of points, the retardation value of 590 nm in the width direction of the thermoplastic resin film that has passed through the tension roll, quickly,
Moreover, it is not particularly limited as long as it can be accurately measured. Further, the number of measurement points measured in the width direction is appropriately set depending on the process capability of the manufacturing method.

The phase difference is measured at the start of the process and at regular and irregular intervals, but the subsequent calculation is performed only when the retardation value at 590 nm deviates from the preset standard value. . The means for comparing the measured data of the phase difference with the setting data of the phase difference provided corresponding to the stretched section length and calculating the corrected stretched section length based on the comparison information is not particularly limited. In order to perform the above calculation quickly and accurately, the same process control microcomputer is preferably used.

The method for calculating the corrected stretched section length using the retardation measurement data is a method in which the retardation measurement data over the entire width of the stretched thermoplastic resin film quickly falls within the standard value. Although not particularly limited, for example, the retardation values of the plurality of points of 590 nm are linearly approximated by the least squares method, and a reference straight line (in a plane including the axes of both rolls of the tension roll with respect to the feed roll) It is a straight line formed by the reference value of the retardation value of 590 nm stretched under the same conditions, and does not necessarily indicate that the feed roll and the pull roll are present in parallel. 590
The method of calculating the correction angle of the feed roll and the tension roll according to a preset value of 590 nm retardation value / stretching section length conversion for the slope of the retardation value of nm is rapid and accurate. It is preferably used from the viewpoint of.

The method for calculating the corrected stretched section length and the corrected angle using the above measured data of the phase difference is a method which has already been empirically obtained, and the amount of some solvent remaining in the stretched thermoplastic resin film during film formation is already obtained. The modified stretch length is calculated by the conversion count which varies depending on the amount. Further, the correction angles of the feed roll and the pull roll are calculated from the corrected stretching section length.

The method of changing the positional relationship between the feed roll and the tension roll for realizing the modified stretch length may be to change the position of the feed roll.
The position of the pulling roll may be changed. or,
The means for changing the position of the roll is not particularly limited, and examples thereof include a position changing device using a pneumatic cylinder such as hydraulic pressure or air, a servo motor, or the like.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to Examples. Example 1 A polycarbonate film having a width of 800 mm and a thickness of 80 μm was stretched at a stretch length of 500 mm at a stretching temperature of 1
590 nm of the stretched polycarbonate film immediately after passing 1.3 times at 60 ° C. and passing through a pulling roll
Was measured at 160 points in the width direction, the retardation value was transmitted to a process control microcomputer, and the measured value was linearly approximated by the least squares method. The retardation value was 10 nm / m. There was a tilt from the standard setting. Then, the inclination from the reference setting of the stretching section length corresponding to the retardation value 10 nm / m having the inclination from the reference setting is calculated, and in the plane including the axis of both rolls of the tension roll with respect to the feed roll. A tilt of 1.2 degrees was calculated, a signal based on the calculated data was transmitted to the tension roll position changing means, the position was changed by the tilt of 1.2 degrees, and the drawing section was stretched with the corrected stretching section length. The inclination from the standard setting of the above retardation values at 160 points in the width direction measured for the uniaxially stretched polycarbonate film obtained with the corrected stretched section length was reduced from 10 nm / m to 3 nm / m, There was no product that deviated from the value, and when this stretched film was used as a retardation plate for liquid crystal devices, the desired clear liquid crystal image was obtained without uneven coloring or uneven contrast.

Example 2 A uniaxially stretched polycarbonate film was produced under the same conditions as in Example 1. The slope of the retardation value obtained from the data obtained by measuring 160 points of the retardation value of 590 nm of the uniaxially stretched polycarbonate film immediately after passing through the tension roll at the time of start was 8 nm / m. The inclination of the corresponding stretch section length from the standard setting was calculated to be 1.0 degree, the position of the tension roll was changed based on the calculated data, and a uniaxially stretched polycarbonate film was produced with the corrected stretch section length. The inclination of the retardation value of the obtained uniaxially stretched polycarbonate film is 8 nm.
/ M to 4 nm / m, and there was no product that was out of the standard value.

[Comparative Example 1] The polycarbonate film of Example 1 was prepared in the same manner as in Example 1 except that the stretched section length was 500 m.
m, stretched 1.3 times at a stretching temperature of 160 ° C., and immediately after passing through the pulling roll, the phase difference in the width direction of the thermoplastic resin film passing through the pulling roll was measured, and spot heating was performed based on the measurement data. A uniaxially stretched polycarbonate film was produced by a usual means for adjusting the stretching temperature including. 5 of the obtained uniaxially stretched polycarbonate film
The retardation value at 90 nm was measured at 160 points in the width direction of the film. The retardation value obtained as a result was 425 nm ± 16 nm. When this stretched film was used as a retardation plate for a liquid crystal device, there was uneven coloring and contrast, and a clear liquid crystal image could not be obtained.

[0019]

The method for producing a retardation film of the present invention comprises:
As mentioned above, the length of the stretch section of the feed roll and the tension roll is variable, and by changing the position based on the phase difference data measured in the process, the response speed is also extremely fast,
Since the retardation in the width direction of the obtained thermoplastic resin film can be uniformly controlled, the dispersion of the retardation value is controlled to produce a high quality retardation film having a uniform retardation value. .

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Claims (1)

[Claims] 1. A means for longitudinally uniaxially stretching a thermoplastic resin film in a stretching section between a feed roll and a tension roll, and measuring the phase difference at a plurality of points in the width direction of the thermoplastic resin film which has passed through the tension roll. Means for comparing the measured data of the phase difference at the plurality of points with the setting data for the phase difference provided corresponding to the stretched section length, and calculating a corrected stretched section length based on the comparison information; A method for producing a retardation film, comprising: a means for changing a positional relationship between a feed roll and a tension roll for realizing a stretched section length.