JPH03235902A - Production of phase difference film - Google Patents

Abstract

PURPOSE:To obtain the phase difference film which is improved in visual sensation characteristic and has good flatness without having the enequalness of stretching by providing a heat relieving area where the temp. ranges from a glass transition temp. to the temp. lower by 10 deg.C than the glass transition temp. in a stretching area. CONSTITUTION:The part between two pairs of nip rolls 2, 2', 3, 3' is set as the stretching area and the longitudinal uniaxial stretching is executed in a 160 to 180 deg.C temp. range. The heat relieving area 10 is provided in this stretching area. This heat relieving area is set at any temp., insofar as the temp. ranges from the glass transition temp. to the temp. lower by 10 deg.C than the glass transition temp. The glass transition temp. varies with the degree of polymn. of the polymer and is usually 145 to 155 deg.C in the case of polycarbonate. The temp. of the heat relieving area 10 is, therefore, set in an about 135 to 155 deg.C. The phase difference film which has the less dependency on visual field angles, is free from unequal colors and has the good film surface shape is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a manufacturing method for improving the optical properties of retardation films used in optical applications.

(Prior Art) A retardation film is a film having birefringence and has recently been used in the field of optoelectronics, and is particularly used as an optical compensation film for liquid crystal displays.

Therefore, as optical properties, it is required to have high birefringence, high transparency, no color unevenness caused by stretching unevenness, and good flatness of the base.

Conventionally, cellulose-based resins and vinyl chloride-based polymer resins (Japanese Patent Publication No. 45-34477, JP-A-56
-125702), polycarbonate polymer resin (No. -125702), polycarbonate polymer resin (No.
Special Publication No. 41-12190, Japanese Patent Publication No. 130703, 1982
No.), acrylonitrile resin (JP-A-56-1307
No. 02), styrene resin (JP-A-56-125703)
No.), Boriosifine resin (Japanese Patent Application Laid-Open No. 60-24502
A so-called circularly polarized 2λ (lambdam) plate with a low retardation value of around 135 nm has been proposed.

In addition, 475 to 625 nI1 of polycarbonate polymer
Manufacturing of a retardation plate with a retardation value of 1 (Unexamined Japanese Patent Publication No. 1983
-189804) has also been proposed.

Although these retardation films have the effect of color removal, which is the original purpose, in the direction perpendicular to the liquid crystal display surface, when the display is viewed from an angle, a slight change in angle can cause a significant color change or screen display. There is a problem with the viewing angle characteristics that the content disappears, which is a drawback that makes it unsuitable for use in liquid crystal displays.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for producing a retardation film that improves viewing angle characteristics, eliminates stretching unevenness, and has good flatness.

(Means for Solving the Problems) The present invention has been completed as a result of repeated research to obtain a retardation film that eliminates the above-mentioned problems.

That is, the present invention includes the following (1) to (3).

(1) In a method for manufacturing a retardation film produced by vertically uniaxially stretching a polycarbonate polymer film, the temperature in the stretching zone is from the glass transition temperature (Tg) of the film to a temperature 10° C. lower than the glass transition temperature. A method for producing a retardation film characterized by having a thermal relaxation region.

(2) The neck-in rate of the film in longitudinal uniaxial stretching is 1
The above (
1) The method for producing the retardation film described above.

(3) Longitudinal uniaxial stretching is performed using two pairs of rolls with different circumferential speeds, the ratio of the distance between the two pairs of rolls to the film width is 5 or more, and the thermal relaxation area and the stretching area other than the thermal relaxation area are At least two or more bath rolls are installed in each, and the angle between the film surface that contacts the bath rolls and the center axis of the bath rolls is 90.
The method for producing a retardation film according to (2) above, wherein

For a birefringent film made by stretching a polymer film, an incident monochromatic light beam with a wavelength of 632.8 nm is used to make an angle of 40 degrees with the normal to the birefringent film surface, and the core film at an incident angle of 40 degrees. The retardation value of R
e (40), the retardation value when incident perpendicularly to the film surface is R (0), and if the value is Re (0) in both the uniaxial stretching direction and the direction perpendicular to 90 degrees (lateral direction), viewing angle dependence It was found that the film achieved its purpose as a retardation film. Films that have a large viewing angle dependence and are not suitable for retardation films were measured using the same method, and the results were as follows:
- It was found that Re (0) with respect to the axial stretching direction and Re (0) with respect to the transverse direction perpendicular to 90 degrees.

The present invention will be explained in more detail.

The present invention relates to a retardation film using a polycarbonate polymer film, but the polycarbonate polymer is not particularly limited.

Generally, any type of polymer classified as a polycarbonate polymer may be used. Furthermore, there are no particular restrictions on the degree of polymerization of the polymer.

Examples of methods for uniaxially stretching the film include a method using two pairs of nip rolls having different circumferential speeds and a method using an extrusion method, but a method using nip rolls is preferred.

The stretching zone is defined as the area between two pairs of nip rolls, and in the case of polycarbonate polymers, longitudinal uniaxial stretching is generally performed at a temperature range of 160 to 180°C.

The present invention is characterized in that a thermal relaxation zone is provided within this stretching zone. This thermal relaxation region may be set at any temperature within the range from the glass transition temperature of the film to be stretched to a temperature 10° C. lower than the glass transition temperature. The glass transition temperature varies depending on the degree of polymerization of the polymer, but in the case of polycarbonate it is usually about 145-155°C. Therefore, the temperature of the thermal relaxation zone is set in the range of about 135 to 155°C. The film length in the thermal relaxation zone is approximately 10 to 10 times the total film length in the stretching zone.
It is preferable to set the ratio to 75%.

It is provided in the latter half of the thermal relaxation zone. When longitudinally uniaxially stretched using two pairs of nip rolls with different circumferential speeds, shrinkage is observed in the width direction. This shrinkage can be adjusted by placing a pass roll in the stretching zone, but the neck-in rate is 10
% or more.

It is preferable to provide a thermal stability region of about 150 to 160° C. in the first half of the drawing region of the present invention. The film length in the thermal stability zone ranges from about 10 to 75% of the total film length in the stretching zone.

The ratio of the distance between the two pairs of nip rolls to the film width is preferably 5 or more, more preferably 10 or more.

Moreover, it is preferable to install at least two or more pass rolls in each of the thermal relaxation zone and the stretching zone other than the thermal relaxation zone.

It is preferable to make the angle between the surface of the film that comes into contact with the pass roll and the central axis of the pass roll at 90 degrees or more because the tension applied to the film becomes constant.

Although retardation films with various retardations can be obtained by the method of the present invention, generally Re (0
) can be used for liquid crystal displays by obtaining a retardation film having a wavelength of 200 to 700 nm.

In addition, in longitudinal uniaxial stretching, the ratio of the width after stretching (neck-in) when the width before stretching in the direction perpendicular to the stretching axis (width direction) is a (neck-in) is in the range of 〉 a-tight 1 to a bow 3. It is preferable to control the Above a -1-S, the viewing angle dependence is small, but the film surface becomes corrugated,
Not suitable for optical applications.

(Example) Example 1 Tg obtained by condensation of phosgene and bisphenol A
150℃ Polycarbonate with a molecular weight of 100,000 is dissolved in methylene dichloride to make a 20% by weight dope, cast on a well-polished metal band machine using the usual casting method, continuously peeled off, and then dried. Thickness 0.10mm,
A highly transparent film with a width of 50 cm was obtained. The retardation value of this film was 5 mm or less.

Using this film, the temperature is set at 155℃ between the primary side (feeding side) nip roll and the secondary side (winding side) nip roll.
The first zone (thermal stability zone) of 2 m, and the second zone of 170℃ 3I1
1 and a third zone (thermal relaxation zone) of 2 m at 145°C,
Two pass rolls were provided in each of the second and third regions, and the peripheral speed of the nip rolls was changed to obtain a retardation film with a retardation value of 580 nm.

The width after stretching was 40 cm.

Example 2 A retardation film having a retardation value of 390 nm was obtained by using the polycarbonate film obtained by the cast lengthening method of Example 1 under the same conditions as in Example 1 but changing the peripheral speed of the nip roll. The width of this film after stretching was 41 cm.

Comparative Example 1 A polycarbonate film with a thickness of 100 μm and a base width of 50 cm obtained by the cast lengthening method of Example 1 was uniaxially stretched in the width direction at 170° C. using an ordinary tenter to obtain a retardation film with a retardation value of 580 nm. . The film width after stretching was 65 cm.

Comparative Example 2 Thickness: 100 μm, Width: 50 μm obtained by the cast lengthening method of Example 1
A polycarbonate film having a diameter of 1.5 cm was uniaxially stretched in the width direction at 170° C. using an ordinary tenter to obtain a retardation film having a retardation value of 390 nm. The film width after stretching was 60 cm.

Comparative Example 3 Thickness: 100 μm, Width: 50 μm obtained by the cast lengthening method of Example 1
A retardation film having a retardation value of 580 nm was obtained under the same temperature conditions as in Example 1 by removing the pass roll from a polycarbonate film having a diameter of 1 cm and using nip rolls having different circumferential speeds. The width after stretching was 40 cm.

Comparative Example 4 Thickness: 100 μm, Width: 50 μm obtained by the cast lengthening method of Example 1
A retardation film having a retardation value of 390 nm was obtained at the same temperature as in Example 1 by removing the pass roll using a nip roll having a different circumferential speed from a polycarbonate film having a diameter of 1 cm. The width after stretching was 41 cm.

Comparative Example 5 The polycarbonate film obtained by the cast lengthening method of Example 1 was processed using nip rolls and bath rolls with different circumferential speeds: 1st zone 155℃ 1 2nd zone 170℃ 3 3rd zone (thermal relaxation zone) 1
The film was longitudinally stretched at 70° C. without so-called thermal relaxation to obtain a retardation film with a retardation value of 580 nm. The width after stretching was 46 cm.

Ta.

Regarding the performance of the retardation films obtained in Examples 1-2 and Comparative Examples 1-5, the results are shown in Table 1.

As can be seen from Table 1, the retardation film according to the present invention was an excellent film with little change in viewing angle, no stretching unevenness, and good film surface condition.

(Effects of the invention) According to the invention, viewing angle dependence is small, color unevenness, and fill 1
A good one-sided retardation film is formed. Furthermore, when this film is used as an optical compensation film in a liquid crystal display, a viewing angle can be obtained in comparison with conventional films.

[Brief explanation of drawings]

FIG. 1 shows the manufacturing method of Example 1. FIG. 2 shows the angle α (angle β) between the film surface that contacts the pass roll and the central axis of the pass roll. The numbers in the drawings have the following meanings. 1: Film 2.2': Primary side nip roll 3.3' = Secondary side nip roll 4.5.6.7: Pass roll 8: 1st zone (thermal stability zone) 9: 2nd zone 10: 3rd zone (thermal relaxation area)

Claims (1)

[Scope of Claims] (1) In a method for manufacturing a retardation film produced by longitudinally uniaxially stretching a polycarbonate polymer film, a temperature range from the glass transition temperature of the film to a temperature 10°C lower than the glass transition temperature is provided in the stretching zone. A method for producing a retardation film characterized by having a thermal relaxation region at a certain temperature. (2) The method for producing a retardation film according to claim (1), wherein the film is stretched so that the neck-in rate of the film in longitudinal uniaxial stretching is 10% or more. (3) Longitudinal uniaxial stretching is performed using two pairs of rolls with different circumferential speeds, the ratio of the distance between the two pairs of rolls to the film width is 5 or more, and the thermal relaxation area and the stretching area other than the thermal relaxation area are At least two or more pass rolls are installed in each, and the angle between the film surface that contacts the pass rolls and the central axis of the pass roll is 90°.
3. The method for producing a retardation film according to claim 2, wherein