JPH05249316A - Production of phase difference film - Google Patents

Abstract

PURPOSE:To decrease the dependence of retardation on an angle by shrinking a stretched thermoplastic resin film or sheet in a stretching axis direction while suppressing the elongation in the directions parallel with the plane of the film or sheet perpendicular to the stretching axis at the time of thermally relieving the above- mentioned film or sheet. CONSTITUTION:The stretched thermoplastic film or sheet shrinks in a stretching direction when this film or sheet is thermally relieved in a non-restrained state at the temp. above the glass transition temp. of the thermoplastic resin film or sheet. The film or sheet necks in and shrinks in the directions parallel with the plane of the film or sheet and perpendicular to the stretching axis at the time of the stretching and, therefore, the film or sheet tends to elongate in the directions parallel with the plane of the film or sheet and perpendicular to the stretching axis at the time of thermal relieving. The film or sheet shrinks in the stretching axis direction and its thickness increases and in addition, the dependence of the retardation on the angle is ameliorated when the elongation in the directions parallel with the plane of the film or sheet and perpendicular to the stretching axis is suppressed to the length shorter than the length at which the film or sheet can elongate in the non-restrained state at the time of thermally relieving.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a retardation film or sheet used in a liquid crystal display device or the like.

[0002]

2. Description of the Related Art A retardation film or sheet comprising a uniaxially oriented thermoplastic resin film or sheet is used for optical compensation for improving the display quality of a liquid crystal display device. It is used as a plate.

An STN type liquid crystal display device using such a retardation film or sheet as an optical compensation plate is lighter and thinner than a two-layer STN type liquid crystal display device using a liquid crystal cell as an optical compensation plate. Although it has advantages such as being inexpensive, it has disadvantages such as poor viewing angle characteristics and poor contrast. These disadvantages have been considerably improved by methods such as laminating two retardation films or sheets, but the viewing angle characteristics have not yet reached a satisfactory level.

The viewing angle characteristics of the liquid crystal display device depend not only on the birefringence of the liquid crystal cell but also on the birefringence of the retardation plate, that is, the angle dependence of the retardation. It is known that in a conventional retardation plate, the smaller the angle dependence of retardation, the better. The angle dependence of the retardation of the retardation film was measured by a polarizing microscope equipped with Senarmont compensator.
In the case of a retardation film made of a thermoplastic resin having a positive intrinsic birefringence, the slow axis is set, and in the case of a retardation film made of a thermoplastic resin having a negative intrinsic birefringence, a fast axis direction. Retardation ratio of the retardation (R ₄₀ ) measured with the retardation film tilted from the horizontal by 40 degrees, and the retardation (R ₀ ) measured without tilt (horizontal state). (R
₄₀ / R ₀ ). The closer the retardation ratio is to 1, the smaller the angle dependence of the retardation.

As a method for reducing the angle dependence of retardation of a retardation film or a sheet, a method of stretching a film in which molecules are oriented in a direction normal to the film surface (Japanese Patent Laid-Open No. 160204/1990). A method of shrinking the film in a direction perpendicular to the stretching axis during uniaxial stretching (Japanese Patent Laid-Open No. 2-191904), and a method of stretching a film formed by applying a liquid polymer material under application of an electric field (Japanese Patent Laid-Open No. No. 285303) has been proposed, but it is hard to say that any of these methods has excellent mass productivity.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that when a stretched thermoplastic resin film or sheet is thermally relaxed, the film or sheet is It was found that a retardation film or sheet having a small angle dependence of retardation can be produced by shrinking the stretching axis direction while suppressing the elongation in the direction parallel to the surface and perpendicular to the stretching axis, and completed the present invention. Came to do.

That is, according to the present invention, when the stretched thermoplastic resin film or sheet is subjected to thermal relaxation at a temperature not lower than the glass transition temperature of the thermoplastic resin, it is parallel to the film surface or sheet surface and perpendicular to the stretching axis. The present invention relates to a method for producing a retardation film or sheet having a small angle dependence of retardation, which is characterized in that the stretching axial direction is contracted while suppressing the elongation in the direction.

Stretched thermoplastic resin film or sheet
When the sheet is unrestrained and subjected to thermal relaxation at a temperature not lower than the glass transition temperature of the thermoplastic resin, the sheet shrinks in the stretching direction. During stretching, since the film or sheet contracts by necking in the direction parallel to the film or sheet surface and perpendicular to the stretching axis, the film or sheet is parallel to the film surface or sheet surface during thermal relaxation. Moreover, it tends to extend in a direction perpendicular to the stretching axis. If the elongation in the direction parallel to the plane of the film or sheet and perpendicular to the stretching axis during thermal relaxation is suppressed below the length that can be stretched in an unrestrained state, the stretching axis direction of the film or sheet contracts. However, as the thickness increases, the angle dependence of the retardation is improved.

Here, the stretching axis means a uniaxial stretching axis in the case of uniaxial stretching, and a main stretching axis in the case of unbalanced biaxial stretching. Perpendicular to the stretching axis means 60 degrees to the stretching axis
A range of 120 degrees, particularly 85 degrees to 9 with respect to the stretching axis
It is a letter that suppresses elongation in the direction of 5 degrees.
It is preferable in terms of the effect of improving the angle dependence of the projection. Then, suppressing the elongation in the direction parallel to the surface of the film or the sheet and perpendicular to the stretching axis has the effect of improving the angle dependence of the retardation, as compared with the case of suppressing the elongation in the other directions. Are better. Suppressing the elongation in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis means keeping the elongation in the direction substantially zero, that is, parallel to the film surface or the sheet surface and perpendicular to the stretching axis. It means not only to keep the length in a certain direction constant, but also to make the elongation in that direction smaller than the elongation in the case where thermal relaxation is performed in an unrestrained state until a desired R ₀ value is reached.

The method for suppressing the elongation in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis at the time of thermal relaxation is not particularly limited. For example, a plate such as a hot plate is brought into contact with a film or a sheet, and the friction force generated by this contact is used to make the film surface or the sheet.
A method for suppressing elongation in a direction parallel to the surface of the film and perpendicular to the stretching axis, a film surface or a sheet surface being perpendicular to the wall and a film or sheet between a pair of parallel walls having a constant interval. −
The film or sheet is placed so that the stretching axis of the sheet is parallel to the wall, and the film surface or sheet is placed more than the distance between the pair of walls.
A method of suppressing the elongation in the direction parallel to the sheet surface and perpendicular to the stretching axis, and preparing a frame having a structure that cannot extend in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis, A method of suppressing the elongation in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis by installing the film or the sheet in this frame can be mentioned. Above all, the methods of and are preferable. In this way, it is possible to easily obtain a thermoplastic resin film or sheet satisfying the following formula by thermally relaxing while suppressing the elongation in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis. You can 0.900 <R ₄₀ / R ₀ <1.100

When heat relaxation is performed while suppressing the elongation in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis,
Although wrinkles may occur, in such a case, it is preferable that the film surface or the sheet surface is thermally relaxed while applying an appropriate pressure. The method of thermally relaxing while applying an appropriate pressure in the direction perpendicular to the film surface or the sheet surface is not particularly limited as long as it can simultaneously heat and pressurize the film or sheet. For example, prepare a frame having a structure in which the film or sheet cannot extend in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis, and the film or sheet is placed in this frame. Install and use a load of the same shape as the film surface or sheet surface to apply heat evenly to the film surface or sheet surface while relaxing the heat or sandwich the film or sheet with a release film. The film or sheet sandwiched by release films is tubular so that the direction parallel to the film surface or sheet surface and perpendicular to the stretching axis of the film or sheet is the same direction as the circumference of the tube. A film is uniformly applied to the film surface or the sheet surface by being wound around the object, and the film or sheet is prevented from extending in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis. Or fixed both ends of the sheet Method for thermal relaxation, and the like in condition.

Stretched thermoplastic resin film or sheet
When heat is relaxed while applying pressure to the sheet, apply a pressure such that the thickness of the film or sheet does not decrease from that before heat relaxation, to the extent that wrinkles do not enter the film or sheet during heat relaxation. As a result, a thermoplastic film or sheet satisfying 0.900 <R ₄₀ / R ₀ <1.100 can be obtained. A pressure in the range of 0.1 g / cm ^{2 to} 10 kg / cm ² is usually used in terms of the uniformity of the film or sheet after thermal relaxation and the relaxation rate.

Stretched thermoplastic resin film or sheet
The sheet may have any orientation as long as it contracts in the stretching axis direction during thermal relaxation and extends in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis.
The method for producing such a film or sheet is not particularly limited, and for example, an unstretched film or sheet is formed by using a known film forming method such as a solution casting method, a press molding method or an extrusion molding method. And the unstretched film or sheet is stretched by a known stretching method such as a tenter stretching method, a roll stretching method, or a roll compression compression stretching method. From the viewpoint of the orientation behavior of molecules in the thickness direction during thermal relaxation and the uniformity of retardation in the film plane or in the sheet plane, a solution cast film or sheet
A method of uniaxially stretching the film by a stretching method between rolls is preferable.

Stretched thermoplastic resin film or sheet
The temperature for relaxing the temperature is not less than the glass transition temperature (Tg) of the thermoplastic resin and less than the melting temperature (Tm),
The temperature may be any temperature at which the thermoplastic resin film or sheet can be thermally relaxed. Tg and T of resin used
The temperature range used varies depending on m, but among them, thermal relaxation in the temperature range of Tg to Tg + 50 ° C. is preferable from the viewpoint of controllability of in-plane retardation and molecular orientation behavior in the thickness direction.

Stretched thermoplastic resin film or sheet
When heat is relaxed while applying pressure to the surface of the glove, a cushioning material is used to reduce temperature unevenness and pressure unevenness.
The temperature and pressure may be transmitted to the film surface or the sheet surface through the cushioning material. In addition, when the stretched thermoplastic resin film or sheet is subjected to thermal relaxation, the stretched thermoplastic resin film or sheet is subjected to a release treatment in order to increase the deformation rate or improve the uniformity of the deformation rate. The surface of the stretched thermoplastic resin film or sheet may be sandwiched by a release agent such as a coated polyester film, or coated with a lubricant such as silicone oil or a molten surfactant.

The thermoplastic resin used for the stretched thermoplastic resin film is not particularly limited as long as it has an intrinsic birefringence, but one having excellent optical properties such as transparency is preferable. For example, polycarbonate, polysulfone, polyarylate, polyether sulfone,
A thermoplastic resin having a positive intrinsic birefringence such as cellulose diacetate or a thermoplastic resin having a negative intrinsic birefringence such as polystyrene, α-methylpolystyrene, polyvinylpyridine, polyvinylnaphthalene, and polymethylmethacrylate can be used. .. Among them, polycarbonate is preferable from the viewpoints of transparency, resistance to heat and humidity and birefringence.

[0017]

Industrial Applicability According to the method of the present invention, a retardation film or sheet having a small angle dependence of retardation and excellent uniformity can be easily manufactured industrially. By using this as an optical compensator, the viewing angle characteristics of the liquid crystal display device can be remarkably improved.

[0018]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 A polycarbonate film having a thickness of 185 μm formed by a solvent casting method was stretched 2.1 times at 184 ° C. by a longitudinal uniaxial stretching method to give a thickness of 98 μm and R ₀ = 867n.
A stretched film having m and R ₄₀ / R ₀ = 1.108 was obtained. This is cut out into a length (vertical direction of the stretching axis) of 9.9 cm and a horizontal (stretching axis direction) of 2.4 cm, and put in a frame having a structure such that it cannot be stretched in the vertical direction (stretching vertical direction). In order to apply pressure uniformly in the direction perpendicular to the surface, a load having the same shape as that of the film on the bottom surface was applied, and a pressure of 70 g / cm ² was applied in the direction perpendicular to the film surface. In this state, the stretched film is kept at a temperature of 165 ° C. for 12 hours while suppressing the elongation parallel to the film surface and in the direction of 90 ° with respect to the stretching axis.
Heat relaxation was performed for 0 minutes. As a result, the height is 9.9 cm and the width is 2.
0 cm, thickness 120 μm, R ₀ = 445 nm, R ₄₀ / R
A retardation film of ₀ = 1.000 was obtained.

Example 2 The same stretched film as that used in Example 1 was cut into a length (vertical direction of the stretching axis) of 9.9 cm and a horizontal (stretching axis direction) of 2.4 cm, and then cut in the longitudinal direction (the vertical direction of the stretching). Is placed in a frame that cannot extend, and a load of the same shape as the film is placed on the bottom surface to apply pressure evenly in the direction perpendicular to the film surface, and a pressure of 235 g / cm ² is applied in the direction perpendicular to the film surface. Applied to. In this state, the stretched film was thermally relaxed for 180 minutes under the temperature condition of 165 ° C. while suppressing the elongation in the direction parallel to the film surface and at 90 ° with respect to the stretching axis. As a result, length 9.9 cm, width 2.1 cm, thickness 1
18 μm, R ₀ = 586 nm, R ₄₀ / R ₀ = 1.047
A retardation film of was obtained.

Example 3 The same stretched film as that used in Example 1 was cut into a length (vertical direction of the stretching axis) of 9.9 cm and a horizontal (stretching axis direction) of 2.4 cm, and was cut in the lengthwise direction (the vertical stretching direction). Is placed in a frame that cannot stretch, and a load of the same shape as the bottom is placed on the bottom to apply pressure evenly in the direction perpendicular to the film, and a pressure of 87 g / cm ² is applied in the direction perpendicular to the film. Applied to. In this state, the stretched film was thermally relaxed for 120 minutes under the temperature condition of 170 ° C. while suppressing the elongation parallel to the film surface and in the direction of 90 ° with respect to the stretching axis. As a result, length 9.9 cm, width 2.1 cm, thickness 12
A retardation film of 2 μm, R ₀ = 519 nm, and R ₄₀ / R ₀ = 1.059 was obtained.

Example 4 A polycarbonate film having a thickness of 200 μm formed by a solvent casting method was stretched 1.1 times at 190 ° C. by a longitudinal uniaxial stretching method to give a thickness of 187 μm and R ₀ = 613n.
A stretched film having m and R ₄₀ / R ₀ = 1.124 was obtained. This is cut out into a length (vertical direction of the stretching axis) of 9.9 cm and a horizontal (stretching axis direction) of 2.4 cm, and put in a frame having a structure such that it cannot be stretched in the vertical direction (stretching vertical direction). In order to apply a uniform pressure in the direction perpendicular to the surface, a load having the same shape as the film on the bottom surface was placed, and a pressure of 63 g / cm ² was applied in the direction perpendicular to the film surface. In this state, the stretched film is kept at a temperature of 165 ° C. for 12 hours while suppressing the elongation parallel to the film surface and in the direction of 90 ° with respect to the stretching axis.
Heat relaxation was performed for 0 minutes. As a result, the height is 9.9 cm and the width is 2.
2 cm, thickness 200 μm, R ₀ = 351 nm, R ₄₀ / R
A retardation film with ₀ = 1.035 was obtained.

Example 5 A polycarbonate film having a thickness of 185 μm formed by a solvent casting method was stretched 1.1 times at 178 ° C. by a longitudinal uniaxial stretching method to obtain a thickness of 170 μm and R ₀ = 650 n.
A stretched film having m and R ₄₀ / R ₀ = 1.100 was obtained. This was cut into a length (direction perpendicular to the stretching axis) of 30 cm and a width (direction of the stretching axis) of 20 cm, which was subjected to a release treatment film (Toyo Metallizing Therapy Q-1 # 188).
Then, a metal plate was placed thereon to apply pressure uniformly in the direction perpendicular to the film surface, and a pressure of 4.5 g / cm ² was applied in the direction perpendicular to the film surface. In this state, the stretched film was thermally relaxed for 120 minutes under the temperature condition of 153 ° C. while suppressing the elongation in the direction parallel to the film surface and at 90 ° with respect to the stretching axis. As a result, length 30.85 cm, width 1
8.8 cm, thickness 185 μm, R ₀ = 200 nm, R ₄₀
A retardation film of / R ₀ = 1.063 was obtained.

Example 6 From a polycarbonate film having a thickness of 185 μm formed by a solvent casting method, a thickness of 138 μm and R ₀ = 61
A film uniaxially stretched in the transverse direction of 9 nm and R ₄₀ / R ₀ = 1.112 was obtained. Vertically (stretching axis vertical direction) 2
It is cut into 00 cm and 12 cm in the horizontal direction (stretching axis direction), and a release film (size: 200 cm in length, 15 cm in width)
(Made by Toyo Metalizing Therapy Q-1 # 18
It was sandwiched by 8), wrapped around an aluminum tube having a diameter of 9 cm and a thickness of 3 mm together with a cushioning material (length 200 cm, width 15 cm) (double-sided flannel), and then tightened. At this time, the edges of the polycarbonate film were fixed so that the length in the longitudinal direction did not extend any further. In this state, the stretched film was thermally relaxed at a temperature of 152 ° C. for 25 hours while suppressing the elongation in the direction parallel to the film surface and at 90 ° with respect to the stretching axis. As a result, length 200 cm, width 11.5 cm, thickness 158μ
A retardation film having m, R ₀ = 421 nm and R ₄₀ / R ₀ = 0.978 was obtained.

Example 7 From a polycarbonate film having a thickness of 185 μm formed by a solvent casting method, a thickness of 148 μm and R ₀ = 99.
A film uniaxially stretched in the transverse direction of ₀ nm and R ₄₀ / R ₀ = 1.167 was obtained. Vertically (stretching axis vertical direction) 2
It is cut out into 00 cm and 12 cm in width (stretching axis direction), sandwiched with a release-treated film (length 200 cm, width 15 cm) (Toyo Metallizing Therapy Q-1 # 188), and buffer material (length 200 cm, width 15 cm) (double-sided flannel) )
Wrap it around an aluminum tube with a diameter of 9 cm and a wall thickness of 3 mm,
I wound it up. At this time, the edges of the polycarbonate film were fixed so that the length in the longitudinal direction did not extend any further. In this state, the stretched film was thermally relaxed for 25 hours under the temperature condition of 153 ° C. while suppressing the elongation in the direction parallel to the film surface and at 90 ° with respect to the stretching axis. As a result, length 200 cm, width 10.2 cm, thickness 182 μm,
A retardation film with R ₀ = 467 nm and R ₄₀ / R ₀ = 1.007 was obtained.

Example 8 From a polycarbonate film having a thickness of 185 μm formed by a solvent casting method, a thickness of 160 μm and R ₀ = 13
A film uniaxially stretched in the transverse direction having a thickness of 33 nm and R ₄₀ / R ₀ = 1.110 was obtained. Vertically (direction perpendicular to the stretching axis)
Cut out to 200 cm and 12 cm in width (stretching axis direction), sandwich with release film (length 200 cm, width 15 cm) (Toyo Metallizing Therapy Q-1 # 188), cushioning material (length 200 cm, width 15 cm) (double-sided flannel) )
Wrap it around an aluminum tube with a diameter of 9 cm and a wall thickness of 3 mm,
I wound it up. At this time, the edges of the polycarbonate film were fixed so that the length in the longitudinal direction did not extend any further. In this state, the stretched film was thermally relaxed for 25 hours under the temperature condition of 153 ° C. while suppressing the elongation in the direction parallel to the film surface and at 90 ° with respect to the stretching axis. As a result, length 200 cm, width 10.1 cm, thickness 198 μm,
A retardation film having R ₀ = 692 nm and R ₄₀ / R ₀ = 0.954 was obtained.

Comparative Example 1 A polycarbonate film having a thickness of 185 μm formed by a solvent casting method was stretched 2.1 times at 190 ° C. by a longitudinal uniaxial stretching method. The film obtained has a thickness of 93μ.
m, R ₀ = 589 nm, and R ₄₀ / R ₀ = 1.114.

Comparative Example 2 From a polycarbonate film having a thickness of 185 μm formed by a solvent casting method, a thickness of 137 μm and R ₀ = 61.
A film uniaxially stretched in the transverse direction of 9 μm and R ₄₀ / R ₀ = 1.112 was obtained. Vertically (direction perpendicular to the stretching axis) 1
It was cut into 0 cm and 10 cm in the horizontal direction (stretching axis direction), and this was relaxed for 2 hours at a temperature of 153 ° C. on a release-treated film (Therapeutic Q-1 # 188 manufactured by Toyo Metalizing Co., Ltd.). As a result, the length is 10.15 cm and the width is 9.6.
5 cm, thickness 141 μm, R ₀ = 406 nm, R ₄₀ / R
A retardation film of ₀ = 1.109 was obtained.

Comparative Example 3 From a polycarbonate film having a thickness of 185 μm formed by a solvent casting method, a thickness of 160 μm and R ₀ = 13
A film uniaxially stretched in the transverse direction of 33 μm and R ₄₀ / R ₀ = 1.110 was obtained. Vertically (direction perpendicular to the stretching axis)
10 cm and a width (stretching axis direction) of 10 cm were cut out, and this was cut on a release-treated film (TOYO METALIZER THERAPY Q-1 # 188) at a temperature of 153 ° C. for 2 minutes.
I relaxed the time. As a result, length 10.4 cm, width 9.1
cm, thickness 169 μm, R ₀ = 621 nm, R ₄₀ / R ₀
A retardation film of = 1.113 was obtained.

Comparative Example 4 From a polycarbonate film having a thickness of 185 μm formed by the solvent casting method, a thickness of 137 μm and R ₀ = 61.
A film uniaxially stretched in the transverse direction of 9 μm and R ₄₀ / R ₀ = 1.112 was obtained. Vertically (direction perpendicular to the stretching axis) 1
It was cut into 0 cm and 10 cm in the horizontal direction (stretching axis direction), and this was relaxed on a release-treated film (TOYO METALIZER THERAPY Q-1 # 188) at a temperature of 158 ° C. for 4 hours. As a result, the height is 10.1 cm and the width is 9.65.
cm, thickness 141 μm, R ₀ = 415 nm, R ₄₀ / R ₀
The retardation film of 1.118 was obtained.

[Procedure amendment]

[Submission date] February 1, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

Comparative Example 4 From a polycarbonate film having a thickness of 185 μm formed by the solvent casting method, a thickness of 137 μm and R ₀ = 61.
A film uniaxially stretched in the transverse direction of 9 μm and R ₄₀ / R ₀ = 1.112 was obtained. Vertically (direction perpendicular to the stretching axis) 1
It was cut into 0 cm and 10 cm in the transverse direction (stretching axis direction), and this was relaxed on a release-treated film (Toray Metallizing Therapeutic Q-1 # 188) at a temperature of 158 ° C. for 4 minutes . As a result, the height is 10.1 cm and the width is 9.65.
cm, thickness 141 μm, R ₀ = 415 nm, R ₄₀ / R ₀
The retardation film of 1.118 was obtained.

Claims (4)

[Claims] 1. A stretched thermoplastic resin film or sheet.
When the sheet is thermally relaxed at the glass transition temperature of the thermoplastic resin or higher, the stretching axis direction is contracted while suppressing the elongation in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis. A method for producing a retardation film or sheet. 2. The manufacturing method according to claim 1, wherein thermal relaxation is carried out in a state where the length in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis is kept constant. 3. The heat relaxation is performed while applying pressure in a direction perpendicular to the film surface or the sheet surface.
The manufacturing method described. 4. Thermal relaxation while applying a pressure in the direction perpendicular to the film surface or the sheet surface while keeping the length in the direction parallel to the film surface or the sheet surface and perpendicular to the stretching axis constant. The manufacturing method according to claim 1, wherein