JPH06148429A - Production of composite phase difference film - Google Patents

Abstract

PURPOSE:To provide the process for production of the composite phase difference film which has an excellent black and white level and good visual field angle characteristic and is low in cost and light in weight. CONSTITUTION:This process for production of the composite phase difference film consists in forming a high-polymer liquid crystal exhibiting a nematic phase or smectic phase on a phase difference film which consists of a thermoplastic high polymer having an optical axis within the film plane and having positive refractive index anisotropy and is subjected to uniaxial orientation and subjecting the films to a heat treatment at a temp. above the transition temp. of the liquid crystal phase/isotropic phase of the above-mentioned high-polymer liquid crystal. The process for production of the composite phase difference film consists in laminating the base material which is formed with the film of the high-polymer liquid crystal by forming the high-polymer liquid crystal exhibiting the nematic phase or smectic phase on the base material having the transition temp. above the liquid crystal phase/isotropic phase of the high- polymer liquid crystal and subjecting the base material to the heat treatment at the temp. above the transition temp. of the liquid crystal phase/isotropic phase and the phase difference film which consists of the thermoplastic high polymer having the optical axis within the film plane and having the positive refractive index anisotropy and is subjected to the uniaxial orientation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing a retardation film used for liquid crystal display devices and the like.

[0002]

2. Description of the Related Art A retardation film is a polymer film having optical homogeneity and durability and having uniaxial orientation,
It is generally used as an optical compensation plate for improving the display quality of liquid crystal display elements. A super twist nematic (hereinafter sometimes referred to as STN) type liquid crystal display device using a retardation film has advantages such as light weight, thinness, and low cost, but has poor viewing angle characteristics and poor black and white level. Had the disadvantages such as. These disadvantages have been considerably improved by a method such as laminating two retardation films, but the viewing angle characteristics have not yet reached a satisfactory level.

The viewing angle characteristics of the liquid crystal display device are largely correlated not only with the angle dependency of the birefringence of the liquid crystal cell for display but also with the angle dependency of the retardation of the retardation film. It is known that the smaller the change in retardation angle, the better.

In Japanese Patent Laid-Open Nos. 2-73327 and 2-105111, the angle change of the background color of a uniaxially oriented birefringent body (liquid crystal cell for display) having positive refractive index anisotropy is described. To reduce the refractive index, an in-plane refractive index is isotropic, but a method using a birefringent layer having a refractive index in the thickness direction larger than the in-plane refractive index is disclosed. As a material having such a refractive index anisotropy, a homeotropic (vertical) oriented compensating liquid crystal cell is exemplified.

Further, in JP-A-2-256023, the use of a film having an optical axis in the direction normal to the film surface and a retardation film having a positive birefringence value makes it possible to change the angle of retardation. It is described that the retardation film can be obtained and the viewing angle characteristics are improved. As a film having an optical axis in the normal direction of the film, a photopolymerizable compound and a liquid crystal monomer are mixed, and while maintaining the alignment of the liquid crystal monomer in an electric field, the polymerization proceeds and the alignment in the normal direction is fixed. How to do is listed.

Japanese Unexamined Patent Publication (Kokai) No. 4-16916 discloses a birefringent layer having a refractive index in the thickness direction larger than the in-plane refractive index, and the birefringent layer is composed of a vertically aligned polymer liquid crystal. Has been done. Regarding the method of vertically aligning polymer liquid crystals, after heating to the liquid crystal temperature, applying an electric field or magnetic field in the thickness direction, and sandwiching it with two substrates whose surfaces are treated with a vertical aligning agent such as a silane compound. ,
A method of vertically aligning at a liquid crystal temperature is disclosed, and it is shown that a retardation film excellent in viewing angle characteristics can be obtained by combining with a retardation film obtained by stretching a polymer.

[0007]

However, when a film having an optical axis in the normal direction of the film and a retardation film are combined, a liquid crystal monomer having a large orientation relaxation in order to have the optical axis in the normal direction of the film. Photopolymerization, external field such as electric field, magnetic field, etc. are required while maintaining the orientation, and sandwiched between two hydrophobized substrates.
A peeling operation was required. As described above, the conventional method has a problem that it is not an industrially advantageous manufacturing method.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have formed a polymer liquid crystal showing a nematic phase or a smectic phase on a uniaxially oriented retardation film. , Excellent in black and white level by heat treatment at a temperature above the transition temperature of liquid crystal phase / isotropic phase,
The present invention has been completed by finding that an inexpensive and lightweight composite retardation film having a good viewing angle characteristic and a simple manufacturing process can be obtained.

That is, the present invention provides (1) a uniaxially oriented retardation film made of a thermoplastic polymer having an optic axis in the film plane and having positive refractive index anisotropy, and a nematic phase or (2) A method for producing a composite retardation film, which comprises forming a polymer liquid crystal exhibiting a smectic phase and heat-treating the liquid crystal phase / isotropic phase transition temperature of the polymer liquid crystal or higher, (2) nematic phase Alternatively, a polymer liquid crystal exhibiting a smectic phase is formed on a substrate having a glass transition temperature of the liquid crystal phase / isotropic phase transition temperature or higher of the polymer liquid crystal, and the liquid crystal phase / isotropic phase transition temperature or higher is obtained. Uniaxially oriented substrate composed of a thermoplastic polymer having an optical axis in the plane of the film and a positive refractive index anisotropy. Characterized by laminating with a retardation film A method of manufacturing a case the phase difference film,
(3) The method for producing a composite retardation film according to (2), wherein the substrate is a polarizing film.

According to the present invention, a composite retardation film in which the anisotropy of the refractive index is controlled, particularly a composite retardation film having a higher refractive index in the direction perpendicular to the film surface can be produced. That is, the uniaxially oriented retardation film having an optical axis in the film plane and having a positive refractive index anisotropy is the A layer,
When a polymer liquid crystal layer exhibiting a nematic phase or a smectic phase is a B layer, and a substrate having a glass transition temperature of the liquid crystal phase / isotropic phase transition temperature of the polymer liquid crystal is a C layer, the B layer is on the A layer. By directly providing, followed by heat treatment at a temperature equal to or higher than the liquid crystal phase / isotropic phase transition temperature of the polymer liquid crystal, or by providing a B layer on the C layer, performing the heat treatment, and then laminating with the A layer. The value of the refractive index in the direction perpendicular to the film surface can be a value between the maximum value and the minimum value of the refractive index in the film surface. When the C layer is provided with the B layer alone, and the optical properties of the C layer are substantially isotropic, the refractive index in the direction perpendicular to the film surface becomes larger than the in-plane refractive index value. .

In order to obtain the above-mentioned anisotropy of refractive index, when the polymer liquid crystal has a positive dielectric anisotropy, the molecular axes in the polymer liquid crystal layer are oriented in the direction perpendicular to the layer surface as an average. (Hereinafter, such an alignment may be referred to as homeotropic alignment). For this purpose, it is preferable to perform vertical alignment treatment on the surface of the layer A or the layer C on which the polymer liquid crystal layer is provided. Here, examples of the vertical alignment treatment include a method of physically or chemically hydrophilizing or hydrophobizing the surface.

As the polymer liquid crystal used in the present invention, either a main chain polymer liquid crystal or a side chain polymer liquid crystal may be used as long as it is a polymer liquid crystal having a nematic phase or a smectic phase in a liquid crystal state. If the transition temperature of the liquid crystal phase / isotropic phase is too high, the glass transition temperature of the substrate used becomes high,
A side chain type polymer liquid crystal having a low transition temperature is preferable because the substrates that can be industrially used are limited.

Examples of the main chain type polymer liquid crystal are wholly aromatic polyester type polymer liquid crystal in which mesogenic groups having the same structure as the low molecular weight liquid crystal are linked by an ester bond, mesogenic groups and polymethylene, polyethylene oxide, polysiloxane. A semi-rigid polyester-based polymer liquid crystal composed of a main chain to which flexibility is imparted by alternately connecting bending chains. The main chain type polymer liquid crystal tends to have a higher liquid crystal phase / isotropic phase transition temperature than the side chain type polymer liquid crystal. Therefore, considering the heat resistant temperature of the base material on which the polymer liquid crystal is laminated, the transition temperature is at most 200 ° C. or lower, preferably 150 ° C. or lower,
It is preferable to carry out operations such as increasing the number of bent chains and suppressing the molecular weight to a low level.

As an example of the side chain type polymer liquid crystal, a mesogenic group is added to a skeleton chain such as methacrylic acid, acrylic acid, polymethylene, polyethylene oxide, and polysiloxane through a spacer consisting of a bent chain as a side chain. Examples include those that are combined. The skeleton chain may be a linear one as well as a linear one. Of these, polysiloxane-based side-chain polymer liquid crystals are preferable from the viewpoint of easily obtaining homeotopic alignment. Since the side chain type polymer liquid crystal tends to have a low transition temperature of the liquid crystal phase / isotropic phase, the transition temperature is 200 ° C. or lower, preferably 170 ° C., so that the transition temperature is practical. It is preferable to consider the length of the spacer and the kind of mesogenic group so that the temperature becomes not higher than 0 ° C, more preferably not higher than 150 ° C.

Examples of the polysiloxane-based side chain type polymer liquid crystal include linear or cyclic polymer liquid crystal having repeating units represented by the following chemical formulas 1 to 14. In each of Chemical formulas 1 to 14 below, the repeating unit number n is an integer of 2 to 6.

[0016]

[Chemical 1]

[0017]

[Chemical 2]

[0018]

[Chemical 3]

[0019]

[Chemical 4]

[0020]

[Chemical 5]

[0021]

[Chemical 6]

[0022]

[Chemical 7]

[0023]

[Chemical 8]

[0024]

[Chemical 9]

[0025]

[Chemical 10]

[0026]

[Chemical 11]

[0027]

[Chemical 12]

[0028]

[Chemical 13]

[0029]

[Chemical 14]

As a method of synthesizing these polymer liquid crystals, a method of adding the vinyl derivative of the side chain to poly (methylsiloxane) is exemplified.

The transition temperature of the crystal phase / liquid crystal phase of these polymer liquid crystals is not particularly limited, and the transition temperature below room temperature can be used.

The thermoplastic polymer having a positive refractive index anisotropy used in the composite retardation film obtained by the production method of the present invention includes polycarbonate, polysulfone, polyarylate, polyether sulfone, cellulose acetate 2,
Examples thereof include cellulose triacetate, polyvinyl alcohol, polyethylene vinyl alcohol copolymer, and polyethylene terephthalate. In particular, when these thermoplastic polymers having positive refractive index anisotropy are used as the base material of the polymer liquid crystal, the retardation does not change in the temperature range where the heat treatment of the polymer liquid crystal occurs, the glass transition temperature Is 1
Thermoplastic engineering polymers of 00 ° C. or higher are preferred. For example, polycarbonate, polysulfone, and polyether sulfone are preferable.

As a method for producing the raw film made of these thermoplastic polymers, a molding method such as a solvent casting method, an extrusion molding method or a press molding method may be used. Examples of the stretching method for making the original film a uniaxially oriented retardation film having an optical axis in the film plane include a tenter stretching method, a roll stretching method, and a roll compression stretching method. In order to obtain a uniform retardation film, it is preferable to stretch the film formed by the solvent casting method by the tenter stretching method.

The substrate for homeotropic alignment of the polymer liquid crystal used in the present invention has a glass transition temperature which is equal to or higher than the transition temperature of the liquid crystal phase / isotropic phase of the polymer liquid crystal used. There is no particular limitation as long as it is transparent, and it may be appropriately selected depending on the polymer liquid crystal used. Since its shape is used in contact with a liquid crystal display cell, a plate-like or film-like one is common. Also,
A hydrophilic or hydrophobic substrate is preferred because of the ease of homeotropic alignment. As the hydrophilic substrate, a substrate having a contact angle with water of 60 ° or less, more preferably 50 ° or less is preferably used. As the hydrophobic substrate, a substrate having a contact angle with water of 85 ° or more, more preferably 90 ° or more is preferably used. Among these, a hydrophilic substrate is particularly preferable because homeotropic alignment can be easily obtained.

More specifically, the hydrophilic substrate is a glass plate; a hydrophilic polymer film such as polyvinyl alcohol or a saponified ethylene-vinyl acetate copolymer; cellulose triacetate or cellulose diacetate film. The surface of which is saponified; those obtained by making the polymer film hydrophilic can be used. Examples of the hydrophilic polymer film include polycarbonate, polysulfone, polyarylate, polyether sulfone, cellulose triacetate, cellulose diacetate, and polyethylene terephthalate. The hydrophilic treatment is not particularly limited, and examples thereof include a treatment with oxygen plasma, a method of applying a hydrophilic polymer on the surface, and a method of applying a surfactant.

Fluorine-based polymer films such as polytetrafluoroethylene and polyvinylidene fluoride as the hydrophobic substrate; polycarbonate, polysulfone, polyarylate, polyether sulfone, cellulose triacetate, 2
Examples thereof include polymer films such as cellulose acetate and polyethylene terephthalate; those obtained by subjecting a hydrophilic polymer film such as polyvinyl alcohol or a saponified product of ethylene-vinyl acetate copolymer to a hydrophobic treatment. Examples of the hydrophobic treatment include a method of applying a fluoropolymer, a method of applying a surfactant such as lecithin, and a method of reacting a silane coupling agent, a titanium coupling agent and the like. These are appropriately selected depending on the polymer film or polymer liquid crystal used.

The silane coupling agent used in the hydrophobic treatment of the present invention is not particularly limited as long as it has a hydrocarbon group or a fluorohydrocarbon group. Specifically, trade name AY43-02l, SZ603 manufactured by Toray Silicone Co., Ltd.
0, SH6040, SZ6070, SZ6072, SZ
6300 and Shin-Etsu Chemical Co., Ltd. product name KBM403, K
BM508 or Asahi Glass Co., Ltd. brand name F-6 etc. are illustrated.

As a substrate in which the polymer liquid crystal is homeotropically aligned, in addition to the above-mentioned materials, a glass plate with a transparent electrode used in a liquid crystal display device, a retardation film made of a thermoplastic polymer, a polarizing film and the surface thereof are used. A protective film can also be used. Further, the above-mentioned glass plate with a transparent electrode, a retardation film, a polarizing film, and those obtained by subjecting the surface of these protective films to a modification treatment such as a hydrophilic treatment or a hydrophobic treatment are exemplified as the substrate. Among these, the use of a retardation film or a polarizing film as a substrate is preferable because it is more industrially advantageous because the number of laminating steps can be reduced.

Next, a method of forming a polymer liquid crystal on a substrate will be described. The method for forming the polymer liquid crystal of the present invention is not particularly limited, for example, the polymer liquid crystal can be dissolved, and the polymer liquid crystal is dissolved in a solvent in which dissolution or swelling of the substrate is small, and then spin coating, After applying a known method such as a roll coating method, a spray coating method, a printing method or a depping method, or heating the polymer liquid crystal to a temperature above the solid phase / liquid crystal phase transition temperature to reduce the viscosity of the polymer liquid crystal, Examples of the method of applying are known methods such as a roll coating method, a spray coating method, and a depping method. Among these coating methods, the spin coating method using a polymer liquid crystal solution, the roll coating method, the spray coating method, the depping method and the like are preferable from the viewpoint of easy production.

The thickness of the obtained polymer liquid crystal phase is not particularly limited, but it is 0.1 μm or more and 10 μm or less in order to obtain good homeotropic alignment and good viewing angle characteristics.
It is preferably 0.2 μm or more and 5 μm or less, and more preferably 0.5 μm or more and 3 μm or less.

The heat treatment temperature of the polymer liquid crystal phase formed on the substrate is preferably equal to or higher than the transition temperature of the liquid crystal phase / isotropic phase of the polymer liquid crystal used. Further, it is preferably below the glass transition temperature of the substrate. Above the glass transition temperature of the base material used, there is a problem in the manufacturing process such as deformation of the base material. These temperature ranges can be appropriately selected in consideration of the transition temperature of the polymer liquid crystal used and the glass transition point of the substrate.

The heat treatment time is 1 minute or longer, preferably 10 minutes.
Minutes or more is good. The heating rate and cooling rate in the heat treatment are not particularly limited, but in order to obtain a uniform homeotropically aligned polymer liquid crystal film, 20 ° C./min or less, preferably 15 ° C./min or less, more preferably 10 ° C./min or less. It is preferable to cool at less than or equal to ° C / min.

The obtained homeotropically aligned polymer liquid crystal film can be used as it is, but for obtaining a composite retardation film, a retardation made of a uniaxially oriented thermoplastic polymer having positive refractive index anisotropy. The orientation may be fixed in order to effectively perform a process such as laminating with a film. Examples of the immobilization method include a method of introducing a polymerizable functional group into the polymer liquid crystal, heating the polymer liquid crystal for alignment, and polymerizing the functional group.

In the present invention, the position of the compensating polymer liquid crystal is not particularly limited, and it may be anywhere between the two polarizing plates of the liquid crystal display. For example, the polymer liquid crystal may be homeotropically aligned using the surface of a polarizing plate, a protective film of a polarizing plate, a transparent electrode, the back side of a transparent electrode, a retardation film, a protective film of a retardation film, etc. as a substrate. The substrate is placed, the polymer liquid crystal is homeotropically oriented, and the polarizing plate, the protective film of the polarizing plate, the back side of the transparent electrode,
You may laminate with a retardation film, the protective film of a retardation film, etc.

To evaluate the viewing angle characteristics of the obtained composite retardation film, the transmission spectrum of the retardation film is measured with a polarization spectrophotometer equipped with a Gram-Thomson prism to determine the retardation. Alternatively, the retardation is determined by a Senarmon birefringence measuring method using a Senarmon compensator with a polarizing microscope. Next, in the case of a retardation film having positive refractive index anisotropy, the retardation (R) measured in a state of being tilted with the slow axis as the rotation axis and the retardation (R) measured in a horizontal state with ₀₎ ratio (R / R ₀₎ is the inclination angle when the 1. 10 (θ _1.10), referred to the value as the viewing angle of the phase difference film. The smaller the change in retardation angle, the larger the tilt angle (θ _1.10 ), that is, the better the viewing angle characteristic.

According to the present invention, a homeotropically aligned polymer liquid crystal film and a retardation film made of a uniaxially oriented thermoplastic polymer having a positive refractive index anisotropy having an optical axis in the film plane are used at the same time. The viewing angle θ
_1.10 can be improved.

[0047]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. Example 1 A polymer liquid crystal in which five units represented by the following chemical formula 15 were cyclically connected was used. Liquid crystal phase of this polymer liquid crystal
The isotropic phase transition temperature was 97 ° C. This polymer liquid crystal was dissolved in acetone to a concentration of 15 wt%. When the glass substrate was ultrasonically cleaned with a detergent (CLEAN ACE manufactured by Shoko Tsusho Co., Ltd.), the contact angle with water was 30.3 °. The polymer liquid crystal solution was applied onto a glass substrate with a spin coater (1H-DX manufactured by Mikasa Co., Ltd.) and dried. The obtained polymer liquid crystal thin film was cloudy. Then 1 glass substrate
Heated for 10 minutes on a hot plate at 30 ° C.
Then, the hot plate was switched off while the glass substrate was left on the hot plate, and the glass substrate was gradually cooled to room temperature over 4 hours. The polymer liquid crystal after cooling was transparent under crossed nicols and had a retardation of 0 nm, but it was found that when the polymer liquid crystal film was tilted from the horizontal plane, the retardation appeared, and thus the liquid crystal was vertically aligned. At this time, the thickness of the polymer liquid crystal layer was measured by a needle-contact type film thickness meter (Alpha Step AS-200 manufactured by Tencor Co., Ltd.) and found to be 2.1 μm.

A polycarbonate raw fabric film having a thickness of 185 μm was obtained by a solvent casting method. A polycarbonate raw fabric was stretched 2.1 times at 184 ° C. by a longitudinal uniaxial stretching method. 98 μm, R ₀ = 572 nm, viewing angle θ _1.10 = 32.2
It was °.

A polycarbonate retardation film and a polymer liquid crystal film on a glass substrate were laminated and the viewing angle was measured to be 45 ° or more, which was superior to the case where the polycarbonate retardation film alone was used. A composite retardation film was obtained. This widening of the viewing angle is due to the homeotropic alignment of the polymer liquid crystal film.

[0050]

[Chemical 15]

Comparative Example 1 A polymer liquid crystal film was obtained in the same manner as in Example 1 except that the glass substrate coated with the polymer liquid crystal was not heated. When the obtained polymer liquid crystal film was observed under crossed Nicols, a minute schlieren texture was observed. The retardation film shown in Example 1 and the obtained polymer liquid crystal film were laminated to obtain a composite retardation film. This composite retardation film was cloudy when visually observed. 3 when measuring the viewing angle
There was almost no change at 2.7 °.

Example 2 When a glass substrate was treated with oxygen plasma, the contact angle with water became 5.2 °. Example 1 except that it was made hydrophilic
A polymer liquid crystal film with a thickness of 1.1 μm was obtained by the same method as described above. This polymer liquid crystal film and the retardation film shown in Example 1 were laminated to obtain a composite retardation film. When the viewing angle of this composite retardation film was measured, a composite retardation film having a viewing angle of 45 ° or more, which was superior to the original retardation film, was obtained.

Example 3 When a glass substrate was treated with a silane coupling agent (AY43-021 manufactured by Toray Silicone Co., Ltd.) to be hydrophobized, the contact angle with water became 87.4 °. After heating, a polymer liquid crystal film having a thickness of 1.5 μm was obtained in the same manner as in Example 1 except that the glass substrate was placed on a stainless steel plate at 20 ° C. and rapidly cooled. This polymer liquid crystal film and the retardation film shown in Example 1 were laminated to obtain a composite retardation film. When the viewing angle of this composite retardation film was measured, a composite retardation film having a viewing angle superior to that of the original retardation film was obtained at 45 ° or more.

Example 4 Polyvinyl alcohol (for liquid crystal alignment film manufactured by EHC) was spin-coated on a glass substrate to obtain a polyvinyl alcohol substrate. The contact angle of the substrate with water was 45.2 °. This polyvinyl alcohol substrate was spin-coated with the same polymer liquid crystal acetone solution as in Example 1. After that, heat treatment was performed in the same manner as in Example 1 to obtain a polymer liquid crystal film having a thickness of 0.7 μm. This polymer liquid crystal film was laminated with the retardation film shown in Example 1 to obtain a composite retardation film.
When the viewing angle of this composite retardation film was measured, it was 3
A composite retardation film having a viewing angle of 7.5 °, which is more excellent than the original retardation film, was obtained.

Example 5 The polycarbonate raw fabric shown in Example 1 was attached to a glass substrate and ultrasonically washed with a detergent, and polyvinyl alcohol was applied thereon in the same manner as in Example 4. At this time, the contact angle to water was It was 45.2 °. A polymer liquid crystal film was formed on this substrate in the same manner as in Example 4, and heat treatment was performed in the same manner as in Example 1 to obtain a polymer liquid crystal film having a thickness of 1.6 μm. This polymer liquid crystal film and the polycarbonate retardation film shown in Example 1 were laminated so that their slow axes coincided with each other to obtain a composite retardation film. When the viewing angle of this composite retardation film was measured, it was 32.0 °, and a composite retardation film having a viewing angle superior to that of the composite retardation film shown in Comparative Example 2 was obtained.

Comparative Example 2 The polycarbonate raw fabric shown in Example 1 was attached to a glass substrate. This polycarbonate raw fabric and a polycarbonate retardation film of R = 512 nm produced in the same manner as in Example 1 were laminated so that the slow axes of the films were aligned to obtain a composite retardation film. When the viewing angle of this composite retardation film was measured, it was 29.0 °,
The viewing angle was deteriorated by laminating the two polycarbonate films so that the slow axes thereof coincided with each other.

Comparative Example 3 A raw polycarbonate sheet was treated in the same manner as in Example 5 except that polyvinyl alcohol was not applied. At this time, the contact angle with water was 80.5 °. An acetone solution of the same polymer liquid crystal as in Example 1 was spin-coated on this substrate to obtain a polymer liquid crystal film. After that, heat treatment was performed in the same manner as in Example 1 and Example 3, but the polymer liquid crystal film observed under crossed Nicols showed a schlieren texture and was not vertically aligned. The polymer liquid crystal on the polycarbonate and the retardation film shown in Example 1 were laminated so that the respective slow axes coincided with each other to obtain a composite retardation film. The obtained composite retardation film was opaque, and when the viewing angle was measured, different values were obtained depending on the location, which proved to be impractical.

[0058]

According to the present invention, the polymer liquid crystal can be formed into a film on the substrate by the coating method, and the polymer liquid crystal can be homeotropically aligned by the subsequent heat treatment. Therefore, according to the present invention, it is possible to easily obtain a composite retardation film having excellent orientation properties and operability and excellent viewing angle properties. Further, by applying these to the STN type liquid crystal display device, it is possible to remarkably improve the display characteristics of the liquid crystal display device, particularly the viewing angle characteristics.

Claims (3)

[Claims] 1. A polymer having a nematic phase or a smectic phase on a uniaxially oriented retardation film made of a thermoplastic polymer having an optical axis in the film plane and having positive refractive index anisotropy. A method for producing a composite retardation film, which comprises forming a liquid crystal film and heat-treating the liquid crystal material at a temperature equal to or higher than a transition temperature of a liquid crystal phase / isotropic phase of the polymer liquid crystal. 2. A polymer liquid crystal exhibiting a nematic phase or a smectic phase is formed into a film on a substrate having a glass transition temperature equal to or higher than the transition temperature of the liquid crystal phase / isotropic phase of the polymer liquid crystal, and the liquid crystal phase / A thermoplastic resin that is heat-treated at a temperature equal to or higher than the transition temperature of an isotropic phase and has a substrate on which the polymer liquid crystal is formed, an optical axis in the film plane, and positive refractive index anisotropy. A method for producing a composite retardation film, comprising laminating a uniaxially oriented retardation film composed of molecules. 3. The method for producing a composite retardation film according to claim 2, wherein the base material is a polarizing film.