JPH0862422A - Phase difference film and its manufacture - Google Patents

Abstract

PURPOSE: To provide a phase difference film which can be used as an optical compensation layer for various types of liquid crystal display devices by providing the film with specific optical characteristics. CONSTITUTION: A thermoplastic resin film is preheated in the condition of Tg<Tp<=(Tg+100 deg.C) (Tg is a glass-transition temperature of thermoplastic resin and Tp is preheating temperature). The preheated film is extended along an axis at a deformation rate of 150-1000%/minute and extension magnification of 2-3 in a condition in which shrinkage does not occur in the orthogonal direction to an extended axis in the condition of Tg<Ts<=(Tg+100 deg.C) (Ts is extension temperature). The film extended along one axis is kept warm (heat treated) for a predetermined time in the condition of (Ts-50 deg.C)<=Ths<Ts (Ths is heat treatment temperature). Thus obtained phase difference film has optical characteristics that retardation value in the face is 50-300nm and the ratio of retardation value in the face to retardation value in the direction of thickness is 0.5 or more and 1.8 or less.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a retardation film.

[0002]

2. Description of the Related Art A retardation film is generally used as an optical compensation layer of an STN type liquid crystal display device, but in recent years, not only for the STN type liquid crystal display device but also for other type liquid crystal display devices. Various applications have also been studied as an optical compensation layer. For example, recently STN
In TN type liquid crystal display devices and the like, special viewing angle characteristics may be required depending on applications, and as a result, retardation films having various optical characteristics may be required depending on applications. Has become.

However, the retardation films currently under development have characteristics close to the uniaxial orientation used in the above-mentioned STN type liquid crystal display device, and EP-A-05.
No. 41308, which is a retardation film having properties close to perfect biaxial orientation, which is composed of an inorganic layered compound layer having different in-plane and in-thickness refractive indices.
The retardation film is limited to the above-mentioned types, and even if they are combined with each other, a retardation film having an intermediate property between these two types of retardation films has not been developed so far.

[0004] In addition, a collection of proceedings of Eurodisplay '93 p. 149, n is used as an optical compensation layer for a bend alignment type OCB mode liquid crystal display device (π cell).
_X = 1.618, n _Y = 1.606, n _Z = 1.49
3. It has been simulated that a retardation film having a refractive index structure with a film thickness of 9.296 μm would be effective. The in-plane retardation value of the retardation film calculated from this is 112 nm, (in-plane retardation value) / (thickness direction retardation value)
The ratio is 0.101.

However, since the retardation film used in the STN type liquid crystal display device has been uniaxially oriented,
The ratio of (in-plane retardation value) / (retardation value in the thickness direction) is 2.0 or more, while EP-A
In the retardation film composed of an inorganic layered compound layer having an in-plane refractive index and a thickness-direction refractive index different from each other as described in JP-A-0541308, the in-plane retardation is 0.
Since only a film having a thickness of up to 50 nm can be obtained, it is not possible to obtain a retardation film having properties that can be used as, for example, the optical compensation layer of the above-mentioned π cell from the films currently developed as a mass production retardation film. For this reason, it is necessary to develop a retardation film having optical properties different from those of the conventional one, and particularly to develop a retardation film using a lightweight thermoplastic resin, and to efficiently and industrially use such a retardation film. It is desired to develop an advantageous manufacturing method.

[0006]

Means for Solving the Problems As a result of studies to solve the above problems, the inventors found that the in-plane retardation value was 50 to 300 nm, and the (in-plane retardation value) / The retardation film having optical characteristics in which the ratio of (retardation value in the thickness direction) is 0.5 or more and 1.8 or less has been successfully developed, and the present invention has been achieved. Further, the in-plane retardation value is 50 to 300 nm, and the ratio of (in-plane retardation value) / (retardation value in the thickness direction) is 0.5 or more and 1.8 or less. The ratio of (in-plane retardation value) / (retardation value in the thickness direction) in which the retardation film and the retardation film composed of the inorganic layered compound layer are laminated is 0.
The development of a laminated retardation film having a thickness of 03 or more and less than 0.3 has been successful and the present invention has been achieved.

That is, in the present invention, the in-plane retardation value is 50 to 300 nm and the ratio of (in-plane retardation value) / (retardation value in the thickness direction) is 0.5 or more and 1.8 or less. A retardation film made of a thermoplastic resin film and a method for producing the same, further, one or more retardation films and one or more retardation films made of an inorganic layered compound layer were laminated (in-plane Retardation value) / (retardation value in the thickness direction) of 0.03 or more and less than 0.3.

As the thermoplastic resin, those having excellent transparency are preferably used. For example, polycarbonate-based resin, cellulose acetate, polyvinyl alcohol,
Examples thereof include polysulfone, polyether sulfone, polyarylate, and the like. Among them, polycarbonate resin and polysulfone are more preferable.

As the thermoplastic resin film, a film produced by using a solvent casting method is usually used. The thickness of the thermoplastic resin film is, for example, 50 to 300 μm, preferably 100 to 200 μm. The retardation film of the present invention can be produced, for example, by the following method.

The thermoplastic resin film produced by the solvent casting method is continuously subjected to preheating, uniaxial stretching and heat treatment in a tenter provided with a preheating portion, a stretching portion and a heat treatment portion in succession. First, preheating refers to a treatment in which the thermoplastic resin film is previously softened by heating so that it can be favorably stretched in the subsequent stretching treatment. The thermoplastic resin film introduced into the device has Tg <Tp ≦ (Tg +
100 ° C) (however, Tg represents the glass transition temperature of the thermoplastic resin and Tp represents the preheating temperature), but the preheating time is for softening the resin as much as necessary and suppressing excessive deformation. Generally, 0.1 minute to 1 minute is preferable.

Next, the preheated film is introduced into the stretched portion and Tg <Ts ≦ (Tg + 100 ° C.) (where Ts
Indicates the stretching temperature. ), In a state in which the shrinkage in the direction orthogonal to the stretching axis does not occur, the deformation rate is 150% / min to 1000% / min, the stretching ratio is 2 to 3 times, and the film is transversely uniaxial in the direction orthogonal to the traveling direction of the film. It is stretched. Here, the stretching temperature, the deformation rate, and the stretching ratio are the type and thickness of the thermoplastic resin film used as the raw fabric, and the required in-plane retardation value of the retardation film, (in-plane retardation value). / (Retardation value in the thickness direction)
Is appropriately selected depending on the value of the ratio, thickness, etc. For example, when a polycarbonate film is used, the stretching temperature is 1
90-220 ° C, deformation rate 150-600% / mi
It is preferable that the stretching ratio is n and the draw ratio is 2 to 3 times. Generally, lowering the stretching temperature or increasing the deformation rate,
Alternatively, if the stretching ratio is increased, the in-plane retardation value tends to increase, and by increasing the stretching ratio, the value of the ratio of (in-plane retardation value) / (thickness retardation value) Tends to grow.

Further, the uniaxially stretched film is introduced into a heat treatment section, and the chuck width (width in the stretching axis direction) after stretching is maintained for the purpose of fixing the orientation of the film, etc.
(Ts−50 ° C.) ≦ Ths ≦ Ts (where Ths indicates the heat treatment temperature), and the temperature is kept for 0.1 minute to 1 minute. This heat retention is usually called heat treatment. At this time, if necessary, the film may be shrunk in the stretching axis direction in the range of 0 to 10%. For contraction, for example, the chuck width may be narrowed so as to have a required contraction rate. Although it can be carried out by a method other than the continuous treatment method of preheating by a tenter, uniaxial stretching and heat treatment, a method using a tenter is preferable in industrial production.

The in-plane retardation value of the obtained retardation film is 50 nm to 300 nm, and the ratio of (in-plane retardation value) / (thickness retardation value) is 0.5 or more and 1.8 or less. And has completely different optical characteristics from the conventional retardation film.

The in-plane retardation value and the ratio of (in-plane retardation value) / (retardation value in the thickness direction) are appropriately selected depending on the application of the retardation film. The in-plane retardation value is preferably 80
nm-200 nm, and the retardation value in the thickness direction is preferably 45 nm-400 nm. The thickness of the retardation film is preferably 50 to 150 μm from the viewpoint of handleability.

The retardation film of the present invention can be used alone or in combination with other retardation films as an optical compensation layer for various liquid crystal display devices. For example, E
P-A-0541308, which is composed of an inorganic layered compound layer having different in-plane refractive index and refractive index in the thickness direction, has an in-plane retardation value of 0 to 50 nm, and has a thickness direction letter -Dation value is 50 nm to 10
It can be used in combination with a retardation film of 00 nm.

The retardation film comprising an inorganic layered compound layer is obtained, for example, by swelling or dispersing an inorganic layered compound in a solvent as described in EP-A-0541308, then coating and drying. be able to. As the inorganic layered compound, for example, a clay mineral can be used. Preferred are sodium tetrasilicate mica and smectite group which are chemically synthesized and have few impurities, and those belonging to the smectite group have montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite and crystal structures similar to them. Examples include chemically synthesized products. As the solvent used for swelling or dispersing the inorganic layered compound, for example,
It can be appropriately selected and used from dimethylformamide, dimethylsulfoxide, nitromethane, water, methanol, ethylene glycol and the like.

In forming the inorganic layered compound layer, as described in EP-A-0541308, in order to improve film-forming properties and mechanical properties such as prevention of cracking of the inorganic layered compound layer. It is preferable to mix an optically transparent hydrophilic resin in the dispersion liquid of the inorganic layered compound, and the volume ratio of the inorganic layered compound / the optically transparent resin is, for example, about 0.1 to 10. . Examples of the optically transparent hydrophilic resin include polyvinyl alcohol. Further, by forming an inorganic layered compound layer on an optically transparent resin film, a retardation film composed of an inorganic layered compound layer reinforced with an optically transparent resin film can be obtained. In the present invention, such an embodiment is also referred to as a retardation film including an inorganic layered compound layer.

The method for laminating the retardation film comprising the retardation film of the present invention and the inorganic layered compound layer is not particularly limited, but for example, the inorganic layered compound layer is directly formed on the retardation film of the present invention and laminated. Or a retardation film comprising an inorganic layered compound layer in which an inorganic layered compound layer is formed on an optically transparent substrate as described in EP-A-0541308 and a retardation of the present invention. A method of laminating the film with an adhesive or a pressure-sensitive adhesive can be used. The number of laminated retardation films and the optical properties of each retardation film, that is, the in-plane retardation and the ratio of (in-plane retardation value) / (retardation value in the thickness direction) are The layered retardation film is appropriately selected according to the optical characteristics finally required.

In addition, when laminating one or more retardation films composed of an inorganic layered compound layer having an inorganic layered compound layer formed on a transparent substrate and one or more retardation films of the present invention, When the retardation film composed of the inorganic layered compound layer has an in-plane retardation, the retardation film composed of the inorganic layered compound layer depends on the finally required optical properties of the laminated retardation film. By laminating each slow axis of the above and each slow axis of the retardation film of the present invention so as to be parallel or orthogonal to each other, it is possible to adjust so as to meet the finally required optical characteristics. A laminated retardation film obtained by laminating one or more retardation films of the present invention and one or more retardation films composed of an inorganic layered compound layer has an in-plane retardation value / (thickness direction). It can be used as an optical compensation layer having a ratio of (retardation value) of 0.03 or more and less than 0.3.

[0020]

The retardation film of the present invention has an in-plane retardation value of 50 to 300 nm and a ratio of (in-plane retardation value) / (retardation value in the thickness direction) of 0.5 or more. It has a novel optical property of 1.8 or less, and can be used alone or in combination with other retardation films as an optical compensation layer for liquid crystal display devices of various systems. Furthermore, a laminated retardation film obtained by laminating one or more retardation films of the present invention and one or more retardation films composed of an inorganic layered compound layer has a (in-plane retardation value) / ( The ratio of the retardation value in the thickness direction is 0.03 or more.
It can be used as an optical compensation layer of less than 3. In addition, according to the method of the present invention, the above retardation film can be efficiently and stably produced with good mass productivity, that is, it is industrially extremely advantageous.

[0021]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The in-plane retardation value was determined by using a polarizing microscope equipped with a Senarmont compensator so that the film surface and the optical system were perpendicular to each other. The retardation value in the thickness direction was calculated according to the following formula. Retardation value in the thickness direction = ((n _X + n _Y ) / 2
−n _Z ) × d (where n _X is the maximum refractive index in the film plane, n _Y is the vertical refractive index of n _{X in} the film plane, n _Z is the refractive index in the film thickness direction, and d is the film thickness. The laminated retardation film obtained by laminating one or more retardation films of the present invention and one or more retardation films composed of an inorganic layered compound layer is a single retardation film. Then, the in-plane retardation value and the thickness direction retardation value were determined in the same manner as above.

Example 1 Polycarbonate (Tg: 14
A continuous film (thickness 140 μm) at 8 ° C. was produced.
This film was introduced into a tenter having a preheating section of 3 m, a stretching section of 6 m, and a heat treatment section of 3 m, and was preheated (temperature 2
20 ° C., 20 seconds), transverse uniaxial stretching treatment in a direction orthogonal to the film advancing direction (deformation speed 200% / min, stretching temperature 207 ° C., stretching ratio 2.2 times) and heat treatment (temperature 18).
A shrinkage rate of 0% at 0 ° C. for 20 seconds was continuously performed. The thickness of the obtained retardation film was 58 μm, the in-plane retardation value was 101 nm, the thickness direction retardation value was 143 nm, and the ratio of (in-plane retardation value) / (thickness direction retardation value) Was 0.706.

Example 2 Polycarbonate (Tg: 14
A continuous film (thickness 140 μm) at 8 ° C. was produced.
This film was introduced into a tenter similar to that used in Example 1, preheated (temperature: 220 ° C., 20 seconds), and transversely uniaxially stretched in a direction orthogonal to the traveling direction of the film (deformation rate 233%). / Min, stretching temperature 200 ° C., stretching ratio 2.4 times) and heat treatment (temperature 180 ° C., 20 seconds, shrinkage ratio in stretching axis direction 8.3%). The thickness of the obtained retardation film was 60 μm, the in-plane retardation value was 117 nm, the thickness direction retardation value was 159 nm, and the (in-plane retardation value) /
The ratio of (retardation value in the thickness direction) was 0.736.

Example 3 Polycarbonate (Tg: 14
A continuous film (thickness: 185 μm) at 8 ° C. was prepared.
This film was introduced into the same tenter as that used in Example 1, preheated (temperature: 220 ° C., 10 seconds), and transversely uniaxially stretched in a direction orthogonal to the traveling direction of the film (deformation rate: 467%). / Min, stretching temperature of 208 ° C., stretching ratio of 2.4 times) and heat treatment (temperature of 200 ° C., 10 seconds, shrinkage ratio of stretching axis direction 0%) were continuously applied. The obtained retardation film has a thickness of 70 μm, an in-plane retardation value of 119 nm, and a thickness direction retardation value of 14
It was 3 nm, and the ratio of (in-plane retardation value) / (retardation value in the thickness direction) was 0.832.

Example 4 A synthetic hectorite (Lapolite) (Lapo) was placed on a film obtained by saponifying the surface of a triacetyl cellulose film having a thickness of 80 μm (Fujitac, manufactured by Fuji Photo Film Co., Ltd.).
Latte: Laponite XLS) 5% aqueous dispersion and polyvinyl alcohol (Kuraray Co., Ltd .: Poval 10)
3. A 2.5% aqueous solution having a saponification degree of 98.5% and a degree of polymerization of 300 was mixed at a ratio of 3: 7 (volume ratio) to obtain an aqueous dispersion, and the film thickness after drying was 23 μm. As described above, a retardation film (hereinafter, referred to as film A) including an inorganic layered compound layer in which the inorganic layered compound layer was formed on the triacetyl cellulose film was obtained. The in-plane retardation value of the film A was 8 nm, and the retardation value in the thickness direction was 370 nm. The thickness of film A is 1
It was 03 μm.

A retardation film prepared in the same manner as in Example 2 was prepared by laminating two films A with an acrylic pressure-sensitive adhesive so that the slow axes were parallel to each other. The laminate was laminated with an acrylic pressure-sensitive adhesive so as to be orthogonal to the axis to obtain a laminated retardation film. The thickness of the laminated retardation film was 316 μm, the in-plane retardation value was 105 nm, and the retardation value in the thickness direction was 101.
It was 2 nm, and the ratio of (in-plane retardation value) / (retardation value in the thickness direction) was 0.104.

Example 5 A retardation film comprising an inorganic layered compound layer (hereinafter referred to as film B) was obtained in the same manner as in Example 4 except that the film thickness after drying was 16 μm. The in-plane retardation value of the film B was 10 nm, and the retardation value in the thickness direction was 305 nm. The thickness of film B was 96 μm. The retardation film produced in the same manner as in Example 2 was laminated with an acrylic pressure-sensitive adhesive so that the slow axis thereof was orthogonal to the slow axis of the film B to obtain a laminated retardation film. The thickness of the laminated retardation film is 211 μm, the in-plane retardation value is 110 nm,
The retardation value in the thickness direction is 545 nm,
The ratio of (in-plane retardation value) / (retardation value in the thickness direction) was 0.202.

Claims (10)

[Claims] 1. An in-plane retardation value is 50 to 30.
A retardation film made of a thermoplastic resin having a thickness of 0 nm and a ratio of (in-plane retardation value) / (retardation value in the thickness direction) of 0.5 or more and 1.8 or less. 2. The retardation film according to claim 1, wherein the thermoplastic resin is a polycarbonate resin or a polysulfone resin. 3. The in-plane retardation value is 80 to 20.
The retardation film according to claim 1, which has a thickness of 0 nm. 4. The retardation film preheats the thermoplastic resin film in the following temperature range: Tg <Tp ≦ (Tg + 100 ° C.) (Tg: glass transition temperature of thermoplastic resin) (Tp: preheating temperature) Within the range, the deformation rate is 1 with the length not to shrink in the direction orthogonal to the stretching axis.
50% / min to 1000% / min, uniaxially stretched at a stretch ratio of 2 to 3 and Tg <Ts ≦ (Tg + 100 ° C.) (Ts: stretching temperature) Heat treatment in the following temperature range (Ts−50 ° C.) ≦ Ths ≦ The retardation film according to claim 1, which is obtained by Ts (Ths: heat treatment temperature). 5. A thermoplastic resin film is preheated in the following temperature range, and Tg <Tp ≦ (Tg + 100 ° C.) (Tg: glass transition temperature of thermoplastic resin) (Tp: preheating temperature) The deformation rate is 150% so that the length does not shrink in the direction orthogonal to
/ Min to 1000% / min, uniaxially stretched at a draw ratio of 2 to 3 times, and Tg <Ts ≦ (Tg + 100 ° C.) (Ts: stretching temperature) (Ts−50 ° C.) ≦ Ths ≦ Ts (Ts: 50 ° C.) Ths: heat treatment temperature), the in-plane retardation value is 50 to
300 nm, (in-plane retardation value) /
A method for producing a retardation film having a ratio of (retardation value in the thickness direction) of 0.5 or more and 1.8 or less. 6. A heat treatment, wherein the length in the direction of the stretching axis is 1
The method according to claim 5, which is performed while shrinking at 0% or less. 7. The method according to claim 5, wherein the thermoplastic resin film is obtained by a solvent casting method. 8. The method according to claim 5, wherein the thermoplastic resin is a polycarbonate resin or a polysulfone resin. 9. The in-plane retardation value is 80 to 20.
The method according to claim 5, which is 0 nm. 10. The in-plane retardation value is 50 to 30.
One or two or more retardation films composed of a thermoplastic resin film having a thickness of 0 nm and a ratio of (in-plane retardation value) / (retardation value in the thickness direction) of 0.5 or more and 1.8 or less. One or two or more retardation films composed of an inorganic layered compound layer are laminated, and the ratio of (in-plane retardation value) / (retardation value in the thickness direction) is 0.03 or more and less than 0.3. Laminated retardation film.