JPH10221525A - Manufacturing of phase-difference film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformalize a retardation value at high precision and uniformly and optically compensate across the approximately whole region by laminating films via a solvent containing thermoplastic resin solvent or thermoplastic resin plasticizer. SOLUTION: Thermoplastic resin films formed by a molten extrusion filming method are extended after being laminated via a solvent containing thermoplastic resin solvent or thermoplastic plasticizer. The thermoplastic resin may be dissolved in the solvent interposed in laminating. It is preferable that the resin dissolved in the solvent is the same kind of thermoplastic resin as the thermoplastic resin film, however, a different kind of thermoplastic resin may be dissolved in the solvent, unless interfering the function as the phase-difference film. It is preferable that the content of the thermoplastic resin dissolved in the solvent is 40wt.% or less. A thermoplastic resin lean solvent may be dissolved in the solvent. It is preferable that the addition quantity of the solvent is 30wt.% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a birefringent retardation film by stretching and orienting a polymer film.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device of a personal computer or a word processor is capable of responding to an increase in display capacity and a large screen and realizing a high contrast.
N liquid crystals have been used. In a display device using an STN liquid crystal, the display color is mainly colored blue or yellow with elliptically polarized light due to the birefringence of the STN liquid crystal. Therefore, it has been studied to make the display color black and white by compensating for the phase difference due to the birefringence of the STN liquid crystal.

As means for compensating for the phase difference, there are a D-STN system using a compensating liquid crystal cell having the same configuration as that of the liquid crystal display cell and having only the phase difference reversed, and an F-STN system using a birefringent film. . The F-STN method uses DS
This is a desirable display device that can be reduced in weight and thickness as compared with the TN method and has cost advantages.

A phase difference compensating plate of the F-STN type has conventionally been produced by stretching an amorphous thermoplastic resin film or sheet. As the thermoplastic resin used, polycarbonate resin, cellulose resin, vinyl chloride resin, acrylonitrile resin,
There are styrene resin, olefin resin, polysulfone resin and the like. These thermoplastic resins are formed into a film or a sheet by a solution casting method, a calendering method, a melt extrusion method, or the like, and are stretched in a longitudinal direction or a transverse direction to obtain a birefringent film to obtain a retardation compensating plate.

A general cell configuration of an F-STN type liquid crystal display element has a structure in which a liquid crystal cell and one or two phase difference compensating plates are sandwiched between two polarizing plates in a parallel Nicols state. A liquid crystal display device is configured by bonding the respective interfaces of the polarizing plate, the phase difference compensator, and the glass surface of the liquid crystal cell via an adhesive layer.

The phase difference compensating performance of the phase difference compensating plate is represented by a so-called retardation value. The retardation value R is represented by the following formula: R = Δn × d where Δn is the anisotropy of the refractive index (that is, birefringence) of the polymer film and d is the thickness of the film.

In a liquid crystal display device, it is strongly required that color unevenness and contrast unevenness hardly occur over the entire surface of the display. To enable such a uniform display, even a phase difference compensator requires a letter. It is necessary that the gradation value is uniform over the entire surface.

Conventionally, in order to obtain a retardation film having a uniform retardation value, a thermoplastic resin film formed by a casting method has been used. According to such a casting film forming method, a retardation film having excellent thickness accuracy and surface smoothness and high optical uniformity can be manufactured. JP 4
JP-A-204503 describes a method in which the solvent content in the casting film-forming method is stretched to 2 to 10% by weight based on the solid content. Japanese Patent Application Laid-Open No. 5-113506 discloses that a methylene chloride solution of polycarbonate is cast into a film, the solvent content of the film is adjusted to 3 to 10% by weight based on the solid content, and then the film is heated in an atmosphere at 155 to 175 ° C. Describes a method of stretching in the direction of film advance.

However, the casting film forming method has a problem that a large amount of solvent needs to be used, the production cost is increased, and environmental hygiene is not preferable. In addition, it is generally necessary to use a base film serving as a casting base material, and the manufacturing process is complicated.

As a method for producing a thermoplastic resin film for an inexpensive and environmentally friendly retardation film, there is a melt extrusion film forming method. JP-A-2-256003 describes a method for producing a retardation film using such a melt extrusion film-forming method. In this publication, when a change in thickness is measured continuously in the length direction. A uniaxially stretched or biaxially stretched thermoplastic polymer film having a pitch of 50 mm or less and having a thickness amplitude of 0.5 μm or more and having no sinusoidal thickness variation exists in a direction perpendicular to the extrusion direction. There has been proposed a method for producing a retardation film by using such a method. It is described that the retardation value of the retardation film thus obtained is 1200 nm or less, and the amplitude of the retardation value is 10% or less.

[0011]

By the way, color unevenness and contrast unevenness in a liquid crystal display device are close to each other when evaluated by incorporating a phase difference compensating plate in the liquid crystal display device.
The evaluation can be made based on whether or not the difference in the retardation value between the points is easy to determine. One criterion for evaluating the unevenness of the retardation compensator is that the unevenness of the retardation is 1 nm / cm or less as a condition that cannot be visually recognized as unevenness.

The thermoplastic polymer film disclosed in JP-A-2-256003 has a pitch of 50 mm, a thickness amplitude of 0.5 μm, and a thickness variation of 0.1 μm / cm. The thickness of the phase difference compensator currently in practical use is about 50 μm, and the phase difference variation is proportional to the thickness variation as is apparent from the above equation 1, so that the practically used phase difference of 400 to 2000 nm , 0.8-4.
0 nm / cm, most of which are not satisfactory as phase difference unevenness.

Therefore, in the method for producing a retardation film by a melt extrusion film forming method, at present, the retardation value has not been made uniform to a level which is sufficiently satisfactory for practical use. When the phase difference compensator was incorporated, there was color unevenness with a fine pitch that could be visually discriminated.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a retardation film having a uniform retardation value with high precision and capable of performing uniform optical compensation over substantially the entire region by a melt extrusion film forming method. It is to provide a manufacturing method.

[0015]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that a method of stretching after laminating and joining thermoplastic resin films formed by a melt extrusion film forming method. It has been found that the above-mentioned object can be achieved by laminating and joining via a solvent containing a solvent for the thermoplastic resin or a plasticizer for the thermoplastic resin.

That is, the present invention relates to a method of forming a thermoplastic resin film formed by a melt extrusion film forming method after laminating the thermoplastic resin films via a solvent containing a solvent of the thermoplastic resin or a plasticizer of the thermoplastic resin. It is characterized by stretching.

In the present invention, a thermoplastic resin may be dissolved in the above-mentioned solvent interposed at the time of laminating. The resin to be dissolved in the solvent is preferably a thermoplastic resin of the same type as the thermoplastic resin film, but as long as the function as a retardation film is not hindered, a different type of thermoplastic resin may be dissolved in the solvent. . The content of the thermoplastic resin dissolved in the solvent is 40% by weight.
The following is preferred. If the content of the thermoplastic resin is too large,
Since the viscosity of the solution to be joined is high, application unevenness occurs or the smoothness is impaired, which causes deterioration in thickness accuracy after joining.

Further, in the present invention, in the above-mentioned solvent,
The poor solvent of the thermoplastic resin may be dissolved. The addition amount of the poor solvent is preferably 30% by weight or less. If the amount of the poor solvent is increased, whitening or the like of the adhesive surface of the film occurs, which leads to a decrease in light transmittance.

In the present invention, the above-mentioned thermoplastic resin or a poor solvent for the thermoplastic resin may be added to the plasticizer interposed at the time of laminating. Preferred addition amounts are the same as in the case of the above-mentioned solvent. Further, in the present invention, the above solvent and the above plasticizer may be mixed and used.

The thermoplastic resin film used in the present invention is not particularly limited as long as it can be used as a retardation film. For example, polycarbonate, polystyrene, polymethyl methacrylate,
Polyvinyl chloride, styrene / acrylonitrile copolymer, polyethylene, polyacrylate, polysulfone,
Polyether sulfone, polyphenylene oxide, diacetyl cellulose, triacetyl cellulose and the like can be mentioned. Among these, particularly, polycarbonate and polysulfone are preferable because the phase difference can be made more uniform.

The solvent used in the present invention is not particularly limited as long as it can dissolve the thermoplastic resin. For example, when the thermoplastic resin is polycarbonate or polysulfone, methylene chloride, anisole, acetophenone, N- Methylpyrrolidone and the like. Also,
Examples of the poor solvent include acetone, ethyl acetate, methyl ethyl ketone, toluene, xylene and the like.

The plasticizer used in the present invention should be selected in consideration of the compatibility with the thermoplastic resin and the like. Examples thereof include phthalic acid, phosphoric acid, adipic acid, and citric acid. And plasticizers such as glycolic acid. Two or more plasticizers may be used as a mixture.

In the present invention, as a method of interposing a solvent or a plasticizer at the time of laminating and joining the thermoplastic resin films, the solvent or the plasticizer may be placed on the inner surface of the thermoplastic resin film immediately before the laminating joint. To
Examples of the method include application by a method such as spraying, coating, and dipping. The amount of application is not particularly limited, but immediately after lamination,
A range where the weight increases by 0.5 to 10% by weight is preferable,
More preferably, the weight is in the range of 1 to 5% by weight. When the amounts of the solvent and the plasticizer applied are small, the reliability of the joint at the joint surface is insufficient, and delamination or the like may occur. On the other hand, if the coating amount is too large, swelling may make it difficult to maintain the shape of the film.

In the present invention, the solvent or the plasticizer is preferably applied to the respective inner surfaces of the films to be joined. However, in some cases, the solvent or the plasticizer may be applied to only one inner surface of the films to be joined. .

In the present invention, it is preferable to dry after stretching and before stretching. Drying is performed by heating medium,
There are a method using hot air heated by a heat source such as steam, a method using radiant heat from a panel heater, and the like.

The stretching method in the present invention is not particularly limited, and any of longitudinal uniaxial stretching using a roll and horizontal uniaxial stretching using a tenter can be applied. Moreover, you may perform sequential biaxial stretching and simultaneous biaxial stretching by these combinations.

The stretching may be carried out in-line with a stretching apparatus directly connected to a film-forming apparatus, or a method of winding and storing a film or sheet once after forming a film, and then applying the film or sheet again to the stretching apparatus. Method may be used,
Preferably, the latter method is employed. This is because, after lamination, the diffusion of the solvent and the like into the entire film is more completely performed, whereby the unevenness in retardation after stretching can be more efficiently eliminated.

Although the detailed reason why a retardation film with less retardation unevenness can be produced by the production method according to the present invention is not clear, it is not clear when a solvent is applied to the joining surface when two thermoplastic resin films are laminated and joined. Alternatively, by applying a plasticizer, a layer containing a solvent or a plasticizer is formed at the interface portion of the joint, but these solvents and the like diffuse throughout the film. When the bonding film undergoes a drying step prior to the stretching step or a preheating step before stretching, the solvent and the like in the surface layer portion of the bonding film volatilize, and a layer containing almost no solvent or the like is formed. It is presumed that after stretching, the surface layer becomes a layer that controls the retardation of the whole film or sheet, and that this layer has a uniform thickness, so that the retardation unevenness as a whole is made uniform.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

Example 1 Two 35 μm-thick polycarbonate films obtained by a melt extrusion film forming method at a melting temperature of 280 ° C.
It joined using the laminator. At the time of this bonding, methylene chloride was applied to the inner surface of each film by spraying. The applied amount of methylene chloride was 2% by weight. After film joining, the film was once wound up and stored, and after 24 hours, it was subjected to longitudinal uniaxial stretching using a stretching machine to obtain a retardation film.

The retardation at 590 nm of the obtained retardation film was measured at a pitch of 5 mm by a rotating analyzer. At the same time, the thickness was measured with a thickness gauge at a pitch of 5 mm. Table 1 shows the average value of the retardation after stretching, and the maximum value of the actually measured values of the retardation unevenness and the thickness unevenness.

Example 2 Two 35 μm-thick polysulfone films obtained by a melt extrusion film forming method at a melting temperature of 350 ° C. were used, and instead of methylene chloride, diethyl phthalate as a plasticizer was sprayed. Except for performing lamination and bonding in the same manner as in Example 1, longitudinal uniaxial stretching was performed to obtain a retardation film. The amount of diethyl phthalate applied was 4.5% by weight. About the obtained retardation film, the same measurement as Example 1 was performed, and the measurement result was shown in Table 1.

Example 3 Two 35-μm-thick polysulfone films obtained by a melt extrusion film forming method at a melting temperature of 350 ° C. were used, and instead of methylene chloride, a 10% by weight solution of anisole of polysulfone was sprayed. Except for performing lamination bonding in the same manner as in Example 1, longitudinal uniaxial stretching was performed to obtain a retardation film. The application amount of the anisole solution was 1.
It was 0% by weight. About the obtained retardation film,
The same measurement as in Example 1 was performed, and the measurement results are shown in Table 1.

Comparative Example 1 A polycarbonate film having a thickness of 70 μm obtained by a melt extrusion film forming method at a melting temperature of 280 ° C. was vertically and uniaxially stretched using a stretching machine to obtain a retardation film. With respect to the obtained film, the same measurement as in Example 1 was performed.
Table 1 shows the measurement results.

Comparative Example 2 A polysulfone film having a thickness of 35 μm and obtained by a melt extrusion film forming method at a melting temperature of 350 ° C. was vertically and uniaxially stretched using a stretching machine to obtain a retardation film. The same measurement as in Example 1 was performed on the obtained film. The measurement was performed for one film and two films, respectively, and the measurement results are shown in Table 1.

[0036]

[Table 1]

As is apparent from the results in Table 1, the retardation films of Examples 1 to 3 produced according to the present invention have the same thickness unevenness as the films of Comparative Examples 1 and 2. And the retardation unevenness is significantly reduced, which is a standard that cannot be visually recognized as unevenness, 1 nm / cm.
It can be seen that:

[0038]

According to the production method of the present invention, a retardation film having a highly uniform retardation value can be obtained inexpensively and in harmony with the environment. Therefore, a liquid crystal display device having a uniform display quality over substantially the entire area can be manufactured at low cost.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 11:00

Claims (1)

[Claims] The present invention relates to stretching a thermoplastic resin film formed by a melt extrusion film forming method after laminating and joining each other via a solvent containing a solvent of the thermoplastic resin or a plasticizer of the thermoplastic resin. A method for producing a retardation film.