JP3014581B2 - Method for producing retardation film - Google Patents

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 having uniform birefringence characteristics.

[0002]

2. Description of the Related Art In a STN (Super Twisted Nematic) type liquid crystal display, a retardation film is provided between a liquid crystal cell and a polarizing plate in order to improve the visibility of an image. The retardation film is obtained by uniaxially stretching a polymer film, and the polymer used is made of various materials such as a cellulose resin, a vinyl chloride resin, a polycarbonate resin, a styrene resin, and a polyolefin resin. It has been known. Among these, polycarbonates obtained by stretching a polycarbonate film in a uniaxial direction (Japanese Unexamined Patent Publication No. 63-2 / 1988)
No. 61302) and a viscosity average molecular weight of 40,000.
A product obtained by stretching the above high-polymerization degree polycarbonate (JP-A-3-181905) and the like are known.

[0003] Retardation (hereinafter abbreviated as R value), which is one of the optical characteristics of a film, is defined as the product of the birefringence value and the thickness of the film. Since the variation in the R value of the retardation film appears as color unevenness of the display screen, the human eye cannot detect the color unevenness as 1.0%.
The following accuracy is required. The R value can be controlled by a film thickness, a stretching temperature, a stretching ratio, and the like. By appropriately determining these conditions, a retardation film having desired characteristics can be obtained.

[0004]

However, in the actual stretching, there is a problem that since the temperature is slightly uneven, the R value of the retardation film obtained therefrom is affected. As reported in Japanese Patent Application Laid-Open No. 3-181905, this problem can be improved to some extent by using a high polymerization degree polycarbonate having a viscosity average molecular weight of 40,000 or more obtained from bisphenol A. Is still inadequate.

In Japanese Patent Application Laid-Open No. 4-204503, a retardation film is manufactured using a methylene chloride-containing polycarbonate film. However, although the R value varies slightly, the solvent content is reduced. Because of the large number, a step for further drying the solvent after stretching is required.

[0006] An object of the present invention is to provide a retardation film having uniform birefringence characteristics which has solved the above-mentioned problems.

[0007]

According to the present invention, when a film made of polycarbonate having a viscosity average molecular weight of 10,000 or more and 200,000 or less is stretched to produce a retardation film, 1,3-dioxolane is added to 0.1. 3 to 5.0
This is a method for producing a retardation film, which comprises stretching a film made of polycarbonate containing 10% by weight.

In the present invention, in producing a retardation film by stretching a polycarbonate film, 10 parts by weight of polycarbonate is added to 25 to 150 parts by weight of a solvent containing 1,3-dioxolane in an amount of 60% by weight or more. 1,3-dioxolane produced by casting the dissolved dope on a support was 0.3 to 5.
It is preferable to stretch a film containing 0% by weight.

There is no particular limitation on the polycarbonate used in the present invention. There is no particular limitation as long as it is a polycarbonate capable of obtaining desired film properties. In general,
Polycarbonate, which is generally referred to as a polycarbonate, is generally referred to as one in which the main chain is connected by a carbonic acid bond by a polycondensation reaction in its synthetic method. Among these, generally, a phenol derivative and a phosgene are generally used. And those obtained by polycondensation from diphenyl carbonate and the like. Usually, a polycarbonate represented by the following repeating unit containing 2,2-bis (4-hydroxyphenyl) propane as a bisphenol component, which is called bisphenol-A, is preferably selected. By appropriately selecting various bisphenol derivatives, A polycarbonate copolymer can be constituted.

[0010] In addition to the bisphenol-A, bis (4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) cyclohexane (hereinafter abbreviated as bisphenol-Z), 9,9-bis (4-hydroxyphenyl) fluorene (hereinafter abbreviated as bisphenol FL), 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane,
2,2-bis (4-hydroxy-3-methylphenyl)
Propane, 2,2-bis (4-hydroxyphenyl)-
2-phenylethane, 2,2-bis (4-hydroxyphenyl) -1,1,1,3,3,3-hexafluoropropane, bis (4-hydroxyphenyl) diphenylmethane, bis (4-hydroxyphenyl) sulfide , Bis (4-hydroxyphenyl) sulfone and the like. It is also possible to use a polyester carbonate partially containing a terephthalic acid and / or isophthalic acid component. By using such a constituent unit as a part of the constituent component of the polycarbonate composed of bisphenol-A, properties of the polycarbonate, for example, heat resistance and solubility can be improved.

The viscosity average molecular weight of the polycarbonate used here is preferably from 10,000 to 200,000. 20,000 to 120,000 is particularly preferred. More preferably, it is 35,000 to 100,000.

When the viscosity average molecular weight is lower than 10,000, the mechanical strength of the obtained film may be insufficient,
On the other hand, a high molecular weight of 200,000 or more is not preferred because the viscosity of the dope becomes too large and causes a problem in handling. The viscosity-average molecular weight refers to the intrinsic viscosity obtained in a methylene chloride solution of polycarbonate, and is determined by Mark-Houink-Sakurad (Mark-Houwink-Sakurad).
It was calculated by substituting into the equation of a). The various coefficients at this time are described in, for example, Polymer Handbook, 3rd revised edition, Wheely (1989) (Polymer Handbook).
3rd Ed. Willley, 1989), pages 7-23.

In the present invention, a film comprising a polycarbonate containing 0.3 to 5.0% by weight of 1,3-dioxolane can be obtained by a solution casting method. That is, a dioxolane solution (dope) of polycarbonate is heated from 20 ° C. to a boiling point of the solvent of about −10 ° C., such as glass, stainless steel, a ferrotype plate, or a plastic film such as polyethylene terephthalate or polyethylene 2,6-naphthalate. Casing on the support and adjusting the surface shape and film thickness with a doctor blade at an appropriate interval. Industrially, an endless metal plate support is generally used. In order to provide a uniform solution layer of a uniform thickness on the support, in addition to the method of sweeping with a doctor blade in this way, for example, a normal thick coating method such as a reverse roll coater or a method of casting from a die may be used. It is possible.

The liquid film cast on the support and smoothed sufficiently by leveling then enters the drying process, in which the purpose of drying is to remove as much solvent as possible (of the leveled film) in as short a time as possible. It is to evaporate without changing the form. Since rapid evaporation often causes undesirable changes such as deformation of the film surface due to foaming, it is necessary to pay close attention to factors that control the drying speed, such as drying temperature and air volume.

Usually, in the early stage of drying, drying is started at a temperature lower than the boiling point of the solvent used, and after the solvent has volatilized to some extent (after the amount of the remaining solvent has become about 35% by weight or less), the temperature is raised. The method is adopted. Next, when the solvent content is 5 to 2
After drying to 0% by weight, the film is peeled off from the support, and further heated and dried until the solvent content becomes 0.3 to 5.0 % by weight.

In the present invention, the solvent used for dissolving the polycarbonate is a dioxolane single solvent or a mixed solvent. In the case of a mixed solvent, it is desirable that 60% by weight or more, preferably 80% by weight or more of dioxolane is used. As the solvent coexisting in an amount of 40% by weight or less, for example, at least one kind of organic solvent selected from cyclohexanone, tetrahydrofuran, dioxane and the like, a stable polycarbonate dope for a cast film of the present invention can be prepared. I can do it. The amount and type of these additions can be determined depending on the purpose of addition of the solvent and its effects, such as improvement of the smoothness of the surface of the cast product (leveling effect), adjustment of the evaporation rate and viscosity of the system.

The dissolution ratio of the polycarbonate in the dope used in the present invention is such that the solvent is 25 to 150 parts by weight per 10 parts by weight of the polycarbonate resin, that is, the concentration of the polycarbonate in the dope is 6 to 10 parts by weight.
The content is desirably 29% by weight, and when the proportion of the polycarbonate is increased, progress of crystallization is observed, and the fluidity is lowered. In addition, the presence ratio of the solvent,
When the amount is more than 150 parts by weight, there is no problem in the storage stability of the dope, but the effective concentration of the polycarbonate is lowered, which is not preferable in practical use. From the viewpoint of the operability of the solution,
More preferably, the solvent is desirably 25 to 100 parts by weight with respect to 10 parts by weight of the polycarbonate resin.

In the present invention, the solvent content in the film is the content in the film immediately before stretching, and the amount is 0.3 to 5.0% by weight, preferably 0.4 to 3.0% by weight. %, More preferably 0.4 to 2.0% by weight.
When the content is 0.3% by weight or less, R due to temperature unevenness during stretching is reduced.
When the value is more than 5.0% by weight, the molecular orientation is hard to occur, and a process for drying the solvent after stretching is required.

In the present invention, the content of the solvent in the film is represented by W ₂ / W ₁ × 100 (% by weight) when the weight W ₁ g of the film containing the solvent and the amount of the solvent W ₂ g are used. It is.

The thickness of the retardation film obtained according to the present invention is not particularly limited, but the solution casting method can be usually advantageously carried out only when the thickness is 500 μm or less, preferably 20 μm or less.
0 μm or less. Practically, 50 to 200 μm is preferable. However, it is possible to obtain a film having a desired large film thickness by utilizing a multi-stage casting method or a laminating method.

In the present invention, the method of stretching the film is not particularly limited, but usually, a method for obtaining a retardation film can be effectively carried out by a longitudinal stretching method using two pairs of rolls having different peripheral speeds, or There is a method of transverse stretching by a tenter method. The stretching temperature, the stretching ratio, and the like are appropriately set in order to obtain a desired R value. Usually, in order to obtain a retardation film, the stretching is preferably performed at a temperature higher than the glass transition point and at a stretching ratio of 1.05 to 3.00 times. The R value is set to an appropriate value according to the application.
For example, when a retardation film is used for a liquid crystal display panel, the R value is generally set in the range of 400 to 650 nm.

[0022]

The present invention will be described below in detail with reference to examples. The measurement items in the examples were measured by the following methods. Residual solvent amount: The sample was dried at 150 ° C. for 16 hours and determined by weight measurement before and after. Retardation: Automatic birefringence meter (K
OBRA-21AD) was used to measure the birefringence at 590 nm of visible light.

Example 1 (1) Production of Film 15 parts by weight of a polycarbonate resin (viscosity average molecular weight 37,000) composed of a structural unit composed of bisphenol A was mixed in advance with 70 parts by weight of dioxolane and 15 parts by weight of dioxane. Was added little by little to the resulting solvent to form a dope.

The dope was cast on a glass plate maintained at 60 ° C. with a doctor blade having a clearance of 0.8 mm, left for about 2 minutes, and then left at 80 ° C. and a wind speed of 0.9 m / sec.
After drying for 5 minutes, the obtained film is peeled off from the glass substrate,
Heat treatment was performed at 130 ° C. and a wind speed of 1 m / sec for 30 minutes, followed by drying.

Thus, a transparent film was obtained. The solvent content of this film was 2.4% by weight.

(2) Production of retardation film The polycarbonate film produced in the above (1) was
After preheating for 1 minute at each of 0 ° C., 170 ° C., and 180 ° C., the film was longitudinally uniaxially stretched at a stretching ratio of 1.4 to obtain a retardation film. Table 1 shows the results of measuring the birefringence characteristics of the obtained retardation film. The thickness of the obtained retardation film was 80 μm, and the solvent content of each film was 0.5% by weight or less.

Example 2 (1) Production of Film A dope was prepared by gradually adding 20 parts by weight of a copolymer of bisphenol A and bisphenol FL (5 mol%) (viscosity average molecular weight 37,000) to 80 parts by weight of dioxolane. It was created. This dope was cast on a glass plate maintained at 60 ° C. with a dart cool blade having a clearance of 0.8 mm to form a dope of about 2 mm.
After standing for 80 minutes at 80 ° C. and a wind speed of 0.9 m / sec for 15 minutes, the obtained film was peeled off from the glass
C. and a heat treatment at a wind speed of 1 m / sec for 30 minutes, followed by drying.

Thus, a transparent film was obtained. The solvent content of this film was 0.9% by weight.

(2) Production of retardation film The polycarbonate film produced in the above (1) was
After preheating for 1 minute at each temperature of 0 ° C., 170 ° C., and 180 ° C., the film was longitudinally uniaxially stretched at a stretching ratio of 1.3 to obtain a retardation film. Table 1 shows the results of measuring the birefringence characteristics of the obtained retardation film. The thickness of the obtained retardation film was 85 μm, and the content of the solvent was 0.5% by weight or less in each of the films.

Example 3 (1) Production of Film A dope was prepared by gradually adding 20 parts by weight of a copolymer of bisphenol A and bisphenol FL (5 mol%) (viscosity average molecular weight 52,000) to 80 parts by weight of dioxolane. It was created. This dope was cast on a glass plate maintained at 60 ° C. with a dart cool blade having a clearance of 0.8 mm to form a dope of about 2 mm.
After drying for 15 minutes at 80 ° C. and a wind speed of 0.9 m / sec, the obtained film was peeled off from the glass substrate,
C. and a heat treatment at a wind speed of 1 m / sec for 30 minutes, followed by drying.

Thus, a transparent film was obtained. The solvent content of this film was 0.4% by weight.

(2) Production of retardation film The polycarbonate film produced in the above (1) was
After preheating for 1 minute at each of 0 ° C., 170 ° C., and 180 ° C., the film was longitudinally uniaxially stretched at a stretching ratio of 1.2 to obtain a retardation film. Table 1 shows the results of measuring the birefringence characteristics of the obtained retardation film. The thickness of the obtained retardation film was 90 μm, and the solvent content of each film was 0.1% by weight or less.

Comparative Example 1 (1) Production of Film 15 parts by weight of a polycarbonate resin composed of bisphenol A (viscosity average molecular weight 52,000) was added to dioxolan 8
A dope was prepared by adding little by little to 5 parts by weight. Clearance 0.8m on a glass plate holding this dope at 60 ° C
m and cast it for about 2 minutes.
After drying at 0 ° C. and a wind speed of 0.9 m / sec for 15 minutes, the obtained film was peeled off from the glass substrate, and was heated and dried at 150 ° C. and a wind speed of 1 m / sec for 60 minutes.

Thus, a transparent film was obtained. The solvent content of this film was 0.1% by weight.

(2) Production of retardation film The polycarbonate film produced in the above (1) was
After preheating for 1 minute at each of 0 ° C., 170 ° C., and 180 ° C., the film was longitudinally uniaxially stretched at a stretching ratio of 1.2 to obtain a retardation film. Table 1 shows the results of measuring the birefringence characteristics of the obtained retardation film.

Comparative Example 2 (1) Production of Film 20 parts by weight of a polycarbonate resin composed of bisphenol A (viscosity average molecular weight 37,000) was mixed with dioxolan 8
A dope was prepared by adding little by little to 5 parts by weight. Clearance 0.8m on a glass plate holding this dope at 60 ° C
m and cast it for about 2 minutes.
After drying at 0 ° C. and a wind speed of 0.9 m / sec for 15 minutes, the obtained film was peeled off from the glass substrate, and was heated and dried at 100 ° C. and a wind speed of 1 m / sec for 10 minutes.

Thus, a transparent film was obtained. The solvent content of this film was 8.0% by weight.

(2) Production of retardation film The polycarbonate film produced in the above (1) was
After preheating for 1 minute at each of 0 ° C., 170 ° C., and 180 ° C., the film was longitudinally and uniaxially stretched at a stretching ratio of 1.5 to obtain a retardation film. Table 1 shows the results of measuring the birefringence characteristics of the obtained retardation film. The obtained retardation film had a solvent content of 3% by weight or more, which was an unfavorable product for liquid crystal display.

Comparative Example 3 (1) Production of Film 20 parts by weight of a copolymer of bisphenol A and bisphenol FL (5 mol%) (viscosity average molecular weight 37,000) was gradually added to 80 parts by weight of methylene chloride. A dope was prepared. The dope was cast on a glass plate kept at 20 ° C. with a dart cool blade having a clearance of 0.8 mm, left for about 2 minutes, and then left at 50 ° C. and a wind speed of 0.9 m / sec.
After drying for 5 minutes, the obtained film is peeled off from the glass substrate,
Heat treatment was performed at 120 ° C. and a wind speed of 1 m / sec for 10 minutes, followed by drying.

Thus, a transparent film was obtained. The solvent content of this film was 2.5% by weight.

(2) Production of retardation film The polycarbonate film produced in the above (1) was
After preheating for 1 minute at each of 0 ° C., 170 ° C., and 180 ° C., the film was longitudinally uniaxially stretched at a stretching ratio of 1.4 to obtain a retardation film. Table 1 shows the results of measuring the birefringence characteristics of the obtained retardation film.

[0042]

[Table 1]

[0043]

According to the present invention, 1,3-dioxolane is used in an amount of 0.3 to 5.0.
Since the amount of change in retardation due to the change in the stretching temperature is small in the polycarbonate film containing the weight%, the variation in the retardation of the stretched film can be reduced. The solvent content of the stretched film is also small. Therefore, according to the present invention, it is possible to produce a stretched film having uniform birefringence characteristics that can be favorably used as a retardation film used in a liquid crystal display device.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C08L 69/00 C08K 5/15 // B29K 69:00 B29L 7:00 (72) Inventor Hideaki Nitta Asahigaoka, Hino-shi, Tokyo 4 Chome 3-2 Teijin Limited Tokyo Research Center (56) References JP-A-7-216077 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 5/30

Claims (2)

(57) [Claims] (1) a viscosity average molecular weight of 10,000 or more and 20 or more;
In producing a retardation film by stretching a film made of polycarbonate of 000 or less, a film made of polycarbonate containing 0.3 to 5.0% by weight of 1,3-dioxolane is stretched. A method for producing a retardation film. 2. A dope prepared by casting 10 parts by weight of a dope in which 10 parts by weight of a polycarbonate is dissolved with respect to 25 to 150 parts by weight of a solvent containing 60% by weight or more of 1,3-dioxolane. , 3-dioxolan in 0.
The method according to claim 1, wherein the film containing 3 to 5.0% by weight is stretched.