JP3062014B2 - Optical polycarbonate film and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical polycarbonate film and a method for producing the same.

[0002]

2. Description of the Related Art Polycarbonate films are used for packaging,
It is used for optical devices, display devices, and other various industrial uses. Recently, it has been attracting attention as a material for a retardation plate, a polarizing plate, a plastic substrate, and the like in optoelectronic devices such as a liquid crystal display device, and is being put to practical use. In particular, in a STN-type liquid crystal display device, which has made remarkable progress among recent liquid crystal displays, a phase difference film used between a liquid crystal layer and a polarizing plate to improve the visibility of an image viewed from the front and oblique directions. It is noted as. This retardation film plays a role of converting elliptically polarized light transmitted through the liquid crystal layer into linearly polarized light. As the material, a uniaxially stretched polycarbonate film mainly composed of bisphenol-A is used. The reasons are as follows: (1) high transparency; (2) relatively easy control of optical anisotropy; (3) relatively high heat resistance; (4) high homogeneity. This is because the properties required of the board are excellent.

However, polycarbonate films comprising bisphenol-A also have disadvantages. This film is generally cast from a methylene chloride solution of polycarbonate made of bisphenol-A from the viewpoint of homogeneity, but since the film for a retardation plate or a liquid crystal substrate is a thick film, it is cast from a high concentration dope. There is a need. However, the solubility of this polymer is about 20% by weight, which is not sufficiently high. In addition, the polymer does not exist stably in the high-concentration dope, and clouding or gelation accompanying crystallization often occurs with time, particularly, clouding (crystallization) often occurs during the film formation process.

Furthermore, the films used in these optoelectronic devices do not adversely affect peripheral parts as electronic parts. For example, they do not decompose when used in a high-temperature, high-humidity atmosphere for a long time to produce chlorine ions and the like. It is also necessary. Usually, a polycarbonate film cast from a methylene chloride solution as described above is used for such an optical application, but it cannot be said that these requirements are satisfied.

[0005] A retardation film or a film for a liquid crystal substrate requires a high degree of surface smoothness and controlled orientation, but it is easy to obtain a high quality product satisfying these requirements from a methylene chloride solution. is not.

[0006] In order to maintain the uniformity of such a film, a casting method of drying a coating film from a solution state is used instead of extrusion molding in order to maintain the uniformity. When preparing this solution (dope), a halogenated hydrocarbon such as methylene chloride has been frequently used as a solvent for polycarbonate so far. However, since these solvents contain halogen, they react with the water vapor component in the air when evaporating and volatilizing the solvent component, for example, a by-product of hydrogen halide represented by hydrogen chloride occurs, It is said that there is a high possibility of causing environmental problems such as corrosion of the substrate or deterioration of the working environment.

[0007] In such a film or substrate (sheet) formed by casting from a dope using a halogen-based solvent, a trace amount of a halogen element such as chlorine remains in a film or a substrate (sheet). Indium oxide) or T
There is a concern about the influence on components such as FT (Thin Film Transistor). This is particularly problematic when casting a film from a polycarbonate solution using a high boiling point halogen-containing solvent.

Furthermore, solvents such as methylene chloride and tetrachloroethane have a good affinity for polycarbonate, and therefore tend to increase the viscosity of the solution. When dissolved at the same concentration, the viscosity becomes extremely high, and It has disadvantages such as causing a problem or making it difficult to dissolve a polycarbonate having a higher degree of polymerization to an advantageous concentration when the viscosity is made the same.

When resin solutions of the same polymer are prepared using different solvents, the viscosity is governed by the interaction between the resin and the solvent. In general, solvents that give solutions with higher viscosities have a higher affinity between resin and solvent than solvents with lower viscosities, and in such solvents the resins are more linearly stretched and are more susceptible to entanglement between molecules. On the other hand, in a solvent having a low affinity, it is said that the resin molecules exist in a more rounded state and in a state where entanglement between the molecules hardly occurs. In general, a methylene chloride solution of polycarbonate has a high viscosity, and a film obtained by casting this solution has a drawback that the film is easily oriented and, as a result, a film having a large retardation is easily formed.

On the other hand, polycarbonate is dissolved in tetrahydrofuran, a solvent containing no halogen element,
It is also possible to prepare a dope. A method of applying the dope to an appropriate substrate and evaporating and drying the solvent to obtain a polycarbonate thin film can be considered. However, tetrahydrofuran is not a good solvent for polycarbonate. For example, in the case of a tetrahydrofuran solution of polycarbonate, if the polycarbonate resin concentration exceeds 10% by weight,
Although it tends to depend on the molecular weight of the polycarbonate, after the resin liquid composition is prepared, the liquid composition changes to a gel state with time, and firstly, an apparent increase in the solution viscosity is recognized. Since the gel becomes a cloudy state and eventually loses fluidity, there is a serious problem in practical use as a dope. In addition, a film having a large film thickness formed by casting a tetrahydrofuran solution is liable to cause cloudiness particularly during drying.

As described above, tetrahydrofuran has a problem in stability. Further, methylene chloride, which is mainly used for dissolving polycarbonate at present, has environmental problems and the like. That is, methylene chloride has a risk of carcinogenicity, and is becoming subject to regulation. In addition, because of its low boiling point (boiling point 41 ° C.), it is easy to volatilize out of the system from the process, and environmental pollution is doubled.

For this purpose, Japanese Patent Application Laid-Open No. 227456/1990 proposes to use dioxane as an alternative solvent. However, dioxane
It is a cyclic ether having an ether bond at the 1,4-position, and its polarities cancel each other out inside the molecule, so it can be judged that the effect of dissolving a polar polymer such as polycarbonate is limited. At a concentration of 20% by weight or more of polycarbonate, it often does not dissolve.

[0013]

SUMMARY OF THE INVENTION The present invention uses a stable, low-viscosity dope containing no halogen, and has optical characteristics,
It is intended to produce an optical polycarbonate film having excellent transparency and the like. Another object of the present invention is to provide a polycarbonate film having excellent optical properties, particularly a film capable of providing a display having little visual field dependency when applied to a liquid crystal display device.

[0014]

Means for Solving the Problems The present inventor has made extensive studies, and has reached the present invention as a result of studying a solvent, film forming conditions, and the like suitable for the production of a cast film.

That is, according to the present invention, when a dope is cast on a support and heated and dried to produce a film, a solvent containing at least 60% by weight of dioxolane is used.
A method for producing a polycarbonate film, comprising using a dope in which 10 parts by weight of polycarbonate is dissolved with respect to 150 parts by weight.

According to the present invention, when a polycarbonate film is produced by a casting method, a polycarbonate dope having excellent storage stability and using a solvent containing dioxolane as a main component is used. Dioxolane is a 5-membered cyclic ether in which the cyclic ether bond is located at the 1,3-position, and has a boiling point at about 76 ° C. at normal pressure.

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 a solvent coexisting in an amount of 40% by weight or less, for example, a stable polycarbonate dope for a cast film of the present invention can be prepared as long as it is at least one organic solvent selected from cyclohexanone, tetrahydrofuran, dioxane, and the like. . 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.

In the present invention, as a solvent used by mixing with dioxolan, methylene chloride, dichloroethane or another halogen-based solvent may be optionally used as long as the amount of halogen remaining in the film does not become excessive. is there. According to the method of the present invention, since the amount of halogen ions (particularly chloride ions) in a film can be suppressed to a low level, the film exhibits excellent performance as a component or an electronic component of a liquid crystal display device used for a long time in a severe environment. There is expected.

Regarding the dissolution ratio of the polycarbonate in the dope of the present invention, the solvent is 25 to 150 parts by weight with respect to 10 parts by weight of the polycarbonate resin, that is, the concentration of the polycarbonate in the dope is 6 to 29% by weight. When the ratio of polycarbonate increases, the progress of crystallization is observed, and the fluidity decreases, which is not preferable. On the other hand, when the content ratio of the solvent exceeds 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, it is more preferable that the solvent is 25 parts by weight to 100 parts by weight based on 10 parts by weight of the polycarbonate resin.

The above-mentioned dope is usually produced by dissolving a polycarbonate in a solvent at a temperature from room temperature to the boiling point of the solvent, but it is preferable to dissolve the polycarbonate at a temperature of from 40 ° C. to 70 ° C.

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, 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.

[0022]

Embedded image

Other than 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 comprising bisphenol-A, the 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. If the viscosity average molecular weight is lower than 10,000, the mechanical strength of the obtained film may be insufficient, and
If the molecular weight is more than 000, the viscosity of the dope becomes too high, which causes a problem in handling. The viscosity average molecular weight was calculated by substituting the intrinsic viscosity of a polycarbonate in a methylene chloride solution into the equation of Mark-Houink-Sakurada (Mark-Houwink-Sakurada). The various coefficients at this time are described in, for example, Polymer Handbook, 3rd Revised edition, Willie Co. (198
9 years) (Polymer Handbook 3rd)
Ed. Willley, 1989), pp. 7-23.

More specifically, the viscosity of the dope is preferably about 500 to 100,000 cps. When the viscosity of the dope is less than 500 cps, the fluidity becomes too high, and handling becomes difficult.
If it exceeds 000 cps, it becomes difficult to obtain a film having excellent smoothness.

Even when the same polymer is dissolved, the viscosity of the system changes depending on the solvent. This is attributed to the difference in affinity between the solvent and the polymer. In this regard,
Since the dioxolane used in the present invention tends to have a low viscosity of the system, it is possible to obtain a solution with a higher concentration if the viscosity is the same, and there is a great industrial value.

According to the present invention, a cast film having a low residual solvent amount can be easily obtained. For example, the boiling point of dioxolane is 76
° C, but there is no significant difference in the amount of residual solvent when treated under similar drying conditions. This is a fact that was presumed to be based on the interaction between the polycarbonate molecule and the solvent molecule, but was not expected at all. For this reason, according to the present invention, dioxolane can be industrially advantageously dried with similar equipment and cost even though it is not a solvent having a lower boiling point than methylene chloride. At the same time, since dioxolane is a non-halogen solvent, as described above, it is advantageous both for the global environment and for the purpose of reducing the chloride ion content in the film.

In the present invention, a film is obtained by casting a polycarbonate solution on a support and then heating to evaporate the solvent. The film production process of the present invention comprises three steps: (1) a casting step, (2) a pre-drying step, and (3) a post-drying step. (1) The casting step is a step of casting the dope on the support, (2) the pre-drying step is a step of evaporating and removing most of the solvent from the cast dope, and (3) the post-drying step remains. This is a step of removing the solvent.

That is, in the present invention, the above-mentioned dope is cast on a support, the film dried until the solvent content becomes 5 to 25% by weight is peeled off from the support, and the film is shrunk in the width direction. A process for producing an optical polycarbonate film, characterized in that the temperature is continuously or sequentially raised and dried in accordance with the transition of Tg 'within a temperature (T) satisfying the following formula (I). .

[0030]

Tg′−50 ° C. ≦ T ≦ Tg ′ (I) [Tg ′ (° C.) is a glass transition point of polycarbonate containing a residual solvent. ]

(1) In the casting step, a method of extruding from a die, a method using a doctor blade, a method using a reverse roll coater, and the like are used. Industrially, the most common method is to continuously extrude a solution from a die onto a supporting substrate on a belt or a drum.

The support to be used is not particularly limited, but a glass substrate, a metal substrate of stainless steel or ferro type, a plastic substrate of polyethylene terephthalate or the like is used. However, a mirror-finished metal substrate is most commonly used to form a film having excellent optical isotropy and uniformity, which is the main feature of the present invention.

The dope temperature at the time of casting of the present invention is 10
C. to 60.degree. C., preferably 30 to 50.degree.
In order to obtain a film having excellent smoothness, the solution extruded from the die needs to be cast and smoothed on a support.
At this time, if the dope temperature at the time of casting is too high, the surface is dried and solidified before smoothing, which is not preferable.

The above-mentioned dope is usually stored at a temperature of not lower than room temperature and not higher than the boiling point of the solvent, but is preferably stored at a temperature of not lower than 40 ° C. and not higher than 60 ° C.

(2) In the predrying step, it is necessary to evaporate and remove most of the solvent from the solution cast on the support in as short a time as possible. However, drying conditions should be carefully selected, since rapid evaporation will cause deformation by foaming. In the present invention, drying is performed at a temperature of 30 to 130 ° C, preferably 40 to 120 ° C. On this occasion,
If the temperature-rise drying is performed sequentially or continuously in this temperature range, efficient drying can be performed without losing a high degree of smoothness.

In order to perform drying efficiently, air may be sent. Generally, a wind speed of 20 m / sec or less, preferably 15 m / sec or less is used. If it is less than this, the effect is not sufficient, and if it exceeds this, it is not preferable because a smooth surface cannot be obtained due to wind disturbance. In this case, it is preferable to use a method in which the wind speed is suppressed in the initial stage of the drying step and the wind speed is increased sequentially or continuously.

At this stage, the film is on the support,
At the end of this step, it is released from the support. At that time, if the amount of the residual solvent is high, the film is soft and the polymer undergoes flow deformation in the film. Generally, the amount of the residual solvent is selected in the range of 5 to 25% by weight, preferably 5 to 20% by weight, and more preferably 10 to 20% by weight.

(3) In the post-drying step, the film peeled from the support is further dried to reduce the residual solvent amount.
The final residual solvent amount is 3% by weight or less, preferably 2% by weight or less. More preferably, it is 1% by weight or less.

In this step, the film is brought into a state capable of contracting in the width direction. That is, it is desirable not to adopt a method of supporting the edge of the film with a tenter.

Generally, in this step, a method of drying the film while transporting the film by a pin tenter method is employed. However, in the tenter method, a non-uniform force is applied to the film due to its own weight, shrinkage due to evaporation of the solvent, or wind pressure. However, the force of winding is apparently slight, but cannot be ignored in the film formation that requires a high degree of optical isotropy as demonstrated in Reference Example 1. In addition, at the stage of entering this step, since a large amount of the residual solvent is contained, the state is particularly susceptible to deformation.

The drying temperature T (° C.) is set so as to satisfy the following formula (I). As demonstrated in Reference Example 2 (FIG. 1), the glass transition point of the polycarbonate largely depends on the amount of the residual solvent, and decreases significantly as the amount of the residual solvent increases. Along with this, the film becomes remarkably deformable. From this viewpoint, the drying temperature in this step needs to be particularly strictly controlled.

In the present invention, the drying temperature is

[0043]

(Tg′−50 ° C.) ≦ T ≦ Tg ′ (I) [where Tg ′ (° C.) is the glass transition point of the film containing the residual solvent. This object is achieved by increasing the temperature continuously or sequentially in accordance with the transition of Tg 'within the temperature (T) range of [1] and drying. Preferably, (Tg ′
−20 ° C.) ≦ T ≦ Tg ′.

Here, Tg 'depends not only on the amount of residual solvent but also on the type of solvent. In the post-drying process, the residual solvent decreases in the process of transporting the film, and accordingly, Tg ′ increases. Therefore, in order to efficiently dry the film without causing distortion in this step, the temperature is raised together with Tg ′. Temperature is T
If the temperature is less than g′−50 ° C., drying cannot be performed efficiently, which is not preferable. Conversely, exceeding Tg 'is not preferable because distortion occurs.

The temperature may be raised continuously, but in terms of equipment, there is a method in which the temperature is divided into 3 to 10 stages, preferably 4 to 7 stages, and the temperature is raised sequentially according to the Tg '. It is preferably adopted. At this time, it is preferable that drying be performed advantageously by blowing air as in the predrying step.

The film transport speed is not particularly limited, but is generally 0.5 to 15 m / min, preferably 1 to 1 m / min.
It is performed in a range of 0 m / min.

As described above, when the resin contains a solvent, its glass transition point (Tg ') is lowered. On the other hand, when the film is stretched in a state containing a solvent, orientation occurs as in the case where no solvent is contained, but the amount of orientation varies depending on the type and content of the solvent. In the case of the polycarbonate film containing dioxolane or a solvent containing dioxolane as the main component of the present invention, when stretched, the degree of orientation (corresponding to the retardation value) of the orientation temperature is low, which is clearly different from that of the film containing the same amount of methylene chloride. Stretching in such a state can be advantageously used when producing a retardation film with little variation in retardation. (Examples 13 to 17)

Thus, the film obtained by the method of the present invention is used when the solvent content in the film is 0.3 to 5% by weight.
, Preferably 0.5 to 3% by weight, a homogeneous retardation film can be obtained.

The thickness of the obtained film is not particularly limited, but is generally 5 to 500 μm, preferably 10 to 30 μm.
0 μm.

In the present invention, the above-mentioned film production step may be performed in air or in an atmosphere of an inert gas such as nitrogen gas or carbon dioxide gas. In particular, the predrying step needs to remove most of the solvent from the solution cast on the support, and is therefore preferably performed in an inert gas atmosphere from the viewpoint of safety and the like.

According to the present invention, the retardation value (R ₀ ) in the direction perpendicular to the film surface and the retardation value (R ₄₀₎ measured with respect to the retardation value at an angle of 40 ° with the slow axis of the film as the tilt axis. ) Which satisfies the following formula (II).

[0052]

(R ₄₀ −R ₀ ) · 10 ⁴ /Mw<3.0 (II) In the formula, Mw represents a viscosity average molecular weight of the polycarbonate. Mw is preferably 40,000 or more and 200,000 or less. The viscosity average molecular weight is a value determined by the above-described method.

When (R ₄₀ −R ₀ ) · 10 ⁴ / Mw is larger than 3.0, the angle dependence of the retardation of the film tends to be large, and particularly, the liquid crystal cell substrate has poor optical isotropy. Chipping is also unfavorable because the retardation value varies greatly at the same time as a raw material for a retardation film.

The thickness of the film of the present invention is not particularly limited, but is 5 to 500 μm, preferably 10 to 300 μm. However, it is possible to obtain a product having a desired large film thickness by utilizing a multi-stage casting method, a laminating method, or the like.

This polycarbonate film for optical use
The dope can be produced by casting the above-mentioned dope on a support and heating and drying it.

[0056]

According to the present invention, the use of a good polycarbonate dope, which is obtained by dissolving a polycarbonate in a solvent containing dioxolane as a main component, has a low viscosity, does not cause an increase in solution viscosity, and does not cause turbidity. A polycarbonate film having excellent transparency and low optical anisotropy can be obtained.

Further, according to the present invention, when casting a film from a polycarbonate solution, a transparent and smooth film excellent in optical isotropy and uniformity can be obtained by strictly controlling the drying conditions. I can do it.

[0058]

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. Heat shrinkage: 140 for a 10 cm sample film
The length before and after heating at 30 ° C. for 30 minutes was measured. Haze value: UV-visible spectrometer (UV-Shimadzu Corporation)
240). Measurement of solution viscosity: Measured at 25 ° C. using a B-type viscometer BH type, manufactured by Tokyo Keiki Co., Ltd. Dope stability: Each resin solution was sealed in a 50 ml sample bottle, allowed to stand at room temperature, the appearance was observed, and the change in the appearance was described as follows. ：: No change in appearance after leaving for 3 days ×: Solidification or cloudiness after leaving for 3 days Retardation: Automatic birefringence meter (K, manufactured by Kanzaki Paper Co., Ltd.)
OBRA-21AD) was used to measure the birefringence value at 590 nm of visible light.

[Example 1] 12 parts by weight of a polycarbonate resin comprising a structural unit composed of bisphenol A (Panlite, registered trademark, L-1225, manufactured by Teijin Chemicals Ltd., molecular weight in terms of viscosity 24,000) was used in an amount of 88 parts by weight of dioxolane. , And the mixture was sufficiently stirred to prepare a dope. The obtained dope was allowed to stand at room temperature, and a change in appearance was observed. However, no increase in viscosity was observed for 7 days after the preparation of the dope, and it was observed that fluidity was maintained.

This dope solution was cast on a glass plate with a doctor blade having a clearance of 0.4 mm, heated at 100 ° C. for 30 minutes, and dried to obtain a transparent film.

Example 2 12 parts by weight of a polycarbonate resin (manufactured by Teijin Chemicals Ltd., Panlite, registered trademark, C-1400, molecular weight in terms of viscosity of 37,000) composed of bisphenol A, 70 parts by weight of dioxolane When the storage stability of the dope dissolved in 1 part by weight and 18 parts by weight of methylene chloride was examined, no change to a gel state was observed after standing for 10 days. Example 1 using this dope
When a film was formed in the same manner as described above, a transparent film was obtained.

Example 3 Polycarbonate resin (Panlite, registered trademark, L-1225, manufactured by Teijin Chemicals Ltd.)
A dope was prepared by gradually adding 15 parts by weight of a viscosity-converted molecular weight (24,000) to a solvent in which 55 parts by weight of dioxolane and 30 parts by weight of dioxane were previously mixed and became uniform.
When the storage stability of this dope was examined, fluidity was observed even after storage for one week, and no gelling behavior was observed.
Using the obtained dope, a film was formed in the same manner as in Example 1 to obtain a transparent film.

[Example 4] (Preparation of dope) The polycarbonate resin shown in Table 1 was added to dioxolane and sufficiently stirred at 50 ° C to prepare a solution. 3 of the polycarbonate resin liquid thus obtained
The viscosity at 0 ° C. was measured using a B-type viscometer. Further, it was left at room temperature and 50 ° C., respectively, and changes in appearance after 3 days were observed. However, all were stable and no change in appearance was observed. The results are summarized in Table 1.

(Production of Film) A dope obtained by dissolving a polycarbonate composed of a structural unit of bisphenol A indicated by * 1 in Table 1 in dioxolane to a concentration of 20% by weight was applied to a glass plate maintained at 60 ° C. The film was cast with a doctor blade having a clearance of 0.8 mm, allowed to stand for about 2 minutes, dried at 80 ° C. and a wind speed of 0.9 m / sec for 15 minutes, and then the obtained film was peeled off from the glass substrate at 130 ° C. and a wind speed of 1 m. / Sec for 30 minutes and dried. Thus, a transparent film (haze value: 0.6) was obtained. The retardation value of this film was 4 nm.

[Comparative Example 1] (Preparation of dope) The procedure of Example 1 was repeated except that the solvent was changed to methylene chloride and the mixture was stirred and dissolved at 25 ° C.
The measurement was performed under the same conditions. These results are summarized in Table 1. As is clear from the results, the solution viscosity measured under the same conditions was about twice that of the dioxolane solution. No change in appearance was observed.

(Production of Film) A film obtained from a dope obtained by dissolving a polycarbonate (C-1400) indicated by * 1 in Table 1 in a concentration of 20% by weight in methylene chloride has a haze value of 0.1. Met. The substrate temperature during this casting was 20 ° C., and the initial drying temperature was 40 ° C. The retardation value of this film was 6 nm.

[0067]

[Table 1]

Examples 5 to 11 and Comparative Examples 2 to 6 (Manufacture of dope) In the same manner as in Example 1, various polycarbonates used in Example 1 shown in Table 2 were used in solvents having various compositions shown in Table 2. The solution was dissolved in the concentration shown in Table 2 and the behavior of the dope was observed. The composition of the solvent, the viscosity of the dope and the stability of the obtained dope were measured in the same manner as in Example 1. The results are shown in Table 2.

(Production of Film) These dopes were cast on a glass plate with a doctor blade having a clearance of 0.8 mm and heated at 80 ° C. for 15 minutes. Table 3 shows the amount of the residual solvent after heating. Thereafter, the film was peeled off from the glass plate and subjected to a heat treatment at a drying temperature and time shown in Table 3 in a state where the film could be contracted in the width direction, and dried to obtain a film having a thickness of about 100 μm. The residual solvent amount, haze value, retardation, heat shrinkage, and turbidity of the film thus obtained were measured, and the results are shown in Table 3.

[0070]

[Table 2]

[0071]

[Table 3]

REFERENCE EXAMPLE 1 A polycarbonate of bisphenol-A origin (viscosity average molecular weight 3.7 × 10 ⁴ ) was dissolved in methylene chloride to prepare a film having a thickness of 102 μm from a 20% by weight solution.

The film was subjected to tensile tests at various temperatures, and the ratio (P / E) between the strength (P) and the elongation (E) was determined within the range of the elastic limit. Also, the phase difference (Re) corresponding to various elongations (E) is measured at the corresponding temperature,
Re / E was determined. Table 4 shows the results.

As is clear from Table 4, P / E and Re
/ E greatly depended on temperature. In particular, P / E sharply decreased when approaching the glass transition point of the film (Tg ′ = 158 ° C.). Re / P obtained from the values of P / E and Re / E is inversely T
It increased sharply as we approached g '. From the value of Re / P, when winding a film having a film thickness of 10 μm and a width of 1 m,
Can be determined, for example, to allow the maximum tension (T) to be suppressed to 10 nm or less. As is clear from Table 4,
T also decreases sharply as the temperature approaches Tg '. For example,
At 100 ° C, up to 20kg is allowed, while 150kg
At 0.7 ° C., a phase difference of 1
Reaches up to 0 nm. This result indicates that, despite the film containing no residual solvent, optical distortion occurs even at a slight force near Tg ′. When the residual solvent is contained, Tg 'is significantly reduced, and thus optical stress is generated by a smaller stress.

[0075]

[Table 4]

Reference Example 2 The polycarbonate used in Reference Example 1 was prepared by converting methylene chloride, 1,3-dioxolan, 1,4
-Dissolved in dioxane, 1,2-dichloroethane and cyclohexanone respectively to prepare a 20% by weight solution. By changing the drying conditions from these solutions, films having a film thickness of 100 μm with different amounts of residual solvent were produced. FIG. 1 shows the glass transition point (Tg ′) of these films.
Shown in As is evident from the figure, Tg 'significantly decreased as the amount of residual solvent increased for all the films examined. In addition, the degree of the decrease largely depends on the type of the solvent.

Example 12 Bisphenol-A and 2,
Viscosity average molecular weight 4.4 × 1 consisting of 2-bis (4-hydroxyphenyl) cyclohexane (molar ratio 95/5)
0 ⁴ A polycarbonate copolymer with 20 wt% solution in 1,3-dioxolane was continuously casting.

The casting apparatus used was a method in which the belt was extruded from a die to a belt, and the belt was connected to a predrying furnace divided into four stages. The post-drying oven used was an oven in which the film separated from the belt was divided into six stages.
After casting using this apparatus, the temperature of the predrying furnace was sequentially increased to 40, 80, and 90 ° C, and finally cooled to 40 ° C. Then, a film having a residual solvent amount of 13.5% by weight was obtained. At this stage, the film was peeled from the belt and then sent to a drying oven. The temperature of the post-drying furnace is set to 40 ° C. (residual solvent amount 13.5%, Tg ′ = 50)
° C), 75 ° C (5.5% residual solvent, Tg '= 91)
° C), 100 ° C (residual solvent amount 3.2%, Tg '= 113)
° C), 120 ° C (residual solvent amount 1.2%, Tg '= 141)
° C), 140 ° C (residual solvent amount 0.8%, Tg '= 145)
° C) to obtain a dried film. The amount of residual solvent in the thus obtained film was 0.3% by weight. The thickness was 100 ± 1.3 μm, which was extremely uniform. The transmittance was 91%. The phase difference (Re) is 17 ± 2.
nm, and the film was extremely anisotropic and its variation range was small.

[Examples 13 to 17] The polycarbonate resins shown in Table 5 were added to dioxolane and sufficiently stirred at 50 ° C to prepare 15% concentration solutions. The polycarbonate resin solution kept at room temperature was cast on a stainless steel substrate kept at 60 ° C. with a doctor blade having a clearance of 0.8 mm, left for about 2 minutes, and then left at 90 ° C. for 10 minutes.
After preliminarily drying at 0 ° C for 20 minutes, the film was peeled off from the substrate, and then main drying was performed at 135 ° C. The film thickness, residual solvent amount, and retardation value of the obtained film were measured, and (R ₄₀ −R ₀ ) · 10 ⁴ / Mw was determined. Table 5 shows the results
Shown in In the table, the letter A at the end of the number indicates a sample at the stage where predrying has been completed, and similarly the letter B at the end of the number indicates a sample after completion of main drying.

Example 18 The polycarbonate resins shown in Table 5 were added to dioxolane and sufficiently stirred at 50 ° C. to prepare a 15% concentration solution. The polycarbonate resin solution maintained at room temperature was cast on a stainless steel substrate maintained at 40 ° C. with a doctor blade having a clearance of 0.8 mm, and allowed to stand for about 2 minutes.
, And the film was peeled off from the substrate. The film thickness, residual solvent amount, and retardation value of the obtained film were measured, and (R ₄₀ −R ₀ ) · 10 ⁴ / Mw was determined.
In this experiment, drying was performed at the same initial temperature as in the comparative example. Table 5 shows the results.

Comparative Examples 7 to 12 The same operation as in Example 18 was carried out except that the solvent was changed to methylene chloride and the mixture was stirred and dissolved at 25 ° C. Dry at 40 ° C for 10 minutes, 80
After drying the film from the substrate at 80 ° C for 80 minutes,
Performed at 0 ° C. for 1 hour. The measurement was performed in the same manner as in the example. The results are summarized in Table 5.

[0082]

[Table 5]

Example 19 A dope was prepared by dissolving a copolymer (viscosity average molecular weight: 37,000) of bisphenol A and bisphenol FL (5 mol%) in dioxolane (resin concentration: 20% by weight). This dope was cast in the same manner as in Example 4 to produce a film. The residual solvent amount of this film was 0.9%. The polycarbonate film thus obtained was heated at 160 ° C, 170 ° C,
After preheating for 1 minute at each temperature of 180 ° C., longitudinal uniaxial stretching was performed to obtain a retardation film. Table 6 shows the results of measuring the birefringence characteristics of the obtained retardation film.

The polycarbonate film of the present invention has a small variation in retardation due to a change in stretching temperature, and thus has a small variation in retardation of the film, and can be favorably used as, for example, a retardation film used in a liquid crystal display device. It is a film having extremely uniform birefringence characteristics.

[0085]

[Table 6]

Comparative Example 13 A dope was prepared by dissolving the copolymer used in Example 19 in methylene chloride (resin concentration: 20% by weight). This dope was cast in the same manner as in Example 4 to produce a film. The residual solvent amount of this film was 2.5%. Using the polycarbonate film thus obtained, a retardation film was produced in the same manner as in Example 4. Table 6 shows the results of measuring the birefringence characteristics of the obtained retardation film.

Example 20 9,9-bis (4-hydroxyphenyl) fluorene and bisphenol-A
(Mole ratio = 25/75) Polycarbonate resin having a bisphenol component (viscosity average molecular weight 5.5 × 10 ⁴ )
15 parts by weight was added to 85 parts by weight of 1,3-dioxolane, and the mixture was stirred at room temperature for 10 hours to obtain a transparent viscous solution. The dope viscosity of this solution was 4.1 at 30 ° C.
× 10 ³ cps, indicating a high solution viscosity. The haze value obtained by placing this solution in a quartz cell having an optical path length of 1 cm was 0.4%, which was extremely high in transparency. Even if this solution is left at room temperature for one week, its haze value is 0.5%.
And no cloudiness or gelation was observed.

The obtained solution was cast on a stainless steel substrate using a doctor knife and dried in a dryer at a wind speed of 1 m / sec at 90 ° C. for 20 minutes and further at 177 ° C. for 60 minutes to obtain a film having a thickness of 97 μm. Was obtained. The residual solvent of the obtained film was 0.33%. The light transmittance of the film was 90.7% for visible light of 500 nm,
The haze value was 0.9%, which was extremely high in transparency. The retardation (Re) measured with visible light of 590 nm was <10 nm, and the optical isotropy was high. The breaking strength of the obtained film was 7.1 kg /
mm ² , elongation at break 95%, initial modulus 205 k
g / mm ² , which was extremely strong.

The unstretched film thus obtained was subjected to 202
The film was uniaxially stretched at 20 ° C. for 20% to obtain an oriented film. Re of this stretched film was 520 nm, and a film having desired birefringence was obtained. This slow axis coincided with the stretching direction, indicating that the film exhibited positive birefringence. The birefringence spot was <10 nm, and the birefringence spot was extremely small.
The Tg of this film was 197.1 ° C., indicating high heat resistance.

Example 21 9,9-bis (4-hydroxyphenyl) fluorene and bisphenol-A
(Molar ratio = 40/60) Polycarbonate resin having a bisphenol component (viscosity average molecular weight 5.7 × 10 ⁴ )
15 parts by weight was added to 85 parts by weight of 1,3-dioxolane, and the mixture was stirred at room temperature for 10 hours to obtain a transparent viscous solution. The haze value of this solution was 0.5%, which was extremely high in transparency. Even when this solution was left at room temperature for one week, the haze value did not change, and no cloudiness or gelation was observed.

The obtained solution was cast on a stainless steel substrate using a doctor knife, and dried in a dryer at an air speed of 1 m / sec at 90 ° C. for 20 minutes and further at 195 ° C. for 60 minutes to obtain a film having a thickness of 97 μm. Was obtained. The residual solvent of the obtained film was 0.27%. The light transmittance of the film was 90.3% and the haze value was 0.5%, which was extremely high in transparency. Further, the retardation (Re) was <10 nm, and the optical isotropy was high. The breaking strength of the obtained film is 7.6 kg.
/ Mm ² , elongation at break 90%, initial modulus 200
kg / mm ² , which was extremely strong.

The unstretched film thus obtained was subjected to 220
The film was uniaxially stretched at 25 ° C. by 25% to obtain an oriented film. Re of this stretched film was 480 nm, and a film having desired birefringence was obtained. This slow axis coincided with the stretching direction, indicating that the film exhibited positive birefringence. The birefringence spot was <10 nm, and the birefringence spot was extremely small.
In addition, the Tg of this film was 214.5 ° C., indicating high heat resistance.

Example 22 1,1-bis (4-hydroxyphenyl) cyclohexane and bisphenol
A (molar ratio = 40/60) polycarbonate resin having a bisphenol component (viscosity average molecular weight 3.6 × 1)
0 ⁴⁾ 20 parts by weight in addition to 80 parts by weight of 1,3-dioxolane, by stirring at room temperature for 10 hours, to obtain a transparent viscous solution.

The solution viscosity was 1.9 × 10 ³ at 30 ° C.
cps. The haze value of this solution was 0.6%, which was extremely high in transparency. Even when this solution was left at room temperature for one week, the haze value did not change, and no cloudiness or gelation was observed. The obtained solution was cast on a stainless steel substrate using a doctor knife, and the wind speed was 1 m.
The film was dried at 90 ° C. for 20 minutes and further at 147 ° C. for 60 minutes in a drier at a rate of 270 ° C./s to obtain a transparent unstretched film having a thickness of 102 μm. The residual solvent of the obtained film was 0.13%. The light transmittance of the film was 91.0% and the haze value was 0.7%, which was extremely high in transparency.
Further, the retardation (Re) was <10 nm, and the optical isotropy was high.

The unstretched film thus obtained was subjected to 171
The film was uniaxially stretched at a stretching rate of 15% at 150 ° C. to obtain an oriented film. Re of this stretched film was 530 nm, and a film having desired birefringence was obtained. Also, this birefringence spot is <10
nm and the birefringence spot was extremely small. The Tg of this film was 166.5 ° C., indicating high heat resistance.

Example 23 1,1-Bis (4-hydro
(Xyphenyl) -3,3,5-trimethylcyclohexa
And bisphenol-A (molar ratio = 57/43)
Polycarbonate resin with bisphenol component (viscosity
Average molecular weight 2.2 × 10^Four) 28 parts by weight of 1,3-geo
Heating and stirring at 50 ° C for 5 hours in addition to 72 parts by weight of xolan
By doing so, a clear viscous solution was obtained. This solution
Has a dope viscosity of 3.2 × 10 at 30 ° C. ^Threecps and high
Solution viscosity. This solution was placed in a quartz cell with an optical path length of 1 cm.
The haze value obtained by putting it in
It was sexy. Also leave this solution at room temperature for one week
Neither the solution viscosity nor the haze value changed.

The obtained solution was cast on a stainless steel substrate using a doctor knife, and the solution was heated at 50 ° C. for 10 minutes and 90 ° C.
The film was heated and dried at 120 ° C. for 10 minutes, at 120 ° C. for 10 minutes and at 160 ° C. for 60 minutes to obtain a transparent unstretched film of 98 μm.
The light transmittance of the obtained film was 9 at 500 nm visible light.
2.0% and a haze value of 0.3% showed that the transparency was extremely high. Further, the retardation (Re) measured with visible light of 590 nm was <10 nm, and the optical isotropy was high. The breaking strength of the obtained film was 6.3 kg / mm ² , and the initial modulus was 196 kg / m.
m ² , which was extremely strong. The glass transition point (Tg) was 207 ° C., indicating high heat resistance.

[Brief description of the drawings]

FIG. 1 shows the relationship between the glass transition point (Tg ′) of a film produced in Reference Example 1 and the residual solvent concentration.

[Explanation of Signs] A When methylene chloride is used as a solvent. B When dioxolan is used as a solvent. When C 1,2-dichloroethane is used as a solvent. D When dioxane is used as a solvent. E When cyclohexane is used as a solvent.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI G02F 1/1335 510 G02F 1/1335 510 // B29L 7:00 C08L 69:00 (72) Inventor Hideaki Nitta Hino-shi, Tokyo 4-3-2 Asahigaoka Tokyo Research Center Teijin Limited (72) Inventor Takeshi Sasaki 4-3-2 Asahigaoka Asahioka, Hino City, Tokyo Inside Tokyo Research Center Teijin Limited (56) References JP-A-191904 (JP, A) JP-A-51-79172 (JP, A) JP-A-2-89006 (JP, A) JP-A-4-201310 (JP, A) JP-A-4-282212 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) B29C 41/00-41/52

Claims (3)

(57) [Claims] A method for producing a film by casting a dope on a support and heating the dope to evaporate a solvent.
Solvent containing 15% by weight or more of dioxolane 25 to 15
A dope in which 10 parts by weight of polycarbonate was dissolved was cast on a support with respect to 0 parts by weight, and the solvent content was 5 to 2 parts.
After drying to 5% by weight, the film is peeled off from the support, and is shrunk in the width direction, in accordance with the transition of Tg 'within a temperature range (T) satisfying the following formula (I). A method for producing an optical polycarbonate film, characterized in that the temperature is continuously or sequentially increased and dried. Tg′−50 ° C. ≦ T ≦ Tg ′ (I) [Tg ′ (° C.) is a glass transition point of polycarbonate containing a residual solvent. ] 2. A polycarbonate having a viscosity average molecular weight of 1
2. The method for producing an optical polycarbonate film according to claim 1, wherein the molecular weight is from 000 to 200,000. 3. The process for producing an optical polycarbonate film according to claim 1, wherein the solvent contains at least 60% by weight of dioxolane and the remaining component is at least one organic solvent selected from the group consisting of cyclohexanone, tetrahydrofuran and dioxane. .