JPH07299828A - Optical polycarbonate film and production thereof - Google Patents

Abstract

PURPOSE:To obtain an optical polycarbonate film excellent in optical characteristics such as transparency or the like. CONSTITUTION:In producing an optical polycarbonate film by spreading a dope over the surface of a support and heating the formed layer to evaporate a solvent, the dope to be used is prepared by a dissolving 10 pts.wt. of polycarbonate in 25-150 pts.wt. of a solvent containing 60wt.% or more of dioxolane. This polycarbonate film has a specific retardation value.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION 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 in various industrial applications such as optical devices, display devices, etc., and has recently been attracting attention as a material for retardation plates, polarizing plates, plastic substrates, etc. in optoelectronic devices such as liquid crystal display devices 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 retardation film used between a liquid crystal layer and a polarizing plate in order to improve visibility when viewed from the front and oblique directions of an image. Be noted as. This retardation film plays a role of converting elliptically polarized light transmitted through the liquid crystal layer into linearly polarized light. A uniaxially stretched film of polycarbonate composed mainly of bisphenol-A is used as its material. The reason is that (1) transparency is high, (2) optical anisotropy is relatively easy to control, (3) heat resistance is relatively high, and (4) homogeneity is high. This is because the properties required for the plate are excellent.

However, the polycarbonate film made of bisphenol-A also has a drawback. From the viewpoint of homogeneity, this film is generally cast from a methylene chloride solution of polycarbonate consisting of bisphenol-A, but the film for retardation plates and liquid crystal substrates is a thick film, and therefore cast from a high-concentration dope. There is a need. However, the solubility of this polymer is about 20% by weight and cannot be said to be sufficiently high. Moreover, the polymer does not exist stably in the high-concentration dope, and white turbidity or gelation occurs with crystallization over time, and in particular, white turbidity (crystallization) often occurs during the film formation process.

Furthermore, the films used in these optoelectronic devices should not adversely affect the peripheral parts as electronic parts, for example, when they are used in a high temperature and high humidity atmosphere for a long period of time, they do not decompose to generate chlorine ions and the like. It is also necessary. Normally, a polycarbonate film cast from a methylene chloride solution as described above is used for such optical applications, but it is hard to say that these requirements are satisfied.

In a retardation film or a liquid crystal substrate film, a high degree of surface smoothness and controlled orientation are required, 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, the film is produced by a casting method in which the coating film is dried from a solution state, rather than by extrusion molding. When this solution (dope) is prepared, halogenated hydrocarbons such as methylene chloride have been frequently used as a solvent for polycarbonate. However, since these solvents contain halogen, when the solvent component is evaporated and volatilized, it reacts with the water vapor component in the air, for example, a hydrogen halide by-product represented by hydrogen chloride occurs, It is said that environmental problems such as corrosion of the substrate and deterioration of the working environment are likely to occur.

Further, although a small amount of halogen elements such as chlorine remain in the film or substrate (sheet) cast from the dope using the halogen-based solvent, the ITO ( Indium oxide) and T
There is concern about the influence on constituent components such as FT (Thin Film Transistor). This is a particular problem when casting a film from a polycarbonate solution using a halogen-containing solvent having a high boiling point.

Furthermore, for example, solvents such as methylene chloride and tetrachloroethane have a good affinity with the polycarbonate, so that the viscosity of the solution tends to increase, and when they are dissolved at the same concentration, the viscosity becomes extremely high, resulting in handling. There is a weak point such as a case where a problem occurs, and conversely, when the viscosity is the same, it becomes difficult to dissolve a polycarbonate having a higher degree of polymerization to an advantageous concentration.

When a resin solution of the same polymer is prepared by using different solvents, its viscosity is governed by the interaction between the resin and the solvent. Usually, a solvent that gives a highly viscous solution has a higher affinity between a resin and a solvent than a solvent that has a low viscosity, and in such a solvent, the resin is more linearly stretched, and entanglement between molecules is more likely to occur. On the other hand, it is said that in a solvent having a low affinity, the resin molecules exist in a more rounded state and in a state in which intermolecular entanglement is unlikely to occur. In general, a methylene chloride solution of polycarbonate has a high viscosity, and a film obtained by casting this solution tends to be oriented, resulting in a film having a large retardation.

On the other hand, polycarbonate is dissolved in tetrahydrofuran, which is a solvent containing no halogen element,
It is also possible to prepare a dope, and a method is conceivable in which this is applied to an appropriate substrate and the solvent is evaporated to dryness to obtain a polycarbonate thin film. However, tetrahydrofuran is not a good solvent for polycarbonate. For example, in the case of a polycarbonate tetrahydrofuran solution, when the polycarbonate resin concentration exceeds 10% by weight,
Although there is a tendency to depend on the molecular weight of the polycarbonate, after the resin liquid composition was prepared, the liquid composition changed into a gel state with time, and an apparent increase in the solution viscosity was observed, and with the occurrence of turbidity, complete The gel becomes cloudy and eventually lacks fluidity, which poses a serious problem in practical use as a dope. Further, a film with a large film thickness cast from a tetrahydrofuran solution is likely to have white turbidity particularly during the drying process.

As mentioned above, tetrahydrofuran has a problem in stability. In addition, methylene chloride, which is mainly used for dissolving polycarbonate at present, has environmental problems. That is, methylene chloride has a carcinogenic potential and is becoming a subject of regulation. In addition, since it has a low boiling point (boiling point 41 ° C.), it easily volatilizes out of the system from the process, and environmental pollution is doubled.

Therefore, as an alternative solvent, JP-A-2-227456 proposes to use dioxane. 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 there is a limit to the effect of dissolving polar macromolecules such as polycarbonate. At a concentration of 20% by weight or more of polycarbonate, it often becomes insoluble.

[0013]

The present invention uses a stable low-viscosity dope that does not contain halogen, and
The object is 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 body having little visual field dependency when applied to a liquid crystal display device.

[0014]

Means for Solving the Problems The present inventor has arrived at the present invention as a result of extensive studies and studies of solvents, film forming conditions, etc. suitable for production of cast films.

That is, according to the present invention, when a dope is cast on a support and dried by heating, a solvent containing 60 wt% or more of dioxolane is added to the solvent.
A method for producing a polycarbonate film, which comprises 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 containing a solvent containing dioxolane as a main component and having excellent storage stability is used. Dioxolane is a 5-membered cyclic ether having a cyclic ether bond at the 1,3-position, and its boiling point at atmospheric pressure is about 76 ° C.

In the present invention, the solvent used for dissolving the polycarbonate is a single solvent of dioxolane or a mixed solvent. In the case of a mixed solvent, it is desirable that 60 wt% or more, preferably 80 wt% or more is dioxolane, and if it is less than 60 wt%, the performance peculiar to dioxolane is not exhibited, which is not preferable. As the solvent coexisting in an amount of 40% by weight or less, for example, if at least one organic solvent selected from cyclohexanone, tetrahydrofuran, dioxane, etc., a stable polycarbonate dope for the cast film of the present invention can be prepared. . The amount and type of these additives can be determined, for example, by improving the smoothness of the surface of the cast molding (leveling effect), adjusting the evaporation rate and adjusting the viscosity of the system, and the purpose and effect of the addition of the solvent.

In the present invention, as a solvent to be mixed with dioxolane, it is possible to optionally use methylene chloride, dichloroethane or another halogen-based solvent within a range in which the amount of halogen remaining in the film does not become excessive. is there. According to the method of the present invention, the amount of halogen ions (especially chlorine ions) in the film can be suppressed to a low level, so that it exhibits excellent performance as a component of a liquid crystal display device or an electronic component that is used for a long time in a severe environment. There is expected.

Regarding the dissolution ratio of the dope polycarbonate 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. Desirably, when the ratio of the polycarbonate is increased, progress of crystallization is observed and the fluidity is lowered, which is not preferable. If the proportion of the solvent present exceeds 150 parts by weight, the storage stability of the dope will not be a problem, but the effective concentration of the polycarbonate will decrease, which is not preferable in practice. From the viewpoint of operability of the solution, it is more preferable that the amount of the solvent is 25 to 100 parts by weight with respect to 10 parts by weight of the polycarbonate resin.

The above dope is usually produced by dissolving polycarbonate in a solvent at a temperature not lower than room temperature and not higher than the boiling point of the solvent, but is preferably dissolved at 40 ° C. or higher and 70 ° C. or lower.

There are no particular restrictions on the polycarbonate used in the present invention. There is no particular limitation as long as it is a polycarbonate that can obtain various desired film characteristics. In general,
Polymer materials collectively referred to as polycarbonates are those in which polycondensation reaction is used in the synthetic method and the main chain is bound by a carbonic acid bond. Among these, generally, a phenol derivative and phosgene are generally used. , 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, which is called bisphenol-A, as a bisphenol component is preferably selected, but by appropriately selecting various bisphenol derivatives, Polycarbonate copolymers can be constructed.

[0022]

[Chemical 1]

As such a copolymerization component, other than 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 which partially contains a terephthalic acid and / or isophthalic acid component. By using such a constitutional unit as a part of the constitutional components of the polycarbonate comprising bisphenol-A, it is possible to improve the properties of the polycarbonate, such as heat resistance and solubility.

The viscosity average molecular weight of the polycarbonate used here is preferably 10,000 or more and 200,000 or less. Particularly preferred is 20,000 to 120,000. When the viscosity average molecular weight is lower than 10,000, the mechanical strength of the obtained film may be insufficient, and 40
If the polymer has a high molecular weight of 50,000 or more, the viscosity of the dope becomes too large and handling problems occur, which is not preferable. The viscosity average molecular weight was calculated by substituting the intrinsic viscosity obtained in a methylene chloride solution of polycarbonate into the equation of Mark-Houwink-Sakurada. Various coefficients at this time are, for example, Polymer Handbook Third Revised Edition, Wheely Co. (198).
9 years) (Polymer Handbook 3rd)
Ed. Willey, 1989), pages 7-23.

More specifically, the viscosity of the dope is preferably about 500 to 100,000 cps. If the dope viscosity is less than 500 cps, the fluidity becomes too high and handling becomes difficult, while the viscosity is 10
If it is more than 10,000 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, which is attributed to the difference in affinity between the solvent and the polymer. In this respect,
The dioxolane used in the present invention tends to lower the viscosity of the system, so that a solution of higher concentration can be obtained with the same viscosity, and its industrial value is large.

According to the present invention, a cast film having a low residual solvent amount can be easily obtained. For example, methylene chloride has a boiling point of 40 ° C., whereas dioxolane has a boiling point of 76.
However, there is no significant difference in the amount of residual solvent when treated under the same drying conditions. This is an unexpected fact, which is presumed to be based on the interaction between the polycarbonate molecule and the solvent molecule. Therefore, according to the present invention, although dioxolane is not a solvent having a boiling point lower than that of methylene chloride, it can be industrially advantageously dried with the same equipment and cost. At the same time, since dioxolane is a non-halogen solvent, it is advantageous to both the global environment and the purpose of reducing the chloride ion content in the film as described above.

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

That is, according to the present invention, the above-mentioned dope is cast on a support, and the film dried until the solvent content becomes 5 to 25% by weight is peeled from the support and is contracted in the width direction. A method for producing an optical polycarbonate film, characterized in that the temperature is raised within a range of temperature (T) satisfying the following formula (I), and the temperature is raised continuously or successively in accordance with the transition of Tg ′ and drying is performed. .

[0030]

## EQU00004 ## Tg'-50.degree. C..ltoreq.T.ltoreq.Tg '... (I) [Tg' (. Degree. C.) is the glass transition point of the polycarbonate containing the residual solvent. ]

(1) In the casting step, a method of extruding from a die, a method of using a doctor blade, a method of using a reverse roll coater, etc. 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 used is not particularly limited, but a glass substrate, a metal substrate such as stainless steel or a ferro type, a plastic substrate such as polyethylene terephthalate, or the like is used. However, a mirror-finished metal substrate is most commonly used for forming a film having a high degree of optical isotropy and uniformity, which is the main object of the present invention.

The dope temperature during casting of the present invention is 10
-60 degreeC, Preferably it is carried out in the range of 30-50 degreeC.
In order to obtain a film having excellent smoothness, the solution extruded from the die needs to be cast and smoothed on the support.
At this time, if the dope temperature during casting is too high, the surface is dried and solidified before it becomes smooth, which is not preferable.

The dope is usually stored at room temperature or higher and the boiling point of the solvent or lower, but it is preferably stored at a temperature of 40 ° C. or higher and 60 ° C. or lower.

(2) In the pre-drying step, it is necessary to evaporate and remove most of the solvent from the solution cast on the support in the shortest possible time. However, the drying conditions should be chosen carefully, as they undergo deformation due to foaming when rapid evaporation occurs. In the present invention, it is dried in the range of 30 to 130 ° C, preferably 40 to 120 ° C. On this occasion,
When the temperature-controlled drying is sequentially or continuously performed within this temperature range, efficient drying can be performed without losing high smoothness.

Further, in order to carry out the drying efficiently, air may be sent. Generally, the wind speed is in the range of 20 m / sec or less, preferably 15 m / sec or less. If it is less than that, the effect is not sufficient, and conversely, if it exceeds it, a smooth surface cannot be obtained due to wind disturbance, which is not preferable. At this time, a method of suppressing the wind speed in the initial stage of the drying process and increasing the wind speed sequentially or continuously is preferably used.

At this stage, the film is on the support,
At the end of this step, the support is peeled off. At this time, if the amount of residual solvent is high, the film is soft and thus the flow deformation of the polymer occurs in the film. Generally, the residual solvent amount 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 amount of residual solvent.
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 made contractible in the width direction. That is, it is desirable not to employ a method of supporting the end portion of the film with a tenter.

In general, in this step, a method of drying while conveying the film by a pin tenter method is adopted. However, in the tenter system, a non-uniform force is applied to the film due to its own weight, contraction due to evaporation of the solvent, wind pressure, or the like. However, although it seems that the force of winding is slight, it cannot be ignored in the film formation of a film which requires a high degree of optical isotropy as demonstrated in Reference Example 1. Moreover, this is especially the case when the process enters this step, since it contains a large amount of residual solvent and is particularly susceptible to deformation.

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

In the present invention, the drying temperature is

[0043]

## EQU00005 ## (Tg'-50.degree. C.). Ltoreq.T.ltoreq.Tg '... (I) [where Tg' (.degree. C.) is the glass transition point of the film containing the residual solvent. This object is achieved by continuously or sequentially raising the temperature in the temperature (T) range of the above] according to the transition of the Tg '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 step, the residual solvent decreases as the film is conveyed, and Tg ′ increases accordingly. 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 it is less than g'-50 ° C, it cannot be dried efficiently, which is not preferable. On the other hand, if it exceeds Tg ', distortion occurs, which is not preferable.

The temperature may be raised continuously, but in terms of equipment, there is a method in which it 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 to dry advantageously by blowing air as in the pre-drying step.

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

As described above, when the resin contains the solvent, its glass transition point (Tg ') is lowered. On the other hand, when the film is stretched in the state of containing the solvent, orientation occurs as in the case of not containing the solvent, but the orientation amount varies depending on the type and content of the solvent. In the case of the polycarbonate film containing the solvent having dioxolane or dioxolane as the main component of the present invention, the stretching temperature dependency of the orientation degree (corresponding to the retardation value) is low when stretched, which is clear to be that of a film containing the same amount of methylene chloride. By stretching in such a state, it can be advantageously used in the case of producing a retardation film having little variation in retardation. (Examples 13 to 17)

Therefore, the film obtained by the method of the present invention has a solvent content of 0.3 to 5% by weight.
A uniform retardation film can be obtained by stretching in the above state, preferably 0.5 to 3% by weight.

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

In the present invention, the film manufacturing process may be carried out in air or in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. Particularly, the pre-drying step is preferably performed in the inert gas atmosphere from the viewpoint of safety, since most of the solvent needs to be removed from the solution cast on the support.

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 by inclining the slow axis of the film by 40 ° with respect to it An optical polycarbonate film having the following formula (II) is provided.

[0052]

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

When (R ₄₀ −R ₀ ) · 10 ⁴ / Mw is larger than 3.0, the angle dependence of the retardation of the film is likely to be large, and in particular, it is optically isotropic as a substrate for liquid crystal cells. There is chipping and, at the same time, the retardation film is unfavorable because it has a large variation in retardation value even as a raw material for a retardation film.

The film 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 optical polycarbonate film is
It can be produced by casting the above-mentioned dope on a support and heating it to dry it.

[0056]

According to the present invention, by using a good polycarbonate dope obtained by dissolving polycarbonate in a solvent containing dioxolane as a main component, the viscosity is low, the solution viscosity is not increased, and no turbidity occurs. A polycarbonate film having excellent transparency and low optical anisotropy can be obtained.

According to the present invention, when a film is cast from a solution of polycarbonate, the drying conditions are strictly controlled to obtain a transparent / smooth film excellent in optical isotropy and uniformity. I can.

[0058]

EXAMPLES The present invention will be described in detail below with reference to examples. The measurement items in the examples were measured by the following methods. Amount of residual solvent: The sample was dried at 150 ° C. for 16 hours, and the weight was determined before and after the measurement. Heat shrinkage rate: 140 cm for sample film of 10 cm
It was also determined by measuring the length before and after heating at 30 ° C. for 30 minutes. Haze value: UV-Visible spectroscope (UV- manufactured by Shimadzu Corporation)
240) was used. Measurement of solution viscosity: Tokyo Keiki Co., Ltd. B type viscometer BH type was used and measured at 25 ° C. Dope stability: Each resin solution was sealed in a 50 ml sample bottle, allowed to stand at room temperature, and its appearance was observed, and changes in its appearance were described as follows. ⊚: No change in appearance after leaving for 3 days ×: Solidification or clouding 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 in visible light of 590 nm.

[Example 1] 12 parts by weight of a polycarbonate resin (Panlite, trade name, L-1225 manufactured by Teijin Kasei Co., Ltd., molecular weight 24,000 in terms of viscosity) of a constituent unit of bisphenol A was added to 88 parts by weight of dioxolane. In addition, the mixture was thoroughly stirred to prepare a dope. The obtained dope was allowed to stand at room temperature and a change in appearance was observed, but no increase in viscosity was observed for 7 days after preparation of the dope, and fluidity was observed to be maintained.

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

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

Example 3 Polycarbonate resin (Tanjin Kasei Co., Ltd. Panlite, registered trademark, L-1225,
15 parts by weight of a viscosity-converted molecular weight of 24,000) was mixed in advance with 55 parts by weight of dioxolane and 30 parts by weight of dioxane, and the mixture was added little by little to a uniform solvent to prepare a dope.
When the storage stability of this dope was examined, fluidity was observed even after storage for 1 week, and no gelling behavior was observed.
A film was formed using the obtained dope 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, the sample was allowed to stand at room temperature and 50 ° C., and the change in appearance after 3 days was observed, but both were stable and no change in appearance was observed. The results are summarized in Table 1.

(Production of Film) A dope prepared by dissolving polycarbonate having a constitutional unit of bisphenol A indicated by * 1 in Table 1 in dioxolane to a concentration of 20% by weight was placed on a glass plate kept at 60 ° C. The film was cast with a doctor blade having a clearance of 0.8 mm, left for about 2 minutes, dried at 80 ° C. and a wind speed of 0.9 m / sec for 15 minutes, and the obtained film was peeled off from the glass substrate at 130 ° C. and a wind speed of 1 m. The heat treatment was performed for 30 minutes at a heating speed of 1 second per second, and the sheet was 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 solution was stirred and dissolved at 25 ° C.
The measurement was also performed under the same conditions. The 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 haze value of a film obtained from a dope prepared by dissolving polycarbonate (C-1400) shown by * 1 in Table 1 in methylene chloride to a concentration of 20% by weight is 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 5-11, Comparative Examples 2-6 (Manufacture of Dope) As in Example 1, the solvents of various compositions shown in Table 2 were mixed with the various polycarbonates used in Example 1 shown in Table 2. The concentrations shown in Table 2 were dissolved and the behavior of the dope was observed. The composition of the solvent, the stability of the obtained dope, and the like 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. The amount of residual solvent after heating is shown in Table 3. After that, the film was peeled from the glass plate and heat-treated at a drying temperature and a time shown in Table 3 in a state capable of shrinking in the width direction to be dried to obtain a film having a thickness of about 100 μm. The amount of residual solvent, haze value, retardation, heat shrinkage ratio, 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 Polycarbonate derived from bisphenol-A (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.

This film was subjected to a tensile test at various temperatures, and the ratio (P / E) between the strength (P) and the elongation (E) was determined within the elastic limit. Also, the phase difference (Re) corresponding to various elongations (E) is measured at the corresponding temperature,
Re / E was determined. The results are shown in Table 4.

As is clear from Table 4, P / E and Re
/ E largely depended on the temperature. In particular, P / E drastically decreased as the glass transition point (Tg '= 158 ° C) of the film was approached. Re / P obtained from the values of P / E and Re / E is conversely T
It increased sharply as it approached g '. From the value of Re / P, when winding a film with a film thickness of 10 μm and a width of 1 m, Re
It is possible to obtain the maximum tension (T) that is allowed in order to keep the value of 10 nm or less. As is clear from Table 4,
T also decreases sharply as the temperature approaches Tg '. For example,
20kg is allowed at 100 ℃, while 150kg is allowed
When a small force of only 0.76 kg is applied at ℃, the phase difference is 1
It reaches 0 nm. This result indicates that optical distortion occurs even with a slight force near Tg ', even though the film does not contain residual solvent. When the residual solvent is contained, Tg 'is greatly lowered, and thus an optical strain is caused by a further minute stress.

[0075]

[Table 4]

Reference Example 2 The polycarbonate used in Reference Example 1 was prepared by using methylene chloride, 1,3-dioxolane, 1,4.
-Dissolved in dioxane, 1,2-dichloroethane and cyclohexanone respectively to prepare a 20 wt% solution. By changing the drying conditions from these solutions, films having a film thickness of 100 μm and different residual solvents were produced. The glass transition point (Tg ') of these films is shown in FIG.
Shown in. As is clear from the figure, the Tg 'decreased significantly as the residual solvent amount increased for all the films examined. Moreover, the degree of decrease depended largely on the type of solvent.

[Example 12] Bisphenol-A and 2,
A viscosity average molecular weight of 4.4 × 1 consisting of 2-bis (4-hydroxyphenyl) cyclohexane (molar ratio 95/5)
Continuous film formation was performed using a 20 wt% solution of the polycarbonate copolymer of 0 ⁴ dissolved in 1,3-dioxolane.

As the casting device, a system was adopted in which the die was extruded into a belt and the belt was connected to a pre-drying furnace divided into four stages. As the post-drying oven, the oven in which the film peeled from the belt was divided into 6 stages was adopted.
After casting using this apparatus, the temperature of the pre-drying furnace was sequentially raised to 40, 80 and 90 ° C. and finally brought to 40 ° C. and cooled. Then, a film having a residual solvent amount of 13.5% by weight was prepared. At this stage, the film was peeled from the belt and then sent to the drying oven. The temperature of the post-drying oven was adjusted to 40 ° C. (residual solvent amount 13.5%, Tg ′ = 50 depending on the residual solvent amount.
℃), 75 ℃ (residual solvent amount 5.5%, Tg '= 91)
℃), 100 ℃ (residual solvent amount 3.2%, Tg '= 113
℃), 120 ℃ (residual solvent amount 1.2%, Tg '= 141
℃), 140 ℃ (residual solvent amount 0.8%, Tg '= 145
(° C.) to obtain a dry film. The residual solvent amount of the film thus obtained 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
The film had a thickness of nm and had a very small anisotropy and a small variation range.

[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 at 90 ° C. for 10 minutes for 12 minutes.
After preliminary 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 to obtain (R ₄₀ -R ₀ ) · 10 ⁴ / Mw. The results are shown in Table 5.
Shown in. In the table, the letter A at the end of the number represents a sample at the stage where the preliminary drying was completed, and the letter B at the end was a sample after the main drying.

Example 18 The polycarbonate resin shown in Table 5 was added to dioxolane and sufficiently stirred at 50 ° C. to prepare a 15% concentration solution. The polycarbonate resin solution kept at room temperature was cast on a stainless steel substrate kept at 40 ° C. with a doctor blade having a clearance of 0.8 mm, and allowed to stand for about 2 minutes, then at 40 ° C. for 10 min at 80 ° C.
It was dried for 80 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 to obtain (R ₄₀ -R ₀ ) · 10 ⁴ / Mw.
In this experiment, it was dried at the same initial temperature as the comparative example. The results are shown in Table 5.

[Comparative Examples 7 to 12] The same operation as in Example 18 was carried out in the same manner as in Example 18, except that the solvent was changed to methylene chloride and the mixture was dissolved by stirring at 25 ° C. Dry at 40 ℃ for 10 minutes, 80
After peeling off the film from the substrate for 80 minutes at
It was carried out at 0 ° C. for 1 hour. The other measurements were 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 of bisphenol A and bisphenol FL (5 mol%) (viscosity average molecular weight 37,000) in dioxolane (resin concentration 20 wt%). A film was produced by casting this dope in the same manner as in Example 4. The residual solvent amount of this film was 0.9%. Polycarbonate film thus obtained, 160 ℃, 170 ℃,
After preheating for 1 minute at each temperature of 180 ° C., longitudinal uniaxial stretching was performed to obtain a retardation film. The results of measuring the birefringence characteristics of the obtained retardation film are shown in Table 6.

Since the polycarbonate film of the present invention has a small amount of change in retardation due to a change in stretching temperature, the variation in retardation of the film is small, and it 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] The copolymer used in Example 19 was dissolved in methylene chloride to prepare a dope (resin concentration: 20% by weight). A film was produced by casting this dope in the same manner as in Example 4. The residual solvent amount of this film was 2.5%. Using the polycarbonate film thus obtained, a retardation film was manufactured in the same manner as in Example 4. The results of measuring the birefringence characteristics of the obtained retardation film are shown in Table 6.

[Example 20] 9,9-bis (4-hydroxyphenyl) fluorene and bisphenol-A
Polycarbonate resin containing bisphenol component (molar ratio = 25/75) (viscosity average molecular weight 5.5 × 10 ⁴ )
A transparent viscous solution was obtained by adding 15 parts by weight to 85 parts by weight of 1,3-dioxolane and stirring at room temperature for 10 hours. The dope viscosity of this solution is 4.1 at 30 ° C.
It was × 10 ³ cps and showed a high solution viscosity. The haze value obtained by putting this solution in a quartz cell having an optical path length of 1 cm was 0.4%, and the transparency was extremely high. Moreover, even if this solution is left at room temperature for 1 week, its haze value is 0.5%.
No white turbidity phenomenon or gelation was observed.

The obtained solution was cast on a stainless steel substrate using a doctor knife and dried at 90 ° C. for 20 minutes and further at 177 ° C. for 60 minutes in a drier having a wind speed of 1 m / sec to give a film thickness of 97 μm. To obtain a transparent unstretched film. The residual solvent of the obtained film was 0.33%. Further, the light transmittance of the film is 90.7% in the visible light of 500 nm,
The haze value was 0.9% and the transparency was extremely high. Moreover, 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 is 7.1 kg /
mm ² , breaking elongation 95%, initial modulus 205 k
It was g / mm ² and was extremely strong.

The unstretched film thus obtained is 202
A oriented film was obtained by uniaxially stretching at 20% at 20 ° C. The Re of this stretched film was 520 nm, and a film having desired birefringence was obtained. This slow axis coincided with the stretching direction and was shown to exhibit positive birefringence. The birefringence unevenness was <10 nm, and the birefringence unevenness 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
Polycarbonate resin containing bisphenol component (molar ratio = 40/60) (viscosity average molecular weight 5.7 × 10 ⁴ )
A transparent viscous solution was obtained by adding 15 parts by weight to 85 parts by weight of 1,3-dioxolane and stirring at room temperature for 10 hours. The haze value of this solution was 0.5% and the transparency was extremely high. Even when this solution was allowed to stand at room temperature for 1 week, its haze value did not change, and no clouding phenomenon or gelation was observed.

The obtained solution was cast on a stainless steel substrate using a doctor knife and dried at 90 ° C. for 20 minutes and further at 195 ° C. for 60 minutes in a drier having a wind speed of 1 m / sec to obtain a film thickness of 97 μm. To obtain a transparent unstretched film. 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 , breaking elongation 90%, initial modulus 200
It was kg / mm ² and was extremely strong.

The unstretched film thus obtained is filled with 220
An oriented film was obtained by uniaxially stretching at 25% at 25 ° C. The Re of this stretched film was 480 nm, and a film having desired birefringence was obtained. This slow axis coincided with the stretching direction and was shown to exhibit positive birefringence. The birefringence unevenness was <10 nm, and the birefringence unevenness was extremely small.
The Tg of this film was 214.5 ° C., showing high heat resistance.

[Example 22] 1,1-bis (4-hydroxyphenyl) cyclohexane and bisphenol-
Polycarbonate resin containing A (molar ratio = 40/60) as a bisphenol component (viscosity average molecular weight 3.6 × 1
0 ⁴ ) 20 parts by weight was added to 80 parts by weight of 1,3-dioxolane and stirred at room temperature for 10 hours to obtain a transparent viscous solution.

The solution viscosity was 1.9 × 10 ³ at 30 ° C.
It was cps. The haze value of this solution was 0.6% and the transparency was extremely high. Even when this solution was allowed to stand at room temperature for 1 week, its haze value did not change, and no clouding phenomenon 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 then at 147 ° C. for 60 minutes in a drier / second dryer to obtain a transparent unstretched film having a film thickness of 102 μm. The residual solvent of the obtained film was 0.13%. Further, 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 filled with 171
A oriented film was obtained by uniaxially stretching at 15% at a stretching rate of 15%. The Re of this stretched film was 530 nm, and a film having desired birefringence was obtained. Also, this birefringent spot is <10
nm, and the birefringence unevenness was extremely small. The Tg of this film was 166.5 ° C., showing high heat resistance.

[Example 23] 1,1-bis (4-hydro)
Xyphenyl) -3,3,5-trimethylcyclohexa
And bisphenol-A (molar ratio = 57/43)
Polycarbonate resin containing bisphenol component (viscosity
Average molecular weight 2.2 x 10^Four) 28 parts by weight of 1,3-Geo
In addition to 72 parts by weight of xoxolan, heat and stir at 50 ° C for 5 hours
By doing so, a transparent viscous solution was obtained. This solution
Dope viscosity is 3.2 × 10 at 30 ° C ³cps and high
It exhibited a solution viscosity of 1. This solution was applied to a quartz cell with an optical path length of 1 cm.
The haze value of 0.3% obtained by putting in
It was good. Also, leave this solution at room temperature for 1 week
However, neither the solution viscosity nor the haze value changed.

The obtained solution was cast on a stainless steel substrate using a doctor knife and kept at 50 ° C. for 10 minutes for 90 minutes.
C. for 10 minutes, 120.degree. C. for 10 minutes, and 160.degree. C. for 60 minutes, and dried by heating to obtain a 98 .mu.m transparent unstretched film.
The light transmittance of the obtained film is 9 at a visible light of 500 nm.
The transparency was 2.0% and the haze value was 0.3%, and 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.
It was m ² and was extremely strong. Further, the glass transition point (Tg) was 207 ° C., indicating high heat resistance.

[Brief description of drawings]

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

[Explanation of symbols]

A When methylene chloride is used as a solvent. B When dioxolane 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.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location G02F 1/1335 510 // B29L 7:00 C08L 69:00 (72) Inventor Hideaki Nitta Tokyo 4-3 Asahigaoka, Hino City, Tokyo Research Center, Teijin Limited (72) Inventor Takeshi Sasaki 4-32, Asahigaoka, Hino City, Tokyo Research Center, Teijin Limited

Claims (7)

[Claims] 1. When casting a dope on a support and heating and drying the dope to produce a film, 10 parts by weight of polycarbonate is added to 25 to 150 parts by weight of a solvent containing 60% by weight or more of dioxolane. A method for producing an optical polycarbonate film, which comprises using a dope in which is dissolved. 2. A polycarbonate having a viscosity average molecular weight of 1
The method for producing an optical polycarbonate film according to claim 1, which is 20,000 or more and 200,000 or less. 3. The method for producing an optical polycarbonate film according to claim 1, wherein the solvent contains 60% by weight or more of dioxolane, and the remaining component is at least one organic solvent selected from the group consisting of cyclohexanone, tetrahydrofuran and dioxane. . 4. The dope is cast on a support, and the film dried until the solvent content is 5 to 25% by weight is peeled from the support, and the film of the following formula (I )
2. The method for producing an optical polycarbonate film according to claim 1, wherein the temperature is raised within the range of temperature (T) satisfying the condition (T) and the temperature is raised continuously or sequentially in accordance with the transition of the Tg ', and the film is dried. ## EQU00001 ## Tg'-50.degree. C..ltoreq.T.ltoreq.Tg '... (I) [Tg' (. Degree. C.) is the glass transition point of the polycarbonate containing the residual solvent. ] 5. A method for producing a film by casting a dope on a support and heating the dope to evaporate the solvent.
Solvent containing 60% by weight or more of dioxolane 25-15
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
After drying to 5% by weight, the film was peeled from the support, and in a state capable of contracting in the width direction, in accordance with the transition of its Tg 'within the range of temperature (T) satisfying the following formula (I). A method for producing an optical polycarbonate film, which comprises continuously or sequentially heating up and drying. ## EQU00002 ## Tg'-50.degree. C..ltoreq.T.ltoreq.Tg '... (I) [Tg' (.degree. C.) is the glass transition point of the polycarbonate containing the residual solvent. ] 6. A retardation value (R ₀ ) in the direction perpendicular to the film surface and a retardation value (R ₄₀ ) measured by inclining the film by 40 ° with the slow axis of the film as the tilt axis are defined by the following formula: An optical polycarbonate film satisfying (II). (R ₄₀ −R ₀ ) · 10 ⁴ /Mw<3.0 (II) [wherein, Mw represents the viscosity average molecular weight of the polycarbonate. ] 7. A viscosity average molecular weight (M
The optical polycarbonate film according to claim 6, wherein w) is 40,000 or more and 200,000 or less.