JPH0564821A - Casting film-forming method - Google Patents

Abstract

PURPOSE:To provide the method for forming polycarbonate film having excellent surface profile without developing surface irregularities, chalking and blushing and further film suitable for optical use such as phase difference. CONSTITUTION:As casting dope, polycarbonate having the intrinsic viscosity, which is not less than 0.8 and not more than 5.0, and the average molecular weight, which is not less than 40,000 and not more than 360,000 is employed and the casting is performed in the form of the dope having the concentration of solid content of 10-25%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting a polycarbonate film, and more particularly to a method for casting a polycarbonate film for a retardation plate used for optical applications.

[0002]

2. Description of the Related Art A polycarbonate film is formed into a film or sheet by a known film forming means, that is, a solution film forming method or a melt film forming method. From the viewpoint of solubility and meltability, a polycarbonate resin having a low molecular weight, that is, a low intrinsic viscosity has been conventionally used. For example, JP-A-2-59702
In the gazette, the intrinsic viscosity is specified in the range of 0.35 to 0.7.

[0003]

However, when a raw material having an intrinsic viscosity as described above is used as a solution, if the casting viscosity is too low, it becomes unsuitable for solution casting. Measures are taken to raise the concentration and lower the solution temperature to increase the apparent viscosity. However, when the solid content concentration is high, leveling during casting is deteriorated and surface unevenness is likely to occur. When a high-concentration liquid is cast, there are problems that the liquid becomes cloudy depending on conditions, or brushing easily occurs during casting. Further, lowering the solution temperature has various problems such as stability of the solution and influence on drying during casting. An object of the present invention is to solve the conventional problems, and to provide a polycarbonate casting film forming method in which the surface condition is excellent without causing surface unevenness, clouding and brushing. Furthermore, it is to provide a film suitable for optical applications such as a retardation plate.

[0004]

The above object of the present invention is to cast a methylene chloride solution of a polycarbonate on a metal support to form a film, and then to dry the film on the support. In a casting film-forming method in which the polycarbonate is peeled off and further dried, a polycarbonate methylene chloride solution having an intrinsic viscosity of 0.8 or more and 5.0 or less and an average molecular weight of 40,000 or more and 360,000 or less is used. , A solid film having a solid content of 10 to 25% is cast.

In the present invention, the use of a polycarbonate having an intrinsic viscosity of 0.8 or more and 5.0 or less corresponds to an average molecular weight of 40,000 or more and 360,000 or less, preferably an intrinsic viscosity of 0.9 or more and 4. 0 or less (average molecular weight is 45,000 or more and 270,000 or less), and more preferably intrinsic viscosity is 0.95 or more and 3.0 or less (average molecular weight is 48,000 or more and 190,000 or less). Here, the average molecular weight is Schn
It was calculated by the formula of ell. That is, there is the following relationship between the average molecular weight M and the intrinsic viscosity (η). [Η] = 1.23
× 10 ^-4 × M ^0.83 . By making a solution having a high molecular weight into a solution dope, the viscosity of the solution becomes high even if the solution concentration is the same as that of a case where the molecular weight is low, so that the casting aptitude is improved. What is the intrinsic viscosity of polycarbonate 0.8 to 5.0?
If it is 0.8 or less, the solution viscosity becomes low, and it is necessary to increase the solid content concentration. At a normal solution concentration, the casting viscosity becomes too low and the casting aptitude becomes poor. On the other hand, if it is 5.0 or more, the solution viscosity is too high, and therefore the amount of the solvent must be increased in order to have the castability. In the present invention, the casting as a dope having a solid content concentration of 10 to 25% is preferably 12 to 22%, more preferably 15 to 20%. Solid content concentration 1
When the amount is 0% or less, the amount of the solvent is large, and therefore the casting speed is reduced due to the drying load, which is not preferable in terms of production efficiency. When the amount is 25% or more, the amount of the solvent is small, the leveling at the time of casting is deteriorated, and the white turbidity or the time of casting is decreased. There is a risk of brushing. Furthermore, in the case of stretching the polycarbonate film to form a retardation plate, a film having a molecular weight of 0.8 or less is an intrinsic viscosity,
The stretching ratio is increased because the molecules are oriented.
Therefore, unevenness during stretching is conspicuous, and it may not be suitable as a retardation plate. To prevent this, the temperature is raised.

[0006]

EXAMPLES The present invention will be described with reference to examples. However, the present invention is not limited to this embodiment. (Comparative Example-1) A polycarbonate resin having an intrinsic viscosity of 0.457 and a molecular weight of about 20,000 was dissolved in methylene chloride to give a solid content of 17% and a viscosity of 33 poise (P). When this was cast on a support from a die, the viscosity was too low, the casting width could not be defined on the support, and it was wider than the die casting width, and was not suitable for casting. Therefore, the solid content concentration was increased to 27% and the viscosity was set to 122P.
However, in this state, the liquid became cloudy and the amount of the solvent was small even when the liquid was cast, so that leveling became difficult and surface unevenness occurred, resulting in poor surface quality.

(Comparative Example 2) A polycarbonate resin having an intrinsic viscosity of 5.5 and a molecular weight of about 400,000 was dissolved in methylene chloride to obtain a solution having a solid content of 12% by weight. .. Therefore, the concentration was lowered to 8% to dissolve. The viscosity at this time was 1100P. Since the viscosity is still high even in this state, the concentration was further lowered, and a casting film was formed at 6%. There was no problem in discharging from the die onto the support, but since the concentration was low, the amount of solvent to be dried increased, and the casting speed had to be reduced by 50%, which was not preferable in terms of production efficiency. In addition, a large amount of solvent is required, which is a cost problem.

Example 1 A polycarbonate resin having an intrinsic viscosity of 0.85 and a molecular weight of about 42,000 was dissolved in methylene chloride to obtain a solution having a solid content of 20% by weight. At this time, the viscosity was 560 P, and it flowed without problems when flowing from the casting die, the amount of solvent was appropriate, evaporation increased, the leveling effect improved, and the flatness was good.

Example 2 A polycarbonate resin having an intrinsic viscosity of 1.30 and a molecular weight of about 70,000 was dissolved in methylene chloride to obtain a solution having a solid content of 17.8%. At this time, the viscosity was 680 P, and it flowed without problems when flowing from the casting die, the amount of solvent was appropriate and evaporation increased, and the solvent vapor around the die was filled with the leveling effect, and the flatness was good.

Example 3 A polycarbonate resin having an intrinsic viscosity of 3.5 (molecular weight of about 232,000) was dissolved in methylene chloride to obtain a solution having a solid content concentration of 12.2% by weight. At this time, the viscosity was 820 P, and it flowed without problems when flowing from the casting die, the amount of solvent was appropriate, evaporation increased, and there was a leveling effect, and flatness was good.

The flatness of the polycarbonate film produced according to the present invention was good. Then, when this film was stretched and compared, it was found that the retardation was likely to occur due to the high molecular weight even if the stretching ratio was low.

(Comparative Example 3) When a cast film of a polycarbonate resin having an intrinsic viscosity of 0.457 and a molecular weight of about 20,000 was stretched to form a retardation plate, the retardation was 570 nm and the 180 ° C. at 180 ° C. % Stretching was required. Since the stretching ratio was large, unevenness in stretching was noticeable and the quality was poor.

(Example 4) A cast film of polycarbonate resin having an intrinsic viscosity of 0.95 and a molecular weight of about 48,000 was used as a film.
When stretched at 70 ° C., the same retardation was obtained at a stretch ratio of 124%, which was good without unevenness. Further, when a film having an intrinsic viscosity of 1.3 and a molecular weight of about 70,000 was stretched at 170 ° C., the retardation was 112% and the retardation was the same. Furthermore, the intrinsic viscosity is 3.
When a film having a molecular weight of about 232,000 was stretched at 170 ° C., the same retardation was obtained at a stretching ratio of 108%, which was good without unevenness.

[0014]

By the casting film forming method of the present invention, a polycarbonate film having excellent flatness can be obtained. When stretched as a retardation film, excellent quality with no unevenness in retardation was obtained. According to the method of the present invention,
The stretching ratio can be made small, and it is possible to perform casting and stretching consistently by installing it in the film forming casting equipment.

Claims (1)

[Claims] 1. A casting film-forming method in which a methylene chloride solution of polycarbonate is cast onto a metal support to form a film, which is then dried, peeled off from the support, and further post-dried. In the method, a polycarbonate methylene chloride solution having a limiting viscosity of 0.8 or more and 5.0 or less and an average molecular weight of 40,000 or more and 360,000 or less is used as a dope having a solid content concentration of 10 to 25% and cast. A casting film forming method comprising: