Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1999-12-16
2001-04-24
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S198000
Reexamination Certificate
active
06222003
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical film. More specifically, it relates to a method for producing an aromatic polycarbonate film having optical transparency and excellent lubricity.
BACKGROUND ART
Polycarbonate film comprising an aromatic polycarbonate resin is used as an electrode substrate and a phase difference sheet of a liquid crystal display apparatus due to its high thermal resistance, transparency and optical elastic modulus and so forth. Especially, aromatic polycarbonate film produced by a casting method is preferably used.
In the production of a film poor in lubricity like an aromatic polycarbonate film having a smooth surface, there have been large practical problems during its production. For example, scratches are generated and fine surface-abrasions are formed while the film runs on a transferring roll system. Its poor taking-up property will cause wrinkles to form on the film during the taking-up process, and abrasions to form due to the friction between films when wound too strongly. Therefore, following countermeasures are currently taken for the film having poor lubricity: a lubricant is compounded in the film (for example, Japanese Unexamined Patent Publication No. 8-334607); a surface protecting film having excellent lubricity is laminated on the film; or the film is wound-up with a spacer between films; and so forth. However, when the lubricant is compounded, the formed film will have a critical problem in optical use because of its lowered transparency. On the other hand, the method that uses the surface-protecting film-spacer is accompanied by a production problem, that is, the production process becomes complicated, and the number of the members which are necessary for production is increased.
In order to solve these problems, for example, Japanese Unexamined Patent Publication No. 8-175808 discloses a process for winding up a lubricant-free film which is characterized in that concavo-convex forms are formed on at least one side of the surfaces at both the edges of the film in such a state that the height of the protruding parts is higher than the average height of the film, and subsequently the film is taken up into a roll shape with a winder. In this method, concavo-convex forms are formed on both the edges of a stretched film formed by a melt extrusion method by pushing a rough-surface processing roll which has been internally heated onto the film. However, the film formed by this method is not preferred for optical use because it has defects characteristic of melt extrusion, that is, foreign materials such as heat degradation products or carbonized products. Further, this method has not only a problem of increased energy cost due to the positive heating of the rough-surface processing roll, but also it has such a problem that when the taken-up film having concavo-convex forms at both the edges is taken out from the roll for processing, the surface of the film sometimes unevenly comes into contact with the surface of the transferring roll, and thereby it is sometimes necessary that both the edges having the concavo-convex forms are cut off before processing. Furthermore, both the edges having the concavo-convex forms can not be used as a film of normal quality, and as a result, the waste parts become large.
Thus, the conventional technologies such as the method to achieve the object by improving lubricity of the film by compounding it with a lubricant, or the method in which the film is taken up after concavo-convex forms have been imparted to the edges of the film, still have problems unsolved.
DISCLOSURE OF THE INVENTION
The present invention is proposed in consideration of the above-mentioned current state. The object of the present invention is to solve the problems of the defects such as scratches, wrinkles or abrasions in the production processes of an aromatic polycarbonate film for optical use and in the processing processes of the film, and provide an aromatic polycarbonate film suitable for optical use, excellent in transparency and surface smoothness, and having excellent lubricity.
The inventors of the present invention had pursued studies zealously to solve the above-mentioned problems, and they found that, in a casting method for producing a film from an aromatic polycarbonate solution, concavo-convex forms can be imparted on a surface of the film under specific conditions in a drying process after solution casting, and reached the present invention.
That is, the present invention provides the following aromatic polycarbonate film suitable for optical use and method for producing the film.
1. An optical film characterized in that an aromatic polycarbonate film produced by a solution casting method satisfies the following requirements (a)-(d) at the same time:
(a) the film is not stretched,
(b) the haze value of the film is 1.0% or less,
(c) the central line average surface roughness of one surface of the film is not more than 3 nm, and the central line average surface roughness of the other surface is from 3 to 10 nm., and
(d) the number of the surface protrusions whose circle equivalent diameters are 30 &mgr;m or more and maximum heights are 3 &mgr;m or more is less than 3 pieces/m
2
on any side of the surfaces.
2. An optical film described in the above 1 characterized in that no lubricant is compounded in the film.
3. A method for producing an unstretched optical film characterized in that, when the film is produced by dissolving an aromatic polycarbonate in a solvent, casting the obtained solution onto a support to form film and drying the formed film, the drying process contains a step where the film formed by a solution cast method is dried at the ambient temperature not above (Y+5)° C. to reduce the concentration X of the solvent in the film to the value satisfying the equation: 25% by weight <X≦45% by weight and a step where the film is subsequently kept in contact with the support at the ambient temperature above (Y+5)° C. and not above (Y+35)° C. until the concentration of the solvent in the film becomes 25% by weight, and the holding time of the film in the step where the film is treated at a temperature above (Y+5)° C. and not above (Y+35)° C. is 3 minutes or more (here, Y is the boiling point of the solvent expressed by the centigrade unit).
Here, throughout the present invention, “the boiling point of a solvent” is defined as follows: it means the boiling point of a compound when said solvent consists singly of the compound; it means the boiling point of the compound constituting a main solvent when said solvent consists of the main solvent and an assistant solvent; and it means the boiling point of the compound having the lowest boiling point among the compounds whose weight ratio is more than 10% by weight based on the total of the compounds when said solvent (the main solvent of said solvent when said solvent consists of a main solvent and an assistant solvent) is a mixture of some compounds.
Further, it is preferred that the step where the film is treated at a temperature above (Y+5)° C. and not above (Y+35)° C. (preferably, above (Y+5)° C. and not above (Y+25)° C. is completed in the reaction time not longer than 8 minutes, at most not more than 15 minutes. Furthermore, the aromatic polycarbonate to be used preferably has a viscosity average molecular weight of 3×10
4
to 7×10
4
, and a bisphenol A-polycarbonate polymer having a viscosity average molecular weight of 3×10
4
to 7×10
4
is more preferred.
4. A method for producing an unstretched optical film described in the above 3 characterized in that the solvent contains methylene chloride in an amount of 95% or more by weight.
Here, the boiling point of methylene chloride is 40° C., and hence (Y+5)° C.=45° C. and (Y+35)° C.=75° C.
5. A method for producing an unstretched optical film described in the above 3 or 4 characterized in that the solvent contains one or two or more selected from methyl alcohol, ethyl alcohol and propyl alcohol in an
Hosoi Masahiro
Nagoshi Tamiaki
Boykin Terressa M.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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