Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
1998-08-14
2001-10-23
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S237000, C264S211120, C425S373000
Reexamination Certificate
active
06306327
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and an apparatus for producing a thermoplastic resin sheet, in which the obtained polypropylene resin sheet or film can be used for the packaging of food, medicine and so on.
2. Description of the Related Art
Of late years, as a transparentizing art of sheet (or film) made out of polypropylene resin, various processes with the use of a metallic endless belt have been proposed.
The greatest advantage of the use of the metallic endless belt is the point that high-glossing of both faces of the sheet can be effectively obtained to continuously transfer a mirror face of the metallic endless belt onto the surface of the sheet.
In order to increase the transparency of the polypropylene resin sheet, however, in addition to the aforementioned high-glossing, it is required that haze (the degree of cloud) inside the sheet is reduced to a low level.
Conventionally, various methods and apparatus for improving the transparency have been proposed.
For example, according to Japanese Patent Application Laid-open No. 6-170919, an apparatus for cooling and solidifying a fused sheet is disclosed, in which the metallic endless belt is provided to be wound on and between a metal roller and an elastic roller, covered with an elastic body on its surface, and after the sheet is guided into the area between the elastic roller and the cooling roller through the metallic endless belt, the sheet is, continuously, cooled while being pressed to a part of the circumference of the cooling roller.
In this case of the apparatus, the effect of immediately cooling the sheet pressed by the cooling roller and the metallic endless belt is insufficient, and in addition, hardness of the elastic body of the elastic roller is higher, so that the sheet is not touch-rolled on its face, with the result that a resin bank is produced or a fine transparency of the sheet cannot be obtained.
In Japanese Patent Application Laid-open No. 6-166089 and Japanese Patent Application Laid-open No. 6-170919, a method for cooling the sheet using the same method after the metallic endless belt is provided to be wound on and between the metal roller and the elastic roller covered with the elastic body on its surface is disclosed, however, the cooling temperature is higher and hardness of the elastic body is higher, so that the immediate cooling effect is insufficient, with the result that the transparent polypropylene sheet cannot be obtained without the use of raw materials consisting of a nucleating agent.
Further, according to Japanese Patent Application Laid-open No. 6-55613, a producing method of a thermoplastic resin sheet is disclosed, in which the sheet of the fusing state, consisting of a nucleating agent or the like, is guided into an area between the cooling roller and the metallic endless belt, and after the sheet is moved while being touched to the cooling roller and the metallic endless belt, the sheet is pressed against the cooling roller from the inside of the metallic endless belt by the aforementioned cooling roller.
In this case of the producing method, the immediate cooling of the sheet starts after the sheet is sandwiched between the cooling roller and the metallic endless belt, so that at the starting point of the immediate cooling, the face pressure is insufficient, with the result that it is difficult to obtain a fine effect of the immediate cooling and a fine surface gloss on the sheet. As a result, the transparency has tried to be improved by adding a nucleating agent or the like, but the degree of transparency may be insufficient if the nucleating agent or the like is not added.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a producing method of a thermoplastic resin sheet, using a producing apparatus in which a metallic endless belt having a mirror face on the surface is provided to be wound on and between a first cooling roller, covered with an elastic member on the surface, and a second cooling roller, and a third cooling roller, having a mirror face on the surface and touching the first cooling roller through a molten thermoplastic resin sheet and the metallic endless belt, is provided to hold the molten thermoplastic resin sheet pressed with the metallic endless belt, which is characterized by guiding the molten thermoplastic resin sheet into the area between the first and third cooling rollers to touch the metallic endless belt, touching the first cooling roller, and the third cooling roller at approximately the same time, while the temperature of the metallic endless belt, directly touching the molten thermoplastic resin sheet, and the third cooling roller is retained to be less than 50° C. and more than the dew-point; touch-rolling the face and cooling the molten thermoplastic resin sheet along a nip width (a length in MD (machine direction) of an elastically deformed area of the elastic member) of more than or the same as 5 mm between the first and third cooling rollers while the elastic member is elastically deformed by a pressing force between the first and third cooling rollers; and cooling, subsequently, the molten thermoplastic resin sheet by touch-rolling the molten thermoplastic resin sheet on the face against the third cooling roller by the metallic endless belt to cool.
The aforementioned molten thermoplastic resin sheet is a thermoplastic resin sheet just after being formed by being extruded from an extruder.
The molten thermoplastic resin sheet in the present invention should be recognized as to also mean a film-state molten thermoplastic resin, too.
As the preferable thermoplastic resin, polyethylene, polypropylene, polyvinyl, chloride, polyvinyl, alcohol, polyethylene terephthalate, polyarylate, polyethylene-2,6 naphthalate, polyethylene- &agr;, &bgr;, bis (2-chlorophenoxyethane-4, 4′-dicarboxylate), polyphenylene oxide, polyester, polyphenylene sulfide, polyether ether ketone, aromaticpolyamide, polyarylate, polyimide, polyamide imide, polyether imide, syndiotactic polystyrene, biphenylether ketone, or the like can be used.
The recommended thermoplastic resin is a polypropylene resin.
As the aforementioned polypropylene resin, a homopolymer of polypropylene, a copolymer (random, block) with ethylene, a composition thereof or the like can be used. A random copolymer with ethylene is especially outstanding in the transparency. Incidentally, in the resin, a nucleating agent, it may consist of a sorbitol type, benzoic aluminum type, sodium type or the like.
And the sheet may be a single layer of thermoplastic resin or multi-layers including a layer of thermoplastic resin.
In the present invention, when the temperature of the metallic endless belt and the roller in order to cool the molten thermoplastic resin sheet exceeds 50° C., a fine transparency cannot be obtained. More preferably, it is less than 30° C. Further, when it is lower than the dew-point, a water-droplet spot is produced on the sheet.
By guiding the molten thermoplastic resin sheet into the area between the first and third cooling rollers to touch the metallic endless belt, touching the first cooling roller, and the third cooling roller at approximately the same time, the molten thermoplastic resin sheet can be touch-rolled and cooled at the same time, resulting in the improved transparency of the thermoplastic resin sheet. It can be assumed, when the molten thermoplastic resin sheet is touched earlier to either the metallic endless belt or the cooling roller, before the mirror face is transferred onto both faces of the sheet, the cooling and caking of the molten thermoplastic resin sheet is advanced.
In the present invention, it is advisable that the degree of the surface roughness of the mirror face of the metallic endless belt and the roller is less than 0.5 S, more preferably less than 0.4 S (Rmax).
As for the material of the endless belt, stainless, carbon steel, titanium alloy or the like can be used. Preferably, martensitic precipitation hardening stainless steel (such as SUS or type) or maraging steel, wit
Fujii Atsushi
Funaki Akira
Uchiyama Katsumi
Yukumoto Tohru
Eashoo Mark
Flynn ,Thiel, Boutell & Tanis, P.C.
Idemitsu Petrochemical Co. Ltd.
Silbaugh Jan H.
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