Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Patent
1995-07-28
1997-10-07
Vargot, Mathieu D.
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
2642102, 26421112, 264237, 264284, 264348, 425 71, 425327, 425377, 4253781, 425385, B29C 4788
Patent
active
056744420
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for manufacturing a thermoplastic sheet or film and an apparatus therefore, which may be optimally used in various industrial applications to provide a package for foodstuffs, stationery document files etc., and various packaging cases.
BACKGROUND ART
The thermoplastic sheet, such as, for example, a crystalline thermoplastic sheet (or a film) is used extensively in various industrial applications, by virtue of its superior characteristics such as heat resistance, various physical properties, chemical resistance and hinging characteristics.
However, neither a process for making a crystalline thermoplastic sheet of improved transparency, gloss and surface flatness nor a technology for making such a sheet at a high-speed has been developed and available.
Known processes for manufacturing the crystalline thermoplastic sheet include the air-knife process, the polishing-roll process, the water-cooling process and the like.
In the air-knife process, it may be difficult to maintain a surface flatness since the film upon which an air is sprayed may be variable, which is caused by a step of tightly urging the film-like fused thermoplastic resin against the cast drum under an air pressure to be injected from the nozzle. Besides, one side of the sheet cannot be cooled rapidly because it is cooled by air. Consequently, the process has a drawback in that it may not produce a sheet of improved transparency, surface flatness and thickness precision etc. Urging forces by an air pressure has approximately a 3000 mm water column as its upper limit, and a production speed of approximately 20 m/minute is a maximum for producing a commercially valuable sheet or film, because the air is directed only at a single point. As a result, this air-knife process is mainly used to make a reduced thickness sheet of approximately 0.2-0.5 mm which would not need particular appearance characteristics. However, this process is not suitable to produce an increased thickness sheet of approximately 0.7 mm or more.
The polishing-roll process is a method for producing a sheet by forcing a film-wise fused thermoplastic resin between a pair of metallic rolls. In this process, the sheet thickness and the surface configuration are imposed simultaneously at a point where a pair of rolls contact each other, and if a drawing-speed is reduced to an order of approximately 4 m/min or less, a sheet of improved surface flatness may be produced. However, when the drawing speed is higher than approximately 6 m/min, a sheet-forming step may not follow such a fast rate, and still produce a commercially usable sheet.
If the reduced thickness sheet of approximately 0.4 mm or less is made in accordance with the polishing-roll process, water's edge-like waves are generated to prevent production of commercially usable sheets.
Many proposals have been made in the water-cooling process, and a typical example is found in Japanese Patent Application Unexamined Publication No. Hei.4-158022. In this sheet manufacturing process, a sheet-like fused crystalline thermoplastic resin is cooled and solidified with water, and then re-heated by heating rollers, to be followed by the step of forcing the sheet between a pair of metallic belts such that its appearance characteristics and its production rate may be improved. Though this process may provide a sheet with an increased transparency, it may substantially compromise its appearance characteristics, since stripe-like patterns may be formed laterally in the sheet when the action of the water's edge-like waves are imposed against the sheet while the fused resin is being cooled by water. The greater the sheet-withdrawal forces are, the more frequently such patterns may be formed.
On the other hand, while a non-crystalline thermoplastic sheet has been manufactured using a similar process, a sheet of improved gloss, and surface roughness may not be successfully provided. Thus, an improvement in this aspect has been desired.
DISCLOSE OBJECTS OF THE INVENTION
A primary
REFERENCES:
patent: 4548778 (1985-10-01), Fujii
patent: 4627804 (1986-12-01), Kobayashi et al.
patent: 5026778 (1991-06-01), Fujii et al.
patent: 5204037 (1993-04-01), Fujii
patent: 5211899 (1993-05-01), Fujii
IPEC Co. Ltd.
Vargot Mathieu D.
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