Mandrel for cooling

Details Mandrel for cooling Mandrel for cooling

1995-01-17

1997-01-14

Davis, Robert

Plastic article or earthenware shaping or treating: apparatus

Including means advancing continuous length work through...

264180, 264560, 264565, 425 721, 425 85, 425445, B29C 4788

Patent

active

055937039

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a mandrel for rapidly cooling a thin film or sheet made from thermoplastic resin extruded from a ring-shaped die by directly contacting the inner part of the melted, tubularly formed thin film with coolant.


TECHNICAL BACKGROUND

The most important aspect as regards technique concerned with producing a thin film made of thermoplastic resin is the way in which the shapeless thin film, without substantially containing a so-called crystallized part, is superior in its drawing properties. Therefore, the film is required to be cooled at as fast a rate as possible. That is, the film is required to be rapidly cooled.
Several indirect cooling methods have been proposed wherein melted thin film is contacted with a mandrel for cooling in which the mandrel is cooled by coolant therewithin. However, the rate of cooling by means of an indirect cooling method is lower than that by means of a direct cooling method wherein the melted thin film is directly contacted by the coolant. Therefore, several kinds of apparatus for cooling by directly contacting the melted thin film extruded in the producing step for producing a tubular thin film made of thermoplastic resin have been provided.
For example, there is known a method wherein the melted thin film is solidified by rapid cooling by pressing the melted thin film against a sidewall located outside of tubes in which coolant flows, the coolant being caused to overflow the tubes and flow downward along the sidewall as the melted thin film is pressed on the sidewall. In such device, the coolant is provisionally stored in the lower bubble formed in the underside of a cooling apparatus, and the coolant is discharged by a siphon or a pump (Japanese Examined Patent Publication No. 35192/1970). In another method wherein spirally formed grooves located under a double tube for setting the diameter of the film, the coolant, other than the overflow coolant, flows within grooves in the double tube whereby high speed film productivity is improved. In this device, the coolant is provisionally stored in the bubble formed in the underside of the cooling apparatus, the coolant being discharged by a siphon or a pump, and the like, (Japanese Examined Patent Publication No. 31473/1971). And in still another method, the melted thin film is solidified by contacting the film with the coolant, and the liquid remaining on the film is removed by suction of the liquid (Japanese Examined Patent Publication No. 2072/1964), or like method.
With respect to the method of cooling by means of overflown coolant in accordance with the above-mentioned Japanese Examined Patent Publication No. 35192/1970 and Japanese Examined Patent Publication No. 2072/1964, the overflown coolant flowing downward has a low current velocity. No matter how fast it may flow, the velocity thereof is the same as that of the thin film moving downward. Accordingly, it is difficult to obtain a uniform thin film without having a shape defect since the coolant flowing downward with the thin film becomes high in temperature due to the remaining heat of the thin film so that the cooling capacity of the apparatus is lowered because of partial boiling of the coolant, or there arises a partial bonding caused by contacting directly melted thin film with the mandrel due to an irregularity in the quantity of flow.
Accordingly, in order to produce a thin film with high speed, it is considered to conduct the process by keeping the temperature of the coolant low. However, there is a commercial limitation in such a method. Therefore, it has not been possible to produce the thin film with high speed.
Further, in such direct cooling method, the coolant is directly contacted with the thin film. Therefore, the thin film is wetted so that it is necessary to remove the coolant from the film. However, it is difficult to remove the coolant completely. Accordingly, there are defects due to irregular heating caused by drips or liquid membrane remaining on the thin film when the coolant flowing in the apparatus

REFERENCES:
patent: 3142092 (1964-07-01), Ralston
patent: 3337663 (1967-08-01), Taga
patent: 3622657 (1971-11-01), North et al.
patent: 3655846 (1972-04-01), Kanoh et al.
patent: 3702224 (1972-11-01), North et al.
patent: 3819776 (1974-06-01), Robinson et al.
patent: 3886243 (1975-05-01), Uemura et al.
patent: 3976410 (1976-08-01), Jack et al.
patent: 4003973 (1977-01-01), Kurokawa et al.
patent: 4203942 (1980-05-01), Sims, Jr. et al.

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