Claims
- 1. A process for cooling a molten film which is extruded from a slot die, comprising the steps of:
- providing a cooling drum having a circumferential surface, the cooling drum being partially immersed in a first water bath;
- providing a second water bath;
- contacting one surface of the molten film, immediately after extrusion of the film from the slot die, to the circumferential surface of the cooling drum so that heat transfer occurs between the one surface of the molten film and the cooling drum and between the other surface of the molten film and the air;
- rotating the cooling drum to move the molten film through the first water bath, whereby the water in said first water bath directly contacts the film to cool and partially solidify the molten film such that it will not prematurely separate from the cooling drum and is removable from the cooling drum without elongation; and
- removing the partially solidified molten film from the cooling drum while it is immersed in the first water bath and moving the removed, partially solidified molten film through water to the second water bath to bring the molten film to a desired final temperature.
- 2. A process as claimed in claim 1, wherein the step of rotating the drum to move the molten film through the first water bath comprises cooling the molten film to a mean transfer temperature of about 100.degree. C. to 120.degree. C.
- 3. A process as claimed in claim 1, wherein the step of moving the partially solidified molten film through the second water bath further comprises cooling the molten film to a final temperature of about 40.degree. C.
- 4. An apparatus for cooling a molten film which is extruded from a slot die comprising:
- a first water bath having a first water level;
- a cooling take off drum having a circumferential surface for receiving the molten film on its circumferential surface directly after the film is extruded, the cooling drum being partially immersed in the first water bath for rotation about its longitudinal axis;
- shaft means for rotating the cooling drum around its longitudinal axis, whereby the cooling drum moves the received molten film through the first water bath so that the molten film is cooled and partially solidified such that it will not prematurely separate from the cooling drum and can be removed without elongation;
- means for removing the partially solidified molten film from the circumferential surface of the cooling drum while it is immersed in the first water bath, and moving the removed partially solidified molten film through water to a second bath having a second water level; and
- means for moving the partially solidified molten film through the second water bath, whereby the molten film is cooled to a desired final temperature.
- 5. An apparatus as claimed in claim 4, wherein the water level in the first water bath is substantially equal to the water level in the second water bath.
- 6. An apparatus as claimed in claim 4, wherein the water level of the first bath is higher than the longitudinal axis of the cooling drum.
- 7. An apparatus as claimed in claim 6, wherein the cooling drum comprises a shaft and a pair of seals on the shaft for mounting the shaft in a respective side wall of the first water bath.
- 8. An apparatus as claimed in claim 4, wherein the first water bath and the second water bath are in communication with one another.
- 9. An apparatus as claimed in claim 4, wherein drum diameter D of the cooling drum is less than or equal to ##EQU8## where d is the thickness of the molten film, .rho. is the density, in kg/m.sup.3, of the molten film, c.sub.A is the specific heat of the film material on the cooling drum, v.sub.A is the circumferential speed of the cooling drum, .lambda. is the thermal conductivity, .alpha..sub.w is the heat transfer coefficient between the molten film and water, .alpha..sub.ST is the heat transfer coefficient between the molten film and the surface of the cooling drum, T.sub..alpha. is the melt temperature, T.sub.u is the transfer temperature and T.sub.w is the water temperature of the first water bath.
- 10. An apparatus as claimed in claim 9, wherein the water level of the first water bath is below the longitudinal axis of the cooling drum and the first water bath with respect to the cooling drum forms an angle of inclusion .alpha..sub.T is from about 150 to 155 degrees.
- 11. An apparatus as claimed in claim 9, wherein the water level of the first water bath is above has an longitudinal axis of the shaft of the cooling drum and the angle of inclusion .alpha..sub.h of the first water bath with respect to the cooling drum of from about 198 to 203 degrees.
- 12. The apparatus as claimed in claim 9, wherein the length L of the molten film in the second water bath is at least equal to ##EQU9## where c.sub.N is the specific heat of the film material in the second water bath and T.sub..omega. is the final temperature of the take-off drum.
Priority Claims (2)
Number |
Date |
Country |
Kind |
3629105 |
Aug 1986 |
DEX |
|
3635302 |
Oct 1986 |
DEX |
|
Parent Case Info
This application is a continuation of application Ser. No. 087,828, filed Aug. 21, 1987, now abandoned.
US Referenced Citations (3)
Foreign Referenced Citations (8)
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JPX |
51-567 |
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Continuations (1)
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Number |
Date |
Country |
Parent |
87828 |
Aug 1987 |
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