Title of Invention

A FILM CASTING MACHINE AND PROCESS FOR PRODUCING POLYIMIDE FILMS

Abstract A film casting machine is provided with a roller having a smooth surface rotatably mounted in a housing with a liftable top cover. The roller is provided with a variable speed drive. A heater is located inside the housing below the roller. An inlet is provided in the housing for providing an inert gas into the housing. A blade assembly is located close to the periphery of the roller for casting film by doctor blading. A feeder plate is located close to the blade assembly for feeding the material to be cast and at least one temperature sensor is provided for sensing the temperature inside the housing.
Full Text The invention relates to a film casting machine and a process for producing a polyimide film.
One of the objective of the invention is to provide a film casting machine which can produce polyimide films of various thickness from polyamic acid solution. Another objective of the invention is to provide a process for producing thin polyimide film which is free of pin-holes and blisters.
U.S. Patent numbers 3,179.814; 3,179,834 and 1,098,556 disoloses laboratory preparation of polyimide film from polyamio acid solution.
The film casting machine according to the invention provides a machine for producing polyimide film of excellent quality on a comercial scale. The method of producing a polyimide film according to the invention uses the film casting machine according to the invention and obtain polyimide film having excellent thermal and electrical insulation whloh can be used for applications which has exacting requirements. Polyimide films of various thickness in the order of tens of microns to hundreds of microns can be produced with the film casting machine according to the invention. The length and breadth of the polyimide film will depend on the size of the roller used in the film casting machine.

Thus the invention provides a film casting machine comprising a roller having a smooth surface rotatably mounted in a housing with a liftable top cover, the said roller being provided with a variable speed drive, a heater located inside the said housing below the roller, an inlet in the housing for providing an inert gas into the housing, a blade assembly located close to the periphery of the roller for casting film by doctor blading, a feeder plate located close to the blade assembly for feeding the material to be cast and at least one temperature sensor for sensing the temperature inside the housing.
The invention also provides a method of producing a polyinide film by casting with the film casting machine described hereinabove, comprising the steps of preparing a polyamic aoid solution having a solid content of 10 to 12.5 percent by weight and a viscosity of 20,000 to 80,000 cps, feeding the said polyamic acid solution to the surface of the rotating roller of the film casting machine through the feeder plate of the film casting machine to obtain a uniform coating on the roller having a desired thickness with the blade assembly, closing the top cover of the housing and purging the space between the roller and housing with an inert gas, heating the film slowly increasing the temperature to a temperature not exceeding 450°C in the inert atmosphere for a period sufficient to convert the polyamic acid film into polyimide film and removing the polyimide film from the roller in a known manner after roller with the film is cooled to a temperature near the room temperature.

The invention is described with reference to the accompanying drawing showing a prefered embodiment of the film casting machine.
Fig. 1 shows the front view of the film casting machine; and
Fig. 2 shows the end view of the film casting machine.
The film casting machine according to the invention comprises a freely rotatable roller (1) mounted inside a housing (8) with a liftable top cover (12). The rotatable roller
sensors tor accurate monitoring of temperature. A blade assembly (10) is provided close to the periphery of the roller (1), for casting the film by doctor blading. A feeder plate (11) is located close to the blade assembly (10) for feeding the material to be cast into a film. Preferably a perforated plate (8) is provided between the heater (7) and the roller (1). The housing is preferably insulated with materials such as ceramic wool and covered with aluminium lining. The heating rate is controlled using a proportional controller. The roller (1) is preferably made of stainless steel with a polished surface. The position of the blade in the blade assembly (10) is adjustable for adjusting the gap between the edge of the blade and the surface of the roller. This will enable casting of film with different thickness. The liftable top cover (12) is an air tight cover to maintain the inert atmosphere in the housing (8) during the casting of film.
The film casting machine is used for casting good quality polyimlde film from polyamic acid by the process described below.
Polyamio acid solution having a solid content of 10 to 12.5X by weight and Brookfield viscosity of 20,000 to 80,000 cps is filtered and degassed under vacuum. The roller (1) is cleaned thoroughly before casting the polyamic acid solution film. The blade assembly (12) is mounte3in front of the roller (1) and a

desired gap is provided between the roller (1) and the blade using feeler gauge. Roller is then driven at low speed preferably about 3 to 4 RPM. Roller speed is adjusted in accordance with the viscosity of the polyanio acid solution and the thickness of the polyamic acid solution film used for casting. Filtered and degassed polyamic acid solution is then charged and spread uniformly on the roller with the help of a feeder plate (11) placed very close to the doctors blade as shown in Fig.2. Feeder plate (11) helps in uniformly spreading the resin across the full length of the roller and finally doctors blade controls precisely the thickness of the film cast on the roller. Excess resin is thrown out by the doctors blade and is collected separately. After the uniform layer of polyamic acid solution of desired thickness is cast on the roller, the feeder plate and the doctors blade are removed slowly and carefully so as not to create any disturbance on the cast film. The housing (8) is then covered with the top cover (12). An inert gas such as nitrogen is purged inside the chamber to maintain a nitrogen blanket around the roller. The roller is then heated using a pre-determined time-temperature cycle. Typical time temperature cycles are shown in table I. Initially the heating rate is kept low to enable the solvent to evaporate slowly and uniformly from the bulk of the cast film. After the bulk of the solvent is evaporated and the film becomes tack-free, heating rate is increased to a temperature at which the polyamic acid gets converted into polyimide film. The temperature is maintained for

sufficiently long for completing the conversion. Prefered temperature at which the temperature is maintained is about 300*^C and for a prefered time of about 1 hour.
Polyimide film thus formed is cooled and removed from the roller and trimmed and characterised for its physical, mechanical, electrical and thermal properties.
The following examples show the prefered process steps for casting polyimide films from polyamio acid solution.
Example 1
2.5 kg of polyamic acid solution having solid content of 11.5X, by weight, inherent viscosity 2.1 dl/g and solution viscosity of 40,000 ops is filtered and degassed under vacuum until the resin solution is completely free from dissolved gases. Doctor"s blade is mounted on the fixtures in front of the roller and the gap between the roller and the blade is adjusted to 0.7 mm with the help of a feeler gauge. The roller is then driven at 3.5 RPM. Filtered and degassed polyamic acid solution is charged on to the roller and spread uniformly with the help of the feeder plate held close to the doctor"s blade. Doctor"s blade finally helps

in laying 0.7 mm thick uniform polyamic acid solution film on the roller and excess resin is thrown out, which is collected separately. After casting the uniform layer of polyamic acid solution film on the roller. the feeder plate is withdrawn and then the doctor"s blade is removed from the fixtures very slowly and carefully so as not to create any disturbance on the cast film. The roller is then covered with the top lid and the temperature inside the housing is raised as per the time-temperature cycle given in table I. Initially the heating rate is kept low at the rate of 10C per hour to allow slow evaporation of the solvent from the bulk of the polyamic acid solution film. The heating rate is maintained till the temperature reaches es*-* and it is held at this temperature for 2 hours. Then the temperature inside the housing is further increased to 100*^0 maintaining the same heating rate. Thereafter, the heating rate is increased to 20*^C per hour till a temperature of t50*-"C is attained. After that the heating rate is further Increased to 40*^0 per hour till the final temperature of 300*^0 is attained. The temperature inside the housing is maintained at this temperature for one hour and then cooled. The film is removed from the roller, trimmed and characterised for its thickness uniformity, mechanical, thermal and electrical properties. Table II gives the properties of the films thus produced.




Siwilar film casting fexperimerits were carried out as in Exanple 1, for casting thinner polytmide films. 1.3 kg of polyamic acid solution is filtered and degassed under vacuum and charged on to the roller. Gap between the roller and the doctor"s blade is set at 0.35 mm. The roller is driven at 4 RPM. After casting uniformly a 0.35 mm thick polyamic acid solution film on the roller. the film is cured in the same manner as described in example 1. The film is then removed from the roller, trimmed and characterised for its properties. Table III gives the properties of the films so produced.


The polyi»ide film produced as described above are suitable for using as thermal and electric insulation material in space applications and other applications were high quality insulation material is required.

WE CLAIM:
1 A film casting machine conprising a roller , an inlet (9> in the housing for providing an inert gas into the housing, a blade assembly (10) located close to the periphery of the roller (1) for casting film by doctor blading, a feeder plate (11) located olose to the blade assembly for feeding the material to be cast and at least one temperature sensor (2) for sensing the temperature inside the housing.
2. The machine as claimed in claim 1, wherein the roller (1) is
mounted on a bearing support (3) and coupled to the variable
speed drive (5) comprising a variable drive motor and reduction
gear.
3. The machine as claimed in claims 1 or 2, wherein a perforated plate (6) is provided between the heater (7) and the surface of the roller (1).
4. A method of producing a polyimide film by casting with the film casting machine claimed in claim 1, comprising the steps of preparing a polyamic acid solution having a solid content of 10

to 12.5 percent by weight and a viscosity of 20,000 to 80.000 ops, feeding the said polyamic acid solution to the surface of the rotating roller (1) of the film casting machine through the feeder plate (11) of the film casting machine to obtain a uniform coating on the roller having a desired thickness with the blade assembly (10), closing the top cover (12) of the housing (8) and purging the space between the roller (1) and housing (8) with an inert gas, heating the film slowly, increasing the temperature to a temperature not exceeding 450**C in the inert atmosphere for a period sufficient to convert the polyamic acid film into polyimide film and removing the polyimide film from the roller im m mmmmmm after roller with the film is cooled to a temperature near the room temperature.
5. The method as claimed in claim 4, wherein during casting rotating the roller (1) at a speed of 3 to 4RPM, heating the roller at a rate 20° per hour till it attains a temperature of 150°C and then heating it at a rate of 40° per hour till it attains 300°C and maintaining the roller at the temperature of 300°C for at least one hour.
6. The method as claimed in claims 4 or 5, wherein the inert gas is nitrogen.

7. A film casting machine, substantially as hereinabove
described and illustrated with reference to the acconpanyinfi
drawings.
8. A method of producing a polyinide film, substantially as
/ ,/4iereinabove described.

Documents:

956-mas-99 abstract.pdf

956-mas-99 claims duplicate.pdf

956-mas-99 claims.pdf

956-mas-99 correspondence others.pdf

956-mas-99 correspondence po.pdf

956-mas-99 description (complete) duplicate.pdf

956-mas-99 description (complete).pdf

956-mas-99 drawing.pdf

956-mas-99 form-1.pdf

956-mas-99 form-19.pdf

956-mas-99 form-26.pdf

956-mas-99 form-3.pdf

956-mas-99 form-8.pdf


Patent Number 214017
Indian Patent Application Number 956/MAS/1999
PG Journal Number 13/2008
Publication Date 31-Mar-2008
Grant Date 23-Jan-2008
Date of Filing 28-Sep-1999
Name of Patentee INDIAN SPACE RESEARCH ORGANISATION
Applicant Address DEPARTMENT OF SPACE, ANTHARIKSHA BHAVAN, NEW BEL ROAD, BANGALORE - 560 094,
Inventors:
# Inventor's Name Inventor's Address
1 SURENDRA KUMAR GUPTA C/O VIKRAM SARABHAL SPACE CENTRE, TRIVANDRUM - 695 022,
2 PARAMESWARAN RAVINDRAN NAIR C/O VIKRAM SARABHAL SPACE CENTRE, TRIVANDRUM - 695 022,
3 LAKHONDE KRISHNAJIROW ANANDAKUMAR C/O VIKRAM SARABHAL SPACE CENTRE, TRIVANDRUM - 695 022,
4 ADIRAJU VENKATA HANUMANTHA RAO C/O VIKRAM SARABHAL SPACE CENTRE, TRIVANDRUM - 695 022,
5 KUCHIBHATLA SITARAMA SASTRI C/O VIKRAM SARABHAL SPACE CENTRE, TRIVANDRUM - 695 022,
PCT International Classification Number C08 G 23/10
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA