Plastic article or earthenware shaping or treating: apparatus – Shaping orifice and downstream work contacting gaseous...
Reexamination Certificate
1999-05-12
2001-08-14
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Shaping orifice and downstream work contacting gaseous...
C425S326100, C425S387100
Reexamination Certificate
active
06273699
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to a method and a device for manufacturing a single or multilayer plastic film from a plastic raw material or a combination of several materials, said materials being extruded from a slot die and then being allowed to cool accompanied by chemical formation of the film material.
BACKGROUND OF THE INVENTION
Film production generally employs a blowing method or a casting method. The starting material is a plastic granulate that has graded properties, but has characteristics that differ from one batch to the next. In addition, the raw material can differ in temperature, moisture content, and aging. Differences in the material, especially the molecular structure, can result in different development of sensible heat in a worm conveyer screw of the extruder, which also influences the result. It is known that a conditioner located between the raw material silo and the extruder can adjust the state of the material suitably for the process.
The actual formation or crystallization then takes place after extrusion when the plastic is already in the film form, during the cooling and hardening of the film.
The quality of the film that is eventually obtained is evidenced by freedom from pinholes, in other words inclusions such as gel bodies, foreign matter, and burned plastic deposits, for example, as well as by the material and thickness homogeneity of the film and its uniform transparency, which has been shown to be an indicator of morphological structure. According to the prior art, when film sections that cannot be used are produced, they are destroyed and an attempt is made to adjust the parameters at the extruder.
However, correction of the factors that influence the quality of the film turns out to be rather complex. Accordingly, it has not yet been possible to perform continuous real-time control of the properties of such films.
SUMMARY OF THE INVENTION
The invention relates to a method and a device for manufacturing a single or multilayer plastic film from a plastic raw material or a combination of several materials, said materials being extruded from a slot die and then being allowed to cool accompanied by chemical formation of the film material. During the cooling process, the extruded film passes through an air section for a certain distance. The device, in the case of blown film, has an extruder, or several extruders for a multilayer film, and a blow mold with an annular nozzle and air nozzles enclosed thereby for forming and maintaining an air bubble in the expelled tubular film.
The invention is intended to improve the possibilities of monitoring the process as the film is manufactured. According to the invention, this is accomplished by the fact that the film is treated by a stream of conditioned air in the vicinity of the air section through which the film material passes during the cooling process after the slot die. The air stream has been conditioned in terms of temperature and air purity. It is blown around the film on all sides, moving it in the same direction as the film cooled by it and shielding it against external influences by a partition or special flow-optimized encapsulation. Formation of the film material in this air section proceeds in a largely uncontrolled fashion. Both additional heat sources and a sudden lateral cold draft or similar asymmetric influences cause the film to shrink more rapidly on one of the two sides than on the other, with the result that the morphology is not even over the circumference and exhibits arbitrary properties in the extrusion direction such as nonuniform plane position, transparency, and bendability. In the case of blown films, these defects account for approximately one half of all the rejects. According to the invention, as a result of the flushing of this area of the air section according to the invention with a conditioned air stream which also includes undisturbed flow and the shielding of this area by encapsulation, the processes during cooling of the film material can be controlled and a possible influence is obtained that allows control with the control loop closed, for example, with constant monitoring of the film transparency.
Secondly, the method according to the invention provides a continuous measurement, as extensive as possible, of characteristic product properties of the cooled finished film, especially its transparency, which is scanned with an optical measuring system so that the product values of the cooled finished film are continuously measured and regulated in real time by controlling influential parameters along the film production line as a function of the measured values. These parameters can also affect only the conditioning of the raw material, but preferably this regulation is also combined with air flushing and encapsulation. As far as the handling of blown films is concerned, a device is especially preferred wherein the chamber adjoining the blow mold in which the extruded film is cooled is encapsulated by a protective housing that encloses this chamber snugly so that disturbing influences such as asymmetric heat radiation from the extruder or a sudden cold draft when the door is opened are kept away from the air stream flowing over the film.
The conditioning of the air flow is intended particularly for controlling the properties of temperature and air purity, especially freedom from particles and microorganisms as well as the moisture content.
When blown film is produced, the foil tube, until it is flattened and wound, has an air section of several meters to travel, for example 10 meters in a large system. According to one special and preferred embodiment of the invention, the air flow along this air section is divided into partial air streams each of which envelops the film, especially the film tube, along a partial stretch and each of which is produced in succession in the flow direction. At the beginning of the next partial air stream, the previous air stream is drawn off again or even deflected outward and carried away, recycled, for example. The partial air streams can therefore be adjusted to meet the local requirements of the tube, for example turbulent in the lowermost portion and uniformly laminar on all sides in the upper sections.
As an example of the dimensioning of such a capsule housing, where the annular nozzle has a diameter of d, the resultant foil tube to be cooled has a diameter of approximately 4d and the surrounding cylindrical capsule housing then advantageously has a diameter of 12d. In smaller systems, a narrower air stream chamber is sufficient while in larger systems of course the air stream chamber is also larger and additional parts of the installation can also be accommodated therein, such as gratings on which personnel walk.
The regulation of the characteristics of the film produced, especially its transparency, in the area downstream from the slot die also influences the conditioning properties of the air in the air stream and the strength and speed of the air stream. As an alternative or in addition, the regulation also influences the conditioning and transport of the raw material, especially the extrusion pressure, temperature, and moisture content, upon which the viscosity of the plastic melt in turn depends.
Further details, advantages, and improvements on the invention follow from the description below of preferred embodiments with reference to the drawings.
REFERENCES:
patent: T915014 (1973-10-01), Goldman
patent: 3555604 (1971-01-01), Pahlke
patent: 3725519 (1973-04-01), Seifried et al.
patent: 3888609 (1975-06-01), Saint Eve et al.
patent: 4399094 (1983-08-01), Fujitani et al.
patent: 4473527 (1984-09-01), Fujisaki et al.
patent: 4728277 (1988-03-01), Planeta
patent: 4749346 (1988-06-01), Planeta
patent: 4842803 (1989-06-01), Bose et al.
patent: 5368460 (1994-11-01), Weavil et al.
patent: 041 803 (1981-12-01), None
patent: 508 167 (1992-10-01), None
patent: 522 487 (1993-01-01), None
patent: 01044624 (1989-02-01), None
patent: WO 91 14173 (1991-09-01), None
Leyson Joseph
Nguyen Nam
Rosden Peter E.
LandOfFree
Device for manufacturing plastic film does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for manufacturing plastic film, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for manufacturing plastic film will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2477300