Device for extruding and smoothing plastic films

Details Device for extruding and smoothing plastic films Device for extruding and smoothing plastic films

1995-02-02

1996-08-06

Nguyen, Khanh P.

Plastic article or earthenware shaping or treating: apparatus

Control means responsive to or actuated by means sensing or...

Control means responsive to product weight or dimension

425363, 425367, 425385, 425461, 2642101, B29C 5904

Patent

active

055428363

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

This invention relates to apparatus for the extrusion and smoothing of plastic films.


BACKGROUND ART

Apparatus consisting of an extruder for extruding a thermoplastic material, a sheet die connected thereto and a smoothing roll mechanism to receive an extruded web between at least two smoothing rolls forming an intermediary slit is commonly used for the extrusion of plastic films and their smoothing on both sides. To ensure a uniform thickness throughout the plastic web when plastic sheets and plastic films of more than 0.5 mm in thickness are produced, it is recommendable to keep a small "stock" of the plastic melt in the shape of a bead in front of the intermediary slit being continually pressed out. By this, the intermediary slit is kept fully charged all the time. The web surfaces formed are already completely smooth while cooling and freezing in the intermediary slit, whereas the core of the web does not freeze before it has passed the intermediary slit and with progressive cooling. By controlling the number of revolutions of the extruder roll mechanism one can ensure that the bead is retained at a substantially constant size for a longer time. Thin film webs, however, already freeze throughout their complete thickness in the narrowest area of the intermediary slit and are no longer thermoplastically mouldable. The bead of moulding material in front of the intermediary slit has to be kept to a minimum size. Smoothing of the film surface is only achievable by exerting high clamping forces which lead to a deflection of the rolls. While this deflection can be equalized in advance by accordingly knobbed rolls, such equalization will only be effective at one special operating point. Outside this operating point differences in the slit width between centre and marginal areas are inevitable, entailing corresponding differences in the resulting film thickness.
Increases in the bead thickness induce extremely high pressures at the slit. Variations in the slit width and the pressures appearing there are caused by inevitable deviations in the roundness of the rolls. Local thickening in the extruded web caused by the extrusion process may lead to such high contact pressures locally that the roil surfaces are permanently deformed. To avoid these problems, rubber rolls partly coated with a lacquer finish are used as counter rolls of the steel smoothing roll. The lacquer finish being very sensitive, however, these rolls are normally of short longevity.
Controlling of extrusion and smoothing of thin plastic films thus requires a careful adherence to constant production conditions and especially the use of film dies having adjustable outlet lips, socalled "flex lips" Nevertheless there are often deviations or troubles in practice which generally cause damages to the roll surface resulting from extreme pressures in the smoothing slit.


DISCLOSURE OF THE INVENTION

The aim of the present invention is to improve apparatus for the extrusion of plastic films comprising forming an intermediary slit to receive an extruded film web high pressures at the slit and the problems involved therewith.
According to the invention, the aforesaid aim is met by apparatus of the known kind including features A, B, C in which at least one roll of a smoothing mechanism is arranged in a movable and elastic way perpendicularly to the contact plane of the intermediary slit, thus modifying the distance between the axes of the two rolls; the pressure at the slit varying within a range of .+-.20% independent of a displacement of the axes; the pressure at the slit being set to a substantially constant size; the pressure at the slit P1 being of a value of 100N/cm relative to the slit length; and the pressure at the slit being adjustable. Thus, a line force at which the rolls of a smoothing mechanism run against each other in the intermediary slit is limited to a size which does no longer cause damage to the roll surface.
It was noticed that with the extremely improved technical possibilities of reducing thickness fluctuations as em

REFERENCES:
patent: 3758657 (1973-09-01), Menzin et al.
patent: 4354814 (1982-10-01), Grimminger et al.
patent: 4372736 (1983-02-01), Gooch et al.
patent: 4477407 (1984-10-01), Hetherington et al.
patent: 4639346 (1987-01-01), Pav et al.
patent: 4810179 (1989-03-01), Cavanagh
patent: 4858139 (1989-08-01), Wirtz
patent: 5011395 (1991-04-01), Kawamata
patent: 5094790 (1992-03-01), Halter
patent: 5167894 (1992-12-01), Baumgarten
patent: 5257923 (1993-11-01), Kagawa
patent: 5263840 (1993-11-01), Heitmann et al.

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