Arrangement for impregnating webs of porous material

Details Arrangement for impregnating webs of porous material Arrangement for impregnating webs of porous material

1996-03-27

1997-11-25

Edwards, Laura

Coating apparatus

Immersion or work-confined pool type

Work extending through pool-confining wall area

118405, 118407, 118419, 118429, B05C 300

Patent

active

056907419

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a device for impregnating webs of porous materials.
It is known from EP 0 173 519 B1, on which the invention is based, to perform the impregnation under increased pressure. By means of this it is possible to place a considerably larger amount of impregnating materials into the substrate than with pressureless impregnation. For example, it becomes possible to impregnate denser paper of small absorption capability. Furthermore, the possibility arises of using impregnating agents of high viscosity, i.e. with an increased solid content and a reduced solvent portion. The required pressure increase is achieved in particular in that the chamber receiving the impregnating agent continuously narrows from the inlet slit in the direction toward the outlet slit. The web passing through pushes the boundary layer adhering to its surface into the narrowed area of the chamber. Because of this the pressure in the chamber continuously increases in the direction toward the outlet slit. In accordance with the information in the said reference, with passage speeds of approximately 45 or 60 m/s, pressures, which lie clearly above 1 MPa, are achieved in the vicinity of the outlet slit. If the impregnating agent is supplied by means of a pressure pump, the static pressure generated by the pressure pump is added to the dynamic pressure generated in the chamber.
With the known pressure impregnating device, sealing of the chamber is connected with considerable problems. Sealing lips are disposed at the inlet slit and the outlet slit which are pressed against the passing web and on the edge zones of the cylinder surface not covered by the web. It has been shown that fluff is separated from the passing web by the sealing lips, collects at the outlet slit and causes interference, which can collect at the outlet slit and can cause interference.
A ring-shaped hollow chamber is located at the front faces of the cylinder between the cylinder surface and the cylinder journal. An annular piston, connected fixed against relative rotation, is seated therein and can slide in the axial direction. The annular piston, which is made of bronze, can be pressed with its end faces tightly against the front faces of the trough by supplying compressed air. Lubricating oil can be supplied through bores to an annular grove disposed in the end face of the annular piston. This seal is very complicated and expensive. In addition it has the disadvantage that impregnating agents can penetrate between the sliding surfaces and glue them shut.
With the known device the cylinder surface is provided over its entire length with thread-like arranged grooves. The grooves are intended to receive liquid impregnating agent which has been pressed through the pores of the material web and to return it into the trough. Air which had been displaced out of the pores by the impregnating agent can also escape through the grooves.
If the width of the web to be impregnated is less than the cylinder length, lateral areas of the cylinders remain uncovered. The result is that impregnating agent flows out through the grooves at the inlet slit and particularly at the outlet slit.
The theme of a publication in DE-Z COATING 9/10, pp. 336 to 341, is the metered application of flowable substances to passing webs with the aid of matrix cylinders. Various matrix shapes are recited, among them in particular those, wherein the cylinder surface is provided with regularly arranged small depressions, identified as "small cups", which for example have the shape of pointed or truncated pyramids and are separated from each other by narrow strips. Application devices are described wherein the matrix cylinder dips into a trough, containing the substance to be applied, with a portion of its circumference. In the process the small cups are filled and the substance is picked up in this way by the rotating matrix cylinder. Excess substance is doctored off, so that the matrix cylinder always carries along the same amount of material. The substance is tr

REFERENCES:
patent: 4740391 (1988-04-01), Long
DE-Z Coating 9/10, pp. 336 to 341 Hugo Klein (1990).

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