Coating apparatus – Solid applicator contacting work – With work-handling or work-supporting
Patent
1997-02-28
1998-09-08
Edwards, Laura
Coating apparatus
Solid applicator contacting work
With work-handling or work-supporting
118249, 118255, 118256, 118261, B05C 100
Patent
active
058039694
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This is a national phase application of PCT/EP95/02602 filed 5 Jul. 1995, published as WO96/07791 Mar. 14, 1996, and based, in turn, upon German application P4431202.4 filed 25 Sep. 1994 under the International Convention.
FIELD OF THE INVENTION
The invention relates to a device for two-sided coating of a web of material, particularly a paper or cardboard web.
BACKGROUND OF THE INVENTION
There are known devices for the two-sided application of glue, starch, carboxymethylcellulose, synthetic glue or pigment dispersions onto paper or cardboard webs, which have two axially parallel pressure rollers next to each other rotatably supported in a frame, and between which a nip is formed through which the paper or cardboard web is guided. At each of the pressure rollers an application and metering system is provided, which first applies a metered film of coating material to their peripheral surface, this film being then transferred to the web in the nip. It is known to support one of the two pressure rollers so that it is circumferentially movable with respect to the other, in order to open the nip for the introduction of a new web.
In the device of DE-C 34 40 634 one of the pressure rollers is swingably supported with respect to the other. The web is guided out of the nip by web guiding elements, e.g. guide rollers, to the following processing stations, which can include e.g. a drier.
It has proven to be very important for achieving an optimal coating quality that the coated paper or cardboard webs are withdrawn from the surfaces of the two pressure rollers along a stable, unchanged web, path. The web held on the rollers by cohesion and adhesion forces, has to be withdrawn as uniformly as possible first from the one roller and then from the second roller, without uncontrolled web motions, i.e. a web waving, occurring between the two pressure rollers. An uncontrolled web path leads to undesirable surface markings.
In order to withdraw the web at first from the first pressure roller and then from the second pressure roller, it is known to influence the adhesion forces acting during web withdrawal in a controlled manner, by means of different materials on the surfaces of the pressure rollers. However, this solution has the drawback that the different roller surfaces can also lead to differences in the quality of the coating.
One can continue to guide the web on one of the pressure rollers for a certain wrapping angle, after it leaves the nip (DE-C 34 40 634). Based on experience a certain web traction force has to be set at a wrapping angle which is not too big.
Since the behavior of the web during withdrawal from the pressure rollers does not depend only on the above-described features of the coating process, but also on the process parameters, such as the amount of coating and the physical parameters of the web and the coating material, the above-described negative effects can occur in the known devices, when, due to a change in the raw materials (web material and/or coating material), the conditions during web withdrawal become unstable. So for instance the web path can become unstable when, after being reset for a new variety, a coating material with considerable higher cohesion and adhesion forces is applied with the unwrapped pressure roller, which causes the web to be locally or totally entrained by the unwrapped pressure roller.
OBJECTS OF THE INVENTION
It is therefore the principal object of the present invention to provide a device overcoming drawbacks of the prior art.
SUMMARY OF THE INVENTION
According to the invention, a device for two-sided coating of a web of material, particularly paper or cardboard web, has two axially parallel pressure rollers rotatably supported next to each other in a frame. One of the rollers is supported circumferentially movable against the other pressure roller in order to form a nip, through which the web of material is guided, and a application and metering system for each pressure roller. One if the two pressure rollers i
REFERENCES:
patent: 5431731 (1995-07-01), Salo et al.
patent: 5503674 (1996-04-01), Hofmann et al.
Dubno Herbert
Edwards Laura
Jagenberg Papiertechnik GmbH
Kateshov Yuri
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