Coating apparatus – Immersion or work-confined pool type – Work-confined pool
Reexamination Certificate
1999-10-15
2002-07-09
Lamb, Brenda A. (Department: 1734)
Coating apparatus
Immersion or work-confined pool type
Work-confined pool
C118S419000
Reexamination Certificate
active
06416580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for application of a liquid or pasty medium on a traveling material web, notably of paper or cardboard.
2. Description of the Related Art
An apparatus for application of a liquid or pasty medium on a traveling material web working in compliance with a conventional method is known, e.g., from U.S. Pat. No. 4,848,268. In this apparatus, two applicator rolls rotating in opposite directions form between themselves a press nip through which the traveling material web passes. Assigned to each applicator roll is an applicator mechanism which applies the liquid or pasty medium via an applicator pressure chamber and a doctor on the surface of the applicator roll. The medium applied on the applicator roll surface is then carried, due to the rotation of the applicator roll, in the press nip between the two applicator rolls. There, the medium is transferred from the roll surface to the relevant side of the material web and pressed at the same time into the material web. This method of application is called indirect application. With both applicator mechanisms in operation, the traveling material web is in this way coated on both sides with the liquid or pasty medium. In another embodiment of the this prior apparatus, also described in U.S. Pat. No. 4,848,268, the pressure chamber applicators are replaced by such forming a sump with an exposed liquid surface and applying the medium from the sump via a doctor on the surface of the applicator roll.
While good results as such are achieved with this indirect application method and pertaining applicators, contaminations are able to separate out of the paper or cardboard of the material web as the medium is pressed in the material web in the press nip, however, and accumulate on the surface of the applicator rolls. This can happen especially with material webs consisting predominantly of recycled paper. Such contaminations accumulated on the roll surface then soil the applicators and can ultimately striate the application film on the applicator roll surface, which striae will then be visible also on the product, i.e., on the coated material web.
What is needed in the art is a method and apparatus enabling the high-quality application of a liquid or pasty medium on a traveling material web, without contaminations contained in or on the material web being able to degrade the quality of application.
SUMMARY OF THE INVENTION
In the method according to the invention, a liquid or pasty medium is applied on at least one side of the traveling paper web in a direct application.
The liquid or pasty medium applied on at least one side of the material web is then pressed in the traveling material web in a separate step. Hence, the direct application of the medium on the material web and pressing the medium in the material web are separate process steps. Since the pressing step follows the application step in the direction of travel of the material web, any dirt particles or contaminants that may separate from the material web in pressing can no longer proceed to the preceding region of application in which the medium is applied on the material web. The separated particles or contaminants can be removed without difficulty in the region of the separate pressing step, and are thus unable after separation to proceed onto the material web and cause impairments of the quality of application. Besides, separation of dirt particles from the material web in the pressing process is a considerably rarer occurrence in the method according to the invention, since the material web was previously coated already with the liquid or pasty medium. Smaller dirt particles are in this way harmlessly incorporated in the applied medium, thereby reducing dirt particle separations while the medium is pressed in the traveling paper web.
In one embodiment of the method for double-sided application of a liquid or pasty medium on a traveling paper web, the liquid or pasty medium intended for each side of the material web is at the same time applied directly on the traveling material web, and the applied medium is subsequently pressed in the traveling material web on both sides simultaneously. This results in a compact two-step process for double-sided application of a liquid or pasty medium on a traveling material web.
Another embodiment of the inventional method for double-sided application of a liquid or pasty medium on a traveling material web includes the following steps:
To begin with, the liquid or pasty medium is applied directly on one side of the traveling material web. In a following step, the medium applied previously on one side of the material web is separately pressed in the traveling material web. This is followed by a third process step, applying the liquid or pasty medium directly on the other side of the traveling material web. In a following fourth step, the medium applied previously on the other side of the material web is pressed separately in the traveling material web. Thus, the double-sided application of a liquid or pasty medium on a traveling material web occurs in this embodiment in four successive steps performed in the direction of material web passage.
The direct application of a desired final amount of application of liquid or pasty medium on any side of the traveling material web can in the previously described variants of the inventional method suitably be carried out in a single application step. In other words, the medium is preferably applied directly on the material web in a single operation, in a way such that the applied amount matches the desired final amount of application. The result is a compact process.
In a further embodiment of the invention, every step of the direct application of the liquid or pasty medium on any side of the traveling material web is divided in the following partial steps:
A first partial step serves to predose a surplus amount of liquid or pasty medium on the relevant side of the material web. A following separate second step consists in the final dosing of the predosed medium quantity applied previously on the respective side of the material web, to the desired final amount of application.
Instead of a direct application finished-dosed in a single step, the direct application of the medium can thus be subdivided according to the embodiment explained above, as desired in two steps, namely a predosing step and a final dosing step. If desired, both embodiments may also be combined, e.g., to the effect that the direct application of the medium on one side of the traveling material web takes place in a single finish-dosing step, while the direct application of the medium on the other side of the material web occurs in a predosing and a final dosing step. This may be suitable, e.g., when it is desired to apply on the two sides of the material web mediums of different consistency, of which one medium allows easy application in a single finish-dosing step, whereas the other medium can be applied better in separate predosing and finish-dosing steps.
A first inventional apparatus for application of a liquid or pasty medium on a traveling material web, notably of paper or cardboard, includes:
an applicator for direct application of a liquid or pasty medium on one side of the traveling material web,
a rotating mating surface carrying the traveling material web along a contact section, and
a press roll rotating relative to the mating surface in opposite direction and serving to press liquid or pasty medium applied on one side of the material web into the traveling material web.
The contact section of the material web on the mating surface, based on the travel direction of the material web, has coordinated with it first the applicator and, spaced from it, then the press roll, with press roll and mating surface forming a nip through which the material web is passed while carried on the contact section of the mating surface.
In other words, the traveling material web is supported along a contact section on the surface of the mat
Kohl Bernhard
Kurtz Rudiger
Kustermann Martin
Satzger Oswald
Trefz Michael
Lamb Brenda A.
Taylor & Aust P.C.
Voith Sulzer Papiermaschinen GmbH
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