Coating processes – With pretreatment of the base
Reexamination Certificate
1998-01-23
2003-09-02
Bareford, Katherine A. (Department: 1762)
Coating processes
With pretreatment of the base
C427S356000, C427S428010, C118S050000, C118S249000, C118S410000
Reexamination Certificate
active
06613386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for direct or indirect application of a liquid or pasty medium onto a traveling material web, notably of paper or cardboard. Furthermore, the invention relates to a method for direct or indirect application of a liquid or pasty medium onto such a material web.
2. Description of the Related Art
Apparatuses and methods for direct or indirect application of a liquid or pasty medium onto a traveling material web are typically used or applied in conjunction with so-called coating systems in order to coat one or both sides of a traveling material web. The web can include, for instance, paper, cardboard or a textile material. One or several layers of the medium, for example, color, starch, impregnating fluid or the like, are applied with an applicator.
In the so-called direct application, the liquid or pasty medium is applied by an applicator directly onto the surface of the traveling.material web. During application, the web is backed by a revolving counter surface, for example, an endless belt, or a counter roll or backing roll. In the indirect application of the medium, the liquid or pasty medium, in contrast, is first applied onto a substrate surface, for example, the surface of a backing roll configured as an applicator roll. The liquid or pasty medium is transferred from the applicator roll to the material web in a nip through which the material web passes.
A categorical apparatus for direct application of a liquid or pasty medium onto a traveling material web, notably of paper or cardboard, is known from German Document No. DE 42 05 313 A1, assigned to the assignee of the present invention. This apparatus includes a rotatable backing roll which in part is wrapped by the material web and supports a side of the material web facing the backing roll. The backing roll surface and the material web form a cuneiformly tapering entrance gore and an exit gore. Furthermore, the apparatus includes an applicator disposed opposite the backing roll and serving to coat a side of the material web away from the backing roll with the medium. A stripper removes a boundary layer of air entrained by the material web. The stripper is arranged, based on the direction of rotation of the backing roll, before the applicator. The air boundary layer stripper serves here to avoid disturbing effects of air in the entrance gore between the material web and the medium applied onto the material web. In other words, an undesirable air inclusion is avoided on the side of the material web on which the medium is applied, that is, on the side away from the backing roll.
Also known, from German Document No. EP 0 556 675 A1, assigned to the assignee of the present invention, is an apparatus comparable with that of the aforementioned German Document No. DE 42 05 313 A1, but for indirect application of a liquid or pasty coating color onto a traveling material web. This apparatus includes a roll applicator with an applicator roll rotating in a coating color sump or bath, as well as a backing roll disposed directly opposite the applicator roll and wrapped in part by a material web. The material web passes through the nip formed by the applicator roll and the backing roll, in which nip the coating color is transferred to the material web. Based on the direction of rotation of the backing roll, an air boundary layer stripper is arranged before the nip and in the cuneiform area formed by the contours of the opposing rolls. The stripper serves, the same as in German Document No. DE 42 05 313 A1, to avoid an undesirable air inclusion on the side of the material web on which the coating medium is applied.
Comparable with the apparatus according to German Document No. EP 0 556 675 A1 for indirect application of a liquid or pasty coating color onto a traveling material web, is a further apparatus disclosed in U.S. Patent Document No. 5,506,005. Instead of an air boundary layer stripper of the previously described type, however, this apparatus possesses a material web pressure system which, based on the direction of travel of the material web, is arranged behind the line of contact between the backing roll and the material web running onto the backing roll. That is, the material web pressure system is arranged behind the cuneiform entrance gore formed by the backing roll surface and the material web, and opposite the material web side away from the backing roll. The apparatus presses the material web onto the backing roll. For that purpose, an air jet is blown at a pressure of at least 2.5 kPa out of the material web pressure system and at the material web surface being coated. The material web pressure system serves to prevent an undesirable air inclusion between the backing roll surface and the material web side facing the backing roll.
With these conventional apparatuses and the associated method, however, it has been found that the air boundary layer entrained both by the material web and the backing roll can proceed easily between the backing roll surface and the material web. This causes the material web to form a bubble at the point of application or on a metering or treatment element preceding or succeeding the point of application. Such a bubble results in coating defects or wrinkles and, thus, in an appreciable impairment of the coating quality. Use of the prior material web pressure system has not, until now, been able to entirely solve this technical problem. It has been noted that, despite high contact pressures, undesirable air inclusions still proceed between the backing roll surface and the material web, specifically with varying material web properties and high web speeds.
SUMMARY OF THE INVENTION
The present invention further improves a categorical apparatus with respect to the previously illustrated difficulties of the air inclusions caused by air boundary layers, and thereby enables an increase in the achievable coating quality. The present invention also creates a suitable method for direct or indirect application of a liquid or pasty medium onto a traveling material web, which method extensively avoids the drawbacks associated with the prior art.
This apparatus for direct or indirect application of a liquid or pasty medium onto a traveling material web, notably of paper or cardboard, includes at least one rotatable backing roll which in part is wrapped by the material web and supports a side of the material web facing the backing roll. The backing roll surface and the material web form a cuneiformly tapering entrance gore and an exit gore. Moreover, the apparatus includes at least one applicator opposing the backing roll. The applicator serves to coat a material web side away from the backing roll with the medium and/or to further treat the coated material web side. The apparatus also includes at least one air boundary layer stripper serving to remove an air boundary layer entrained by the backing roll and/or the material web. The stripper is arranged before the applicator, based on the direction of rotation of the backing roll. The at least one air boundary layer stripper is arranged in the entrance gore between the backing roll surface and the material web side near the backing roll. To be understood as an applicator in the purport of the invention is any suitable applicator, for example, nozzle applicators, open-jet nozzle applicators (“Jet-Flow-F”), so-called SDTA applicators (short dwell time applicators), LDTA applicators (long dwell time applicators), applicators with an applicator chamber, and the like.
The inventors of the present invention have recognized that particular significance attaches, in view of the underlying technical problem, to the effect of the air boundary layer entrained by the backing roll surface and the material web side facing the backing roll. The inventional arrangement of the air boundary layer stripper can easily and effectively remove, deflect or bar the air boundary layer, entrained by both the backing roll and the material web side near the backing roll, before the materia
Bareford Katherine A.
Taylor & Aust P.C.
Voit Sulzer Papiermaschinen GmbH
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