Coating apparatus – Solid applicator contacting work – Movably mounted applicator
Reexamination Certificate
1999-11-24
2003-07-08
Lamb, Brenda A. (Department: 1734)
Coating apparatus
Solid applicator contacting work
Movably mounted applicator
C118S414000
Reexamination Certificate
active
06589340
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a machine designed for direct or indirect application of a liquid or viscous coating medium onto a moving surface.
2. Description of the Related Art
Coating machines for direct or indirect application of a liquid or viscous coating medium onto a moving surface are generally well known and considered as state-of-the-art (ref GB 2 040 738 A). In the case of direct application, the moving surface includes an outer surface of a material web such as paper or cardboard. In the case of indirect application, the moving surface includes an outer surface of a transfer element, preferably a transfer roll which transfers the coating medium onto the material web. In order to achieve a uniform coating with such a coating mechanism, a coater must be uniformly supplied with a coating medium. That means that the pressure of the incoming coating medium has to be equally applied onto the coater across the entire coating width so that the coater is uniformly lifted off the moving surface to form a metering slot of the desired width. This applies to the application of a coater blade, as well as to a smooth or profiled coater rod. The “profile” of the coater rod can be generated by way of wire sheathing, machining, etching, or forming of impressions onto its surface.
GB 2 040 738 does not deal with the problem of achieving a uniform coating, but introduces a concept that is capable of compensating for the surface wear of the coater bed supporting the coater rod. It should be further noted that GB 2 040 738 describes the coating medium being supplied to the coater as already having taken the shape of a thin film. An older, re-published document DE 197 23 458 A1 discloses a coating mechanism, which includes an accumulator chamber positioned downstream of the coater, whose boundaries are formed by an accumulator chamber inlet limiting element at the moving surface entrance and a coater at the moving surface exit. The main purpose of the accumulator chamber inlet limiting element is to keep air bubbles from entering the accumulator chamber.
It cannot be discerned from GB 2 040 738 A that the coating quality can be influenced by the accumulator chamber positioned in front of the coater and by altering its geometry. The movement of the limiting surface of the coater facing the moving surface towards the moving surface serves to balance the wear in the intake area of the coater rod. This is only possible because the coating medium is supplied in form of a thin film and does not accumulate or “back up” in front of the coater rod.
In terms of the subject matter, DE 197 213 458 differs by the fact that the accumulator chamber is open on one side; that means it is not bound by an accumulator chamber limiting element.
SUMMARY OF THE INVENTION
The present invention provides a coating mechanism that is capable of uniformly applying a liquid or viscous coating medium onto a moving surface. A machine is designed for direct or indirect application of a liquid or viscous coating medium onto a moving surface. In the case of direct application, the moving surface is an outer surface of a material web, such as paper or cardboard. In the case of indirect application, the moving surface is an outer surface of a transfer element, preferably a transfer roll designed to transfer the coating medium onto a material web. The machine further includes a coating mechanism with a coater bed and a coater, which, together with the moving surface, establish a metering slot.
A limiting surface of the coater positioned at the inlet of the moving surface forms an accumulator chamber designed to accumulate or collect the coating medium transported by the moving surface. This chamber includes an opening at the side of the chamber opposing the feed direction of the moving surface. This chamber gradually decreases in volume in the feed direction of the moving surface. Such a chamber further includes an adjusting mechanism in order to alter the relative position of the limiting surface with respect to the moving surface and to thereby alter the shape of the accumulator chamber.
The present invention has distinct advantages over prior art coating mechanisms. By providing a chamber ahead of the coater in which the coating medium accumulates, a transverse flow patterns builds upstream of the coater, i.e., the flow has components in a direction perpendicular to the moving surface. This cross-flow leads to a more even distribution of the coating medium across the width of the moving surface on one hand, and, on the other hand, to a more balanced pressure distribution of the accumulated coating medium. This has the consequence that the coater receives the coating medium more evenly, resulting in overall improvements in coating quality.
An additional advantage of the accumulator chamber can be realized by changing the geometry of the accumulator chamber by use of an adjusting mechanism. This alters the hydrodynamic pressure in a very specific manner, which, in turn, affects the coating thickness without having to change the feed speed or the viscosity of the coating medium.
When applying a coating mechanism that employs a coater rod, the provision of the accumulator chamber has the further advantage of minimizing the influence of the coater rod diameter, i.e., the surface curvature of the coater rod, on the hydrodynamic pressure acting upon it. More specifically, the combination of a coater rod having a small diameter and a limiting surface designed as described by the present invention can result in conditions that are normally only achievable with very large diameter coater rods. This allows for the advantages of coater rods with small diameters, such as the easier handling, lower manufacturing cost, etc., to be combined with the advantages of large diameter coaters such as the increased amount of coating medium that can be applied onto the moving surface per unit time, as well as the lower pressure being exerted onto the moving surface, etc.
Additionally, when applying the coating mechanism in accordance to the present invention, it requires only a reduced number of coater rods with varying diameters to cover the full operating spectrum of the coating procedure.
Finally, the even distribution of the coating medium in the accumulator chamber, and therefore, the improved pressure distribution in the coating medium, allows the pre-metering amount to be lowered, which, in turn, lowers the total amount of circulating coating medium and, hence, the required pumping power.
It should be noted here that the above mentioned optimization of the operating conditions can be achieved not only with smooth coater rods, but also with profiled coater rods. An optimum color distribution can be achieved when using jets (for example slotted jets or spray jets, etc.) for the pre-metering of coating films in film presses.
In general, this coating mechanism can be applied in coating equipment, which is commercially available through the corporation of the applicant under the name “Speedsizer”, “SpeedCoater” and “SpeedFlow”. Further advantages include the capability of achieving targeted shear stresses of the coating medium in the accumulator chamber, as well as the capability of affecting the mold clamping force of the coater bed to avoid color circles on the coater rod or to avoid coater rod vibrations.
The above indicated advantages can be achieved especially when the length of the accumulator chamber, as measured in direction of feed, is between 2 mm and 100 mm, preferably between 5 mm and 50 mm, and/or when the width of the accumulator at the inlet is between 0.5 and approximately 5 mm, preferably between 0.5 mm and approximately 2 mm, as measured in a direction that is perpendicular to the direction of feed as well as perpendicular to the transverse direction of the moving surface. If the feed speed of the moving surface is relatively low, i.e. 900 m/min, an accumulator chamber length that is comparatively large with a relatively small inlet width can be applied. With an averag
Bernert Richard
Mendez-Gallon Benjamin
Lamb Brenda A.
Taylor & Aust P.C.
Voith Sulzer Papiertechnik Patent GmbH
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