Coating apparatus – Solid applicator contacting work – With work-handling or work-supporting
Reexamination Certificate
1999-06-07
2001-11-27
Edwards, Laura (Department: 1734)
Coating apparatus
Solid applicator contacting work
With work-handling or work-supporting
C118S249000, C118S259000, C118S126000
Reexamination Certificate
active
06322627
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for the application of a liquid or viscous coating medium onto a moving fiber material web, such as a paper or cardboard web.
2. Description of the Related Art
Devices for applying a coating medium onto a fiber web typically include an applicator unit and a first backing element. The first backing element is assigned to an applicator unit around the circumference of which the fiber material web travels at least partially. A leveling and/or metering device is assigned to a second backing element around the circumference of which the fiber material web travels at least partially.
Devices of this type where the fiber material web is guided around two separate backing elements, specifically backing rolls—one at the location of the coating medium application and the other at the location of leveling and/or metering of the applied layer, respectively—are described in German patent document nos. 43 38 776 A1, 94 21 631 U1, 37 15 307 C2 and EP patent document no. 0 651 095 A1.
For example, German patent document 43 38 776 A1 deals with the risk of creation of wrinkles in the fiber material web in the area between the applicator device and the leveling/metering device when both of these devices operate against one and the same backing roll. In order to rectify these problems it is suggested in German patent document 43 38 776 A1 to assign separate backing rolls to the applicator unit and to the leveling/metering device respectively, and to control the speed of the two backing rolls in such a way that a desired web tension is assured. This solution has the disadvantage that it requires the two backing rolls to be driven at synchronized speeds, and also requires a complex and costly control system for the entire coating line or the fiber material web production line, due to the consideration of the speed dependency of the two backing rolls.
SUMMARY OF THE INVENTION
The present invention provides a device for the application of a liquid or viscous coating medium onto a moving fiber material web which prevents the formation of wrinkles in the fiber material web. The surface characteristics of the first backing element and the second backing element are matched to one another such that the fiber material web may move at least relative to the first backing element. Through targeted control of the surface characteristics of the two backing elements, only the surface of the backing roll assigned to the leveling and/or metering device represents a fixed point relative to the fiber material web. The backing element assigned to the leveling and/or metering device and the fiber material web is in substantially slippage free contact with the fiber material web, while the backing roll assigned to the applicator unit and the fiber material web undertakes relative movement in the direction of fiber material web flow when necessary to prevent the formation of wrinkles in the fiber material web. This dislocation of the two backing rolls relative to each other, even without matching the speeds of the two backing rolls to each other, maintains a fiber material web tension which eliminates wrinkle formation. Although reference has been made in the prior text and will be made in the following text to backing rolls, it is to be understood that one or even both of the backing elements may be a continuous belt or, preferably, a continuous belt which runs around a backing shoe in the area of the applicator unit or the leveling and/or metering device.
There are various ways to achieve substantially slip free contact of the fiber material web with the surface of the second backing roll while there is at least a certain amount of relative movement of the first backing roll. In accordance with the first embodiment of the present invention, this is, for example, achieved by at least the surface of the first backing element being soft. A soft surface is understood to be a surface which meets the following conditions:
4 mm<
t·h
8
·c
<13 mm
whereby the thickness “t” of the surface layer, for example, the roll cover, is stated in millimeters, “h
8
” is the hardness of the surface material according to Pusey & Jones hardness testing, and “c” is a constant with the value (1 mm)/(25.4 P&J). The effect of this first variable is based on the surface of the first backing roll being elastic so that negligible fluctuations of the web tension are compensated for, at least in part, by the “spring effect” of the soft surface of the first backing roll. The hardness of the surface of the first backing element has a value of at least 50 P&J (hardness testing according to Pusey & Jones). The surface of the first backing element is therefore substantially softer than, for example, the surface of applicator rolls in long dwell time applicators, or LDTA applicators. The surface hardness of the second backing element has a value of between approximately 50 Pusey & Jones and approximately 100 Pusey & Jones, preferably of between approximately 60 Pusey & Jones and approximately 80 Pusey & Jones. Thus, the first backing element may has a softer surface than the second backing element.
A second embodiment of the present invention provides that the surface of the first backing element has lower friction characteristics than the surface of the second backing element. In this embodiment, the surface of the first backing element has a friction coefficient &mgr; of 0.45 max, preferably of 0.15 max. Such low friction coefficients are provided, for example, when the surface of the first backing element is constructed of chrome, “Chrome-Slick”, ceramic, and other similar low-friction materials. In this instance, the fiber material web reacts to variations in the web tension through a slipping movement relative to the surface of the first backing roll.
A third embodiment of the present invention consists in that the surface of the first backing element is definably rougher than the surface of the second backing element. The surface of the first backing element has a median roughness depth that is an arithmetic median roughness value (according to DIN 4768) of between 1.5 &mgr;m and 63 &mgr;m, preferably of between 6.3 &mgr;m and 30 &mgr;m. The roughness of the first backing roll results in an air boundary layer forming on the surface thereof during rotation. In the area of the backing roll that is encircled by the fiber material web, this air boundary layer forms an air cushion on which the fiber material web “floats”. The air layer allows a relative movement between the backing roll and the fiber material web. The rough configuration of the roll surface enables the surface to exhibit a low dynamic friction coefficient which is dependent upon the prevailing operating conditions.
The three previously discussed embodiments can be realized simultaneously on one and the same backing roll, and in any preferred combination. For example, the roughness according to the third embodiment may be provided in a surface cover of the backing roll, which would consist of a soft material, i.e., through embedded fibers in the soft material (“suede effect”). In this combination, the “floating effect” of the roll surface roughness will dominate at high operating speeds, while the “spring effect” of the soft roll surface material will ensure a relative movability between the fiber material web and first backing roll at lower operating speeds.
Yet another embodiment of the present invention is realized with both backing elements being backing rolls, and whereby the distance “a” between the shafts of both backing rolls conform to the following conditions:
555 mm<
a<
0.5·((&ngr;
max
+&ngr;
min
)/
&ngr;
max
)·(
W/D
)·1500 mm
whereby &ngr;
max
is the maximum provided running speed of the web, &ngr;
min
is the minimum provided running speed of the web, W is the fiber material web width and D is the diameter of the second backing roll.
The unsupported length of the fiber material web between the two backing rolls is selected to be such that fluctuations in tension
Edwards Laura
Taylor & Aust P.C.
Voith Sulzer Papiertechnik Patent GmbH
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