Coating apparatus – Projection or spray type – Endless conveyer for work
Patent
1993-07-28
1995-10-31
Housel, James C.
Coating apparatus
Projection or spray type
Endless conveyer for work
118325, 118DIG4, B05C 500
Patent
active
054625980
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a coating device of the curtain type and finds application in particular in the coating of photographic film supports.
BACKGROUND OF THE INVENTION
FIG. 1, to which reference is now made, illustrates an embodiment of a conventional curtain coating machine as described for example in European Patent 107 818. In the following, the surfaces of the lip body, which will be discussed in more detail later, and the other surfaces of the coating device, are described with reference to the plane of the curtain. The front face of the coating device, that is to say the surface of the lip over which the coating product flows before leaving the coating device will be assumed to be positioned to the left of the observer.
The surfaces of the coating device are assumed to be portions of planes determined by a rotation in a clockwise direction, or in the opposite direction, with respect to the plane of the curtain itself. The positive angles correspond to rotations in a clockwise direction; the negative angles correspond to rotations in an anti-clockwise direction. The positive surfaces indicate surfaces whose angle of rotation is positive; the negative surfaces indicate surfaces whose angle of rotation is negative. As mentioned above, the front face designates in a general sense the surfaces over which the coating product flows before leaving the coating device, whilst the rear face designates the surfaces over which the coating product is deemed not to flow.
According to the embodiment shown in FIG. 1, a conventional curtain coating device comprises a feeding system from which flows a coating composition comprising at least one layer.
The feeding system shown comprises two slots 2, 3 from which two layers flow, superimposed on a slightly inclined flow surface 4. The device also comprises a lip 5 from which the coating composition leaves the device along a negative front surface 6, forming a curtain. The curtain then flows onto a moving support (not shown), which is driven for example by means of a suitable cylinder. The said lip comprises in addition a rear surface 7, which is negative, at least at its lower part, and a chamfer 8 between the bottom ends of the said front and rear surfaces, the chamfer 8 also defining a negative surface. FIG. 2 shows the lip 5 in more detail. In this example the front face of the lip forms a curve of radius R=48 mm; the angle .alpha. defined by the lower part of the rear surface of the lip with respect to the vertical is 15.degree.; the angle .beta. formed by the chamfer with respect to the horizontal is 15.degree.; the angle .gamma. formed by the tangent at the chamfer on the front face of the lip with respect to the vertical is 40.degree., all these angles being given in absolute values. In reality, according to this patent EP 107 818, the rear face of the lip defines a negative surface, as do the front surface 9 and the chamfer 8, the angles .alpha., .beta., .gamma. being negative with respect to the plane of the curtain. The main problem resulting from such a design lies in the fact that it is not suitable for high flow rates of coating composition. The flow rates suggested in this patent vary in fact between 1 and 1.17 cm3/cm/s, which for some applications may prove insufficient. In reality, with higher flow rates, when the negative angle .gamma. defined by the front surface 9 with respect to the vertical is relatively large, that is to say greater than 10.degree. (and all the more so 40.degree., as suggested in the patent EP 107 818), such a design accentuates the defect in the curtain which is commonly referred to as "curtain bendback". Such a phenomenon describes the fact that the curtain, in general, does not fall vertically from the line of the chamfer where it leaves the lip. In reality, even if the lower end of the lip body is vertical, the curtain formed by the coating composition leaves the lip at a certain angle with respect to the vertical. This angle is referred to as the curtain bendback angle. From the lip to the support
REFERENCES:
patent: 3867901 (1975-02-01), Greiller
patent: 4109611 (1978-08-01), Fahrni et al.
patent: 4222343 (1980-09-01), Zimmerman et al.
patent: 4328414 (1982-05-01), Atalia
patent: 4443504 (1984-04-01), Burket et al.
patent: 4569863 (1986-02-01), Koepke et al.
Stephan F. Kistler, "The Fluid Mechanics of Curtain Coating and Related Viscous Free Surface Flows With Contact Lines", Nov. 1983.
D. A. Dittman et al, Research Disclosure No. 14715, Curtain Coating Apparatus, Jul. 1976.
Baumlin Jean-Marie
Servant Jeanne D.
Eastman Kodak Company
Freed Rachel Heather
Housel James C.
Ruoff Carl F.
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