US3638604A - Apparatus for coating strip-form substrates - Google Patents

Abstract

A machine for coating a layer of a viscous emulsion on a movable support having a feed means operatively associated with the support with a narrow gap between the feed means and the support for forming the viscous emulsion into a layer on the movable support. The feed means contains a chamber opening into the narrow gap, and the machine is arranged so that the viscous emulsion fed from the chamber and formed by the narrow gap is under an adjustable static differential in pressure between the inlet end of the narrow gap which has a lower pressure on the emulsion and the outlet end of the gap which has a higher pressure. A cavity in a wall-adjoining the chamber in the feed means has one opening into the chamber sidewall and containing a compressible gas acts as an air cushion and reduces the variations in pressure on the feed material during feeding as the gas is enclosable within the cavity by the passage of feed material through the chamber.

Description

United States atent Herzhoif et al. 1 1 Feb. 1, 1972 [54] APPARATUS FOR COATING STRIP- 3,206,323 9/1965 Miller et al ..118/50 X FORM SUBSTRATES Primary Examiner-John P. McIntosh [72] Inventors: Peter Herzhoff, Leverkusen; Hans Gref, c n and Hutz Cologne-Stammherm; Rolf Behr, Leverkusen; Fritz Maus, CologneFlittard; [57] ABSTRACT Wolfgang Schweicher; Willi Wasser, both of Level-kusen; Josef Friedsam, A machine for coating a layer of a viscous emulsion on a Langenfeld; Kurt Bmwatzki, opladenq movable support having a feed means operatively associated all Germany with the support with a narrow gap between the feed means [73 1 Assignce. Agfa cevaert Akfiengeseuschafl Lave and the support for forming the viscous emulsion into a layer kusen, Germany on the movable support. The feed means contains a chamber opening into the narrow gap, and the machine is arranged so Filedl 1 that the viscous emulsion fed from the chamber and formed by the narrow gap is under an adjustable static differential in [211 Appl- 797809 pressure between the inlet end of the narrow gap which has a lower pressure on the emulsion and the outlet end of the gap [52] U.S. Cl ..118/50, 1 18/410 which has a higher pressure. A cavity in a wall-adjoining the [51] Int. Cl. .rBOSc 5/02 chamber in the feed means has one opening into the chamber [58] Field of Search .1 18/50, 410, 41 1,412, 50.1 sidewall and containing a compressible gas acts as an air cushion and reduces the variations in pressure on the feed [56] References Cited material during feeding as the gas is enclosable within the cavity by the passage of feed material through the chamber. UNITED STATES PATENTS 3,067,060 12/1962 Glaus ..1' 18/324 x 2 Clams 1 Draw PATENTEDFEB HHTZ 3.538.604

INVENTOR I;:

APPARATUS FOR COATING STRIP-FORM SUBSTRATES This invention relates to a process for coating substrates in strip form with viscous solutions, preferably with photographic emulsions, in which the substrate is wetted in a sealed coating chamber whose end at the point where the emulsion emerges is formed by a coating gap several times wider than the wet finished layer is thick, and in which to counteract the forward movement of the moved substrate, layer formation is effected under an adjustable static pressure differential between the inlet end and outlet end of the gap, the lower pressure prevailing at the inlet end.

It has been found in practice that static pressure differentials equivalent to a water column of from 20 to 250 mm. are needed to form the required thicknesses with conventional emulsions.

One disadvantage affecting the practical application of the process is that an alternating pressure is superimposed upon the static pressure difierential as a result of inevitable vibration in the coater, producing periodically alternating thick and thin zones, so-called cross cuts," in the emulsion layer leaving the coater. For example, vibrations affecting the coater at a frequency of 25 c./s. are inevitable despite careful antivibration screening on account of the three-phase motors which rotate in the coating machine at a speed of approximately 1,500 r.p.m., corresponding to 25 c./s. If this vibration has an amplitude of only 2;; for example, this gives rise to an alternating pressure of approximately 50 mm. of water, in other words a value which is comparable to the static pressure differential governing layer thickness.

It has now been found that this alternating pressure emanating from vibration can be reduced to a harmless extent by providing inside the emulsion chamber of the coating machine a cavity in which a cushion of air is enclosed when the coating chamber is full. This cavity advantageously extends over the entire width or almost over the entire width of the coating machine.

In this way, both the air and the emulsion volume behave like two series-arranged elastic media the softer of which, namely the air, eventually determines the amplitude of the alternating pressure created. At a given frequency and vibration amplitude, the amplitude of this alternating pressure is proportional to the resistance of the medium of sound waves. The resistance of air to sound wave is lower by a factor of 3,600

than that of water, which means that the alternating pressure created is reduced by this factor. Accordingly, the residual-alternating pressure amplitude is three to four times smaller than the static pressure differential governing layer thickness at the coating gap, with the result that it is no longer able to produce any noticeable cross cut in the coating.

The apparatus according to the invention is diagrammatically illustrated by way of Example in the accompanying drawmg.

A roll 5 provides a rotatable support for the substrate to be coated as it passes the coating machine 4. A gap 6 is defined between the substrate supported by the roll 5 and the coating machine 4. A chamber 3 at the inlet end of the machine provides a low pressure at the inlet end of the gap. The coating machine 4 is provided with an internal emulsion chamber 2 which is supplied with coating material as indicated by the arrow in the drawing. A cavity 1, in which a cushion of air is provided, is in communication with the chamber 2.

What we claim is:

1. In an apparatus for coating a layer of viscous material on a movable substrate which includes the combination of a movable substrate, a sealed coating chamber for wetting the substrate, a viscous material for feeding onto said movable substrate, a coating machine for depositing the viscous material on the substrate containing the sealed coating chamber and being operatively associated with the substrate having one end associated with the substrate so as to form a narrow gap between the coating machine and the substrate, the gap having an inlet end at which the substrate enters the gap and an outlet end at which the substrate departs from the gap, and including means in the combination or applying a static pressure differential at a lower pressure at the inlet end and a higher pressure at the outlet end of the narrow gap, and in which the viscous material is fed from the coating machine through an opening from the chamber into the narrow gap, the improvement consisting of a cavity laterally adjoining the said chamber having an opening into the chamber through a chamber sidewall and containing a compressible gas, said gas being encloseable within said cavity by said conveyed viscous material to maintain said static pressure differential and reduce variations in pressure on said feed material.

2. An apparatus as claimed in claim 4, wherein the cavity occupies substantially the entire width of the coating machine.

Claims (1)

1. 2. An apparatus as claimed in claim 4, wherein the cavity occupies substantially the entire width of the coating machine.

Images