Coating processes – Frictional application
Patent
1999-03-17
2000-12-19
Bareford, Katherine A.
Coating processes
Frictional application
427286, 427287, 427314, 427318, 427359, 427365, 118 68, 118 77, 118118, 118119, B05D 312, B05C 1102
Patent
active
061624896
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method and apparatus for the continuous application of liquid or semi-liquid coatings to a moving substrate strip.
The invention has been developed primarily for the application of coatings of paint to substrates of metal strip, for example steel strip, and is described primarily in that context hereinafter. However, it will be apparent that the invention is applicable to the application of other liquid or semi-liquid coatings to substrates or strip other material, provided that the substrate or strip is substantially impervious to the coating.
BACKGROUND OF THE INVENTION
The large scale application of paint to substrates such as steel strip in continuously operating, steel finishing mills is a highly developed art but has been restricted hitherto to the production of mono-chrome product, wherein a uniform coating is applied to the whole of at least one side of the strip. Such an application is disclosed in EP-494672.
The present invention overcomes that limitation of the prior art, and provides for the continuous, simultaneous application of different coatings to each of two, contiguous, longitudinally extending zones of the strip.
DISCLOSURE OF THE INVENTION
The applicants have found that if two closely adjacent but noncontiguous beads of liquid or semi-liquid coating material are maintained in an upstream nip defined by a moving strip and a doctor roll extending transversely of the strip, then a steady state condition may be attained such that the strip emerging downstream of the roll is coated with coatings respectively derived from each bead and those coatings are in contact with each other but without substantial intermingling. Furthermore, the junction line between the emergent coatings may be straight and fixedly positioned on the strip. Thus, if two beads of similar, but differently coloured, paint compositions are so maintained, the result is a neatly striped product.
According to one aspect of the invention, there is provided a method of coating a strip including the steps of moving the strip to be coated through a smoothing device including a doctor roll to form an upstream nip between the strip and the doctor roll, at least two closely adjacent nip lengths, and for delivery into the respective nip lengths at rates which maintain a bead of coating material in each nip length; a stripe of coating material being formed from each nip length on said strip as the strip passes through the nip.
It is preferable that the coating materials are liquid or semi-liquid when deposited on the strip and the coating materials delivered into each nip length preferably have different physical characteristics.
The reference to the coating materials having different characteristics includes coating materials having different colours.
In preferred embodiments, boundary means similar to said partition means may be provided at each edge of the strip. These boundary means may be immediately adjacent the strip, that is to say they may contact the respective edges of the strip passing between them, or they may overlie and contact narrow edge margins of the strip. In the latter case the boundary means may have a width about equal to half that of the, or each, partition means.
In preferred embodiments, the deposition rates of the coating materials are selected and controlled to ensure that the individual beads of coating material in the respective nip lengths have substantially constant volumes under steady state operation. This requires the deposition rate for each nip length to substantially equal the rate at which material escapes from each nip length. When the doctor roll pressure is set to product coating of desired thickness and there is just sufficient spreading of the material escaping from each nip length by the doctor roll to produce a continuous uninterrupted downstream coating.
When the respective coating compositions are of substantially the same viscosity, the individual beads are not only substantially constant in steady state volume but are also substantial
REFERENCES:
patent: 4002780 (1977-01-01), Reade et al.
patent: 4344989 (1982-08-01), Thornton et al.
patent: 5281435 (1994-01-01), Buecher
patent: 5407697 (1995-04-01), Buecher et al.
Derwent Accession No. 69270B/38, class M 13, JP 79-025 538 (Daido Kohan KK (NIPA)) Aug. 29, 1979.
Buecher Udo Wolfgang
Davies Mark John
Horton Trevor James
Bareford Katherine A.
BHP Steel (JLA) Pty Ltd
Kerins John C.
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