Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Patent
1986-11-07
1988-02-09
Beck, Shrive P.
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
427 33, 118303, 118629, B05B 508, B01J 200
Patent
active
047241543
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the electrostatic application of films on free flowing products such as pellets, granules, crystals or powders in the manufacturing processes used in the agricultural, chemical and pharmaceutical field. More particularly, the invention relates to a method of and apparatus for the electrostatic application of films or coatings on such products.
Various techniques for the electrostatic application of coating materials on free flowing products are known from EPA Nos. 0085149, 0127566 and 0148772.
EPA No. 0127376 discloses a method and apparatus for electrostatic application of a coating material to a non-conducting or poorly conductive product, wherein the product falls in a circular or cylindrical curtain around a linear electrode having a first polarity and is sprayed with finely divided spray of either liquid or powder coating material carrying a charge of opposite polarity.
One object of the present invention is to further improve the uniformity of an electrostatically applied coating, whether the product be of electrically conductive or of electrically non-conductive material.
According to the present invention we propose a method for electrostatic application of a coating material on a product to be coated which product may be either of electrically conducting or non-conducting material, comprising causing the product to descend in free fall in the form of spaced curtains across two streams of electrostatically charged coating material directed laterally of the curtains from opposite sides thereof, wherein the two streams are charged with opposite polarity and such that an electrostatic charge opposite to that of the stream is imparted to that side of each of the two curtains towards which the stream is directed causing attaction between the coating material and the product.
Also according to the present invention, we propose apparatus for electrostatic application of a coating material on a product to be coated which product may be of either electrically conducting or electrically non-conducting material comprising a feeding device from which in use, the product is caused to descend in free fall in the form of spaced curtains, two electrostatic spraying devices arranged below the feeding device to direct streams of electro-statically charged coating material laterally of the free falling curtains from opposite sides thereof, the spraying devices being adapted respectively for connection to high voltage sources of opposite polarity, whereby, in use, a different electrostatic charge is applied to each of the two streams of coating material and an electrostatic charge opposite to that of the stream is imparted to that side of each of the two curtains towards which the stream is directed causing attraction between the coating material and the product.
One embodiment of the apparatus according to the present invention comprises a hopper, for the product material and having spaced outlet openings, preferably straight, arranged such that, in use, the product material is caused to fall freely in the form of two parallel and equal curtains.
One or more electrostatic spraying devices such as atomiser(s) and/or diffuser(s) are arranged and orientated so as to direct a spray of electrostatically charged coating material across the whole width of the free falling product material curtains, from opposite sides thereof.
When an electrostatic charge of opposite sign is applied to the spraying devices between which the two curtains fall, an electric field is established the intensity of which depends upon the potential difference (typically in the range 70 to 100 Kv) applied to the devices and the distance between the electrodes thereof and the free falling curtains of product material.
Fall of the product in the form of two parallel curtains, symmetrically within the electric field, deforms the pattern of lines of force causing them to converge in the product.
Thus the system is similar to a plane condenser in which the two opposed atomisers with flat blades are the capacitor plates, t
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patent: 2270341 (1942-01-01), Ransburg
patent: 2334648 (1943-11-01), Ransburg et al.
patent: 3240212 (1966-03-01), Royster
patent: 3666523 (1972-05-01), Nau
patent: 4116163 (1978-09-01), Torelli
patent: 4243696 (1981-01-01), Toth
Cosentino Roberto F.
Pensa Carlo M.
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