US 2555519 A
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V. W. TOLLE ETAL METHOD OF PAINTING ELECTROSTATICALLY NONCONDUCTING ARTICLES June 5, 1951 Filed March 11, 1947 HEAT/N6 Z emu/vase M 0 as K 5 O w; Em v N i M A VP V 6 Patented June 5, 1951 T I UNITED STATES PATENT OFFICE METHOD OF PAINTING ELECTROSTATI- CALLY NONCONDUC' IING ARTICLES Vance W. Tolle and Paul E. Ludy, Dayton, Ohio,
assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application March 11, 1947, Serial No. 733,756
heated to a selected and controllin temperature.
In carrying out the above object, it is a further object in some cases, to heat the paint prior to its application to a selected and controlled temperature.
Another object of the invention is to provide a method for painting rubber steering wheels and the like in an electrostatic field wherein the rubber steering wheel includes an insert of metal and wherein the entire steering wheel is heated to a temperature of between 175 and 225 F., whereupon the paint is applied in the electrostatic field.
In carrying out the above object, it is a further object, inlsome cases, to heat the paint prior to panying drawings wherein Fig. '1 illustrates schematically a plan view of an apparatus for electrostatically spraying steering. wheels and wherein Fig. 2 is a section taken through line 22 of Fig. l.
The use of electrostatic fields in the applicafor such spraying is shown and described in" Ransburg et al. Patent No. 2,247,963. The basic principle of painting in an electrostatic field is to cause the article to be sprayed to act as one electrode of the circuit and to provide another electrode surrounding the article connected to the other side of the circuit. Both electrodes are attached to apparatus for producing an electrostatic charge which causes an electrostatic field to be set up between the two electrodes. The article to be sprayed is positively charged while the other electrode carries the negative charge. The paint, when sprayed in this field, is attracted to the positively charged electrode since the positive electrode is always of a greater size than the negative electrode. In this manner,
paint particles are directed to their point of application whereby loss of paint is reduced and a better application thereof is obtained.
Spraying of articles in electrostatic fields is very successful where the articles themselves are 'of a conductive nature for example, metal. We
have found, however, that where non-conductive articles are to be sprayed, that such articles must be backed-up with a satisfactory metal electrode or must include metal inserts therein in order to accomplish the end desired. In each case, the application of the paint is not entirely satisfactory since the non-conductive surface to be coated does not appear to properly attract the paint to cause a uniform layer or coating to form.
In order to correct this difficulty and make the application of electrostatic spraying of nonconductive articles completely satisfactory, we have found that by heating the article to a relatively high temperature that the paint particles are more uniformly attracted whereby a satisfactory paint coating is obtained.
Specifically, we heat the non-conductive article, for example, selected from the group consisting of rubber, reclaimed rubber, and synthetic elastomers, such as, butadiene-styrene copolymers or mixtures thereof etc., in the form of a steering wheel etc., having a metal insert therein, to a temperature between 150 to 250 F., wherein this temperature is maintained at the surface of the article during the electrostatic spraying operation. Preferably, a temperature of from 200 to 250 F., gives optimum results but in all cases throughout the temperature range noted, the results are highly superior to those obtained when no heat is utilized.
In some cases, for example with butadienestyrene copolymer articles it is desirable to include a conductive material such as a conductive carbon black, metal powder etc., in relatively small quantities, for example, from 1% to 2% by weight in the compound. This carbon black tends to make the compound a better electrode in the electrostatic equipment. The heating of the article should be carried out prior to the spraying of the paint as before. It is understood that the black can be used up to 30% and above but it serves no useful purpose for the painting over the preferred limits.
Another embodiment relates to the heating of the paint per se. We have found that if the paint is maintained at a temperature of between and F., that the entire process is further improved and more reliable results are obtained. This is particularly true in low ambient temperatures which causes a roughness in the paint surface if the paint remains cold. By heating the paint to a standardized temperature during the spraying operation, all of these variable factors are eliminated and a surface of greater uniformity is obtained. Also the quantity of thinner may be reduced to provide greater thickness of paint film.
Referring particularly to the drawings, a schematic apparatus for spraying steering wheels is shown wherein in Fig. 1, indicates a heating chamber having a conveyor 22 passing therethrough. The conveyor 22 has a plurality'of spindles 24 thereon which are adapted to support steering wheels 26 which are to be painted.
so that uniform spraying of the paint may be obtained. In practice, we prefer to turn the wheels about 12 revolutions during the spraying operation. The negative electrode is shown at 28 .and consists of a plurality of wires-which are disposed as a canopy over the conveyor so that the wheels pass thereunder. The spindles and the wheels which act as one electrode and the other electrode are suitably connected to an apparatus 30,:capable of establishing an electrostatic field therebetween. A plurality of spray nozzles 32 are provided which spray .a mist of paint within the electrostatic field whereby the particles of paint are attracted to the wheels and uniformly coat the same. One or more coats of paint may be utilized wherein the wheels are nature areto be coated, and in this respect, it .is manifest that the scope of the invention is such to adequatelyfcover these variations.
While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might he adopted, all coming within'thescope of the claims which follow.
What is claimed islas follows:
1. In the method of coating a substantially electrically non-conductive article made from a material selected from'the class consisting of rubber and synthetic elastomers, which article includes a metal insert therein, with a solvent containing paint, the steps of; heating the article to a temperature of from 150 F. to 250 F.,
passing the heated article into an electrostatic field of defined character, and simultaneously Each spindle preferably rotates on the conveyor q "painted.
4 spraying a solvent containing paint on the article whereby a uniform, strongly adhering coating is obtained.
2. In the method as claimed in claim 1, including the added step of heating the paint prior to spraying to a temperature of from to 120 F.
3. The method as claimed in claim 1,, wherein the non-conductive article includes a conductive material dispersed therethrough in quantities of from .1 to 2% by weight.
4. In the method of coating a substantially electrically non-conductive article made from material selected from the class consisting of rubber .and synthetic elastomers including a metal insert therein with a solvent containing paint, the step of heating the article to a temperature in the neighborhood of 200 to 205 F., passing the heated article into an electrostatic field of defined character wherein the article itself forms. one. of the electrodes, and simultaneously spraying paint on the article wherein the particles of paint spray carry a charge opposite to that=carried by the article whereby a .uniform, strongly adhering coating .is obtained.
5. The methodas claimed in claim 4 including the added step .ofheating .the paint to a tempera ture of between 85 and 120 IT, prior to the spraying step.
6. The methodas claimed in claim 4 wherein the article includes from 1% to 2% by weight of a conductive carbon black intimately dispersed therethrough.
7. In themethod of painting steeringwheels including a compounded rubber covering on a reinforcing steel spider, the-steps .of; heating the steering wheel to a temperature of approximately 200 F., passing said steering wheel in the heated condition into an electrostatic field of. defined character wherein the steering wheel forms one electrode of the circuit, and simultaneously .spraying solvent containing paint at a tempera-- ture of about F.,. onto the surface'of the wheel wherein the particles of paint spray carry a charge Qpposite to that carried by the wheel for forming ,a uniform, strongly adhering .coating thereon, and finally cooling the wheel so VANCE W. TOLLE. PAUL E. LUDY.
REFERENCES CITED The following references are of record in the file of this patent: