US2530738A - Method of coating metal surfaces - Google Patents

Description

Patented Nov. 21, 1950 METHOD OF COATING METAL summons Clayton I. Spessard, Pittsburgh, Pa., assignor, by

mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York No Drawing. Application February 4, 1947, Serial No. 726,435

1 Claim.

This invention pertains to an improved technique in applying decorative and protective coatings to metal surfaces.

In coating metal surfaces, for instance, automobile bodies, a smooth, glossy finish of high depth is desired. However, the surface of fabricated metal articles often contains roughened areas which may be caused by scratches, marred sections, joints, weld lines, pitting or surface irregularities in the metal. It is now conventional practice to apply what is termed a sanding surfacer to automobile bodies prior to the deposition of the finish or top coating.

The purpose of the sanding surfacer" is to fill all cracks or irregularities in the metal. A smooth surface is then obtained by sanding.

. This sanding surfacer and primer usually comprises an alkyd resin or oleoresinous vehicle heavily loaded with fillers, such as Whiting, asbestine minerals, diatomaceous earth, or other siliceous minerals. This sanding surfacer sets up to a cheesy film of poor cohesive properties and the film, in consequence, is very readily lacquer, properly formulated for durability and strength, the primer or sanding surfacer remains as a vulnerable point in the coating system.

One object of the present invention is to obtain a smooth, glossy finish on metals, wherein sanding is required to smooth out surface irregularities, without weakening the overall protective coating. Another object is to provide a composition which serves both as the sanding surfacer and the final coating.

These objects are accomplished through the proper application of finely divided vinyl chloride resins suspended in organic liquids. Such suspensions are hereinafter termed organosols. The liquid components of an organosol comprise liquids of two types. The first type, which is present as a minor constituent, comprises liquids having solvating power for the vinyl chloride resins Such solvating liquids include ketones, alkyl phthalates and other esters. The second type of liquid which is present in major amount, is a hydrocarbon of either the aromatic or aliphatic series. The hydrocarbons serve asdiluents, but the greater ability of aromatic hydrocarbons to swell the vinyl chloride resin should.

be recognized. In general, more of the solvating liquids are required in the suspending media when aliphatic hydrocarbons, rather than aromatic hydrocarbons, are employed as the diluents. When blends of aromatic and aliphatic hydrocarbons are employed as diluents, the amount of the solvating liquid in the suspending media should be adjusted in accordance with the ratio of aliphatic to aromatic hydrocarbons in the blend. For each combination of solvating liquid and diluent there will be found an optimum ratio of solvating liquid to diluent at which the organosol will have a minimum viscosity. In general the organosols will be formulated within the range, together with pigments and fillers as desired:

Parts by weight Vinyl chloride resin 25 to 45 solvating liquid (plasticizer, ester, or

ketone, or mixtures thereof) 5 to 29 Diluent (hydrocarbon) 31 to In practicing this invention, the organosol is spread over the metal surface by spraying, dipping, roller coating or other suitable means, and baked at temperatures not exceeding 250 F. As a result of this treatment, the volatile hydrocarbons and solvating liquids are removed and the resin is only partially solvated or fused. As a result, the film existing on the metal at this stage is non-homogeneous and it has poor cohesion, toughness and strength. In this gelled but not completely fused condition, the film is very readily abraded with sandpaper or other abrasives, and it may be rubbed to a smooth surface with a minimum of eflort. After sanding, the film is baked at a temperature above 300 F., preferably at 350 to 400 F. This final baking completes the solvation or fusion of the film to a homogeneous state. In this form, the film is homogeneous, tough, strong and hard and very resistant to abrasion.

In achieving the final fusion of the resin, it is desirable that some of the solvating liquids still be present, and this necessitates that all or a substantial portion, say 25 to of the solvating liquid, be composed of liquids which are substantially non-volatile at 250 F. at atmospheric pressures. This portion of the solvating liquid usually comprises the ester plasticizer which is normally included to give desired flexibility to the final coating.

Although the physical properties of the fused film are excellent, the surface of the film is often fiat or non-reflective as a result of the sanding. Th surface of the film may be burnished or made glossy by various procedures. One of these procedures involves rubb ng the film with a polishing compound followed, if desired, by a waxing operation. Also a top coating of an organosol may be applied to the sanded surface, omitting the preliminary baking and carrying out the baking in one stage at temperatures of 300 to 400 F. When baked in this manner coatings deposited from organosols develop a moderately glossy finish. Another method of developing a glossy finish on the sanded organosol coating is to spray the film with an active solvent for the resinous binder, such as mesityl oxide or isophorone, followed by a brief bake at 300 to 400 F. A final method invoives depositing a film of a more soluble vinyl resin from solution in an organ c solvent and then baking. This latter procedure develops a substantially higher gloss than applying a top coating from an organosol.

The treatments involving polishing and waxing should be carried out after the sanded film has received its final bake, but the other treatments may be carried out immediately after the sanding operation as baking is required with each of these operations. ments give better results if carried out after the sanded film has been baked at temperatures of 300 to 400 F.

The organosols employed in the practice of this invention may be prepared by charging the ingredients in any order to a pebble mill or other grindng apparatus and thoroughly dispersing the resin by grinding for from 24 to 48 hours. Best results are obtained if the grinding operation is carried out at temperatures below about 50 to 60 C.

The vinyl chloride resins employed in the organosols are preferably those which have been prepared by the emulsion polymerization of vinyl chloride, or the emulsion copolymerization of vinyl chloride with another monomer, and isolating the vinyl chloride resins in finely divided form by coagulation of the emulsion. In the case of the copolymers, the vinyl chloride comprises at least 80% by weight of the copolymer. Monomers which may be copolymerized with vinyl chloride include vinyl acetate, vinyl propionate, methyl acrylate, ethyl acrylate, acrylonitrile, dimethyl .fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate and vinylidene chloride. All of such vinyl chloride resins are characterized by relative insolubility in organic solvents and form at most only dilute solutions, say 5% to by weight in acetone or methyl ethyl ketone.

As noted previously, a plasticizer is usually included in the organosol constituting part or all of the solvating liquid. Plasticizers employed in this invention may be any of the typical esters used with vinyl chloride resins, such as those disclosed by M. C. Reed, Industrial and Engineering Chemistry, vol. 35, page 896 (1943).

The solvating liquid may also include a ketone, such as acetone, ethyl ketone, dipropyl ketone, methyl isobutyl ketone, mesityl oxide, isophorone,

acetonyl acetone and pentanedione 2-4 or an glycol.

The preparation of organosols is more fully discussed in my application Serial No. 524,911, filed March 3, 1944, entitled Vinyl Resin Suspen- SiOIIS, now Patent No. 2,427,513, and. in applica- I-lowever, these latter treat- 4 tion Serial No. 542,432, filed June 27, 1944, by G. M. Powell and T. E. Mullen, entitled Vinyl Resin Suspensions, now Patent No. 2,431,078, and assigned to the same assignee as the present application.

The following examples Will serve to illustrate this invention:

EXAMPLE 1 The following ingredients Were charged to a small pebble mill and ground for 48 hours:

Organosol Per cent by weight Emulsion copolymer of vinyl chloride, 96%, vinyl acetate, 4%, average molecular weight by Staudingers method, about 23,000 35.3

Di-2-ethylhexyl phthalate 7.1 Carbanthrene red 1.7 Cadmium red 2.7 2-ethylhexyl acetate 7.9 Xylene 45.3

At the end of the grinding period a fluid organosol was discharged from the mill and diluted with a mixture of isophorone (20% by weight) and a petroleum naphtha of high flash point (balance) until the viscosity of the organosol was 18 seconds measured in a Ford viscos meter with a No. 4 tip. Two steel panels were then coated and baked for 30 minutes with a primer coating of the following compositions:

Primer Percent by weight Chrome orange pigment 25.3

Copolymer of vinyl chloride, 87%, vinyl acetate, 13%, average molecular weight about 10,000 14.8 Dibutoxyethyl phthalate 3.9 Solvent thinner n 56.0

Methyl isobutyl ketone, 40 Methyl amyl ketone, 10% Toluene, 40 Xylene, 10%

Overlacquer Percent by weight Copolymer of vinyl chloride, 90%, vinyl acetate, 10%, average molecular weight about 16,000 5.0 Methyl ethyl ketone 26.0 Methyl isobutyl ketone 32.5 Isophorone 3.5 Toluene 29.5 Xylene 3.5

Both panels were then placed in an oven at 350 F. for 30 minutes. The lacquered panel presented a smooth, glossy, enamel-like appearance after baking, and such a finish was imparted to the unlacquered panel in a conventional manner, using a rubbing compound and a polishing wax.

EXAMPLE 2 An organosol of the following composition was prepared as described in Example 1:

Organosol Percent by weight Emulsion copolymer of vinyl chloride, 96%, vinyl acetate, 4%, average molecular This organosol was diluted with a thinner in the amount of 30% by weight of the organosol. The thinner was composed of a by weight solution of a copolymer of vinyl chloride 86%, vinyl acetate 14%, average molecular weight about 6,000, in a mixture of isophorone by weight) and a petroleum naphtha of high flash point (balance).

A steel panel was then coated with a baked primer as a described in Example 1. The organosol was then sprayed on to the primed panel. Unlike the organosol coating described in the previous example, this coating could be airdried for long periods without cracking. The coating was air-dried for minutes and then partially fused by baking at 250 F. for 10 minutes. After cooling the coating was sanded to a smooth surface with No. 400 sandpaper using water lubrication.

The sanded coating was then sprayed with an overlacquer of the following composition:

Overlacquer Percent by weight Copolymer of vinyl chloride, 87%, vinyl acetate, 13%, average molecular weight The sanded and lacquered panel was placed in an oven at 350 F. for 30 minutes. The coated panel exhibited excellent gloss, smoothness and depth of finish.

EXANIPLE 3 An organosol of the following composition was prepared, as described in Example 1:

6 Organosol Percent by weight Emulsion copolymer of vinyl chloride, 96%,

vinyl acetate 4%, average molecular 0 weight about 23,000 29.8

Di-2-ethylhexyl phthalate 5.9 Indanthrene blue 1.5 Carbanthrene yellow 0. 1 Lead titanate 0.6 Methyl isobutyl ketone- 1.9 2-ethylhexyl acetate 7.4 Xylene 52.8

One hundred (100) parts by weight of the organosol were blended with parts of a solution of a vinyl resin noteworthy for its adherence to metals. The solution had the following composition:

Solution Percent by weight Copolymer vinyl chloride, 86%, vinyl acetate, 13%, maleic acid, 1%, average molecular weight 10,000 15.0 Methyl isobutyl ketone 21.0 Xylene 64.0

Overlacquer Percent by weight Copolymer of vinyl chloride, 87%, vinyl acetate, 13%, average molecular weight 10,- 000 10.0 Copolymer of vinyl chloride, 86%, vinyl acetate, 14%, average molecular weight 6,000 6.6 Methyl isobutyl ketone 41.7 Toluene 41.7

The sanded and lacquered coating was then baked for 30 minutes at 350 F. The coated panel after baking had a smooth, glossy surface. The adhesion of the coating to the metal was quite adequate, but was not quite as strong as obtained in the previous examples in which the panels had been precoated with a baked primer.

Modifications of the invention other than as described in the previous example are included within the scope of the invention as defined in the appended claim.

I claim:

Process for forming a smooth coating on metallic articles having surface irregularities which comprises applying to the metal surface at room temperature a fluid suspension of 25 to 45 parts of a finely divided vinyl chloride resin containing from to polymerized vinyl chloride in a non-solvent mixture composed of 31 to 65 parts of a liquid hydrocarbon of the group consisting of xylene and toluene and 5 to 29 parts of a solvating liquid atleast 25% by weight of said solvating liquid being composed of an ester plasticiger for: inyl chloride resins and the balance of said; solvating liquid being selected from the group consisting of acetone, diipropyl ketone, methyl isobutyl ketone, mesityl oxide, isophogone, acetonyl acetone, pentaned-ione-ZA, ethyl acetate, isopropyl acetate, butylacetate, methyl a nyl acetate, 2-ethy1-butyl acetate, 2-ethy1hexyl aeetate, methoxyethyl acetate, ethoxyethyl acetate, diethylene glycol monoethyl ether acetate and diethylene glycol monobutyl ether acetate, forming a non-homogeneous easily abraded film err said metal surface by baking the applied suspension at a temperature not exceeding about 259 F- nd t er y on y pa ia ly us n t finely-div ded r s n, me han cal y a g d film to. obtain. a smo th surface thereon, a

thereaf er ak n sai film at, a. temper ure of 3 to- 4 .0. F- to, vform a s rio h tou h nd ad e nt c ating on sa m t surface- CLAYTON 1. SPESSARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED. SIAT PATENTS Number Name DBJ 1,904,417 Crystler Apr. 18, 1932 1,912,372 Jacobson et a1. June 6, 1933 2,245,708 Patton June 17, 1941 15 2,270,662 Raney Jan. 20, 1942 2,279,771 Austin; Apr. 14, 1942 2,427,513, spessard fl -1 Sept. 16,1 1 947 2,431,078 Powell a ---i-r Nov, 18,1947

Certificate of Correction Patent No. 2,530,738 November 21, 1950 CLAYTON 1. SPESSARD It is hereby certified that error appeers in the printed specification of the above numbered patent requiring correctlon as follows:

Column 3, line 66, for the word methyl read ethyl;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice. Signed and sealed this 23rd day of January, A. D. 1951.

THOMAS F. MURPHY,

Assistant C'ommz'ssz'oner of Patents.