US2375823A - Polishing composition - Google Patents

Description

ted May E5, 3945 POLISHING COWOSITION Albert Saunders, Maplewood, and Loy S. Engle,

Harrington Park, N. 3., assignors to Interchemical Corporation, New York, N. Y., a corporation of Ohio No Drawing. Application October 16, 1941, Serial No. 415,212

Claims.

This invention relates to po s g P tions and methods particularly useful in the elimination of blemishes in baked resin finishes on automobile bodies and the like. In particular, it relates to the use of certain calcium silicates as polishing agents for this purpose.

In the past, the most common finish for automobile bodies has been a thermoplastic coating such as nitrocellulose lacquer. In order to give such finishes a gloss surface, it is necessary to sand and polish them. While the polishing is an expensive process, it satisfactorily leads to a high gloss surface, probably because the plastic fiow of the finish under the heat of polishing eliminates the fine scratches which are necessarily produced by the abrasives used. The blemishes or damaged places which occur not infrequently in the handling of automobile body parts may easily be repaired and rendered indistinguishable from the remainder of the surface by sanding and polishing the patch in the same way that the Whole finish is sanded and polished.

Heat-hardened finishes, in which term We include all those finishes containing resins which are hardened rather than softened by the application of heat and are customarily baked after application to convert the resin to the heathardened condition, have the advantage of providing gloss surfaces without sanding or polishing. For this reason, a considerable economy could be introduced by using such finishes instead of thermoplastic finishes on automobile body parts, were it not for. the fact that no method of eliminating blemishes in baked resin finishes has been known. Consequently, when baked resin finishes are used, any body part containing a blemish caused by scratchin or chipping in handling must be completely refinished. This eliminates the economies which would otherwise be present in the use of baked resin finishes.

The diificulty in patching baked resin finishes arises from the ract that, no matter how smooth the surface of the patch and the surface of the main body of the finish may be, the outline of the patch is clearly visible owing to the absence of a polishing operation on the non-patched parts of the automobile body which would blend the patch with the main body of the finish as in the case of thermoplastic finishes. Attempts to eliminate the lin of demarcation in patched baked resin finishes by a polishing operation have proved unsuccessful, for the fine scratches formed by fine abrasive polishes are not eliminated by plastic flow as in the case of thermoplastic fin- .polishingmaterial. The hazy appearance of the polished areas arises not merely from the presence of fine scratches, but from the presence of debris or minute particles and shavings of the baked resin contained in the scratches. It is this debris which scatters incident light and gives the appearance of haze. It is possible to eliminate the debris or shavings from the scratches and thus to produce a finely scratched area which does not difler in appearance from the unscratched and unpolished gloss areas of' the surface by flocculating the debris into asglomerations with the abrasive, which can be rubbed from the surface. This method of polishing forms the subject matter of a co-pending application of one of the co-inventors here with others, Serial No. 393,934, filed May 17, 1941.

As disclosed in the above application comparatively few of the fine abrasive powders which are used as polishing agents have the property of fiocculating with particles of baked resin. Those which have this property may be selected and identified by the following test:

The abrasive powder to be tested is mixed with fragments (or a powder) of the resin of which the surface to be polished is made- (or a resinous material substantially identical therewith) and the mixture is wet with the liquid to be used as the vehicle in applying the abrasive powder. Ordinarily, water is the most practical vehicle. The mixture is then observed through a microscope using a magnification of from to diameters. In case the particles of the mixture are seen to form agglomerations in the liquid the abrasive powder is shown to have the property of fiocculating with the baked resin particles in the liquid. With respect to non-aqueous vehicles, the abrasive particles might acquire, on

preliminary mixing, an electrical charge ODDO- site to that of the resin fragments, with consequent agglomeration of the materials. The materials may be redispersed by rubbing the particles unless the redispersion is opposed by thephenomenon of flocculation mentioned above. This agglomeration due to electrical (or static) charges must not be confused with the true flocculation phenomenon, as the former is not a measure of the ability of the abrasive to remove the debris from the surface grooves. Of course, an aqueous vehicle is generally a sufllciently good electrical conductor to prevent accumulation of these static charges.

The principal difficulty encountered with the best polishing agents described in the aboveidentified patent application has been lack of stability on storage in a vehicle. The polishing agents tend to react in aqueous media, to produce materials which can no longer be successfully used in polishing.

Another difficulty frequently encountered with these polishing agents has been dusting of the polish on the buffing wheels, apparently due to too rapid drying of the aqueous vehicle.

This invention provides an inexpensive polishing composition which is stable on storage, and which at the same time will remove the haze from non-thermoplastic resinous finishes quickly. The composition includes a new abrasive material stable on storage in aqueous systems,

and in its preferred form it is combined with certain water-miscible vehicles. The abrasive powder which contributes to the superior qualities of this polishing composition is an alkalinereacting, precipitated, hydrated, calcium silicate. Preferably, the calcium silicate is in finely divided form (average particle size under 1 micron). A typical product of this type is available in the market under the trade name "Silene, and is manufactured by the Pittsburgh Plate Glass Company. This product has an approximate analysis of:

Per cent by Weight CaO 18.00 SiOz 64.00 H2O (loss at 105 C.) 4.00 Loss on ignition 14.00 NaCl .35

Other properties are:

pH in water suspension 10.10 Specific gravity 2.25 Bulk density (powder) lbs./ cu. ft 15 to 16 Refractive index 1.463

Silene exhibits the flocculation with fragments of non-thermoplastic resins which is characteristic of abrasive powders capable of polishing these resinous finishes, when subjected to the flocculation test described above; but unlike hitherto available abrasive powders capable of producing optimum gloss, or freedom from haze, mixtures of Silene with aqueous vehicles maintain their polishing properties on prolonged standing. Furthermore, results superior to any obtained with heretofore known polishing compositions can be obtained if the vehicle in which the Silene is to be used is selected from a small and special group. The vehicles which have been found to yield superior polishing compositions with Silene, and hence are included in this invention, are ethylene glycol, formamid and glycerol, and they are preferred in the order given. Although these three vehicles may be used undiluted with the Silene it is more economical' to add water to the composition, and in some cases the presence of water is beneficial. The proportion of Silene to vehicle is not critical, the criterion being that of obtaining a smooth, easily workable paste. The compositions were tested by rubbing various resinous surfaces, such as phenol-formaldehyde, ureaalkyd, oleoresinous and alkyd, which had been dulled by rubbing with a fine abrasive, followed by rubbing with McAleers polish. The latter polish reduced the dullness left by the abrasive, but the resinous surfaces were still hazy or semimatte in appearance. After cleaning the surfaces with a hydrocarbon solvent to remove wax, they were rubbed with typical compositions made in accordance with this invention until a highly I glossy surface free from haze and exihibiting no visual difference from the rest of the finish was produced. These compositions are described in the following examples.

Eiample 1 A polishing composition was made by mixing Parts by weight Ethylene glycol 75 Silene" 33 Water may be added if desired, but this composition produced the haze-free gloss with least rubbing or labor without dilution.

Formamid 25.0 Water 25.0 Silene 22.5

This polish produced the desired gloss with the least labor and in the least time of all of the polishes, when used on a urea-alkyd resin. baked finish, but it was not as satisfactory as the composition of Example 1 when used on other resinous surfaces.

Example 3 The polishing composition consisted of Parts by weight Glycerol 37.5 Water 12.5 Silene 23,0

This polish quickly removed the haze from the resinous surfaces, but it was not quite as efficient as the polish of Example 1.

The Silene was tried with numerous other vehicles and combinations of vehicles, and with nearly all of them results were obtained which were superior to those obtainable with other abrasives or powders in the same vehicles. In particular, the Silene could be successfully used with waxes wherein the vehicle was in the form of an emulsion, without the loss of polishing power which is characteristic of other powders in the presence of waxes or oils. However, water or a water-miscible liquid must be present in the vehicle in order to obtain satisfactor results. Of all of the vehicles tried, three compounds gave polishing compositions with the Silene" which were outstanding in their ability to produce haze-free surfaces with a minimum of rubbing. These vehicles, which are illustrated in the examples, are ethylene glycol, formamid and glycerol.

We claim:

1. The method of polishing a non-thermoplastic resinous finish, which comprises subjectin it to the action of a polishing agent in an aqueous vehicle, the polishing agent consisting essentially of a hydrated calcium silicate having an average particle size below about 1 micron, and containing about 18% by weight CaO, 64% by weight SiOz, and 14% by weight combined water.

aeraeee 2. A polishing composition characterized by its ability to produce a haze-free, glossy surface on non-thermoplastic resinous finishes, which comprises an aqueous liquid polishing vehicle having dispersed therein a polishing abrasive consisting essentially of a hydrated calcium silicate powder containing about; 10% by weight (3210, 64% by weight SiOz, and 14% by weight of chemically combined water.

3. A polishing composition characterized by its ability to produce a haze-free, glossy surface on non-thermoplastic resinous finishes, which comprises an emulsion polishing vehicle, one phase of which is an aqueous liquid, said vehicle hav-