CA1201257A - Water and oil repellent coatings and method of making - Google Patents

Abstract

WATER AND OIL REPELLENT COATINGS
AND METHOD OF MAKING

ABSTRACT
Surfaces of inorganic or pigmented organic substrates are rendered capable of repelling water and oil by rubbing a gelatinous highly hydrated metal oxide uniformly over the surface to virtual dry-ness and then applying an organic combining compound.

Description

WATER ANV OIL REPELLENT COATINGS
AND METHOD OF MAKING

This Application is a Divisional of Serial Number 402,334 filed 5 May 1982.

This invention relates to the formation of water and oil re-pellent coatings on inorganic substrates. More particularly the inYen-tion relates to the formation on glass, ceramic, metal, porcelain,highly pigmented enamel, and other receptive substrates of coatings which are both repellent to water and oil and also resistant to abrasion.
The invention therefore finds utility in the coating and protection of lenses, windshields, ceramic tiles, metal and enameled pourîng spouts and the like.
Many types of water and oil repellent coatings have previously been described. Silicones and metallic soap are typical. Such coatings are easily removed by rubbing The present invention provides water and oil repellent coatings which are also resistant to abrasion and are self-healing, by a method involving first rubbing to uniform virtual dryness on the substrate an aqueous slurry of gelatinous highly hydrated metal oxlde to fonn an organic-receptive prime coat, and then applying over the prime coat a combining compound containing carbon atoms to provide water and oil repellency.
Examples of hydrated metal oxides most suitable for khe first application step include those of zirconium, aluminum, iron, tin, chro-mium and titanium. Those of nickel, cobalt and cerium provide useful but somewhat less effectiYe prime coats. All are best prepared by alkaline precipitation. e.g. with ammonium hydroxide, from aqueous so1utions of the metal salts. The precipitates are gelatinous and have been referred to in the literature both as oxides and as hydroxides, and also as containing indeterminate amounts of water of hydration.
They are applied as an aqueous paste or slurry, which ls rubbed uni-~orm1y over the surface of the substrate until the water content isevaporated and/or absorbed and the surface is Yirtu~lly dry.
The presence of trace amounts of an innocuous lubricant such as a polyethylene glycol in the slurry aids in keeping the oxide in suspension, reduces the physical drag experienced during the nearly dry to dry rubbing stage while applying the oxide to the substrate, and improves the uniformity of the coating, but is not essential.
When applying the metal oxide layer to a surface by hand, it has been found that d slowly absorbent type of applicator with la-tively open structure is desirable. Clean cotton balls or padding aregood examples of a preferred material. More dense and highly absorbent materials, such as paper toweling, do not work as well in most instances.
The slower wAter absorbing rate of the cotton allows a longer period of application through the critical nearly dry to dry rubbing stage. The open structure of the cotton prevents buildup of excess oxide particles which might cause streaking or scratching. For machine application9 a rotating bristle brush has given good results, with brushing again being continued until all the visible water has evaporated and the surface is clean and dry. Rubbing or brushing is continued until the surface sheen, normally visib'le under reflected light, is ready to disappear, i.e. the coating is virtually dry.
Materials for the second application step include a very large number of compounds. Included are alcohols, ketones, hydrocarbons, halogenated hydrocarbons, fatty acids, fatty acid salts, animal oils, silicones, siloxanes, fluorocarbons. They may be applied in any conven-ient manner, as by dipping, rubbing, spraying, brushing, or exposure to vapors. Normally solid materials may be applied in solution or disper-sion, or by rubbing, followed by heating if desired.
The coatings of this invention are extremely water repellent and resist prolonged soaking even in sea water. They exhibit substan-tial repellency toward oil and grease, making such contamination easy to remove. They show a high resistance to abrasion, and an unexpected self-healing property. For example, if the organic second coating should accidentally be removed, e.g. by abrasion or chemical action, the affected area is found rapidly to regain its repellency on subsequent contact with soap, motor oil, skin oil or other appropriate organic substance.
Water repellency is indicated by a high angle of water drop contact as well as by the tendency of water to run off or to collect in droplets when poured or sprayed on the surface. Oil repellency is indicated by d tendency for a light oil, such as "3-in-1" lubricating oil, to quickly congeal into small beads when rubbed onto the surface.
Brief contact of the second coating material with the dry first coating is adequate in most instances to develop signlflcant water re-pellency. Repellency may be improved in many cases by curing or aging for a short time at moderately elevated temperatures or for somewhat longer periods at lower temperatures after the second coating has been applied.

~S~ 7 Although the coatings are highly abrasion resistant, it has been found possible to remove them, for example from flat glass plate test panels, by prolonged vigorous rubbing with a mild abrasive such as a slurry of ~325 mesh calcium carbonate powder applied with a motorized lamb's wool polishing pad. Similar technlque slerves as the basis for a test method useful in comparing various coatings for abrasion resistance.
About 1/2 gram of a slurry containing 7-1/2 grams of "atomite" Fine cal-cium carbonate powder in 100 grams of water is applied to the test panel and rubbed with a 3x3 cm. velour pad carrying a load of one kg. and re-ciprocating through a stroke of 6.3 cm. at 100 cycles per minute. Thetest is carried to the point at which the first visual evidence of perma-nent wetting occurs at the surface, indicating localized complete removal of the oxide coating. "Atomite"*2.5 micron mean particle size calcium carbonate is a product of Thompson, Weinman and Co.
Example 1 To an aqueous solution of zirconium oxychloride is added ammo-nium hydroxide ln slight excess, with formation of an insoluble gelatinous precipitate of highly hydrated zirconium oxide. The precipitate is re-covered by vacuum filtration and preferably washed free of water-soluble materials. The mushy or paste-like filter cake contains approximately seven percent of material not volatilized (NVM) in four hours in a 250 F. oven. A 27 gram portion is diluted with 23 ml. of water to a barely flowable consistency. The resulting suspension contains, by calculation, four percent of non-volatile matter and represents a preferred dilution.
A two gram portion of the diluted slurry is transferred to the surface of a 20 x 20 cm. clean glass plate and rubbed uniformly over the surface, using a cotton ball and continuing the rubbing until the surface appears dry and all streaks are removed. At this point the surface is optically clear and may be easily wet with water.
The treated surface is next wiped with a cotton ball which has been dipped in a solution of one gram stearic acid in 100 gm. methanol.
The surface is kept wet with the solution for 1-1/2 to 2 minutes. The panel is allowed to dry for about 20 - 30 minutes and ls then washed with soap and water to remove any surplus stearic acid, rinsed, and again allowed to dry. The treated surface is now non-oily, has a very smooth and slick feel when rubbed with a dry cloth or tissue, and is water and oil repellent and abrasion resistant. In the rub test, conducted within 3 or 4 hours af$er completion of the treatment it withstands 400 to 450 cycles.
*Trade mark Other panels are treated in the same manner but with the hy-drated oxide at other concentrations, and both with and without an added polyethylene glycol lubricant9 in this case methoxypolyethylene glycol of 5000 mol. wt. In all cases the coatings show excellent water and oil repellency. The resistance to abrasion is maximized at the 3 to 5X
NVM level and at that level is not affected by the addition of the lubri-cant. However at lower concentrations of the oxide, and at much higher ratios of lubricant to oxide, the resistance to abrasion is markedly dimished.
%NVM 7 4-4 3.6 3.6 2.9 2.2 1.4 %PEG O O O .13 .15 .16 .2 cycles 250-300 300-350 300-350 350 175 50 30 Other gelatinous highly hydrated metal oxides and mixtures are prepared from solutions of the reactants noted, and are applied, treated and tested in the manner described under Example 1, to provide water and oil repellent coatinys with abrasion resistance as indicated in the following Examples. All proportions are by weight.
Ex. Metal_salt(s) PrecipitantRub test, cycles

2 3 - ZrOC12.8H20 2.4 - CrC13.6H20 NH40H 400-450

3 Fe(N3)3 9H2 250-300 3a FeC12.4H20 NaA12 3H2 100-150

4 AlC13 6H2 NH40H 350 SnC12.2H20 350-400 6 SnCl~.5H20 " 150 7 CrC13 6H2 " 450 B TiC14 " 75-100 9 Zrcl2 8H2 NaA12-3~2 300 3 - ~rOC12.8H20 1.7 - SnC12.2H20 NH40H 125 11 ~n~03)2.6H20 K2SnO3-XH20 125 12 3 - ZrOC12.8H20 2.2- AlC13.6H20 NH40H 300 ~2~ ;7 Ex. Metal salt~s)Precipitant Rub test, cycles 13 3 CrC13 6H20 2.3-FeC13.6H20 NH40H 350 14 3 - ZrOC12.8H20 2.4-CrC13.6H20 " 450 Using the procedures described under Example 1, a number of representative second coatings are applied over the hydrated zirconium oxide first coat. After the final drying, the panels are heated for 45 minutes at 250F. They are again washed and are then tested in the rub test with results as listed. All are water and oil repellent.
E Second coat Rub test cycles isopropanol 150 16 methanol 225 17 acetone 225 18 methyl ethyl ketone 200-225 19 carbon tetrachloride 150 trichloroethane 200-250 21 linolenic acid 125 22 oleic acid 125-150 20 23 mineral oil 75 24 100- trichloroethane, 1- stearic acid 225 100- trichloroethane, 1- paraffin 200 26 25- acetone, 75- methanol 250 27 100- methanol, 0.4- sodium stearate 150 28 Stoddard solvent 100-125 29 30- propyleneglycol, 20- propanol, .25- stearic acid 300 30- propyleneglycol, 20- methanol 200 31 30- propyleneglycol, 20- methanol, .25- ammonium stearate 225 32 30- propyleneglycol, 20- methanol, .25- myristic acid 275 33 100- MK, 1- dimethylsilicone 300 34 100- trichloroethane, 1- dimethylsilicone 125 35 35 fluorocarbon oil 75 36 100- MEK, 1- dimethylsilicone 200 37 stearic acid powder 200 38 cetyl alcohol powder 100-125 39 ammonium stearate powder 300 -,:

%~i;7 Ex. Second coat Rub test?_cycles potassium stearate powder 125-150 41 propyleneglycol, propanol, stearic acid vapor 300 As before noted the zirconium oxide first coat is of itself easily wet with water. After curing for 45 minutes at 250F. it is somewhat water repellent but fails in the rub test after only d few cycles.
Applied directly to a clean glass surface, the methanol-stearic acid solution provides poor water repellency and fails immediately in the rub test. The mixture of dimethylsilicone and methyl ethyl ketone under the same conditions provides moderate water repellency but fails after five cycles in the rub test. A monomeric silane, "Silane 8-5479"
of Dow Corning Corp., said to form a water repellent surface on glass, is much more resistant but fails after only 50 rub test cycles. These silicone single coat systems, while showing some water repe11ency, were noticeably poorer in this respect than either the silicone or stearic acid so7ution applied as a second coat over the hydrated metal oxide first coat. The repellency observations included a noticeable Jifference in the water drop contact angle as well as in water runoff.
It has been emphasized hereinbefore that the hydrated metal oxide coating must be applied by rubbing to virtual dryness prior to application of the organic combining coat. However, it has surprisingly been found possible to combine the two coating compositions and apply the mixture successfully in a single operation, as will now be described.
Example 42 Gelatinous highly hydrated zirconium oxide, 7% NYM 24 water 75 mica powder 15 delaminated kaolin 15 stearic acid 6 methoxypolyethylene glycol 0.15 The well blended and stably emulsified mixture is applied in the manner described for the hydrated metal oxide in Example 1, i.e. by rubbing a small portion uniformly over the clean glass substrate surface using cotton balls or pads. After being rubbed to virtual dryness, the surface is found to be water and oil repellent and resistant to abrasion.
In probable explanation, it appears that the stearic acid is more strongly attracted to, or has a greater affinity for, the inorganic suspending agents than to the glass or the metal oxlde while the water ~2~ ;7 !

is still present. During removal of the water, the attraction is lessened until the acid combining agent is released to interact with the completed oxide coating and impart the desired repellency.
The same technique has been found effective with other hydrated metal oxides, e.g. aluminum oxide and a mixture of zirconium and chro-mium oxides, and with talc as the inorganio particulate suspension agent.
These single application systems have produced well bonded water repel-lent coatings on glass, glazed porcelain or ceramic insulators, and on painted automobile bodies.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1, A fluid coating composition useful in applying a water and oil repellent and abrasion resistant surface layer to a receptive sub-strate by a single step method involving uniformly rubbing the composition to virtual dryness onto the substrate surface, said composition being an aqueous suspension of components comprising a gelatinous highly hydrated metal oxide, an inert particulate suspension agent, and a combining com-pound containing carbon atoms and having an affinity for said suspension agent.

2. A coating composition useful in forming an oil-repellent transparent surface finish on smooth clean glass surfaces by a process involving rubbing the composition over said surface until substantially completely dry, said composition comprising: water; a hydrous oxide of a metal selected from the class consisting of zirconium, aluminum, iron, chromium, tin, titanium, and mixtures thereof; an inert absorbent parti-culate material, to which stearic acid has a strong affinity in the presence of water, selected from the class consisting of talc, mica, delaminated kaolin, and mixtures thereof; and a water insoluble organic material adapted to combine with the oxide and comprising stearic acid.

3. Composition of claim 2 wherein is included a lubricity additive of methoxypolyethylene glycol, propylene glycol, or a mixture thereof.

4. Composition comprising a gelatinous highly hydrated metal oxide, a combining compound containing carbon atoms, and an inert particulate suspension agent having an affinity for said compound in presence of water, in an aqueous slurry.

5. A slurry of gelatinous highly hydrated metal oxide having enhanced rubbing characteristics when applied to a substrate by rubbing to virtual dryness, said slurry containing a polyethylene glycol in an amount not greater than about 0.2% of the aqueous vehicle and sufficient to impart improved lubricity to said slurry.