US3544349A

US3544349A - Method of protecting finished surfaces

Info

Publication number: US3544349A
Application number: US693135A
Authority: US
Inventors: Robert A Isaksen; Robert V De Shay
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1967-12-26
Filing date: 1967-12-26
Publication date: 1970-12-01
Anticipated expiration: 1987-12-01
Also published as: FR1600974A; GB1257919A; DE1816980A1

Description

'U.S. Cl. 1176 United States Patent Officc 3,544,349 Patented Dec. 1, 1970 3,544,349 METHOD OF PROTECTING FINISHED SURFACES Robert A. Isaksen and Robert V. De Shay, East Longmeadow, Mass., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Dec. 26, 1967, Ser. No. 693,135 Int. Cl. B44d 1/14; B32b 15/08 Claims ABSTRACT OF THE DISCLOSURE Disclosed herein is a method for the temporary protection of surfaces coated with a permanent cured resin system. The temporary coating is applied at a time when the permanent coating is less than fully cured. The temporary coating comprises a blend of two interpolymers: the first, an interpolymer comprising an ethylenically unsaturated monoor poly-carboxylic acid containing from 3 to 6 carbon atoms and a vinylidene ester of a saturated aliphatic acid, said saturated acid containing from 1 to 6 carbon atoms; the second, a vinylidene aromatic hydrocarbon and an alpha-beta ethylenically unsaturated dicarboxylic acid, its anhydride or half-ester and mixtures thereof. Preferably, the first interpolymer is comprised of vinyl acetate and crotonic acid and the second interpolymer is comprised of styrene and a half-ester of maleic acid. When no longer needed, the coating is removed from the finished surface by washing with an aqueous alkaline solvent.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a method of protecting a substrate coated with a permanent cured resin system with a temporary coating applied while the permanent coating is in a less than fully cured condition. The temporary coatings exhibit excellent toughness, hardness and moisture resistance and can be removed when no longer needed with an aqueous alkaline detergent solution.

Description of the prior art A perennial problem among manufacturers of finished goods is the method by which these goods may be delivered to the distribution points and arrive there in essentially the same undamaged condition they were in when they left the factory. It is the alleviation of this problem, of course, that provides the basis for the whole packaging industry. Certain goods, however, because of their size, bulk or shape, do not lend themselves readily to normal packaging procedures. This problem is particularly acute in the automobile industry where automobiles must be shipped by truck or rail substantial distances from the assembly plants to dealers showrooms. In transit they are continually subjected to surface damage from dirt, corrosive atmospheres, flying pebbles, salt spray, water, ice, etc. Putting each unit into a large, wellpadded box similar to those in which large household appliances are shipped would undoubtedly solve this problem, but the increased shipping costs brought about by the immobilization of the automobile, i.e., it could not be driven onto the truck or railroad car, would be prohibitive. In the past, it has been the practice to coat the finished automobile with a microcrystalline wax for protection of the finish in transit. These waxy coatings have, however, exhibited some undesirable qualities. First, they are sprayed onto the unit to be protected from dispersion in organic solvents. These expensive solvents are lost in the process, adding to the cost of the operation. Further, money must be expended to protect the personnel involved from the solvent fumes. In addition, the presence of the organic solvents presents problems during the application of these coatings to the so-called green automotive enamels. By green enamel is meant one that is less than fully cured. Where organic solvents are present, it is necessary that the permanent enamel be fully cured before application of the temporary coating in order to preclude the possibility of undesirable side reactions between the solvents and the enamel. The advantage to being able to coat a green enamel is one of time-saving in the assembly process and, as a consequence of this, reduced cost. Second, the waxy coating easily picks up and retains dust and dirt. This is particularly undesirable for two reasons: (1) the dirt particles will be present during the coating removal step at the dealers showroom and can scratch or mar the finish during the process; (2) the exposure of the automobiles to the eyes of the public while they are being transported across the country is a valuable form of advertising. It is important to the manufacturer that his products present as attractive an appearance as possible during such exposure. The waxy coatings now used detract from the smoothness and glOSS of the automotive finish and together with the dirt that quickly becomes embedded in them present a most shabby appearance. Finally, when the car arrives at the dealers, a great deal of time and eifort must be expended in removing the waxy coating. A special soap to which has been added an organic solvent is required. Thus, costs are again increased. Therefore, a need exists for a protective coating which can be easily and cheaply applied to the less than fully cured enamels at the factory, which will enhance the appearance of the car or other article during transportation, rather than detract from it and which may be quickly and easily removed at the destination with a minimum of effort and cost.

SUMMARY OF THE INVENTION According to the present invention, a method is provided whereby surfaces coated with a permanent cured resin system are protected by the application thereto of a temporary protective coating based upon a blend of two interpolymers; said coating being hard, tough and water resistant and capable of being removed from the substrate when the need for it no longer exists, by Washing with an aqueous alkaline solution. More particularly, the present invention relates to a method by which substrates are coated with a curable resin system, are partially cured either at room or elevated temperatures and then, before curing is complete, are further coated with a blend of: (A) 5-95 by weight of a first interpolymer comprising: (1) about 0.5 mole percent to about 20 mole percent of an ethylenically unsaturated monoor poly-carboxylic acid containing 3 to 6 carbon atoms, and correspondingly, (2) about 99.5 mole percent to about mole percent of a vinylidene ester of a saturated aliphatic acid, said saturated acid containing 1 to 6 carbon atoms; and correspondingly, (B) 5% by weight of a second interpolymer comprising a vinylidene aromatic hydrocarbon and an alpha-beta-ethylenically unsaturated dicarboxylic acid monomer, its anhydride or half-ester with a l18 carbon atom monohydric alcohol and mixtures thereof.

The interpolymers may be blended by any of the several methods well known in the art. The preferred method of blending the two interpolymers for low cost and ease of handling is to dissolve them with stirring in a solvent system in which both are soluble. The use of water containing a small amount of ammonia has been found particularly advantageous. It has further been found advantageous to add a small quantity of a miscible aliphatic alcohol as an aid incontrolling the solution viscosity. The particular alcohol to be used and the quantity in which it will be present is not critical, but will be determined by the particular case and the ends sought to be achieved.

It is, therefore, an object of the present invention to provide a method for the protection of substates having at least one finished surface.

It is a further object of this invention to provide a method for the protection of substrates having at least one finished surface by applying thereto coatings which may be fully removed from the substrates by washing with an aqueous alkaline solution.

. It is a further object of this invention to provide a method for the protection of substrates having at least one finished surface by applying thereto coatings which exhibit toughness, hardness, and resistance to moisture and dirt.

It is a still further object of this invention to provide a coating which may be applied to an uncured enamel.

These and other objects may be readily appreciated by those skilled in the art byIeference to th following description of the preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 'The above and other objects of this invention are accomplished by first applying to a substrate a coating composition capable of being cured. These curable coatings are well known in the art and the particular one to be used will depend upon the circumstances in the individual case. For example, in the automobile industry a melamine-acrylic enamel is commonly used. Other permanent-type curable resins which are operable within the scope of this invention, include, for example, phenolics, polyurethanes, melamine-formaldehyde resins, ureaformaldehyde resins, maleic adducts of fatty acid esters of styrene-'allyl alcohol copolymers, etc. This permanent coating is then partially cured, curing conditions being dependent upon the particular coating chosen. In most cases, partial curing will be carried out at elevated temperatures after a short period of air drying. As is Well known in the art, the air drying permits evaporation of volatile solvents which could cause bubbles in the finished coating, and use of elevated temperatures permits a faster rate of cure. The coatedsubstrate is then cooled at least to a point below the boiling temperature of the solvent system of the temporary coating to -be applied. Next, and before the permanent coat has completely cured, the temporary coating is applied. This temporary coating is based upon a blend of two interpolymers. The first interpolymer comprises about 0.5-mole percent to about 20 mole percent of an ethylenically unsaturated monoor poly-carboxylic acid containing 3 to 6 carbon atoms, and correspondingly, about 99.5 mole percent to about 80 mole percent of a vinylidene ester of a saturated aliphatic acid, said saturated acid containing from 1 to 6 carbon atoms. This first interpolymer is limited to resins that are soluble in aqueous alkali. For ready solubility, it is necessary to use an interpolymer having at least 0.5 mole of unsaturated carboxylic acid for every 99.5 moles of vinylidene ester. Owing to the solubility restriction, the saturated organic acid forming the vinylidene ester is limited to one containing 1 to 6 carbon atoms. The more preferred range is from 2 to 4 carbon atoms for reasons of easy solubility and convenient polymerization rates. Examples of these acids are formic, acetic, propanoic, butanoic, pentanoic, hexanoic acids, their isomers and mixtures thereof. For the same reasons as above, the unsaturated acid in this interpolymer is limited to monoor poly-carboxylic acids containing 3 to 6 carbon atoms. A more preferred range for ease of solution and polymerization is 3 to 4 carbon atoms. Examples of these acids are acrylic, methacrylic, crotonic, isocrotonic, 3-butenoic, angelic, tiglic, senecioic, hydrosorbic, alpha-methylene butyric, maleic, fumaric,

glutaconic, etc. The most preferred interpolymer is one of vinyl acetate and crotonic acid, owing to the relative ease by which copolymerization may be carried out. The upper limit of the concentration of the unsaturated acid is about 20 mole percentabove this the interpolymer becomes undesirably water sensitive. For better adhesion, water insensitivity and convenient polymerization rate, acid concentrations ranging from 2 to 10 mole percent are more preferred. For the optimum in adhesion, aqueous-alkaline solubility, water insensitivity and commercially feasible polymerization rates, an acid concentration ranging from 3 to 5 mole percent is most preferred.

The second interpolymer is one of a vinylidene aro matic hydrocarbon with an alpha, beta-ethylenically unsaturated monomer selected from the group consisting of dicarboxylic acids, their anhydrides, their half-esters with 1-18 carbon atom monohydric alcohols and mixtures thereof.

The term vinylidene aromatic hydrocarbon should be interpreted to include alkyl and halogen derivatives wherein the alkyl or halogen groups are attached to the nucleus, or to the vinylidene group, or to both. Examples are styrene, vinyl naphthalene, alpha-methylstyrene, vinyl toluene, 2,4-dimethyl styrene, o-, m-, p-chlorostyrene, 2,5- dichlorostyrene, 2-methyl-4-chlorostyrene, etc.

Monohydric alcohols containing l-18 carbon atoms includemethanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, hendecanol, dodecanol, tridecanol, tetradecanol, ,pentadecanol, hexadecanol, heptadecanol, octadecanol, their isomers and mixtures thereof.

The ratio of one interpolymer to the other in the blend may vary over wide limits and still retain operability. The proportion of one interpolymer may vary from 5 to weight percent while the other interpolymer correspondingly varies from 95 to 5 weight percent. A one to one ratio of the preferred vinyl acetate/crotonic acid copolymer. to the preferred styrene/maleic half-ester copolymer has been found to exhibit the optimum in toughness, film forming characteristics, adhesion, hardness, water resistance, blocking resistance and ease of removal from the permanently coated substrate.

The following examples are presented in illustration of the invention and are not intended as limitations thereof. Where parts are mentioned, parts byweight are intended unless otherwise described.

Example I 85 parts of water, 1 part of 28% aqueous ammonia and 10.6 parts of SD-30 alcohol are introduced into a suitable vessel. (SD-30 alcohol is ethanol which has been denatured by adding 10 gallons of methanol to gallons of ethanol). To the solvent system is then added, with stirring, 2.5 parts of an interpolymer of vinyl acetate and crotonic acid wherein the crotonic acid constitutes 5 mole percent of the interpolymer and 2.5 parts of an interpolymer of styrene and a maleic acid half-ester; the ester having been formed from an 80/20 mixture of secondary butyl alcohol and methanol.

Example II T A 4 x 8 steel test panel is sprayed with a melamineacrylic enamel which is commonly used in the automotive industry for painting automobile bodies. The enamel is diluted to a viscosity of 18 seconds in a #4 Ford cup with a suitable solvent in order to insure ease of sprayability. Sufiicient paint is applied to provide, a film thickness of approximately 1 to 1 /2 mils when dry. The enamel is allowed to dry in the air at room temperature for 20 minutes. It is then baked for 30 minutes at 250 F. At this point it is not completely cured. The panel is removed from the oven and allowed to coolto a point at which it is still warm to the touch (approximately 60 C.). The cooling time is about 5-10 minutes. A 10% solids solution of the blend prepared in Example I is sprayed onto the warm panel, enough of the wet coating being applied to provide a /21 /2 mil thick coating when dry. The panel is then put back in the oven for 1 minute at 250 F. When dry, the panels are seen to possess an attractive deep gloss and a smooth hard surface. The panels are subjected to 100% relative humidity and a temperature of 100 F. in a humidity cabinet. The surface coating is found to be undamaged thereby. Finally, the top coating is easily removed by washing with an ordinary commercially available anionic household detergent dissolved in warm water.

Example III Part A.-2.5 parts of the vinyl acetate/crotonic acid interpolymer of Example I and 7.5 parts of the styrene/ maleic half-ester interpolymer of Example I are dissolved in 90 parts of SD- alcohol. After solution has been attained, 50 parts of 2-ethoxyethanol is added.

Part B.-Part A is repeated using 7.5 parts of the vinyl acetate/crotonic acid interpolymer and 2.5 parts of the styrene/maleic half-ester interpolymer.

Part C.-Part A is repeated using 10 parts of the vinyl acetate/crotonic acid interpolymer and no styrene/maleic half-ester interpolymer.

Part D.-Part A is repeated using 10 parts of the styrene/maleic acid half-ester and no vinyl acetate/crotonic acid interpolymer.

Part E.-The solution of Parts A-D are applied to partially cured enamel-coated panels as in Example II. The panels are subjected to accelerated weathering tests in a Weather-O-Meter. After the weathering, the coatings are removed from the substrates by washing with the detergent solution of Example H. It is found that films of Part A and Part B are easily removed from the substrates but that the films of Part C and Part D are very diflicult to remove, requiring much more time and effort. This shows that the coating systems of the present application are superior with respect to removability to systems containing only one of the components. As seen above, ease of removability is economically important to the distributor.

Example IV Examples I and II are repeated using 5 parts of a vinyl acetate/crotom'c acid interpolymer containing 3 mole percent crotonic acid and 95 parts of a styrene/maleic acid half-ester wherein the ester has been formed using 2- butoxyethanol. Results equivalent to those described in Example H are obtained.

Example V Examples I and II are repeated using 95 parts of the vinyl acetate/crotonic acid interpolymer of Example I and 5 parts of the styrene/maleic acid methyl half-ester. The film obtained thereby is found to be somewhat softer than that of Example I, but is still hard enough to be operable.

It is obvious, of course, that various additives such as plasticizers, pigments, dyes, fillers, extenders, wetting agents and the like may be added to these compositions without departing from the scope of this invention.

The process of this invention may be employed to protect the finished surfaces of such commercial products as automobiles, appliances, furniture, architectural structures, etc.

Although spraying has been the only method of application recited in the examples, any conventional method of coating application may be used, e.g. brushing, dipping, etc.

It is obvious that many variations may be made in the products and methods set forth above without departing from the spirit and scope of this invention.

What is claimed is:

1. A method for the protection of finished substrates which comprises:

(A) applying to the substrate a first coating comprising a curable resin system,

(B) partially curing said curable coating,

(C) applying to said partially cured first coating a second coating comprising a solution of a blend of:

(1) 595% by weight of a first interpolymer comprising:

(a) about 0.5 mole percent to about 20 mole percent of an ethylenically unsaturated carboxylic acid containing at least one carboxyl group and further containing 3-6 carbon atoms, and correspondingly,

('b) about 99.5 mole percent to about mole percent of a vinylidene ester of a saturated aliphatic acid, said saturated acid containing 1-6 carbon atoms, and correspondingly,

(2) 5% by weight of a second interpolymer consisting of:

(a) a vinylidene aromatic hydrocarbon and,

(b) an B-ethylenically unsaturated monomer selected from the group consisting of dicarboxylic acids, anhydrides of dicarboxylic acids, half-esters of dicarboxylic acids with alcohols containing 1-18 carbon atoms and mixtures thereof, and

(D) drying said second coating.

2. The method of claim 1 further comprising, after the final drying step, the step of removing the second coating by washing with an aqueous alkaline solvent.

3. The method of claim 1 wherein the ethylenically unsaturated carboxylic acid of the first interpolymer is crotonic acid.

4. The method of claim 1 wherein the vinylidene ester of a saturated aliphatic acid is vinyl acetate.

5. The method of claim 1 wherein the second interpolymer comprises styrene and a half-ester of maleic acid.

6. The method of claim 1 wherein the ratio of the first interpolymer to the second interpolymer is 1:1.

7. The method of claim 1 wherein the substrate is steel.

8. The method of claim 1 wherein the first coating is a melamine-acrylic enamel.

9. The method of claim 1 wherein the partial curing of the first coating is effected at elevated temperatures.

10. The method of claim 7 wherein the substrate is an automobile 'body.

References Cited UNITED STATES PATENTS 3,063,873 11/1962 Saroyan 1176 3,119,712 1/1964 Esswein 117-75 3,156,580 11/1964 Howard 117-75 3,262,807 7/ 1966 Sterman et al. 1176 WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner US. Cl. X.R.