US2315347A - Coating composition - Google Patents

Description

Patented Mar. 30, 1943 COATING comrosrnon Walter K. Moflett, South River, N. 3..

EJ. du Pont de Ncmours & Company, Wilmington, Del., a corporation of Delaware Application July i2, 19s9,

' No Drawing.

assignor to Serial No. 284,094 8 Claims, (01. 260-16) This invention relates to improved coating compositions and more particularly to cellulose nitrate coating compositions which are to discoloration from contact with oils and greases.

Recent advances in the development of cellulose nitrate enamels for automotive and industrial finishing fields and especially for-the finishin of automobiles have provided outstanding improvements in general durability and more particularly in the "elimination or reduction in chalking tendencies, a deficiency generally encountered in the earlier finishes when exposed to the atmospher'ic elements. This defect has been largely overcome through the use of special'or specially treated pigments on specific types of vehicles. However, in certain instances, these finishes which exhibit superior chalk resistance have proven to be defective in their resistanceto "oil spotting" or discoloration when mineral oils or reases are broughtin direct contact therewith.

This defect is particularly significant and more frequently encountered in automobile finishes where grease and oil may inadvertently come in contact with the finish from overhead conveyor systems used in assembling the car or during servicing and lubricating of the automobile before or after delivery to the consumer. The new hypoid gear lubricants are quite injurious in this respect. Oilspotting is also sometimes caused by the oil-containing rubbing compounds employed in conventional rubbing operations performed after application of the coating composition to bringout high lustre in the finish. Discoloration from this source is particularly a parent when the rubbing compound is permitted to remain on the finish during temporary shutdown periods.

The effect of such all or grease on the finish is not a softening or destructive action on the film but rather an unsightly discoloration which increases in intensity on exposure to light and which is especiallypronounced in the light colored finishes, including metallicFflnishes consisting of low pigmented enamels containing finely ground aluminum, which are, generally popular at the present time. The effect seems highly resistant I chalk resistance.

composition which affords a finish highly to "oil spott or discoloration from contact with mineral oils and greases. Another object of the invention is the provision of a cellulose nitrate coating composition which afiords a finish durability including superior excellent outdoor further object is the provi- I sion'oi a cellulose nitrate coating composition which affords a finish that may be readily rubbed and polished. A still further object is the provi sion of a cellulose nitrate coating composition which ailords a finish that is adherent, flexible and substantially non-thermoplastic under a buffing wheel.

These objects are accomplished by means of a composition which is normally non-gelling, com

to be permanent since it cannot beremoved'by' any known cleaning or polishing means without removing excessive amounts of the finish film and, thereiore presents a serious problem in the finishing of surfaces which may be exposed to contact, with mineral oils and greases. v

This inventiomtherefore, has as a primary obiect the provision of a cellulose nitrate coating prising cellulose nitrate, certain non-drying vegetable oil modified alkyd resins and an aliphatic dicarboxylic acid.

Some oi the aforementioned acids have been proposed as gel inhibitors in cellulose nitrate compositions which normally tend to gel rapidly during shelf storage, particularly in basic pigments such as zinc oxide. These compositions may include also certain vegetable oil modified alkyd resins which increase gelation tendencies probably because of a high acid hum her or because they are modified with an oxidizing oil such as linseed oil.

In contra-distinction, the present invention is directed to cellulose nitrate compositions which do not'normally gel in the complete absence or an for any inhibiting agent. However, an entirely un- 45,-'expected and important improvement is now made available through the use of the aforementioned acids for the express purpose ofv providing e. finish which is highly resistant to discoloration from mineral oils and greases, a desirable property which bears no relation whatsoever to gelation tendencies. a

The preferred embodiment of the invention is illustrated by the following examples which are not intended to limit the invention except as indicated in the appended claims, since variathe presence of tions will occur to those skilled in the art without departing from. the spirit and scope thereof.

The malic acid solution consisted of a 30% solution of malic acid in denatured ethyl alcohol.

The resin solution oi. the above example consisted of a mixture of 30 parts of toluol and 70 parts of a synthetic resin which is a reaction product Per cent Giycerine 18.2 Phthalic anhydride 36.6 Coconut oil 47.2

This resin was prepared by first heating the glycerlne and coconut oil at a temperature between 380 and 400 F. until a homogeneous solution was obtained. The phthalic anhydride was then added and heating continued at about 480 F. until an acid number oi 5-6 was obtained.

The charge was blanketed with carbon dioxide during the preparation of the resin.

The enamel composition of Example 1 which contains cellulose nitrate, resin, plasticizer and malic acid in the ratio of parts by weight of cellulose nitrate, 9 parts by weight oimodified alkyd resin, 2.5 parts by weight of plasticizer, and 0.23 part by weight of malic acid, was prepared by first dispersing the pigment in a cellu lose nitrate colloid adjusted to a suitable consistency by the addition of solvents and diluents by a kneading treatment described in U. S. Patent 2,052,470. This pigmented intermediate was then placed in an agitator mixer together with the remaining ingredients including the synthetic resin and malic acid solutions, and the mixture thoroughly agitated until a homogeneous enamel product was obtained.

Erample 2 I Per cent by weight Cellulose nitrate (low viscosity) 13.1 Ethyl alcohol (denatured) 6.9 Chrome yellow pigment 12.0 Isobutyl acetate 14.4 Methyl ethyl ketone 19.5 Petroleum naphtha (till-129 C.) 5.1 Ethyl acetate 6.4 Isobutyl alcohol 5.0 Malonic acid solution 1.0 Castor oil 2.9 Dibutyl phthalate 4.3 Synthetic resin solution 9.4

The enamel composition of Example 2 which contains cellulose nitrate, resin, softener, and

m-alonic acid in the ratioof 10 parts by weight of cellulose nitrate, 5 parts by weight of modified alkyd resin, 3.3 parts by weight of plasticizer and 0.23 part by weight or malonic acid, was prepared in accordance with the procedure described for Example 1.

The viscosity characteristic of the cellulose nitrates utilized in the examples was about 3 seconds as determined in accordance with A. S. T. M. Specifications D-301-33T, Formula 3.

In order to determine whether a finish is reslstant to oils and greases an arbitrary test was devised which consists of soaking a felt pad one inch square and 1 inch in thickness with a heavy automotive transmission 011, preferably a hypoid gear lubricant and placing this oil-soaked pad on the surface 01 a finished panel for 24 hours atroom temperature. The pad is removed and excess oil wiped oil with a dry cloth or with a cloth wetted with petroleum naphtha. The, finish is then examined for discoloration. A

short exposure to direct sunlight seems to accentuate the discoloration if any is present.

The application of this test to finishes prepared byspraying 3 coats suitably thinned of the compositions of Examples 1 and 2 on steel panels primed and surfaced with conventional undercoats failed to show any discoloration whatsoever, whereas finishes prepared in the same manner with compositions in which no malic acid or equivalent described herein was included an i which were otherwise identical with the composi-- tions of Examples 1 and 2 showed serious disv coloration.

The aliphatic dicarboxylic acids both unsaturated and saturated including hydroxy acids of this class, appear to aflord the desired results of markedly reducing or completely eliminating discoloration from oils and greases in'the com- Positions of the present invention. Malic, malonic, maleic, tartaric, adipic, succinic. and oxalic are exemplary of the types of acids which have been found suitable. Malic and malonic acids are particularly effective. Phthalic acid, an arcmatic dicarboxylic acid, or its anhydrlde, is also of utility although somewhat less effective than malic or malonic acid.

Other methods 01 dispersing the pigment in the vehicles of the invention may be employed 11 desired such as by grinding in ball mills, roller mills,

buhrstone mills or from pigment pulps-according' to the process described in U. S. Patent 2,110,745.

In order to provide a superior enamel which maintains highest chalk resistance combined with resistance to mineral oils and greases when the dicarboxylic acids or the present invention are included and which aflords satisfactory working properties, the resin should be modified with from not less than to not more than 60% and prererably with from 40 to of coconut oil or similar non-gelling, nonhydro non-drying oil such as cottonseed or with blown oils of these types. Compositions containing alkyd resins modified with hydroxy oils, such as castor oil,

are not preferred in the present invention because oi the poor durability and reactivity with reactive type pigments which are imparted to :ellulose nitrate coating compositions by such modified resins.

Inany event, the non-gelling, non-drying oil modified alkyd resin must be prepared so that the acid number is kept as low as possible, preferably not mor than 5 or 6 and, in any event, should be kept below 10. Resins of substantially higher acid number have a. tendency to gel and also cannot be used with reactive type pigments such as 7 zinc oxidebecause ofpoor stability of the compositionsduring store-seas evidenced by gelling and/orthe'formationof grit. Such reactive type pigments as referred to in the trade indicate pig- .ments which chemically react with the liquid or solid. ingredients in the composition in which they are incorporated.

Optimum resistance to oil spotting combined with maximum durability including superior chalk resistance are obtained when the cellulose nttrate aik'yd resin-plasticizer ratios and the non-gelling, non-hydroxy, non-drying vegetable oil modified alkyd resin compositions which include the commonly used pigments or other coloring matter such as antimony oxide, titanium dioxide, titanate, pigments, iron blue pigments.

' chrome pigments, para and toluidine toners, ma-

amount of dicarboxyiic acid employed are kept within definite limits. These ratios should be such that for each 10 parts by weight of cellulose nitrate. the amount of alkyd resin is kept below 10 parts but not less than about 5 parts. If the roons, carbon black, ultramarine blue, burnt umber, iron oxide, etc. If zinc oxide, a basic type pigment, is employed to any considerable extent 'inthe compositions of the present invention, little if any improvement in resistance to oil-spotting is obtained by the use of the above described dicarboxyiic acids which are otherwise so outstandingiy effective. The invention is particularly valuable when employed with the light colored socalled pastel shade andmetallic enamels which proportion of alkyd resin to cellulose nitrate is increased by a small amount as. for instance, to 1 part of alkyd resin to 1 'partof cellulose nitrate,

the compositionswhile possibly useful for some industrial purposes even with somewhat higher proportions of the modified alkyd resin, are of no value practically for the present primary purpose of finishing automobiles because the conventional sanding, rubbing and polishing operations employed in this industry cannot be satisfactorily practiced. The amount of plasticizer is about 2 parts when the maximum quantity of resin is used and about 5 parts when'the minimum amount of resin is used.

These acids are preferably incorporated in an amount between 0.2% and 2.0% based on the a total weight of the composition to be treated. In

most cases an amount of between 0.2% and 0.6% is quite effective, particularly in the case of the more preferred acids, namely, malic acid and malonic acid. Excessive proportions are to be avoided since in such cases there may be a tendency for the acid to exude on the surface of the widely used in the art, and many other equivalent materials may be satisfactorily substituted therefor. Suitable solvents and 'diluents include esters of lower fatty acids. for example, ethyl acetate,

butyl acetate, amyi acetate, isobutyl acetate, butyl proplonate and the like, ketones such as methyl ethyl ketone, alcohol ethers and their esters, such as ethylene glycol monoethyl ether acetate and ethylene glycol monomethyl ether acetate. lower aliphatic alcohols and aliphatic and aromatic hydrocarbon diluents such as petroleum naphtha and toluene. v

The plasticizers and softeners which may be I employed in the compositions of the present invention include conventional materials such as castor oil, blown castor oil, aryl sulfonamides including ortho, meta and para toluene ethyl sulfonamides and mixtures of these, aryl and alkyl esters of phosphoric acid, dibutyl tartrate, di-

cyclohexyl phthalate, diethyl phthalate and the phthalate esters of ether alcohols, such as the phthalate, ester of ethylene glycol monomethyl ether.

The invention is operative for cellulose nitratehave been a considerable source of complaint in the previously available enamels because of poor resistance to oils and greases where discoloration is more pronounced.

Although phthalic anhydride is the preferred acid radical in the alkyd resin ingredient of the improved compQsitionsother'acids such as succinic, malic, adipic, maleic, sebacic, etc may be substituted wholly or in, part for the phthalic anhydride, but best results are secured when phthalic anhydride is present in preponderant proportionss J Suitable resins for the improved compositions may also be prepared using other poiyhydric alcohols including ethylene glycol and higher homologs, diethylene g ycol and other polyslycols;

polyglycerols; pentaerythritol and sorbitol.

The compositions of the invention are generally useful in finishing surfaces which may be exposed to direct contact-with oils and greases. They are particularly useful for finishing automobiles where contact with lubricating o ls and greases and oil-containing rubbing compounds is more frequently encountered.

The new compositions have shown a number of important advantages when employed in the suggested utilities. In the first place, they have exhibited an unexpected and decisively superior resistance to spotting or discoloration of the finish from oily rubbing and polishing compounds and from direct contact with oils and greases which sometimes reach the finish of an automobile through careless servicing of the car before or after delivery to the customer. This defect of "oil spotting was quite common in commercial finishes heretofore'available and caused frequent consumer complaint and costly rejections in the final inspection in the manufacture of new automobiles. Furthermore, the new compositions are adherent andfiexible and afford excellent durability, including superior resistance to chalking,

thus preserving the original gloss and lustre for extended periods during exposure to atmospheric conditions. The enamels of the present invention provide finishes of satisfactory working properties which do not become thermoplastic or soften under the rubbing and polishing operations normally practiced in the automotive industry. The satisfactory working properties of the improved compositions as controlled by the particular proportions previously indicated are of considerable importance inasmuch as previously known compositions containing related'ingredicuts are usually quite defective. in this respect,

making them entirely unsuited for the'present purpose. Substantial economies are represented in the new finishes in that assembly line rejections and consumer complaints necessitating touching up or refinishing of automobiles because of oil spotting" discoloration are practi' cally eliminated.

As many widely different embodiments of the invention may be made without departing from the spirit and scope thereof, it will be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

l. A coating composition which is highly resistant to oils and greases consisting of (A) a normally non-gelling coating composition containing cellulose nitrate and a non-gelling, nonhydroxy, non-drying vegetable oil modified alkyd resin characterized by an acid number or less than 10 and (B) in addition-thereto an aliphatic dicarboxylic acid in the proportions of between 0.2 and 20% by weight of the total coating composition.

2. Composition of claim 1 in which the aliphatic dicarboxylic acid is malic acid.

3. Composition of claim 1 in which the aliphatic dicarboxylic acid is malonic acid.

4. The composition of claim 1 in which the alkyd resin is modified with from 85 to 60 per cent of the non-hydroxy, non-drying vegetable oil.

5. Composition of claim 1 in which the alkyd resin is modified with coconut oil.

6. Composition of claim 1'in which said modified alkyd resin is a glyceryl phthalate resin.

'7. Composition of claim 1 in which the aliphatic dicarboxylic acid is present in an amount of about 0.5% by weight of the total coating composition.

8. A normally non-gelling, weather-resistant cellulose nitrate coating composition which is highly resistant to oils and greases consisting of (A) a normally non-gelling composition containing cellulose nitrate, a plasticizer, an alkyd resin modified with 35-60% of a non-hydroxy, nondrying vegetable oil, said resin having an acid number of less than 10 and being present in said composition in a proportion by weight of at least 5 parts as a minimum but less than 10 parts as a maximum for each 10 parts of cellulose nitrate, said plasticizer being present in the proportion by weight of about 2 partsvas a minimum and 5 parts as a maximum and (B) in addition thereto an aliphatic dicarboxylic acid in the proportion of between 0.2 and 2.0% by weight of the total coating composition.

' WALTER K. MOFFETT.