US2752267A - Coating compositions and method of coating - Google Patents

Description

COATING COMPGSITHGNS AND METHOD OF COATING No Drawing. Application June 29, 1953, Serial No. 364,921

11 Claims. (Cl. 117--79) The present invention relates to novel coating compositions and, more particularly, to primers which are primarily adapted for, although not limited to, use in the application of hot coal tar coatings to steel pipe lines and the like.

Hot coal tar coatings which normally comprise pitch and a finely ground mineral filler are used extensively in coating underground pipe lines for all types of service. Sometimes, the pipe is coated in sections at a mill site and at other times in the field over the trench. In either case, however, the usual procedure is a two-step operation, first the application of a primer followed by a drying period of from three to twenty-four hours and then the application of the hot coal tar enamel to the dry primer.

The primer is ordinarily a cut-back of the same pitch or at least a pitch similar to the one used in the hot coating. The use of a primer is necessary to Wet the pipe thoroughly and to establish a good bond between the hot coating and metal. Without primer, the hot coating is chilled so rapidly on hitting the pipe, that it loses all fluidity and cannot form a satisfactory bond. With primer, the hot enamel possesses enough heat to soften the thin pitch film and fuse it into onecontinuous coating firmly bonded to the metal.

Generally speaking, the primers available today give adequate performance and serve the purpose for which they are intended. However, such primers do suffer from the disadvantage that they require a relatively long time to dry. This, of course, means that a great amount of time is wasted waiting for the primer to dry, so that the outer hot coal tar enamel might be applied thereto. Furthermore, when pipe sections are primed in the mill, the primed pipe sections must be stored, generally in special drying racks, thus requiring the use of substantial amounts of storage space and labor for handling.

As will be appreciated from the foregoing, there is" a definite need in the industry for fast drying primers, e. g., primers which dry sufiiciently to permit coating a pipe section with the hot coal tar enamel within just a few minutes after priming. Accordingly, the principal object of the present invention is to provide fast drying coating compositions which are especially and uniquely adapted for use as primers in the application of hot coal tar enamels to metal articles, e. g., steel pipe sections.

A further object of the invention is the provision of novel primers which are free from the disadvantages noted above in connection with conventional pitch primers and which permit substantial reductions in storage space, labor and time in the application of hot coal tar enamels.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit atent F 2,752,267 Patented June 26,. 1956 2 and scope of. the invention: will become apparent to those skilled in the art from this detailed description.

In order toincrease the drying characteristics of a paint or other coating composition, it: is usually conventional practice to: utilize a more volatile solvent than is normally included in the composition. However, this technique cannot be used. to modify conventional pitch primers. because of the incompatibility" of most volatile solvents with pitch. In addition, ahigh solvent content in pitch primers. causessludging and precipitation of the free carbon in the pitch. Accordingly, the. present fast drying primer compositions are substantially and uniquely different from the pitch primers generally in use today.

Broadly stated, the primer compositions of the. invention comprise chlorinated: rubber, heavy creosote and a volatile solvent for the chlorinated rubber; Such compositions have been: found. to give excellent bonds. between surfaces primed therewith and coal tar enamels over substantially wider temperature ranges, i. e;, about 5 F; lower and 20 F. higher than the conventionalv pitch cut-back primers- Intact, when working with the present primers, it has been noted that the surfaces coated there.- with and hot coal tar enamel are: extremely hard to remove, even at a temperature of 25 F. below zero. In contrast, ordinary enamels and cut-back pitch primers shatter off in large sheets at this temperature. Furthermore, it has been found that primers of the invention dry so rapidly as to permit theapplication thereon of hot coal tar enamels ina very' shortperiod of'time; e. g, in about five minutes.

The desirable characteristics of the present primers; as noted above, are unique" for a number of reasons. In the first place, when heavy creosote is applied by itself to a pipe for priming purposes, three or more days are required for the creosote to' form a satisfactory bond. Likewise, chlorinated rubber, if used by itself, as a primer is unsatisfactory since it' deposits" a film from solution which is extremely hard and brittle. Nevertheless, when these two materials are combined with a volatile solvent, ac.- cord'ing to the invention, the resulting primers represent a substantial improvement over conventional pitch-containing primers as noted above.

The heavy creosote which is utilized in the primers of the invention is that commonly referred to in the coal tar industry as wax oil. This is a material which is obtained by distillation of coal tar. It has the following characteristics Specific gravity: 1 .150 to 1200- at 38 C.- Distilling range:

0300 C., 10% max.

0-355 C., 50% max.

Any of the commercially available chlorinated rubbers may be used in the present invention. Onesuch product is that sold by the-Hercules Company under the trade name Parlon.

The proportion of chlorinated rubber to heavy creosote can be rather widely varied. However, to givesatis factory bonds, the primer should contain from about one to 3 parts by weight of heavy'creosote per part of chlorinated rubber. Especially desirable primers are obtained when the amount of heavy creosote is-betwee nabout 1.5 and 2 times by weight of the chlorinated rubber content.

Any volatile solvent for both the chlorinated rubber and heavy creosote may be used in the primers: of the invention, provided it is compatible with both the chlo rinated rubber and wax oil. Solvents of varying degrees of volatility can be used, the choice of any particular solvent, depending upon just how rapidly it is desired to have the primer dry on application. As typically suitable solvents, there may be mentioned xylol, toluol, benzene and carbon tetrachloride.

Mixtures of these solvents, e. g., xylol and carbon tetrachloride, may also be used to advantage. However, alcohols are not suitable because of their incompatibility with the wax oil and chlorinated rubber.

The proportion of solvent, or solvents, to solids, i. e., chlorinated rubber and wax oil, in the compositions of the invention can be widely varied and will necessarily depend upon such other factors as the viscosity desired and the method in which the primer is to be applied. However, the solvent content should not be less than the solids content, on a Weight basis and, generally speaking, the primers should comprise from 50 to 90% by weight of solvent and from 50 to by weight of solids. Primers containing from 70 to 90% by weight of solvent and 30 to 10% by weight of solids give the best results and are preferred.

The primers of the invention can be prepared by mixing the solvent, chlorinated rubber and wax oil together in any convenient manner, e. g., by first forming a blend of the heavy creosote and chlorinated rubber and, thereafter working the solvent into the blend. Other ingredients, such as inhibitors, e. g., epichlorohydrin, to prevent breaking down of the chlorinated rubber, may also be incorporated into the primers.

The invention is further illustrated, but not limited, by the following examples of suitable primers, prepared according to the invention, wherein the parts referred to are on a weight basis.

All of the specific compositions set forth above, when applied to steel pipes in conventional manner, e. g., by spraying or brushing, were found to give excellent bondings between the coated pipes and hot applied coal tar enamels. Particularly desirable bondings were obtained with the formulations of Examples 2 and 3, although all of the mixtures shown dried sufiiciently hard within five minutes to permit application thereon of conventional hot coal tar enamels.

It will be appreciated that various modifications can be made in the primers of the invention. For instance, in the primers described in the foregoing examples, carbon tetrachloride is used, primarily for the purpose of increasing the flash point of the resulting primers. However, this solvent may be replaced or the content thereof varied from that shown in the examples, without deviating from the present invention. Hence, it is not intended that the scope of this invention be limited by the foregoing description, except as defined in the following claims.

I claim:

1. A fast drying primer comprising chlorinated rubber, heavy creosote and a volatile solvent for said chlorinated rubber and heavy creosote.

2. A primer as claimed in claim 1, comprising from one to 3 parts by weight of heavy creosote per one part by weight of chlorinated rubber.

3. A primer as claimed in claim 1, comprising from about 1.5 to 2 parts by weight of heavy creosote per one part by weight of chlorinated rubber.

4. A primer as claimed in claim 1, comprising from 50 to 90% by weight solvent and from 50 to 10% by weight of heavy creosote and chlorinated rubber.

5. A primer as claimed in claim 1, comprising from one to 3 parts by Weight of heavy creosote per one part by weight of chlorinated rubber, from 50 to 90% by weight of solvent and from 50 to 10% by Weight of heavy creosote and chlorinated rubber.

6. A primer as claimed in claim 1, comprising from about 1.5 to 2 parts by weight of heavy creosote per one part by weight of chlorinated rubber, by weight of a solvent mixture comprising carbon tetrachloride and xylol and 20% by weight of chlorinated rubber and heavy creosote.

7. A fast drying primer comprising 13 parts heavy creosote, 7 parts chlorinated rubber, 40 parts carbon tetrachloride and 40 parts Xylol.

8. A fast drying primer comprising 12 parts heavy creosote, 8 parts chlorinated rubber, 40 parts carbon tetrachloride and 40 parts Xylol.

9. In the art of coating metals with hot coal tar enamel by a method including the steps of first applying a primer to the metal, drying said primer and thereafter applying the hot coal tar enamel to the primed metal, the improvement which comprises utilizing as the primer, a composition comprising chlorinated rubber, heavy creosote and a volatile solvent for said chlorinated rubber and heavy creosote.

10. In the art of coating metals with hot coal tar enamel by a method including the steps of first applying a primer to the metal, drying said primer and thereafter applying the hot coal tar enamel to the primed metal, the improvement which comprises utilizing as the primer, a composition comprising chlorinated rubber, heavy creosote and a volatile solvent for said chlorinated rubber and heavy creosote in the proportions of from one to 3 parts by weight of heavy creosote per part of chlorinated rubber, from 50 to by weight of solvent and from 50 to 10% by weight of heavy creosote and chlorinated rubber.

11. Metal articles having a coating thereon comprising chlorinated rubber, heavy creosote and a volatile solvent for said chlorinated rubber and heavy creosote.

References Cited in the file of this patent UNITED STATES PATENTS 1,890,723 Deseniss Dec. 13, 1932 2,287,218 Young June 23, 1942 2,302,583 Shutt Nov. 17, 1942 2,390,408 Young Dec. 4, 1945 OTHER REFERENCES Kolke: Farben Zeitung, 36, page 909 (1935). (Copy in Library.)

Am. Inst. Min. and Met. Eng: Contribution No. 122 (1942).

Claims (1)

1. 9. IN THE ART OF COATING METALS WITH HOT COAL TAR ENAMEL BY A METHOD INCLUDING THE STEPS OF FIRST APPLYING A PRIMER TO THE METAL, DRYING SAID PRIMER AND THEREAFTER APPLYING THE HOT COAL TAR ENAMEL TO THE PRIMED METAL, THE IMPROVEMENT WHICH COMPRISES UTILIZING AS THE PRIMER, A COMPOSITION COMPRISING CHLORINATED RUBBER, HEAVY CREOSOTE AND A VOLATILE SOLVENT FOR SAID CHLORINATED RUBBER AND HEAVY CRESOSOTE.