US2797168A - Coating composition - Google Patents

Description

United States Patent O ice COATING COMPOSITION John R. Gimler, Morristown, N. J.

No Drawing. Application December 1, 1953, Serial No. 395,607

2 Claims. (Cl. 106-468) This invention relates to c'oatingcompounds, more particularly compositions for coating and sealing cartons or packages of goods which must be protected from the damaging effects of the weather, more particularly the effects of moisture and humid air which may corrode or otherwise damage the goods.

For example, in the case of a large number of products required for military uses, it is necessary that the goods be packaged for transport to the point of use in a suitable container or wrapping and that the latter be enveloped with an applied coating or sealing compound intended to prevent the ingress of moisture or humid air through the container or wrapping to an extent such as which would enable it to come into contact with and deleteriously affect the goods.

With that in view, the container or wrapped package of the goods is customarily provided with a seal coating applied thereto in the form of a molten thermoplastic composition, the container or package being completely immersed therein so as to provide a coating film or layer of desired thickness over the entire surface thereof.

Having in view the requirements that must be met by the coating film, from the standpoint of its application to the package, the atmospheric and other conditions which are encountered before the packaged item is removed and put to its intended use, the compositions heretofore employed for this purpose, and more particularly those which conform to the requirements of certain Federal specifications for such products, have consisted of certain petroleum waxes, more particularly a so-called microcrystalline wax. Microcrystalline waxes are well known and have heretofore also been widely used, in combination with certain additives, as adhesive for uniting plies of paper or the like and as moisture-proof coatings upon paper, cardboard, or the like.

These microcrystalline waxes are, generally speaking, amorphous, substantially saturated compounds formed from high-boiling-point, non-saturated petroleum derivatives by polmerization or condensation. When combined with certain additives, they may be rendered resistant to moisture penetration and sufficiently adherent to serve as a bond between fibrous sheets. They'may be distinguished from the usual saturated hydrocarbons known as parafiine, by their relatively higher melting-point.

The microcrystalline Waxes heretofore employed as dip coatings for containers or wrapped packages of goods have melting points of about 130 F.

When used as a dip coating compound for the purposes above-mentioned, it is required, particularly in order to conform to certain Federal specifications for such coat ings, that they exhibit the following physical character istics:

1. That they show no brittleness sufiicient to cause failure of the coating-when in the form of a film of a thickness as much as A and subjected for considerable periods of time to temperatures below minus 20.". F., and in some casesaslow as minus 65 F 2. That the applied film of the coating exhibit no flow- Patented June 25, 1957 ing characteristics or excessive tackiness when subjected to temperatures of the order of F. to F.;

3. Adequate tensile strength of the coating film;

4. Adequate resistance to abrasion of the coating film;

5. Adequate low moisture vapor transmission properties;

6. An increase not exceeding one percent in weight when immersed in water for one week;

7. A penetration (standard needle, 5 seconds, 100 grams) of not more than 60 nor less than 30.

The microcrystalline wax compositions heretofore employed as protective coatings for military packages, for example packages of rations, replacement parts, medical supplies, ammunition, and numerous other items, while satisfactory for protection of the packaged goods destined for use under climatic conditions encountered in the Warmer theaters of operation, have been found to be totally unsatisfactory when subjected to conditions encountered in areas having much colder climate, suchas is the case for example in Korea.

It has been found that under the latter conditions, the microcrystalline wax compositions employed prior to my invention as dip coating of packages of military goods or the like failed of their purpose in that they exhibit internal cracking or crazing whenencountering temperatures of the order of minus 20 -F., or lower. Apparently this cracking or crazing results from internal strains due to contraction of the film when subjected to such cold shock.

Attempts made to rectify this inadequate resistance to cold shock on the part of microcrystalline wax, by modifying the same with substances designed to function as plasticizers, such as naphthenic petroleum oils have shown that while improving the low temperature shock resistance of the composition these modifiers do not eliminate thetendency of the compound to suffer internal crazing when exposed to temperatures substantially below minus 20 F. and furthermore serve to reduce the melting point of the compound below the required minimum.

Efforts made to remedy both these drawbacks in such mixtures of microcrystalline wax and plasticizer by in-' corporating therein various metallic stearates, such as those of lead, calcium, barium, lithium and aluminum, have failed to give the desired results. Among other objections, the stearates of calcium, lithium, barium-and the higher melting-point stearates of aluminum can be uniformly incorporated in the compound only with great ditficulty and, moreover, these additives are found to crystallize out of the compound at the normal dip coating temperatures. The stearates of lead, as well as the low melting point stearates of aluminum, are incapable of imparting to the compound the necessary resistance to low emperature crazing, are only moderately effective in raising the melting-point of the plasticized microcrystalline wax, and'in the case of the aluminum stearates, cause undesirable foaming when incorporated in the molten wax.-

The principal object of the present invention is to provide a composition suitable for use as a coating to be applied to containers or'packages. of' goods, more particularly goods used by the. military, and which such coating is capable of being applied as a continuous'film-on such containers or packages 'by immersion'thereof in a bath of the molten compound, the compound'possessing properties which will satisfy the several requirements above enumerated.

A further object of the invention is to provide a compo-; sition of the character indicated, which may be compounded and shipped in bulk for application at the point wherethe goods to be protected thereby are packaged or wrapped for shipment.

Still another object is to provide a-dip coating composition of the' character indicated, which whe'n utilize'ii as and for the purposes aforesaid will serve elfectively to prevent damage to or deterioration of the packaged or wrapped item by ingress of moisture or moisture-laden atmosphere or by escape of moisture from the packaged product, as in the case of food or the like.

Theseand other-objects of the invention, and the advantages thereof, will be readily apparent to those skilled in the 'art from the more detailed description below. j According to the invention, the coating composition comprises a mixture of microcrystalline wax, a plasticizer for-the wax, more particularly a naphthenic oil'derivative of petroleum of relatively low pour point, and a substance functioning to impart to the composition substantially complete resistance to internal crazing at temperatures, substantially below minus 20 F., and at the same time to provide a composition having a softening point higher than 150 F.

More particularly, according to the invention, this last named ingredient of the composition is the zinc soap of stearic acid. I havefound that when employed in a proportion of from about 0.75 to 1.5 percent by weight of the composition, the resultant product possesses the properties indicated and fully meets the rather severe requirements of the military, as exemplified by the physical characteristics above enumerated.

In the composition made according to the invention, the naphthenic oil plasticizer is employed in an amount of about five to ten percent by weight of the wax.

Example I Minimum Maximum Ideal Mlerom'ystalllne Wax Plastlcizer Zinc stearate In the above formulation, the plasticizer used was a naphthenic oil having a pour point of minus 60 F., obtainable from Socony Vacuum Oil Company under its trade designation Solvaloid L. The zinc stearate was a technical grade obtainable on the open market. The microcrystalline wax was a material obtainable from Socony Vacuum.0il Company under its trade designation S/V-2305, and had a melting-point of 155 F. min. (ASTM).

In compounding the composition, the molten microcrystalline wax may be pumped into a jacketed, steamheated mixing tank provided with a paddle or so-called lightning type agitator, and while subjecting the wax to slow speed agitation therein, the plasticizer and the zinc stearate may be added. Since the zinc stearate melts at approximately 257 F., it is not necessary, or advisable, to permit the temperature of the batch to exceed the range of 275 to 300 F. When the batch is completely homogeneous, it may be screened to remove any extraneous foreign matter and then pumped to a tank car for shipment or packaged as required.

Alternatively, in making this composition, a masterbatch ofthe plasticizer and the zinc stearate may be formed under moderate agitation in a suitable tank or churn, and when completely homogeneous, the masterbatch may be pumped at the required rate to the steamheated mixing tank containing the melted wax. In this procedure, as in the one first mentioned, the temperature in the mixing tank must be above 260 F.'in order properly to incorporate the zinc stearate, but it is neither necessary nor advisable that the temperature therein exceed 300 F. When the mixture is homogeneous, that is to say, free from specks of zinc stearate, it may be run through a screen and either pumped to a tank car or packaged as required, for shipment.

The compound illustrated in this example had a softening point of approximately 153 F., and a penetration of approximately 41 (standard needle, grams, 5 seconds). When tested under ASTM test method D98848T (73 F. at 50% relative humidity) this product showed zero moisture vapor transmission during a 168 hour test. As to homogenity, it showed no separation and no residue when heated at 210 F. for 72 hours.

Samples of the product cast in molds so as to have a cross-section of one by two centimeters and pulled in a Scott tensile testing machine at the rate of 2.5 inches per minute showed an average tensile strength of approximately 14 pounds per square inch.

The time required for a coating film of & inch thickness to set completely was between 45 and 50 seconds. When tested by immersion in water for one week according to the water-absorption test set forth in the applicable Federal Specification, its water absorption was nil.

A test package containing a solid object, wrapped in scrim cloth laminated to a layer of polyethylene conforming to applicable Federal Specification for such wraps, and then coated by dipping twice in the molten compound of this example, showed no flaking or cracking of the coating after three weeks exposure to a temperature of 65 below zero Fahrenheit. The compound showed no discontinuities in congealing from its liquid to the solid state.

Even a inch thick film of the composition passed the standard /z' mandrel test at that low temperature.

In referring to the resistance of the coating film to cracking when subjected to those low temperatures, it should be borne in mind that this means its resistance when applied to the surface of a solid object, for if the object to which it is applied is of a character or conformation such as itself to undergo contraction or similar distortion, these latter influences may cause the coating to crack. Thus, for example, if the coating composition of my invention is applied to the surface of a partially-filled container or to the surface of a wrapping which consists of material such as scrim cloth laminated to cellophane or the like, the flexibility of the container in the one case, or the cellophane in the other case, may itself cause it to undergo such distortion as thereby to cause the film of the coating composition to crack, whereas this would not occur if the coating material of the invention is applied, as intended, to a relatively firm, rigid surface which itself does not undergo shrinkage or similar distortion when subjected to such low temperatures.

Example II Although the product made according to Example I above set forth possesses, among its other desirable physical characteristics, the ability to withstand the effects of cold shock to the extent of complete resistance to internal cracking or crazing when subjected to temperatures well below minus 20 F., its softening point of approximately 153 F. does not provide suflicient heat stability to enable it to resist flowing or so-called run-off at temperatures above F., say at a temperature of F. In certain instances it is necessary that the compound, in addition to resistance to such cold shock shall possess also the ability to withstand run-off at a temperature of approximately 165 F.

This latter property is provided in the embodiment of the invention represented by the present example. According to this example, there is included in the composition a substantial proportion of a microcrystalline wax having a melting point of approximately F., along with the microcrystalline wax included in Example I, viz., the one designated S/V2305. For best results, the 180 F. melting-point microcrystalline wax is employed in a ratio of approximately one part thereof with 8 to 10 parts of the S/V2305 microcrystalline wax, by weight. Furthermore, as will be noted from the figures given below, the naphthenic hydrocarbon plasficizer is employed in an amount of approximately based on the combined weight of both microcrystalline waxes present in the compound, in contrast to approximately 6% by weight g of plasticizer in relation to the microcrystalline wax pres- Microcrystalline wax (180 F. melting-point) 10.0 Pl asticizer (as in Example I) 8.0 Zinc steal-ate- 1.0

This product has a specific gravity of 0.8375 and Weighs 6.98 pounds per gallon. Tested as hereinabove set forth, it exhibited no cracking or flaking at a temperature of minus 20 F. and no run ofi. at 160 F. Likewise, it met by a considerable margin the other requirements as to physical properties enumerated above for use as a dip coating compound for protecting packages or containers of the class to which reference has been made.

The term consisting essentially of as used in the claims to define the ingredients present in the claimed composition is intended to exclude the presence of other materials in such amounts as to interfere substantially with the properties and characteristics possessed by the composition set forth, but to permit the presence of other materials in such amounts as do not substantially affect said properties and characteristics adversely.

Having described my invention, what I claim is:

1. A coating composition characterized by substantially complete resistance to internal cracking or crazing when in the form of an applied film on a substantially rigid surface and subjected to temperatures of the order of minus F., and having a softening point not substantially below F., said composition consisting of approximately 93 parts by weight of microcrystalline wax, approximately 6 parts by weight of a naphthenic petroleum oil having a pour point of minus 60 F., and approximately 1% by weight of zinc stearate.

2. A coating composition characterized by substantially complete resistance to internal'cracking or crazing when in the form of an applied film on a substantially rigid surface and subjected to temperatures substantially below minus 20 F., and exhibiting heat stability sufficient to prevent it from running ofl? a surface at temperatures of the order of F. to F., said composition consisting of approximately 81% of a microcrystalline Wax having a melting-point of 155 F., approximately 10% of a microcrystalline wax having a melting-point of F., approximately 8% of a naphthenic petroleum oil having a pour point of minus 60 F, and approximately 1% of zinc stearate, all by weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,099,880 Ellis Nov. 23, 1937 2,348,689 Abrams et al. May 9, 1944 2,375,348 Cohen May 8, 1945 2,464,759 Camp Mar. 15, 1949 2,546,328 Arabrian et al Mar. 27, 1951 2,595,158 McCue et al. Apr. 29, 1952 2,641,551 Smith et al. June 9, 1953

Claims (1)

1. A COATING COMPOSITION CHARACTERIZED BY SUBSTANTIALLY COMPLETE RESISTANCE TO INTERNAL CRACKING OR CRAZING WHEN IN THE FORM OF AN APPLIED FILM ON A SUBSTANTIALLY RIDIG SURFACE ANS SUBJECTED TO TEMPERATURES OF THE ORDER OF MINUS 60*F., AND HAVING A SOFTENING POINT NOT SUBSTANTIALLY BELOW 150*F., SAID COMPOSITION CONSISTING OF APPROXIMATELY 93 PARTS BY WEIGHT OF MICROCRYSTALLINE WAX, APPROXIMATELY 6 PARTS BY WEIGHT OF A NAPHTHENIC PETROLEUM OIL HAVING A POUR POINT OF MINUS 60*F., AND APPROXIMATELY 1% BY WEIGHT OF ZINC STEARATE.