US 3001963 A
Description (OCR text may contain errors)
" 3,001,963 Patented Sept. 26, 1961 The present invention relates to wax compositions which are useful in coating operations and more particularly to a method of inhibiting the foaming tendency of such wax compositions.
As is well known to those familiar with the art of coating paper with wax, one method in common practice is to dip the paper in a hot molten wax bath whereby the paper is coated with the wax and rendered waterproof. It is also known that in general molten waxes have marked foaming tendencies and as a result foaming problems must be dealt with. When this foam is stable it solidifies on the surface of the paper with the result that the paper is only partially covered with wax. If a container prepared from such paper is filled with a liquid, the liquid penetrates the paper through the areas which had been covered by the foam thereby weakening the paper container causing bulging and leaks. Furthermore, such a container is unattractive.
It is, therefore, a principal object of the present invention to provide a non-foaming wax composition. Another object of my invention is to provide a combination of certain components when used in critical ratios which will eliminate foaming tendencies of waxes. Another object of this invention is to provide a non-foaming wax containing a minor amount of this critical combination of additives. Other objects and advantages of my invention will become apparent as the invention is hereinafter more thoroughly described.
As used herein and in the appended claims the term wax includes parafiin wax as that term is commonly understood and in addition the parafiin wax may contain such materials as higher boiling distillate waxes, microcrystalline wax, polyethylenes, and perhaps other additives. In general, the term paraffin wax is used to define the hard, crystalline wax commonly obtained from petroleum distillates, derived from mineral oils of the mixed base or paraffin base type. By the present refining methods, crude petroleum oil is subjected to distillation whereby it is separated into a series of fractions known as parafiin distillates. The Wax is separated from the paraffin distillate by chilling and filtering or by the use of a solvent, as for example, propane or a ketone such as methyl ethyl ketone. The wax obtained by either of these two methods contains from 10 to 50 percent oil and is generally referred to as slack wax. This slack wax is subjected to a sweating operation to remove the oil. The resulting wax usually contains 3 to 6 percent oil, but by proper sweating the oil content may be reduced to less than 1 percent. Also, the oil content may be reduced to an acceptable value by other methods such as solvent deoiling or press de-oiling. The final product is known as refined wax or parafiin wax and is graded according to tensile strength, melting point, oil content, hardness, etc.
In brief, I have found that the foaming tendencies of wax can be substantially if not completely eliminated, economically and simply by incorporating in the wax a minor amount of a mixture, consisting of a polymeric vinyl ester and stearic acid when these two components are used within a critical range of ratios by weight, as an antifoamant. Suitable polymeric vinyl esters are those strated by the following test.
described in US. Patent 2,841,558, issued July 1, 1958. Of the esters listed in the foregoing patent I generally prefer to use polyvinyl caproate. This product is available commercially from the Monsanto Chemical Company under the trade designation PC-l344. As to the stearic acid any edible grade is satisfactory.
The quantity of the antifoamant mixture added to the wax will depend upon a number of factors. Thus the exact quantity of the antifoamant added will depend upon the particular vinyl ester polymer used and the relative quantities of the ester and acid making up the antifoamant. In general, when the preferred ester polyvinyl caproate is employed as the active component of the antifoamant mixture it may be used in amounts ranging from about 1 to 25 p.p.m. of the total wax composition. Amounts less than 1 p.p.m. are insufficient to reduce the foaming characteristics of the wax and amounts used in excess of 25 p.p.m. produce very little additional improvement in the wax composition.
As to the upper limit of stearic acid used that may be approximated by considering the following theory. While I do not wish to be bound by this or any other theory as to how my results are obtained, I believe that the correct explanation is substantially as follows: The polyvinyl ester is actually the component which reduces the foaming tendency of the wax and for that reason will be identified as the active component in the antifoamant composition. Stearic acid on the other hand acts merely as a carrier or as a dispersant for the ester, thus making it possible to obtain a uniform mixture of the wax and ester. As is well known to those skilled in the art, stearic acid does not deteriorate a wax; actually stearic acid is normally used as a wax additive in candle and crayon manufacture to improve the so-called wax properties of the wax. As a consequence, considering that factor alone, the upper limit of the stearic acid content is not critical. Generally, however, I prefer not to use an amount exceeding 0.1%. This is true because stearic acid is an odoriferous compound capable of imparting its characteristic odor to wax when blended with wax in an amount greater than 0.1%. In addition, stearic acid is more costly than wax and as a consequence it is not economical to employ a larger amount than necessary to perform its function as a dispersant for the polyvinyl ester.
In order to disclose the nature of the present invention still more clearly the following illustrative example will be given. It is to be understood that the invention is not to be limited to the specific conditions or details set forth in this example except as such limitations are specified in the appended claims. As used herein and also in the claims percent is by Weight.
The relative effectiveness of the various combinations of polyvinyl caproate and stearic acid may be demon- Briefly, this test consists in dipping the paper in a hot molten wax bath whereby the paper is more or less uniformly coated with the wax. The paper is then removed, allowed to cool and the uniformity or nonuniformity of the wax coating noted. Where excessive foaming is present the coating will be nonuniform, exhibiting a large number of bubbles or blisters. If the wax coating is uniform, showing no bubbles or blisters, no foam is indicated. Numerical values are then given on a demerit scale over a range varying from 0 to 8. In this method a rating of 8 is very poor indicating excessive foam. A rating of 2 is very good and the numeral Zero indicates that the coating is practically perfect, showing the absence of all foam. The wax used in this test had a melting point of about F. as determined by the ASTM melting point method.
Example Anti Foamant Foam Polyvinyl Stearlc Rating Caproate, Acid,
percent percent Wax (control) 0.0 0.0 6 Wax+5 p.p.m. polyvinyl caproate 50. 60. 0 1 Wax+5 p.p.m. polyvinyl caproatm 0. 5 99. 5 0 Wax+25 p.p.m. polyvinyl caproate 10.0 90. 0 0 Wax-+500 p.p.m. polyvinyl caproate- 100. 0 0.0 5 Wax+0.l% stearlc acid. 0. 0 100.0 6
From the data summarized in the example above it will be seen that I have provided an efiective and economical method of inhibiting the foaming of wax. It is economical because only very small amounts of the antifoamant are required. These data show further than neither of these additives is effective as an antifoamant when used alone. This is true even when a relatively large quantity of the single additive is used. Another important feature of my invention which may not be readily apparent from the foregoing data is that even though a relatively large amount of stearic acid compared to the polyvinyl caproate is used that is not objectional. This is true since stearic acid is an edible product and for that reason a wax containing my antifoamant may be used for coating milk and other food containers.
While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto since many modifications may be made in the example, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.
The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:
1. A substantially anhydrous wax composition of improved antifoaming properties intended to be used in the molten state comprising a parafiin wax and an antifoamant comprising a mixture of polyvinyl caproate and stearic acid wherein the relative proportions of said polyvinyl caproate and said stearic acid in said mixture varies from .5 to 99.5% and to 50% respectively characterized further in that the amount of polyvinyl caproate in said Wax composition varies from 1 to 25 p.p.m.
2. The product of claim 1 wherein the relative proportions of polyvinyl caproate and stearic acid is 10 and respectively.
3. The product of claim 1 wherein the relative proportions of polyvinyl caproate and stearic acid is 0.5 and 99.5 respectively.
4. The product of claim 1 wherein the relative proportions of polyvinyl caproate and stearic acid is 0.5 and 99.5 respectively, characterized further in that the amount of said polyvinyl caproate in the wax composition is equal to about 5 p.p.m.
References Cited in the file of this patent UNITED STATES PATENTS Trusler June 7, 1955 2,841,558 Fields et al July 1, 1958