US3354106A - Sealing wax composition - Google Patents

Description

United States Patent 3,354,106 SEALENG WAX COMPOSITION Stephan Ilnyckyi and David M. MacLeod, Sarnia, 0ntario, Canada, assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Apr. 29, 1965, Ser. No. 452,021 3 Claims. (Cl. 260-285) This application is a continuation-in-part of our copending application, Ser. No. 223,528, filed Sept. 13, 1962, now abandoned.

The present invention is concerned with a new and improved wax composition and, more particularly, relates to the use of such composition in the coating of materials such as paper and related substances, which materials are used for the wrapping of foodstuffs such as bread and the like. In accordance with the present inven- -tion, a superior sealing wax is formulated by incorporating therein a critical amount of an ethylene-vinyl ester copolymer as, for example, a copolymer of ethylene and vinyl acetate. The improved sealing characteristics of the additive for use in a wax composition to produce a high quality sealing wax is secured by carefully controlling the conditions by which the copolymer is manufactured.

In the refining of hydrocarbon oils such as petroleum oils, it is known to segregate paraffin waxes from so-called paraffin distillates, waxy lobes and the like. The overhead or paraffin distillate fraction, for example, has a boiling range of about 580 F. to 850 F. and a viscosity of about 80 S.U.S. at 100 F. A heavy lubricating oil distillate side stream, for example, has a boiling range of about 800 F. to 1000 F. and a viscosity of about 50-70 S.U.S. at 210 F. The residuum comprises all the hydrocarbons boiling above this range and, for example, has a viscosity from about 150 to 200 S.U.S. at 210 F. Crystalline or paraflin wax produced from the paraffin distillates have melting points which range from about 120 F. to 150 F. This type of wax is characterized by large well-formed crystals that can be readily separated from the oil. Furthermore, this type of wax generally contains a relatively small amount of oil and can be refined with comparative ease.

The segregation of these waxes is secured by a number of processes. For example, it is known to chill the selected wax containing fraction in order to secure crystallization of the wax and to remove the wax crystals from the oil by filtering, centrifuging and the like. It is also known to use various dewaxing solvents such as liquid normally gaseous hydrocarbons, such as propane, as well as other solvents, such as methyl ethyl ketone, methyl isobutyl ketone, and the like. It is also known to utilize in dewaxing operations solvent mixtures wherein one solvent comprises a Wax precipitating solvent while the other comprises a solvent having a high solubility for oil. A solvent mixture of this character, for example, comprises 40% by volume of toluene and 60% by volume of methyl ethyl ketone. In utilizing a mixture of this character, it has been the practice to add the mixture in toto or incrementally to the waxy distillate as it is being chilled. In dewaxing operations, it is also known to use various filter aids and other agents in order to render the dewaxing and filtering operations more efficient.

The wax segregated from the hydrocarbon oil, usually termed slack wax, contains from about 10% to 40% of oil. The slack wax is refined usually by conventional sweating to produce crude scale wax in a manner to reduce the oil content to less than about 5% by weight. The slack wax may be distilled to obtain the desired boiling range wax prior to sweating, if desired. This crude scale wax generally has an oil content of about 2% to 3% by weight. In order to remove this oil from the scale wax to produce a refined wax, such as a refined parafiin, having an oil content below about .5%, usually below about .3%, various procedures have been proposed and employed.

Alternatively, the slack wax may be processed by a solvent deoiling process, to remove oil from the wax. In this, the wax is dissolved in such solvents as methyl isobutyl ketone, methyl ethyl ketone, or mixtures of methyl ethyl ketone and toluene in a ratio of approximately to 25, respectively. The wax solution is cooled to produce crystallization and the crystallized wax is removed by a process such as filtration. The filter cake of crystallized wax may be washed with cold solvent to remove occluded oil solution. The wax so produced may be an unfinished refined paraflin wax or an unfinished microcrystalline wax, depending on the nature of the slack wax feed, and on the selection of crystallization conditions. After oil removal from the wax, it is subjected to a finishing process such as clay percolation or hydrofining. In the latter, the process involves treating the unfinished wax with hydrogen gas, at 500-800 p.s.i., at 500600 F., in contact with cobalt molybdate catalyst. Or, at lower pressures such as 200 p.s.i., a nickel catalyst may be used. The hydrogen treated wax product is greatly improved with respect to color, odor and purity.

It is also known in the art to segregate microcrystalline waxes from residual oils. As pointed out heretofore, these crystalline waxes are normally produced from residuums which boil above about 1000 F. and have viscosities in the range from to 200 S.U.S. at 210 F. These microcrystalline waxes are characterized by very minute crystalline forms and which melt in the range from about 145 F. to F. These microcrystalline waxes from residual oils are of a relatively high melting point and of different crystalline structure. The microcrystalline waxes may be prepared from any of the paraflin or mixed base crude oils. The undistilled residue may be treated with sulfuric acid and neutralized to remove the tarry matter and unsaturated hydrocarbons. The undistilled residue also may be deasphalted. The treated stock, containing a fairly high percentage of wax, as evidenced by a very high pour point, may be dewaxed by blending with 3 a dewaxing, solvent, such as propane, methyl ethyl ketonebenzol, or petroleum naphtha and chilled, and filtered or centrifuged to separate the waxy fraction from the residual lubricating oil solution.

This dewaxing operation produces a wax fraction containing some oil and solvent. The wax after removal of the solvent has a melting point of from about 130 to 180 F. The wax may be again put in solution with more solvent or naphtha and chilled and filtered or recentrifuged to further reduce the oil content. The wax which separates in either of these operations is referred to as crude microcrystalline wax. The wax separated in the second crystallization process after stripping to remove solvent is fairly dry and of a low oil content. This was should not be confused with petroleum jellies which contain large amounts of oil. The crude microcrystalline wax may be again put into solution with naphtha and filtered through clay or an equivalent material in order to improve its color. The clay filtered solution is distilled to remove the naphtha, the residue being a refined petrolatum' wax having a melting point within the range of about 140 to 180 F. Alternatively, the microcrystalline wax may be hydrogen treated to improve its color and odor, such as by hydrofining at about 600 F., 600 psi. of hydrogen, using cobalt molybdate catalyst. The source of the crude oil and the oil content of the refined microcrystalline product will affect the melting point of the final wax product. The refined microcrystalline Wax, sometimes called amorphous wax, is as pointed out, of a very small crystal structure.

It is also known in theart to segregate microcrystalline waxes from distillate lubricating oils. These distillate type microcrystalline waxes differ in characteristics from the residual type microcrystalline waxes hereinbefore described. Thus, the distillate Waxes are lower in viscosity and are generally finished to a higher degree of purity, such as freedom from color and odor. Furthermore, the distillate microcrystalline waxes have two advantages over the residual microcrystalline waxes from the standpoint of ease of manufacture. Namely, first, the distillable nature of the wax makes it possible to manufacture specific microcrystalline wax fractions for use in specific product applications; and, second, the distillate waxes can be more readily and more economically refined with respect to color and odor than can the residual microcrystalline waxes. These features of distillate microcrystalline wax (low viscosity, high purity, select fractionation, economy of finishing) have been found to be of particular value in the present invention.

The distillate microcrystalline waxes are manufactured from distilled waxy lubricating oil fractions from crude oil. These fractions will vary with regard to distillation range, depending upon the desired viscosity grade of the lubricating oil ultimately produced. Thus, a number of fractional cuts may be taken across the lubricating oil distillation range, to produce different lubes. The entire range may cover a distillation from about 650-1180 F. (760 mm. basis). Each of the fractional waxy lubricating oil cuts are processed to remove the waxy components by a process such as dewaxing by solvent crystallization.

As hereinbefore described, this comprises dissolving the waxy distillate in such solvents as methyl ethyl ketone, methyl isobutyl ketone and mixtures of methyl ethyl ketone and toluene, cooling the solution to cause crystallization of the wax, then filtering to separate the lubricating oil and the slack wax. The slack wax is then processed to further. remove oil from it by a procedure such as solvent deoiling. In this operation, the excess oil is removed from the slack wax, by the solvent crystallization technique, while at the same time the solvent and temperature conditions are controlled to achieve a fractional crystallization of the wax fraction. Thus, a slack wax may be crystallized first at a relatively high temperature to separate the most crystalline, paraffinic and high melting wax components present in the slack wax as the solid phase. The

Al. melting point may range from to F., depending on the properties of the slack wax feed and the crystallization temperature.

The filtrate phase is then further cooled to cause a second crystallization of the Wax which is microcrystalline in nature, and of lower melting point than the first Wax cut. Waxes in this fraction vary from 125140 F. melting point. By selection of the solvent composition and crystallization temperature, the exact properties of the separated wax can be controlled. The filtrate from the second crystallization contains the oil which was removed from the wax fractions. Both the first and second fractions of wax contain about 0.2 to 1.5% oil, this generally being 0.3 to 1.0% oil. These deoiled wax fractions may then be finished to the desired degree of purity with respect to color and odor by one of several methods, such as the hydrogen treating (hydrofining) or absorption (clay percolation) methods previously described. As a final manu facturing operation, the paraffin or microcrystalline wax may be distilled again to further separate specific wax fractions.

The various waxes produced by the methods hereinbefore described, while they may be used for the coating of materials such as paper, which materials are subsequently used for the wrapping of foodstuffs, are not entirely satisfactory due to their low sealing strengths. These waxes are principally used in packaging because of their ability to resist the passage of Water or water vapor. However, in many cases, as pointed out, a vary important property of a wrapping wax is its ability to form a strong seal between two pieces of paper. Bread Wrapping papers and laminated wrappings are typical examples of applications where strong seals are very necessary. It therefore follows that the measure of the strength of wax seals is a very important part of the value of waxes for such wrapping uses. In accordance with the present invention, the sealing characteristics of the Waxes are materially improved by the incorporation therein of a particular copolymer of ethylene and vinyl acetate, which copolymer is secured in a manner as hereinafter described.

In accordance with the present invention, the copolymerization process is conducted in a solvent as, for example, naphthalene or isobutyl alcohol. It is preferred, however, to use a benzene solvent. The initiator comprises a peroxy compound, preferably di-tertiary-butyl-peroxide. The temperature of the copolymerization reaction is critical and is in the range from about 265 to 285 F. A very desirable temperature is about 270 F. The pressure is in the range from about 700 to 5000 pounds, preferably 800- 2000 pounds. The autoclave or similar equipment containing the solvent, initiator and vinyl acetate is purged with nitrogen, then with ethylene before charging with a sufiicient amount of ethylene to yield the desired pressure when heated to the reaction temperature. During the copolymerization, additional ethylene is added to maintain the pressure at the desired level. Polymerization is considered complete when the pressure drops less than 50 p.s.i.g. per hour. The product is stripped free of solvent and unreacted vinyl acetate under vacuum. The specific ethylene-vinyl acetate copolymers that are useful when blended into the aforementioned waxes and which thus result in polymer-wax blends of vastly improved sealing strengths are characterized by the following properties:- They have number average molecular weights ranging between about 3,000 and about 15,000, preferably between about 3,500 and about 8,000. They contain vinyl acetate in the range between about 15% and about 34% by weight, preferably between about 25 and about 30 wt. percent. They have specific viscosities measured at 1% concentration in toluene at 125 F. ranging between about 0.28 and about 0.9, preferably between about 0.35 and about 0.65.

A number of operations were carried out wherein copolymers were produced under different pressures and other varying conditions. These copolymers were then tested as seal improvers in wax compositions with the results as shown in the following tables.

TABLE 1. IMPROVED COPOLYMERS OBTAINED AT LOW TEMPERATURES AND PRESSURES Number average molecular wt.

4, 200 2, 500 3, 000 Vinyl acetate content, wt. perce 30 30 30 gpelclific giiscostiziily "i1. (2.6%.- dd t 0. 37 0. 23 0. 28

ea 'n ren inc a i e in wax) .1 240 24 90 1 Cryoscopic in phenanthrene. (All molecular weights stated herein are number average molecular weights).

2 1 wt. percent copolymer in toluene at 125 F. Q

a Base wax consists of a blend of 95% of 148 F melting po nt parafiin wax arid 5% of 140 F. melting point microczystallme wax, sealing strength 15 gm. inch.

From the above it is apparent that the sealing strength of the wax was strikingly improved when the product was produced at a temperature of about 275 F. as compared to producing the product at a temperature of about 300 F. In cases A and B it is seen that the number average molecular weight obtained under lower temperature reaction conditions was higher for case A. It is desired to have a molecular weight at least as high as 3000 and up to 15,000, preferably between above 3500 and about 8000. Comparing cases A, B and C, it is seen that for copolymers of equal vinyl acetate content, the best seal improvement is obtained with the highest molecular weight or the highest specific viscosity.

TABLE 2. OPTIMUM VINYL ACETATE CONTENT OF CO- POLYMER 1 1 wt. percent copolymer in toluene at 125 F.

2 Base wax consists of a blend of 95% of 148 F. melting point paraffin wax and 5% of 140 F. melting point microcrystalline wax, sealing strength 15 gm./inch.

Did not dissolve.

From the above it is apparent that when the copolymerization is carried out at a temperature in the range from about 270 to 285 F., a very potent sealing improver is secured. As shown in Table 2, the improvement in sealing strength of the waxes increases with high vinyl acetate content of the copolymer as, for example, in the range from about 25 to 34%. At about 35%, the copolymer becomes insoluble in the wax.

Thus, the potency of these copolymers as seal improvers is increased by increasing the vinyl acetate content. However, this increase is limited by the solubility of the copolymer in the wax. The potency is also increased by increasing the molecular weight of the copolymer and the molecular weight should be at least 3000. Generally, the molecular weight of the copolymer increases With de creasing temperature of synthesis but this is limited to a minimum of about 270 F. due to the reduced activity of the monomers at lower temperatures. Below 270 F., the yield of copolymer would be too low because the rate of reaction is much reduced. Thus, a large increase in the sealing strength of waxes can be secured by using the copolymers of the present invention. The amount used is preferably in the range from about to 50% of the copolymer by weight depending upon the quality of the Wax. A very desirable amount to use is in the range from about to about 25% of the copolymer, preferably 6 about 20% by weight based upon the amount of wax present.

A number of copolymers were prepared in a manner as shown in the following table.

TABLE 3. SYNTHESIS OF SEALING STRENGTH IMPROVERS FOR WAXES [Ethylene vinyl acetate copolymers] Ref. Conditions Ref. A B C Wax Pressure, p.s.i.g 900 900 2, 400 Temperature, F 275 270 270 Vinyl acetate, g 140 140 140 Vinyl acetate, gJmin- At start 0 583 D-t-BPO 11. 9 11.9 11.9 D-t-BPO, gJmin {3.2 g. at 0.2+ 045 1, 400 6 Yield, g./V A g 3.11 2. 37 4.33 Peroxide etliciency 36. 6 28. 0 51 0 Vinyl acetate, Wt. percent- 30. 2 27. 2 Number average molecular wt. 4, 200 6, 500 Dropping point, F 167 5 247 Spec. Viscosity, 0.377 0.386 0.86 20% in Ref. Wax: 5

Blocking, F. 118 120 121 121 Sealing Strength, gms./inch 15 240 180 72 Viscosity at 210 F., S.U.S 46 255 267 1, 300

1 Di-t-butyl peroxide.

2 Grams copolymer/gram peroxide.

3 Cryoscopic in phenanthrene.

4 1 wt. percent copolymer in toluene at 125 F.

5 95% of 148 F. melting point parafiin wax and 5% of F. melting point microcrystalline wax.

Blocking test, ASIM-D-1465.

7 Sealing strength, sea-led according to proposed method ASTM 1958 page 1094. Pulled apart as described in The Mechanism of the Fracture Wax Seals, Roger M. Butler, David M. MacLeod, and Joseph M. Cahill, Published in TAPPI, Vol. 41, No. 7, July 1958.

It is essential that the wax have a high blocking point because rolls of wax paper may be subjected to elevated temperatures in storage prior to use. Any blocking (sticking together) may render the Wax paper unfit for use. From the above, it is apparent that the present additive did not degrade the wax in this respect, as might be expected to occur with soft copolymers of relatively low molecular weight. It is preferred that the base wax composition comprise a mixture of paraflin wax and a microcrystalline wax wherein the amount of paraffin Wax prescut is in the range from about 80 to 95% by weight, and the amount of microcrystalline Wax present is in the range from about 2 to 20% by Weight. It is also preferred that the parafiin wax have a melting point in the range from about 140 to 160 F. and that the melting point of the microcrystalline wax be in the range from about 135 to F.

What is claimed is:

1. Improved parafl'iin Wax composition having incorporated therein from about 10 to 50% by weight of a wax-soluble copolymer of ethylene and vinyl acetate, said copolymer having a number average molecular weight in the range from about 3,500 to about 8,000 and having a vinyl acetate content in the range from about 15 to about 34% by weight, said copolymer having a specific viscosity (1 Wt. percent copolymer in toluene at 125 F.) in the range from about 0.35 to about 0.65.

2. Improved wax composition of high sealing strength which comprises from about 80 to 98 wt. percent of a paraflin wax and from about 2 to 20 wt. percent of a microcrystalline wax, said wax composition having incorporated therein, based upon the total waxes, from about 10 to 50 wt. percent of a wax-soluble copolymer of ethylene and vinylacetate, said copolymer having a number average molecular weight in the range from about 3,500 to about 8,000, having a vinyl acetate content in the range from about 15 to about 34% by Weight, and the specific viscosity (1 wt. percent copolymer in toluene at 125 F.) is between about 0.35 to about 0.65.

3. Composition as defined by claim 2 wherein the melting point of the parafiin Wax is in the range from about 140 to 160 F. and wherein the melting point of 3,048,553 8/1962 Moss. the microcrystalline wax is from about 135 F. to about 3,093,623 6/1963 llnyckyj 26047.3

145 F. 3,178,383 4/1965 Stout.

References Cit d 3,189,573 6/ 1965 Oken.

UNITED STATES PATENTS 5 2,703,794 3/1955 Roedel- MORRIS LIEBMAN, Przmary Exam'mer.

3,025,167 3/ 1962 Butler. E. A. AMERNICK, Assistant Examiner.

Claims (1)

1. IMPROVED PARAFFIN WAX COMPOSITION HAVING INCORPORATED THEREIN FROM ABOUT 10 TO 50% BY WEIGHT OF A WAX-SOLUBLE COPOLYMER OF ETHYLENE AND VINYL ACETATE, SAID COPOLYMER HAVING A NUMBER AVERAGE MOLECULAR WEIGHT IN THE RANGE FROM ABOUT 3,500 TO ABOUT 8,000 AND HAVING A VINYL ACETATE CONTENT IN THE RANGE FROM ABOUT 15 TO ABOUT 34% BY WEIGHT, SAID COPOLYMER HAVING A SPECIFIC VISCOSITY (1 WT. PERCENT COPOLYMER IN TOLUENE AT 125*F.) IN THE RANGE FROM ABOUT 0.35 TO ABOUT 0.65.