US2780556A - Microcrystalline wax compositions - Google Patents

Description

Feb. 5, 1957 mpwum p A. A. SCHAERER 2,780,556

MICROCRYSTALLINE WAX COMPOSITIONS Filed Nov. 26, 1954 2 Sheets-Sheet l SEALING STRENGTH G/IN.

TEMPERATURE c FIG. I

EAST TEXAS SHORT RESIDUE MICROCRYSTALLINE WAX (MR 43C) DOWTHERM (CHLORINATED HYDROCARBON) ISOLUBEUSOMERIZED WAX FRACTION) BRIGHT STOCK FRACTION EAsT TEXAS 25o NEUTRAL EAST TEXAS 25o NEUTRAL,POLYAROMATICS(4 RINGS AVERAGE) EAST TEXAS 25o NEUTRAL,SATURATED POLYCYCLIESM RINGS AVERAGE) INVENTOR;

AUGUST A. SCHAERER HIS AGENT Feb. 5, 1957 Filed Nov. 26, 1954 PS N Q A. A. SCHAERER 2,780,556

MICROCRYSTALLINE WAX COMPOSITIONS 2 Sheets-Sheet 2 TEMPERATURE 0 FIG. 2

EAST TEXAS SHORT RESIDUE MIGROCRYSTALLINE WAX(M.F. 43C) CHOLESTANE (MR 756C) CHRYSENE PERHYDROCHRYSENE I (M.F. 107C) PERHYDROCHRYSENE n (MP. 26C) INVENTOR:

AUGUST A. SCHAERER HIS AGENT United States Patent MICROCRYSTALLINE WAX COMPOSITIONS August A. Schaerer, Orinda, Calif., assignor to Shell Development Company, New York, N. Y., a corporation of Delaware Application November 26, 1954, Serial No. 471,198

12 Claims. (Cl. 106-270) This invention relates to hydrocarbon wax compositions. More particularly, it is concerned with microcrystalline (amorphous) wax compositions having improved sealing strength over a wide temperature range, as well as improved brittle point characteristics. Petroleum waxes are classified as paraffin waxes (i. e. those predominating in straight chain parafiin hydrocarbons) and microcrystalline, or amorphous waxes (i. e. those predominating in isoand cycloparafiins).

Generally, hydrocarbon waxes are produced from oily wax masses recovered from petroleum lubricating oil stocks during the treatment of such lubricating oil stocks to remove therefrom materials which markedly reduce the fluidity of the oil when it is cooled to low temperatures, such as 0 C. and the like. In order to produce lubricating oils with given viscosity characteristics, the base stock is generally first separated into different fractions by distillation under reduced pressure and the distillate fractions, as well as the residual fraction, are subsequently dewaxed to remove'the higher melting hydrocarbons present and to produce an oil with a suitable pour point.

The present invention is not concerned with paraffin crystalline waxes, such as are normally produced from distillate lubricating oil fractions by a dewaxing process. On the contrary, it is concerned with microcrystalline or amorphous waxes, which are normally obtained from the residual fractions containing higher boiling lubricating oil fractions. The waxes obtained from residual petroleum oils, such as by means of vacuum distillation of the latter, are of relatively high molecular weight and appear to be of an entirely difierent character from parafiin wax, The mass thereof, which to the unaided eye appears to have no crystalline character. and to be amorphous, has somewhat plastic characteristics and has refractive indices indicating the principal components to be non-straight-chain hydrocarbons, such as mixtures of isoparafiinic, naphthenic and aromatic hydrocarbons. Magnification reveals a microcrystalline structure, hence, the name microcrystalline wax.

Microcrystalline waxes are employed to a large extent in wax compositions used for sealing purposes,such as in wax papers and the like. Particularly where these papers are to be employed at relatively low temperatures, such as in the wrapping of frozen food containers, the properties of the wax must be examined over a widetem' perature range. Thus, the waxes should ideally possess good sealing characteristics over a temperature from about 30 C. to at least about +30 C. Itis common knowledge that many microcrystalline waxes do not have satisfactory sealing strengths over such a wide temperature range, although they may possess excellent sealing strength properties at some particular narrow range of temperatures. Due to the relatively high molecular weight of the individual wax molecules contained within a typical naturally-occurring microcrystalline wax, it will be understood that the precise reason for the lack of optimum wide temperature properties is not easily "ice ascertainable. However, it has been found that the physical properties of the wax and particularly those of brittle point and sealing strength depend to a large extent upon the basic configuration of the individual wax components and upon the ratio of wax structures exhibiting optimum physical properties With other wax structures showing poor properties.

In some rare cases, it may be possible to alter the steps entailed in the wax production so as to include or remove desirable or undesirable fractions (as the case may be) in order to alter one or more of the physical properties of these waxes. However, it will be understood that the alteration of refinery processes involves many considerations other than the production of optimum characteristics in one product from such a complex operation. By altering the constitution of a microcrystalline wax by modification of the refining processes therefor, it will be recognized that the properties and yields of oils separated therefrom also will be radically altered; and that these changes may not at all times be desirable. Moreover, it is obvious that the physical properties of an amorphous wax will not only depend upon the refining steps by which it is derived but also upon the geographical location of the crude oil from which it is obtained. The ratio of specific structures will vary widely dependent upon the source of the crude oil as has been shown by innumerable analyses of the latter.

The sealing strength of a microcrystalline wax has been found to be dependent upon the structure of the wax molecule. On the other hand, the melting point of the microcrystalline wax is largely dependent upon the longest straight-chain segment in said molecule. This straightchain segment can exist at two principal points in the molecule, assuming that microcrystalline waxes seldom, if ever, are composed entirely of normal paraflins. Assuming, on the contrary, that microcrystalline waxes are, for the most part, mixtures of branched or cyclic hydrocarbons, the longest straight-chain portion thereof may occur as an alkyl substituent attached to a cyclic nucleus, any branching of the alkyl being relatively near said nucleus, the remaining tail being substantially unbranched. On the other hand, a type of wax molecule structure is possible wherein the longest straight-chain portion thereof is modified at or near both ends of the chain, one end of the chain being modified at least with a cyclic nucleus, and the opposite end being modified either by a second cyclic nucleus or more probably by branching of the chain.

It has been determined that the optimum sealing strength properties over a wide temperature range of a microcrystalline wax are obtained by waxes predominating in structures of the second type. This appears to be due to the fact that at the setting point of the wax and for a range of about 30? therebelow the non-straightchain portions of the wax molecule do not actually crystallize but remain in a more or less liquid state. The properties of the wax molecules are such that in the case of the first (less desirable) type of microcrystalline wax, wherein the longest straight-chain portion of the molecule is unmodified at one end thereof, true crystallization may more easily occur with other wax molecules also present in the mixture. On the other hand, wax molecules wherein both ends of the longest straight-chain portion are modified either by branching or by cyclic nuclei exhibit co-crystallizing tendencies. The tendency to crystallize throughout all portions of the wax molecule appears to be directly related to the wide temperature sealing strength and brittle point properties of the wax.

It will be seen, therefore, that alterations in the composition of the microcrystalline wax which increase the ratio of wax. molecules having structures wherein both ends of the straight-chain segment are protected by branched or cyclic structures would be highly desirable but as mentioned hereinbefore is usually impractical due to over-all refinery operating considerations. Hence, any operation or alteration of the microcrystalline wax which would prevent or retard the crystallization of the entire wax molecule and thereby improve the wide temperature sealing strength properties would be highly desirable.

It is an object of the present invention to improve the wide temperature sealing strength properties of microcrystalline waxes. It is a second object of this invention to improve (lower) the brittle point properties of said waxes. It is a further object of this invention to improve the recited properties of microcrystalline waxes without any substantial alteration in the refinery operations producing microcrystalline waxes. Other objects will appear hereinafter.

Now, in accordance with the present invention, it has been found that the sealing strength properties and brittle point of microcrystalline waxes can be substantially improved by modification of the wax with the addition of polycyclic substantially saturated hydrocarbons containing a maximum of one double bond per molecule and having an average of between about 3 and about 4 fused rings per molecule. More particularly, it has been found that highly optimum results are obtained when the proportion of such hydrocarbons in the amorphous wax composition is between about 2% and about 8.5% by weight thereof. Preferably, the proportion of polycyclic materials as defined above is between about 3% and about 7% by weight.

It will be understood that the precise function of these added polycyclic hydrocarbons is not fully elucidated at the present time. However, it is believed (although applicants claims are not based upon this theory) that the added polycyclic material associates with the polycyclic portions of the microcrystalline wax molecules and further tends to prevent them from crystallizing throughout the entire structure particularly at the relatively low temperatures which are important in sealing strength characteristics. On the other hand, being such highly cyclic structures for a given molecular weight, such added hydrocarbons are either of relatively low melting point or are, in fact, often oily in character at or slightly above normal room temperatures. Consequently, if an excessive amount of an additive is employed, the sealing strength of the amorphous wax is ruined completely due to the oily character imparted to the wax. Hence, it has been determined that the effectiveness of the added polycyclic material is obtained only when the latter substances are employed within the critically defined percentage ranges. The precisely maximum effect will vary from one microcrystalline wax to another, depending upon the individual wax molecule structures and upon the setting point (or melting point) of the wax.

It has been determined that it is norm-ally necessary to employ substantially saturated fused ring molecules since the corresponding unsaturated structures do not have the desired effect upon seal strength. Moreover, it has been determined that highly polymeric substances such as the polymethacrylate and vinyl polymers are substantially useless for wide temperature sealing strength improvement although they may have a moderate eifect at some specific relatively low temperature range. It is the intent and result of the present invention, as compared with this, to improve the sealing strength characteristics over a wide temperature range so as to enable the production of microcrystalline waxes useful from temperatures of about -40 C. to about +40 C.

The following list of three and four fused ring substantially saturated hydrocarbons contains typical species of substances useful for addition to the subject microcrystalline waxes. However, it will be understood that mixtures of these hydrocarbons with other materials may be employed as well. Furthermore, mixtures of naturally occurring hydrocarbons falling within the definition given hereinbefore may be isolated or concentrated and added to microcrystalline waxes in order to obtain the desired improvement in both sealing strength and brittle point properties. Hence, the definition of the desired class of materials will be understood to include average figures as well as specific structures. Accordingly, the limitation of between 3 and 4 fused rings will be understood to include mixtures wherein the average of fused rings present is within this figure. Preferably, the fused rings are fused into a single nucleus such as found in hydrogenated phenanthrenes or hydrogenated chrysenes, for example. The term substantially saturated will be understood to mean that the subject polycyclic hydrocarbons may have no more than about one double bond per molecule and preferably the molecule is completely saturated.

The polycyclic materials, such as those listed hereinbelow, preferably have between about 14 and about 45 carbon atoms per molecule and may be modified by the presence on these polycyclic nuclei of substituents other than hydrogen, such as branched or straight-chain alkyl radicals having from one to 18 carbon atoms each. Chole stane and other alkyl substituted cholanes are examples of this type of structure. As will be seen by the data following hereinafter, the precise isomer employed (where isomers are possible) appears to be immaterial since two isomers of perhydrochrysene having widely differing melting points both produced the desired improvement in wide temperature sealing strength characteristics.

List of suitable hydrocarbons Tricyclooctanes Hydrogenated pyraeenes Tricyclononane Hydrogenated isonaphthofluorenes Hydrogenated a-anthrindans Hydrogenated aceanthrenes Hydrogenated acenaphthenes Hydrogenated naphthacenes Hydrogenated chrysenes Hydrogenated benzophenanthrones Hydrogenated triphenylenes Hydrogenated pyrenes Ergostanes Hydrogenated dicyclopentanaphthalenes In the investigation of the present subject a number of diiferent types of hydrocarbons were tested for their potential value in improving the wide temperature sealing strength of microcrystalline waxes. Figure 1 gives the results of some of these tests, in which 5% by weight of each of the additive materials was employed. It will be found by reference to this figure that polycyclic saturated hydrocarbons are substantially superior to all other types of materials tested. The microcrystalline wax employed in these tests had a melting point of 43 C. and, as will be seen by reference to Figure 1 exhibited excellent sealing strength at a temperature of about 28 C. However, the sealing strength fell off rapidly on either side of this optimum temperature thus showing its unsuitability for use as a paper coating wax, particularly for use in freezer wrappers.

The addition of a chlorinated hydrocarbon actually degraded the sealing strength properties of the wax. The use of an isomerized Wax fraction caused a. slight improvement in the low temperature sealing strength properties but degraded the sealing strength at temperatures above about 7 C. The use of a residual oil fraction (Bright Stock) containing a wide variety of hydrocarbon structures was little better than isomerized wax as an improving agent for the microcrystalline wax. A somewhat greater improvement was encountered when a medium viscosity lubricating oil was employed. However, such an oil contains not only polycyclic saturates but also substantial proportions of aromatics and aliphatic hydrocarbons. Consequently, the improvement was limited to low temperature sealing strength improvement at the expense of sealing strength degradation at about the softening point of the wax.

Segregation of the polycyclic aromatics from this same medium viscosity lubricating oil provided a limited improvement over the use of the full range lubricant. However, as Curve 6 indicates, the saturated polycyclics containing an average of about 4 fused rings isolated from the same lubricating oil source provided a substantial increase in sealing strength characteristic not only at temperatures below about 10 C. but also at temperatures up to about the melting point of the microcrystalline wax.

This phenomenon was investigated further by the utilization of 5% by weight, based on the microcrystalline wax, of specific, substantially pure chemical compounds, such as cholestane and perhydrochrysenes. The effect of these is shown in Figure 2. The same microcrystalline wax was employed in these experiments. The addition of cholestane to the microcrystalline wax caused a substantial improvement in the over-all sealing strength characteristics over the entire testing range. A further indication that the fused rings should be saturated is seen in the comparison on Figure 2 between chrysene and the two isomeric perhydrochrysenes. It is clear from the curves given therein that the hydrogenated isomers were substantially superior to the aromatic polycyclic material for the present purpose.

The sealing strengths were determined by sealing two strips of aluminum foil together with 0.03 g./in. of the wax compositions. The unsealed ends of the strips one inch in width were fixed in two arms of an apparatus which pulled the two foils apart at an angle of 180 and at a rate of seven inches per minute. The force required to maintain this speed was continuously recorded and is expressed in terms of g./ in.

As stated hereinbefore, the fused polycyclics also substantially improved the brittle point characteristics of the subject waxes. Brittle point is defined as the temperature at which a specimen 0.02 inch thick cracks when bent suddenly through an angle of 90. The following table illustrates this property, 4% by weight of the additive being used:

Brittle Sample Composition Point F A Microcrystalline wax, 135.6 F 20 B Same+cho1estane O Same+perhydroehrysene (M. P. 107 0.)

I claim as my invention:

1. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 2% and about 8.5% by weight of polycyclic substantially saturated hydrocarbons containing a maximum of one double bond per molecule and having an average of between about 3 and about 4 fused hydrocarbon rings per molecule.

2. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 3% and about 7% by weight of polycyclic substantially saturated hydrocarbons containing a maximum of one double bond per molecule and having an average of between about 3 and about 4 fused hydrocarbon rings per molecule.

3. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 2% and about 8.5% by weight of polycyclic substantially saturated hydrocarbons having a maximum of one double bond and an average of about 3 fused hydrocarbon rings per molecule.

4. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto be tween about 2% and about 8.5 by weight of polycyclic substantially saturated hydrocarbons having a maximum of one double bond and an average of about 4 fused hydrocarbon rings per molecule.

5. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 2% and about 8.5 by weight of saturated hydrocarbons having an average of between about 3 and about 4 fused hydrocarbon rings per molecule.

6. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 3% and about 7% by weight of saturated hydrocarbons having an average of between about 3 and about 4 fused hydrocarbon rings per molecule.

7. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 3% and about 7% by weight of fully saturated hydrocarbons having an average of about 3 fused hydrocarbon rings per molecule.

8. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon Wax having added thereto between about 3% and about 7% by weight of fully saturated hydrocarbons having an average of about 4 fused hydrocarbon rings per molecule.

9. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 3% and about 7% by weight of substantially saturated polycyclic hydrocarbons predominating in hydrocarbons having hydrogenated chrysene nuclei.

10. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 3% and about 7% by weight of substantially saturated polycyclic hydrocarbons predominating in hydrocarbons having cholestane nuclei.

11. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 3% and about 7% by weight of cholestane.

12. A wax composition having improved seal strength characteristics comprising a major proportion of a microcrystalline hydrocarbon wax having added thereto between about 3% and about 7% by weight of perhydrochrysenes.

References Cited in the file of this patent UNITED STATES PATENTS 2,443,221 Bergstein June 15, 1948 2,500,426 Moose Mar. 14, 1950 2,636,003 Capell et al. Apr. 21, 1953 2,668,790 Good et al Feb. 9, 1954 2,671,051 Moore Mar. 2, 1954

Claims (1)

1. A WAX COMPOSITION HAVING IMPROVED SEAL STRENGTH CHARACTERISTICS COMPRISING A MAJOR PROPORTION OF A MICROCRYSTALLINE HYDROCARBON WAX HAVING ADDED THERETO BETWEEN ABOUT 2% AND ABOUT 8.5% BY WEIGHT OF POLYCYCLIC SUBSTANTIALLY SATURATED HYDROCARBONS CONTAINING A MAXIMUM OF ONE DOUBLE BOND PER MOLECULE AND HAVING AN AVERAGE OF BETWEEN ABOUT 3 AND ABOUT 4 FUSED HYDROCARBON RINGS PER MOLECULE.

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