US2942766A - Wax coating compositions - Google Patents

Description

June 28, 1960 s. w. FERRIS WAX COATING COMPOSITIONS Filed Feb. 27, 1959 HH T mum EI- L RR EEE mm "FF Vuv Wax Strip 1 4" Thick Miles of Fiber lLb. of Wax HHH T. 06 ma I- E L RRR IEE um HF... n "6 l0 muv O o o Q 5 8. s wok-$52k 8 1 Wax Strip 1 0" Thick Miles of Fiber lLb. of Wax 3 OO nid INVENTOR. SEYMOUR W. FERRIS 2,942,766 WAX COATING COMPOSITIONS Seymour W. Ferris, Chester, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Filed Feb. 27, 1959, Ser. No. 796,161 17 Claims. (Cl. 229-31) This invention relates to the preparation and use of improved wax-coating compositions and more particularly to petroleum wax-coating compositions which are resistant to flaking during use.- The wax compositions of the present invention are particularly useful in the preparation of food containers which are subjected to refrigeration conditions during use, for example, milk containers.

Food products which need to be kept under refrigeration are often packaged in paper containers which have a surface coating of petroleum Wax. For example, containers made from paperboard which has been coated with petroleum wax are widely used for dispensing milk. Wax-coated papers also are used widely as wrappers for frozen food products such as vegetables, meats and the like.

While wax-coated paper containers are highly satisfactory in many respects for food packaging, there are certain drawbacks which tend to limit their usefulness. One is that under low temperature conditions resulting from refrigeration, rough handling of the containers or food packages tends to cause the wax to crack and flake ofl, so that wax flakes may appear in the food product. In the use of wax-coated milk containers the wax is subjected to thermal shock when the cold milk is introduced into a container which is at a higher temperature, and this tends to cause the Wax to crack and break off into the milk. Also, with food products, such as meat, which are wrapped in waxed paper and then are frozen for storage, the wax sometimes sticks to the meat when it is unwrapped.

In order to minimize flaking of wax from containers relatively soft waxes generally have been utilized for coating the containers. However, this is disadvantageous in that the softer waxes more readily rub off from the container when it is handled or carried in contact with clothing.

The present invention provides improved petroleum wax-coating compositions which, when applied to food containers or wrappers, are highly resistant to flaking under conditions of general use. According to the invention, an improved wax-coating composition is prepared by incorporating in a petroleum wax a small amount of fine fibers having short fiber lengths. It has now been found that the presence in the wax of a small percentage of fibers which have diameters that are sufficiently small and lengths within the hereinafter described range will substantially prevent flaking of the wax with out adversely affecting any of its other desirable properties as a coating material for food packages. The invention also permits the use of waxes which are harder than those normally used and thus provides coating compositions which have little or no tendency to rub oif from the food container during handling.

The coating compositions of the present invention are prepared by mixing into a molten petroleum wax an appropriate small amount of fine fibers having the proper dimensions. This results in improved wax-coating compositions in which the presence of the fibers is practically unnoticeable. The amount of fibers which should be employed varies with the diameter of the particular fiber used but generally should be less than 1.0% by weight, for example, in the range of 0.0l0.50%. Best results generally are obtained by using about 0.l0,20% fibers having a denier in the range of 1-10. Fibers having con- United States Patent 0 2,942,766 Patented June 28, 1960 ICC siderably higher denier can be used and the flaking tendency of the wax thereby can be greatly reduced; however, it is generally desirable to employ fibers having a denier less than 20 which corresponds to exceedingly small fiber diameters, although a denier as high as 50 can be used in some cases. Also a denier less than 1, e.g. 0.5, can be used in cases where the strength of the fiber is high. While the term denier normally is used only in connection with synthetic fibers, the above specified denier values are intended to apply to both synthetic and natural fibers used for the present purpose.

The length of the fibers employed is a particularly important factor in producing the improved coating composition provided by the present invention. It has been found that if the fibers are too short, protection against flaking of the wax will not be secured. For example, compositions prepared with fine fibers having a length of one millimeter showed substantially no improvement with respect to flaking as compared to the wax alone. 0n the other hand, fibers having a fiber length in the range of A3 inch to inch give excellent results. As a general range for practicing the invention, the fiber length should be inch to /z inch, with the length selected in any given case depending largely on the particular fibers and amount thereof employed. The main factor that determines the maximum length that should be used is the tendency of the fiber material to mat when it is mixed with the liquid wax if the fibers are too long. It has been found, for example, that with rayon or nylon fibers having deniers within the preferred range of 1-10, a tendency toward matting appears when the fiber length exceeds A inch. On the other hand, when stifier fibers are employed, there is less tendency to mat unless the fiber length is substantially greater than A inch. In any case it is desirable that the length of the fibers be less than /2 inch in preparing the compositions of the present invention and it is distinctly preferable to use fibers having a length in the range of A; inch to A inch.

Numerous kinds of fibers can be used in practicing the invention, the primary requirement being that the fibers be composed of a material which is substantially insoluble in molten petroleum wax. The material need not be completely insoluble as long as fibers of the specified denier values will remain in the amount specified when the composition is maintained in molten condition for a prolonged time. It is preferred for the present purpose to select fibers which are somewhat wrinkled or crimped or which have rough surfaces.

The following are specific examples of types of fibers that can be employed: nylon, rayon, Orlon, cotton, silk, jute, asbestos, fiberglass, silicon plastics and camel hair. Any of the synthetic resin fibers which are substantially insoluble in hydrocarbons can be used with good results. Particularly useful materials for practicing the invention are the fibers prepared from solid polyolefins such as linear polyethylene and crystalline polymers of propylene, butylenes, pentenes, hexenes or the like. These polyolefins are especially advantageous in that they have densities close to the densities of petroleum waxes and hence have little tendency to settle out of the molten wax. In commercial practice the usual procedure for preparing waxcoated paper containers involves merely dipping the containers in a bath of the molten wax and then allowing them to drain. If fibers are used which have relatively high densities in preparing the coating compositions of the present invention, the fibers may tend to settle from the bath during the subsequent coating operation. This can be overcome by providing stirring means to keep the fibers in suspension. However, when the fibers employed are solid polyolefins, the need for stirring means is eliminated since convection currents in the bath and the mild tend to flake during rough usage.

agitation caused by dipping the containers are sufiicient to keepthe fibers suspended.

I The tabulated results show that'all of the fiber-contain- Waxes which can be used in practicing the present theva'riousgrades of availablewaxes that make them particularlysuitable for the applications inwhi ch they are 't obe used; The waxes may contain small; amounts of various solubleadditives,*such as antioxidants or low molecular weight polyolefins, whichare customarily used 'toprovide additional desirable qualities. For example, waxtcompositionsprepared according to the invent on may also contain small amounts of relatively low molecular weightpolyethylene to improve nonscufling characteristics, appearance, modulus of rupture and thelike.

Inorder to investigate the eifectiveness of fibers in preventing flaking of wax and to-determine the conditions for securing best results, a simple procedurewas devised for testing wax compositions prepared according to the invention." Specimens of the compositions were prepared by casting the molten material in'rectangular molds having i a width of 3' inches and a length of 6 inches, cooling to room temperature and then removing the wax slab from the mold and, cutting it into /2 inch x 3 inch strips; Specimens were prepared in this manner .withthree difierent thicknesses, viz. inch, inch and A inch. Each specimenlwas, subjected to a fracturing procedure by fold ing a paper towel around it and then sharply bending it lengthwise-around the circumference of a cylindrical four ounce bottle having a diameter of about 1% inch. This caused each strip to crack widthwise in a number of places. The towel was then unfolded and the number of total fracs tures andalso the number of fractures where the adjacent wax pieces had held together by virtue of the presence of the fiber material were determined. The specimen was then rated as to its non-flaking quality by calculating the percentage of the totalfra ctures where a complete break had not occurred. 7 For example, if a strip fractured'in ten places but only two of them were a complete brealgthe degree of nonflaking protection would be rated as 80%. The rating serves as a useful index as to whether or not a food container coating made from the composition would Since the above-described test conditions are rather severe, a high rating according to the test is a good indication that coatings made from the test composition would not tend to flake off of a container even when it is subjected to rough handling.

The above-described procedure was utilized for testing compositions made from petroleum wax with rayon fibers and with nylon-fibers. The petroleum wax used was a deniers; andthe resulting ratings obtained were as shown 1n the accompanying, table.

. 7 G. of Miles of Type of Fiber Denier Length, Fiber 'Fiber Rating,

Inch per lb. perlb. percent 1 of Wax of Wax 0 0 l. 5 is 0. l. 7 100 1.5 %a 0.10 1.7 '100 l. 5 Mi 0. 10 l. 7 i 100 3.0 $6 0. 10 0.85 100 3. 0 /1 e 0. 10 0.85 100 3. D 34 0:10 0. 85 100 5. 5 it a 0. 10 0. 46 90 5. 5 is 0.30 1.38 100 3. 0 I is 0.10 0. 85 100 3.0 its 0.10 0.85 90 3. 0 366 0.30 2. 55 100 3. 0 l4 0. 10 0. 85 r 100 3. 0 34 0. 2. 100

iug compositions listed had excellent nonfiaking qualities. With no fibers in the wax all of the fractures were complete breaks, whereas the specimens which contained fibers showed very few and mainly nocomplete breaks. These results indicated that any ofthe listedfib'er-.containing compositionswould provide an excellent coating for milk containers orother food packages.- 5 1 7 Q t The foregoing tests were all made with Wax strips which 'had a thickness of fl inch. Further tests were made under still more severe conditionsjby using specimens which had greater thicknesses. Figs. 1 and 2 show results in the form of curves plotted from the'data obtained with specimenshaving thicknesses of /4 inch and 4. inch re spectively. These figures show thc rating (i.e.- percent fractures which held together) as afunction of the miles offiber per lb. of wax for-three diiferent fiberlengths, namely, ii1ch,- inch and 41 inch. Each curve is based upon tests on rayon fibers having'deniers of 1.5, 3.0

and 5.5 and is-drawn -as a smoothed curve through the points obtained with all of the denier sizes, By reference to Fig. 3, the value for total miles of fiber per lb. of wax can be converted to grams of fiber, per, 1'00 grams of wax for each denier size. 7 a V a V Referring to Fig.1 which is for wax strips 4 inch thick and hence represents the most severe testing condi tion, it can be seen that if fibers having /iin ch length are used 'at least about two miles of total fiber length per lb. of wax should beemployed to secure the best obtainable protectionagainst flaking. On theother hand', with inch fiber length at least about five miles of fiber length per lb. of wax should be employed to secure such protection. Further, with A5 inch' fiber length only an 80% rating can be obtained even when the total fiber length is increased to eight miles. In view of the severity of the test, however, such rating indicates high resistance to flaking in actual food packaging use.

Fig. 2 is for strips A3 inch thick and hence represents less severe testing conditions. From this figure it can be seen that 100% ratings were obtained with inch length fibers when the total fiber length increasedto about one mile per lb. of wax. With inch and fiber lengths approximately two miles of total fiber length was required to reach a rating of 100%. i

The various test results made indicate that to secure the best protection against flaking of the wax composition, the amount of fibers incorporated therein should be'sufficient to provide a total fiber length inthe range of 1-8 miles per lb. of wax. While these seem like surprisingly high length values, reference to Fig. 3 will show that the amount of fibers in the wax composition is quite small. Other petroleum waxes give similar results to those obtained with the particular wax described above. 7

A further embodiment of the invention involves using fibers in the form of. fine tubes rather than solid fibers. This provides a means of regulating the effective density of the fiber particles so that such density will approximate that of the molten wax. In this embodiment, when the wax-fiber mixture is first prepared by heating the wax .and then mixing in the fibers the elfective density of the heated and the density of the molten wax atthetemperw ture that will be employed in the subsequent operation of coating a container. Duringzthe preparation of the composition expansion ofair from the tubular fiber will 'occur and the'amount forced out of it will dependupon the temperature to which the wax is heated. The temperature should be selected so that during the subsequent coating operation the weight of the fiber'materi-alin the tubular particle plus the weight of the wax and air therein at the operating temperature will approximate the weight of an equivalent volume of the molten wax at the operating temperature. In place of air the tubular fibers can,

if desired, be filled with an inert gas such as nitrogen or carbon dioxide before being incorporated in the wax. By utilizing tubular fibers in accordance with the above-described embodiment a fiber material which has a density considerably higher than that of wax can be used and the efiective particle density can be made to approximate the wax density so that settling of the fiber from the molten bath will not occur during the coating operation.

Still another embodiment of the invention which can be employed advantageously when the fiber material has a relatiavely high density involves the use of fibers which have entrapped gas bubbles. Fibers can be made commercially with discontinuous gas spaces and the efiective fiber density can be regulated through the proportion of bubbles entrapped in the fiber. In the present embodiment fibers prepared in this form are selected to have an efiective particle density approximately equivalent to the density of the wax in which they are incorporated. Compositions in which the fiber particles have substantially no tendency to settle from the wax can readily be prepared in this manner.

I claim:

1. A flake-resistant wax-coating composition composed mainly of petroleum wax and 0.01l.0% of fine fibers having a fiber length of 5 inch to /2 inch.

2. A composition according to claim 1 wherein the fibers are of tubular form containing entrapped air and the effective particle density thereof approximates the density of the wax.

3. A composition according to claim 1 wherein the fibers contain entrapped gas bubbles in amount such that the efiective particle density of the fibers approximates the density of the wax.

4. A flake-resistant wax-coating composition composed mainly of petroleum wax and 0.0l-0.5 of fibers having a denier of -20 and a fiber length of 5 inch to inch.

5. A composition according to claim 4 wherein the fibers are composed of a solid polyolefin.

6. A composition according to claim 4 wherein the fiber length is /s inch to inch.

7. A composition according to claim 6 wherein the amount of fibers is 0.l'0-0.20%.

8. A container for food packaging in which the container wall has a surface coating of petroleum wax having incorporated therein 0.01-1.0% of fine fibers having a fiber length of fi inch to /2 inch.

9. A container for food packaging in which the container wall comprises paper having a surface coating of petroleum wax having incorporated therein (MM-0.50% of fibers having a denier of 05-20 and a fiber length of 5 inch to /8 inch.

10. A container according to claim 9 wherein the fibers are composed of a solid polyolefin.

11. A container according to claim 9 wherein the fiber length is /s inch to A inch.

12. A container according to claim 11 wherein the amount of fibers is 0.10-0.20%.

13. Method of preparing a flake-resistant wax-coating composition which comprises incorporating in a petroleum wax 0.01-1.0% of fine fibers having a fiber length of 1 inch to /2 inch.

14. Method of preparing a flake-resistant wax-coating composition which comprises incorporating in a petroleum Wax OBI-0.50% of fibers having a denier of 05-20 and a fiber length of 5 inch to inch.

15. Method of preparing a container for food packaging which comprises coating surfaces of a container with a coating composition composed mainly of petroleum wax and 0.01-l.0% of fine fibers having a fiber length of ,5 inch to A2 inch.

16. Method of preparing a container for food packaging which comprises coating surfaces of a paper container with a coating composition composed mainly of petroleum wax and OBI-0.50% of fibers having a denier of 0.5-20 and a fiber length of $5 inch to inch.

17. A flake-resistant wax-coating composition composed mainly of petroleum wax having incorporated therein fibers having a denier of 05-20, the length of the individual fibers being in the range of A inch to inch and the total length of the fibers per pound of wax being in the range of 1-8 miles.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. 9. A CONTAINER FOR FOOD PACKAGING IN WHICH THE CONTAINER WALL COMPRISES PAPER HAVING A SURFACE COATING OF PETROLEUM WAX HAVING INCORPORATED THEREIN 0.001-0.50% OF FIBERS HAVING A DENIER OF 0.5-20 AND A FIBER LENGTH OF

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