US3305383A

US3305383A - Method for fabricating improved liquidcontaining fibrous cartons

Info

Publication number: US3305383A
Application number: US269730A
Authority: US
Inventors: Travis L Gordy
Original assignee: Continental Oil Co
Current assignee: ConocoPhillips Co
Priority date: 1963-04-01
Filing date: 1963-04-01
Publication date: 1967-02-21
Anticipated expiration: 1984-02-21
Also published as: FR1397524A; BE662005A; NL6403180A; GB1002917A

Description

United States Patent "ice 3,305,383 METHOD FOR FABRICATING IMPROVED LIQUID- CONTAINING FIBROUS CARTONS Travis L. Gordy, Ponca City, Okla, assignor t0 Continental Oil Company, Ponca City, Okla, a corporation of Delaware No Drawing. Filed Apr. 1, 1963, Ser. No. 269,730 9 Claims. (Cl. 117-45) This invention relates to a method for fabricating cartons of fibrous material, such as paper, for the packaging of liquids or moist solids. More particularly, the present invention relates to a method for enhancing the moisture permeability resistance of paperboard substrates and to the improved cartons fabricated therefrom.

It has recently become :a practice in the manufacture of paperboard cartons for the packaging of milk, frozen foods, and the like, to coat the flat carton blanks with a thermoplastic resin, such as polyethylene, or a blend of a thermoplastic resin and paraffin wax. Of the latter coating compositions, blends of paraffin wax and a copolymer of ethylene and vinyl acetate have been recently proposed. While both the polyethylene coated cartons and the cartons coated with the wax-copolymer blends are superior in many respects to cartons coated solely with wax, they nevertheless exhibit an increased tendency to develop leaks along bend or score lines located at, or adjacent, the bottom of the carton, particularly under service conditions.

The leakage which often occurs in liquid-containing cartons coated with the above-described materials is due to a combination of several factors. In the fabrication of the cartons, the coating is applied to a scored substrate prior to folding same to the configuration of the finished carton. Upon folding the coated substrate, the coating is mechanically strained in the vicinity of the bend or score lines and as a consequence invariably develops cracks, pinholes or fissures. These defects expose fibers in the substrate to the liquid contained in the carton. Cracking of the coating is particularly pronounced at the corners of the carton where the flat blank has been folded along several converging lines. Moreover, the tendency of the coating over the fold or score lines at the bottom of the carton to develop flaws is aggravated by the recurring mechanical shock and jostling to which the filled cartons are subjected in being transported, stored and displayed in sales outlets.

After cracks have developed in the coating at, or in the immediate vicinity of, the fold or score lines, the liquid in the carton contacts the fibers in the substrate and is transmitted by them in a wicking or capillary action to the surrounding substrate area and to the outside of the carton. The bottom corners of the carton are usually the first points to develop leakage followed by the bend lines at the bottom of the carton and the bend line and seams at the sides of the cartons.

Leakage of the type described may be reduced by materially increasing the thickness of the coating material applied to the entire surface of the stock. This approach, however, results in substantially increased costs and furthermore does not provide an entirely satisfactory solution to the problem of corner and score line leakage. The present invention, on the other hand, provides a method for fabricating paperboard cartons coated with nominal thickness of a water impermeable coating which have less propensity to leak or to become weakened as a result of small holes or breaks in the coating.

In brief, the present invention comprises impregnating a flat carton blank (or a sheet of paperboard having a plurality of carton patterns) at certain confined areas with a normally solid hydrophobic material, such as the 3,305,383 Patented Feb. 21, 1967 various waxes. The critical areas are, as previously explained, the areas along the bend lines at the bottom of the carton and extending up the sides thereof. The wax or water resistant material is applied to the side of the fiat blank which will become the inside of the carton. Some benefit may be obtained by similarly treating the same areas on the opposite side of the blank (the outside surface of the carton) although this is generally not required and, of course, increases the cost of fabrication. Moreover, treating the outside surface of the carton in the manner indicated detracts from the general appearance of the carton.

After treating the inside surface of the cartons in th manner described, the flat blank or substrate is, if required, heated to facilitate penetration of the water resistant material into the stock in the areas where same had been applied.

The final step of the process is the application to the entire stock of a thermoplastic resin containing coating such .as, for example, one of the types mentioned hereinabove. This may be accomplished in a number of ways, such as by curtain coating, or by roll coating. These techniques are well known to the art and the details of their performance do not constitute novel features of the present invention. After the application of the thermoplastic resin containing coating, the cartons are folded in their final configuration and bonded along seam lines as required.

Cartons constructed by the method of the present invention have been demonstrated by tests to be clearly superior in structural stability and durability to cartons which are coated with thermoplastic resin containing coating compositions but which have not been treated with a waxy material in the manner described. The amount of wax applied to the critical areas of the carton in accordance with the invention does not significantly add to the cost of fabricating the carton.

From the foregoing description, it will have become apparent that it is a major object of the present invention to provide a method for economically fabricating fibrous cartons for containing liquids and moist solids, which cartons are less susceptible to the development of leaks and moisture seepage.

Another object of the invention is to improve the service life and mechanical durability of fibrous material cartons which in use are employed to contain liquids, frozen foods and the like.

A further object of the invention is to provide a method by which fibrous cartons may be made leak resistant much more economically than by the method of increasing the thickness of the synthetic resin containing coatings heretofore applied to such cartons.

An additional object of the invention is to provide improved fibrous cartons for containing liquids and moist solids, which cartons demonstrate less propensity to develop leaks or weakened areas than fibrous cartons previously used for this purpose.

Other objects and advantages of the invention will be come apparent from the following detailed description of the invention.

As stated in the brief general description of the invention set forth above, the initial step of the process of the invention comprises applying a waxy material, usually in the form of a thin coating, along and proximately adacent to the score or bend lines of the carton stock. In general, a band having a width of from about /2 to of an inch will be applied to the bend or score lines, although the primary requirement of the areal size of such bands is that they be sufficiently wide to assure that the area of the stock which will sustain mechanical stressing during the folding and commercial use of the carton be coated with the wax.

The type of waxy material which is applied to the carton stock is subject to considerable variation and the main requirements of this material are that it meet certain functional demands. These demands are that the waxy material with which the blank is treated shall be capable or rendered capable of penetrating into the fibers of the stock, and, by coating such fibers, imparting a water resistance or water repellency to the fibers in the body of the stock. A further property of the waxy material which is employed for treating the stock is that this material should be compatible with the coating material employed in the sense that the wax does not interfere with bonding between the final coating material and the fibers of the carton. In most instances, if proper penetration of the wax has been effected, the last requirement will be satisfied in that very little or no wax is left accumulated at the surface of the fibrous stock after it has been treated and prepared for receiving the final coating.

The importance of the several properties or characteristics required of the hydrophobic material used for treating the carton stock will vary according to the type of stock utilized, its thickness, the type of final coating composition which is to be employed and, if necessary, the extent to which it is desired to heat the stock to flash or drive said material into the fibers thereof.

A number of waxes or waxy substances meet the above-described requirements and can be utilized for treating the fibrous stock according to the process of the present invention. Suitable among such waxes are of either animal, vegetable or mineral origin. Synthetic waxes are also applicable. The waxy materials which, in addition to meeting the above-prescribed requirements, are otherwise particularly operable in the invention, can be defined broadly as opaque or translucent hydrophobic organic substances having a melting point between about 40 C. and 90 C. and which upon melting yield relatively low viscosity liquids. Waxes having higher melting point and viscosity characteristics can also be used if applied in a solvent system.

Although a variety of waxes can be employed for treating the fibrous stock in accordance with the process of the present invention, the waxes derived from petroleum are preferred. These are commonly referred to as paraffin waxes, or simply paraffins, and microcrystalline waxes. Petroleum waxes are the waxy constituents occurring in various fractions of most crude petroleum. They are most often derived from the fractionated cuts obtained upon distillation of the crude petroleum. The parafiin waxes manifest melting points in the range of about 47 to 65 C. and Saybolt viscosities in the range of from about 35 to 55 S.S.U. at 210 F. and are further physically characterized by crystallizing into large, well-formed distinct crystals of the plate and needle types. The physical characteristics of a parafiin wax may vary as indicated depending upon the crude petroleum source, the portion of the crude which is used for wax production and the differences in refining techniques. In order to illustrate further the various types of paraffin waxes that are preferably utilized in this invention, a brief description will be given of the procedure employed in the manufacture thereof.

The customary fractionation of crude petroleum stocks yields light fractions or cuts comparatively rich in wax components which, as hereinbefore indicated, are termed parafiin or distillate wax. These pa-rafiin rich fractions .are normally liquid at elevated temperatures and upon cooling to lower temperatures, the wax content readily precipitates. After satisfactorily cooling a wax distillate, the precipitate is recovered by a filtering process in the form of slack wax. Slack wax normally contains from to 40 percent by weight oil content. Next, the slack wax is sweated, or solvent deoiled to reduce the oil content to the extent desired in the end product. If the final oil content is between about 0.5 to 1.5 percent by weight, the product may be called either a crude scale or semirefined product. The fully refined product usually contains less than 0.5 weight percent of oil, and has been decolored to obtain a white wax. The sweating and solvent deoiling processes are well known in the art.

In treating stocks according to this invention, scale wax, semi-refined wax, or mixtures of the refined wax with either slack wax or scale wax or semi-refined Wax can be employed. Additionally, as hereinbefore indicated, waxes of animal, vegetable, or synthetic origin can be employed in combination with the parafiin wax. Also, microcrystalline waxes derived from petroleum residues can also be used. For convenience, in the subsequent discussion of the invention, the term paraflin wax will be employed in contemplation of various waxes and combinations thereof as mentioned above.

The method of suitably applying the waxy material to the score or bend lines of the carton stock is a relatively simple operation. For example, a rotogravure process or a felt covered roll for rolling molten wax onto the carton in the critical areas can be used. Alternately, the wax can be brushed or sponged on the score lines or applied in any other suitable manner provided the amount of the coating is not excessive in view of certain requirements to be discussed next. The 'wax used in treatment of the stock should be as uniformly applied as possible. It is further desirable that neither too much nor too little wax in terms of weight be applied to the carton. An excessively light coating reduces the protection against leakage which is afforded by the treatment. On the other hand, an excessively heavy coating of wax results in a residual layer or coating of the wax being left on the surface of the stock with the result that such residual layer may interfere with the bonding of the final coating composition to the fibers of the stock or may result in a finished container blank having an overall greater thickness at the treated areas that would interfere with the machineability of the blank. It may also be undesirable to apply too much wax because of the possibility of the wax penetrating completely through the blank with the result that the outside of the carton will be stained and unsightly.

The weight of the wax coating which is most desirable as determined by the general criteria outlined above will obviously be dependent on the nature of the stock which is utilized, its porosity, the thickness of the stock and the temperature and duration of any heating treatment which may be necessary to drive the wax into the fibers of the stock, and the final service requirements of the container. It will thus be necessary in any given situation to empirically determine the optimum weight of the wax coating which is applied along the bend or score lines of the carton. By way of example, it has been found that fibrous stocks having a thickness of 0.022 inch and used to fabricate coated half-gallon milk containing cartons require a wax treatment coating of at least about 0.009 gram per square inch of the surface area coated to obtain substantially improved resistance to leakage. However, treatment of cartons with as little as 0.006 gram of wax per square inch provided coated cartons having significantly improved leakage resistance as compared with similarly coated cartons where no wax treatment in accordance with this invention was observed.

Upon application of the waxy material to the score or bend lines of the carton stock, same is caused to penetrate the interstices of the stock provided the material is not completely and satisfactorily absorbed on contact therewith. In instances where complete absorbtion of the wax does not occur following its application, the stock is placed in a suitable heating zone, such as a constant temperature oven, and heated to a sufficient extent to permit the wax to penetrate into the fibers of the board without passing completely through the stock and appearing on the outside surface thereof as an unsightly stain. The temperature should be sufliciently high, however, that substantially all the wax penetrates down into the fibers of the carton and very little residual wax is left as a film at the inner surface of the stock.

It will be apparent from this description for effecting penetration of the waxy material that the temperature and duration of heating, if such be needed, will be dependent both upon the properties or characteristics of stock employed, the thickness of the stock and the type of waxy material used in the treatment step. We have generally determined, however, that a temperature between about 225 F. and 450 F. is sufficient in most instances. The application of heat to the wax pretreated carton stock may therefore be simultaneously accomplished with the preheating of the stock which has been found to improve the results obtained in applying the final coating composition to the stock and which has been described in copending application for United States Letters Patent Serial Number 268,146 filed March 26, 1963. In accordance with the disclosure of the aforesaid co-pending application, the preheating of the stock prior to application of certain coating compositions thereto over the entire area of the stock has been found to be especially helpful in improving the continuity and uniformity of such coatings as applied through the coating technique known as curtain coating. A preferred practice of the process of the present invention therefore contemplates the use of the wax treating step and the heating of the stock to flash or drive the wax into the fibers thereof in combination with the process of applying the final coating to the stock through a curtain coating procedure. After impregnating the fibers of the carton stock along the score lines with a waxy material applied and heated in the manner described, the flat blank is, when the final coating is to be applied by curtain coating, passed through a gravitating or falling curtain of the final coating composition in a manner well-understood in the art. Although the use of the curtain coating technique to apply the final coating composition to the entire surface area of the stock is a preferred method of applying such final coating, as previously indicated herein, other coating techniques, such as dip or roll coating, may also be used, as well as extrusion coating in the case of polyethylene and the like.

A number of different types of final coating compositions may be employed to completely cover both surfaces of the carton blank. Examples of such compositions include polyethylene, polyvinylidene chloride emulsions and hot melt blends of petroleum derived wax, i.e., parafiin wax, with certain copolymers, such as copolymers of vinyl acetate and ethylene, and copolymers of ethylene and ethyl acrylate. Cartons of excellent durability and leak resistance can be prepared in accordance with this invention, utilizing blends of paraffin wax with ethylene-vinyl acetate copolymers, and such blends are preferred for utilization as the final coating composition.

The ethylene-vinyl acetate copolymers which are blended with petroleum derived wax in forming the preferred final coating composition used in practicing the invention are characterized in having a polymerized vinyl acetate content of from about to about 40 percent by weight, and, more preferably, from about 25 to 35 percent by weight. These copolymers can be conveniently prepared by copolymerizing a mixture of ethylene and vinyl acetate in the presence of a free-radical catalyst, e.g., tertiary butyl hydroperoxide, in a suitable reactor at a pressure of from about 15,000 to about 30,000 pounds per square inch and a temperature of from about 150 C. to about 250 C. By varying one or several of the reaction conditions enumerated, various molecular weight copolymers can be obtained. Ordinarily in this art, the molecular weight of the resultant copolymer is generally not expressed as such because of the difficulty and uncertainty of reliably ascertaining this property. Accordingly, an alternate and the preferred manner of specifying the molecular weight characteristic of such copolymers is 6 in terms of the polymers melt index as determined by A.S.T.M. D123857T. Briefly stated, this test consists of determining the amount in grams (melt index value) of the copolymer that can be pressed through a standard orifice in ten minutes at F. with a piston weighing 2150 grams. The ethylene-vinyl acetate copolymers especially useful herein exhibit melt indices ranging between about 3 and 300, and preferably between about 3 and 30.

A highly effective blend which may be utilized as the final coating composition comprises between 20 percent and 70 percent by weight of an ethylene-vinyl acetate copolymer of the type described with the remainder, except for a small amount of commonly used wax additives, consisting of petroleum-derived wax which may be either paraffin wax or microcrystalline wax, or both. The exact proportions used will depend upon the final properties desired. This blend, as well as other wax-copolymer blends, may suitably be prepared by first heating about one-half of the total wax content of the final blend to a temperature of between 250 F. and 300 F. in a high shear mixer. The wax is then stabilized by adding approximately 25 parts per million of a suitable oxidation inhibitor to the wax in the mixer. All of the copolymer resin is then blended into the hot wax to form a resinwax concentrate in which no discreet particles of the copolymer can be discerned. The balance of the wax is next added to the blend concentrate, and the total mixture is blended to a uniform consistency. The composition is then ready for application to the carton blank and is preferably applied through the use of the curtain coating technique hereinbefore mentioned and described in detail in the co-pending application to which reference has been made.

When the final coating of the thermoplastic resin containing composition is to be applied to the carton stock by a curtain coating procedure, some additional resistance to leakage and enhanced structural durability may be obtained by applying slightly thicker layer or film of the final coating to the score or bend lines of the carton than is applied to the remaining surface area of the carton. This technique, which will hereinafter be termed ridge coating, increases the cost of fabrication only slightly and it has been found that the ridge coating procedure in combination with the wax pretreating step of the process hereinbefore described will in many instances more than justify the slight increase in fabrication costs which is incurred. The additional thickness of the final coating which is applied to the score lines may easily be as little as about /2 mil without sacrifice of the benefit obtained through ridge coating.

After application of the thermoplastic resin-containing composition as a final coating to the flat carton stock, the carton is folded along the appropriate bend or score lines into its final configuration and is sealed along suitable seams. The folding and sealing techniques are wellknown in the art and constitute no part of the present invention.

Extensive leaking resistance tests of the cartons of the invention have clearly indicated that such cartons possess considerably better durability and are less prone to develop leaks at the lower corners and bottom thereof than those cartons which have been merely coated with thermoplastic resin containing compositions without benefit of the waxy material treatment prescribed by this invention.

In order that the nature and objects of the present invention may be more completely understood, the following detailed examples are given in which all parts are parts by weight unless otherwise stated. These examples are set forth primarily for the purpose of illustration and accordingly, any enumeration of details contained therein should not be interpreted as a limitation on the invention except as indicated in the appended claims.

Example 1 In this example, a plurality of one-half gallon paperboard carton blanks were impregnated with refined paraf fin wax at the bottom score lines thereof in accordance with the method of this invention, and thereupon a coating of a wax-ethylene/vinyl acetate copolymer was applied to each side of the wax impregnated blank. The blanks were then fabricated into cartons employing a conventional carton-forming procedure which firstly involved heat-sealing the sides of the carton. Next, the bottom portion of the carton was folded at the score lines provided in this area and heat sealed. The top portion of the carton was then partly sealed, leaving a provision for introducing a test liquid thereinto. For comparison purposes, similar cartons were prepared from blanks coated cycle, the cartons were examined for signs of leakage. Identical test cycles were repeated until all or a major portion of the cartons had failed. Carton failure as contemplated in this test consists of a development of a leak which traverses the entire thickness of the stock as evidenced by appearances of the blue coloring material in the solution at the outside of the carton. Results obtained in this series comparative testing, together with details as to the preparation and construction of the carton, are outlined in the following Table 1. Results are expressed as percent carton failures after indicated days of testing.

TABLE 1 Days of Repeated Durability Testing Carton Treatment Group Group 1. Wax treated .009 gm./in. along bottom score; ridge coated with 3 mil film on 0 0 0 O 0 G 12 12 inside bottom score lines and balance of carton coated with 1.5 mil film inside and out; wax-copolymer blend. Group 2 Wax treated .009 gin/in. along bottom score; no ridge coating; final coating 0 0 0 1 1 12% 23 60 thickness using wax-copolymer blend 1.4 to 1.6 mils on both sides of carton. Group 30-. No wax treatment: final coating thickness using wax-copolymer blend 1.0 0 13 72 96 98 100 to 1.8 mils: no ridge coating. Group 4..-. Commercially available polyethylene coated cartons O 3% 21 86 96% 100 on both sides with a paratfin wax-ethylene/vinyl acetate copolymer composition but which had not been wax treated in accordance with the method of this invention. Additionally compared in this series of tests were commercially available polyethylene coated one-half gallon paperboard cartons.

The wax-ethylene/vinyl acetate copolymer coating composition employed in this example was as follows:

Ethylene/vinyl acetate copolymer 38 Microcrystalline wax (M.P. 180l85 F.) 30 Paraffin wax (M.P.'122l27 F.) 30 Low molecular weight polyethylene 2 2530% polymerized vinyl acetate; melt index 10-20.

The above-described coating composition was applied to the carton blanks by means of a curtain coating procedure.

All of the fabricated cartons employed in the series of tests in this example were subjected to the following durability test procedure: The individual cartons were filled with a water-solution containing one percent lactic acid and sufiicient methylene blue dye to aid in detecting cartpn leaks. The filled cartons were then sealed and regular dairy cases of the smooth bottom type were stocked with each type of the cartons tested in this series. Each case was then placed in a dropping machine which lifts and immediately drops the case onto a hard surface from a height of /8 inch over a period of ten seconds at a rate of 144 drops per minute. After the lO-second dropping period, the cartons were removed from the case and stored for approximately 22 hours at 40 F., after which the cartons were placed in a warm, humid atmosphere It is to be noted that in the above table, the wax treated cartons in Groups 1 and 2 were so treated only along and adjacent to the bottom score line. This merely represents an arbitrary requirement of the testing procedure employed. However, it is to be appreciated that wax treating of all of the score lines existing on the carton blank is contemplated in order to provide a carton which exhibits maxi-mum leakage resistance.

Example 2 In this example, various groups of cartons were fabricated from blanks which had been impregnated with refined parafiin wax in accordance with this invention and coated upon both sides with a coating composition identical to that described in Example 1. The wax treating and coating variants employed in preparing the respective groups of blanks of this example are described in Table 2. Cartons fabricated from the respective groups of blanks were tested in a modified durability test substantially conforming to that described in Example 1 with the exception that the dairy case containing the test cartons was dropped from a height of inch for 15 seconds at a rate of 144 drops per minute. The storage conditions and manner of examining the cartons essentially corresponded to that observed in the test procedure described in Example 1. The test cycles were repeated until 100 percent of the cartons had failed or 96 test hours had elapsed. In this particular evaluation, commercially available polyethylene coated cartons from three sources, including those identified as Group 4 in Table l, were compared with the cartons (designated Groups 5-10) which had been wax treated along the bottom score lines of the blank in accordance with this invention. The results of this evaluation are set forth in the followto sweat for a period of two hours. Following this test 00 ing T bl 2;

TABLE 2 Percent of Cartons Leakin Carton Treatment g Group Alter After After After 24 hrs. 48 hrs. 72 hrs. 96 hrs.

Group 5. Wax treated, 0.029 gmJin. along bottom score; coating thickness 2 mils inside and out 0 0 22 78 Group G Wax treated, 0.024 gn1./in. along bottom score; coating thickness 2 mils, inside and out 0 22 78 Group 7 Wax treated, 0.022 gmJin. along bottom score; ridge coated, 2.53.0 mils along bottom score; 0 22 55 S9 coating thickness 1.5 mils, inside and out. Group 8 Wax treated, 0.035 gmJin. along bottom score; ridge coated, 2.5-3.0 mils along bottom score; 0 33 6G 80 coating thickness 1.5 mils, inside and out. Group 9 Wax treated, 0.022 grn./in. along bottom score; coating thickness 1.5 mils, inside and out 0 45 Group 10 Wax treated, 0.015 gm./in. along bottom score; coating thickness 1.5 mils, inside and out 0 00 100 (similar to Group 1, Table 1). Group 11 Same as Group 4 in Table 1 33 100 Group 12..-, Final coating polyethylene, commercially available cartons, Manufacturer B. 0 100 Group 13.... Manufacturer C 0 45 100 What is claimed is:

1. A method of coating 21 paperboard substrate whereby improved cartons for the packaging of high water content comestibles can be fabricated therefrom, which comprises; impregnating the substrate with a wax at those portions thereof which are mechanically strained when the substrate is folded into a carton configuration, said impregnation being effected on the surface of the substrate which will constitute the inside surface of the carton, and thereupon uniformly coating both sides of the substrate with a thermoplastic resin-containing composition comprising a mixture of from about 80 to about 30 parts of a petroleum wax selected from the group consisting of paraffin wax, microcrystalline wax and mixtures thereof and from about 20 to about 70 parts of an ethylene/ vinyl acetate copolymer having a vinyl acetate content between about and 40 percent by weight and a melt index in the range of from about 3 to 300.

2. A method of coating a paperboard carton blank whereby improved cartons for the packaging of high water content comestibles can be fabricated therefrom, which comprises; impregnating the blank with a wax at those portions thereof which are mechanically strained when the blank is folded into a carton configuration, said impregnation being effected on the surface of the carton blank which will constitute the inside surface of the carton, and thereupon uniformly coating both sides of the blank with a thermoplastic resin-containing composition comprising a mixture of from about 80 to about 30 parts of a petroleum wax selected from the group consisting of parafiin wax, microcrystalline wax and mixtures thereof and from about 20 to about 70 parts of an ethylene/ vinyl acetate copolymer having a vinyl acetate content between about 10 and 40 percent by weight and a melt index in the range of from about 3 to 300.

3. A method in accordance with claim 2 wherein said wax used for impregnating is a petroleum derived wax.

4. The method in accordance with claim 3 wherein said petroleum derived wax is paraffin Wax.

5. The method of coating a paperboard carton blank which comprises impregnating the blank with a wax along and adjacent the lines at which the blank will be bent in folding same to achieve a carton configuration, said impregnation being effected on the surface of the blank which will constitute the inside surface of the carton and 10 thereupon uniformly coating both sides of the blank with a thermoplastic resin-containing composition comprising a mixture of from about 80 to about 30 parts of a petroleutn wax selected from the group consisting of parafiin wax, microcrystalline wax and mixtures thereof and from about 20 to about parts of an ethylene/vinyl acetate copolymer having a vinyl acetate content between about 10 and 40 percent by Weight and a melt index in the range of from about 3 to 300.

6. The method in accordance with claim 5 wherein said wax used for impregnating is a petroleum derived wax.

7. The method in accordance with claim 6 wherein said petroleum derived wax is paraffin wax and the amount of impregnation thereof effected ranges between about 0.006 and 0.03 gram per square inch of the area to which said wax is applied.

8. An improved paperboard carton, suitable for packaging of high water content comestibles, said carton having (1) petroleum-derived wax impregnated on the inside surface at those portions thereof which are mechanically strained as a result of folding the carton blank into a carton, and (2) a coating on both sides thereof, including the previously wax impregnated portions, of a waxcopolymer blend comprising a mixture of from about to about 30 parts of a petroleum wax selected from the group consisting of paraffin wax, microcrystalline wax and mixtures thereof and from about 20 to 70 parts of an ethylene/vinyl acetate copolymer having a vinyl acetate content between about 10 and 40 percent by weight and a melt index of from about 3 to 300.

9. A carton as described in claim 8 wherein said petroleumderived wax used for impregnation is a paraffin wax.

References Cited by the Examiner UNITED STATES PATENTS 2,676,745 4/1954 Geisler 2293.1 X 2,984,585 5/1961 Sherman 117-92 X 2,999,765 9/1961 Boenau 11792 X 3,137,436 6/1964 Moors et al 2293.1 X 3,181,765 5/1965 Bonzagni et a1. 117-158 X 3,205,186 9/1965 Zaayenga 117155 X WILLIAM D. MARTIN, Primary Examiner. H. W. MYLIUS, Assistant Examiner.

Claims

1. A METHOD OF COATING A PAPERBOARD SUBSTRATE WHEREBY IMPROVED CARTONS FOR THE PACKAGING OF HIGH WATER CONTENT COMESTIBLES CAN BE FABRICATED THEREFROM, WHICH COMPRISES; IMPREGNATING THE SUBSTRATE WITH A WAX AT THOSE PORTIONS THEREOF WHICH ARE MECHANICALLY STRAINED WHEN THE SUBSTRATE IS FOLDED INTO A CARGON CONFIGURATION, SAID IMPREGNATION BEING EFFECTED ON THE SURFACE OF THE SUBSTRATE WHICH WILL CONSTITUTE THE INSIDE SURFACE OF THE CARTON, AND THEREUPON UNIFORMLY COATING BOTH SIDES OF THE SUBSTRATE WITH A THERMOPLASTIC RESIN-CONTAINING COMPOSITION COMPRISING A MIXTURE OF FROM ABOUT 80 TO ABOUT 30 PARTS OF A PETROLEUM WAX SELECTED FROM THE GROUP CONSISTING OF PARAFFIN WAX, MICROCRYSTALLINE WAX AND MIXTURES THEREOF AND FROM ABOUT 20 TO ABOUT 70 PARTS OF AN ETHYLENE/VINYL ACETATE COPOLYMER HAVING A VINYL ACETATE CONTENT BETWEEN ABOUT 10 AND 40 PERCENT BY WEIGHT AND A MELT INDEX IN THE RANGE OF FROM ABOUT 3 TO 300.