US3012707A - Polymer coating system - Google Patents

Description

Dec. 12, 1961 D. M. GRAY 3,012,707

POLYMER COATING SYSTEM Filed Nov. 6, 1957 2 Sheets-Sheet 1 INV EN TOR.

Daniel M L ng BY A TWENEYS Dec. 12, 1961 D. M. GRAY POLYMER COATING SYSTEM 2 Sheets-Sheet 2 Filed Nov. 6, 1957 i -"Hi INVENTOR. fiazziel M ray Y I M A 7'7'0RNEY5 United States Patent @fiice 7 3,012,707 Patented Dec. 12, 1961 ,012,707 POLYMER COATING SYSTEM Daniel M. Gray, Sewickley, Pa., assignor to American- Marietta Company, Stoner-Mudge Co. Division, Chicago, 111., a corporation of Illinois Filed Nov. 6, 1957, Ser. No. 694,777 14 Claims. (Cl. 229-51) The present invention relates to a heat scalable container blank and to a heat sealed container which can be produced therefrom.

More particularly, the invention relates to metal foilcoated paperboard containers which are heat sealed at an adhesive coated side seam thereof with limited migration of the adhesive side seam coating into the paperboard to provide a secure seam which is strongly adherent to the metal foil and to the paper. Because of the limited migration of the adhesive side seam coating, the paperboard does not become deeply saturated with the said adhesive and the seam is stronger than the substantially unsaturated paperboard. As a result the side seam will not open until a force is applied adjacent the side seam coating which is sufficient to delaminate the substantially unsaturated paperboard underlying the side seam coating.

When a sufiiciently strong force is applied, the side seam will pull apart cleanly through delamination of the paperboard to open the container without pulling part of the foil away from its backing. The container is thus opened solely through delamination of the paperboard to thereby avoid injury to the appearance of the container and interference with the accessibility of the opened container.

The invention provides a resilient coated adhesive seam which is uniformly strongly bonded along its entire length. This uniformity in the strength of the bond along the entire length of the seam prevents unbalanced opening stresses from being transmitted to small sections of the foil along the seam to cause delamination or stripping of the foil from its paperboard backing at these small sections.

It is conventional to apply a stripe of heat-sealing lacquer in position to be sandwiched between the opposite ends of a piece of paperboard when it is formed into a cylinder having its opposite ends in overlapping relation along one side of the cylinder. A pair of heating elements are pressed against opposite sides of the seam to soften the lacquer sufficiently to cause it to bond between the metal foil-lining of one of said ends, and the paperboard surface of the other of said ends. In achieving a strong mechanical bond with lacquer adhesives on bibulous surfaces, it is necessary that under heating conditions the lacquer anchor into or penetrate into the bibulous surface. The lacquer contains resins which are sulficiently low in molecular weight to be readily soluble in the organic solvents used as the medium for applying the adhesive and these low molecular weight resins, under heat, are sufliciently fluid and mobile to penetrate substantially below the adhesive interface.

The fluidified resins which thus migrate into the absorbent paperboard tend to saturate the paperboard with resin and to locally starve the seam between the foil and the paperboard. There results a localized strengthening of the paperboard which is not uniform and, in the same localities, a. weakening of the seam between the foil and the paperboard. I

The seam itself does not have great resistance to being pulled apart transversely of its length when the overlapped ends of the container blank are pulled apart, particularly when the seam is starved through adhesive migration. As a result of the adhesive migration discussed hereinbefore and of the lack of resistance to transverse tearing possessed by the seam itself, local variations of strength of adhesion of the lacquer between the overlapped ends of the locally saturated paperboard and of the adhesive holding the foil to the paperboard backing causes the seam lacquer to pull apart of the paperboard out of the opposed end in some places along the length of the seam, while in other places along the length of the seam the foil is pulled away from its paperboard backing. This latter effect causes strips of foil to be torn away from the backing and to be pulled across the opened seam.

This tearing away of the foil from the paperboard backing does not happen as frequently when the heating elements are applied in exact alignment with the center of the seam'lacquer, or when the heating elements are offset away from the side of the seam stripe which is reached last as the side seam is pulled open. However, this undesirable separation of the foil from the paperboard backing occurs frequently when the heating elements are offset in the other direction, toward the side of the seam stripe which is reached first as the seam is opened. Since it is difiicult to align the heating elements perfectly every time, the problem has been presented of how the seam can be bonded without the risk of tearing the foil when the seam is opened.

In accordance with the present invention, a novel adhesive seam is provided which has been found to prevent the tearing of the foil away from the paperboard backing when the seams of such containers are opened by pulling the seam apart. The seam of the invention is formed by a polyvinyl resin having high molecular weight which is not soluble to any appreciable extent in organic solvents and which does not become fluid and mobile under heat scaling conditions. This polyvinyl resin is preferably applied in one application as a plasticized dispersion at a much greater thickness than the conventional sealing lacquer; e.g., the thickness of conventional lacquer applied in one application is about 0.25 ml or less, whereas the seam of the invention is applied in one application in thickness of about 1 to about 3 mils. Such increased thickness, the reduced fluidity of the high molecular weight resins under heat sealing conditions, and the inherent strength and resilience of the seam of the invention, prevents the seam from being locally starved through migration of a limited weight of sealing composition into the porous paperboard to eliminate local weaknesses in the seam and local strengthened areas in the deeply saturated paperboard and thereby prevents rupture of the seam stripe and of the overlying foil when the seam is opened. In addition to such resistance to local weaknesses, the seam of the invention is resilient so that stresses are uniformly transmitted along the length of the bond with the foil and the seam is strongly adhered to the foil so that the seam is tightly sealed, even. though it is free of the problem of foil delarnination and tearing when the scam is pulled apart to open the container. The seam composition is non-toxic, odorless and tasteless.

The accompanying drawing illustrates the application of the invention to a typical foil-lined paperboard body of a typical container of the kind used for prepared biscuit dough. In the drawing:

FIG. 1 illustrates a cylindrical tube of such a foil-lined paperboard container, which has been scaled along the side scam in accordance with the invention;

FIG. 2 illustrates a generally rectangularcontainer blank having an adhesive stripe across the same;

FIG. 3 shows an enlarged detailed section, partially broken away, taken through the container body illustrated in FIG. 1, perpendicular to its central axis; and showing a pair of opposed heating elements scaling the seam; and

FIG. 4 shows a section corresponding to FIG. 3 after the container side seam has been opened without delaminating the foil; and

FIG. shows a section similar to FIG. 4 but showing the entire circumference of the container on a smaller scale and a view illustrating the effects of delamination of the foil along a part of the opened seam when a conventional seam striping lacquer is applied.

Referring now more particularly to the drawing, FIG. 1 shows a conventional cylindrical container body formed by overlapping the opposite ends of a laminated sheet 12 of paperboard 14 having metal foil 16 adhesively secured to the interior side of the paperboard, the laminated sheet being shown in FIG. 2 and the adhesive securing the foil to the paperboard extending across the whole area of the laminate to substantially uniform-1y bond the same together over the entire mating surfaces thereof. The laminated sheet 12 has its opposite ends 18 and 20 overlapped to form the side seam of the body 10, and a stripe 22 of adhesive in accordance with the invention is interposed between the ends 18 and 20 to seal them together. The stripe 22 is applied to the foil at one of the ends as by roller coating or in any other suitable manner to provide a stripe layer having a thickness of at least 1 mil and preferably about 2 mils to deposit a heavy coating which, after baking in a single application, is thick and resilient before the ends are overlapped. After the ends are overlapped, a pair of heating elements 26 are pressed against the overlapped ends as shown in FIG. 3 to heat seal the adhesive to the paperboard 14 on the outside of the inner end 20. The heat softened adhesive cannot migrate extensively into the paper because the high molecular weight resin plasticizer mass does not become fluid and mobile during heat sealing. The seam cannot become starved of adhesive for the same reason and for the further reason that there is preferably a greater weight and thickness of coating than can conveniently be applied from solution. The limited penetration of the coating 22 into the paperboard 14 is shown by the shading 24 in FIG. 3. The outer end 18 has a projecting tab 28 which can be grasped to pull open the side seam, as illustrated in FIG. 4. When that occurs, the adhesive 24 holds firmly to the foil 16- on the end 18 and to the paperboard 14 and the paperboard 14 is delaminated and tears away from itself at the end 20 as is illustrated in the drawing by numerals 29 and 30. As a result, there is no delamination of the foil 16, such as is illustrated in FIG. 5, where a conventional seam lacquer 31 is employed for the stripe 22 and the metal foil tears as shown at 32. The saturated paperboard is indicated by shading at 33.

The sealing compositions of the invention are constituted by a dispersion of finely divided polyvinyl resin having a molecular weight generally above 20,000. The preferred polyvinyl resins possess intrinsic viscosities in cyclohexanone at 20 C. above 1.2 and preferably between 1.4 and 1.6, and are polymers of high molecular weight comprising at least about 90% by weight of vinyl chloride. In particular, there may be used vinyl chloride polymers and copolymers of vinyl chloride with up to about 10% by weight of another vinyl material selected from the group consisting of vinyl acetate, vinylidene chloride and mixtures thereof. Adhesion to the aluminum or other metal foil is necessary and this is provided by the presence in the polyvinyl resin dispersion of a component promoting adhesion to metal such as an acidic component which is conveniently provided by the inclusion in the dispersion of from about 5-25% by weight of a second resin, compatible with the polyvinyl resins referred to above and containing a small quantity (OJ-4%) of unreacted carboxyl groups. This second resin preferably contains vinyl chloride in major amount (60-96%) and it may be constituted by a resin having a molecular weight of less than 20,000, e.g., 7,00018,000.

The dispersions of the invention contain plasticizer for the said polyvinyl resin and these dispersions may be of 4- either the plastisol or organosol type, the latter being preferred and being characterized by the presence of a liquid volatile organic solvent which may soften but not dissolve the polyvinyl resin component of the dispersion at room temperature.

Various agents of a polar nature are known for the purpose of promoting adhesion of vinyl halide containing polymer coatings to metal surfaces and these may be employed for this same purpose in accordance with the invention. It should be observed that the inclusion of an adhesion promoting agent to enhance adhesion to the metal foil is necessary in order to produce a secure seam which Will not open inadvertently until a force sufiicient to delaminate the paper is applied. However, the inclusion of any specific adhesion promoting agent does not constitute the primary feature of the present contribution.

Among the many polar adhesion promoting materials which may be employed are those described in the United States patent to W. W. Castor and F. R. Stoner, Ir., No. 2,231,407, these being alkyd resins. Further, cresol and xylenol-aldehyde reaction products may be employed as taught in the United States patent to F. R. Stoner, Jr., and D. M. Gray, No. 2,293,413. Olcoresinous varnishes may also be employed as taught in the United States patent to C. E. Maier, No. 2,380,456, the United States patent to D. M. Gray and G. L. Reymann, No. 2,780,564, and the United States patent to N. F. Barr, No. 2,793,141.

To illustrate the above, the ortho-cresol/forrnaldehyde condensation product set forth in Example I of said Patent No. 2,293,413 may be used to replace, on an equal weight basis, the maleic acid tripolymer resin which is used hereinafter in Example I for the purpose of promoting adhesion to the metal foil surface. The results produced by this substitution are approximately comparable to the results reported in Example I herein.

There may still further be employed to promote adhesion to the metal foil surface, copolymers of butadiene and acrylonitrile such as the copolymer produced by copolymerizing acrylonitrile with a stoichiometric excess of butadiene in the presence of Water, an emulsifier such as a condensation product of naphthalene with formaldehyde sulphonate, potassium persulfate and an activator such as the propionitrile derivative of a cyanoethylated amine. The copolymerization is described at pages 171 and 172 of Polymer Processes edited by C. E. Schildknecht, 195 6, Interscience Publishers, New York.

A particularly preferred adhesion promotor for use in accordance with the present invention is the alkaline saponification reaction product produced by reacting solid particles of a vinyl halide-vinyl fatty ester copolymer with a strongly basic alkaline material in alcoholic medium.

The alkaline saponified copolymers of vinyl chloride and vinyl acetate which are employed in accordance with the present invention contain from about -92% by weight of vinyl chloride component and these copolymers have been saponified while in suspension in alkaline alcoholic medium in order to convert a portion of the vinyl acetate to vinyl alcohol to produce at least about 2% and preferably at least 3% by weight of vinyl alcohol and to dehydrohalogenate the copolymer to produce an average unsaturation of at least about 1.0 double bond per copolymer molecule. Preferred partially saponified copolymers have a corrected iodine number from 2 to 10. The conversion of vinyl acetate or other fatty acid ester in the copolymer molecule to vinyl alcohol should not exceed and is preferably less than 78%, particularly where the copolymer is of low molecular weight.

Preferably, saponification of the vinyl chloride-vinyl acetate copolymers is effected by saponifying the copolymer in solid, finely divided form suspended in alcohol medium with a limited concentration of a strongly basic material so that a limited vinyl alcohol content can be accompanied by substantial unsaturation in the substantial absence of degradation. The saponified copolymer preferably is washed with alcohol and water to a salt content of less than 1% by weight. The predominant unsatura- 'tion in the copolymer is polyene unsaturation which is not necessarily conjugated and preferred copolymers contain at least 3 double bonds per copolymer molecule in a major proportion of the copolymer molecules which are present.

The saponified dehydrohalogenated (unsaturated) copolymers of vinyl chloride and vinyl acetate which are used as adhesion promoters for dispersion resins in accordance with the invention possess a molecular weight in the range of about 5,000-25,000. The higher molecular weight copolymers may be saponified to a somewhat greater extent than the low molecular weight copolymers, a maximum vinyl alcohol content of about by weight being permissible with copolymers having a molecular weight of about 18,000 or higher. Preferably, the vinyl alcohol content does not exceed 6% by weight.

When unsaturated partly saponified vinyl chloride-vinyl acetate copolymer adhesion promoters containing 90 92% by weight of vinyl chloride are employed, it is preferred to employ copolymers of lower molecular weight (below about 18,000) to insure optimum compatibility with the polyvinyl resin during the baking operation.

The alkaline suspension saponified copolymers of vinyl chloride and vinyl acetate are employed in admixture with the polyvinyl resins of the invention in an amount of from about 3% to 25% by Weight based on the weight of the mixture. Preferably, at least about 7% by weight of the alkaline hydrolyzed copolymer of vinyl chloride and vinyl acetate is employed. Normally, it is not necessary to employ more than about 20% by weight of the copolymer of vinyl chloride with vinyl acetate based on the weight of the mixture thereof with the polyvinyl resin.

In accordance with preferred practice of the present invention, a copolymer of a vinyl halide, preferably vinyl chloride, with a vinyl fatty ester, preferably vinyl acetate, is saponified in the form of a slurry of the solid, finely divided copolymer in a substantially anhydrous liquid medium containing a lower aliphatic alcohol, e.g., methanol, and saponification is effected employing a strongly basic material selected from the group consisting of alkali metal hydroxides, alkali metal alcoholates and quaternary ammonium hydroxides. The strongly basic material is normally employed in smallconcentration and stoichiometric quantities of strongly basic material are used based on the desired conversion to vinyl alcohol and removal of hydrogen choride.

This slurry is then reacted at a temperature ranging the desired unsaturation. p

The alkaline saponified copolymers'which are preferably employed are described at length in the co-pending application-of Xavier V. Laporta, filed October 24, 1957, the disclosure of which is hereby incorporated. In the said Laporta application it is indicated that the saponification reaction normally requires a reaction period of at least one quarter hour, that the copolymer is dispersed in the alcoholic medium in the form of'fine particles to produce slurries containing from to 60% by weight of solid material based on the weight of the .liquid organic medium and that the concentration of strongly basic material be between 0.018 and 0.18 mol pound of akaline hydroxide per 100 pounds of slurried saponifiable resin. It

is further indicated that the saponified product is thoroughly washed, preferably by successive alcohol and water washes, to reduce the salt concentration to less than one percent by weight. While the alkaline saponified copolymers which are de scribed above are preferred, copolymers of vinyl chloride and vinyl acetate containing a major proportion of vinyl ,chloride and which have been saponified in either acid or alkaline mediums while in solution may also be used in minor proportion to promote adhesion to metal.

The liquid components (plasticizer and solvent) are generally present to provide an initial viscosity of about 200 to about 10,000 centipoises. A minimum proportion of plasticizer is preferred to provide minimum fluidity during the heat sealing operation and it is therefore preferred to employ solvent to reduce the viscosity to the desired extent.

The present preferred example of high molecular weight polyvinyl resin is a copolymer of vinyl chloride and vinyl acetate consisting of about to about 96% by weight of vinyl chloride, the balance being vinyl acetate; e.g., Vinylite VYNV1 of Union Carbide and Carbon Corp., New York, N. Y., a high molecular Weight copolymer of vinyl chloride and vinyl acetate in proportions by weight of about /5, having a specific gravity of about 1.39 and intrinsic viscosity in cyclohexanone at 20 C. of 1.53. Another example of a suitable high molecular weight polyvinyl resin is Geon "121 of B. F. Goodrich Chemical Company, Cleveland, Ohio, which is a polymer of vinyl chloride having a specific gravity of about 1.40 and an intrinsic viscosity of about 0.67 (0.4% solution in nitrobenzene at 20 C.).

The acidic resin component of the invention has as its essential constituent one or a mixture of copolymers of (a) a vinyl halide, preferably vinyl chloride; ([2) a vinyl ester of a lower saturated fatty acid, preferably vinyl acetate; and (c) an aliphatic alpha, beta-mono-olefinic carboxylic acid (preferably maleic acid) or anhydride, the amount of carboxylic acid combined in the copolymer beingbetween about 0.1% and about 4% by weight of the whole copolymer, and the carboxyl groups in the copolymer being substantially unreacted. The optimum amount of maleic acid, When it is used as the third component of the copolymer, is about 0.3% to 3% by weight of the total acidic copolymer. The proportion of the vinyl halide component (a) in the copolymer is in the range of about 60% to about 96% by weight of the total copolymer, the balance being the said components (b) and (c) of the copolymer. The present preferred example of the acidic resin component is a copolymer of vinyl chloride, vinyl acetate and maleic acid in proportions by weight of about 86/ 13/ l, as exemplified by VMCH of Bakelite Company, Union Carbide and Carbon Corporation, of New York, N. Y.

The. plasticizer component of the invention is any plasticizer for the polyvinyl resin component which boils above 200 C., and is fluid at about 25 C. (average room temperature). Such plasticizers are known in the art, and include one or a mixture of organic acid esters having such boiling and fluid characteristics; e.g., dialkyl esters of dicarboxylic acids such as esters of phthalic acid such as di-(Z-ethylhexyl) phthalate, di-butoxyethyl phthalate, di-ethoxy ethyl phthalate,.and di-ethoxy ethoXy ethyl phthalate; esters of ad-ipic acid such as di-butoxyethyl adipate and di-methylcyclohexyl adipate; esters of sebacic acid such as di-methoxyethyl sebacate; and esters of sulfonic acids such as o-cresyl p-toluene sulfonate. Of these plasticizers, di-(Z-ethylhexyl) phthalate and o-cresyl p-toluene sulfonate are presently preferred.

The solvent component is selected from known solvents, including a proportion of one or a mixture of bons; e.g., benzene, toluene and xylene and their liquid homologs, and condensed aromatic hydrocarbon liquid solvents (e.g., methyl naphthalene). The maximum proportion of aromatic hydrocarbon solvents in the total solvent mixture used in the composition, varies with the varying proportions and constituents of the plasticizer component and the polyvinyl resin component. The proportions and constituents of the polyvinyl resin component and plasticizcr having been selected, the amount and constituents of solvent component are selected to cause the composition as a whole to have an initial viscosity of about 200 to about 10,000 centipoises.

The dispersion of the invention when applied in a thickness of from 1-3 mils is baked for from 2 to minutes at a temperature of from 330 F. to 360 F.

The following examples serve to illustrate the invention, all parts being by weight.

EXAMPLE 1 33.8 parts of a high molecular weight polyvinyl chloride-vinyl acetate copolymer resin (Vinylite VYNV- 1); 6.9 parts of a low molecular weight polyvinyl chloride-vinyl acetate-maleic acid tripolymer resin (Vinylite VMCH); 14.3 parts plasticizer (dioctyl sebacate); 15.3% diisobutyl ketone; 20.8 parts xylol and 8.9 parts Apco thinner (a hydrocarbon solvent) were placed in a pebble jar mill and ground for 24 hours. The resulting dispersion had an initial viscosity of about 800 cps. at 80 F. and theoretical solids of 55%. The dispersion was then applied to the aluminum side of commercial aluminum laminated fiber carton stock by roller at 1.0- 1.5 mil thickness and baked 2 minutes at 350 F. The coating was then heat sealed to the paperboard with opposed platens as shown in FIG. 3 for about 5 seconds at approximately 350 F. using a pressure of about 40 p.s.i.g. When the seal was broken the desired effect was obtained; that is to say, the breaking of the seal delarninated only the paper side of the board, and left the aluminum film and the seam itself intact, as shown in FIG. 4.

The improved results obtained by use of the composition prepared as described in Example 1 are shown in the following Table I:

Adhesionto aluminum foil Excellent" Excellent. Heat Sealing Properties (5 seconds at, 350 F.) ,do Do. Tearing of aluminum foil Extensive. None.

EXAMPLE 2 33.8 parts of Vinylite VYNV-1, 6.9 parts of Vinylite VMCH and 40.7 parts of the ester plasticizer dioctyl phthalate were ground in a pebble jar mill for 24 hours to produce a dispersion of the plastisol type containing 50% by weight of particulate solids. This dispersion was roller coated in a stripe to the aluminum side of commercial fiber carton stock (aluminum foil adhesively bonded to paperboard) and the coating was baked for 2 minutes at 350 F. Opposed platens at a temperature of 350 F. were pressed against the overlapping portion of the carton stock as shown in FIG. 3 and a pressure of 40 p.s.i.g. was applied for 5 seconds. A secure bond was obtained which, when torn apart, separated solely by delamination of the paperboard. The aluminum foil remained intact and did not tear.

Examples 1 and 2 were repeated using corresponding weights of a high molecular weight copolymer of 91% by weight of vinyl chloride and 9% by weight of vinyl acetate having a specific gravity of 1.37 and an intrinsic viscosity of 1.38 measured in cyclohexanone at C.

(Vinylite VY CM) and also with a copolymer of vinyl chloride and vinyl acetate containing by weight of vinyl chloride and 5% by weight of vinyl acetate and having a specific gravity of 1.39 and an intrinsic viscosity in cyclohexanone at 20 C. of 1.25 (Vinylite VYNW presently identified as Vinylite VYDR). Approximately comparable results were achieved.

Example 2 was repeated using a vinyl polymer of high molecular weight containing 99%+ by weight of vinyl chloride and having a specific gravity of 1.40 and an intrinsic viscosity at 20 C. in cyclohexanone of 1.58. Excellent results were obtained.

A preferred alkaline suspension saponificd copolymer of vinyl chloride and vinyl acetate for use in accordance with the present invention is produced in the following manner:

EXAMPLE 3 12 pounds of Vinylite VYLF (a copolymer of vinyl chloride with vinyl acetate in a weight ratio of 87: 13 having an intrinsic viscosity at 20 C. in cyclohexanone of 0.24, a specific gravity of 1.24 and a particle size range of -250 microns) are slurried in 24 pounds of anhydrous methanol in the presence of 0.48 pound of potassium hydroxide and heated with stirring at 63 C. for 3 hours. The supernatant liquid was then removed and the saponified resin particles were washed successively, with methanol and then with cold water. Each wash had twice the volume of the supernatant liquid which was removed. The final resin had a vinyl alcohol content of 3.6% and contained substantial unsaturation.

Examples 1 and 2 were repeated using in place of the 6.9 parts of Vinylite V MC 6.9 parts of the saponified copolymer of Example 3. Approximately comparable results were achieved.

Pigments, dyes, waxes and other non-reactants may be added to the composition of the invention for decorative purposes and the like, without otherwise materially affecting the significant characteristics of the composition. In addition, the composition of the invention may be modified with additives to enhance special properties.

While I have described present preferred embodiments of the invention and methods of practicing the same, it will be recognized that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

I claim:

1. A container blank comprising a laminate of paperboard and metal foil, said paperboard and said foil being coextensive with one another and adhesivcly secured together substantially uniformly over the mating surfaces thereof, said metal foil having a coating adhered thereupon in a stripe extending across said laminate adjacent one edge thereof, said coating being constituted by a thermally fused dispersion comprising a finely divided polyvinyl resin comprising at least about 90% by weight of vinyl chloride and having a molecular weight above about 20,000, a component promoting adhesion to metal and a liquid dispersant comprising a plasticizer for said polyvinyl resin.

2. A container blank as recited in claim 1 in which said polyvinyl resin has an intrinsic viscosity in cyclohexanone at 20 C. between 1.4 and 1.6.

3. A container blank as recited in claim 1 in which said polyvinyl resin is selected from the group consisting of vinyl chloride polymers and copolymers of vinyl chloride with up to about 10% by weight of vinyl acetate, copolymers of vinyl chloride with up to about 10% by Weight of vinylidene chloride and mixtures thereof.

4. A container blank as recited in claim 1 in which said plasticizer is a liquid dialkyl ester of a dicarboxylic acid boiling above 200 C.

5. A container blank as recited in claim 1 in which said metal foil is aluminum foil.

6. A container blank as recited in claim 1 in which said coated stripe has a thickness of at least about 1 mil. 7. A container blank as recited in claim 1 in which said component promoting adhesion to metal is a polyvinyl resin containing from 0.1% to 4% by weight of unreacted carbonyl groups, said polyvinyl resin containing unreacted carboXyl groups being present in said dispersion in an amount of from 5% to 25% by Weight.

8. A container blank as recited in claim 7 in which said polyvinyl resin containing from 0.1% to 4% by weight of unreacted carboxyl groups comprises a vinyl chloride copolymer containing from 60% to 96% by weight of vinyl chloride, an alpha-beta-ethylenically unsaturated carboxy material selected from the group consisting of maleic acid and maleic anhydride with the remainder of said last named polyvinyl resin being a vinyl material copolymerizable with said vinyl chloride.

9. A container blank as recited in claim 8 in which said polyvinyl resin containing from 0.1% to 4% by weight of unreacted carboxyl groups has a molecular weight in the range of from 7,000 to 18,000.

10. A container blank as recited in claim 1 in which said component promoting adhesion to metal is a polar resin.

11. A container blank as recited in claim 10 in which said component promoting adhesion to metal is a partially saponified copolymer of vinyl halide and vinyl fatty acid ester containing from 80% to 92% by Weight of vinyl halide, said saponified copolyrner having a vinyl alcohol content of from about 2% to about 10% by Weight and an unsaturation indicated by a corrected iodine number of from 2 to 10, said partially saponified copolymer being present in said dispersion in an amount of at least about 3% by weight.

12. A container blank as recited in claim 1 in which said dispersion contains a proportion of liquid dispersant at the time of application to have a viscosity upon application in the range of from 200 to 10,000 centipoises.

13. A container blank as recited in claim 12 in which said high molecular weight polyvinyl resin is a copolymer of from to 96% by weight of vinyl chloride with vinyl acetate constituting the remainder of said copolymer and said copolymer having an intrinsic viscosity of about 1.5 in cyclohexanone at 20 C.

14. A container comprising a cylindrical container body formed by a laminate of paperboard and metal foil, said paperboard and said foil being substantially coextensive with one another and adhesively secured together substantially uniformly over the mating surfaces thereof, said laminate having its opposite ends overlapping with said metal foil being positioned on the inside of said container, said foil having a coating adhered thereupon in a stripe extending across said laminate adjacent the outer of said overlapped opposite ends, said coating being constituted by a thermally fused dispersion comprising a finely divided polyvinyl resin comprising at least about 90% by weight of vinyl chloride and having a molecular weight above about 20,000, a component promoting adhesion to metal and a liquid dispersant comprising a plasticizer for said polyvinyl resin, said overlapped opposite ends of said laminate being heat sealed by the application of heat and pressure to secure said ends together to form said container and said polyvinyl resin resisting migration into said paperboard during said heat sealing by virtue of its high molecular weight whereby when said overlapped ends are pulled apart, said foil does not tear and separation is effected by delamination of said paperboard.

References Cited in the file of this patent UNITED STATES PATENTS 2,814,428 Magill Nov. 26, 1957

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