US3295486A

US3295486A - Gasket composed of a panel liner and an annular sealing ring for closures

Info

Publication number: US3295486A
Application number: US393789A
Authority: US
Inventors: Charles W Simons; Robert S Holdsworth
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co
Priority date: 1964-03-16
Filing date: 1964-09-01
Publication date: 1967-01-03
Anticipated expiration: 1984-01-03

Description

Jan. 3, 1967 C W. SIMONS Original Filed March 16, 1964 ET AL 3,295,486

GASKET COMFOSED OF A PANEL LINER AND AN ANNULAR SEALING RING FOR CLOSURES 2 Sheets-Sheet 1 LACQUERED TINPLATE SHEET PLASTISOL FUSE COATING ON SHEET FORM CLOSURE SHELL DEPOSIT ANNULAR PLASTISOL IN RING OF SHELL VINYL LACQUER FUSE PLAST'ISOL IN SHELL F l G. I

FUSED PLASTISOL OR ORGANOSOL COATTNG FUSED PLASTISOL RING INVENTORS ROBERT S. HOLDSWORT CHARLES W. SIMONS ATTORN EY 1967 c. w. SIMONS ETAL 3,295,486

GASKET COMPOSED OF A PANEL LINER AND AN ANNULAR' SEALlNG RING FOR CLOSURE S Original Filed March 16, 1964 2 Sheets-Sheet 2 v| NYL LACQUER' -=&eaeaea :maa

FUSED PLASTISOL FUSED AN SOL CELLULAR RING F l G. 5 OR PLASTISOL COATING INVENTORS ROBERT S. HOLDSWORTH CHARLES W. SIMONS BY WZQZZ, X24; M/

ATTORNEY United States Patent C) 3 Claims. (Cl. 113121) This invention relates to container closures and to a method of making such closures. More particularly, this invention relates to crown closures having a unitary gasket composed of a thin panel liner and an annular sealing ring integrated therewith.

This application is a division of application Serial No. 352,192, filed on March 16, 1964, and now abandoned.

Crown closures are produced by forming a sheet of tinplate into a crown shell, coating the inner surface with a film of lacquer or varnish and then inserting or forming a sealing element (gasket) within the shell. The lacquer or varnish is so selected as to afford protection of the contents in the container against possible deleterious effects of the metal of which the crown cap is made. Typical coating materials include oleoresinous, phenolic, epoxy and vinyl lacquers, either alone or in combination.

Plastisols are currently used to form seals for crown closures. These compostions basically comprise a vinyl resin dispersed in a plasticizer in which the resin is insoluble at room temperature but is capable of solvating the resin at an elevated temperature. The plastisol may, in addition, contain other conventional ingredients, such as lubricants, fillers, stabilizers and pigments. A crown gasket is made by one method wherein a smalll amount of the plastisol is placed in an inverted crown and the crown is spun to cause the plastisol to flow to the outside edge and assume the configuration desired. Thereafter the lined crown is heated to flux the plastisol. Another method includes the steps of depositing a specified amount of plastisol onto the panel of the crown, applying a plunger to distribute the plastisol over the cap surface and thereafter fluxing the composition.

The conventional practice of preparing crown closures has certain disadvantages. The principal purpose of an inside lacquer coating is to protect the tinplate from corrosion that might be caused by the bottled contents and/ or the atmosphere. The lacquer is generally applied by means of a coating roller and frequently the surface of the roller is uneven or contains pores which cause pinholes in the lacquer film. Pinholes can also develop after periods of storage of the bottled contents, particularly in warm climates. On the other hand, if the film weight of the lacquer is too light, the resulting coating is not scratch resistant. In order to overcome the breaks in the lacquer film, the industry frequently resorts to applying a second coating over the first lacquer coating. The double coating technique necessitates a second operating step with a concomitant increase in manpower and lacquer requirements.

The current method of applying gaskets to the lacquered shell requires that the gasket in the panel area have a thickness of between about 8 and mils. This concentration of gasket in the panel area increases the probability of contamination of the bottle contents since it is known that the plasticizer in the plastisol is extractable to a certain extent and, therefore, the plasticizer is in contact with the bottle contents. In addition, since a majority of the plastisol compositions contain a vinyl chloride polymer prepared by emulsion polymerization, residual emulsifier is exposed to the bottle contents and thereby contributes to contamination.

3,295,486 Patented Jan. 3, 1967 It is, theerfore, an object of this invention to provide a crown closure and sealing element which overcomes the aforestated disadvantages. This objective is realized by providing a gasket having an impervious thin film of a resinous composition disposed over the lacquered panel portion of the crown and a sealing element of greater thickness positioned in the annular region of the shell. The panel film is derived from a vinyl resin plastisol or organosol having less than 50% plasticizer and the annular sealing element is derived from a vinyl resin plastisol having a plasticizer content in excess of 65% The panel liner is hard and resistant to moisture and staining in the panel area and can be applied over single coatings of lacquer. The thick annular sealing element surmounts the lip of the container, such as a bottle, and insures a tight seal in spite of glass irregularities which may exist in the lip. The lacquer which coats the bare metal of the shell is of the vinyl or modified vinyl type which, because of its compatability with the plastisol or organosol, assures strong bonding of the components.

The present invention permits the use of'two materials of differing compositions for forming the sealing gasket. One of the compositions is applied to the inside panel portion of the closure element and may consist of a vinyl resin plastisol or organosol having a plasticizer content less than 50% based on the weight of the resin. The composition produces a hard panel covering which is resistant to moisture and staining in the panel area.

The second composition which is used is a plastisol having plasticizer content greater than 65 based on the weight of the resin and it is deposited as an annular ring in the shell. This composition when fluxed is soft and yielding and adapts itself well to any irregularities which may exist in the mouth of the container. The ring is preferably formed from a plastisol which includes a blowing agent and thereby yields a cellular gasket of greater resiliency when fiuxed.

The amount of sealing compositions used can be reduced by closely controlling the amount deposited in the panel and the amount which is placed in the annular area. The low amount of plasticizer in the composition which covers the panel area reduces the taste contribution from the liner to the pack and also reduces cost. By virtue of this invention, the thickness of the gasket in the panel ranges between about 2 to 4 mils which is well below the thickness of 8 to 15 mils of the conventional type.

In the drawings:

FIG. 1 represents a flow sheet which diagrammatically illustrates the successive steps of preparing a gasketed closure element;

FIG. 2 shows a diametrical sectional view of a crown and a gasket of this invention positioned therein;

FIG. 3 is a View similar to FIG. 2 in which the annular ring has a cellular structure.

The gasketed closure element is prepared first by providing a sheet of metal plate, such as tin-plate, having a protective coating thereover. This coating may be one derived from a lacquer consisting of a vinyl resin alone or in combination with one or more of oleoresinous, epoxy or phenolic components. A satisfactory coating composition is a lacquer derived from polyvinyl chloride or a major amount of vinyl chloride copolymerized with up to 20% of vinyl acetate in combination with the aforementioned components. These lacquers are described in U.S. Patent No. 2,380,456.

A thin :film of a vinyl resin plastisol or an organosol is then applied over the lacquer. The application of the film may be accomplished by roller coating, spraying the whole sheet, spray-ing selected spots conforming to disced areas, or by gravure or screen printing selected spots. A clear plastisol may be used where a transparent liner is desired and pigmented compositions may be used for forming a low cost gasket. The film composition is then fused and bonded to the lacquer coating by any of several well known methods of fusing vinyl chloride polymeric compounds, such as passing over heating panels, through a hot air oven, etc. A typical heating cycle would be completed in three minutes at 350 F.

After the panel film has been fused, closure elements are then formed by conventional procedures such as stamping. An annular ring is then placed in the stamped shell by a lining process or by adhering a molded ring in place. Thereafter the closure composite is heated to fuse the annular plastisol ring which may be accomplished between 20 seconds and 5 minutes at oven temperatures between about 300 F. and 450 F. Because of the compatibility of the vinyl components, the finished gasket may be considered unitary in that the sealing ring and panel liner are fused together which inturn are fused to the vinyl lacquer.

The vinyl resin plastisols which are particularly suitable in this invention include plasticized vinyl chloride resin compositions although other acid-resistant thermoplastic resins may be .used. These include polyvinyl acetate, polyvinyl butyrate, copolymers of vinyl chloride and vinyl acetate, polyvinyl alcohol, polyvinylidene chloride, and copolymers of vinylidene chloride and a vinyl aromatic compound, such as styrene. The preferred resin is plasticized polyvinyl chloride.

The plasticizer employed may be any of the well known non-volatile plasticizers for vinyl resins which solvate the resin at elevated temperatures. These include such primary plasticizers as dioctyl phthalate, diisooctyl phthalate, didecyl phthalate, di(n-octyl, n-decyl) phthalate, acetyl tributyl citrate, dioctyl sebacate, dihexyl adipate, dioctyl adipate, 2-ethylhexyl diphenyl phosphate, and tricresyl phosphate. Polymeric plasticizers, such as polyesters derived from dibasic acids and glycols, may also be used. Secondary plasticizers, such as petroleum residue products commonly used as rubber softeners and plasticizers, may be used to supplement or replace a 'part of the primary plasticizer. The selection of particular plasticizers is dependent upon the end use to which the gasket is put. F or example, tricresyl phosphate and secondary petroleum plasticizers are unsuitable for food packaging. The percentage of theplasticizer in the composition which is used for lining the panel portion of the closure may range from about 15% to 50%. Amounts below 15% do not provide a formulation which can be worked satisfactorily.

and amounts above 50% yield a liner from which the plasticizer is exudable and the liner is too soft to offer scratch resistance. In the plastisol formulation which is used as the annular sealing ring, the plasticizer may range from about 65% to 150%. The use of amounts below 65 does not provide a resilient ring and amounts above 150% yield rings which can cut through with high crowning pressures and are too permeable to carbon dioxide to hold carbonation. In both instances the percentages of plasticizer are based on the weight of the vinyl resin.

In addition to having a higher percentage of plasticizer, the plastisol composition from which the annular sealing ring is prepared preferably includes a blowing agent to form a cellular gasket. The blowing agents are employed in a finely divided state in the range of about 1 to 3 microns and are so selected that their decomposition temperatures are slightly below the final fluxing temperature of the vinyl resin composition. A difference between maximum fluxing temperature and decomposition of the blowing agent of about 15 C. to 30 C. is satisfactory. By so choosing the blowing agent, it is possible to produce expansion when the resin composition is in a fairly tough gel state, i.e., when it is not so fluid that blowing will cause perforations in the surface of the mass nor so well gelled as to prevent proper expansion of gas.

There are numerous chemical blowing agents which are suitable for developing the proper cell structure in the ring. Among those which can be used are azodicarbonamide, 3,3'-disulphonhydrazido diphenylsulfone, dinitrosopentamethylene tetramine, diazoaminobenzene, and I The quantity p,p'oxybis (benzene sulfonyl hydrazide). of blowing agent may vary from between about 0.2% to 5.0% based on the weight of the resin. Good cell formation together with an impervious surface are realized when 0.4% to 2.0% of blowing agent is used in the plastisol formulation.

In addition to the resin, plasticizer and blowing agent, various other additives may be included to modify the plastisol compositions. These include fillers, such as anhydrous calcium sulfate, talc, wood flour, diatomaceous earth and asbestos; stabilizers, such as tetrasodium pyrophosphate, tribasic lead silicate, calcium stearate, zinc stearate, dibasic lead stearate, organo-tin complexes, epoxy resins and epoxidized oils of fatty acids; pigments such as carbon black, titanium dioxide and aluminum powder; and dispersing agents, such as zinc resinate, lecithin, glycol stearate, propylene glycol laurate and glycerol monooleate.

As indicated hereinbefore, an organosol may be substituted for the plastisol in forming the panel liner. These compositions are somewhat similar to plastisols but include an organic solvent which is used as a dispersion medium to permit uniform spreading of the coating. Solvents which are particularly elfective in such compositions include esters and ketones, for example, methyl ethyl ketone and methyl isobutyl ketone. The plasticizers are generally the same as those used in plastisol formulations.

The plasticizer and solvent tend to wet and swell the,

resin while a diluent, such as aromatic or aliphatic hydrocarbons, controls the swelling and reduces viscosity and cost. The usual compounding ingredients such as fillers, stabilizers and color pigments which are used in plastisols may be added to the organosol, if desired. After an organosol coating is applied to the metal sheet, it is necessary to bake it at 250 F. to 350 F. for l to 5 minutes to gain complete fusion.

It is preferred to apply the plastisol composition which forms the annular ring by means of conventional high speed lining machines. In this method a small amount of the plastisol is placed in the corner of a closure shell and the shell is then spun about its axis to distribute the plastisol over the annular area in a uniform ring. The

plastisol is particularly adapted to this method of lining stamping or molding. In addition, it serves to conserve the amount of plastisol used and improves its sealing performance. 7

Because of the high proportion of individual air cells in the ring, it compresses easily and grips the container lip providing a seal at the inside and outside as well as the top. The extensive sealing area insures tight sealing in spite of glass irregularities in the lip of the mouth container such as a bottle. The cellular. material also minimizes the possibility of glass chipping during the capping or crowning step.

An alternate method of forming a gasket is to line an annulus of'the plastisol (about 0.1 g.) by means of a lining machine on an internally-lacquered shell and then deposit a metered amount (about 0.07 g.) of plastisol or organosol composition in the center of the crown panel and spin the crown until the composition meets the ring. The reverse procedure of first spinning the panelcomposition and then lining the annular ring is also effective.

The invention is further illustrated by the following examples. Examples 1 to 3 set out typical compositions which are useful for coating the panel portions of vinyl lacquered shells and Examples 4 and 5 illustrate suitable compositions for forming the annular ring. The composition of Example 4 contains a chemical blowing agent which when fused yields a cellular ring and the composition of Example does not contain a blowing agent.

Example 1 [Grey-colored plastisol] Parts by weight Polyvinyl chloride 100 Dioctyl phthalate Dioctyl adipate 30 Zinc and calcium stearates 1 Epoxidized soybean oil 3 Polyethylene glycol 400 monooleate 1 Titanium dioxide/carbon black dispersed in dioctyl phthalate 4 Example 2 [Clear plastisol] Parts by weight Polyvinyl chloride 100 Dioctyl adipate 30 Calcium and magnesium fatty acid soaps 1 Epoxidized soybean oil 3 Example 3 [Pigmented organosol] Parts by weight Polyvinyl chloride 100 Dioctyl adipate Dioctyl phthalate 10 Ground calcium carbonate 10 Calcium and magnesium fatty acid soaps 1 Methyl isobutyl ketone 5 Mineral spirits 5 Titanium dioxide/carbon black dispersed in diocty phthalate 3 Example 4 [Grey composition containing chemical blowing agent] Parts by weight The compositions of Examples .1 to 5 are well suited for use as gaskets in vinyl lacquered crown shells. Any

of the panel compositions of Examples 1 to 3 may be combined and interchanged with either composition of Example 4 or 5 depending on whether a clear or pigmented panel is desired coupled with either a cellular or solid ring.

The panel portion of the gasket is exposed to the contents of a container and includes no more than 50% plasticizer based on the weight of the resin, thus minimizing the possibility of extractables. It is essentially impervious to the transfer of moisture and fully protects the metal panel of the closure from attack by the contents of the container.

The plastisol composition from which the annular ring is derived contains more than plasticizer based on the weight of the resin and provides an effective sealing element which exhibits sufficient tolerance to imperfect glass. When a blowing agent is included in the composition, the fluxed ring is composed of a resilient mass having a uniform fine cell size. The use of a cellular ring together with the panel coating maximizes the effectiveness of the overall gasket and permits low film weights to be used.

The panel also constrains displacement of the ring during the capping operation when the ring is being compressed and deformed. Thus, the use of a low plasticizer containing panel and a high plasticizer containing sealing ring provides an effective combination for the functions of panel protection and container sealing.

We claim:

1. A method of forming a closure element which consists of providing a lacquered sheet of metal plate, coating the lacquered surface with a liquid vinyl resin composition having between about 15% to 50% of a plasticizer based on the weight of the resin, fusing the coating on said lacquered sheet, forming closure shells of the coated sheets, depositing an annular ring of a plasticized vinyl resin composition having between about 65% to of a plasticizer based on the weight of the resin on the inner surface of said shell, and fusing the annular deposit in said shell.

2. A method according to claim 1 wherein the composition which is used to coat the laquered surface of the metal plate is a polyvinyl chloride plastisol.

3. A method according to claim 1 wherein the composition which is used to coat the lacquered surface of the metal plate is a polyvinyl chloride organosol.

References Cited by the Examiner UNITED STATES PATENTS 2,663,909 12/1953 Maier et al 1138O 3,005,433 10/ 1961 Risch li1312l 3,029,765 4/1962 Navikas ll3l21 3,131,081 4/1964 Husum 1l380 CHARLES W. LANHAM, Primary Examiner.

D- GRE s tant Examiner.

Claims

1. A METHOD OF FORMING A CLOSURE ELEMENT WHICH CONSISTS OF PROVIDING A LACQUERED SHEET OF METAL PLATE, COATING THE LACQUERED SURFACE WITH A LIQUID VINYL RESIN COMPOSITION HAVING BETWEEN ABOUT 15% TO 50% OF A PLASTICIZER BASED ON THE WEIGHT OF THE RESIN, FUSING THE COATING ON SAID LACQUERED SHEET, FORMING CLOSURE SHELLS OF THE COATED SHEETS, DEPOSITING AN ANNULAR RING OF A PLASTICIZED VINYL RESIN COMPOSITION HAVING BETWEEN ABOUT 65% TO 150% OF A PLASTICIZER BASED ON THE WEIGHT OF THE RESIN ON THE INNER SURFACE OF SAID SHELL, AND FUSING THE ANNULAR DEPOSIT IN SAID SHELL.