US2373847A - Coated foil closure - Google Patents

Description

Filed Aug. 3, 1940 Ap ril 17, 1945.

Jig. 1.

l7elal Foil 1O Coaiing INVENTORS zf/YDKEWG OSBORNE THOMAS M H144 Patented Apr. 17, 1945 coa'rno FOIL CLOSURE Andrew G.

Osborne, New Kensington, and

Thomas M. Hill, Arnold, 2a., asslgnors 'to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsyivania Application August 3, 1940, Serial No. 350,560

9 Claims.

This invention relates to closures for containers, particularly cup-like or the hood typ Closures for containers such as glass bottles.

The invention is particularly concerned with pliable metal foil closures of the hood type which are provided with a coating having both lubricating and sealing properties. Prior tothis invention no foil closure of this-character has been satisfactorily produced with a coating on the iner surface thereof capable of heat-sealing the closure to a container to form a substantially hermetic seal, or capable of cold-sealing a closure to a container to form a substantially fluid-tight seal, especially without heat softening of the coating. Likewise prior to this invention, many inbricants used for facilitating drawing of a closure and removal thereof from a container have not been fully satisfactory, particularly when used on a closure having a decorative or like lacquer coating on an external surface. Ordinary lubrieating materials either harmfully attack the decorative or like coating or fail to suiiiciently well lubricate and adhere to the foil, as it is formed into a closure, to permit ready removal of the closure from a container.

Previous foil closure coatings, whether for seal- A object of this invention to provide an improved ing or for lubrication, have been found upon test.

or use to be open to many objections. these materials have exhibited good closure sealing properties but have lacked good metal-adherence properties. Many closurecoating materials exhibit a marked lack of metal-adherence properties by tending to peel away from metal foil during handling, winding and unwinding thereof, or during drawing of the foil into cuplike closures. On the other hand, many closure coating materials which exhibit good metal-adherence properties are poor sealing materials. Likewise many such materials are not capable of properly lubricating the closure forming dies during drawing of cup-like closures, nor are they capable of facilitating the removal of a closure thermore, such characteristics prevent free re'- Some Of cup-like foil closure with a sealing or lubricating coating on the inner surface thereof. Further objects are to provide on such aclosure a coating adapted to both thermoplastic or heat-sealing of the closure to a container at. temperatures around to F. and to cold-sealing of the closure to a container at temperatures as low as those ordinarily encountered in packaging refrigerated foodstuffs, such as milk.

Another object is-to provide a cup-like foil clo-' sure with a lubricating coatingewhich will facilitate drawing of the closure, and removal of such a closure from a container. Another object is to form a drawn, .cup -likefoil closure from foil provided wtih a coating material adapted to function as a sealing or lubricating material without destruction of the coating during fabrication of the closure. It is particularly an object to provide a closure coating of the character here mentioned which is adherent to metal foil and which will retain its continuity and not tend to transfer or ofiset onto surfaces into contact with which it is brought.

Another object is to provide a closure sealing coating which has suflicient flexibility to with stand deformation necessitated by application of theclosure to a container. Another object is to provide a cup-like foil closure with a coating capabl e of effecting a vacuum tight seal between the closure and a container. Another object is to pr'ovide a cup-like foil closure with a sealing coating which is protective to the foil and nontoxic, one suitable for use in the closing of containers filled with foodstuffs such as milk and fruitfjuices.

Another object'is to provide a cup-like foil closure with an improved coating comprised of a wax-miscible vehicle and a suitablewax. A particular object of the invention is toprovide a cup-like aluminum foil closure drawn from a foil blank having a continuous coating comprised of a metal-adherent, substantially unoxidized condensation derivative of rubber, and a wax which will not soften at ordinary handling and operat-. ing temperatures.

Other objects and advantages of the invention will appear as the description thereof proceeds.

The property of sealing a foil closure to a container; usually when moderate heat and pressure are applied, is a characteristic of certain wax coatings. However, such coatings can only be applied, as a practical matter, to the foil before formation of the closure. Since wax coatings do not adhere well to metal foil, the operation of drawing a cup-like ,foil closure from a blank of metal coated with wax usually removes substantially all of the wax coating from the foil .forming the closure. When it is attempted to insure the presence of wax on the foil by using large quantities of waxto form the coating, diificulty in keeping the closure forming dies free of the wax is encountered. It will be recognized, then, that closures which are drawn from ordinary wax coated foil cannot be expected to have suflicient wax retained on the sealing surfaces thereof to serve either as a sealing material or as a lubricating material.

On the other hand, closures formed of foil coated with ordinary adhesive and thermoplastic materials are incapable of satisfactory use for one or another of several reasons. For instance, it has been found that many adhesive or thermoplastic materials donot have good metal-adherence characteristics; or in cases where such materials adhere well to metal, they do not have sufficient flexibility or moldability to permit sealing the closure to the container; or in many cases they are incapable of facilitating ready removal of a closure from the container.

A coating material for a cup-like foil closure has been discovered, however, which may be applied to foil from which cup-like or hood type closures are to be drawn, and which will adhere to the metal, will not transfer or offset, and will facilitate removal of the closure from a container. This material and modifications thereof are suitable for heat-sealing Or cold-sealing a closure to a container. When the coating is applied to foil even in small quantities, it is useful as a closure lubricating material.

It has been found that a coating material having the desired characteristics set forth above may be produced by dissolving a wax in a suitable vehicle. It has been found that a lacquer-like vehicle, which is readily miscible with wax and which is adherent to metal foil, may be employed to support and carry large quantities Of wax in solution therewith and to, in effect, bind the wax to metal foil from which a cup-like closure may be drawn. -It is a further discovery that variations in type'and proportion of wax and waxmiscible vehicle, and in the thickness of the coating formed therefrom and applied to the foil, can be made to adapt the coating to heat-sealing or cold-sealing of closures to containers and to adapt the coating to lubrication of closures during fabrication and removal thereof. A coating material made in accordance with the invention retains the desirable metal adherence and non-tackiness properties of the vehicle which is employed, and further retains the desirable sealing and lubrieating characteristics of the wax which is employed, without producing any undesirable characteristics in the coating or destroying any of the desirable characteristics of its constituents.

A drawing forming part of this specification illustrates various phases of the invention. In the drawing:

Fig. l is a side view of a metal foil blank provided with a. coating conforming to the invention;

Fig. 2 15a side view, partly in section, of a cuplike or hood type 1011 closure formed from a coated blank such as is shown in Fig. 1; and

Fig. 3 is a side view, partly in section, of a cuplike or hood type closure as it appears when it is applied on a typical container.

The drawing illustrates various stages in the formation of a cup-like coated metal foil closure and the application thereof to a container. A metal foil blank III is shown in Fig. 1 having a coating material H, to be more fully described. on one surface thereof.

A cup-like foil closure ll, shown in Fig. 2, may be fabricated from the metal foil blank ID by the usual drawing operation, retaining the coating material H on the inner surface thereof. The closure 13, shown in Fig. 2, is provided with a pull tab H which may be employed to tear oil and remove the closure II from a container. The pull tab It forms no part of the present invention. and it may or may not be provided on the closure 13 as is desired.

The closure I3 is particularly well adapted to the sealing of milk or fruit juice bottles, and such a container I6 is shown in, Fig. 3 with a closure I3 applied thereto. The container I6 is provided with a bead I l at its orifice. The bead has a downwardly directed shoulder Or flange I8 for retaining the closure II when it is pressed into conformity therewith. Suitable lugs or projections is are provided below bead l1 and merging therewith for obliterating the detents 20 formed in the lower portion of the skirt of closure 13 when it is applied to container Ii. Numerous types of container and mechanical closure retaining means thereon are, of course, suitable to the practice of this invention, the container l6 shown in Fig. 3 being illustrative only.

The pliable metal foil or light metal closure l3, having a desired continuous coating II on the inner surface thereof, may be produced and applied to a container l6 for sealing foodstuffs such as milk or fruit juicesby the procedure set forth hereinafter.

The preferred coating material, before application, is made up of a lacquer-like vehicle, a wax and a suitable solvent. The preferred lacquerlike vehicle has as its base a substantially unoxidized condensation derivative of rubber marketed under the trade name Pliolite" by the Goodyear Tire and Rubber Company, Inc., and described in the United States patent to Endres, No. 2,052,391. A lacquer-like vehicle having such a base is a "metal-adherent material, miscible with large quantities of wax. It may be purchased in various grades distinguishable by softening point tests of the base material during its manufacture. It is preferred that a grade of the condensation derivative of rubber be employed which has a minimum of tackiness, i. e. which is not highly sensitive to ordinary temperatures, and which has the property of strong adherence to metal, particularly to aluminum foil, if such is the material to which a coating is tobe applied. The grade of vehicle having the condensation derivative of rubber found best suited to the practice of this invention as its base is the Plicote" lacquer sold by the Watson Standard Company of Pittsburgh, Pennsylvania, under the numerical trade designation V-l107-M. This lacquer is one which has a base material manufactured by the Goodyear Tire and Rubber Company, Inc. and identified by its numerical trade designations,

1385.? This nitro-cellulose lacquer is usually "P843" or T1233! It has a selected softening point which characterizes the base material after its manufacture of about 71 F.

Lacquers are formulated from the above condensation derivative of rubber by dissolving the same in a suitable solvent. The preferred lacquer or lacquer-like vehicle consists of about 30 per cent by weight of the condensation derivative of rubber as a base and about 70 per cent by weight of a solvent such as toluol. Other suitable solvents are xylol, petroleum naphtha, butyl acetate,

' or mixtures of such materials. The above proportions may, of course, be varied somewhat to conform to various operating conditions. The base material is dissolved or cu in the solvent in the usual manner, preferablywith some agitation.

A lacquer or lacquer-like vehicle formedin substantially the above proportions is capable of dissolving and carrying large quantities of waxes such as paraflin and petroleum waxes which remain mixed with the base material even after volatilization of the solvent, as when a coating film is formed and dried. The dissolving of wax in the lacquer does not noticeably diminish the film-forming and metal-adherence properties characterizing the lacquer. Therefore, this lacquer may be employed as a vehicle for carrying and supporting a wax to form a coating material. Any paraflin or petroleum type wax havin a melting point from about 132 to 180 F..is suitable for the preparation of a coating material by mixture with the above described vehicle. It is preferred that a paraflin or petroleum type wax having a melting point of aboutl41 to 143 F. be employed, particularly one having a sharply defined melting point in the named range. Sharpness of melting point is most desirable for heat-sealing purposes. Waxes having melting points below about 141 F. exhibit sensitivity to heat, and can be satisfactorily used incoatings only when the coated foil or closures fabricated therefrom are not subjected to unusual handling or storage temperatures. Waxes having'melting points above about 143 F. may require, when used in a coating material, higher sealing temperatures, when closures are to be heat-sealed to containers.- 7 The wax chosen for use in the coating material may be mixed with the lacquer-like vehicle in proportions of about 4 to 16 ounces of wax to each gallon of the above described 30 per cent base vehicle; The coating on the completed closure consists of a vehicle base containing about 10 to 30 per cent wax. The preferred proportion is about 8 to 12 ounces of wax to each gallon,

which provides a coating on the closure of a vehicle base containing about to per cent wax. Higher proportions of wax may in some cases undesirably load the vehicle, creating a tendency for excessive quantities of the wax to exude or appear .at the surface of a film formed by the coating material and to transfer or offset from the coating. Smaller proportions of wax decrease the sealing ability of films formed of the coated material, but for a wide range do not interfere with the lubricating characteristics of the coating.

Another example of a. coating material conforming to the invention may be mentioned. It has been found that a lacquer-like vehicle of the nitrocellulose type is also adapted to serve as a coating material vehicle in the practice of this invention. A useful nitro-cellulose type of lacquer is the clear lacquer marketed by E. I. du Pont de Nemours and Company under the numerical trade designation prepared with solvents in the proportion of "about per cent base and per cent solvents. A 40 per cent base nitro-cellulosetype vehicle is miscible with wax of the character above described in proportions up to about 8 ounces of wax to each gallon of vehicle. Higher amounts of wax are not readily miscible in this nitro-cellulose type of vehicle. The properties of the nitrocellulose type. vehicle make a coating prepared higher temperatures may be necessary to the eflicient use of this second type of coating material when it is desired to effect a heat-seal between a closure and a container, but otherwise comparable results are obtainable with both types of coating material.

Either of the coating materials above described may be applied to metal foil from which may be fabricated metal closures by the usual methods. Any suitable pliable metal foil or light gauge sheet metal may be employed for forming coated closures of the hood type in the practice of this invention. Foil is usually defined as metal of about 0.0005 to about 0.005 inch gauge, but the invention should not be confined to metal of such thicknesses only. A preferred closure material is aluminum foil of about 99.35 per cent to about 99.5 per cent purity in gauges of about 0.003 to 0.004 inch. In this specification and in the claims the metal material of the closure is referred to as foil or pliable metal, which terms areused with reference to the above explanatory remarks.

The thickness of the film of coating material upon the foil may be expressed in terms of weight of coating per unit area. A light sealing coating is one in which there are about 300 milligrams of coating film per square foot of foil surface. A heavy: sealing coating is one in which there are about 1300 milligrams of coating film per square foot. Coated foil for the formation of cup-like closures preferably. has asealing coating present in the proportions of about 600 to 800 milligrams per square foot. Foil coated with a film of such weight is suitable both for heat-sealing and cold- Coatings lighter than the preferred coating do not seal closures to containers as well as the preferred coating; and coatings heavier than the preferred coating tend to more easily be stripped from the foil. However, a range of coating thicknesses from 300 to 1300 milligrams per square foot have been found in generalto be useful. While it is difficult to determine the thickness of a coating in linear measure, it is estimated that a coating weighing about 700 milligrams per squarefoot of area has a thickness on the order of about 0.0003 inch.

It has been a further discovery, however, that the coating material herein described is eminently suited for use as a foil or closure lubricating coating. For this purpose a coating material may be applied to the foil in film thickness ranging from about 5 milligrams per square foot to and including thicknesses in the above described sealing ranges. when lubrication is the sole purpose. to

be served by the coating material, the wax content canbe conveniently reduced to about 4 ounces of wax to each gallon of about 30 per cent base vehicle, applied in film thicknesses from about 5 to milligrams per square foot.

A lubricating coating of' the material described herein has been found to be an excellent drawing lubricant. Furthermore, because of its quality of strong adherence to the foil and its quality ently as a lubricating material.

Foil which has-been coated and prepared as set forth above may be drawn to form closures in the usual manner. If it is desired, the top panels 1 [of the coated closures may be embossed with the Liusual decorative or trade designs. It is desirable, however, for good heat-sealing purposes that any embossing in the top panels of the coated closures be confined to areas inside the sealing surfacesof the closures. 'In other words, embossing appearing on the peripheral edges of the closure will interfere with the successful use of the closure for making a vacuum tight seal. V

A closure l3 prepared in the manner of the invention may be applied to a container I by molding thesame into conformity with the container orifice. Compressible rubber sealing heads are preferably employed, and closure applying apparatus such as is disclosed in United States patent to Hogg, No. 2,112,842 is eminently suited to the app y n of closures prepared in accordance with this invention to containers.

Closures prepared in the manner of the invention are adapted to be heat-sealed to containers in' the following manner. Fruit Juices are ordinarily packaged in glass containers at temperatures of around 140 to 180 F. Containers are filled with fruit juices at such elevated temperatures, thus heating the container to approximately those temperatures. A coated foil closure applied to a container at such temperatures will a vacuum quickly, spray or water cooling of closure and container may be resorted to.

Likewise closures prepared in the manner of the invention may be employed for closing containers packaged at ordinary or low temperatures. In such cases, moderate amounts of sealing pressure will mold the closure and coating material into conformity with the orifice of the container, and irregularities therein, to a suflicient degree to produce a fluid-tight seal even though there be no heat softening of the coating material on the closure. Of course, in cases of either heat-sealing or cold-sealing, the closure should preferably be mechanically secured to the container in some suitable manner such as that shown in Fig. 3 of the drawing.

Coated closures of the invention have been found eminently suited to the vacuum sealing of hot packed foodstuffs, including fruit juices. They have likewise been found eminently suited to the cold-sealing of bottle containing milk. It has been found that bottles containing milk which have been sealed with the closure coated in the manner of the invention are particularly well protected against contamination. Furthermore, it has been found that closures coated in the manner of the invention are particularly well adapted to prevent capillary seepage offiuids into milk containers and to prevent leakage of milk out of milk containers. These improvements have of strength, flexibility and abrasion resistance, it has been found that such a lubricating film perbeen noted particularly when the container is filled with foodstuffs difilcult to retain by ordinary closures.

A further usefulness of the coated closure of the invention has been in connection with the application and removal of closures to and from containers, especially those having complex closure retaining devices at the orifice thereof. It has been found that closures coated in the above described manner, whether with a sealing coating or with a lubricating coating, are much more easily removed from container having complex closure retaining means than are any ordinary closures.

Although certain specific embodiments of the invention have been described hereinabove by way of illustration, it is to be understood that the invention is not limited'thereto but may be otherwise practiced and applied within the scope of the appended claims.

. What is claimed is:

l. A cup-like metal foil closure including a fiexible coating adhering to the inner surface of the metalfoil, said coating being comprised of a waxmiscible, lacquer-like vehicle base and a wax miscible therein, said base being characterized by continuity and adherence to the metal foil of the closure, said wax having a melting point above about 132 F.

2. A drawn cup-like metal foil closure having a continuous and flexible sealing coating adhering to the inner surface thereof, said coating consisting of a wax-miscible, lacquer-like vehicle base containing between about 10 and 30 per cent wax miscible therein, said base being characterized by adherence to the metal foil or the closure and continuity after die drawing thereof, said wax having a melting point above about 141 F.

3. A drawn cup-like metal foil closure having a continuous and flexible coating adhering to the inner .surface thereof, said coating being comprised of a wax-miscible, lacquer-like vehicle base anda wax miscible therein, said base being characterized by adherence to the metal foil of the closure and continuity after drawing thereof, said wax having a melting point above about 132 F., said coating being adapted to heat-seal the closure to a container upon application of moderate pressure at temperatures between about to F.

A. A hood-type pliable metal closure for sealing containers such as glass bottles and including a flexible sealing coating adhering to the inner surface of thepliable metal, said coating being comprised of a wax-miscible, nitro-cellulose base lacquer characterized by strong adherence to the metal of the closure and continuity after forming thereof, and a wax having a melting point above about 141 F. miscible therein and present in an amount proportional to about 4 to 8 ounces to each gallon of a lacquer containing about 40 per cent of said nitro-cellulose base as measured before application of said coating.

5. A drawn hood-type pliable metal closure for sealing containers such as glass bottles provided with a flexible sealing coating adhering to the inner surface thereof, said coating being comprised of a wax-miscible, nitro-celluiose base lacquer characterized by strong adherence to the metal of the closure, continuity, and resistance to abrasion during drawing of the closure, and a petroleum-type wax having a melting point of about 141 to 143 F., said wax being miscible therein and present in an amount proportional asvasu 5 toaboutl parttoeveryfito'lpartsbyweightof said nitro-cellulose base,

6. In combination, a container and a closure heat-sealed to said container, said closure comprising a metal foil cup-shaped blank reformed onto the exterior mouth surface of said container and a sealing film on the inner surface of said blank securing said blank to said container in a fluid impervious relationship by adhering-to the exterior mouth surface thereof, said him being tacky only above about 120 1".

7. In combination, a container and a closure heat-sealed to said container, said closure comprising a metal foil cup-shaped blank reformed onto the exterior mouth surface of said container and (a sealing film on the inner surface of said blank securing said blank to said container in a fluid impervious relationship by adhering to the exterior mouth surface thereof. said film adhergo and about 20 to 25 per cent wax having .a meltin: more strongly to said blank than to said container surface and being tacb only above about 120'F.

8. In combination, a container and a closure heat-sealed to said container, said closure comprising a metal foil cup-shaped blank reformed 10 than to said container surface and being nontacky below about 120? F.

9. A hood-type pliable metal closure for sealin; containers such as glass bottles and including a flexible sealing coating adhering to the inner is surface of the pliable metal, said coating being comprised of a wax-miscible, substantially unoxidized condensation derivative of rubber characterized by strong adherence to the metal of the closure and continuity after forming thereof,

in: point above about 141 F.

ANDREW G. OSBORNE. 'I'HOLQQS M. HILL.

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