US2835926A - Art of making closure members by depositing and curing a compound in the closure shell and thereafter molding - Google Patents

Description

May 27, 1958 c. E. MAIER ET AL ART OF MAKING CLOSURE MEMBERS BY DEPOSITING AND CURING A COMPOUND IN THE CLOSURE SHELL AND THEREAF'TER MOLDING Filed Nov. 1950 INVENTORS MW W pmN EN M Z M L ET .wfi i 2 cm u /fi w ATTORNEYS United States Patent Ofice 2,835,926 Patented May 27, 1958 ART OF MAKING CLOSURE MEMBERS BY DE- POSITING AND CURING A COMPOUND IN THE CLOSURE SHELL AND THEREAFTER MOLDING Curtis E. Maier, Riverside, Halford E. Brockett, Lombard,

and Ralph A. Larson, Chicago, Ill., assignors to Coutinental Can Company, Inc., New Yorlr, N. Y., a corporation of New York Application November 8, 1950, Serial No. 194,686 3 Claims. (Cl. 18-59) This invention relates to the rapid production of closure seals for containers, including the forming of a shaped cushion pad or sealing member.

It has been proposed and is a practice to form such crown seals with the usual metal shell having a cushion pad therein, made of rubber composition, or of a like elastomer compound. However, when the composition is introduced in the form of a solution or emulsion, for the necessary liquidity of application, rotation of the shell is required for distribution, the composition is not form-maintaining in itself, a lengthy period is required for elimination of the solvent or like vehicle, and the distribution cannot be controlled with assured accuracy, nor can special contours in the sealing area or in the center be attained for maximum sealing efficiency and minimum use of material. Also, curing could only be effected after such solvent was eliminated. On the other hand, when the composition was introduced as a blank, care was required for producing the necessary adhesion in the crown shell and high pressures and temperatures were required for molding. Further, if the blank or disc is cut out from a web, either frame scrap loss or reworking cost is involved; and at least one additional operation is involved in cutting and placing the blank or disc.

When a crown seal is to be used for capping a bottle or other container, the cushion pad serves to conform to the possibly irregular lip of the container, providing a gasket between such lip and the closing face of the metal crown shell itself. The crown seal usually has a further demand upon it, being that of preventing contacts of the contents of the container with the metal at the inner face of the crown shell. These two requirements may be satisfied by materials insoluble and essentially non-permeable to the contents of the container, but in practice such materials do not demand as great a thickness for protection against penetration as is required for providing the necessary sealing gasket for conformation to the container lip. Accordingly, it is preferred in accordance with this invention to provide a crown seal in which the sealing member or cushion pad has a thick outer annular portion for engagement with the container lip, and a thinner central portion to provide the assurance against contact of the contents of the container with the metal of the crown shell.

It has been found that by using compositions formed by dispersing fine particles of a resin such as vinyl resin in a liquid plasticizer, it is feasible to deposit a quantity of such semi-liquid, pastry dispersion in a closure shell, heat the closure shell with the mass therein and thereby cure the composition by causing the plasticizer to dissolve portions of the resin particles so that a form-maintaining button-like centrally located body is produced, along with causing the plasticizer adjacent the shell to effect adhesion to the lacquer coating so that the body adheres firmly to the shell: thereafter placing the shell with the adherent central button mass therein on a heated platen, and employing a heated punch for shaping the mass to the desired contour by causing radial outward movement ofthe thermally fluidified material and there-' by forming a substantially uniform, thermoplastic, shaped cushion pad which upon cooling maintains desirable characteristics of a tough resilient liner under the conditions of service. That is, the fusion or dissolution of the vinyl resin into the stated plasticizer, with production of adhesion, occurs under the inexpensive conditions of a hot air oven, for example, wherewith the shell and mass may thereafter :be stored and handled as a unit, even with hoppering, without danger of accidental separation or of loss of material by adhesion to or gouging by another shell.

In this practice, the closure shell with a centrally located body or button adherent thereto can be handled as a unit without particular troubles during bulk storage, hopper feeding, and like steps of economic production. Therewith, also, these units may then be subjected to the action of a heated punch and shaped to an optimum contour for economy of material and performance as a seal, under appropriate and commercially feasible conditions of temperature, pressure and time: and the volume of the completed seal can be determined by the original quantity introduced into the shell, as there is no volatile 7 component which need be driven off during the operations and the final volume is essentially the same as the measured original volume.

An example of practice of the invention is shown on the accompanying drawing, in which Fig. l is a diagrammatic showing of the successive steps of producing a crown seal or cap according to this invention. Fig. 2 is an axial cross-section through such a crown seal.

In Fig. l, a series of crown shells are shown advancing through the several steps of operation.

The crown shells may be prepared in the customary fashion by providing a sheet of steel or tin plate, with lithographed advertising matter on one face, and with a coating of a vinyl resin lacquer at the other or inner face, as more closely described hereinafter. The sheets thus coated and baked are then passed through punch presses in the presently customary fashion for example, whereby several hundred such crown shells are blanked and formed from a single sheet.

The composition of resin particles with plasticizer, the resin being essentially insoluble in the plasticizer at room temperature but soluble therein at an elevated temperature so that upon cooling a form-maintaining permanent, rubbenlike gel results, is called a paste-resin in the plastics industry. The plasticizer liquid is not an active solvent of the resin at a temperature of fluid flow of the resin plate, such as at room temperature or at a temperature of 110 to 115 F., but is an active solvent thereof at a higher and fiuxing temperature such as 275 to 375 F. For present purposes, they are characterized in that they contain no foreign material as a fiuidifying agent, which must be expelled to produce the final gel: and since the action is largely one of fluxing or intersolution of the resin and plasticizer, there is essentially no change in volume as the hot mixture changes to the gel form.

Such crown shells may then be passed through the steps of the present procedure, as indicated in Fig. 1 by the successive crown shells 10, 12, 22, 23, 24, 25, and 26.

The first step, after a crown shell such as 10 is introduced to the procedure, is that of depositing in the j concave-upward crown shell, illustratively crown shell 12, a quantity of the illustrative mixture of vinyl resin The present preference is for the crown and plasticizer. shell to be cold when the deposit begins; but it may be pro-heated if desired. This deposit may be accomplished by warming the material to a temperature of about 1109 F. to F., and then passingit to and through the nozzle 11 and thus providing the deposit of a standard quantity 14 in the crown shell 12. The nozzle and material may be kept warm by suitable means, such as infrared radiation from the electric bulb 13. It has been found that a volume of 100 to 400 cubic millimeters is a desirable quantity, the smaller volumes being usable with short-skirt shells, and the larger volumes with the so-called standard-skirt shells; it being understood that smaller volumes are permissible when the containers to be sealed are known to have close tolerances for irregular lip surfaces as compared with some bottles where greater allowances by greater thicknesses of cushions and corresponding larger volumes of paste are required. in general, the lower limit of volume for a specific employment depends upon the degree of sealing efliciency required as the sealing efiiciency decreases with the volume of compound, particularly in the lower ranges. The upper limit depends upon the amount of compound that can be put into the shell without interfering with the sealing, and on economics. Under these conditions, the introduced material 14 forms a button of about thrceeighths of an inch to three-quarters of an inch diameter at the center of the cap, as indicated by the mass 714. It will be noted that the nozzle 11 can be accurately alined with the axis of the crown shell 12, as indicated by the center line CL, and therewith the fluid discharged by the nozzle forms a flattened mass essentially concentric with the crown shell.

The next operation is that of passing the crown shell, illustratively the crown shells 22, 23, 24, 25, through a heated zone, illustratively shown as the hot air oven having a hot air inlet 21. This oven has the conveyer belt 23 for advancing the crown shells, each with its charge 14 of material, from an inlet to an outlet. Thereby, the mass of material 14 is heated until the plasticizer dissolves the vinyl resin particles, thus attaining a greater viscosity and providing the mass of material with a formmaintaining consistency. The plasticizer in contact with the lacquer coating when present inside of the respective crown shell also exerts a solvent action thereon, and provokes a union between the mass of material 14 and the lacquer coating on the crown shell, so that adhesion occurs. When no inside lacquer is employed, the mass adheres directly to the shell.

As a crown shell leaves the oven 20, it may be stored in hot or cooled condition, or may be advanced immedi ately to the shaping operation. Thus the unitary nature of the shell and its adherent mass 14 permits a wide latitude in processing: whereby large quantities of such units may be made up in a continuously operating central machine, and in part immediately shaped and completed while still hot, with permissive delays incident to temporary shut-downs or changes in the shaping equipment, and with use of more than one shaping machine supplied from the single depositing and curing apparatus: or the units may be cooled and kept for later shaping at such central plant, or delivered to other plants for the shaping thereat.

When the unit is to be immediately shaped, after leaving the oven 20, it is subjected to further heating and shaping operations, which may be accomplished by immediately placing it, such as the crown shell .26, upon a platen which is heated by burning gases coming from the supply pipe 31. A punch 32 is brought down into forcible contact with the cured mass of material in the crown shell 26, and produces a shaping of the same in counterpart to the shape of the lower end of the punch: in the illustrated form, a central concentric projection 33 causes the central part of the thermoplastic mass to be forced radially outward, while leaving a thin central web, and establishing a thicker surrounding annular portion. This punch 32 is heated, as illustrated by the electric heating wire 34.

The crown shell with its shaped and completely cured (ill 4' cushion pad therein is removed from the platen 30 and punch 32, and upon cooling is ready for use.

The completed crown seal or cap has the parts shown in Fig. 2, in which the circular end portion 40 is bounded by a smoothly curved top corner radius 42 leading to the corrugated skirt portion 43. The outer surface has a lacquer coating 44 which has been baked until it is free of tackiness or flow at the temperatures of operation during the process and steps shown in Fig. 1. The inner surface has a lacquer coating 45 with vinyl resin ex posed the surface thereof, and with the shaped mass of cushion material bonded to this lacquer. The shaped mass itself has a thin central web portion 47 opposite the hole in the mouth of the container, and a thicker annular portion 48 for contact with the lip of the container. in practice, it is preferred to have the thickness of the web portion 47 about 4 to 10 thousandths of an inch, while the annular portion may have a thickness of 12 to 40 thousandths of an inch.

The lacquer for the inner surface of such compound lined crowns may desirably be selected in accordance with the material employed for the compound and in accordance with the intended contents of the container to be sealed. For example, a vinyl lacquer prepared as described in the Maier et a1. Patent No. 2,380,456, with percent of vinyl chloride-vinyl acetate cop'olyrner resin and 2! percent of oleoresinous modifier produces a satis factory adhesion. When the crown seals are to be employed with carbonated beverages, it is preferred to employ a trimer lacquer having a corresponding solids formulation of 80 percent of vinyl chloride-vinyl acetate copolymerized in the presence of maleic anhydride as a modifier, for example, in the respective ratios of 87:l2:1, together with 20 percent of a phenolic resin derived from ortho-cresol and formaldehyde. Either of these lacquers can be prepared in an organic solvent, such as 70 percent xylol and 30 percent isophorone, with 20 percent solids, for roller coating. For spraying, more volatile solvent, such as toluol, methyl ethyl ketone, and methyl isobutyl ketone, can be used. After applying and drying, the coating is baked.

The composition forming the principal mass of the shaped cushion pad has two basic ingredients comprising an elastomer and a plasticizer therefor, the plasticizer being so selected that the elastomer is essentially insoluble therein at room temperature, but is soluble at some elevated temperature. These two ingredients are ground together to form a paste which is flowable under the conditions stated, and may also include other components such as inert fillers to limit cutting, pigments, modifying resins to assist control of physical properties, stabilizers for the resins and other components, waxes to prevent' blocking and to reduce moisture vaporv and gas permeability, etc. However, these other materials are not essential in the composition, but may be employed to contribute to the desired properties for the particular employment. In general, the formulations described in the Foye United States Patent No. 2,489,407 or in South African Patent No. 2,556/47 may be employed, noting that the tiller and other components may be omitted if so desired.

The elastomer component may be a vinyl resin of the class inclusive of polyvinyl chloride, copolymers of vinyl chloride and vinyl acetate such as the 97:3 percent copolymer, vinylidene chloride polymers, and copolymers of vinyl chloride and vinylidene chloride. The chloride content should be high, when the seal is to resist aqueous liquids; such as 9t) percent vinyl chloride in a copolymer.

Among the plasticizers useful are those which have a very slow wetting or dissolving action upon the selected vinyl resin at room temperature and at temperatures up to around F. The ester type plasticizers of vinyl resins have this general characteristic, and require higher temperatures for producing penetration, diffusion, and inter-solution. A preferred plasticizer is dioctyl phthalate: others are dibutyl phthalate, dioctyl sebacate, and tricresyl phosphate. The plasticizer should be liquid at the temperature of use.

The ratio of the elastomer and plasticizer, by weight, may be from 6:4 to 4:6, with preference for a ratio of about 1:1.

Such compositions can be introduced at about 110 F. to 115 F. through the nozzle 11, and then be treated in the oven 20, and thereafter be shaped by the action of the heated platen 30 and the heated punch 32, resulting in the production of a resilient, tough, olasticized resin mass, having an elongation at break, when a specimen is tested for strength, of 150 to 340 percent, for example, with the usual values being above 250 percent.

Illustrative of the conditions for the curing operation is the employment of a hot air oven having a high velocity circulation of air for heating the compound at a temperature of 325 F. to 400 F., the time in the oven being from 30 seconds to 5 minutes. For example, a time of 45 seconds at 380 F. is satisfactory with a volume of 200 cubic millimeters.

The temperature and pressure employed for the shaping operation depends upon the material of the compound, and upon the shape of the crown shell and the shape to be given the cushiion pad. For a crown shell having a one-sixteenth inch radius at the top corner, 100

to 200 pounds per square inch pressures are useful with a size and shape of cushion pad as illustrated in describing Fig. 2: when concentric rings are to be provided at the annular portion 48, 500 to 1000 pounds per square inch pressures are desirable. correspondingly, when the top corner radius of the crown shell is three thirty-seconds of an inch, pressures of 250 to 500 pounds per square inch should be used in forming a flat-top ring or annulus.

The temperature employed for the molding depends in practice upon the characteristics of the original coating lacquer 45 and the composition for the cushion material. When this lacquer is of vinyl chloride-acetate polymer, with the oleoresinous modifier as described above, the temperature can range from 325 F. to 350 B: when the so-called trimer of vinyl chloride-acetate and maleic anhydride is employed, the temperature may range from 325 F. to 375 F.

The time required for molding is from 6 to 20 seconds. It will be noted that for economy this time should be kept as short as possible.

An optimum condition, with a crown shell having a one-sixteenth top corner radius, the cushion pad having a shape as indicated in Fig. 2, with the inside lacquer coating 45 of the trimer resin, was a combination of 375 F., 150 pounds per square inch, and 12 seconds for shaping. When the crown shell had a three thirty-seconds inch top corner radius, with the same pad shaping and internal lacquer, the combination of 375 F, 700 pounds per square inch, and 20 seconds for shaping was satisfactory. No serious deterioration occurs even though the material is held for a far longer time in the heated condition.

It will be noted that the course of operation is such that, if desired, the hot crown shells, with cured cushion material therein, in the form of a central button 14, can be immediately taken up and handled mechanically for the shaping operation, without intermediate cooling: so that in effect the curing operation amounts to a pie-heating stage for the shaping step.

The paste resin as originally deposited is a semi-fluid sticky mass which flattens out by gravity into a button and clings to the crown shell, but may be wiped otf, and parts of the mass are removed upon contact of any solid object; also, flow occurs if the shell is tilted, so that the preferred uniform concentric disposition is lost. Hence, at this stage the crown shell with its deposit cannot be handled roughly nor can the mass be brought in contact with another crown shell. After curing in the oven 20,

however, the sticky deposited composition has changed to a physical condition wherein the surface is no longer tacky and the mass cannot be gouged away by simple contact, and therewith the vat clinging mass has passed to a state of adhesion which prevents accidental separa' tion: and flow no longer occurs if the shell is left in tilted condition.

While the invention has been illustrated by a practice of making crown seals with lacquered metal shells having corrugated skirts of circular outline, and employing the stated materials and conditions, it will be understood that it may be embodied in other forms within the scope of the appended claims.

We claim:

1. The method of forming sealing pads for closure seals, which comprises depositing in a closure shell to form a r substantially at the center of the shell a quantity or a semi-liquid paste composition consisting for essential components thereof of a normally liquid plasticizer and a finely divided resin which is paste-forming with the plasticizer at a temperature below the fiuxing temperature of the resin-plasticizer components, said composition being capable upon being heated to the fluxing temperature of the resin-plasticizer components thereof of forming a permanent rubbery gel, heating and thereby effecting adhesion of the mass and until the resin particles have completely dissolved into the plasticizer, and thereafter pres hr; a heated forming plunger against the mass While t osure shell is on a heated support for producing radial outward flow and thereby shaping the same into a sealing pad of the desired contour.

2. The method of forming sealing pads for closure seals, comprising positioning a closure shell in horizontal position with the skirt upward, discharging into the closure shell a quantity of a semi-liquid pasty material comprising particles of a resin dispersed in a fluid resin plasticizer and thereby forming a central deposit therein, heating the said material in the shell by hot air directed upon the exposed surface thereof and upon the shell for producing adhesion to the shell and until the resin particles have completely dissolved into the plasticizer, and thereafter pressing a heated forming plunger against the material while the closure shell is on a heated support for producing radial movement of parts of the mass of material and thereby shaping the same into a sealing pad having an annular thickened portion and a central thin portion.

3. The method of forming sealing pads for crown seals, which comprises positioning an internally lacquered a closure shell in horizontal position with the skirt upward, depositing at a temperature of about to F. into the crown shell a quantity of 100 to 400 cubic millimeters of a semi-liquid paste composition consisting for essential components thereof of a finely divided vinyl resin and a normally liquid ester plasticizer of the vinyl resin which forms a fluid paste with the resin at said temperature, said composition being capable upon being heated to a fiuxing temperature of 325 to 400 F. and thereafter being cooled of forming a permanent rubbery gel, said deposit occupying a central portion of said shell, heating the deposit at a temperature of about 325 F. to 400 F. whereby to cause the resin particles to completely dissolve in the plasticizer, thereafter pressing a heated forming plunger against the deposited and finned material While the closure shell is on a heated support for shaping the same into a sealing pad of the desired contour in contact with and adherent to the shell.

References Cited in the file of this patent UNITED STATES PATENTS 1,373,060 Eberhart Mar. 29, 1921 1,486,937 Taliaferro Mar. 18, 1924 2,144,495 Humphrey Jan. 17, 1939 FOREIGN PATENTS 500,298 Great Britain Feb. 7, 1939 Dedication 2,S35,926.0m'tis E. Mac'er, Riverside, Halford E. Bwocicett, Lombard, and Ralph A. Lawson, Chicago, Ill. ART OF MAKING CLOSURE MEMBERS BY DEPOSITING AND CURING A COMPOUND IN THE CLOSURE SHELL AND THEREAFTER MOLDING. Patent dated May 27, 1958. Dedication filed June 8, 1965, by the assignee, Continental 0cm Company, Inc.

Hereby dedicates to the public the term of said patent subsequent to October 13, 1970.

[Ofiioz'al Gazette Aug. 10, 1965.]

Claims (1)

1. THE METHOD OF FORMING SEALING PADS FOR CLOSURE SEALS, WHICH COMPRISES DEPOSITING IN A CLOSURE SHELL TO FORM A MASS SUBSTANTIALLY AT THE CENTER OF THE SHELL A QUANTITY OF SEMI-LIQUID PASTE COMPOSITION CONSISTING FOR ESSENTIALLY COMPONENTS THEREOF OF A NORMALLY LIQUID PLASTICIZER AND A FINELY DIVIDED RESIN WHICH IS PASTE-FORMING WITH THE PLASTICIZER AT A TEMPERATURE BELOW THE FLUXING TEMPERATURE OF THE RESIN-PLASTICIZER COMPONENTS, AND COMPOSITION BEING CABABLE UPON BEING HEATED TO THE FLUXING TEMPERATURE OF THE RESIN-PLASTICIZER COMPONENTS THEREOF OF FORMING A PERMANENT RUBBERY GEL, HEATING AND THEREBY

Images