US2654913A - Art of making closure seals by molding and curing - Google Patents

Description

C. E. MAIER Oct. 13, 1953 ART OF MAKING CLOSURE SEALS BY MOLDING AND CURING Filed July 27, 1950 mma .WMU Wma Ww QM.

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Patented Oct. 13, 1953 ART F MAKING CLOSURE SEALS BY MOLDING AND CURING Curtis E. Maier, Riverside, lll., assignor to Continental Can Company, Inc., New York, N. Y., a corporation of New York Application July Z7, 1950, Serial No. 176,217

(Cl. lll-59) Claims. l

This invention relates to the rapid production of crown closures 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 was 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 efliciency 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 out 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 satised by materials insoluble and essentially non-permeable to the contents of the container, but in practice such materials do notdemand as great a thickness for protection against penetration as is required for providing the necessary sealing gasket for conformation to the container lin. 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 iine particles of resinin a liquid plasticizer, a composition is obtained which can be used in liquid condition and a measured I amount placed in a crown shell :and then shaped and cured by heating the crown shell and a shaping punch for producing a. temperature in the plasticizer which causes it to dissolve the resin, so to speak, so that a substantially uniform, thermoplastic, shaped cushion pad is produced: and thereafter to cool the same so that the established shape is thereafter maintained under the conditions of service. That is, the resin fuses or dissolves into the said plasticizer to establish such amass.

By such practice, there is no :material loss, as the measured amount of liquid is delivered into each shell; there is no volatile component to be driven oit; the composition can be molded under low pressures, so that the equipment need not be designed for high pressures; the compound can be molded easily to produce a iinal article having the optimum contour for economy in material and performance as a seal; and at appropriate and easily attainable temperatures the pasty compound is fused or iiuxed to form a tough resilient liner within a time which is very short compared to that for curing rubber or like compositions or for driving water or solvents out of liquid compositions containing the same as a distributing or fiuidifying agent. w

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

In Fig. l, a series of crown shells I0 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 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 plasticlzer, the resin being essentially insoluble in the terial as a iluidifying agent, which must be expelled to produce the nal gel: and since the action is largely one of iluxing or inter-solution of the resin and plasticizer, there is essentially no change in volume as the hot mixture changes to the gel form.

Such aV crown shell may then be started through the present procedure, as indicated by Fig. 1. 'I'he rst step after introduction to the procedure is that of introducing into the concaveupward crown shell a quantity of the mixture of vinyl resin and plasticizer. The present preference is for the crown shell to be cold when the deposit begins; but it maybe preheated if desired. This deposit may be accomplished by warming the material to a temperature of about 110 to 115 F., to facilitate ow, and then pass it to and through the nozzle II and provide a deposit of a standard quantity in theV crown shell I2 as shown beneath the said nozzle. The

nozzle and material may be kept warm by infrared radiation from the indicated electric bulb I3. 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 knownto 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 efficiency required'as the sealing eiiiciency 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 economies. Under these conditions, the introduced material I4 forms a button of about three-eighths of an inch to three-quarters of an inch diameter at the center of the cap, as indicated by the mass I6 in the crown shell I 1, which indicates a crown shell between the time of delivery of the composition into the same, and the time of molding and curing the composition.

The crown shell, with the button of composition therein, is then brought to a heating platen illustrated as a hot plate having a heater 2l therebeneath, and providing an upper surface upon which rests a crown shell 22 having therein a charge of composition which is undergoing molding and curing. For the purpose of shaping the mass, a punch'23, having an outer diameter closely corresponding to the inside diameter of the crown shell, is moved down into the crown shell. This punch is illustrated as having heating means such as the electric heating wire 24 therein. The lower'end of the punch can have a shaped projection 25, of lesser diameter and extending below the general annular area, at the center of the bottom of the punch.

Under the influence of the heat delivered into the mass from the hot plate 20 and the heated punch 23, the composition flows under the pressure, and establishes a shape determined by the crown shell acting as a mold, and by the punch acting to form the later-exposed surface of the cushion piece. The temperature and pressure are maintained until this fluidizing has caused the material to assume the intended final form, and until the resin particles have fused into the plasticizer, and the entire mass has become homo- 4 geneous and form-maintaining at the temperature of treatment.

The article thus produced, as shown in Fig. 2, has the usual circular metal closure portion 30, and the crimped skirt wall 3 I. The outer surface of these metal parts has the coating 32, which may include advertising matter over the area 30, for example, together with an internal lacquer coating 32 on the skirt walls 3|. The cushion pad of the shaped and cured mass is formed by a thin central portion 33, and a thicker annular portion 34: this cushion pad or sealing member as a whole having its surface adjacent the part 30 of the crown shell adhered to the internal lacquer coating 32' originally provided on the metal sheet, so that a secure and tight bond exists therebetween. 'Ihe 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 al. Patent 2,380,456, with per cent of vinyl chloride-vinyl acetate copolymer resin and 20 per cent of oleoresinous modifier produces a satisfactory adhesion. When the crown seals are to be employed with carbonated beverages, itis preferred to employ a trimer lacquer having a corresponding solids formulation of 80 per cent of vinyl chloride-vinyl acetate copolymerized in the presence of maleic anhydride as a modifier, for example, in the respective ratios of 87:12:1, together with 20 per cent of a phenolic resin derived from ortho-cresol and formaldehyde. Either of these lacquers can be prepared in an organic solvent, such as 70% Xylol and 30% isophorone, with 20% solids, for roller coating, For spraying, more volatile solvents, 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 vapor and gas permeability, etc. However, vthese 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 2,489,407 or in South African Patent 2,556/47 may be employed, noting that the filler anddother components may be omitted if so 'desire 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 per cent 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 90 per cent 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 115 F. The ester type plasticizers of vinyl resins have this general characteristic, and require higher temperatures for producing penetration, diffusion, and intersolution. 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 plasticzer, 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 to 115 F. through the nozzle Il, and then caused to flow, be shaped, and cured, by the action of the hot plate 20 and the heated punch 23, resulting in the production of a resilient, tough plasticized resin mass.

Illustrative of the condition for the molding and curing operation is the employment of 10 to 30 pounds pressure per square inch in a crown shell having a one-sixteenth inch radius at the top corner, or 10 to 100 pounds per square inch in a crown shell having a three thirty-seconds inch radius at the top corner, with the punch designed as shown in Fig. l, to produce a smooth frusto-conical surface for the annulus 34 shown in Fig. 2. In general, the pressure is dependent (a) upon the design of the punch, the more complex shapes of seals requiring higher molding pressures; and (b) upon the volume of compound being used, as higher pressures are desirable with the lower volumes.

The temperature employed for causing the fiow and molding of the composition to shape, in

practice, depends upon the characteristics of the original coating lacquer 32. When this lacquer is of vinyl chloride-acetate polymer, with the oleoresinous modifier as described above, the temperature can range from 275 F. to 350 F.: when the so-called trimer of vinyl chloride-acetate and maleic anhydride with O-cresol phenolic resin is employed, the temperature may range from 300 F. to 375 F.

The time required for heating and molding is only two or three seconds: the additional time required for completing the diffusion and curing in the mold depends upon the temperature and pressure conditions used. For example, using a temperature of 325 F. and 30 pounds per square inch pressure, the time required for producing a completed cure with a 97:3 vinyl chloride-acetate copolymer, with dioctyl phthalate plasticzer, is from four to thirty seconds: a stable and formmaintaining body results in two to three seconds, and a thorough diffusion and general homogeneity occurs within thirty seconds. In general, it is preferred to employ relative higher temperatures, to shorten the total time. However, the materials are of low heat-transmission, so that about six seconds is presently regarded as a commercially minimum time under a condition such as 375 F. with 75 pounds per square inch pressure.

As a specific example, with the use of the trimer lacquer upon the interior of the crown shell, a temperature of 350 F., and a pressure of 25 pounds per square inch, six seconds was found to produce a satisfactory molding and curing cperation, for producing a liner having a frusto conical annular surface in a crown shell having a one-sixteenth inch radius at the top corner. When the crown shell had a three thirty-seconds inch radius at the top corner, the pressure was increased to 30 pounds per square inch, for producing a molding and curing in six seconds at a temperature of 350 F.

While the invention has been illustrated by a practice of making crown seals with lacquered metal shells, 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.

I claim:

l. The method of forming sealing pads for closure seals, which comprises depositing in a closure shell having an internal. lacquer coating, a measured quantity of 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 fluxing temperature of the resin-plasticzer components, said composition being substantially free from vaporizable components and'capable, upon being heated to the fluxing temperature of the resin-plasticizer components thereof and thereafter'being cooled, of forming al permanent rubbery gel having essentially the same volume as said measured quantity, pressing a heated forming plunger into sealing relation with the shell and against the deposited material for shaping the same into a sealing pad of the desired contour, and maintaining said shaped pad under heat and pressure at a fluxing temperature until the shaped pad has adhered to the closure shell and the said resin-plasticzer components have fiuxed togather.

2. The method of making crown seals having therein a shaped and cured cushion pad, which comprises providing a crown shell having an internal lacquer coating exhibiting a vinyl resin at the exposed side thereof, depositing in the crown shell and upon said exposed coating face thereof a measured quantity of a semi-liquid mass essentially free from vaporizable components comprising particles of a vinyl resin dispersed in a fluid vinyl resin plasticzer, heating the mass and concurrently therewith confining and compressing the saine in the crown shell by a heated shaping surface while heating and thereby shaping the mass and provoking adhesion of the mass to said lacquer coating and dissolution of the vinyl resin particles into the plasticizer to constitute an essentially uniform mass of the same volume as said measured quantity.

3. The method of forming sealing pads for crown seals, which comprises depositing at a temperature of about 110 to 115 F. into a lacquered metal crown shell a.` measured quantity of to 400 cubic millimeters of a semi-liquid paste composition substantially free from vaporizable` components and consisting essentially 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 275 to 375 F. and thereafter being cooled, of forming a permanent rubbery gel of the same volume as said measured quantity, pressing a heated forming plunger against the deposited material for confining and shaping the same into a sealing pad of the desired contour, and maintaining said shaped pad at 275 to 375 F. and under a pressure of 10 to 100 pounds per square inch until the shaped pad has adhered to the closure shell and the said resin-plasticizer components have fiuxed together.

4. The method of making crown seals having therein a shaped and cured cushion pad, which comprises providing a crown shell having an internal lacquer coating, depositing in the crown shell and upon a part of said coating a measured quantity of a semi-liquid pasty mass essentially free from vaporizable components comprising particles of a resin disposed in a fluid plasticizer of the resin, heating the mass, and pressing a heated forming surface upon the mass in theA crown shell while so heating and thereby distributing and shaping the mass and provoking adhesion of the mass to said lacquer coating, and fluxng of the resin particles with the plasticizer to constitute an essentially uniform mass.

5. The method of making closure seals, which comprises depositing at a temperature of fluid .flow into a cold internally-lacquered closure shell a measured quantity of resin paste essentially free from vaporizable components having as dominant gel-forming elements thereof nely divided resin particles suspended in a resin plasticizer Which is not an active solvent of the resin at said temperature of fluid flow of the resin paste and which is an active solvent thereof at a higher and uxing temperature, pressing a forming surface against the deposit and thereby distributing and shaping the same, and then heating the shell and surface and maintaining the deposit at a fluxing temperature and confined between the shell and said surface until the resin and plasticizer have fluxed together and constitute a form-maintaining gel adherent to said shell and having the same volume as said measured quantity.

CURTIS E. MAIER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,486,937 Taliaferro Mar. 18, 1924 2,489,407 Foye Nov. 29, 1949 2,498,489 Haggart Feb. 21, 1950 FOREIGN PATENTS Number Country Date 500,298 Great Britain Feb. '7, 1939

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