US2823422A

US2823422A - Manufacture of closure seals having formed cushion pads therein

Info

Publication number: US2823422A
Authority: US
Inventors: Julius L Schneider
Original assignee: Continental Can Co Inc
Current assignee: Continental Can Co Inc
Priority date: 1950-11-08
Filing date: 1950-11-08
Publication date: 1958-02-18
Anticipated expiration: 1975-02-18
Also published as: GB751163A; BE529212A; FR1105041A; NL92618C

Description

Feb. 18, 1958 J, L. SCHNEIDER 2,823,422

MANUFACTURE OF CLOSURE SEALS HAVING FORMED CUSHION PADS THEREIN Filed Nov. 1950 INVENTOR ATTORNEYS United States atent MANUFACTURE OF CLOSURE SEALS HAVING FORMED CUSHION PADS THEREIN Julius L. Schneider, Chicago, Ill., assignor to Continental Can Company, Inc., New York, N. Y., a corporation of New York Application November 8, 1950, Serial No. 194,662

6 Claims. (Cl. 18-59) This invention relates to the manufacture of closure seals having formed cushion pads therein.

It has previously been proposed to make closure seals by employing a plastic material which is shaped by the action of a punch and thereby caused to conform to the shape of the crown shell, providing the pad in the form of a structure having a thin central portion and a thicker annular portion for engaging with the lip of the container to be sealed by the closure seal. In practice, some difliculties have arisen with variations 'of the plasticity of the material, wherewith imperfections occurred at the annular portion, and flash was developed at the periphery, extending into the region of the corrugated skirt parts of the crown shell. Such flash was particularly undesirable when the flow of the material was not regular, as for example when the mass developed a complete fill of the molding parts at one point of the periphery while another part of the periphery was unfilled: as in such cases the protrusion of flash is local and eflicient use of the volume of material is not attained. Two serious difficulties due to such flashing are the appearance of the finished closure, and the possibility that the flashed material may loosen or be detached and thereby interfere with the sealing.

A feature of the present invention is to prevent the formation of such flash, by confining the plastic material during its flow, so that a cushion pad of the intended form is produced, and the extrusion of flash is eliminated.

Another feature of the invention is the use of a platen and punch set for shaping such cushion pads, in which the platen supports the crown shell and employs the same as a female mold for the shaping of the cushion pad, while the punch is effective to displace the plastic material, to confine it, and to cooperate with the shell in securing a cushion pad of the intended shape. In a preferred form of practice for this feature, the supporting surface of the platen, which acts as an anvil, has a lesser curvature, for example being flat, than the usual internally radiused or dome-like surface of the bottom of the crown Another feature of the invention is a method of shaping a cushion pad in a crown shell, by engaging the periphery of a punch surface with an inner surface of the crown shell and thereafter exerting pressure upon the pad material to distribute it into the desired shape and therewith confining the material for preventing theformation of flash and for assuring the production of a cushion pad surface competent of sealing against the container lip, and also assuring adhesion of the pad to the crown shell adjacent the outer edge of the pad.

A further feature of the invention is the manufacture of a crown seal comprising a crown shell and a cushion pad, this cushion pad having a thin central portion and a thicker annular portion for engaging the lip of the container to be sealed, the annular portion being thicker at its outer periphery than at its inner periphery.

A further feature of the invention is the manufacture of a crown seal comprising a crown shell and a cushion pad therein, the cushion pad having a thin central portion and a thicker annular portion, the annular portion having a bevel at its outer periphery leading from the exposed lipengaging surface of the annular portion to the top corner radius of the crown shell.

This essential elimination of flash permits the em-. ployment of lesser quantities with assurance of having a proper sealing surface and thickness on the cushion pad, as it is no longer necessary to make allowance for flash. On the other hand, the confinement of the mass of material during the shaping operation establishes a greater tolerance with respect to the quantity of material used in the blank, and the positioning of this charge within the crown shell.

With these and other features as objects in view, an illustrative practice of the invention is shown on the accompanying drawings in which:

Fig. 1 is a view showing a metal crown shell, partly in radial section and partly in elevation, to show a standard conformation thereof.

Fig. 2 shows such a crown shell present on a platen, and having a charge of cushion pad material therein.

Fig. 3 shows the structures as in Fig. 2, with a punch exerting pressure upon the material being shaped to form the cushion pad.

Fig. 4 shows the structures of Fig. 3, with the punch having been brought down to its final relative position, and having accomplished the shaping of the plastic material into the cushion pad.

Fig. 5 shows the shaped crown seal comprised of crown shell and formed cushion pad, in diametrical section.

As shown in Fig. l, the crown shell employed in crown seals of current practice is made of sheet metal by blanking and forming operations so that it has a concavely domed bottom portion 10 with a smoothly curved periphery leading to a corrugated skirt portion 11. This smoothly curved peripheral portion 12 is known as the top corner radius. As manufactured, the crown shells of Fig. l have the corrugated skirt portion 11 extending angularly outward from the junction with the top corner radius 12. In present practice, the crown shells as formed in the punch press have a domed bottom with a radius in the range of six inches to eight inches: this shape of bottom is referred to as top radius.

According to the present invention, such a crown shell is placed on a platen 15, Fig. 2, which in the preferred form as illustrated, has a flat top surface for receiving the domed bottom 10 of the crown shell. It is preferred to have this platen heated to a temperature of flow of the plastic material as by a gas flame 16.

A standard quantity of the plastic material is measured and deposited as the mass 17 in the crown shell S shown in Fig. 2. This material is preferably of thermoplastic nature, so that it can be made more fluid by heating: and exhibits elasticity in its final cooled condition.

In Figure 3, a punch 20 has been brought down into contact with the mass 17, and has begun to deform the same by causing parts of the mass to flow relatively radially outward from the position shown in Fig. 2. In the illustrated preferred form, the punch 20 has a projecting central part 21 having a fiat end surface. This punch has a conical shoulder surface 22 leading to the rebated part 23 of the end surface of the punch 20 which is to produce the exposed surface of the thicker annular portion of the cushion pad: in the illustrated prefered form, this surface 23 is also of conical shape. At the outer part of the end surface of the punch 20, it is provided with a projecting rib 24, which extends beyond the surface 23. The rib 24 has a fiat lower surface and sloping inner and outer surfaces 26, 27, each of. which may be formed as a cone having an apex half-angle of 16. The outer surface 27 leads to the maximum external diameter of the punch 20, this maximum external diameter at the upper end of the surface 27 being slightly les's'than the internal diameter of the crown shell at the region where the top corner radius 12 joins the skirt 13, wherewith the rib 24 can make contact with the inner surface of the crown shell at this top corner radius.

The platen 15 and the punch 20 are preferably heated to facilitate the thermoplastic flow of the material 17.

The punch 20 is brought down forcibly and the material begins to flow radially outwardly from the axis of the crown shell and towards the top corner radius 12 and skirt 11 of the crown shell. This flow of the material 17 permits the punch 20 to move further into the crown shell so that the outer edge of the projecting rib 24 on the punch 20 seats (Fig. 3) in the top corner radius 12 near the juncture with the crown skirt 11, thus forming a seal between the periphery of punch 20 and the crown shell. As the material 17 continues to flow, the periphery of the punch 20 applies pressure to the periphery of the crown shell, thereby preventing flashing past the positive seal between the periphery of the punch and the crown shell,

and also causing the peripheral parts of the domed crown shell surface 10 to move downward toward the platen so that with the continued downward movement of the central end surface 21 of the punch, a continued outward flow of the material occurs to fill the space adiacent the surfaces 22, 23 and the rib 24, therewith forming the cushion pad with a thin central portion 25 opposite the flat end surface 21 of the punch and a thicker annular portion 26 formed by the walls at the shoulder 22, the surface 23, and the inner surface of the peripheral rib 24. It will be noted that the presence of the rib 24, and the contact or close cooperation of the outer surface of the punch 20 and the top corner radius 12 of the crown shell, at a circular line near the juncture of the corner radius with the skirt 11, totally prevents the extrusion of flash, or at most permits only such minor quantity of material to move across the lower surface 25 of the rib 24 that finally no such material lies adjacent or in the corrugated parts of the skirt. In the relative positioning of parts shown in Fig. 4, the punch 20 has acted upon the mass 17 of material to give it a final shaping, and therewith the bottom 10 of the crown shell has been flattened and rests upon the platen 15 over essentially its entire area.

The pressure contact as shown in Fig. 4 may be maintained for the period of time desired and requisite for the shaping operation; and if the material of the mass 17 is of curable or vulcanizable nature, the punch and platen may then be maintained at a temperature for curing or vulcanizing the material, the contact being maintained until the mass is form-maintaining, or even until the curing or vulcanizing has been completely efiected.

When the pressure between the punch 20 and the platen 15 is released, the material of the crown shell returns elastically, and the crown seal thus produced is as shown in Fig. 5, being essentially in the same relative position of parts as in Fig. 1. In practice,'it has been found that molding pressures up to 150 pounds can be employed with the presently standard sheet metal crown shells, without permanent distortion thereof.

In the preferred illustrative formof Fig. 5, it. will be noted that the cushion pad has the thin central portion;

inter-solution.

30 which may have a thickness of 4 to 10 thousandths of an inch: together with a thicker annular portion 31 for engaging the lip of the container to be closed by the crown seal, having a thickness of 20 to 38 thousandths of an inch at its thickest part. In a crown seal for a bottle, for example, using a shell of standard diameter, the central portion 30 (formed by part 21 of the punch) may be about 0.735 inch, the annular portion 31 may be formed by a conical punch surface having an angle of 12 relative to the flat bottom 21 of the punch: and the side faces of the rib 24 may each have an angle of 16 relative to the axis of the punch, the flat on the rib having a width of about 0.008 inch, with an external diameter of about 1.026 inch and forming a plane spaced about 0.030 inch from the plane of the bottom 21; and the punch body having a diameter of 1.0525 inch. Thus, in this preferred form, the annular portion is not of uniform thickness, but has a greater thickness at its outer periphery 27 than at the inner periphery 28. An incidental result of employing the rib 24 on the punch, is that the annular portion 31 has a beveled outer edge 32 leading from the point of maximum thickness, in the illustrative form, to the top corner radius of the metal shell, thus providing a shape which permits some displacement of the annular portion 31 under the pressure and conditions of sealing and crimping, and assists in assuring adequate and proper contact with the container lip which permits the completed seal to resist leakage of gas or product through the seal.

The material employed for the plastic mass 17 may be of any suitable thermoplastic elastomer type, competent to resist the contents of the container to be sealed, such as natural or synthetic rubber compound, synthetic resin materials, and the like.

For example, paste resins can be employed, in which the basic ingredients are an elastomer and a plasticizer therefor, the plasticizer being so selected that the clastomer is not actively soluble, i. e. essentially insoluble, therein at room temperature, but is soluble at some elevated fluxing temperature. These two ingredients are ground together to form a paste which is fiowable at, say, to F, and the paste may also include other components such as inert fillers to limit cutting, modifying resin to assist control of the physical properties, stabilizers for the resin and other components, waxes to prevent blocking and to reduce moisture vapor 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 and in South African Patent No. 2556/47 may be employed, noting that the tiller and other componentsmay 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 90 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 115 F; The ester type plasticizers of vinyl resins have this general characteristic, and require higher temperatures for producing penetration, diffusion, and

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. 7

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

Standard quantities of such paste resins may bedeposited in successive crown shells, and these in turn brought onto a hot platen and engaged by the hot punch. This engagement may occur while the deposited mass is essentially in its original condition, or the loaded shells may previously be moved through an oven, for example, so that a preliminary or partial curing is accomplished before the shaping is effected. The pressure required for shaping the mass depends upon the composition employed and the degree of curing which has been effected prior to the engagement, and upon the temperature of the mass during the shaping operation. In practice it has been found that paste resins in original condition require less than 30 to 50 pounds per square inch pressure for the shaping operation itself, wherewith a total pressure of 100 pounds is effective with the standard size of crown seal for producing the shaping of the mass and also the aforesaid resilient flattening of the domed bottom. ,Correspondingly, with partially or completely cured paste resin masses, shaping has been accomplished in standard crown shells with pressures of 150 pounds or less.

When a rubbery or other non-fluid composition is employed for the pad, the charge may be introduced into the crown shell in the form of a disk or partly shaped blank, the completion of the shaping and the adhesion being accomplished by the use of the hot platen and the hot punch 20. A suitable rubbery composition has rubber as an elastomer base which can be modified as desired by fillers, lubricant, and vulcanization agents. An illustrative formulation is:

Parts by weight Crepe rubber (natural latex rubber) 88 Semi-solid isobutylene polymer 12 Hydrated precipitated calcium silicate 63 Clay 65 Zinc oxide 5 Stearic acid 2 Heptylated diphenylamine l Dipentamethylene thiuram tetrasulfide 1 Tetramethyl thiuram monosulfide 1 /2 It is preferred to have the inner surface of the crown shells lacquered during manufacture. For example, a vinyl lacquer prepared as described in the Maier et a1. Patent No. 2,380,456, with 80 percent of vinyl chloridevinyl acetate copolymer resin and percent of oleoresinous modifier produces a satisfactory adhesion. When the crown seals are to be employed with carbonated beverages, beer, fruit juices, vinegar, etc., 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 85: 13:2, together with 20 percent of a phenolic resin derived from orthocresol. 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.

Such an internal lacquer coating is illustrated by the inner lining 40 in Fig. 5. The customary external advertising is also illustrated as an outer lacquer coating 41.

It will be understood that the invention is not restricted to the forms of practice shown, and that the same may be practiced in many ways within the scope of the appended claims.

I claim:

1. The method of forming a closure seal with a cushion pad in a closure shell, said shell having a resiliently yielding internally concave domed bottom portion joined by a top corner radius portion with a skirt extending from the top corner radius portion, which comprises depositing a charge of plastic material in the closure shell, engaging a limited central part of the outer surface of the bottom portion with a supporting surface, engaging a punch end surface with said charge and pressing therewith against the same and producing plastic flow and adhesion over said bottom portion and toward the top corner radius portion, effecting a sealing engagement of the periphery of said punch surface with the top corner radius portion prior to the flow of the charge material past said periphery and thereby confining the charge between said punch surface and the closure shell, continuing the movement of the punch surface toward the supporting surface while the periphery of the punch surface remains in engagement with the top corner radius portion so that the resilient domed bottom portion of the closure shell yields and is flattened and the charge material continues its confined flow for filling the spaces adjacent the container-engaging surfaces of the cushion pad without formation of flash material, and thereafter withdrawing the punch surface and permitting the said flattened bottom portion to return to domed shape.

2. The method as in claim 1, in which the punch has at its periphery an axially extending rib for said sealing engagement with the top radius portion of the closure shell, and said punch end surface also has radiallyinward from said rib a rebated annular surface portion effective for providing in the cushion pad a thick part for engaging the container lip, said rib being effective in determination of the flow of the plastic material adjacent said top corner radius portion.

3. The method as in claim 1, which includes interposing a rib projecting axially from the aforesaid punch end surface into the path of radially outward flow of the plastic material for determination of such flow adjacent the said top corner radius portion of the closure shell, said interposing being accomplished concurrently with effecting the said sealing engagement.

4. The method as in claim 1, in which the plastic material for the cushion pad is a thermoplastic, and which includes the heating of the punch and supporting surfaces for assuring the flow of the confined plastic material into conformity with the closure seal and the punch surface.

5. The method as in claim 1, in which the material for the cushion pad is a paste resin comprising of a thermoplastic resin and a plasticizer with the thermoplastic resin not actively soluble in the plasticizer at room temperature and soluble therein at an elevated fluxing temperature to form an elastic mass, and in which there is heating of the punch and supporting surfaces to a temperature for effecting solution of the thermoplastic resin in the plasticizer.

6. The method as in claim 1, in which the material for the cushion pad is a vulcanizable elastomer composition capable of thermoplastic flow, and in which there is heating of the said punch and supporting surfaces to a temperature effective for softening the said composition upon contact therewith and initiating vulcanizing thereof.

References Cited in the file of this patent UNITED STATES PATENTS Re. 19,536 Parks Apr. 16, 1935 304,252 Beher Aug. 26, 1884 345,962 Finch July 20, 1886 713,844 Boylan Nov. 18, 1902 827,799 Grove et a1 Aug. 7, 1906 1,087,710 Bogdanffy Feb. 17, 1914 1,209,980 Lawson Dec. 26, 1916 1,486,937 Taliaferro Mar. 18, 1924 1,928,987 Warth Oct. 3, 1933 FOREIGN PATENTS 587,355 Great Britain Apr. 23, 1947