GB2195623A - Plastic closure with shaped gasket - Google Patents

Abstract

A threaded plastics closure which requires a low application torque comprises an end panel 2, a skirt 3 and a gasket 7' extending from a peripheral portion of the end panel to a portion of the skirt, the gasket being inclined in relation to the surface of the end panel at the point 8' of contact with the container 6 so as to form an angle beta ' with the end panel of from about 25 DEG to about 90 DEG . The sloped gasket allows for the reduction of application torque while providing a satisfactory seal. The gasket may be planar, concave, convex or toroidal and may be retained by one or more retention means on the end panel and skirt. The gasket is made from a plastisol or a hot melt composition. <IMAGE>

Description

SPECIFICATION Plastic closure with shaped gasket This invention relates to a plastic closure and gasket for use as bottle caps or jar lids. More particularly, this invention relates to a plastic closure having a gasket with a specific configuration which allows for low application and removal torques and the use of less material than conventional gaskets in plastic closures.

Background of the Invention The container industry currently uses plastic closures to seal containers holding a variety of products. These plastic closures are generally lined with a gasket material which forms a seal between the closure and the container to prevent leakage and ensure the integrity of the packaged goods.

These gaskets are generally formed by the following methods: a.) by lining the closure with a plastisol material such as polyvinyl chloride and a plsticizer, spinning the closure to spread the plastisol and fluxing the material in situ to form the gasket; and b.) by applying a hot melt material to the closure to form an in situ gasket.

These methods and the gaskets formed by them are generally satisfactory. However, there are several disadvantages. The most important of which is the need for a high application torque to apply the closure to a container. For example these torque requirements vary from 17 to 25 inch-pounds of torque for a 28 mm closure. This high torque causes great stress upon the closures, containers and filling equipment. The industry prefers a lower torque value of about 12 to 15 inch-pounds.

To achieve these lower torque values, various devices have been used such as the addition of excess lubricants and slip agents to the gasket material, the use of softer gasketing materials, or the use of separately formed, disc-like gaskets which are retained by mechanical means within the closures. All of these have proven in some way unsatisfactory. The addition of lubricants can effect the sealing ability of the gasket as well as cause an offtaste in the product. Softer gaskets do not seal as well as the traditional gaskets. They also suffer from cut through in which the container rim actually divides the gasket into two or more pieces. This affects the closure's ability to reseal after opening. The separately formed gasket requires an additional step in forming the disc-like gasket and placing it into the closure.It also is more costly in that it uses an additional amount of gasketing material. The separately formed gasket also requires precise placement. If improperly placed, the gasket may leak or may not allow the closure to be applied to the container.

The present invention overcomes the problems of the traditionally lined plastic closures and the modified closures discussed above. The present invention allows the use of lower application torques by modifying the gasket and/or closure configuration to reduce the resistance of the gasket against the container during application.

Objects and Summary of the Invention It is an object of the present invention to provide a threaded plastic closure which can be applied to a container with low torque, for example preferably with 12 to 15 inch-pounds torque for 28 mm closures.

It is an another object of the present invention to provide a plastic closure for use on threaded containers, the closure comprising an end panel and a skirt depending downwardly from the end panel and a gasket formed in situ in the closure, the gasket extending from a peripheral portion of the end panel to a portion of the skirt so as to form an angle with the end panel from about 25 to about 90".

A further object of the present invention is to provide a plastic closure having a substantially flat end panel and a threaded cylindrical skirt depending downwardly from the end panel, the end panel having a first gasket retention means, the skirt having a second gasket retention means and a gasket formed in situ between the first and second gasket retention means, an outer surface of the gasket forming an angle with the substantially flat end panel, the angle being from about 250 to about 90".

Another object of the present invention is to provide a gasket in a plastic closure in which the outer surface of the gasket forms an angle with the surface of the end panel of from about 25 to about 90".

An object of the present invention is a method of forming a gasket in a plastic closure in which the outer surface of the gasket forms an angle with the surface of the end panel of from about 25 to about 90".

An object of the present invention is a method of forming a gasket in a plastic closure which allows for the use of low application torque when the closure is secured to a container, The method involves the steps of lining the gasket material into the closure in a manner which will cause the gasket material to form an angle of from about 25 to about 90" with the end panel of the closure.

It is another object of the present invention to provide gasket retention means on the end panel and skirt of the closure which retain and shape the gasket so that the gasket forms an acute angle with the end panel.

The present invention is a plastic closure having a gasket configuration which allows for the application of the closure to a container with low torque. The closure has a gasket which is inclined to the plane of the closure's end panel. The angle is between about 25 and 90". The gasket is lined into the closure and may be of a hot melt or plastisol material.

These and other objects of the present invention will be clear to one skilled in the art from the drawings, specification and claims of the present application.

In the Drawings Figure 1 is a longitudinal sectional view of a typical plastic closure and its gasket.

Figure 2 is a longitudinal sectional view of a plastic closure showing a first embodiment of the present invention.

Figure 3 is a longitudinal sectional view of a second embodiment of the present invention.

Figures 4-7 are longitudinal sectional views of other preferred embodiments of the present invention.

Detailed Description of the Invention A typical plastic closure as applied to a threaded container is shown in Fig. 1. The closure 1 has an end panel 2 which is substantially flat and a skirt 3 which depends downwardly from the end panel 2. The skirt 3 contains a series of threads 4 which interlock with the threads 5 of the container 6. A formed in situ gasket 7 is located upon the end panel and extends slightly upon the skirt. The gasket 7 and the container 6 meet at the upper rim portion of the container. As can be seen, the gasket at the point 8, at which the gasket and container meet, is broad and substantially' flat. This point 8 forms an angle ss with the outer surface of the end panel 2. The angle ss is generally between 0 and 10 .

Fig. 2 discloses an embodiment of the present invention. The plastic closure 1 is similar to that of Fig. 1, having an end panel 2 and a skirt 3 with threads 4 which interlock with the threads 5 of the container 6. The gasket 7', however, is different. The gasket 7', rather than being substantially flat as the gasket 7 of Fig. 1, is substantially sloped. The point 8', at which the container and gasket meet, is substantially narrower and more inclined and forms an angle ff with the end panel which is much greater than the angle ss shown in Fig. 1. The angle ss is generally from about 25 to about 90" and preferably between about 40 to 70".

While not wishing to be bound to any particular theory of invention, Applicants provide the following non-binding illustrative explanation of its invention.

Generally, containers today are sealed by automated machines. These machines grasp the container, fill it and seal it with a closure. The amount of torque used to secure the closure to the container is constant for a given run of containers.

With a closure, such as that shown in Fig. 1, this torque is set at a high level, approximately 17-25 inch-pounds for 28 mm closures. At this torque level, the closure is adequately sealed to the container. At lower torque values, the seal is incomplete resulting in leaks and/or contaminated products.

As can be- seen from Fig. 1, the gasket 7 is relatively flat and broad at the point 8 where the gasket 7 contacts the container. This area is substantially large and as the application torque is constant, the resultant compressive force per square unit of area (force/unit2) is low.

In the present invention, the gasket 7' is inclined and relatively narrow at the point 8' where the container contacts the gasket 7'. The area of contact between the gasket and container is reduced, thereby increasing the amount of force/unit2. Thus the present invention is able to lower the required application torque to 12 to 15 inch pounds and achieve the same or better compressive force/unit2 and sealing ability as the closure of Fig. 1.

Fig. 3 shows another preferred- embodiment of the present invention. Gasket retention means 11 and 12 are shown on the end panel and skirt. These means help to secure or lock the gasket into the closure and prevent its rotation or release. In addition, these retention means can be used to limit the area to which the gasket material is applied and preferably can be used to define the angle ss' of the gasket. The retention means can be any commonly used in plastic closures such as undercuts shown as 11 in Fig. 3, ribs shown as 12 in Fig. 3, beads1 lips, etc.

While Fig.' 3 shows retention means upon both the end panel and the skirt, it is clear that the retention means may be used on just the skirt or just the end panel if desired.

The outer surface of the gasket may be of any shape, though preferably it is planar as shown in Fig. 2, concave as in Fig. 3, convex as in Fig. 4, partially convex as in Fig. 5 or toroidal as in Fig. 6. The shape is not critical to the invention so long as the angle ff formed between the outer surface at the point where the container first meets the gasket and the end panel is from about 25 to about 90".

Fig. 7 shows another preferred embodiment in which the corner 13 of the closure where the end panel and skirt meet is substantially modified and shaped so as to cause the gasket to assume a similar shape. It is clear that the closure's corner can be molded in any shape desired such as planar (as shown), concave, convex or toroidal so long as it does not interfere with the closing of the closure on the container. An additional advantage to this embodiment is the reduction in the amount of gasketing material required in each closure while obtaining the desired shape, slope and sealing result.

The plastic closure 1 may be formed of any suitable thermoplastic or thermosetting polymer, for example, an olefin polymer. Specific examples include but are not limited to polypropylene, polyethylene, an ethylene-propylene copolymer and a blend of polypropylene and polyethylene.

The gasket may be formed of any suitable thermoplastic or thermosetting polymer. Preferably, the gasket is made from either a plastisol or a hot melt composition.

Specific examples of plastisols useful in this invention include but are not limited to vinyl polymers, particularly a vinyl chloride polymer such as vinyl chloride or a copolymer of vinyl chloride with vinyl acetate. Other vinyl copolymers can also be used such as a copolymer of vinyl chloride and N-cyclohexyl maleiimide.

The plastisol also contains a conventional plasticiser in any conventional proportion, generally from 60 to 85 weight parts of plasticiser per hundred parts of vinyl polymers or copolymers.

Suitable plasticizers include for example di-2-ethylhexyl phthalate, diisooctyl phthalate, diisodecyl phthalate, butyl benzyl phthalate, acetyl tributyl citrate, ethyldiphenyl phosphate, diisobutyl phthalate and various adipate-based plasticisers.

When a plastisol is used, it is important that the plastisol have rheological properties which allow the plastisol to retain its shape as lined even when subjected to fluxing temperatures. The addition of thickeners which help the plastisol retain its shape is preferred. Thickeners are well known and include for example Cab-O-Sil M-5 by Cabot Corp., a colloidal silica material.

In addition, the plastisol may contain other conventional ingredients such as pigments, fillers, heat stabilisers or blowing agents.

Hot melt materials are well known. Compositions suitable for use in this invention include but are not limited to ethylene homopolymers and/or copolymers, for example an ethylene vinyl acetate copolymer and one or more resins, such as a rosin ester type resin. The hot melts may also contain other conventional ingredients such as surfactants, pigments and fillers.

The gasket material may be applied to and formed in the plastic closure by any conventional method for plastisols or hot melts.

If a plastisol, the method would include lining the plastisol into the closure in its desired shape and location and then fluxing the plastisol to cause the vinyl polymer to absorb the plasticiser and form the solid gasket. One method is to heat the lined closure in a hot air oven. A preferred method is that disclosed in U.S. 4,304,744 in which the plastisol, after lining, is preheated in a hot air oven and then fluxed with microwave energy. This process is advantageous in that the microwave energy only affects the plastisol as the plastic of the closure is substantially transparent to the microwave energy and is therefore not substantially heated. This process avoids the melting or distortion of the closure. If a blowing agent is used, it should be triggerable in a microwave environment.

A method of lining the closure with a hot melt is to heat the hot melt material, which is solid at room temperature, to a temperature at or above its melting point. The molten hot melt is then lined into the closure in its desired configuration and location. No further heating of the closure or hot melt is required. A further cooling step may be used if necessary or desired to solidify the hot melt rapidly. Optionally, in applying the hot melt, a foaming gas or gas producing agent may be added to the molten material before lining so as to form a foamed gasket.

The gasketed closures, formed as described above, are then applied to the containers by rotating the closure, the container, or both so as to cause the threads of the closure and container to engage and draw the closure and container toward each other and seal the container against the gasket.

In order to evaluate the improvement afforded by the present invention, comparative tests were made using a 28mm. plastic closure made by W. R. Grace & Co. as shown in Fig. 1 of U.S. 4,585,135 and having gasket angles ranging from 7" to 70". The results of these comparative tests are given as follows: A series of closures were lined with a plastisol material at angles ranging from 7" to 70". The plastisol was fluxed by the method of 4,304,744 in a W. R. Grace & Co. DARAWAVEB microwave oven.

The lined closures were then applied to a standard set of glass bottles by a Zalkin capper, Model No. TML-1B with a W-1 closing heat. The closures were applied at two different, low torque levels, 12 inch-pounds (dynamic) and 10 inch-pounds (dynamic).

The sealing performance of each of the closures was determined by the Secure Seal Test (SST), using an Owen Illinois Secure Seal Tester. SST values were recorded in pounds per square inch (psi).

The test was performed by introducing gas at a controlled rate into the headspace of a sealed container which was submerged in a waterbath. The pressure was increased to 100 pounds per square inch and held there for one minute. The pressure was then increased to 150 pounds per square inch where it was held for an additional minute. The pressure was increased to 175 Ibs./in2 for another minute and then finally increased to 200 Ibs/in2 for 30 seconds. Containers which were securely sealed showed no signs of gas leakage. Containers which were not securely sealed were revealed by the emission of bubbles escaping from the closure area. The pressure at which a container was observed to leak was recorded. Those which did not leak were recorded as having a value of 200 psi.

TABLE I SST Value (psi) at Application Torque of 12 inch-pounds (dynamic) Angle (degrees) SST Value (psi) 7 179 10 174 26 200 41 195 50 200 70 200 TABLE II SST Values (psi) at Application Torque of 10 inch-pounds (dynamic) Angle (degrees) SST Value (psi) 7 163 10 130 26 172 42 200 50 200 70 200 In addition, a hot melt gasketed closure was tested for a SST value, the results of which are shown in Table Ill. The test was the same as described above, although only two gasket angles were used, 8" and 42", and the application torque was 12 inch-pounds (dynamic).

TABLE 111 Angle (degrees) SST Value (psi) 8 130 42 200 A closure should have a minimum SST value of at least 175 psi. Preferably the value is close to 200 psi and most preferably is 200 psi.

As can be seen from the tables above, the venting pressure results (SST values) increased with the present invention, regardless of the gasketing material used.

All of the closures made in acc6rdance with the present invention showed acceptable if not, optimal SST values. The comparative closures had either unacceptable values or minimally acceptable values.

While this invention has been described mainly in relation to its use as a 28 mm closure, it is clear that it may be used on closures or other sizes such as 70 mm closures or 120 mm closures. Likewise, while particularly pointing out in the examples its use on a glass container it is not meant to limit the invention to that type of container. The present invention may be used on any threaded container whether formed of glass, plastic or another suitable material.

The present invention represents an important improvement in the container industry, eliminating one of the problems which has plagued the use of plastic closures.

While this invention has been described with reference to its preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents as fall within the true spirit and scope of this invention.

Claims (31)

1. A gasket for use in a plastic closure suitable for a container having a threaded neck, the closure having an end panel and a threaded skirt portion depending downwardly from the end panel, the gasket comprising a plastic material lined into and confined to a peripheral portion of the closure and inclined from the end panel to a portion of the skirt above the threads.

2. A gasket according to claim 1 wherein the plastic material is inclined with respect to the end panel at an angle of from substantially 25 to substantially 900.

3. A gasket according to claim 2 wherein the plastic material is inclined at an angle from substantially 40 to substantially 70".

4. A gakset according to claim 1 wherein the plastic material has an outer surface shape which is planar, concave, convex or toroidal.

5. A plastic closure for use on threaded containers comprising a substantially flat end panel and a skirt depending downwardly from the end panel and a gasket formed in situ in the plastic closure, the gasket extending from a peripheral portion of the end panel to a portion of the skirt so as to form an angle with the end panel of from substantially 25 to substantially 90".

6. A plastic closure according to claim 5 further comprising one or more retention means upon the end panel and skirt of the closure for holding the gasket in place.

7. A plastic closure according to claim 6 wherein the retention means are undercuts, beads, lugs, lips or ribs.

8. A plastic closure according to claim 6 or 7, wherein the retention means are located upon the end-panel and the skirt so as to retain the gasket at a desired angle to the end panel.

9. A plastic closure according to any one of claims 5 to 8, wherein the gasket has an outer surface shape which is planar, concave, convex or toroidal.

10. A plastic closure comprising a substantially flat end panel, a cylindrical skirt depending downwardly from a peripheral portion of the end panel, the skirt having threads upon its lower portion, the end panel having a first gasket retention means located at a peripheral portion of the end panel, the skirt having a second gasket retention means located at a position away from the end panel and above the threads of the skirt, and a gasket formed in situ extending from the first gasket retention means of the end pariel to the second gasket retention means of the skirt, an outer surface of the gasket forming an angle with the end panel of from substantially 25 to substantially 90" and the outer surface of the gasket having a shape which is planar, concave, convex or toroidal.

11. A plastic closure according to any one of claims 5 to 10, wherein the gasket is formed of a hot melt material.

12. A plastic closure according to any one of claims 5 to 10, wherein the gasket is formed of a plastisol material.

13. A plastic closure according to any one of claims 5 to 12, wherein the angle between the end panel'and the gasket is from substantially 40 to substantially 70".

14. A plastic closure for use on containers comprising an end panel and a threaded skirt depending downwardly from the end panel, the end panel being substantially planar, an inclined shoulder formed at a junction between the end panel and the skirt, the inclined shoulder forming an angle with the planar surface of the end panel of from substantially 25 to substantially 90 , and an in situ formed gasket covering the inclined shoulder.

15. A plastic closure according to claim 14, wherein the gasket conforms to the inclined shoulder and assumes a same angle as the shoulder.

16. A plastic closure according to claim 14 or 15, wherein the angle is from substantially 40 to substantially 70".

17. A plastic closure according to any one of claims 14 to 16, wherein the gasket is formed of a plastic material that is softer than the plastic closure.

18. A plastic closure according to any one of claims 14 to 17, further comprising a first retention means for holding the gasket, and a second retention means for holding the gasket, the first retention means being located on the end panel adjacent the inclined shoulder and the second retention means being located on the skirt adjacent the inclined shoulder.

19. A plastic closure according to claim 18, wherein the first and second retention means are undercuts, beads, lugs, lips or ribs.

20. A plastic closure according to any one of claims 14 to 19, wherein the inclined shoulder has an outer surface which is planar, conclave, convex or toroidal in shape.

21. A gasket substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

22. A plastic closure substantially as hereinbefore described with reference to, and as illus traced in, the accompanying drawings.

23. A method of forming a gasket in a plastic closure to reduce application torque comprising the steps of lining a plastic gasketing material into a plastic closure at a peripheral edge of an end panel of the closure so that an outer surface of the gasket forms an angle of from substantially 25" to substantially 900' with the end panel.

24. A method according to claim 23 wherein the plastic gasketing material is a hot melt.

25. A method according to claim 23, wherein the plastic gasketing material is a plastisol.

26. A method according to any one of claims 23 to 25, further comprising the step of treating the plastic gasketing material after it has been lined into the closure to secure the gasket in place.

27. A method according to claim 26 when appendant to claim 25, wherein the treatment step is to subject the plastic gasketing material to heat.

28. A method according to claim 26 when appendant to claim 24, wherein the treatent step is to cool the plastic gasketing material.

29. A method according to any one of claims 23 to 28, wherein the angle is from substantially 40" to substantially 70".

30. A method according to any one of claims 23 to 29, wherein the outer surface of the plastic gasketing material as it is lined is planar, concave, convex or toroidal in shape.

31. A method of forming a gasket in a plastic closure, substantially as hereinbefore described with reference to the accompanying drawings.