CONTAINER CLOSURE HAVING AN IMPROVED SEALING LINER

Abstract: The present invention provides a liner (20) for a closure (10). The liner (20) comprises an ethylene and vinyl acetate copolymer, or an ethylene and vinyl acetate copolymer and an ionomer, and the liner (20) resists scuffing and stringing. The present invention also provides a closure (10) comprising a top wall (14) having an interior surface (14a) and an exterior surface (14b), a peripheral skirt (16) disposed about said top wall (14) and circumscribing the interior surface (14a), means on the skirt (16) for attaching the closure (10) to a container, and a sealing liner disposed on the interior surface of the top wall, the sealing liner (20) comprising an ethylene and vinyl acetate copolymer, or an ethylene and vinyl acetate copolymer and an ionomer.

Description: CONTAINER CLOSURE HAVING AN IMPROVED SEALING LINER This invention relates to a closure for a container having a sealing liner. More particularly, this invention relates to a composition for a sealing liner for a closure. Many liquid products are packaged in containers which have openings that must be sealed with some type of closure. For example, a bottle that contains a carbonated beverage typically has a removable closure that must provide the necessary sealing of the pressurized contents of the bottle. While metal closures are well known in the art, molded plastic closures have met with widespread commercial success in the marketplace. In many closures, it is desirable to include a sealing liner in an outer closure cup or shell of the closure. Sealing liners for closures are known to those skilled in the art, and are typically formed of materials which are less rigid (i.e., more compliant) than the material from which the outer cup is made. The sealing liner forms a seal between the container and the outer closure cup. Preferably, the seal that is formed by the closure prevents the contents of the container, including pressurized gas, from spilling or being released from the container. Furthermore, the closure prevents contamination of the contents of the container. A satisfactory sealing liner must provide for an acceptable removal torque of the closure for ease of removal by consumers and satisfactory performance when the sealed container is subjected to various environmental stresses such as temperature, pressure and humidity changes. The sealed container must also be able to withstand 30 mechanical shock. Furthermore, a suitable liner for use in connection with a closure must not scuff or string when the closure is applied to or removed from the container. If scuffing or stringing occurs, the closure may not seal properly or particles of liner material may undesirably be introduced into the contents of the container. The present invention provides a sealing liner for a closure that comprises an ethylene and vinyl acetate copolymer, or an ethylene and vinyl acetate copolymer and an ionomer. The present invention also provides a closure comprising a top wall having an interior surface and an exterior surface, a peripheral skirt disposed about said top wall and circumscribing the interior surface, means on the skirt for attaching the closure to a container, and a sealing liner disposed on the interior surface of the top wall, the sealing liner comprising an ethylene and vinyl acetate copolymer, or an ethylene and vinyl acetate copolymer and an ionomer. A lubricant and colorant are additionally incorporated into the liner composition. The figure is a view in cross-section of a closure having a sealing liner. The present invention provides a sealing liner for closures that is scuff and string resistant. The liners comprise an ethylene and vinyl acetate copolymer. Alternatively, the liners comprise an ethylene and vinyl acetate copolymer and an ionomer. The closure of the present invention may be any closure that is known in the art in which the use of a liner is desirable, including plastic or metal closures. Preferably, however, the closure is a plastic closure. The container for which the closure is designed to seal can also be selected from containers known to those skilled in the art, such as glass or plastic containers. In accordance with the present invention, the closure includes an outer plastic cup or shell which contains a sealing liner which may be compression molded in situ on the interior of the shell, or the liner may be introduced into the shell by other means known to those skilled in the art. For a representative plastic closure with a compression molded sealing liner, see U.S. Patent Nos. 4,984,703 and 4,497,765. A typical closure having a sealing liner is shown in Figure 1. The closure 10 includes an outer closure cup 12 having a top wall 14, the top wall having an interior surface 14a and an exterior surface 14b. A depending annular peripheral skirt 16 is disposed about the top wall and circumscribes the interior surface of the top wall. The peripheral skirt typically contains a means for attaching the closure to the container. Such means may include, but are not limited to, threads 18, so that the closure may be screwed onto the container. In general, the closure may be removed and replaced on the container as desired. A sealing liner 20 of the present invention is disposed on the interior surface of the top wall for sealing engagement with the associated container. Vent groves 22 facilitate release of gas pressure from within the container attendant to closure removal, with the closure including a tamper band 24 for providing evidence of opening. The band 24 can be configured in accordance with U.S. Patent No. 4,938,370. The liners of the present invention comprise an ethylene and vinyl acetate copolymer. As used herein the term "copolymer" shall include block, random alternating and graft copolymers. The vinyl acetate can be present in the copolymer in the range of about 20% to about 40% by weight of the copolymer. More preferably, the vinyl acetate is found in the copolymer in the range of about 25% to about 35% by weight of the copolymer. Most preferably, the vinyl acetate is found in the composition at about 28% by weight of the copolymer. The ethylene-vinyl acetate copolymer may have a weight average molecular weight in the range of about 32,000 to about 270,000. Preferably, the molecular weight of the ethylene- vinyl acetate copolymer is in the range of about 100,000 to about 150,000, and most preferably, in the range of about 110,000 to about 115,000. It is contemplated that a mixture of two or more ethylene and vinyl acetate copolymers may be used in the liner compositions. For example, the copolymers can have different molecular weights and/or contain different amounts of vinyl acetate. The sealing liner may also comprise an ionomer. An ionomer is an ionically crosβlinked thermoplastic resin generally prepared by neutralizing a copolymer containing pendant acid groups, e.g., carboxylic acid groups, sulfonic acid groups and/or phosphonic acid groups, with an ionizable metal compound, e.g., a compound of the monovalent, divalent and/or trivalent metals of Group I, II, III, IV-A and VIII of the periodic table of the elements. A preferred group of ionomer resins is derived from a copolymer of at least one alpha- olefin and at least one ethylenically unsaturated carboxylic acid and/or anhydride. Suitable alpha- olefins include ethylene, propylene, 1-butene, 1- pentene, 1-hexene, 1-heptene, 3-methylbutene, and the like. Suitable carboxylic acids and anhydrides include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, fumaric acid, maleic anhydride, and the like. The foregoing copolymers advantageously contain from about 0.2 to about 20 mole percent, and preferably from about 0.5 to about 15 mole percent, carboxylic acid groups. Particular examples of such copolymers include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene- itaconic acid copolymers, ethylene-methyl hydrogen maleate copolymers, ethylene-maleic acid copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylate copolymers, ethylene- methacrylic acid-ethacrylate copolymers, ethylene- itaconic acid-methacrylate copolymers, ethylene- itaconic acid-methacrylate copolymers, ethylene- ethyl hydrogen maleate-ethyl acrylate copolymers, ethylene-methacrylic acid-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid-vinyl alcohol copolymers, ethylene-acrylic acid-carbon monoxide copolymers, ethylene-propylene-acrylic acid copolymers, ethylene-methacrylic acid-acrylonitrile copolymers, ethylene- umaric acid- inyl methyl ether copolymers, ethylene-vinyl chloride-acrylic acid copolymers, ethylene- inylidene chloride- acrylic acid copolymers, ethylene-vinylidene chloride-acrylic acid copolymers, ethylene-vinyl fluoride-methacrylic acid copolymers and ethylenechlorotrifluoroethlyene-methacrylic acid copolymers. The copolymers may also, after polymerization but prior to ionic crosslinking, be further modified by various reactions to result in polymer modifications that do not interfere with their subsequent ionic crosslinking. Halogenation of an olefin acid copolymer is an example of such polymer modification. The preferred ionomers are obtained by reacting the foregoing copolymers with a sufficient amount of metal ions as to neutralize at least about 5 percent by weight and preferably from about 20 to about 80 percent by weight, of the acid groups present. Suitable monovalent metal ions include Na + , K + , Li + , Cs + , Rb + , Hg + and Cu + . Suitable divalent ions include Be , Mg + , Ca +2 . Sr +2 , Ba +2 , Cu +2 , Cd +2 , Hg +2 , Sn +2 , Pb +2 , Fe +2 , Co +2 , Ni +2 and Zn +2 . Suitable trivalent metal ions include Al +3 , Sc +3 and Y +3 . The preferred metals suitable for neutralizing the copolymers used herein are the alkali metals, particularly cations such as sodium, lithium and potassium, and alkaline earth metals-, in particular cations such as calcium, magnesium and zinc. Also, it is contemplated that one or more ionomers may be used in the present invention. Preferred ionomers include a partially neutralized zinc salt of an ethylene and 15 wt.% methacrylic acid copolymer and a partially neutralized sodium salt of an ethylene and 11 wt.% methacrylic acid copolymer. These compositions may be obtained from Du Pont as Surlyn 1702 and Surlyn 8660 ionomers. The term "Surlyn" is a registered trademark of Du Pont. The ionomer may be found in the liner composition in the range of about 0.5% to about 30% by weight of the liner composition. Preferably, the ionomer may be found in the liner composition in the range of about 0.5% to about 15%. Most preferably, the ionomer may be found in the liner composition in an amount in the range of about 0.5% to about 10%. If the liner composition contains an ionomer, the ethylene-vinyl acetate copolymer can be found in the liner composition in an amount in the range of about 70% to about 99.5% by weight of the entire liner composition. Preferably, the ethylene-vinyl acetate copolymer can be found in the liner composition in the range of about 85% to about 99.5%. More preferably, the ethylene-vinyl acetate copolymer can be found in the liner composition in the range of about 90% to about 99.5%. The sealing liner composition of the present invention may also include various other components that are known to those skilled in the art. Examples of other materials which may be included in the liner composition are lubricants and colorants. Examples of suitable lubricants include, but are not limited to, stearates and fatty amides, such as Kemamide-E ® (also called erucamide) , which can be obtained from the Witco Corporation. Examples of suitable colorants include, but are not limited to, phthaloblue, which may be obtained from Quantum Chemical Corporation. Typical liners for closures are round disks and can have various diameters. In general, liners have a diameter in the range of about 25 mm to about 50 mm, with 28, 38 and 43 mm being preferred. In addition, the thickness of a liner may vary. A liner may have a uniform thickness or a liner may have different thicknesses at different portions of the liner. For example, some liners are thicker at the edge portion than at the central portion of the liner. A preferred thickness at the central portion of the liner is about .011 in. The following examples are intended to illustrate specific embodiments of the invention and are not intended to limit the scope of the specification, including the claims, in any manner. Examples General Protocol For String and Scuff Tests In general, stringing and scuffing are the result of the physical contact, i.e., rubbing, between the liner and the seal area of the container finish during closure or opening of the container. During the closure process, small fragments of the liner material, which is softer than the container finish, may be partially or completely severed or abraded from the bulk liner material. These fragments of liner material are called either scuffs or strings depending on their shape. Typically, a string is a long, slender strand of liner material having a larger length than diameter, and a scuff is a balled-up or abraded piece of liner material, which is approximately symmetrical or globular. The test and control closures are lined and molded on the same molding and lining machine. The control closures are made immediately before the test closures. The internal diameter of the liners must be measured before the string test is performed, and the internal diameters must be statistically the same for both the control and the test closures. The closures are applied to empty PET [poly(ethylene terephthalate)] finishes, using, for example, an ALCOA 201 capping machine at 12 in lbf static torque, 50 lbf topload and 340 rpm spindle speed. First, the bottle finish is dipped into water. Then a closure is applied to the bottle finish by hand and hand-tightened to where the closure is slightly tight. (The bottle does not need to be filled with a liquid.) The closure is then firmly seated using a capper. The closure is then removed and visually inspected for stringing and/or scuffing. A liner composition according to the present invention was made by mixing about 90% by weight of the entire liner composition of ethylene and vinyl acetate copolymer with about 10% by weight of the liner composition ionomer (Surlyn 8660) , which is the partially neutralized sodium salt of an ethylene and methacrylic acid copolymer, and which may be obtained from E.I. Du Pont de Nemours & Company, Wilmington, DE. The ethylene and vinyl acetate copolymer had a molecular weight of about 112,000 and contained about 28% by weight vinyl acetate. In addition, about one part per hundred of the liner composition of a colorant (phthaloblue from Quantum) was added, and about one part per hundred of a lubricant (Ken-amide-E ® erueamide) was added to the composition. The above-described composition was found to process at a low temperature of about 350°F. with excellent pellet stability and was used to make sealing liners for closures. The liners were then tested for stringing and scuffing in accordance with the above protocol, using as a control a commercially available liner composition that comprises an ethylene and vinyl acetate copolymer, containing about 9 wt.% vinyl acetate comonomβr. The results showed that there was a significant improvement in stringing and scuffing resistance, as none of the liners tested made from the above-described composition showed stringing or scuffing. In contrast, about 30% of the control liners showed stringing and/or scuffing. Example 2 The liner composition of Example 1 was employed, except that the composition contained no ionomer. The results showed a significant improvement in stringing and scuffing resistance as none of the liners tested showed stringing or scuffing. However, about 30% of the control liners tested showed stringing and/or scuffing.

Claims: C L A I M S 1. A sealing liner for a closure, the liner comprising: an ethylene and vinyl acetate copolymer having in the range of about 20% to about 40% by weight vinyl acetate. 2. The sealing liner of claim 1, wherein the copolymer contains in the range of about 25% to about 35% by weight vinyl acetate. 3. The sealing liner of claim 1, wherein the copolymer contains about 28% by weight vinyl acetate. 4. The sealing liner of claim 1, wherein the liner further comprises a lubricant. 5. The sealing liner of claim 1, wherein the liner further comprises a colorant. 6. A sealing liner for a closure, the liner comprising: an ethylene and vinyl acetate copolymer and an ionomer. 7. The sealing liner of claim 6, wherein the copolymer contains in the range of about 20% to about 40% by weight vinyl acetate. 8. The sealing liner of claim 6, wherein the ethylene and vinyl acetate copolymer comprises in the range of about 70% to about 99.5% by weight of the liner composition; and the ionomer comprises in the range of about 0.5% to about 30% by weight of the liner composition. 9. The sealing liner of claim 6, wherein the ethylene and vinyl acetate copolymer comprises in the range of about 85% to about 99.5% by weight of the liner composition; and the ionomer comprises in the range of about 0.5% to about 15% by weight of the liner composition. 10. The sealing liner of claim 6, wherein the ethylene and vinyl acetate copolymer comprises in the range of about 90% to about 99.5% by weight of the liner composition; and the ionomer comprises in the range of about 0.5% to about 10% by weight of the liner composition. 11. The sealing liner of claim 6, wherein the ionomer comprises a copolymer of at least one alpha-olefin and at least one unsaturated carboxylic acid or acid anhydride, partially neutralized by a monovalent, divalent or trivalent metal cation. 12. The sealing liner of claim 11, wherein the copolymer contains acid groups about 5 to 80 percent by weight neutralized with an alkali metal or alkaline earth metal cation. 13. The sealing liner of claim 11, wherein the ionomer comprises a partially neutralized zinc or sodium salt of an ethylene and methacrylic acid copolymer. 14. A closure comprising: a top wall having an interior surface and an exterior surface, a peripheral skirt disposed about said top wall and circumscribing said interior surface, means on said skirt adapted to attach the closure to a container; and a sealing liner disposed on the interior surface of the top wall, said sealing liner comprising an ethylene and vinyl acetate copolymer having in the range of about 20% to about 40% by weight vinyl acetate. 15. The closure of claim 14, wherein the copolymer contains in the range of about 25% to about 35% by weight vinyl acetate. 16. The closure of claim 14, wherein the liner comprises a disk with a central portion having a thickness of about .011 in. 17. The closure of claim 14, wherein the liner comprises a disk having a diameter in the range of about 25 mm to about 50 mm. 18. A closure comprising: a top wall having an interior surface and an exterior surface, a peripheral skirt disposed about said top wall and circumscribing said interior surface, means on said skirt adapted to attach the closure to a container; and a sealing liner disposed on the interior surface of the top wall, said sealing liner comprising an ethylene and vinyl acetate copolymer and an ionomer. 19. The closure of claim 18, wherein the copolymer contains in the range of about 20% to about 40% by weight vinyl acetate. 20. The closure of claim 19, wherein the ionomer is about 5 to about 80 weight percent zinc or sodium neutralized ethylene methacrylic acid or ethylene acrylic acid copolymer having an acid content before neutralization of about 0.2 to about 20 mole percent.

Inventors: BHOJRAJ NAVEEN, JACOBSON MARK STEWART, BHOJRAJ, NAVEEN, JACOBSON, MARK, STEWART
Applicants: ALCOA CLOSURE SYSTEMS INT INC, BHOJRAJ NAVEEN, JACOBSON MARK STEWART, ALCOA CLOSURE SYSTEMS INTERNATIONAL, INC., BHOJRAJ, NAVEEN, JACOBSON, MARK, STEWART
Application year: 1995
Main classification: B65D41
IPC codes: B65D41, C09K3