A SUBSTANTIALLY LINEAR POLYETHYLENE SEALING LINER FOR A CLOSURE

Abstract: The present invention provides a liner (20) for a closure (10). The liner (20) comprises substantially linear polyethylene, and an ionomer or a copolymer of ethylene and acrylic acid. The liner (20) resists scuffing and stringing. The present invention also provides a closure 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 (20) disposed on the interior surface (14a) of the top wall (14), the sealing liner (20) comprising substantially linear polyethylene and an ionomer.

Description: A SUBSTANTIALLY LINEAR POLYETHYLENE SEALING LINER FOR A CLOSURE 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 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 substantially linear polyethylene, and an ionomer or a copolymer of ethylene and acrylic acid. 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 substantially linear polyethylene 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 substantially linear polyethylene, and an ionomer or a copolymer of ethylene and acrylic acid. 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, such as an aluminum closure. 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, the disclosures of which are hereby incorporated by reference. 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 disclosure of which is hereby incorporated by reference. The liners of the present invention comprise substantially linear polyethylene, which is typically a copolymer of ethylene and a C 3" C 20 a lP na "°l e f^ n ' and preferably, a copolymer of ethylene and 1-octene. Examples of ethylene and 1-octene copolymers may be found in U.S. Patent Nos. 5,272,236 and 5,278,272, the disclosures of which are hereby incorporated by reference. The term "copolymers" as used herein shall include block, random alternating and graft copolymers. The substantially linear polyethylene may comprise 1-octene in the range of about 3% to about 25% by weight of the substantially linear polyethylene. Preferably, the substantially linear polyethylene can comprise 1-octene in the range of about 5% to 25% by weight. More preferably, the substantially linear polyethylene can comprise 1-octene in the range of about 10% to about 25%. The density of the substantially linear ethylene/alpha-olefin copolymers is from about 0.865 to about 0.94 g/cm 3 , preferably from about 0.865 to about 0.932 g/cm 3 , and most preferably from about 0.865 to about 0.915 g/cm 3 . The density is measured in accordance with ASTM D-792. The substantially linear polyethylene can have a weight average molecular weight in the range of about 27,000 to about 220,000. Preferably, the substantially linear polyethylene has a molecular weight in the range of about 32,000 to about 110,000. More preferably, the substantially linear polyethylene has a molecular weight in the range of about 38,000 to about 68,000. The substantially linear ethylene/alpha-olefin copolymers have a melt- index in the range of about 0.1 to about 100 g/10 min., preferably about 1 to about 60 g/10 min., and more preferably, about 5 to about 30 g/10 min. The melt index (I 2 ) is measured in accordance with ASTM D-1238 (conditions 190°C./2.16kg) . The substantially linear polyethylene 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 substantially linear polyethylene can be found in the liner composition in the range of about 85% to about 99.5%. More preferably, the substantially linear polyethylene can be found in the liner composition in the range of about 90% to about 99.5%. The sealing liner can also comprise an ionomer. An ionomer is an ionically crosslinked thermoplastic resin generally prepared by neutralizing a copolymer containing pendant acid groups, e.g., carboxylic acid groups, sulfonic acid groups and/or phoβphonic acid groups, with an ionizable metal compound, e.g., a compound of the monovalent, divalent and/or trivalent metals of Group I, II, IV-A and VIIIB 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-pβntene, 1-hexβne, 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 forgoing copolymers advantageously contain from about 0.2 to about 20 mole percent, and preferably from about 0.5 to about 10 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-methyl 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-fumaric acid- vinyl methyl ether copolymers, ethylene-vinyl chloride-acrylic acid copolymers, ethylene- vinylidene chloride-acrylic acid copolymers, ethylene-vinylidene chloride-acrylic acid copolymers, ethylene-vinyl fluoride-methacrylic acid copolymers and ethylene- chlorotrifluoroethylene-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 100 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 +2 , Mg +2 , Ca +2 , Sr +2 , Ba +2 , Cu +2 , Cd +2 , Hg +2 , Sn +2 , Pb +2 , Fe +2 , Co +2 , Ni +2 and Zn . 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 Surlyn 1702, which is a zinc salt of an ethylene and methacrylic acid copolymer and Surlyn 8660, which is a sodium salt of an ethylene and methacrylic acid copolymer. Both Surlyn 1702 and Surlyn 8660 may be obtained from E.I. Dupont de Nemours & Company, Wilmington, DE. 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%. In another embodiment of the invention, a sealing liner for a closure may comprise substantially linear polyethylene and a copolymer of ethylene and acrylic acid. The acrylic acid can be found in the copolymer in the range of about 3% to about 20% by weight of the copolymer. Preferably, the acrylic acid can be found in the range of about 5% to 18%, and most preferably, at about 15%. The copolymer of ethylene and acrylic acid may be found in the liner in the range of about 2% to about 10% by weight of the liner. Preferably, the copolymer may be found at about 3% to about 7% by weight, and most preferably, at about 2%. The melt index of the copolymer of ethylene and acrylic acid is about 1.5 to about 400 g/10 min. Preferably, the melt index is about 40 to about 100 g/10 min., and most preferably, about 60 g/10 min. An example of a suitable copolymer of ethylene and acrylic acid is Primacor™ 5980, which may be purchased from The Dow Chemical Company. Examples of other suitable copolymers of ethylene and acrylic acid may be found in U.S. Patent Nos. 4,500,664, 4,988,781 and 4,599,392, the disclosures of which are hereby incorporated by reference. The sealing liner compositions 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, βtearates and fatty amides, such as Kemmamide-E ® (also called erucamide) , which can be obtained from the Witco Corporation. Examples of suitable colorants include, but are not limited to, thaloblue, 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 of the liner than at the central portion of the liner. A preferred thickness at the central portion of the liner is about .011 in. The following example is intended to illustrate a specific embodiment of the invention and is not intended to limit the scope of the specification, including the claims, in any manner. Example General Protocol For Sfr y ing »nd Scuff Teats 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. Liner Composition A liner composition was made by combining 10% by weight of the liner composition ionomer with 90% by weight of the liner composition substantially linear polyethylene. The ionomer was Surlyn 1702 from Dupont, which is a zinc salt of an ethylene and methacrylic acid copolymer. The substantially linear polyethylene was a copolymer of ethylene and 1- octene, which can be obtained from The Dow Chemical Company of Midland, MI, sold under the name AFFINITY SM-1300, which has a weight average molecular weight of about 41,700, a melt index of about 30 g/10 min., and a density of about 0.902 g/cm . Lubricant (Kemmamide-E ® ) in an amount of one part per hundred and colorant (Thaloblue) in an amount of one part per hundred were also added to the liner composition. The resultant liner composition was subjected to scuff and string testing and showed no scuffing and stringing. The control, Alphaseal 240 6C, which is a commercially available liner composition comprising an ethylene and vinyl acetate copolymer that can be obtained from Alpha Chemical of Massachusetts, showed about 30% stringing or scuffing.

Claims: C A I M S 1. A sealing liner for a closure, the liner comprising: substantially linear polyethylene and an ionomer. 2. The sealing liner of claim 1, wherein the substantially linear polyethylene is a copolymer of ethylene and a C 3 -C 20 alpha-olefin. 3. The sealing liner of claim 1, wherein the substantially linear polyethylene is a copolymer of ethylene and 1-octene. 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: from about 70% to about 99.5% by weight of the liner substantially linear polyethylene that comprises a copolymer of ethylene and 1-octene, the octene being present in the copolymer in the range of about 3% to about 25% by weight of the copolymer, and the copolymer having a weight average molecular weight in the range of about 27,000 to about 220,000; and from about 0.5% to about 30% by weight of the liner and ionomer. 7. 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 substantially linear polyethylene and an ionomer. 8. The closure of claim 7, wherein the liner comprises substantially linear polyethylene that is a copolymer of ethylene and 1-octene. 9. The closure of claim 7, wherein the liner further comprises a lubricant. 10. The closure of claim 7, wherein the liner further comprises a colorant. 11. The closure of claim 7, wherein the liner comprises a disk with a central portion having a thickness of about .011 in. 12. The closure of claim 7, wherein the liner comprises a disk having a diameter in the range of about 25 mm to about 50 mm. 13. The sealing liner of claim 1, wherein the substantially linear polyethylene 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. 14. The sealing liner of claim 1, wherein the substantially linear polyethylene 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. 15. The sealing liner of claim 1, wherein the substantially linear polyethylene 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. 16. A sealing liner for a closure, the liner comprising: substantially linear polyethylene and a copolymer of ethylene and acrylic acid. 17. The sealing liner of claim 16, wherein the substantially linear polyethylene is a copolymer of ethylene and a C 3 -C 20 alpha-olefin. 18. The sealing liner of claim 16, wherein the substantially linear polyethylene is a copolymer of ethylene and 1-octene. 19. The sealing liner of claim 16, wherein the liner further comprises a lubricant. 20. The sealing liner of claim 16, wherein the liner further comprises a colorant. 21. The sealing liner of claim 16, wherein the copolymer of ethylene and acrylic acid is found in the liner in the range of about 2 to about 10% by weight of the liner. 22. The sealing liner of claim 16, wherein the copolymer of ethylene and acrylic acid contains about 3 to about 20% by weight of the copolymer acrylic acid. 23. The sealing liner of claim 16, wherein the copolymer of ethylene and acrylic acid has a melt index of about 1.5 to 400 g/10 min. 24. A sealing liner for a closure accord¬ ing to claim 1, substantially as hereinbefore described. 25. A sealing liner for a closure accord¬ ing to claim 6, substantially as hereinbefore described. 26. A closure according to claim 7, sub¬ stantially as hereinbefore described. 27. A sealing liner for a closure accord¬ ing to claim 16, substantially as hereinbefore described.

Inventors: BHOJRAJ NAVEEN, GUTIERREZ GENARO A, MARKOVICH RONALD P, WHETTEN ALAN R, BHOJRAJ, NAVEEN, GUTIERREZ, GENARO, A., MARKOVICH, RONALD, P., WHETTEN, ALAN, R.
Applicants: ALCOA CLOSURE SYSTEMS INT INC, BHOJRAJ NAVEEN, GUTIERREZ GENARO A, MARKOVICH RONALD P, WHETTEN ALAN R, ALCOA CLOSURE SYSTEMS INTERNATIONAL, INC., BHOJRAJ, NAVEEN, GUTIERREZ, GENARO, A., MARKOVICH, RONALD, P., WHETTEN, ALAN, R.
Application year: 1995
Main classification: B65D41
IPC codes: B65D53, C08L23