GB2130574A - Process for sealing a glass container with a thin closure - Google Patents

Abstract

The lip of a glass container is prepared for sealing with a thermoplastic- coated foil by applying at least one layer of an adhesive comprising a mixture of ethylene-acrylic acid copolymer of melt index </=300 and a silane, pref. N-( beta -aminoethyl)- gamma -aminopropyl- trimethoxysilane. The lip may previously have been flame-treated. Advantage: long-term leak- resistance after hot-filling.

Description

SPECIFICATION Process for sealing a glass container with a thin closure Background of the invention The present invention relates to a process for sealing an imperforate thin flexible type closure to the finish lip of a glass container, typically a wide mouth jar-type container. Typically, such processes involve providing an imperforate thin flexible closure, usually an aluminum metal foil, which has its underside coated with a heat-sealable thermoplastic, such closure adapted to securely engage the upper finish lip of a glass container. In usual practice, the upper finish lip of the glass container is coated with a heat-sealable adhesive composition suited to provide an interface between the thermoplastic coated imperforate thin flexible closure and the glass surface of the container.

A number of approaches have been taken to sealing dry food or cold-filled food products such as dry soup, refrigerated dairy products and the like. For example, British Patent Application 2030103 A, published April 2, 1980 disclosed a metal foil, applied over the opening and the rim of a glass container which is secured to the rim by a heat-activatable adhesive upon the application of heat and pressure in order to produce a bond between the glass vessel and the metal foil, without diffusion or harming of the adhesive bond occuring when the vessel holds water-containing contents, a bond promoter such as silicon organic compound, for example a silane, with an affinity for the glass, is applied to the rim of the vessel or incorporated in the adhesives. The process is not apparently directed toward hot-filling applications.

Japanese Patent No. J5 077-447 related to a container with an easy-open cover and bearing publication date May 14, 1982, and assigned to Toyo Seikan Kaisha discloses a container formed by lapping a film or sheet made of a laminate consisting of a plastic sheet or a metal foil and a plastic sheet, e.g., a hot-bonding plastic material. The hot-bonding plastic material laminated to the metal foil is selected from the group including a modified olefinic resin such as an acid-modified polyolefin, an ionomer, an ethylene-vinyl acetate copolymer, an ethylene-unsaturated carboxylic acid or its ester copolymer or a blend of any of the above-mentioned, or a polyamide.Further provided is an opening smaller than the diameter of the weakened line-provided portion to be opened when being used on the inside portion of the easy-open cover in such a way that the small diameter opening of the film or sheet is superimposed over the weakened line-provided portion of the easy-open cover by turning its hot-bonding plastic film side toward the easy-open cover. The lapped portion is bonded by heating a portion outside of the weakened line-provided portion to be opened.

German Patent Application P28 48 568.9 discloses a process for sealing of glass containers with the synthetic material coated on metal foils. The process includes the steps of coating the rim of the glass container with a binding agent to more securely affix the synthetic material coated metal foil to the glass container. The binding agent is a purely organic or water-containing solution of alkyl trialkoxy silane, of an alkyl trichlorosilane,the alkyl group of which carries a substituentwith one amino-, epoxy-, vinyl-, acrylo- or methacrylo- group or an organic solution of a monomeric or polymeric titanic acid ester. The coating is applied, dried and the sealing foil subsequently sealed on, in a known manner, by pressing onto the upper lip of the glass container with the aid of a heat sealing head.Ketones, particularly acetone, is disclosed as the preferred organic solvent for the alkyl trialkoxy silane, the alkyl trichloro silane or for a mixed alkyl-alkoxychlorosilane. For the titanic acid esters, however, a benzene-based solvent system is employed.

Each solvent system requires the use of a volatile organic compound.

British Patent Specification 1538642 discloses a sealed container, comprising a glass jar having a mouth with an upwardly facing surface, a metal foil membrane spanning the container mouth and heat-sealed thereto, and a heat and pressure deformable plastic snap-cap over said container mouth and foil membrane, the mouth of the container being provided with a raised bead on the upwardly facing surface extending continuously around the mouth, the cap having a thickness over the outwardly facing surface of at least twice the height of the bead, the bead and foil member being impressed into the plastic material of the snap-cap. The metal foil membrane may include an ethylene-acrylic acid copolymer resin of activation temperature of 275-325"F. as an undercoating for intimate contact between the foil membrane and the container bead.

German Patent Document DE 3011761A1 entitled "Method for the Joining of Substrates by Heat Sealing" based on file no. P3011761.4-43, application dated March 1980 discloses a method for sealing glass-to-glass or glass-to-metal to form a package to contain dry soup, yogurt or similar cold-filled food products.The container and closure are secured together by a heat-sealable adhesive which has been prepared by hydrolysis and polycondensation of: a) at least one organosiloxane of the general formula I RmSiX4-m (i) in which R signifies alkyl, alkenyl, aryl, alkylaryl or arylalkyl, X represents hydrogen, halogen, hydroxyl, alkoxy, acyloxy or -NR12 (R1 = hydrogen and/or alkyl) and m has the value of 1,2 or 3, and at least one of the following components (b), (c) and/or (d): b) one or more silicon-functional silanes of the general formula II SiX4 (ill) in which X has the earlier given meaning but not all remainders are hydrogen; c) one or more difficulty volatilizable oxides soluble in the reaction medium or one or more compounds of an element of the principal groups la to Va or of the secondary groups IVb or Vb of the periodic system forming such a difficulty volatilizable oxide; d) one or more organo-functional silanes of the general formula III Rn(R"Y)pSiX(4-n-p) (Ill) in which R and X have the earlier mentioned meaning, R" represents straight chained or branched alkylene, which can be interrupted by oxygen- or sulfur atoms or by NH-groups, phenylene, alkylphenylene or alkylenephenylene, Y signifies a halogen or in a given case a substituted amino- or in a given case substituted anilino-, aldehyde-, keto-, carboxyl-, hydroxyl-, mercapto, cyano-, hydroxyphenyl-, carboxylic acid, alkyl ester-, sulfonic acid-, phosphoric acid-, acryloxy-, methacryloxy-,glycidyloxy-,epoxide-,orvinyl group, n has the value 0, 1 or 2 and p the value 1,2 or 3, where n + p has the value 1,2 or 3; in presence of the water quantity stoichiometrically required for the hydrolysis as well as in a given case of a condensation catalyst and/or a solvent, where in the case of the starting components (a) and (d) also oligomers of these silanes can be used, which are soluble in the reaction medium.

A number of problems have been inherent in the approaches described above when they are applied to hot-filled food applications. For example, when such approaches as those described above are used for hot-filling of acidic food products, like orange juice, or hot-filling of non-acidic products, like jellies, jams, tomato sauces, catsup and the like, into glass containers using the adhesive described above and the use of plastic coated thin metal closures described above, a number of problems have occurred. One critical problem is the premature release of the closure from the heat-sealable adhesive on the finish lip of the glass container immediately after the package is filled, sealed and moved to a cool-down station. During hot filling, the container is heated by its hot-filled contents.Also, as the heat and pressure sealing head seals the closure to the container, it adds a significant amount of heat to the package. Such combined heat input causes some of the water in the package to vapourize. Such vapor pressure causes the thin metal closure to balloon outwardly under the pressure. Such force and ballooning of the closure cause premature release of the closure in an unacceptably high proportion of cases. During the later stages of such a cooling process after input heat is finally lost, a partial vacuum is formed on the interior of the container and the closure collapses inwardly. Such a vacuum causes increased stress on the seal between the metal foil closure, the heat-sealable finish lip applied adhesive and the finish lip of the glass container.Many failures of the seal are experienced when adhesives and processes, which are well-suited for cold-fill applications, are used for hot-fill applications. Such failures of the seal cause leakage of the package and renders the contents contaminated and commercially useless.

Further, upon long term storage, on the order of a few months to a year, the packages develop leaks due to long term storage instability of the adhesives used when contacted with high moisture foods, such that atmospheric contamination enters the food containing package thereby again rendering the package valueless. This deficiency in long term storage durability of the package is particularly critical in hot-filled food applications which typically have long shelf residence times. Further, hot-filled food packages exhibit a partial vacuum on the interior of the container which adds a higher level of mechanical stress to the bond between the thin flexible metal closure, the heat-sealable adhesive and the glass container finish lip.

Also, many of the adhesives discussed above do not show long term product resistance characteristics, especially when brought into contact with highly acidic, high moisture, fruit juices and tomato based food products. Accordingly, the heat-sealable adhesives themselves lose their ability to seal the package over long term storage under stress and food contact. Further, many of the currently used processes require coating mutliple separate layers of different solutions, for example, adhesives, cross-linkers, bonding agents and the like, onto the container finish lip. This requires additional processing steps and a substantially higher capital investment in machinery and a multiplicity of different solutions. Such solutions require time to compound, are often not storage stable and in most cases incorporate organic solvents. Such solvents are, in many instances, not approved for food contact. Also, such solvent based adhesive compounds require special employee protection and environmental control practices, equipment and procedures which militate against their use in many circumstances. Obviously, the use of environmental pollution control equipment is disadvantageous to the low cost manufacture of commodity hot-filled food products. Accordingly, there exists a need in the art for a process and complementary heat-sealable adhesive formulation suited for use in hot-fill food packaing uses which is simply, reliable, organic vapor-free and which provides a cool-down stable and long shelf life stable package.

Summary of the invention An object of the present invention is to provide a sealed container and a process for the manufacture thereof suitable for containing hot-filled food products, which container has increased resistance to leak-formation after being filled with a hot food product and having the closure applied thereto and being cooled to ambient temperature.

Another object of the invention is to provide a sealed container and a process for the manufacture thereof suited for containing hot-filled food products which container exhibits increased resistance to long term storage stress without forming leaks between the heat-sealable adhesive layer and the glass container of the thin flexible closure.

These and other advantages of the present invention are realized by a process for sealing a glass container, which container has an upper finish portion terminating in a finish rim or lip portion which process comprises heating at least the finish lip portion of the glass container to an elevated temperature for a time sufficient and at a temperature sufficient to oxidize any organic materials coated upon the lip of the finish. Subsequently, at least one layer of a heat-sealable adhesive is coated upon the upper lip of the finish, which heat-sealable adhesive will form a bond between a thin flexible metal closure which has been coated with an organic thermoplastic material and the upper finish lip of the glass container.The heat-sealable adhesive according to the present invention is an aqueous admixture of a silane and an ethylene-acrylic acid copolymer wherein the ethylene-acrylic acid copolymer has a melt index of about 300 or lower. Subsequent to the application of the heat-sealable adhesive, the adhesive is dried, and a thin imperforate metal-plastic laminate closure is pressed onto the glass container and heat and pressure sealed thereupon by a conventional heat sealing, pressure applicating means.

The container formed according to the present invention is particularly well-suited to containing hot-filled food products and shows high resistance to leak-formation during the filling, sealing and cool-down process and is further particularly resistant to leak-formation during long term storage or handling.

Brief description of the drawings The above objects and advantages of the present invention will become readily apparent to one skilled in the art from the following detailed description of the preferred embodiment of the invention, the appended claims and the accompanying drawings at which: Figure 1 is an exploded view of an imperforate metal foil/thermoplastic film laminate flexible closure and the heat-sealable adhesive coated upper finish lip of a glass container; Figure 2 is a schematic representation of the process of the present invention for preparing, filling and sealing the package according to the present invention; and Figure 3 is a schematic representation of the process for cooling hot-filled containers incorporating the improved heat-sealable adhesive according to the present invention.

Detailed description of the preferred embodiment The preferred embodiment of the present invention is illustrated by way of example in Figures 1-3. With specific reference to Figure 1, there is illustrated a glass container, in partial sectional view, generally designated by reference numeral 10. The glass container 10 terminates at an upper finish portion 12 which defines an opening into the container 10. The finish portion 12 terminates at its uppermost portion in a finish lip portion 14. Typically, the finish lip portion 14 is a flat or slightly rounded portion as is conventional with wide mouth glass containers. A thin layer of a heat-sealable adhesive 16 is disposed upon the finish lip portion 14 of the container 10.A thin imperforate flexible membrane-type closure 18 of a complementary geometry to the finish portion 12 of the container 10 is disposed above the container and suited for attachment to the finish portion 12 of the container 10 by engagement of the closure 18 to the finish lip portion 14. Typically, the closure 18 includes a metal foil portion 20 and a thermoplastic heat-sealable film portion 22. The heat-sealable film portion 22 may itself be a laminate laminated thereto structure as described in detail hereinafter.

In the preferred embodiment of the invention, the heat-sealable adhesive 16 comprises a mixture of a silane compound and an ethylene-acrylic acid copolymer having 80 percent ethylene and 20 percent acrylic acid, by weight, in the copolymer structure and having a melt index below 300. The most preferred melt index is on the order of 75. It has been discovered according to the present invention that an ethylene-acrylic acid copolymer of a melt index between 75-300 provides an excellent, high hot tack strength heat-sealable adhesive for use in hot-fill food processing without the use of organic solvents in the adhesive.

As used herein, melt index is defined as the amount, in grams, of a thermoplastic resin which can be forced through a 0.0825 inch orifice when subjected to 2160 grams of force in 10 minutes at 190"C.

A preferred silane compound is Union-Carbide organofunctional Silane Al 120, which is a N-(betaaminoethyl) gamma-amino-propyl-trimethoxysilane, which is a diamino-functional silane. The preferred silane described above is soluble in water which makes it particularly suitable to hot-fill food packaging uses wherein no organic solvents may be used in the compounding of the heat-sealable adhesive. All components of the adhesive must be suited for food contact use under the food and drug laws and most organic solvents are not so approved. The preferred silane is a straw-colored liquid having a specific gravity of 1.03 at 25"C., a refractive index of 1.448 (nD25 C.) and a flash point of 280"F.

The preferred ethylene-acrylic acid copolymer has a melt index of around 300 or below and is capable of forming a water-based, organic solvent-free dispersions at room temperature. Such a resin is currently available from Dow Chemical Company as Product No. PE 483. A more preferred resin is an ethylene-acrylic acid copolymer of a melt index of around 75.

The metal foil 20 of the closure 18 is an aluminum metal of a thickness between 1.5 and 2.5 mil. The thermoplastic heat-sealable film 22 laminated onto the metal foil 20 can be a Surlyn material supplied by E.I.

duPont deNemours & Company, an ethylene-acrylic acid copolymer of any desired melt index or a laminate structure including a nitrocellulose polymer in contact with the aluminum film and itself coated with a polyvinyl butyral polymer to form an aluminum-nitrocellulose-polyvinyl butyral laminate. A preferred material is Surlyn Grade No. 1652 an ionomer resin having zinc counter ions with a melt index of 5.0. All three of the above discussed closures 18 are suited for use with the improved heat-sealable adhesive disclosed herein. Each closure will form excellent hot-filled packages with the new adhesive disclosed herein which exhibit short term stability upon cooling from elevated hot-fill temperatures to room temperature and exhibit excellent long term durability without forming a high percentage of leaks in the manufactured containers.

The process according to the present invention for preparing and filling the containers 10 is best illustrated at Figure 2. A treated container supply station 24 provides a continuous supply of glass containers 10 for use in the process of the present invention. The glass containers 10 provided by supply station 24 are treated in accordance with conventional glass container manufacturing techniques wherein the surface has been treated over the exterior of the container 10 with combinations of thin transparent coatings. Frequently, such containers are treated with tin tetrachloride to form a so-called hot-end coating while the containers 10 possess considerable heat of manufacture.The containers 10 are further coated with polyethylene, oleic acid or other lubricious organic material coatings which are applied in the form of so-called cold-end treatments to improve contact scratch resistance. It has been discovered according to the present invention that the containers should preferably be treated, to achieve optimum results, to remove or substantially oxidize the cold-end treatment materials, like oleic acid, prior to application of the heat-sealable adhesive layer 16.

Flame treatment stage 26 achieves the total or partial oxidative removal of the cold-end treatment lubricious materials by subjecting at least the finish lip portion 14 of the container 10 to a high oxygen content flame to oxidize the cold-end treatment materials. Typically, the finish lip portion 14 is raised to about 300 F. for a few seconds to effectively remove a substantial amount of the cold-end treatment material. It has been further determined according to the present invention that long term storage stability and leak-resistance of the package is improved when the finish lip portion 14 is subjected to a plurality of flames in a serial fashion.For example, the finish lip portion 14 or so-called mouth of the container 10 is passed under a lineal series of ribbon-type gas burners which produce an oxygen-rich gas flame to oxidize or burn off the organic constituents of the aforesaid cold-end treatment of the finish lip portion 14. In the preferred practice of the invention, three ribbon-type gas burners directed to the finish lip portion 14 remove sufficient cold-end treatment to facilitate operability of the heat-sealable adhesive layer 16 during post-fill, cool-down and long term storage.

After the flame treatment stage 26, the glass containers 10 are preferably placed in a cooling stage 28 wherein the finish lip portion 14 cools from around 300 C. to a temperature on the order of 120-140 F. Such a lower temperature facilitates the application of the heat-sealable adhesive disclosed herein but does not delay processing of the containers 10 by a substantial time as would be required to cause the containers 10 to reach ambient temperature.

Subsequent to the cooling stage 28, the glass containers 10 are delivered to an adhesive application stage 30 wherein a coating of the heat-sealable adhesive is applied to the finish lip portion 14to form a thin film to about 50 microns thick. Any conventional application methodology may be employed; however, an overhead roller coating device suited for continuous adhesive application to a linear array of containers 10 is preferred. Such an overhead roller coating device would consist of a cylindrical rubber, or other resilient material, roller which is downwardly biased to forcibly contact the container finish lip portion 14 during its passage therebeneath.The rollers are typically mounted transverse to the direction of the container travel and is adapted to apply on the order of 0.025 mg/square millimeters of dried coating equivalent per contact with the finish lip portion 14. Coating weights as low as 0.0075 mg/square millimeter can be used but such minimal loading does not always compensate for surface irregularities in the finish lip geometry. Weights above 0.015 mg/square millimeter are preferred. A practical upper range is about 0.08 mg/square millimeter.

Subsequent to the adhesive application stage 30, the containers are delivered to a drying stage 32 wherein a forced drying of the heat-sealable adhesive layer 16 occurs. In the preferred practice of the invention, a quartz infrared heater bank is used which supplies 1.15 micron radiant energy to the containers 10 to raise them in a very short period of time, for example 6 seconds, to about 160 F. Such a temperature thermally dehydrates the adhesive compound and causes it to form a tenacious seal with the finish lip portion 14.

After the initial coating and drying steps, the resultant article is a glass container with a coating of the heat-sealing adhesive dried upon the finish lip. Such an article is a composite container which is storage stable and may be shipped as discrete article of commerce to a filling plant or may be filled immediately.

For many applications when very difficult to store food products are used, it is preferred that the coated dried containers as they exit drying stage 32 are recycled via return loop 33 to the adhesive application stage 30 for a second 0.025 mg/square millimeter dried coating equivalent application of adhesive and subsequently, again encounter the drying stage 32 for a second drying step wherein the second coating of adhesive is dried into tenacious sealing engagement with the first adhesive coating. While for many applications, it is not required to doubly coat the finish lip portion 14, if there is a very flat lip, when finish lips are somewhat irregular, as is typical in commodity containers, a second application of adhesive is required to achieve the best results for excellent sealing durability on cool-down and for best long term storage of a container.Such double coating results in containers which can hold hot-filled high acid, high moisture content foods, like fruit juices, during cool-down and during long shelf storage with minimal leakage.

After the containers 10 can exit the drying stage 32, they are delivered to a hot-filling and closure application stage 34 illustrated at Figure 3. At stage 34 a hot food product on the order of 170-210"F. is placed in the container 10. Subsequent to the filling of the container 10 with the hot food product, the closure 18 is applied to the finish lip portion 14 and sealed thereto by a conventional sealing head. Such a sealing head applies heat and downward pressure to the closure 18 to force the thermoplastic heat-sealable film 22 of the closure 18 into tenacious engagement with the heat-sealable adhesive layer 16 which is in intimate contact with the finish lip portion 14.After the containers are filled and sealed, they are delivered to a multiphased cooling stage 36 wherein they are cooled from the 170-210"F. filling temperature to ambient temperature.

The hot-filled containers are processed within the multiphase filling stage 36 to a hot-filled container supply stage 38 which places the containers in a linear array for delivery to a primary hot water treatment stage 40. Containers arriving from the hot filled container supply 38 contain a product that is typically between 170-21 0'F. The primary hot water vapour treatment stage 40 subjects these containers to a hot water vapour of about 140-180"F. for a period of between one minute and ten minutes, typically about three minutes for a 180 water temperature.The containers are delivered from the primary hot water treatment 40 to a secondary hot water treatment stage 42 wherein they are subjected to an 80-1 200F. hot water spray for about one minute to about ten minutes, typically about three minutes at about 80"F. water spray temperature. The 120 F. containers are transferred from the secondary hot water treatment stage 42 to a cold water treatment stage 44 wherein the sealed containers are subjected to a cold water bath or spray on the order of 65-76"F. for 20-30 minutes.

It has been discovered that when hot-fill applications are required for such foods as orange juice, catsup, mustard, tomato pastes and sauces, jellies, jams and similar hot-fill requiring food products, that by practicing the process of the present invention, in conjunction with the heat-sealable adhesive disclosed herein, sealed containers exhibit excellent resistance to leakage during the multiphase cooling stage 36, shown in detail in substages 38-44, and show excellent resistance to leak-formation during long term storage, for periods of a few months up to a year.

As disclosed herein before the heat-sealable adhesive, according to the present invention, is a silane compound admixed with an ethylene-acrylic acid copolymer having a melt index below 300 and an ethylene content of 80 percent with an acrylic acid content of 20 percent. A suitable ethylene-acrylic acid copolymer is available from Dow Chemicals, U.S.A. as product PE 483 having the following physical properties when purchased as a dispersion: Solids content, percent 25 Viscosity, Brookfield, 50 rpm 100-200 pH 9-10 Surface tension, dyne/cm 46-49 Weight per gallon, pounds 8.22 Density, liquid, gm/cc at 25"C. 0.985 Density, solids, gm/cc at 25"C. 0.960 Vehicle Ammonia Water Volatile Organic Compounds None Acid Number (Dow) 156 Melt Index (ASTM D-1238) 300 gm/10 min.

Melting Point (Dow, DSC) 85"C. (185"F.) Vicat Softening Point (ASTM D-1525) 50 C. (122"F.) Ultimate Tensile Strength (ASTM D-638) (for compression molded samples) 1600 psi Tensile Yield (ASTM D-638) (for compression molded samples) 900 Percent Elongation (ASTM D-638) 300 Typically, the silane component of the heat-sealable adhesive comprises between 4 and 12 percent by weight of the total in the dried film of adhesive.

The non-organic solvent containing adhesive according to the present invention typically includes about 25 grams of the copolymer dispersed in 100 grams of water with about 2 grams of silane contained therein.

Typically, the non-solvent containing adhesive is prepared as in the following example. The copolymer containing water based dispersion, preferably Dow 483 disclosed above, is placed in a mixing vessel and stirred at a sufficient speed to just form a vortex. A minimal vortex is desirable since a high vortex action causes too much air entrapment in the dispersion which is disadvantageous. After a slight vortex has been established in the copolymer dispersion water, three parts by volume of 58 percent by volume ammonium hydroxide is added per 100 parts by volume of the copolymer dispersion. The ammonium hydroxide is first poured into the vortex slowly to facilitate proper mixing of the ammonium hydroxide into the copolymer dispersion to assist in forming a stable emulsion.Next, two parts by volume of the silane, preferably Union-Carbide Al 120 silane, is slowly added per 100 parts by volume of copolymer dispersion by pouring the silane into the vortex of the mixture. The mixture is slowly stirred, with minimal vortex, for 2-3 minutes to form a stable non-organic solvent containing dispersion which when coated onto a glass container finish lip portion forms a heat-sealable adhesive layer 16 according to the present invention. For high speed coating lines occasionally the above-described adhesive mixture foams upon application by high speed rollers. In such event afterthe addition of the silane, an additional 4 parts by volume of one percent ammonium hydroxide is stirred in and the resulting adhesive stirred for 2-3 minutes.

To demonstrate the excellent durability of a package according to the present invention, the following tests were conducted.

Eleven wide mouth glass containers are coated twice with an adhesive of the following composition: 100 parts by volume Dow Chemical U.S.A. copolymer 483; 3 parts by volume 58 percent (so-called concentrated) ammonium hydroxide; 2 parts by volume Union-Carbide A1120 silane and 4 parts by volume of one percent ammonium hydroxide in deionized water, all constituents added in the order given and under the conditions exemplified immediately above. The eleven containers are coated with the adhesive mixture.

The coated containers are heated to 140"F. for 15 minutes after the first adhesive application stage 30 application. After the second application of the adhesive via return loop 33 the containers are heated to 200"F. for 45 minutes.

The coated containers are emersed in a 140"F. water bath to simulate commercial hot-filling line container preheaters. Next, the containers are filled to the brim with 21 0'F. orange juice. Preshaped 2 mil aluminum closures, with a Surlyn undercoat, are placed on the containers and heat-sealed with a conventional heat-pressure sealing head. The sealing head conditions are as follows: Seal spring surface temperature 385-405 F.

Seal pressure 6 bars Crimp Pressure on Lip Edge 3.5 bars Seal Time 1 second After sealing, the containers are cooled for 3 minutes in a 180"F. water vapor chamber. Next, the containers are cooled for 3 minutes in a 120"F. water spray. Finally, the containers are cooled for 3 minutes in a 72"F.

water stream. No leaks were detected.

After cooling to 720F. the sealed containers are placed in a vacuum desiccator. A vacuum equal to seven inches of mercury is applied to the vacuum desiccator and held for one minute. Next, the vacuum is increased to 26 inches of mercury for 5 seconds. No leaks were detected.

This test demonstrates the cool-down durability and durability under substantial vacuum draw of the package according to the present invention.

A second test was performed to illustrate the durability of a package according to the present invention when subjected to hot-filling, primary and secondary heat treatment and cold water treatment to approximate commercial food packaging operation.

A heat-sealable adhesive dispersion is prepared as follows: 3500 milliliters of ethylene-acrylic acid copolymer Type PE-483 is stirred to form a vortex as described above and then 105 milliliters of ammonium hydroxide, 58 percent by volume, is slowly added to the vortex of the stirring copolymer dispersion. Next, 70 milliliters of Union-Carbide organofunctional silane Type A 1120 is stirred into the vortex of the solution.

Subsequently, 280 milliliters of a solution of one part by volume ammonium hydroxide and 100 parts by volume distilled water is added to the above solution to decrease foaming upon application when using a roller system as described above.

Next, 13 wide-mouthed containers are coated twice as described above by roller-coating means with the adhesive dispersion to form about a 0.05 mg/square millimeter weight layer of dried adhesive. The first coating of heat-sealable adhesive is dried for 15 minutes at 140"F. and the second coating is dried for 45 minutes at 200"F., and the containers are cooled to room temperature after each adhesive drying cycle.

Before filling with hot-filled product, each container is dipped in a 140"F. water bath to simulate a bottle warmer in a commercial filling line. Subsequently, the containers are filled to overflowing with 170"F.

strawberry jelly. Next, an aluminum foil closure as described above with an undercoating of Surlyn brand ionomer resin Type 1652 on its underside is placed on the container mouth. The closure is heat-sealed thereupon with a conventional heat-pressure sealing head under the same conditions as specified in the previous example. After sealing, the containers are force-cooled in a 180"F. hot water primary hot water treatment stage 40 for three minutes. Subsequently, the containers are moved to a secondary hot water treatment stage 42 wherein they are subjected to a spray of 120"F. water for three minutes. Next, the containers are moved to a cold water treatment stage 44 and subjected to a 78"F. cold water stream for three minutes. Subsequently, all containers are cooled in ambient air to room temperature.

After cooling to ambient temperature, the sealed containers are placed in a vacuum desiccater for testing.

During the test any rupture of the seal will become evident by the release of air bubbles from the package.

Each container is placed in a water-filled vacuum desiccator and exposed to a vacuum equal to seven inches of mercury which is applied and held for one minute. After the one minute, the vacuum is increased to 26 inches of mercury and held thereat for five seconds.

As a result of the above test, 12 of the 13 containers survived both the low vacuum and high vacuum test conditions. Only one container failed the test with such failure due to a crack in the glass wall of the container.

Another test was conducted to the determine the long term storage durability of the package. In this test, 14 containers were filled as described immediately above with 210"F. orange juice and sealed. The containers were first tested under the seven inch vacuum as described above for one minute, and the 26 inch vacuum as described above for five seconds. No failures were detected. Subsequently, the sealed containers were stored for 22 days in a 100"F. accelerated aging room. One day in the accelerated aging room at 1 00'F.

is approximately equal to three days under normal use conditions. All containers after long term storage were again subjected to a seven inch vacuum desiccation test for one minute. No leaks were detected in any of the 14 containers after long term storage as described above.

Claims (37)

1. A process for sealing a container finish, said container finish being glass and having an upper finish lip, comprising: a. applying a layer of a heat-sealable adhesive to said finish lip, said heat-sealable adhesive including an admixture of a silane and an ethylene-acrylic acid copolymer, said copolymer having a melt index of about 300 or less; b. drying said layer of said heat-sealable adhesive on said finish lip; c. filling said container with a hot food product; and d. applying a thin flexible imperforate closure to said finish lip and applying heat and pressure to seal said closure to said finish lip, said closure including a first upper metal layer and a second lower thermoplastic layer, said thermplastic layer in contact with said heat-sealable adhesive.

2. The process defined in claim 1 wherein said container is made entirely of glass.

3. The process defined in claim 1 wherein said heat-sealable adhesive layer is between 0.0075 - 0.08 mg per square millimeter of finish lip surface area.

4. The process defined in claim 1 wherein said silane is a diamino-functional silane.

5. The process in claim 4 wherein said diamino-function silane is N-(beta-aminoethyl) gamma-aminopropyl-trimethoxysilane.

6. The process defined in claim 1 wherein said copolymer has a melt index of between about 75 and about 300.

7. The process defined in claim 1 wherein said copolymer includes 80 percent ethylene and 20 percent acrylic acid in its structure.

8. The process defined in claim 1 wherein said adhesive is dried by exposure to infrared radiation.

9. The process defined in claim 1 wherein said thermoplastic layer is an ethylene-acrylic acid copolymer.

10. The process defined in claim 1 wherein said thermoplastic layer is a first sublayer of nitrocellulose coated onto said aluminum and a second sublayer of polyvinyl butyral coated onto said first sublayer.

11. The process defined in claim 1 further including the steps of applying a second layer of said adhesive onto said finish lip and drying said second layer prior to filling said container with said hot food product.

12. A process for forming a composite container, said composite container having a glass finish portion, with the finish having an upper finish lip, comprising: a. applying a layer of a heat-sealable adhesive to said finish lip, said heat-sealable adhesive including an admixture of a silane and an ethylene-acrylic acid copolymer, said copolymer having a melt index of about 300 or less; and b. drying said layer of said heat-sealable adhesive on said finish lip.

13. The process defined in claim 12 wherein said heat-sealable adhesive layer is between 0.0075 - 0.08 mg per square millimeter of finish lip surface area.

14. The process defined in claim 12 wherein said silane is a diamino-functional silane.

15. The process in claim 14wherein said diamino-functional silane is N-(beta-aminoethyl) gammaamino-propyl-trimethoxysilane.

16. The process defined in claim 12 wherein said copolymer has a melt index of between 75 and 300.

17. The process defined in claim 12 wherein said copolymer includes 80 percent ethylene and 20 percent acrylic acid in its structure.

18. The process defined in claim 12 wherein said adhesive is dried by exposure to infrared radiation.

19. The process defined in claim 12 further including the steps of applying a second layer of said adhesive onto said finish lip and drying said second layer.

20. A composite container comprising: a unitary hollow container having an upper glass finish portion, said finish having an upper finish lip; and a layer of a heat-sealable adhesive on said finish lip, said adhesive including an admixture of a silane and an ethylene-acrylic acid copolymer, said copolymer having a melt index of 300 or less.

21. The container defined in claim 20 wherein said layer of adhesive is between 0.0075 - 0.08 mg per square millimeter of finish lip surface area.

22. The container defined in claim 20 wherein said silane is a diamino-functional silane.

23. The container in claim 22 wherein said diamino-functional silane is N-(beta-aminoethyl) gammaamino-propyl-trimethoxysilane.

24. The container defined in claim 20 wherein said copolymer has a melt index of between 75 and 300.

25. The container defined in claim 20 wherein said copolymer includes 80 percent ethylene and 20 percent acrylic acid in its structure.

26. A process for producing a hot-filled food product package, said package including a glass container, a closure and a heat-sealable adhesive sealing said closure to said container, said container having an upper finish lip, comprising: a. applying a layer of a heat-sealable adhesive to said finish lip, said heat-sealable adhesive including an admixture of a silane and an ethylene-acrylic acid copolymer, said copolymer having a melt index of about 300 or less; b. drying said layer of said heat-sealable adhesive on said finish lip; c. filling said container with a hot food product; d. applying a thin flexible imperforate closure to said finish lip and applying heat and pressure to seal said closure to said finish lip, said closure including a first upper metal layer and a second lower themoplatic layer, said thermoplastic layer in contact with said heat-sealable adhesive;; e. contacting the sealed container with water for a time between 1 and 10 minutes, said water at a temperature of between 140-180 F.; f. contacting the sealed container from step e. with water from a time between 1 and 10 minutes, said water at a temperature of between 80-120"F.; and g. contacting the sealed container from step f. with water for a time between 20 and 30 minutes, said water at a temperature of between 65-76"F.

27. The process defined in claim 26 wherein said heat-sealable adhesive layer is between 0.0075 - 0.08 mg per square millimeter of finish lip surface area.

28. The process defined in claim 26 wherein said silane is a diamino-functional silane.

29. The process defined in claim 28 wherein said diamino-functional silane is N-(beta-aminoethyl) gamma-amino-prnpyltrimethoxysilane.

30. The process defined in claim 26 wherein said copolymer has a melt index of between about 75 and about 300.

31. The process defined in claim 26 wherein said copolymer includes 80 percent ethylene and 20 percent acrylic acid in its structure.

32. The process defined in claim 26 wherein said adhesive is dried by exposure to infrared radiation.

33. The process defined in claim 26 wherein said thermoplatic layer is an ethylene-acrylic acid copolymer.

34. The process defined in claim 26 wherein said thermoplastic layer includes a first sublayer of nitrocellulose coated onto said metal layer and a second sublayer of polyvinyl butyral coated onto said first sublayer.

35. The process defined in claim 26 including the steps of applying a second layer of said adhesive onto said finish lip and drying said second layer prior to filling said container with said hot food product.

36. A process as claimed in claim 1, claim 12 or claim 26, substantially as described with reference to the drawings.

37. A composite container as claimed in claim 20, substantially as described with reference to the drawings.