USE OF A FLUID BINDER COMPOSITION IN THE PREPARATION OF SEALING COMPOUNDS FOR CLOSURE SYSTEMS FOR JARS AND BOTTLES

Abstract: The invention relates to the use of a fluid binder composition in the preparation of sealing compounds for closure systems for glass jars and bottles. The binder composition comprises a polyester and a crosslinker that contains epoxy groups. The polyester can be a carboxyl functional polyester having an acid value between 20 and 600 mg KOH/gram resin and having a molecular weight (Mn) between 300 and 6000. The crosslinker can be a bisphenol-A-epoxide or an epoxyfunctional crosslinker comprising at least one C5 to C26 aliphatic chain.

Description: USE OF A FLUID BINDER COMPOSITION IN THE PREPARATION OF SEALING COMPOUNDS FOR CLOSURE SYSTEMS FOR JARS AND BOTTLES The present invention relates to the use of a fluid binder composition in the preparation of sealing compounds for closure systems for jars and bottles. Jars and bottles, which are often glass jars and bottles, come in many sizes and shapes. They may be closed and sealed in a variety of ways. The closure's main function is to hold the product in the glass jars and bottles and to provide an easy means of opening and sometimes reclosing the glass jar or the bottle. Some glass jars and bottles require a seal that will prevent liquid products from leaking and air from contaminating the product. In "Packaging Technology" (August/September 1982, pages 16-22) a review of the basic closures and the methods used for applying these closures is disclosed. Four types of closures frequently used are for example caps, plugs, fitments and innerseals. Caps may be described by the ways in which they are fastened to the bottle. The many variations in their style and construction make caps appropriate for many different sizes, and shapes of bottles and types of products. Special characteristics can be added to the cap designs to make them clidproof, tamper evident, product dispersing, or easy to open. A screw cap is held on the bottle by threads in the cap. These threads engage similar threads on the neck of the bottles. Screw caps are frequently made of metal or plastic. Lug caps are similar to screw caps except the lugs formed on the side of the cap are positioned under projections on the container neck. The lug cap is released or applied by making less than a one- quarter turn. The screw cap requires one or more complete turns for application or removal. Lug caps are normally made of metal, and can be used for glass containers that are vacuum sealed, because of their strength and ease of opening. Sealing compounds for closures for glass jars and bottles are, for example, disclosed in Viewpoint, 67, 37th Annual Set 1990, pages 34-35 by Peter Nϋssen. The sealing compound comprises the binder composition and additives such as for example pigments and fillers. The binder compositions for the sealing compound must be approved for direct food contact. An important function of the sealing compound is to protect the packed product to maintain its nutritional value, texture, color and flavor when purchased and used by the consumer. To meet these requirements, the organic sealing compound must be free of any material which might extract into the packed product and must maintain its integrity over the product recommended shelf life. On the whole, current commercial sealing compounds for these closures have met all these performance criteria. The sealing compound is often based on plasticized polyvinylchloride (PVC) , so called polyvinylchloride plastisol. The article "PVC in container coatings and approaches to its replacement" by M. Hickling (Polymeric Materials Science and Engineering, Volume 65, American Chemical Socienty Fall Meeting 1991, New York, pages 285- 286) elucidates that there exists a need for PVC replacement by other resins. The performance offered by PVC coatings is somewhat offset by the fact that PVC degrades above 100°C by elimination of HCl. The release of HCl can initiate corrosion reactions particularly on steel substrates. Hence, great care is needed in PVC plastisol formulation to ensure fineness of grind and adequate thermal stabilization. This degradation has caused complications in recycled and incineration of PVC containing waste. The chlorine content of steel recovered from such waste has been considered too high for many uses, but the amount of steel recovered in this way is rarely high enough to be significant. The polyenes produced also undergo secondary reactions in which it is possible to produce aromatic groups. These may generate dioxins whose presence can be detected in the emissions from incinerators burning PVC containing materials. The most dramatic reaction to this has been in Holland where it was claimed that the detection of dioxins in milk sold through supermarkets resulted from contamination of cattle grazing land by a waste incinerator. This claim led to demands by environmental groups (supported by supermarkets in the Netherlands and Germany and later by major food and beverage packers) for the removal of PVC from packaging. The aim is to remove PVC from sealing compounds for glass jars and bottle closures such as, for example, screw caps, twist off caps and lug caps. The closure systems are preferably of metal or plastic. It is the object of the present invention to provide a binder composition which can be used to replace PVC containing compositions in the preparation of sealing compounds for closure systems for jars and bottles. These compositions have particularly to meet requirements relating to, for example, sterilization and pasteurization properties, the absence of solvent in the composition, the approval for food applications of the binder compositions and good adhesion on the adhesive coating. The sealing compounds are essential in meeting the vital requirement of a total hermetic seal in all forms of packaging. The demands on compounds are diverse. For example, it must be guaranteed that under no circumstances the products packed could be contaminated either biologically or chemically. Even under adverse conditions the contents must remain hermetically sealed in the container. The sealing compound must be resistant to products packed and should not be detrimental to the quality of the contents. The process and processing have to provide for a high manufacture output. The sealing properties have to be maintained for long periods of time and without any significant ageing. Demands on sealing compounds for closures for glass jars and bottles are very stringent due to the requirement for reuse, special properties are necessary to withstand the sterilisation process. The invention is characterized in that the binder composition is substantially solvent-free and comprises a polyester and a crosslinker that contains epoxy groups. The binder composition results in a liquid 100% solids compound. The viscosity of the fluid binder composition may range from that of pourable liquids to that of heavy pastes. The composition is substantially solvent free. In general, this means that the binder composition may contain less than 5% by weight of a solvent, such as for example xylene, butylglycol or propyleneglycolmonomethyl- etheracetate. Sealing compounds comprising the binder composition according to the present invention which are applied in jars and bottles closures result in an excellent behaviour with respect to said requirements and they withstand the impact of superheated steam on closing and offer opening to torgues within the specification tolerances. Preferably, the polyester is a carboxyl- functional polyester. Preferably the polyesters have an acid value between 20 and 600 mg KOH/gram resin, preferably between 100 and 300 mg KOH/gram resin. The molecular weight (Mn) may range between 300 and 6000 (determined by gel permeation chromatography (GPC); polystyrene standard). The glass transition temperature of the polyester may range, for example, between -60°C and 10°C. A carboxyl-functional polyester can be obtained by causing a polyalcohol to react with an acid or an acid anhydrides by choosing a certain molar ratio of the polyalcohols and the acids or acid anhydrides. This ratio may vary for example between 1:2 and 1:1 for the preparation of the carboxyl functional polyester. Suitable polyalcohols for the preparation of the polyester include, for example, ethylene glycol, propylene glycol (1,2), dipropylene glycol, tripropylene glycol, propylene glycol (1,3), methylpropylene glycol 1,3, diethylene glycol, triethylene glycol, butanediol (1,2), butanediol (1,3), butanediol (1,4), hexanediol (1,6), neopentyl glycol, 2,2,4 trimethylpentanediol (1,3), ester of hydroxypivalic neopentyl glycol, cyclohexanedimethanol, bisphenol-A-bishydroxyethyl ether, trimethylolpropane and/or pentaerythritol. A suitable acid for the preparation of the polyesters includes, for example, isophthalic acid, terephthalic acid (dimethylester of terephthalic acid or isophtalic acid), adipic acid, fumaric acid, sebacic acid, hexahydroterephthalic acid, decanedicarboxylic acid, azelaic acid, 5-t-butylisophthalic acid and/or dimerised fatty acids or acid anhydrides such as phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, pyromellitic anhydride and/or hexahydrophthalic anhydride. The esterification reaction is preferably carried out in a nitrogen atmosphere at temperatures of between 180°C and 260°C. Catalysts such as dibutyltin oxide, tinchloride or tetrabutoxy titanate, and antioxidants such as triphenyl phosphite may be used as additives. The water released during the reaction is preferably removed by distillation. The desired degree of esterification can be reached by means of azeotropic distillation or vacuum in the last phase. Suitable crosslinker containing epoxy groups include, for example, bisphenol-A-epoxy compounds, hydrogenated bisphenol-A-epoxy compounds, aliphatic epoxy compounds, epoxidized alkyd resins, epoxydized fatty borates, di-, tri-, and oligoesters of polyalcohols such as glycerol, trimethylpropane, pentaerytritol, dipentaerytritol and unsaturated fatty acids, and/or trisglycidylisocyanurate (TGIC). According to a preferred embodiment of the invention the crosslinker is a bisphenol-A-epoxide or an aliphatic epoxy compound comprising at least one C s to C 26 aliphatic chain. Suitable bisphenol-A-epoxides are for example the various Epikote* types. Another suitable epoxy-functional crosslinker comprises at least one C s to C 26 aliphatic chain provided that the epoxy functionality is carried on the aliphatic chain. The aliphatic chains can be linear or branched. The aliphatic chains carrying the epoxy functionality are preferably linear. The epoxy functional crosslinker can also comprise several aliphatic chains at least one of which carries epoxy functionality wherein the chains are linked via ester, amide, urethane or ether groups. As evident, it is not required that each chain carries an epoxy group. The epoxy functionality is greater than 1, preferably greater than 2. Preferably, the aliphatic chain contains 6 or more and in particular 12 or more carbon atoms. Preferably the aliphatic chain contains 22 or less carbon atoms. The oxirane oxygen content of the crosslinker in general is higher than 1 wt.%, preferably higher than 2 wt.%. In general the oxirane oxygen content of the crosslinker will be lower than 20 wt.%, in practice mostly lower than 15 wt . % . The crosslinker preferably comprises an aliphatic ester carrying an epoxy group. When the crosslinker comprises aliphatic esters, the C 5 to C 26 aliphatic chains of the crosslinker are linked via ester groups. Exemplary esters include the methyl ester of linoleic acid, the tert.-butyl ester of linolenic acid, and epoxidized oil. Examples of these crosslinkers are epoxidized oils wherein the oil is linseed oil, soybean oil, safflower oil, oiticica oil, caraway seed oil, rapeseed oil, castor oil, dehydrated castor oil, cotton seed oil, wood oil, vernonia oil (a natural oil), sunflower oil, peanut oil, olive oil, soybean leaf oil, maize oil, fish oil such as, for example, herring or sardine oil, and non-cyclic terpene oils. Preferably the epoxidized oil is preferably epoxidized soybean oil and/or epoxidized linseed oil. Preferably the binder composition according the invention preferably includes a small but effective amount of catalyst for the reaction between the polyester and the crosslinker. Suitable catalysts are listed in Madec et al.. Kinetics and Mechanisms of Polyesterifications. Advances in Polymer Science, 182-198 (1985), the complete disclosure of which is incorporated herein by reference, can, in principle, be used. Examples of suitable classes of catalysts are N- dialkylamine pyridines, tertiary amines, imidazole derivatives, guanidines and cyclic amine compounds. If desired, the catalysts may be blocked. Specific examples of catalysts include N-dimethylamino pyridine, benzotriazole, triethylamine or triphenylamine, 4,5-diphenyl imidazole, 1-ethyl imidazole, 2-methyl imidazole, 4-methyl imidazole, ethyl imidazole carboxylate, 5,6-dimethyl benzimidazole, 1-benzyl imidazole, imidazole or 1,1-carbonyl diimidazole, benzyltrimethylammoniumchloride, cholinechloride, trifenylethylfosfoniumbromide, tetramethyl guanidine (TMG) , isocyanate-TMG adducts (e.g., isophorone diisocyanate-di-tetramethyl guanidine, tolonate-HDT-tetramethyl guanidine, or TMXDIdiTMG) , acetyl-TMG, 2-phenyl-l,1,3,3-tetramethyl guanidine, l,5-diazabicyclo[4,3,0]non-5-ene and 1,5,7- triazabicyclo[4,4,0]dec-5-ene. Other catalysts include tetraalkyl phosphonium bromide, tetrabutyl ammonium fluoride, cetyl triethyl ammonium bromide and benzothiazole. According to a preferred embodiment of the invention the catalyst is a metal salt of a carboxylic acid or an alcohol or is a metalhydroxyde. Preferably the salts are based on saturated aliphatic mono- and dicarboxylic acids and saturated aromatic carboxylic acids, having 3-25 carbon atoms and more preferably having 6-24 carbon atoms. In general, the pK a of the carboxylic acid is greater than 3 and smaller than 10. Suitable carboxylic acids include for example saturated aliphatic mono- and dicarboxylic acids, unsaturated aliphatic acids, carbocyclic carboxylic acids, heterocyclic carboxylic acids, hydroxycarboxylic acids, alkoxycarboxylic acids, oxocarboxylic acids, aminocarboxylic acids and amidecarboxylic acids. Preferably, the acids are selected from decanoic acid, octanoic acid, neodecanoic acid, stearic acid, lauric acid, decanedicarboxylic acid, benzoic acid or an acid obtainable with the Koch-reaction. Suitable alcohols include for example monohydric alcohols, diols and triols such as for example methanol, ethanol, propanol, isopropanol, butanol and isomers thereof, glycol, neopentylglycol, butanediol, hexanediol, cyclohexanedimethylol, glycerol, trimethylolpropane and tris(hydroxyethyl)isocyanurate. Preferably the metals are lithium, sodium, potassium, caesium, magnesium, calcium, beryllium, tin, copper or zinc. The most prefered metals are lithium and sodium. Preferably, sodium or lithium salts of (C 6 -C 24 ) carboxylic acids are used. Very suitable salts for use as a catalyst according to the invention are sodium stearate, lithium stearate, lithium acetate, sodium benzoate, sodium neodecanoate, lithium benzoate, sodium laurate, lithium laurate, lithium adipate, sodium octanoate, lithium octanoate, lithium neodecanoate and lithium versatate. According to another preferred embodiment of the invention, the catalyst is sodium stearate, lithium stearate, sodium neodecanoate or lithium neodecanoate. As metal hydroxide, sodium hydroxide, potassium hydroxide and caesium hydroxide are preferably used. Other suitable lithium derivatives include for example lithium alkanolates such as lithium butanolate, lithiumtriazole, lithiumimidazole and lithium hydroxide. The weight ratio between the carboxylic groups of the polyester and the epoxygroups of the crosslinker is generally between 100:50 and 100:300. The amount of catalyst is generally between 0,01 and 5% by weight, relative to the binder composition. The sealing compound according to the present invention may, if desired, also contain additives such as, for example, stabilizers, plasticizers, hardness modifiers, fillers, pigments, flow agents and lubricants. Suitable plasticizers include for example phtalates, sebacates and adipates in amounts between, for example, 2 and 50% by weight. Suitable hardness modifiers include for example acrylics, maleic anhydride-styrene copolymers and polyamide. The binder composition of the present invention can, if desired, be supplied as a single component system. In a single component system a large part or all of the polyester and substantially all of the crosslinker are supplied as a mixture. A single component binder system can be obtained by mixing the crosslinker with the polymer at a temperature below 70°C to form a homogenous mixture. A sealing compound can be prepared by mixing the binder composition with a catalyst and, optionally, a pigment, plasticizers, filler and other additives and optionally additional curing agents at a temperature of for example between 20°C and 70°C. Instead of using the binder system as a single component, the various ingredients of the binder composition can also be mixed with the other ingredients of the compound during the preparation of the compound. The catalyst and additives also can be added either to the polymer or to the crosslinker. The catalyst and/or the curing agent can also be added during compound preparation, together with the plasticizer, pigments and the fillers. The catalyst and additives can, if desired, be applied as a masterbatch. Such a masterbatch can be a mixture of the polymer resin that is also used for the binder composition or another - not reactive - resin with the catalyst and optionally all or a part of the additives. A two-component (or two-package) system for the preparation of the sealing compound comprises a first component consisting essentially of all or a large part of the polyester and the crosslinker, and a second component consisting essentially of the polyester and a catalyst for the curing reaction between the polymer and the crosslinker (masterbatch). The sealing compound according to the invention can for example be applied by a nozzle lining process. The compound is injected into the channel located in the lug caps perimeter and must be able to flow into the overlapping section. The compound can be preheated before injection. Generally the comound comprising the binder composition according to the present invention and additives can be cured at temperatures between 180° and 260°C during 1-20 minutes. US-A-3548026 discloses a coating compostion comprising an organic solvent solution of an epoxy resin blended with a carboxyl terminated polyester. These solvent-based coatings can be applied as coatings for bottle caps. However, the present invention is not directed to a coating but relates to a sealing compound. The requirements for a sealing compound are completely different from the requirements for a coating. Also JP-A-54141810 discloses a solvent and polyester based coating agent for glass bottles. However, also JP-A-54141810 does not relate to sealing compounds. WO-A-8707903 relates to a sealing element for bottles and jar closures, consisting of a synthetic halogen-free polymer. WO-A-8707903 does not disclose or give any suggestion for the use of the polyester according to the present invention. This invention will be further described based on the following non-limiting examples. Example I Preparation of a polvester resin and a binder compostion 5.8 moles propyleneglycol (PG) , 1.43 moles trimethylolpropane (TMP), 10.0 moles adipic acid (AA) and 0.05 parts by weight dibutyltinoxide were heated in a glass reaction flask with a mechanical stirrer, a thermometer and a distillation arrangement with vigreux, in a nitrogen atmosphere. The esterification reaction started at 150°C and the reaction water formed was removed by distillation. The maximum reaction temperature was 230°C. At 230°C vacuum distillation was started until an acid number of 120 mgKOH/g resin was reached. The molecular weight (Mn) was 1300. The polyester was cooled down. The binder composition was prepared at 80°C by mixing 200 g of the polyester, 75 g bisphenol-A-epoxide (Epikote 828™) and 2,75 gram tetraalkylphosphonium- bromide. The compound was applied on a precoated m * etal substrate (precoated with an epoxy-phenolic lacquer) with a layer thickness of 1 mm. The compound was cured for 3 minutes at 240°C in an oven. The cured compound had a shore A hardness of 60- 70. The adhesion of the compound on the lacquer was good. The use of the PVC-free binder composition acording to the present invention resulted in a sealing compound having good sterilisation properties. Although the present invention has been described in detail with reference to its presently preferred embodiments, it will be understood by those of ordinary skill in the art that various modifications and improvements to the present invention are believed to be apparent to one skilled in the art. Accordingly, no limitation upon the invention is intended, except as set forth in the appended claims.

Claims: C I M S 1. Use of a fluid binder composition in the preparation of sealing compounds for closure systems for jars and bottles characterized in that the binder composition is substantially solvent-free and comprises a polyester and a crosslinker that contains epoxy groups. 2. Use of a binder composition according to claim 1, characterized in that the polyester is a carboxyl functional polyester having an acid value between 20 and 600 mg KOH/gram and a molecular weight (Mn) between 300 and 6000. 3. Use of a binder composition according to any one of claims 1-2, characterized in that the crosslinker is a bisphenol-A-epoxide or an epoxyfunctional crosslinker comprising at least one C 5 to C 26 aliphatic chain. 4. Use of a binder composition according to any one of claims 1-3, characterized in that the composition contains 0,01-5% by weight of a catalyst. 5. A sealing compound for sealing closure systems for jars and bottles comprising a binder composition according to any one of claims 1-4 and additives. 6. A process for the preparation of a sealing compound for closure systems for jars and bottles characterized in that the compound according to claims 5 is cured at a temperature between 180°C and 260°C during 1-20 minutes. 7. A closure for jars and bottles based on a compound according to claim 5 or a compound obtainable according to claim 6.

Inventors: GRISNICH WILLEM, WESTERHOF WILHELMINA, GRISNICH, WILLEM, WESTERHOF, WILHELMINA
Applicants: DSM NV, GRISNICH WILLEM, WESTERHOF WILHELMINA, DSM N.V., GRISNICH, WILLEM, WESTERHOF, WILHELMINA
Application year: 1995
Main classification: C08L67
IPC codes: C08L67, C09K3