SEALING COMPOUND AND ITS USE FOR PRODUCING PRESSURE-TIGHT CONTAINERS

Abstract: The subject of the present invention is a sealing compound which comprise A) from 20 to 95 % by weight of at least one compound having on average at least 2 isocyanate groups per molecule, the isocyanate groups each being blocked, B) from 1.5 to 30 % by weight of at least one di- and/or polyamine, C) from 0 to 50 % by weight of at least one further organic polymer, D) from 0 to 60 % by weight of pigments and/or fillers, E) from 0 to 50 % by weight of one or more reactive diluents, and F) from 0 to 35 % by weight of auxiliaries and additives, characterized in that the sealing compound comprises G) from 1 to 40 % by weight of at least one adhesive, the sum of the proportions by weight of all components A) to G) employed in the sealing compound being in each case 100 % by weight.

Description: Sealing compound and its use for producing pressure- ight containers The subject of the present invention is a sealing compound which comprises A) from 20 to 95% by weight of at least one compound having on average at least 2 isocyanate groups per molecule, the isocyanate groups each being blocked, B) from 1.5 to 30% by weight of at least one di- and/or polyamine, C) from 0 to 50% by weight of at least one further organic polymer, D) from 0 to 60%. by weight of pigments and/or fillers, E) from 0 to 50% by weight of one or more reactive diluents, and F) from 0 to 35% by weight of auxiliaries and additives. The present invention relates, furthermore, to processes for preparing the sealing compound, to processes for producing closures, especially for the pressure-tight sealing of packaging containers, using this sealing compound, and to such closures. Sealing compounds of the type specified at the outset are already known from EP-B-542 766. According to EP-B-542 766, these sealing compounds are employed in producing closures for food packaging containers. The use of the sealing compounds to produce pressure-tight containers, on the other hand, is not described in EP-B-542 766. In the field of pressure-tight containers, especially for the transportation and storage of liquid goods, for example paints and inks and other industrial products subject to labeling requirements (e.g. chemicals or other environmentally hazardous goods) , there is an increased requirement for containers which meet the appropriate standards relating to sealing without an additional clamping ring. At the same time, however, these containers should also be easy to open without the use of special tools . Consequently, EP-B-546 051 proposed applying, to an already applied sealing compound, an adhesive which ensures both the sealing of the containers without an additional clamping ring and the trouble-free opening of the containers. This solution proposed in EP-B-546 051, however, has a number of disadvantages. For instance, the additional application of an adhesive requires another process step in producing the closures, which is associated with further costs and high time consumption. Furthermore, there is the possibility that after the containers have been opened/closed a number of times constituents of the adhering layer will enter the contents, leading to complaints on the part of the filling plants. The present invention is based, accordingly, on the object of providing a sealing compound which allows the production of pressure-tight containers, the containers being intended to meet the corresponding standards (for example German Hazardous Goods Ordinance Rail and Hazardous Goods Ordinance Road, Appendix A5) in relation to pressure tightness without the use of an additional clamping ring and without the additional application of an adhesive to the sealing compound. Furthermore, the sealing compound should show little or no migration of the constituents of the sealing compound into the packaged product. In addition, the sealing compound should also meet the other requirements commonly set, for example in relation to chemical resistance and elasticity. Finally, the sealing compound should be able to be applied and cured on the existing plant. This object is surprisingly achieved by the sealing compound of the type specified at the outset, which is characterized in that it comprises G) from 1 to 40% by weight of at least one adhesive, the sum of the proportions by weight of all components (A) to (G) employed in the sealing compound being in each case 100% by weight. Further subjects of the present invention are processes for preparing the sealing compound, processes for producing closures, especially for the pressure-tight sealing of packaging containers, using this sealing compound, and such closures . It is surprising and was not foreseeable that with the aid of the sealing compound according to the invention it is possible to produce pressure-tight containers which comply with the standards customarily set for such containers, even without an additional clamping ring and without the additional application of an adhesive. At the same time it is also surprising that the sealing compound, and especially the adhesive component, exhibits extremely little or no migration into the product - both during storage of the containers and after the containers have been opened. Moreover, it is advantageous that by virtue of the addition of component (G) the properties of the sealing compound, for example in respect of chemical resistance and elasticity, suffer little or no significant adverse effect. Another advantage, finally, is that the sealing compound can be applied on the plant which is customarily employed. In the following text, then, the individual constituents of the sealing compound according to the invention will first of all be explained in more detail. Compounds suitable as component (A) of the sealing compound are all those having on average at least two isocyanate groups per molecule. The isocyanates in this case can be monomers or oligomers and also prepolymers having at least 2 NCO groups per molecule. The prepolymers can have been prepared, for example, by the reaction of a diisocyanate with a chain extender. The isocyanate groups of component (A) are not free but are present in blocked form. It is preferred to employ blocked isocyanates which at room temperature are liquid or are present as a solution or dispersion. It must also be ensured that, in the case of food packaging, the migration rate of the structural components of the isocyanate compound, for example blocking agent, into the product is as low as possible. Examples of suitable blocking agents of component (A) are, in particular, compounds unobjectionable from the standpoint of foodstuffs law, for example amino acids, cyclized amino acids and sugars, and also, for example, malonic acid and malonic esters. Other possible blocking agents are oximes, for example acetoxime, diethyl ketoxime, acetophenone oxime, cyclohexanone oxime, cyclopentanone oxime, formaldoxime, acetaldoxime, and also phenols and caprolactams . When these blocking agents are employed, however, it should be ensured that no problems occur as a result of migration of residues of blocking agent into the product. Isocyanates suitable as the isocyanate component are, in particular, all those which, in the form in which they have been fully reacted with one of the above-mentioned blocking agents, are preferably liquid and lead to systems which preferably have Shore A hardnesses (DIN 53 505) of between 20 and 80. Preferably, furthermore, the isocyanate component should not be readily volatile at room temperature. Examples of suitable isocyanates are di- and/or trimerized 2,4- and 2,6-tolylene diisocyanate, di- and/or trimerized hexamethylene diisocyanate, alone or in a mixture with small amounts of monomeric tolylene or hexamethylene diisocyanate, respectively. Also suitable are chain-extended diisocyanates, especially chainextended tolylene or hexamethylene diisocyanate. Chain extenders employed are diols and/or triols and/or polyols and also mixtures of diols with tri- and/or polyols. It is preferred to employ di- and/or trimerized tolylene diisocyanate or tolylene diisocyanate which has been chain-extended with a diol and/or triol . Component (A) is employed in the sealing compound in an amount of from 20 to 95% by weight, preferably from 25 to 90% by weight, based in each case on the overall weight of the sealing compound. Compounds (component (B) ) suitable for crosslinking the blocked isocyanates, which are employed in an amount of from 1.5 to 30% by weight, preferably from 2 to 20% by weight, based in each case on the overall weight of the sealing compound, are di- and/or polyamines, especially diamines which are liquid at room temperature, particularly preferably liquid cycloaliphatic diamines, for example 4,4- diamino-3 , 3-dimethyldicyclohexylmethane, 4 , 4-diaminodicyclo- hexylmethane, polyoxypropylenetriamine having a mean molecular weight MW of from 400 to 450, and also liquid polyaminoamides such as, for example, the commercial product "Versamid 100" from the company Schering AG, and liquid polyaminoamides prepared by condensation of di- and trimeric fatty acids with aliphatic amines, and also amines having a low melting point. The amino groups of the amino compounds employed are generally primary and/ or secondary in nature. By means of the ratio of isocyanate component (A) and amine component (B) established in each case in the sealing compound it is possible, as by appropriate choice of components (C) and (G) and the selection of the particular auxiliaries and additives employed, to influence the tack of the sealing compounds within certain limits. The isocyanate component (A) and the amine component (B) are therefore employed in the sealing compounds according to the invention preferably in amounts such that the proportion of component (A) to component (B) is between 7 : 1 and 15 : 1, particularly preferably between 10 : 1 and 14 : 1. As a further constituent (C) the sealing compound may also, if desired, include at least one further organic polymer, preferably at least one further plastic and/or elastic and/or reactive organic liquid and/or pulverulent polymer. This component (C) is employed in the sealing compound in an amount of from 0 to 50% by weight, preferably from 1 to 35% by weight, based in each case on the overall weight of the sealing compound. Examples of suitable modifiers (component (C) ) are styrene- butadiene copolymers, styrene-butadiene-styrene rubber, relatively high molecular mass polyethylene homo- and copolymers, relatively high molecular mass ethylene-vinyl acetate copolymers, relatively high molecular mass vinyl acetate-ethylene copolymers, polystyrene, polyvinyl alcohols, polyamides, acrylate polymers, nitrile rubbers, polyurethane precondensates, epoxy resins, polyesters, sugars, etc. Through the selection of the nature and amount of these modifiers it is possible to control specifically the properties of the sealing compound, for example the flexibility. This, however, is known to the skilled worker, and the most favorable type and amount of these modifiers in each case can readily be determined with the aid of a few routine experiments. As a further constituent the sealing compound also contains from 0 to 60% by weight, preferably from 0 to 30% by weight, based in each case on the overall weight of the sealing compound, of pigments and/or fillers, such as, for example, titanium dioxide, synthetic iron oxides, organic pigments, for example phthalocyanines, tartrazines, ultramarine blue, Pigment Yellow 83, Pigment Orange 43, Pigment Orange 5, Pigment Red 4, and also magnesium silicates and aluminum silicates, amorphous and pyrogenic silica, barium sulfate, carbon black, talc, kaolin and chalk (component (D) ) . To establish a favorable application viscosity the sealing compound may also comprise from 0 to 50% by weight, preferably from 0 to 20% by weight, based in each case on the overall weight of the sealing compound, of one or more reactive diluents (component (E) ) . Examples of suitable compounds are preferably polyfunctional amines, especially cycloaliphatic diamines, for example cyclohexylpropylenediamine etc. In addition, however, it is also possible to employ polyols, for example propylene glycol and diethylene glycol and also reactive oils, for example vegetable oils containing OH groups, as reactive diluents. However, they have the disadvantage of a lower reactivity in comparison with polyamines. Finally, the sealing compound according to the invention may also comprise from 0 to 35% by weight, preferably from 1 to 20% by weight, based on the overall weight of the sealing compound, of other auxiliaries and additives (component (F) ) . Examples thereof are, in particular, low molecular mass plasticizers, for example phthalates, citrates, sebacates, octoates and the like, and also other customarily employed auxiliaries and additives, for example silicone oils . Further examples of compounds employed as component F are waxes and silicas for obtaining specific flow properties (thixotropic agents) and, in the case of foamed sealing compounds, blowing agents, for example azodicarboxamides or sulfohydrazides . Preferably, however, the sealing compound according to the invention contains less than 1% by weight, with particular preference essentially no lubricants, since the customarily employed lubricants reduce the tack of the sealing compound. The sealing compound is employed primarily for use in closures for pressure-tight containers of the type specified at the outset. Alternatively, it can be employed as a foamed sealing compound. In general the foaming of the sealing compounds brings about a reduction in the Shore A hardness (measured in accordance with DIN 53 505) , an increase in the flexibility, a more favorable weight/volume ratio, and the obtention of a better sealing function as a result of better deformability. The tack of the sealing compound is affected only slightly, in general, by the addition of foaming agents . It is essential to the invention that the sealing compound contains from 1 to 40% by weight, preferably from 5 to 25% by weight, based in each case on the overall weight of the sealing compound, of at least one adhesive. Adhesives suitable in principle for use in the sealing compound according to the invention are all adhesives, especially all adhesives which at room temperature are liquid or highly viscous. In this case, component (G) can also be employed in the form of a liquid or highly viscous solution or dispersion. Also suitable in principle are so- called hotmelt adhesives. Component (G) is generally selected such that at least some of component (G) is located on the surface of the sealing compound, after the sealing compound has been applied, and ensures heightened adhesion or adhesion promotion of the sealing compound relative to the counterpart of the closure (for example metal or further sealing compound) . In the sealing compound according to the invention it is possible, for example, to employ adhesives based on tall resins and/or colophony resins and the like. The adhesives preferably employed in the sealing compound according to the invention are low molecular mass, branched or, preferably, linear or substantially linear homo- and/or copolymers of aliphatic, ethylenically unsaturated hydrocarbons having 2 to 6 C atoms, for example polybutene and/or polyisobutylene or polyisobutene and/or ethylene-propylene copolymers and/or ethylene-vinyl acetate copolymers. The preparation of the sealing compound takes place by mixing the individual components, with or without first adding the insoluble components, for example pigments, to component (A) and - where necessary - carrying out dispersion using the dispersing equipment customary in the coating industry. In the case of the preparation of non- foamed sealing compounds, mixing or dispersing is usually carried out under vacuum. The sealing compound prepared in this way generally has Shore A hardnesses (DIN 53 505) of between 20 and 80, preferably between 25 and 70. The amount in which the sealing compound is applied depends on the geometry of the closure part, on the intended use of the packaging and whether the sealing compound is foamed or not. For use in pressure-tight containers, the sealing compound according to the invention is usually applied in a coat thickness of from 0.2 to 20 mm, preferably from 1 to 10 mm. To produce the closures in accordance with the process according to the invention the above-described sealing compound is applied to the closures, preferably by means of the known "injection process". In this process, the sealing compound is injected or pressed at slightly elevated temperature, usually from about 30 to 70°C, in the uncured, pastelike state, from one or more nozzles, into the closure parts, which are set in rotation using a suction cup or the like at high rotational speed. Owing to the centrifugal forces, the sealing composition is transferred in the desired contour and form. After this inflow is complete, curing of the sealing compound takes place at temperatures between 150°C and 240°C for a drying time of from 1 to 5 min (conditions depending on recipe) . Drying, and the equipment employed for it, are likewise known and therefore require no further explanation here. The closure which is to be coated with the sealing compound is understood as being all parts of the packaging material which are connected to the body of the packaging. In particular, however, the sealing compounds are applied in pressure-tight containers as are employed for the transportation and the storage of liquid products, for example paints and inks, or other chemicals (for example goods subject to labeling requirements, which in some circumstances may be environmentally hazardous) . The sealing compound according to the invention is suitable, for example, for application in the containers described in EP- B-546 051, with sealing being ensured without an additional clamping ring and without the additional application of an adhesive . These closures may consist of metals, such as aluminum, black plate, tinplate and various ferrous alloys, to which a passivating layer based on nickel compounds, chromium compounds and tin compounds may have been applied. In the process according to the invention the sealing compound can be applied to coated closures, but in particular, owing to the good adhesion to metals, can also be applied to uncoated closures. Suitable coating compositions are the coating materials, customary in the packaging industry, based on epoxy-phenolic resin, acrylate resin or polyester, or organosols . However, these coating materials are known (cf. e.g. H. Kittel, Lehrbuch der Lacke und Beschichtungen [Textbook of Paints and Coatings] , Volume IV, Lack- und Beschichtungssysteme, Formulierung [Paint and coating systems, formulation] , Verlag W.A. Colomb in der H. Heenemann GmbH, Berlin- Oberschwandorf 1976) and therefore require no more detailed description here. The invention is illustrated in more detail below with reference to working examples. Unless expressly stated otherwise, all indications as to parts and percentages are by weight. First of all, the sealing compounds of Examples 1 to 5 and of Comparison Example 1 are prepared from the components indicated in Table 1 by mixing. The tack (manually) and the exudation behavior (manually and visually) of these sealing compounds are assessed. The results of these investigations are likewise shown in Table 1. Table 1: Composition of the sealing compounds in parts, and properties of the sealing compounds Key to Table 1 : 1) : commercial, ε-caprolactam-blocked polyisocyanate (commercial product Desmodur® BL 1100 from the company Bayer AG) 2) : 4,4 diamino-3 , 3-dimethylcyclohexylmethane [sic] 3) : commercial polymethyl methacrylate having a softening temperature of about 130°C and a TΛmax of about 136°C 4) : commercial plasticizer based on diisononyl phthalate 5) : commercial silicone oil having a viscosity of 340 cPs at 25°C 6): commercial, low molecular mass, room-temperature- liquid polyisobutylene having a number-average molecular weight of 1300, a density at 20°C of 0.89 g/cm 3 and a viscosity at 100°C of about 500 mm 2 /s 7) : commercial, low molecular mass, room-temperature-liquid polyisobutene having a kin. viscosity at 100°C of 180 -240 mm 2 /s , a density at 20°C of 0.887 g/cm 3 and having a number- average molecular weight of 940 8) : commercial, low molecular mass, room-temperature-liquid polyisobutene having a kin. viscosity at 100°C of 570 -650 mm 2 /s 9) : commercial, room-temperature-liquid, low molecular mass polybutene having a viscosity at 99 °C of 635 - 690 cSt 10) : The tack was assessed manually (finger test) (sat. = satisfactory; unsat . = unsatisfactory). 11): The exudation was assessed manually and visually (sat. = satisfactory; unsat. = unsatisfactory). 12) : Very severe exudation

Claims: Patent claims : 1. Sealing compound which comprises A) from 20 to 95% by weight of at least one compound having on average at least 2 isocyanate groups per molecule, the isocyanate groups each being blocked, B) from 1.5 to 30% by weight of at least one di- and/or polyamine, C) from 0 to 50% by weight of at least one further organic polymer, D) from 0 to 60% by weight of pigments and/or fillers, E) from 0 to 50% by weight of one or more reactive diluents, and F) from 0 to 35% by weight of auxiliaries and additives, characterized in that the sealing compound comprises G) from 1 to 40% by weight of at least one adhesive, the sum of the proportions by weight of all components (A) to (G) employed in the sealing compound being in each case 100% by weight. 2. Sealing compound according to claim 1, characterized in that it contains from 5 to 25% by weight, based on the overall weight of the sealing compound, of at least one adhesive. 3. Sealing compound according to claim 1 or 2, characterized in that it contains at least one adhesive which at room temperature is liquid or highly viscous (component (G) ) . 4. Sealing compound according to one of claims 1 to 3 , characterized in that it comprises as adhesive (component (G) ) polybutene and/or polyisobutene. 5. Sealing compound according to one of claims 1 to 4, characterized in that it comprises A) from 25 to 90% by weight of at least one compound having on average at least 2 isocyanate groups per molecule, the isocyanate groups each being blocked, B) from 2 to 20% by weight of at least one di- and/or polyamine, C) from 1 to 35% by weight of at least one further organic polymer, D) from 0 to 30% by weight of pigments and/or fillers, E) from 0 to 20% by weight of one or more reactive diluents, F) from 1 to 20% by weight of auxiliaries and additives and G) from 5 to 25% by weight of at least one adhesive (G) , the sum of the proportions by weight of components (A) to (G) being in each case 100% by weight. 6. Sealing compound according to one of claims 1 to 5 , characterized in that it comprises as component (A) isocyanates which are liquid at room temperature and/or as component (B) polyamines which are liquid at room temperature . 7. Sealing compound according to one of claims 1 to 6, characterized in that it comprises as component (A) compounds based on tolylene diisocyanate and/or as component (B) 4, 4-diamino-3 , 3-dimethyldicyclohexyl- methane and/or polyoxypropylene triamine having a mean molecular weight M w , of 400 - 450. 8. Process for preparing sealing compounds according to one of claims 1 to 7 by mixing and, if desired, dispersing components (A) to (G) . 9. Process for producing closures, in particular for the pressure-tight sealing of packaging containers, in which a sealing compound is applied to the closures and stoved, characterized in that a sealing compound according to one of claims 1 to 7 is applied. 10. Closure for packaging containers, characterized in that it has been prepared by a process according to claim 9. 11. Use of a composition which comprises A) from 20 to 95% by weight of at least one compound having on average at least 2 isocyanate groups per molecule, the isocyanate groups each being blocked, B) from 1.5 to 30% by weight of at least one di- and/or polyamine, C) from 0 to 50% by weight of at least one further organic polymer, D) from 0 to 60% by weight of pigments and/or fillers, E) from 0 to 50% by weight of one or more reactive diluents, F) from 0 to 35% by weight of auxiliaries and additives and G) from 1 to 40% by weight of at least one adhesive, the sum of the proportions by weight of all components (A) to (G) being in each case 100% by weight, as a sealing compound, especially for closures of pressure- tight containers.

Inventors: NUESSEN PETER, PETERS JENS, NUESSEN, PETER, PETERS, JENS
Applicants: NUESSEN PETER, PETERS JENS, PPG INDUSTRIES INC, NUESSEN, PETER, PETERS, JENS, PPG INDUSTRIES, INC.
Application year: 1997
Main classification: C09K3
IPC codes: C08G18, C08L23, C09J175, C09K3