Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1999-12-06
2001-04-17
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C524S492000, C524S497000, C524S423000, C524S493000, C524S494000
Reexamination Certificate
active
06217960
ABSTRACT:
The invention relates to an interior coating material for container closures, based on resin, to a process for preparing such an interior coating material, and to uses of such an interior coating material for producing coated container closures which may or may not comprise sealing materials. —Container closures is the term for closures which are screwed on, placed on, inserted in or formed onto container apertures. Examples are screw caps or crown corks for food containers which hold at least partly liquid foods, liquid preserving agents or beverages. Container closures for this end use are subject to particular requirements. On the one hand, the sealing provided to the contents must be liquid-tight and, in the case for example of contents which include or give off gases, must be gastight as well. On the other hand, the base material of the container closures must be protected against corrosive attack by the contents. An interior coating material of the invention can in principle, however, be used for non-food container closures as well. Base materials employed in principle are both polymeric materials and metallic materials, examples being sheet iron (in general, coated electrolytically with tin), sheet aluminum or tinplate, the metallic materials in particular having acquired wider currency. Gastight sealing is generally achieved by means of a seal which is manufactured, for example, from an elastomer and which when the container is in the closed state is arranged in the region of the sealing faces of the container aperture and of the container closure. Seals of this kind are either prefabricated from an appropriate sealing material and inserted into the container closure or applied, as it were, as a coating on the inside of the container closure. In addition, however, it is generally necessary, especially when using metallic materials as the base materials for a container closure, to protect the entire inner face Of the container closure against corrosive attack by the contents through the application of an interior coating material. This interior coating material is then arranged between the sealing material and the base material of the container closure. The coating itself can be of single-coat or else multi-coat design, for example with a primer coat and a topcoat. In the latter case, the expression interior coating material designates a coating material for producing the topcoat. Consequently, such an interior coating material must on the one hand be suitable for food contact (in accordance with statutory regulations) and on the other hand must be chemically inert (to the contents). Also of particular importance is the fact that the interior coating material must show good adhesion both to the base material (or to the primer coat) and to the sealing material. Finally, the interior coating material is required to have physical properties which ensure no processing problems in the roller coating technology that is customary in the manufacture of container closures. In this technology, a tin-plated iron sheet, for example, is first of all provided with a coating of the interior coating material by means of roller coating. The container closures are then obtained from the coated sheet by means of cutting and/or shaping tools and are provided with the sealing material. In principle, however, it is possible to apply the sealing material to the coated sheet before cutting or shaping.
Interior coating materials of the type specified at the outset are known, for example, from reference U.S. Pat. No. 3,183,144. These known interior coating materials are formed essentially from synthetic resins. Examples indicated of synthetic resins are phenol-formaldehyde condensates, oleoresins and epoxy resins. A common feature of all these known interior coating materials is that their solids content is relatively low, namely below 40% by weight. It would in contrast be desirable to be able to operate with a higher solids content, since then less solvent would be required. Less solvent would entail not only lower solvent costs but also, in particular, a lower level of solvent emission on application. Moreover, according to experience to date, the solids content cannot be raised simply by adding, say, TiO
2
, since this will adversely, affect the physical and/or chemical properties of the coating material. Up until now, therefore, a level of 40% by weight for the overall solids content has been regarded as an upper limit if processability, and physical and/or chemical properties, are still to satisfy these requirements.
Against this background, the technical problem on which the invention is based is to specify an interior coating material whose solids content is markedly increased but which nevertheless satisfies all the requirements in respect of the physical and/or chemical properties and processability, the adhesion between interior coating material and base material (or primer coat) and between interior coating material and sealant coat, and the resistance to aggressive contents.
In order to solve this technical problem the invention teaches an interior coating material for container closures, having the following components: a) a polymer from the group consisting of epoxy resins based on bisphenol A diglycidyl ether or bisphenol F diglycidyl ether, epoxidized novolaks, phenol-formaldehyde condensates, acrylate resins, polyester resins and melamine resins, or a mixture of such polymers, b) a halogenated polymer from the group consisting of polyvinyl chlorides (PVC), or a mixture of such halogenated polymers, c) a substance from the group consisting of TiO
2
, SiO
2
, Fe
x
O
y
and BaSO
4
, or a mixture of such substances, and d) a customary solvent or a mixture of such solvents, the amounts of components a), b) and c) employed being chosen subject to the proviso that the ready-to-apply interior coating material has an overall solids content of more than 40% by weight, with the proportion (based on the solids) of the employed component b) and c) to the employed component a) being greater than 0.5:1 and with the proportion (based on the solids) of component b) to component c) being within the range from 0.5:1 to 10:1. —Epoxidized novolaks are epoxidized polycondensates of formaldehyde and phenols, which are prepared under acid catalysis. Novolaks contain no methylol groups and belong to the group of the phenolic resins. It is also possible in principle, however, to employ phenolic resins which do not belong to the novolaks group. Acrylate resins are thermoplastic or heat-curable resins which are obtained by homo- or copolymerization of (meth)acrylic esters. Functional groups, such as hydroxyl or carboxyl groups, can be introduced by way of comonomers. Polyester resins are polycondensation products of carboxylic acids having a functionality of two or more with alcohols. Melamine resins are polycondensates of melamine with carbonyl compounds, especially with formaldehyde, possibly modified with urea and/or phenol. The group of the polyvinyl chlorides also includes those halogenated vinyl chloride polymers which are modified with, for example, (meth)acrylates, vinyl acetate, maleic acid, vinylidene chloride or acrylonitrile. Examples of customary solvents are butanol, butylglycol, diacetone alcohol (4-hydroxy-4-methyl-2-pentanone), hydrocarbons, and solvents obtainable commercially under the designations Imsol R or Solvesso 150. Imsol R is a mixture of dimethyl esters of adipic, glutaric and succinic acids.
The following substances are particularly preferred as components a) and c). A particularly suitable component a) is a preferably thermoplastic acrylate resin. Such resins preferably also comprise high molecular mass, noncrosslinking polyacrylate resins which as monomers preferably include acrylic acid, acrylonitrile, acrylamide and also modifications and mixtures thereof. The preferred component c) is essentially TiO
2
. For coloring or for adjusting the gloss it is possible, for example, to add small amounts of iron oxide pigments (Fe
x
O
y
) and/or SiO
2
.
The invention is based on the
Groen in't Woud Wilhelmina Andrea Marie
Schoots Johannes
Altman Deborah M.
PPG Industries Ohio Inc.
Rajguru U. K.
Seidleck James J.
Uhl William J.
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