Stock material or miscellaneous articles – Composite – Of epoxy ether
Utility Patent
1999-08-09
2001-01-02
Dawson, Robert (Department: 1621)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C525S438000, C525S533000
Utility Patent
active
06168865
ABSTRACT:
The present invention relates to a coating composition comprising one or more hydroxyl-containing, modified or nonmodified polyesters and one or more hydroxyl-reactive crosslinkers.
The invention additionally relates to processes for preparing these processing compositions and to their use for coating metal substrates, especially for the exterior coating of packaging containers.
Packaging containers, for example cans, tubes, canisters, pails and the like, generally have a coating on their exterior faces that serves primarily for decoration and to protect the packaging containers against corrosion. For this reason, a fundamental requirement of suitable coating compositions is unhindered processing and the development of flawless surfaces. The flawless decoration must, however, withstand the sometimes extreme stresses in the course of preparation and use of the packaging containers (folding, flanging, deformation, sterilization, pasteurization, etc).
The exterior coating of packaging containers generally consists of a multicoat system comprising a basecoat as support for the decoration, a coating of printing ink and, if desired, a colorless protective coat, the so-called “silver varnish”. Particularly stringent requirements are placed on basecoats which are not provided with a colorless protective coating as outer finish. Such basecoats are also known under the name non-varnish outer coating.
Non-varnish outer coatings must be particularly compatible with the subsequent printing; in other words, they must be readily printable and exhibit good adhesion promotion and a good condensation effect. The resulting coatings must be of high gloss, i.e. have a degree of gloss (60° reflection angle)>80 and high whiteness and must possess high abrasion resistance and a smooth surface structure, i.e. must, for instance, exhibit no craters or the like. In addition, they must have these good properties even after the conditions of sterilization and/or pasteurization.
Non-varnish exterior coatings of this kind are known (cf. e.g. Ullmanns Encyklop{umlaut over (a)}die der technischen Chemie, 4th edition, 1978, volume 15, pages 713-714). Base raw materials for these coatings are modified alkyd resins, epoxy resins, epoxy resin esters, polyester and polyacrylate resins and also usually amino- or phenol-formaldehyde resins or isocyanates as crosslinking components.
With the increasing production speed of the coating lines for two-piece beverage cans and the like, and the high stress on the applied coating composition in the so-called “spin necking” process, in which the cans are subjected to very high deformation in their upper region, great problems occur with the known exterior can coatings. For instance, it must be ensured, even with the extremely severe deformation during spin necking, that there is no damage to the coating film. This requirement can only be met by means of coating compositions which lead to flexible coating films. On the other hand, however, it must also be ensured that the resulting coatings withstand the extreme mechanical stresses in the course of both can production and can filling. This means that the resulting coating films must have high abrasion resistance and a correspondingly high hardness, especially scratch hardness. It is true that isocyanate-crosslinked systems meet the requirement for good elasticity coupled with good hardness, but such systems have the disadvantage of a marked tendency to yellow in the case of pigmented white paints.
A further disadvantage of the known coating compositions is that they are conventional, i.e. organically dissolved, systems. Because of the prescribed application viscosities, these coating compositions usually comprise between 30 and 50% by weight of organic solvent, resulting in severe pollution of the environment as a result of solvent emission when the coatings are baked. Accordingly, increased efforts are being made to provide aqueous systems.
U.S. Pat. No. 4,247,439 and European Patents Nos. 6334 and 6336 disclose hydrolysis-stable aqueous coatings, in particular for interior can coating, which are obtained from esterification products of epoxy resins with carboxyl-functional polyacrylate resins.
Furthermore, U.S. Pat. No. 4,212,781 discloses resin mixtures which can be dispersed in an aqueous, basic medium and are obtained by copolymerization of ethylenically unsaturated monomers, in part containing carboxyl groups, in the presence of an aliphatic or aromatic 1,2-diepoxy resin using at least 3% by weight, based on the monomer weight, of benzoyl peroxide or equivalent initiators. The resin mixtures known from U.S. Pat. No. 4,212,781 can be crosslinked with amino resins. They are particularly suitable for the spray coating of beverage cans.
DE-A 34 46 178 discloses water-thinnable compositions for the coating of metal cans, the polymer present in the composition consisting of a reaction product of acrylic monomers, a high molecular weight epoxy resin, a phenol-formaldehyde resin and a free-radical initiator.
The prior-art aqueous systems for the exterior coating of two-piece beverage cans are primarily employed on aluminum substrates. They have the disadvantage that on problematic substrates, for example deep-drawn and wall-ironed beverage cans made of tinplate, they offer inadequate surface protection.
Moreover, the international patent applications with the international publication numbers WO 88/01287 and WO 91/10712 disclose coating compositions for interior can coating where the binder is obtainable by first of all esterifying an epoxy resin with a polyester and, in the presence of this reaction product, preparing an acrylate copolymer. A disadvantage, however, is that the process for preparing the binders is very complex.
Finally, WO 90/10678 discloses conventional coating compositions for exterior can coating, comprising as binders hydroxyl-containing, modified or nonmodified polyesters and/or hydroxyl-containing acrylate copolymers and/or hydroxyl-containing epoxy resins and, as crosslinkers, blocked isocyanates and/or amino resins. Further details regarding suitable binder mixtures are, however, not present in WO 90/10678. Rather, it is essential to the invention that these coating compositions described in WO 90/10678 contain a wax paste as lubricant which comprises at least one polyolefin wax, at least one hydroxyl-containing acrylate copolymer, optionally one or more melamine-formaldehyde resins and organic solvent. A feature of these coating compositions known from WO 90/10678 that is in need of improvement is the pasteurization resistance of the resulting coatings.
The object of the present invention is therefore to provide a coating composition which is suitable for the coating of metal substrates, especially for the exterior coating of packaging containers, preferably deep-drawn beverage cans, and which should be available for use both conventionally and in the form of aqueous binder dispersions. The coatings produced from these coating compositions should combine good hardness with a high elasticity so as to withstand the mechanical stresses in the course of can production and can filling. Furthermore, the coatings should have a smooth surface structure, a high degree of gloss and good printability, and should in particular possess good adhesion to the various can materials, for example tinplate, blackplate and surface-treated steel and also aluminum. Furthermore, the coating compositions under discussion should be capable of application using the customary equipment.
In the case of the aqueous coating compositions, they should as far as possible attain the level of properties of known conventional exterior coatings in respect of hardness, elasticity, adhesion and resistance to pasteurization and to solvents. Furthermore, such aqueous coating compositions should preferably exhibit a long shelf life of the binder dispersions.
This object is achieved in accordance with the invention by a coating composition of the type specified at the outset which are characterized in that the coating composition comprises a
Chmielewski Dietmar
Keweloh Ludger
Kipp Jörg
Köster Bernhard
Vogdanis Lazaros
Altman Deborah M.
Aylward D.
Dawson Robert
PPG Industries Ohio Inc.
LandOfFree
Coating agent, process for producing the same and its use,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coating agent, process for producing the same and its use,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coating agent, process for producing the same and its use,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2546759