COATING COMPOSITION AND ITS USE AS A PRIMER FOR PLASTICS SURFACES

A coating composition and its use as a primer for plastics surfaces This invention relates to a coating composition based on ethylene/vinyl acetate copolymers, chlorinated polyolefins, epoxy resins and organic solvents which is particularly suitable for use 'is a primer or coupling agent for coatings on plastics substrates. The invention also relates to the use of the coating composition as a primer on plastics surfaces.

The coating of plastics surfaces, particularly poly¬ propylene surfaces, with coating compositions is often problematical on account of the poor adhesion properties of the coating compositions. This applies in particular to the coating of plastics parts in vehicle construction and in the repair of vehicle parts, particularly based on plastics. The coating of polypropylene surfaces has proved to be particularly difficult. For example, the poly- propylene has to be pretreated to obtain favorable adhesion of coating compositions, particularly fillers and paints.

The object of the present invention is to provide a primer which is particularly suitable for the coating of plastics substrates and enables the plastics substrates to be painted with favorable adhesion without any need for complicated pretreatment.

According to the invention, this objected is achieved by the provision of a coating composition containing a) 1 to 5% by weight of one or more ethylene/vinyl acetate copolymers containing 27 to 42% by weight vinyl acetate units, b) 0.5 to 5% by weight of one or more chlorinated poly¬ olefins with a chlorine content of 10 to 25% by weight, c) 0.01 to 5% by weight of one or more epoxy resins based on aromatic polyols with epichlorohydrin, d) 85 to 98.49% by weight of one or more organic solvents and, optionally, paint auxilliaries, pigments and/or fillers.

The coating composition according to the invention contains 1 to 5% by weight and preferably 2 to 4% by weight ethylene/vinyl acetate copolymers. The chlorinated poly- olefin, which may also be a mixture of several chlorinated polyolefins, is present in a quantity of from 0.5 to 5% by weight and preferably from 2 to 3% by weight. The epoxy resins which the coating composition according to the invention contains are present in a quantity of from 0.01 to 5% by weight and preferably in a quantity of from 0.05 to 1% by weight.

Suitable ethylene/vinyl acetate copolymers are the copolymers which are typically used, for example, for hotmelt adhesives and which are soluble in typical lacquer solvents. Ethylene/vinyl acetate copolymers suitable for use in accordance with the invention preferably have a vinyl acetate content of 27 to 42% by weight. Examples of suitable ethylene/vinyl acetate copolymers are the com- mercial products ELVAX which have vinyl acetate contents of from 27 to 42% by weight and more especially from 30 to 40% by weight.

Suitable chlorinated polyolefins are, for example, chlorinated polyethylene, chlorinated polypropylene or 2 5 mixtures thereof and, more preferably, chlorinated poly¬ propylene of the type typically used for paint resins. A chlorine content of 10 to 25% by weight is preferred.

Chlorinated polyolefins of the type in question are commercially available products.

The epoxy resin used in the coating composition according to the invention is a reaction product of an aromatic polyol, more especially a bisphenol, such as bis- * TRADE-MARK phenol A, bisphenol B and bisphenol F, with epichloro- hydrin. Reaction products of bisphenol A and epichloro- hydrin are particularly preferred. The preferred molecular weights are in the range from about 250 to 750 for an epoxide value of from 0.3 to 0.7 (number of mois epoxide oxygen per 100 g resin). Examples are commercial products suitable for paint purposes, for example a reaction product of bisphenol A and epichlorohydrir» having a molecular weight of from about 350 to 400 and an epoxide value of from about 0.50 to 0.55.

The coating compositions according to the invention contain from 85 to 98.49% by weight of an organic solvent.

Suitable organic solvents are any of the organic solvents typically used in paints which are suitable for dissolving the other constituents. Preferred organic solvents are aromatic solvents, such as for example xylene and, more preferably, toluene, optionally in admixture with one another and with other solvents.

In addition to the above-mentioned quantities of individual components, the coating compositions according to the invention may contain other constituents, including for example typical paint auxiliaries, pigments and/or fillers.

The coating compositions according to the invention are ready-to-use, for example sprayable, compositions.

They are preferably applied by spraying. The compositions according to the invention may be sprayed, for example, as primers onto plastics surfaces. Any plastics surfaces are suitable, plastics of the type used in motor vehicles being particularly suitable. It has surprisingly been found that the coating composition according to the invention may be used in particular as a primer for polypropylene surfaces, so that there is no need for any of the special pretreat- ments hitherto necessary for the painting of polypropylene substrates.

Accordingly, the coating compositions according to the invention are particularly suitable for use as primers for surfaces that are difficult to paint, particularly plastics surfaces and, preferably, polypropylene surfaces, of the type used in the construction and repair of motor vehicles.

Accordingly, the coating compositions according to the invention are particularly suitable for the painting and repair of motor vehicles and moi-.or vehicle parts having plastics surfaces.

The paint coatings are applied by the two-coat or three-coat process. Depending on the level of stressing envisaged, they are applied by the two-coat system (par¬ ticularly for internal stressing) or by the three-coat system (particularly for external stressing). As a primer, the coating composition according to the invention is applied, for example, by spraying to the substrate to be painted. Subsequent drying in air, for example for about minutes, is sufficient, although oven drying is also possible. Typical fillers and/or finishing paints, for example typical car repair paints, preferably elasticized two-component polyurethane products, may then be applied to the coating obtained.

EXAMPLE A coating composition was prepared by dissolving 2.6 parts by weight of an ethylene/vinyl acetate copolymer containing 33.0% by weight vinyl acetate, 6.6 parts by weight chlorinated polyolefin (40% in xylene) containing 18 to 23.5% by weight chlorine and 0.1 part by weight of an epoxy resin based on bisphenol A and epichlorohydrin having a molecular weight of approximately 370 in 18 parts by weight toluene. The composition was then diluted to a sprayable viscosity with 72.7% by weight toluene.

The coating composition thus obtained was sprayed onto a degreased, cleaned polypropylene surface in a layer thickness of 4 /jm. The coating thus applied was dried in air for 20 minutes and overpainted with a polyurethane filler and then with a polyurethane paint. An excellently adhering coating of optically satisfactory appearance was obtained.