The present invention pertains to a hardenable copolymer of tetrafluoroethylene (C.sub.2 F.sub.4), at least one other monomer selected from chlorotrifluoroethylene (C.sub.2 F.sub.3 Cl) or vinylidene fluoride (C.sub.2 H.sub.2 F.sub.2), an allylic polyol, and an allylic or acrylic monomer with a fluorocarbon chain. This copolymer is soluble in organic solvents and is particularly recommended for the fabrication of paints and varnishes whose principal properties include resistance to stains and soiling.
The fluorinated polymers are known for their good mechanical properties and their excellent resistance to chemical products and weather. However, their lack of solubility in conventional solvents prevents their use for certain applications such as resin for paints and varnishes where their properties are desired for the production of coatings with good resistance and easy maintenance.
In order to take advantage of the properties of the fluorinated polymers while avoiding their drawbacks, attempts have been make to make them soluble in the conventional organic solvents. In order to accomplish this, it is known to diminish the crystallinity of the fluorinated polymers by copolymerization of ethylenically unsaturated monomers, at least one of which is fluorinated. Because of its low crystallinity, such polymers generally have mediocre mechanical properties and, particularly, poor hardness. For this reason, it is desirable for certain applications, particularly when employing them in the fabrication of paints and varnishes, to preserve a sufficient degree of rigidity and to make them hardenable by incorporating functional groups in their structure.
Such hardenable fluorinated copolymers are described in French Patent No. 2,488,260. They have fluorine atoms at the alpha position of the principal chain which is indispensable for a product with good aging properties. The presence of fluorine atoms at the alpha position of the principal chain also brings to bear an effect of not retaining dust which is manifested by the fact that fluorinated paints soil less quickly then other paints. However, the presence of the fluorine at the alpha position of the principal chain is markedly insufficient to assure, in particular, protection against graffiti in the case of light-colored paints where a "ghost" image of the inscription will always subsist even after cleaning. In attempting to improve this stain-resistance characteristic, many solutions have been envisaged, principally involving the techniques described in the documents below.
In order to prevent coatings from becoming soiled quickly by dust, there is proposed in EP 186,186 a soil-resistant coating characterized by the combination of a fluorinated polymer that has reactive sites with specific fluorcarbon compounds of the type: EQU CF.sub.3 --(CF.sub.2).sub.n --CH.sub.2 --CH.sub.2 --OH EQU or EQU OH--CH.sub.2 --CH.sub.2 --(CF.sub.2).sub.m --CH.sub.2 --CH.sub.2 --OH
The addition of these products in small quantities generally does not have a stain-resistant effect. In larger amounts, they limit the cross-linking capability of the film and subsequently lead to the flotation of pigments in the paints and varnishes and thus have a negative impact on the regularity of the colors applied.
In EP 311,052 there is described a soil-resistant coating obtained by combination of a fluorinated polymer and a specific copolymer containing fluorine in the form of a polyfluorocarbon chain and molecular constituents from a hydrophillic monomer. The introduction of this specific copolymer does not have a favorable effect on the aging characteristics of the coating.