Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
1999-02-01
2001-09-18
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C525S440030
Reexamination Certificate
active
06291624
ABSTRACT:
The present invention relates to a novel family of compositions containing masked isocyanates and polyols. The invention relates more particularly to powders, including mixtures of powders, and to their use as powder in coatings.
For reasons associated with protection of the environment and safety at work, it is increasingly sought to eliminate the use of solvents in coating techniques and particularly paint. More particularly, reducing VOCs (Volatile Organic Compounds) is an increasingly current preoccupation in the paint and varnish industry. With this aim, the development of products with higher solids content makes it possible to decrease the amounts of solvents required to achieve the application viscosity, and thus to reduce the solvents evaporated during drying of paint film.
Another alternative is to use products in aqueous phase in which the water has replaced the organic solvents as the agent carrying the organic binder. However, a small amount of organic solvent is required to use and form the film of paint. Furthermore, they give rise to water-soluble residues which may be tricky and expensive to process.
In this context, coating techniques using powders are increasingly being developed. A few details of this technique should be given herein in order to gain a better understanding of the present invention. The technique uses a very finely powdered material for which air acts as a vector.
In general, an electrostatic charge of several kilovolts applied between a gun and the article to be painted allows the coating precursor powder, which will be sprayed by the applicator gun, to be attracted and retained.
Firing of the article between 150 and 200° C. allows melting, spreading and then crosslinking of the paint powder (paint being considered the ultimate example for coatings) in order to obtain a uniform and homogeneous layer of the coating.
This technique is non-polluting and has an application yield of close to 100% by virtue of the possibility of recycling the unused powder.
Among the families of products which may be used in this field, mention should be made of those which are the subject of the following summary:
The majority of the market is occupied by so-called “epoxy-polyester hybrid” powder paints, followed by polyesters and polyurethanes, and then so-called “epoxy” powders.
In order to obtain good quality strength on exteriors (in particular with respect to UV radiation and moisture), it is essential to use coatings based on TGIC-polyester or polyurethane which, alone, make it possible to achieve the required levels of performance.
The coating powders may be in several finishes (surface aspect, color, sheen, etc.).
The technique used to achieve these effects is different for conventional liquid paints and powder paints.
When it is desired to modify the sheen, the addition of fillers such as silicas, carbonates of calcium or barytas makes it possible to reduce the sheen in a range from 50 to 90%, but matt finishes cannot be obtained.
In the present invention, a hardened, smooth or structured coating which, when applied to a metal support, has a coefficient of reflection which is at most equal to about 50% at a 60° angle of incidence is defined as a matt or satin system.
However, the systems which are the most difficult to obtain correspond to coatings which are quite clearly matt, that is to say having a sheen of less than about 30% for a 60° angle of incidence or less than about 40% at an 85° angle of incidence.
One of the techniques most commonly used in order to obtain matt finishes comprises combining compounds with very different reactivities.
This is achieved by mixing paint powders having short and long gel times. In this way, microscopic heterogeneity will be obtained at the surface of the coating, thus creating the desired matt effect.
Other techniques make it possible to reduce the sheen of paints. They comprise using additives or waxes but, on the one hand, they are not sufficient by themselves and, on the other hand, when they are used alone, they generally have reproducibility problems and/or mechanical properties that are really quite insufficient, and/or do not allow them to be used externally due to their yellowing or the deterioration of the film due to bad weather.
The system most commonly used externally is that known under the name dry-blend, according to which low sheen is obtained by blending extruded and ground powder paints which each have a very different reactivity. Besides the fact that this system is time-consuming and that it involves the manufacture (extrusion, grinding, blending) of several paints, it exhibits a reduced uniformity of the degree of sheen desired, thereby requiring more steps than usual and involving additional cost.
The compounds obtained from the crosslinking reactions should also not be harmful either to human or animal health or to the environment.
For further details regarding the techniques of powder painting, reference may be made to the following books:
P. Grandou and P. Pastour: Peintures et Vernis [Paints and Varnishes]:
I les constituents
II techniques et industries [techniques and industries]; published by Hermann;
R. Lambourne:
Paints and Surface Coatings, theory and practice; published by Halsted Press;
Powder Coating. The Complete Finisher Hand Book; the Powder Coating Institute;
Myers and Long:
Treatise on Coatings, 5 volumes; published by Marcel Dekker.
Accordingly, one of the aims of the present invention is to provide a composition which makes it possible to obtain coatings by the so-called powder technique.
One of the aims of the present invention is to provide a composition which makes it possible to obtain coatings with good resistance to bad weather.
Another aim of the present invention is to provide a composition which makes it possible to obtain matt and/or satin coatings.
Yet another aim of the present invention is to provide a composition of the above type which is easy to use.
These aims and others which will appear hereinbelow are achieved by means of a composition which contains, for successive or simultaneous addition:
an isocyanate which is at least partially masked, having a glass transition temperature (sometimes denoted by the abbreviation Tg) of at least about 20° C., advantageously of at least 40° C., and a degree of liberation (with respect to the masking agent) at 120° C. of not more than 5%;
a polyol having the following characteristics:
a glass transition temperature (sometimes denoted by the abbreviation Tg) which is at least equal to about 40° C., advantageously at least equal to about 50° C.;
a hydroxyl number at least equal to about 10 mg/g, advantageously at least equal to about 15 mg/g;
an average molecular mass Mn at least equal to about 1000 g/mol and advantageously to 2000 g/mol.
In the present description, the term “about” is used to emphasize the fact that the value is rounded up and that, when the figure(s) furthest to the right of a number are zeros, these zeros are positional zeros and not significant figures unless, of course, otherwise stated.
This composition already had a major advantage over the prior art: the above aims and others which will become apparent hereinbelow by means of a composition, in particular of the above type, which also contains at least one, advantageously two, and preferably three of the following characteristics:
the presence of a carboxylic function, in particular in the form of a mixed masked isocyanate (see below);
the presence of a solid esterification catalyst (see below);
a matt-effect wax (see below).
The carboxylic function is advantageously in intimate mixture with the isocyanate component of the composition. It is even desirable for the carboxylic function to be grafted onto the isocyanate system via an agent bearing both a reactive function (i.e., having a so-called labile hydrogen) with the isocyanate function and a carboxylic function (COOH in salt form or, advantageously, in free form). It is highly desirable for this agent bearing a carboxylic function to be a masking agent.
It is preferable fo
Ardaud Pierre
Bernard Jean-Marie
Vogin Bernard
Williams Francis John
Burns Doane Swecker & Mathis L.L.P.
Gorr Rachel
Rhodia Chimie
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