Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-04-21
2002-05-07
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S109000, C522S011000, C522S112000, C522S104000, C522S107000, C522S150000, C522S153000, C522S154000, C525S028000, C525S032100, C525S032200, C525S036000, C427S508000, C427S512000, C428S480000, C428S482000, C428S500000
Reexamination Certificate
active
06384102
ABSTRACT:
DESCRIPTION
The present invention relates to novel radiation-curable powder compositions comprising a mixture of at least one semi-crystalline polyester containing end methacryloyl groups and of at least one acrylic copolymer containing ethylenically unsaturated groups, as well as to the preparation and to the uses of the said compositions.
More particularly, the -present invention relates to powder compositions curable by ultraviolet irradiation or by accelerated electron beams, the binder of which is composed of a mixture of at least one semi-crystalline polyester containing end methacryloyl groups and of at least one acrylic copolymer containing ethylenically unsaturated groups, and preferably acryloyl or methacryloyl groups, and which lend themselves to the production of paint and varnish coatings exhibiting a unique array of properties, inter alia excellent hardness and flexibility, notable resistance to solvents and at the same time good stability on storage.
Heat-curable powder compositions are well known in the state of the art and are widely used as paints and varnishes for coating the most diverse objects. The advantages of these powders are manifold; on the one hand, problems due to solvents are completely eliminated and, on the other hand, the powders are 100% used, insofar as only the powder in direct contact with the substrate is retained by the latter, the excess powder being, in principle, fully recoverable and reusable. This is why these powder compositions are preferred with respect to coating compositions which are provided in the form of solutions in an organic solvent.
Heat-curable powder compositions have already found a wide outlet in the coating of domestic electrical appliances, automobile industry accessories, metal furniture, and the like. They generally contain heat-curable organic compounds which constitute the binder for the paint, fillers, pigments, catalysts and various additives for adapting their behaviour to their use.
Different types of heat-curable powder compositions exist. The- most well known compositions contain, as binder, polyesters containing carboxyl groups or hydroxyl groups, acrylic copolymers carrying glycidyl, carboxyl or hydroxyl groups, and the like, as a mixture with crosslinking agents containing functional groups capable of reacting with the functional groups of the abovementioned polymers.
The acrylic copolymers containing glycidyl, carboxyl or hydroxyl groups used in heat-curable powder compositions are typically composed of alkyl acrylates and methacrylates, of vinyl or allyl monomers, of acrylamides, of acrylic or methacrylic acids, or of hydroxyalkyl or glycidyl acrylates and methacrylates. These acrylic copolymers exhibit glass transition temperatures of the order of 45 to 85° C.; it is necessary to use acrylic copolymers having such glass transition temperatures because, at lower temperatures, the compositions are unstable and reagglomerate during storage.
The viscosity at melting of the acrylic copolymers is also high, of the order of 10 to 10,000 mPa·s at 200° C. (cone/plate method). This high viscosity of the acrylic copolymers causes a series of problems. This is because, during the melting of the compositions which contain them, for the preparation of coatings, the flow of the coating is slowed down by the high value of the viscosity.
Finally, another problem lies in the stoving temperature of the heat-curable compositions containing acrylic copolymers carrying glycidyl, carboxyl or hydroxyl groups. In fact, even on carefully choosing the crosslinking agent and an appropriate catalyst for the reaction between the functional group of the acrylic copolymer and that of the crosslinking agent, it is never recommended to carry out the stoving of such compositions at temperature below 140° C., for a time of at least 10 minutes. If lower stoving temperatures are applied, the coatings obtained generally exhibit a poor surface appearance. It would therefore be desirable to find a means of lowering this temperature and this stoving time.
Moreover, even under ideal conditions, the coatings obtained from heat-curable compositions containing acrylic copolymers always exhibit a lack of flexibility and of impact resistance.
Provision has more recently been made, in order to solve the problems of flexibility and of impact resistance, for the addition of a semi-crystalline polyester containing carboxyl groups or hydroxyl groups to the heat-curable powder compositions involved here, as described in Patent Application WO 94/01505.
However, in spite of their advantageous properties, the semi-crystalline polyesters of the state of the art also exhibit significant disadvantages on an industrial scale, even if these semi-crystalline polyesters are used as an additional component for modifying commercially available conventional acrylic copolymers or polyesters.
In fact, the coatings obtained from such compositions containing semi-crystalline polyesters exhibit a reduced surface hardness (HB pencil hardness).
Moreover, in order to be curable at a moderate temperature, generally at least 140° C., acrylic copolymers require the presence of a crosslinking agent and of a catalyst. Now, for the preparation of the powder, the acrylic copolymer must be melted with the crosslinking agent, the catalyst and the other additives in an extruder at a temperature in the region of the crosslinking temperature of, the system. It follows that, without specific precautions, an undesirable premature crosslinking of the binder, by reaction between the acrylic copolymer and the crosslinking agent, already takes place during the preparation of the powder. This premature crosslinking of the binder can, without specific precautions, cause blocking of the extruder, which presents a not insignificant real danger. A powder thus prepared produces defective coatings because of the presence of gelled particles. Moreover, at the time when the molten film has to be spread over the substrate to be coated, the presence of an excessively large amount of crosslinking catalyst causes premature crosslinking, which brings about a rapid rise in the viscosity of the coating. This rise in the viscosity prevents good spreading, which results in malformations of the coating obtained, such as orange peel and the like.
In order to overcome these disadvantages, and with the aim of further lowering the stoving temperature and time for curable powder compositions containing acrylic copolymers, attempts have recently been made to use compositions curable by ultraviolet radiation or by electron beams. With this aim, use has been made of unsaturated acrylic copolymers, for example. Thus, in Patent Application WO 93/25596, good spreading of the coating and coatings having good flexibility have been obtained, by virtue of a low viscosity and of a low glass transition temperature, the powder being melted between 100 and 150° C. for a time of 10 to 30 minutes. However, this low glass transition temperature is the cause of a lack of stability on storage and of reagglomeration of the powder after a prolonged storage time at 40° C.
Consequently, it would be highly desirable to be able to have available novel binders for the manufacture of powder compositions which can be cured by ultraviolet irradiation or by accelerated electron beams and which no longer exhibit the disadvantages recalled above, due to the fact that the mechanism of crosslinking is no longer concomitant with that of melting of the powder. Such binders should make it possible to prepare powder compositions which can be cured at low temperatures, for example 100 to 150° C., and which can be rapidly melted, as during short periods of 1 to 5 minutes, before irradiation. In addition, these compositions should both exhibit good stability on storage and ensure production of paint or varnish coatings possessing excellent physical properties, in particular as regards the fluidity in the molten state, the surface appearance, the surface hardness, the flexibility and the resistance to solvents.
The surprising discovery has now been made
Loosen Patrick
Loutz Jean-Marie
Maetens Daniel
Moens Luc
Van Kerckhove Marc
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
McClendon Sanza L.
Seidleck James J.
UCB S.A.
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