Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1998-03-06
1999-11-09
Marquis, Melvyn I.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525902, 525106, 525474, 525479, 525 63, C08L 8300
Patent
active
059816597
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to the use of precrosslinked silicone elastomer particles with an organic-polymer shell as a formulation constituent in powder coatings, and to powder coating compositions based on thermoplastic or thermosetting binders comprising precrosslinked silicone elastomer particles with an organic-polymer shell.
BACKGROUND OF THE INVENTION
Powder coatings consist of solid binders based on thermoplastic or thermosetting polymers, such as epoxy, polyurethane, acrylic or polyester resins, on pigments and on further additives, for example crosslinking catalysts. These compositions are applied in powder form to predominantly metallic substrates. The thermoplastic or thermosetting binders mentioned are generally hard but brittle; to improve the film properties, therefore, impact modification of the polymer systems is frequently necessary.
In order to obtain good impact strengths while retaining the existing, desired polymer properties such as hardness, dimensional stability and mechanical strength, the impact modifier must be incorporated into the thermoplastic or thermosetting systems in the form of separate, discrete microphases with optimized particle size and particle morphology. This can be carried out in a controlled and reproducible manner only by employing the impact modifier in the form of particles with a defined size and a defined size distribution as blend component. In addition, the particulate modifier must be highly compatible with the polymer matrix. In that case, the domain sizes of the modifier phase are defined exactly by way of the particle diameter. Only in the case of complete phase separation does no undesirable plastification of the polymer matrix occur, which would result in a loss of or adverse effect on the properties of the polymer matrix such as hardness, dimensional stability and mechanical strength.
Silicones are known as modifiers for thermoplastics or thermosets and are of particular interest since they not only increase the impact strength but also improve low-temperature flexibility, weathering resistance, resistance to temperature change and chemical resistance of thermoplastic and thermosetting organic-polymer systems. Generally disadvantageous, however, is the fundamental incompatibilty of silicones with organic polymers. Because of this incompatibility, the use of silicone oils and silicone resins as additives to binders for powder coatings generally gives rise to problems with processing, such as contamination in the mixing and extrusion equipment. On application it is possible for defects in flow to occur, and migration of the silicones produces problems with adhesion and in the context of overcoatability.
In U.S. Pat. No. 5,280,098, epoxy-functional silicone resins are described as sole binder or as binder constituent, in combination with organic resins, for the formulation of powder coatings. The introduction of the epoxide groups is intended to improve the elasticity and the compatibility with the organic resin. The concept of controlled microphase separation cannot be realized with the epoxy-functional silicone resins, since they do not have a particulate structure with a defined particle diameter.
U.S. Pat. No. 5,227,435 proposes the substitution in powder coatings of the polyester binder by silicone-modified polyesters which are obtained by condensing OH-functional siloxanes with glycol, followed by esterification with carboxylic acids and reaction with anhydrides. EP-A 275051 relates inter alia to acrylate-grafted silicone resins which are described as binders for powder coatings having an improved profile of properties of the coating films obtainable therewith.
A disadvantage of the procedure according to U.S. Pat. No. 5,227,435 and EP-A 275051 is that the silicone copolymers described therein are described as binders for replacing the conventional thermoplastics or thermosets. Consequently, the silicone constituent must be incorporated into the respective polymer system by complex chemical reaction, each specific binder system ha
REFERENCES:
patent: 5223586 (1993-06-01), Mautner et al.
patent: 5227435 (1993-07-01), Kang et al.
patent: 5280098 (1994-01-01), Witucki et al.
patent: 5587424 (1996-12-01), Langstein et al.
Deubzer Bernward
Geck Michael
Goeblmeier Walter
Patrick Ekkehard
Marquis Melvyn I.
Milstead Mark W.
Wacker-Chemie GmbH
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