Agitating – Method
Reexamination Certificate
1999-11-19
2001-06-05
Soohoo, Tony G. (Department: 1723)
Agitating
Method
Reexamination Certificate
active
06241382
ABSTRACT:
The present invention relates to a process for producing powder coating materials comprising lustre pigment.
Coatings are produced generally by applying complete coating compositions, i.e. coating systems which at the time of application contain all the necessary components, such as binders, pigments, fillers, additives, solvents, etc., of a coating.
Powder coating materials, i.e. solvent-free and eco-friendly coating systems, are usually also applied as complete, materially uniform systems. In some cases this leads to great technical problems, especially in the case of powder coating materials comprising lustre pigment.
The powder coating material is generally produced by dry mixing of the various components of the powder coating material, such as resin, curing agents, pigments, levelling agents, etc. This mixture is then fed in a suitable melt mixer in which the components are mixed in the melt at an elevated temperature. The liquid homogeneous melt material mixture produced by the extruder is converted to flake form on cooling.
The grinding process, which follows flake conversion in the case of conventional powder coating production, is suitable only for powder coating materials which do not include lustre pigments; this is because the platelet-shaped lustre pigments, during the process of grinding the flakes to powder, are mechanically destroyed, which results in reductions in gloss and in the loss of the optical properties actually desired.
In general, powder coatings are produced by applying the powder coating material, which consists of fine particles, to the substrate that is to be coated, using electrostatic powder spraying equipment—for example, by means of corona or tribo charging. The powder coating material can of course also be applied using fluidized-bed coaters.
There is therefore a great need for a simple and cost-effective process for producing powder coating materials comprising lustre pigment which exhibits little if any of the disadvantages of conventional processes.
Surprisingly, a very gentle process for producing powder coating materials comprising lustre pigment has now been found, in which the platelet form of the lustre pigments is very substantially retained and there is virtually no effect on the optical properties. The term lustre pigments as used herein embraces metallic pigments in particular and pearl lustre pigments most especially.
The invention provides a process for producing powder coating materials comprising lustre pigment, characterized in that
(A) the starting materials, consisting of the customary powder coating components and one or more lustre pigments, are first of all introduced into the filling chamber of a first vessel (
1
) which has a mixing element (
3
) and is provided if desired with a thermostat (
4
), subsequently a supercritical fluid is admitted to the filling chamber, and finally the starting materials are mixed in the presence of the supercritical fluid
and
(B) the mixture of the customary powder coating components and one or more lustre pigments and the supercritical fluid is transferred by a distributor (
6
) into a second vessel (
2
), the distributor having a plurality of nozzles with an aperture diameter of from 0.0025 cm to 2.5 cm, and in the course of transfer the second vessel is maintained at an internal pressure of from 0 bar to 350 bar and at a temperature of from −85° C. to 200° C.
The invention additionally provides powder coating materials obtainable by this process which are notable for their high proportion, i.e. in particular 10-50% by weight, of lustre pigments, and provides for the use of the powder coating materials for colouring and tinting other powder coating materials by means, for example, of the dry-blend process, which is known, inter alia, from EP 0 176 132.
The process of the invention permits the simple and cost-effective production of powder coating materials comprising lustre pigment which feature a high lustre. Furthermore, the process of the invention produces powder coating materials of high flowability, frequently without the need to add flow aids; should, however, the addition of a flow aid be desired in a particular instance, the amount of flow aid required to obtain a certain level of flowability is substantially lower than for powder coating materials not produced in accordance with the invention.
For the production of the powder coating materials comprising lustre pigment, there are provided at room temperature one or more lustre pigments and the customary powder coating components with or without customary additives, a source of a supercritical fluid, a first vessel with a mixing element, and a second vessel. The lustre pigments and the customary powder coating components along with the supercritical fluid are introduced into the first vessel and a homogeneous powder coating solution/dispersion is prepared. Where the powder coating material comprising lustre pigment includes conventional pigments and fillers in addition to the lustre pigments, it is advisable first of all to disperse the customary powder coating components with the conventional pigments and/or fillers under relatively high shear conditions beforehand. Subsequently, the lustre pigments are then added, and are mixed under lower shear conditions with the powder coating components. Thereafter, the contents of the first vessel are transferred to the second vessel, which is under a lower pressure than the first vessel.
In accordance with the process of the invention, the lustre pigment component is incorporated securely into the powder coating particles. It is particularly surprising that the powder coating materials produced by the process of the invention and comprising lustre pigment exhibit a high gloss and that none of the problems otherwise common with powder coating materials comprising lustre pigment arise. A point worthy of emphasis is the ease of handling, in comparison to prior art mixing arrangements, of the mixing apparatus used in accordance with the invention, which can be operated even for small batches and can be cleaned quickly and with ease.
The proportion of the lustre pigment component in the finished powder coating material can be between 0.1 and 50% by weight, in particular between 1 and 20% by weight, based on the mass of the mixture.
The lustre pigment component can comprise commercial metal pigments in powder form, e.g. Standard® from Eckart, lustre pigments, such as Paliocrom® pigments from BASF and especially pearl lustre pigments, as are described, for example, in the German Patents and Patent Applications 14 67 468, 19 59 998, 20 09 566, 22 14 545, 22 15 191, 22 44 298, 23 12 331, 25 22 572, 31 37 808, 31 37 809, 31 51 343, 31 51 354, 31 51 355, 32 11 602, 32 35 017 and 38 42 330 and are marketed by Merck KGaA, Darmstadt under the tradename Iriodin®. Particularly preferred pearl lustre pigments are TiO
2
/mica pigments and/or Fe
2
O
3
/mica pigments. The lustre pigment used, for example, can also be graphite, coated graphite, TiO
2
, SiO
2
and Al
2
O
3
platelets, BiOCl, chiral nematic crosslinked liquid-crystal platelets, the latter as marketed, for example, by Wacker, FRG, dielectric layer pigments, e.g. from Flex, USA, or holographic flake pigments, as known, for example, from U.S. Pat. No. 5,415,950. The lustre pigment employed can also be a mixture of the pigments stated.
Suitable powder coating components are all raw materials employed in conventional powder coating materials. Resin components are, in particular, reactive epoxies, polyesters, polyurethanes or acrylates; also suitable in principle, however, are other polymers which can be both reactive and thermoplastic. Particular preference is given to polyester systems, epoxy systems and polyester-epoxy systems.
In addition, the powder coating materials of the invention may also include further components, such as curing agents, levelling agents, flow aids, stabilizers, pigments and/or fillers, for example. Examples of further possible additives are tribo additives.
Both liquids and gases are used as supercritical fluid.
Kieser Manfred
Stahlecker Otto
Merck Patent Gesellschaft mit beschrankter Haftung
Millen White Zelano & Branigan P.C.
Soohoo Tony G.
LandOfFree
Method for producing powder lacquer containing gloss pigments does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing powder lacquer containing gloss pigments, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing powder lacquer containing gloss pigments will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2513037