Process for producing a powder coating material; a powder coating material; and the use of effect pigments

Method for preparing powder coating material; powder coating material; and use of colorful effect pigments

The present invention relates to a method for preparing powder coatings, in which binders, pigments, fillers, additives, and crosslinking agents used as appropriate are mixed in advance, and processed in an extruder in the form of a melt as appropriate to obtain a uniform mixture. And extruded granules, after cooling, grind to obtain trimmed powder coating.

As a solvent-free and environmentally friendly coating system, powder coatings are important and superior to solvent-containing coatings in many applications. They are usually composed of binders, pigments, fillers, and additives and crosslinking agents used as appropriate. They are in the form of fine particles and are usually applied to a variety of different substrate surfaces by static electricity, and the substrate surfaces are cured by baking or ray energy.

In the fluidized bed sintering method, the powder is suspended in a fluidized tank by air. When the heated substrate is immersed in the suspended powder, the polymer powder melts on the working part. It has been known that fluidized sintered powder is used to produce color effect coatings, where there is a problem of separation of color effect pigments and polymers during the fluidization process.

Basically, powder coatings can be colored with all known pigments (including known color effect pigments, which in turn include pearlescent pigments based on mica).

Pearlescent pigments are mica flakes coated with metal oxides, which are used in a variety of technical fields. They can be obtained from, for example: Merck, the registered name is lriodin. These pigments are described in, for example, German patents and patent applications 14 67 468, 19 59 998, 2009 566, 22 14 545, 22 15 191, 22 44 298, 23 13 331, 25 22 572, 31 37 808, 31 37 809, 31 51 343, 31 51 356, 31 51 355, 32 11 602, 32 35 017, 33 34 598 and 35 28 256.

Powder coatings are usually made by mixing the aforementioned components and homogenizing the mixture in a molten state in an extruder. The pressed solid agglomerates of powder coating are passed to the grinder. The powder coating is ground here to the particle size required for the application.

However, special problems occur when flake-shaped color effect pigments are used in pigment powder coatings. Because the grinding method is used during the preparation of powder coatings, most of the pigment flakes will be destroyed and the gloss effect will be reduced. Therefore, it is currently impossible to mix color effect pigments into the starting materials used to prepare powder coatings, which are different from other pigments, and then press out and grind the mixture.

To prevent the flakes of fancy effect pigments from being damaged, they can be mixed into powder coatings after grinding (dry blending). Here, the disadvantage of accumulation or depletion of the pigment on the surface of the object to be coated is observed. The reason is that the charge behavior of the powder-coated particles and the color effect pigment particles is different. High-quality methods (such as combining methods, such as the use of electrostatic force to make the blended pigments uniformly adhere to the surface of the powder-coated particles) can only solve part of the separation problem.

DE 24 34 855 describes a method for preparing powder coatings with metallic colorability, in which a brushing method is used to fix the pigment flakes on the surface of powder coated particles. The combination of powder coatings and color effect pigments with mechanical energy and possible heat energy.

The equipment required to achieve this goal is very complicated, which reflects the high manufacturing cost of gloss pigment powder coatings. In addition, the gloss of the powder coatings thus obtained is usually insufficient.

The purpose of the present invention is to avoid the aforementioned shortcomings of the prior art and to specifically propose a method for preparing powder coatings. Part of the prepared powder coatings are color effect pigments. Its purpose is to avoid the aforementioned accumulation or exhaustion of the pigment on the target to be coated and still make the coating have excellent gloss.

It has been surprisingly discovered that the use of surface-modified color effect pigments coated with low-molecular-weight polyethylene or polypropylene does not cause damage to the color effect pigment flakes encountered during grinding.

Surface-modified pearlescent pigments coated with polymers are already known, especially from German Laid-Open specification DE-A43 17 019. The pigments described in the patent specification of this application include pearlescent pigments coated with polyethylene wax. Although the patent specification of this application states in the preface: surface-coated and modified pigments can be used in varnishes, powder coatings, paints, printing inks, plastics, etc., especially cosmetic blends, but there is no mention of coating The pigments are used in the grinding method. In addition, those skilled in the art know from the references at the time that when used in powder coatings, the pigments must be added to the powder coatings sequentially, as described above. In fact, a thin layer of flake-like color effect pigments with polyethylene wax or polypropylene wax will improve the mechanical stability of the pigment, and even the grinding process will not damage the gloss.

Accordingly, the present invention proposes a method for preparing the aforementioned powder coatings, in which binders, pigments, and fillers, additives, and crosslinking agents used as appropriate are mixed in advance, and are extruded in the form of a melt as appropriate. The homogeneous mixture and extruded granules are obtained by in-machine processing, and after cooling, a finished powder coating is obtained by grinding, wherein at least a part of the pigments comprises surface-modified color effect pigments coated with low molecular weight polyethylene or polypropylene.

The preparation of the powder coating of the invention is simple and easy to operate. It is comparable to the usual way of preparing powder coatings. The binder component and the pigment component (which may include coated color effect pigments and other standard pigments) and fillers, additives and curing agents used as appropriate are mixed with a slurry mixer or an inversion mixer (for example) . During this procedure, the components can be blended simultaneously or continuously into the adhesive components. The mixture is homogenized in the extruder in the form of a melt, and after leaving the extruder, it is cooled and approximately separated. In the grinder, it is ground to the final fineness of the powder coating.

Compared with previous techniques, the powder coating obtained by the method of the present invention provides significant advantages; because it is not separated, the application reliability is improved. Because no combination method or similar compound method is required, the preparation cost is reduced. It is also possible to prepare powder coatings that can be used to rub static electricity, which was not possible before. In addition, powder coating concentrates containing fancy effect pigments can also be prepared by the method of the present invention.

The present invention also provides a powder coating composition, which contains binders, pigments and fillers, additives and crosslinking agents used under appropriate conditions, wherein at least a part of the pigments comprise surface-modified coatings with low molecular weight polyethylene or polypropylene Color effect pigments.

The color effect pigments are preferably mica pigments (pearlescent pigments) coated with metal oxide one or more times. Use these pigments to achieve the best results for gloss and color effects. But other decorative effect pigments that can be used include coated Al ₂ O ₃ Flakes, bismuth oxychloride (BiOCl), aluminum flakes, Variocrom or Paliocrom pigments (from BASF), LCP pigments (liquid crystal polymer pigments), coated glass flakes or with 3 to 9 layers (in 3, 5 Or 7 layers is better) multi-layer pigments.

Color effect pearlescent pigments can also be prepared by chemical or physical deposition in the vapor phase (CVD (chemical vapor deposition) or PVD (physical vapor deposition)), or can be prepared by deposition in an aqueous solution.

Based on the total amount of all the constituents, the content of the colorful effect pigments ranges from 0.1 to 50% by weight. Use a smaller amount, the effect is not fully displayed, and a larger amount will impair the effect. Based on the total weight of the powder coating, the content of the colorful effect pigment is preferably 0.5 to 30% by weight, preferably 0.5 to 10% by weight, and very preferably 1 to 7% by weight.

As far as the powder coating of the present invention is concerned, all commercially available powder coatings based on reactive epoxides, polyesters, polyacrylates or polyurethanes and other polymers (reactive or thermoplastic) can be used . Particularly preferred ones are polyester powder coatings, polyacrylate powder coatings, polyurethane powder coatings, epoxy-based powder coatings or polyester-epoxy-based powder coatings.

Based on the total weight of the color effect pigment and polyethylene or polypropylene, the coating amount of polyethylene or polypropylene of the color effect pigment is preferably 15 to 50% by weight, preferably 15 to 40% by weight, and particularly preferably 15 to 35% by weight. .

The low molecular weight polyethylene or polypropylene used is preferably polyethylene or polypropylene having a molecular weight of 1,000 to 20,000 daltons.

The particle size of the flower color effect pigment is preferably 5 to 200 microns; when the flower color effect pigment is a pearlescent pigment, the particle size of the latter is preferably 5 to 100 microns, preferably 10 to 60 microns.

The powder coating of the present invention can be applied to any desired substrate material. Examples of substrate materials are: metals (such as: iron, steel, aluminum, bronze, brass) and metal fingers, glass, ceramics and concrete. Sexually modified surfaces can also be non-conductive surfaces, such as wood (such as furniture), glass, ceramics, plastics, inorganic building materials or other materials, which are used for decoration and/or protection purposes.

To improve the surface quality, one or more clear coatings can also be applied to the powder coating. The effect of this application is usually not only to improve the appearance but also to improve the durability of the coating. But this transparent final coating is not absolutely necessary.

The present invention also proposes the use of surface-modified color effect pigments coated with low molecular weight polyethylene or polypropylene to prepare an extruded and ground mixture containing binders and pigments, as well as fillers, additives, and curing agents used as appropriate. Powder coating.

Hereinafter, the present invention will be explained with reference to supplementary examples and comparative examples.

Instance

5% low molecular weight polyethylene coated Iriodin163 (polyethylene wax with molecular weight <100,000g/mol; the content of polyethylene is 30% by weight based on Iriodin pigment) and epoxy, acrylic or poly Commercially available powder coatings based on esters are introduced into the powder coating manufacturing method, mixed in advance, pressed out and ground. After that, it is conveniently applied with an electrostatic device.

Comparative example

5%Iriodin163 is introduced into the powder coating manufacturing method together with other required raw materials, mixed in advance, extruded and ground. After that, it is conveniently applied with an electrostatic device.

The metal sample plates coated with the samples of the example and the comparative example were compared with the naked eye. The former exhibited a good to excellent luster and luminescence effect, while the sample from the comparative example had no pearly luster or luminescence effect visible to the naked eye.