Coating from a powder paint having an antisticking effect and process for its preparation

The present invention relates to a coating from a powder coating material with anti-adhesion effect and a method for its preparation.

Powder coatings and the corresponding coating materials are known in the prior art in a wide range of diverse applications. The customary coating formulations, the binders, pigments, fillers and additives include, used. Conventional binder combinations are<ul><li>Epoxy resin / hardener powder,</li><li>Polyester / epoxy powder,</li><li>Polyester / Glycidylhärter powder,</li><li>Polyurethane powder based on polyester / isocyanate hardener or acrylate / hardener powder.</li></ul>

Such coatings are used predominantly on metallic substrates, but also on glass, ceramics and heat-resistant plastics. The underlying specifications include here the broad field of all technical n applications, as well as decorative applications. Particularly where decorative applications come to fruition, the contamination of surfaces for care coated surfaces in practice is a significant problem. In addition to the normal contamination by conventional air constituents and emissions are increasing contamination caused by spray paints, paint with markers, etc., troublesome and expensive to eliminate, if at all possible.

This stubborn dirt by solvent-based paints, dyes, inks, etc. are to be summarized here below under the heading graffiti.

Since the paint of an object makes necessary particularly excellent adhesion to the base, all the coatings, as well as the powder coatings used are characterized, by excellent adhesion to the substrate. The so-called. Isotropy of paint films also means that not only on the bottom, but also on the surface, especially when a strong adhesion is present with solvent-based paints, markers, etc., which is already applied crosslinked powder coating film. This requirement results in graffiti Remove dirt only with considerable effort from the surface powder-coated parts, if they can be removed at all.

The application of liquid applied, often solvent-based, house paints is known to provide surfaces of buildings, bridges etc. with a coating thereby allowing a cleaning after Pollute with graffiti that the graffiti completely with the so-called anti-graffiti coating is removed from the building.

Other solvent-containing coating materials based on polyester / polyisocyanate / solvent are known for example from EP 0442272 A2. Here a coating with the help of dissolved in solvents additives is equipped with a non-stick effect, which allows the removal of contaminants from the surface. In a curing process, the additives are incorporated here in the coating. A disadvantage is the use of solvents in this case is mainly due to the substantial environmental impact, which is not given in the use of powder coatings as a coating material.

For high-value commodities, which carry a powder coating, bans on the one hand, the procedure of applying a coating, which is peeled off when cleaning because the powder coating is applied prior to the installation of the assets. Secondly, however, has such a powder coating all the benefits of a low-emission coating, combined with excellent technological properties. A powder coated object that is contaminated with graffiti is, however, no longer to clean normally. It must be replaced.

The invention is based on the object to develop a powder coating, which already carries a non-stick effect of graffiti in itself, without the known properties of the powder coating are impaired. It is thus to provide a film, on the one hand, the adhesion to the substrate ensures other hand, a permanent non-stick effect, which involves no negative effects on other specification points.

According to the invention the object is achieved in that the coating is formed from a powder coating of a commercial binder / hardener combination, which is prepared by a non-stick additive is added.

This form binder / hardener combinations commercially available formulation, the starting point of manufacturing varnish with anti-adhesive effect. This base is known of their properties and the production process sufficiently and advantageously, the invention provides here a process technology easily integrated into the manufacturing process extension of usual production. As additives are inventively natural and synthetic waxes and oils, as well as silicone and siloxane compounds, especially polysiloxane. This painting a surface is created, which is being rich footed or more of said non-stick additives and thus has the desired non-stick effect, without the known properties of the powder coating are impaired. In particular, powder coatings with additives in the form of waxes and / or oils can used there where the risk of leaching of additives from the surface of secondary importance.

According to the invention it is preferred that the Anithaftadditiv is compiled into the paint film to achieve a long-term non-stick effect even under unfavorable conditions. This is the case for example with the weather and additional contamination exposed decorative surfaces. These can be cleaned at relatively low cost using a powder coating according to the invention often without the coating to be renewed or the part in question needs to be replaced.

according to claim 3 a further development of the powder coating according to the invention is characterized in that the used non-stick additive diffuses during the coating process, mainly to the surface. Thus, the non-stick additive is to a large extent exactly where it is needed due to its characteristics.

There are known additives, which diffuse to the surface in the powder paint film during application and baking. However, these usually have the disadvantage that they cause adverse effects on the surface, or that they are washed out after some time from the surface, as they are not fixed herein. So then disappears and the non-stick effect of such a coating. By cross-linking or incorporating the additives of this process of washing in a paint of the invention is suppressed, the coating thus retains its properties permanently. In conjunction with claim 2, the non-stick additive is closely tied to the surface of the coating fixed in the paint film and is therefore at a comparatively low dosage in sufficient quantity available permanently.

Preferably, the non-stick additives with chemically reactive groups using a special production technique, the masterbatch technology, introduced in the powder coating. So they can diffuse during application and baking in the liquefaction stage of the film at the surface and upon further progress of the firing process in the crosslinking mechanism integrated by chemical reactions.

As basic binders may be used, which can form a crosslinked film with the appropriate curing agents advantageously all known powder coating binders. Preferably, OH-containing polyesters are used, which are cured with isocyanate groups-containing polymers. Powder coatings of this chemical basis are known as polyurethane powder coating and described for example in DE 44 06 157th

As an additive anti-stick additives are used in this invention, which carry chemical functionality such as epoxy, carboxyl or hydroxyl groups and their functionality to the binder / hardener systems used is matched. For use in the polyurethane powder coating materials preferably employed preferably these non-stick additives carry OH functionality. The result is a powder coating material with anti-adhesion effects or anti-graffiti property, which can be prepared and processed according to known methods.

Above all, polyurethane systems apart from by favorable curing conditions, good Überbrennbarkeit, high weather and UV resistance and great flexibility reserve. In a preferred embodiment, the combination of hydroxy-functional polyester and blocked isocyanate polymer is used.

As the base polyester polyesters are used with hydroxyl numbers of 30 to 150, preferably 40 to 100. The acid values ​​lie at max. 15, preferably max. 10. As a crosslinking agent blocked isocyanate polymers are used, preferably those based on isophorone diisocyanate adduct capped with contents of NCO of 5 to 40 wt .-%, preferably 10 to 20 wt .-%. Blocking agents preferably used Epsilon-Caprolactam. The cleavage temperature is between 120 and 175 ° C, preferably of 140 to 170 ° C. The melting point is between 70 and 100 ° C, preferably between 80 and 90 ° C. The ratio polyester: isocyanate is between 95: 5 and 50:50, preferably between 92: 8 and 60:40. The free isocyanate content is below 2%, preferably below 1%.

As anti-adhesion additive is a polydimethylsiloxane is used, carrying the functional groups for use in polyurethane powder coatings is preferably a polyester-modified hydroxyl-functional polydimethylsiloxane. This additive has an OH number between 20 and 120, preferably between 30 and 50. The melting point is between 40 and 80, preferably between 50 and 60 ° C.

Due to the OH functionality for chemical integration into the crosslinking process, the chemical structure of the additive is so created that melting points are present in the above area. A direct incorporation into the powder coating is ruled out, since the extrusion temperatures are above the melting point. Therefore, the additive is pre-dispersed in with the aid of per se known masterbatch technology in a binder to allow for incorporation into the powder coating. Of the anti-adhesion additive are amounts from 0.5 to 10%, preferably 2 to 4% is used.

The basic formulation of the polyurethane is determined in the particular application to the demands of the technological properties. The introduced by the additive amount of OH groups is offset to the OH groups of the polyester and co-sponsored in the stoichiometry, which underlies the crosslinking with isocyanate. Here, the usual crosslinks are used depending on the requirements of the powder paint films, that is stoichiometric crosslinking, overcrosslinking upon acceleration of the reaction, under crosslinking while increasing the flexibility and filling of the film. A corresponding exemplary formulation is in the sample. 1

The flow of the coating is characterized as follows: The described formulation is for powder coating extruded at normal extrusion conditions, ground and applied by conventional application tools and baked. For the presentation of non-stick effect, the baked coating films were subjected to a standardized test method a cleaning process.

<b>example 1</b>

Polyurethane powder coating with anti-graffiti effect

<dl id="dl0001" compact="compact"><dt>30.0 wt .-%</dt><dd>Polyester Resin, hydroxyl number 85</dd><dt>18.0 wt .-%</dt><dd>Blocked IPDI adduct 15 wt .-% NCO blocked</dd><dt>0.9 wt .-%</dt><dd>Anti-crater and leveling additive polyacrylate, adsorbed on silicon dioxide</dd><dt>15.0 wt .-%</dt><dd>Masterbatch su</dd><dt>0.5 wt .-%</dt><dd>benzoin</dd><dt>25.0 wt .-%</dt><dd>pigment TiO₂ Rutile type, chloride</dd><dt>10.6 wt .-%</dt><dd>Filler barium average particle diameter 1 micrometer</dd></dl>

masterbatch

<dl id="dl0002" compact="compact"><dt>80.0 wt .-%</dt><dd>Polyester resin so</dd><dt>20.0 wt .-%</dt><dd>Polyester modified hydroxy functional polydimethylsiloxane, hydroxyl number 40</dd></dl>

The results of the examination of the anti-adhesion effect are summarized in the table below for conventional powder coating binder, a normal commercial polyurethane powder coating and a polyurethane powder coating according to the invention.

The experiment was carried out by exposure to 2 kg, surface about 30 cm², Humidified pulp. Rubbing with 10 g of a commercially available surfactant-containing cleaning agent.

The counting of strokes occurs as single stroke. <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Powder coating system</entry><entry namest="col2" nameend="col2" align="center">individual strokes</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Polyester / Primid</entry><entry namest="col2" nameend="col2" align="right">20 (bad cleaning)</entry></row><row><entry namest="col1" nameend="col1" align="left">Polyester / glycidyl oxygen verb.</entry><entry namest="col2" nameend="col2" align="right">20 (bad cleaning)</entry></row><row><entry namest="col1" nameend="col1" align="left">polyurethane</entry><entry namest="col2" nameend="col2" align="right">20 (bad cleaning)</entry></row><row><entry namest="col1" nameend="col1" align="left">Polyurethane non-stick effect (Ex. 1)</entry><entry namest="col2" nameend="col2" align="right">5 (good cleaning)</entry></row></tbody></tgroup></table></tables>

From this table, the excellent result of a powder coating according to the invention in its application can be seen as a powder coating film.

An inventive powder coating is particularly advantageous where used where arrive decorative surfaces powder topcoats or powder one layer systems are used. In the form of a powder coating thus weatherproof coatings with anti-graffiti properties are realized for the first time. Here are advantageously used powder coatings formulation of common application, which are commonly used for primers or Einschichtanwendungen where other technological values ​​are in the foreground as the weather resistance. These coatings are modified according to the invention in their composition, thus expanding their properties, without losing their current benefits.