WO2008014527A1

WO2008014527A1 - Method for producing powder coatings containing at least one film-forming polymer component and hard material particles

Info

Publication number: WO2008014527A1
Application number: PCT/AT2007/000301
Authority: WO
Inventors: Thomas Schmidt; Harald SÜSS; Gerald Hemedinger
Original assignee: Tigerwerk Lack- U. Farbenfabrik Gmbh & Co. Kg.
Priority date: 2006-08-01
Filing date: 2007-06-20
Publication date: 2008-02-07
Also published as: AT503115B1; AT503115A4

Abstract

Method for the production of heat- and radiation-curable powder coatings that contain at least one film-forming polymer component and hard material particles with a Mohs hardness of > 7 as the non-film-forming component, said coatings being non-damaging to installations in the course of their production and processing, in particular extruders, mixers, or similar. According to said method, microscale hard material particles coated with polymer material and/or wax are added to the polymer component that forms the main constituent and consists of at least one primary particulate, film-forming polymer material, in order to increase abrasion resistance.

Description

Expired for the production of at least one film-forming polymer component and hard powder particles containing powder coatings

5 The invention relates to a process for the preparation of at least one film-forming polymer component and hard particles with a Mohs hardness> 7 as non-film-forming component containing, in the course of their production and processing equipment, especially extruder, mixer and application equipment gentle, heat and radiation curable powder coatings , I O

Powder coatings have found wide application in the coating of materials such as metal, glass, ceramics, etc. due to the high efficiency of the process and the favorable assessment from the perspective of environmental protection.

15 A variety of different binder systems, pigments, fillers and additives have opened up powder coatings for a wide range of applications. For example, decorative coatings, corrosion protection systems, heat-resistant coatings, weather-resistant coatings on facades and vehicles as well as diverse functional coatings in glossy to matt, smooth to textured finishes have long since stood the test

2 0 of the technique.

Despite their economic advantages and their large number of possible applications powder coatings are also some limitations, compared with wet paints, too own. The absence of solvents as well as restrictive specifications of the binders

For example, with regard to glass transition temperature and viscosity ranges, it is difficult to produce particularly wear-resistant, abrasion-resistant powder coatings.

As in many cases, the decorative appearance of the powder-coated objects a

Although it is desirable that these retain their flawless appearance as much as possible, increasing the abrasion resistance of powder coatings has long been a concern. In addition, it can lead to functional limitations due to wear, since with the decrease in the layer thickness of a paint coating, of course, its protective effect against the substrate 35 decreases.

ERSÄTZBLATT (RULE 26) US 2004/0063813 A1 describes that powder coating compositions containing reactive nanoparticles have many aspects, including their wear resistance, of conventional powder coatings - these are those without the corresponding particles or those in which the nanoparticles used are unmodified and thus are not covalent Experienced binding to the binder - are superior. Within the meaning of the aforementioned document, the reactive nanoparticles are inorganic particles in the size range between 1 and 400 nm, which are equipped by chemical modification of their surface with organofunctional groups capable of producing covalent bonds to binder components of the powder coating formulation in question; those thus allow a permanent connection between the binder and the particles distributed therein.

It turns out, however, that in the case of the powder coatings formulated according to US 2004/0063813 A1, the improvement in abrasion resistance is not particularly great. Thus, the comparison of Examples 1 (Comparative Example) and 4 (Inventive) in the Taber Abrasion Test shows a reduction in the amount of abrasion by less than 20%. Our own investigations on this topic led to similar results.

DE 102 48 799 A1 discloses liquid-coating compositions comprising inorganic particles, which are characterized in that they contain, if appropriate in addition to other hard-material particles, micro-hollow particles of materials of Mohs hardness> 5.5. Measured together, the particles have an average particle size of from 0.01 to 20 .mu.m, preferably from 0.05 to 15 .mu.m, very particularly preferably in the range from 0.25 to 10 .mu.m and especially from 0.5 to 7 .mu.m. Due to the low average specific gravity of those micro-hollow particles and the low viscosity inherent in the liquid formulations, these preferentially accumulate on the surface of the coating and make it particularly hard and abrasion-resistant, while any other hard material particles also provide hardness in the underlying layers. According to the teaching of this disclosure, for reasons of transparency, it is advantageous to use particles which are substantially smaller than 0.5 μm, while in order to achieve particular hardness the particles should in many cases be significantly larger than 1 μm.

The coatings according to DE 102 48 799 A1 can be so wear-resistant in the case of high proportions of corresponding particles that they can be used in the Taber abrasion test in comparison to the unmodified coatings suffer only a fraction of their abrasion. However, the said DE-A1 gives no indication as to how the disclosed strategies for the production of scratch-resistant, abrasion-resistant powder coatings can be applied, but rather implicitly excludes such transfer by pointing to the importance of the thin liquid of liquid coatings for the functioning of the process in question.

DE 103 00 118 A1 describes the improvement of the abrasion resistance of coating compositions based on liquid, curable polyurethane compositions by the addition of wax-coated polyamide particles. From the disclosed examples, there is a significant reduction in the proportion of material removed in the Taber Abrasion Test; Material removal is reduced by up to two-thirds when wax-coated polyamide particles are added.

EP 1 245 627 A2 describes radiation-curable liquid coatings based on acrylates which are produced by the use of so-called nano / micro hybrid systems or micro hybrid systems based on nanoscale or microscale oxidic particles which act as an organic binder by an in situ reaction Acrylic monomers are provided with an organosilicon sheath, having a much higher abrasion resistance compared to unmodified acrylic-based liquid coatings. According to the disclosure of this document, the obligate micro-scale particles to be used are preferably corundum with an average grain diameter of 13 μm.

5 According to the teaching of EP 1 245 627 A2, the organosilicon coatings are those of

Particles in the acrylic monomers as a matrix at 60 - 70 ⁰ C made, a temperature range, with which in view of the much higher viscosities and process temperatures in the production of powder coating binders not acheived. The much higher viscosities of the powder coating binders O lead beyond the standard method for preparation of powder coatings, the at about 90 - running 140 ⁰ C extrusion process to such high shear rates, that the use of microscale corundum or similar hard materials in powder coating formulations inevitably very strong Wear on the valuable machinery would result. DE 44 26 831 A1 relates to radiation-cured mixtures based on acrylate oligomers, which are substantially increased in their abrasion resistance by addition of at least 1% of a combination of finely divided inorganic compounds of high hardness - corundum, silicon carbide, quartz and tungsten carbide. The size of the hard material particles is between 1 and 50, preferably 5 to 20 microns. Here, too, a transfer to powder coatings with very heavy wear on the machines is to be expected.

EP 0 539 385 B1 describes processes by means of which numerous substances whose passage through the extruder is unfavorable for a great variety of reasons and therefore must be avoided, can be preserved in a durable manner on the particles of a primary fluorine-forming component. This is preferably done by working the mixture of the particles of that primary film-forming component with the particles of the additive in a high-speed mixer. As a result of the high mechanical energy introduced into the mixture, the mass increases in temperature; the additive particles are inseparably "agglomerated" with the particles of the primary film-forming component, unlike conventional blending, and in particular embodiments of the process, carefully dosed solvents can also be used for surface-solubilization (tackification) of the primary O film-forming component. n) or carefully dosed solutions or dispersions of

Polymers, which in turn cause a partial sticking between the primary and the additive particles are used. The agglomerates are initially moved while cooling and / or removal of the solvent (s) used and finally fall in free-flowing form. 5

EP 0 539 385 B1 refers to the advantageous use of the process for producing abrasion-resistant powder coatings which can be prepared by agglomerating abrasive constituents such as corundum (Mohs hardness 9) or metal carbides onto a primary powdery film-forming component. On the other hand, the production of urea-containing powder coatings by conventional methods, in which all constituents of the formulation, ie including the hard material particles, are first dry-premixed and then extruded would lead to unacceptably high levels of wear inside the extruder. It is not surprising, however, that when using abrasive particles and a procedure according to EP 0 539 385 Bl instead of the extruder, the high-speed mixing tool is exposed to heavy wear, all the more so as in this process every single hard particles in the course of the process repeatedly in intensive Contact 5 with the high-speed rotor and the inside wall of the mixer must come and go, the process should lead to the desired goal. In addition, of course, the conveying and spraying equipment used in the powder coating application are subjected to very strong wear, since most of the hard material particles are located on the outside of the agglomerates produced.

I O

EP 1 095 110 Bl relates to the reduction of the gloss level or other changes in the appearance of powder coatings. This is done according to disclosure by mixing a film-forming powder coating component, a fbildbildenden or rύcht-film-forming, modifying the appearance

15 component, and another additive component, which are certain combinations of alumina (also known as DAl ₂ O ₃ = corundum), aluminum hydroxide and wax-coated, preferably amorphous silica, or optionally the latter alone. Preferably, the last three substances are not more than 1 micron in size.

20

EP 1 095 110 Bl does not disclose anything with regard to the abrasion resistance according to their teachings produced coatings, nor are indications of a possible wear of equipment parts to find therein.

It is to be noted that the state of the art does not disclose powder coatings which have a significantly higher Taber abrasion resistance compared with conventional powder coatings and which do not cause any wear on the contacting parts of the system during their manufacture and processing which goes beyond what is necessary for conventional powder coatings is common.

30

Surprisingly, it has now been found that the production of hard material particles with a Mohs hardness> 7 containing powder coatings in an agglomeration process and their processing for producing abrasion resistant powder coatings without wear damage to the equipment involved while avoiding the above Disadvantages of the prior art is possible if, according to the invention, micro-scale hard particles coated with polymeric material and / or wax are added to the main component of the polymer component comprising at least one primary particulate film-forming polymer material to increase the abrasion resistance. Unexpectedly, it has also been found that the use of polymeric and / or wax-coated hard particles, even when merely blended with a primary particulate film-forming polymer component, results in substantially segregation-stable powder coating qualities which enable the production of abrasion resistant powder coatings.

For carrying out the process according to the invention, it is particularly advantageous according to embodiments of the invention if at least one primary particulate, film-forming polymer component is mixed with at least one particulate, non-film-forming component of hard material particles enveloped with polymeric material and / or wax or else joined by agglomeration.

As a film-forming component can serve curable polymer systems. A curable polymer system comprises i. a. one or more hardener component (s); Alternatively, also koreaktive polymers can be used. The curing of these polymers can be effected by heat and / or radiation energy (UV, electron beam).

Suitable binders for the thermosetting polymer systems are carboxyl-functional polyesters in a preferred manner and / or hydroxyl-functional polyesters, (meth) acrylic resins - carboxyl, hydroxyl or glycidyl-functional - or epoxide resins.

For curing carboxyl-functional resins, epoxide-functional components are frequently used. These may be either epoxy-functional resins such as condensation products of bisphenol A and epichlorohydrin, or low molecular weight compounds such as triglycidyl isocyanurate. Further potential hardeners of carboxyl-functional resins are D-hydroxyalkylamides. Isocyanate-functional hardeners can be used for the reaction of hydroxyl-functional resins, furthermore amine-formaldehyde condensates such as melamine resins, urea-formaldehyde resins or also glycoluril systems.

The hardeners suitable for reaction with (meth) acrylic resins as well as co-reactive polymers are based on the functional groups available in the acrylic resin analogously to the previously discussed polyesters. For curing glycidyl-functional (meth) acrylic resins, longer-chain aliphatic dicarboxylic acids, moreover also their anhydrides, can be used.

For the curing of epoxy resins, for example, aniinofunctional substances come into consideration; another possibility is carboxyl-functional polymers (polyesters, [meth] acrylates).

As radiation-curable polymers can serve unsaturated polyester resins. For their curing, other unsaturated substances such as acrylurethanes or vinyl ether urethanes can be used.

The size of the particles of the film-forming component (s) is usually between 10 and 120 microns, with an average value between 15 and 75 microns. The glass transition temperature (s) are usually in the range of 35 to 85 ° C, preferably from 40 to 75 ° C and particularly preferably from 45 to 70 ⁰ C.

Alternatively, thermoplastic polymer systems can be used as film-forming component 5. Examples are fluorocarbon polymers -. As polyvinylidene fluoride -, plasticized polyvinyl chloride, polyethylene, ethylene-vinyl acetate copolymers and polyamides.

The aforementioned polymer systems may optionally contain further substances such as pigments, fillers O and additives.

As pigments, inorganic substances such as titanium dioxide, chromium (III) oxide ₅ carbon black or iron oxides, furthermore organic pigments such as phthalocyanine, azo, anthraquinone, thioindigo or quinacridone pigments can be used. For example, as fillers Barium sulfate and calcium carbonate usable. For example, leveling agents, UV and oxidation stabilizers, curing accelerators and degassing aids can be used on additives.

The particulate film-forming polymers used according to the invention as the primary film-forming component are widely used as powder coating. For example, Pieter Gillis de Lange, Powder Coatings - Chemistry and Technology, Vincentz Network, Hanover, 2004, provides a very detailed and up-to-date overview of the topic.

It has been found that although powder coatings prepared using particles with a Mohs hardness <7 have demonstrated improvements in abrasion resistance over unmodified powder coatings in the Taber abrasion test, these improvements are rather modest.

In contrast, according to a preferred embodiment of the invention corundum, silicon carbide and / or boron carbide are used as the hard material particles. According to the invention the hard material particles have a particle size in the range of 1 to 50 microns, preferably 5 to 30 microns.

The waxes and polymers which can be used according to the invention for the production of the sheath on the abovementioned hard material particles are diverse. Preference is given to using substances which, taken in finely divided form, are also used on their own as additives in powder coatings, and among these preferably semicrystalline materials. According to a preferred embodiment of the invention, the shell of the hard material particles consists of optionally amide- or PTFE-modified polyethylene and polypropylene waxes, of amide waxes or combinations thereof.

The wax envelopes can be applied to the particles by methods known per se; as an example, the possibility of spray-drying or spray-micronization may be mentioned.

The agglomerates of primary film-forming component and the wax-coated and / or polymer-coated hard material particles are prepared by known processes, such as for example, in EP 0 539 385 B1. However, according to the invention it is also possible to mix the components only loosely with one another, the abrasion resistance of the powder coatings obtainable from such mixtures corresponds to that obtained by agglomeration to a large extent.

In any case, the powder coatings according to the invention, in addition to their high abrasion resistance, are distinguished by the fact that they do not wear the relevant equipment more heavily during their manufacture and processing than do the masses serving as the primary film-forming component.

The following examples are intended to illustrate the pronounced abrasion resistance of the powder coatings according to the invention. At the same time, the concrete representations should not have any limiting character.

Examples

In all examples, the following film-forming polymer component is used, but without being limited to the polymer component indicated below:

composition

The raw materials were premixed in a mixer of the type Pilot 3 from Thermo Prism for 2 minutes at a speed of 2500 min -i and then over a Extruder type Prism Twinscrew 16 mm, screw length = 24-fold screw diameter, extruded (temperature control of the heating zones in the direction of material flow: 100, 130 and 125 ^° C., speed 400 min ^-1 ) The cooled extrudate was crushed, ground on a classifier mill and screened with a grain upper limit of 85 microns.

Hard material component in all examples according to the invention:

Fine corundum of grain size F 320, coated with DEUREX® 9720 (polyethylene). The wax content of the hard material component was 31.8 wt .-%.

Wear-reducing components according to the prior art in comparative examples:

Polyamide 12 - particles of average particle size ~ 20 microns, natural colors (Vestosint 2158 nf, Degussa), and detto, according to DE 103 00 118 Al coated with 4% wax (micronized Fischer-Tropsch / PTFE wax).

Example 1 (agglomerated powder coating end product, according to the invention)

In the friction mixer of a heating / cooling mixer combination TSHK / KGU in laboratory version (10 1 nominal volume, Fa. Papenmeier), 2430 g of the above powdery, film-forming polymer component and 70 g of the wax-coated hard material component were introduced. Subsequently, the mixing tool was put into operation and up to a maximum peripheral speed of 27 m / sec. moved until it reached an internal temperature of 52 ° C. By taking back the

Speed, this temperature was kept constant for 2 minutes. Subsequently, the material was transferred to the downstream cooling mixer and further stirred with cooling until the melt temperature was below 30 ° C.

A subsequent examination of the heating / cooling mixer combination used showed no signs of wear. Example 2 (Loosely mixed powder coating end product, according to the invention)

972 g of the above powdery, film-forming polymer component and 28 g of the wax-coated hard material component are mixed for 2 minutes at a speed of 1500 min ^-1 in a Pilot 3 mixer from Thermo Prism.

A subsequent examination of the mixer used showed no signs of wear.

Comparative Example 1

972 g of the above powdery, film-forming polymer component and 28 g of the above

wax-coated polyamide particles mentioned are mixed together analogously to Example 2.

Comparative Example 2

972 g of the above powdery, film-forming polymer component and 28 g of the above-mentioned uncoated polyamide particles are mixed together analogously to Example 2.

Comparative Example 3

The above powdery film-forming polymer component is used without any additive.

Processing:

The powder coatings from the above-mentioned examples and comparative examples were applied to test plates made of aluminum, size 100 × 100 × 0.7 mm, with a Gema Easy Tronic coating system, layer thickness about 100 μm. Subsequently, the

Powder coatings baked in a convection oven of the type Heraeus UT 12 at 160 ⁰ C for 15 minutes. To investigate the Abrasionspotenzials the novel powder coatings 200 kg each of the respective powder coatings were further (DDF pump 20-40 ^® from. Ramseier Technologies AG spray gun EasyTronic Select ^® from. ITW Gema) processed through an industrial coating line. A subsequent examination showed no evidence of excessive wear, as observed when processing powder coatings containing conventional hard particles, 2x1.

Testing the abrasion resistance:

The abrasion resistance was determined by means of Taber® Abraser 5130 from BYK-Gardner on the basis of DIN 68861 T2. As abrasive sandpaper strips of the type S-33, which were replaced after 100 revolutions against new. The weight loss of the specimens after 200 revolutions and a load of 500 g was determined.

Results:

The following results represent the respective averages of 3-fold determinations.

In summary, it can be said that powder coatings provided with polyamide particles as a non-film-forming component, whether coated with wax or not, have a weight loss of the order of about 10%, compared to unmodified powder coatings (Comparative Example 3). On the other hand, without significant influence on the type of film-forming polymer component used, the use of wax-coated hard material particles as non-film-forming component causes weight loss of the order of 40% compared to unmodified powder coating.

Claims

Claims:

5 1. A process for the preparation of at least one film-forming polymer component and hard particles having a Mohs hardness> 7 as non-film-forming component, in the course of their production and processing equipment, especially extruders, mixers or the like. Gentle, heat and radiation curable powder coatings, characterized in that micro-scale hard material particles coated with polymeric material and / or wax are added to the polymer component comprising at least one primary particulate, film-forming polymer material forming a main component to increase the abrasion resistance.

2. Method according to claim 1, characterized in that at least one primary particulate, film-forming polymer component having at least one particulate, non-film-forming component is mixed with hard material particles coated with polymeric material and / or wax.

20 3. The method of claim I _3, characterized in that at least one primary particulate, film-forming polymer component with at least one particulate, non-film-forming component of coated with polymeric material and / or wax hard material particles is connected by agglomeration. 25

4. The method according to any one of claims 1 to 3, characterized in that are used as the hard particles corundum, silicon carbide and / or boron carbide.

5. The method according to any one of claims 1 to 4, characterized in that the

30 hard particles have a particle size in the range of 1 to 50 microns, preferably 5 to 30 microns.

6. The method according to any one of claims 1 to 5, characterized in that the shell of the hard material particles modified from optionally amide or PTFE Polyethylene and polypropylene waxes, consist of amide waxes or combinations thereof.