Powder coating and method for producing a powder coating

Abstract

The invention relates to a powder paint comprising at least one base powder paint and at least one effect powder paint having effect pigments, said effect pigments being dispersed in a melt made from transparent effect powder paint. The invention also relates to a method for producing said type of powder paint and to an effect powder coating containing said type of powder paint.

Claims

1. A powder coating, comprising at least one opaque basic powder coating B and at least one ground effect powder coating A comprising effect pigments, wherein the effect pigments comprised in the effect powder coating A are, at least partially, coated with a transparently curing powder coating matrix.

2. The powder coating of claim 1, wherein the powder coating comprises the effect powder coating A in admixture with the opaque basic powder coating B in a mass ratio of 1 to 50% of effect powder coating and 50 to 99% of opaque basic powder coating.

3. The powder coating of claim 1, wherein the effect pigments are metallic-effect pigments.

4. The powder coating of claim 1, wherein the effect pigments are pearlescent and/or interference pigments.

5. The powder coating of claim 1, wherein the average diameter of the effect pigment particles dispersed in the powder coating amounts to at least 80% of the average diameter of the original effect pigment particles.

6. The powder coating of claim 1, wherein the average diameter of the effect pigment particles dispersed in the powder coating amounts to at least 90% of the average diameter of the original effect pigment particles.

7. A method for preparing a powder coating of claim 1, the method comprising blending the at least one opaque basic powder coating B and the at least one ground effect powder coating A, wherein the effect powder coating A is produced by a method comprising: melting a transparent powder coating to produce a transparently curing powder coating melt; stirring at least one effect pigment into the transparently curing powder coating melt, cooling the transparently curing powder coating melt; and grinding the cooled melt to produce the effect powder coating A.

8. The method for preparing a powder coating of claim 7, wherein at least one effect pigment is added to the transparently curing powder coating melt during an extrusion process via at least one side feeder.

9. An effect powder coating, wherein the pigment particles contained in the coating are, at least partially, coated with a transparent matrix and at least one channel formed from said transparent matrix extends from at least one effect pigment particle to the surface of the coating, wherein said channel has a depth of at least 5 m.

10. The effect powder coating of claim 9, wherein the channel has a depth of at least 10 m.

11. The effect powder coating of claim 10, wherein the channel has a depth of at least 20 m.

Description

DESCRIPTION OF THE DRAWINGS

(1) The present invention will be explained in greater detail by the following Examples and Figures, without being limited thereto, however.

(2) FIG. 1: Effect color approx. RAL 9007, glossy, inclination angle approx. 0

(3) FIG. 2: Effect color approx. RAL 9007, glossy, inclination angle approx. 45

(4) FIG. 3: Effect color approx. RAL 9007, glossy, inclination angle approx. 75

(5) FIG. 4: gray matte metallic, inclination angle approx. 0

(6) FIG. 5: gray matte metallic, inclination angle approx. 45

(7) FIG. 6: gray matte metallic, inclination angle approx. 75

(8) FIG. 7: dark gray matte metallic, inclination angle approx. 0

(9) FIG. 8: dark gray matte metallic, inclination angle approx. 45

(10) FIG. 9: dark gray matte metallic, inclination angle approx. 75

(11) FIG. 10: Cross-section polish of a coating layer prepared with the powder coating according to the present invention; the pigment particles (light rods) are located in a channel of transparent, translucent powder coating, due to which the opaque, colored powder coating is visible. The substrate (light aluminum sheet) is visible to the right of the coating layer, while the dark embedding material of the compact can be seen on the left.

(12) FIG. 11: The channel of transparent coating extends about 60 m deep into the coating layer; the pigment embedded therein is thus visible when looking onto the surface.

(13) FIG. 12: The pigment is located about 10 m below the surface, embedded in transparent powder coating and therefore visible.

(14) FIG. 13: The pigment is embedded up to 25 m deep in the transparent coating. All around, the opaque, colored coating can be seen.

(15) FIG. 14: Cross-section polish of a sample prepared with powder coating, wherein the pigment has been introduced into a colored, opaque coating during the extrusion process. The pigments are deeply embedded in the coating matrix and are NOT visible.

(16) FIG. 15: Cross-section polish of a sample prepared with powder coating, wherein the pigment has been mixed into a colored opaque coating by means of bonding. The pigments are deeply embedded in the coating matrix and are NOT visible.

(17) FIG. 16: Cross-section polish of a sample prepared with powder coating, wherein the pigment has been mixed into a colored opaque coating by means of bonding. A portion of the pigment particles is present at the surface and is visible (effect factor), while the remaining pigment particles are located in the coating matrix and are thus NOT visible.

(18) FIG. 17: Extruder screw with mixing elements

(19) FIG. 18: Bonded pigment, 200 magnification; pigment slightly damaged (owing to shear forces acting in the bonding mixer)

(20) FIG. 19: Aluminum pigment, introduced into the extrusion process, addition directly with premix; large portion of pigment particles has been destroyed

(21) FIG. 20: Aluminum pigment, introduced during the extrusion process, addition via side feeder, screw configuration with mixing elements as shown in FIG. 17; pigment particles are only slightly sheared

(22) FIG. 21: Aluminum pigment, admixed according to the dry blending method

(23) FIG. 22: Aluminum pigment, introduced during the extrusion process via side feeder, low shear force, side feeder arranged in the rear third of the extruder, screw configuration with conveying elements downstream from the side feeder inlet

(24) FIG. 23: For comparison with FIG. 22, pigment dry blend, admixed (NO shear forces), 100 magnification; pigment particle form round or oval, only few small pigment fragments

(25) FIG. 24: Pigment incorporated during the extrusion process via side feeder, 100 magnification, large portion of the pigments still round/oval, only few fragments

(26) FIG. 25: Pigment introduced at the beginning of the extrusion process, 100 magnification, irregular shape of pigment particles, large number of small fragments

(27) FIG. 26: Image of a powder coating chip, pigment introduced via side feeder, 200 magnification (powder coating chips which were evaluated immediately after leaving the extruder and cooling roll (pressing into wafers, cooling and mechanical crushing))

(28) FIG. 27: Powder coating chip, pigment introduced at the beginning of the extrusion process, 200 magnification (powder coating chips which were evaluated immediately after leaving the extruder and cooling roll (pressing into wafers, cooling and mechanical crushing))

(29) FIG. 28 Pigment master batch (pigment in colorless), addition via side feeder, 200 magnification (pigment extruded into transparent powder coating, ground, coated onto an aluminum sheet and baked)

(30) FIG. 29 Pigment master batch, addition at the beginning of the extrusion process, 200 magnification (pigment extruded into transparent powder coating, ground, coated onto an aluminum sheet and baked)

EXAMPLES

(31) The present invention will now be described in greater detail in the following Examples, without being limited thereto, however.

(32) The powder coating according to the present invention can, for example, consist of two components, wherein one component is the transparent effect powder coating A and the other component is an opaque colored basic powder coating B.

Example 1

(33) A transparent and colorless powder coating was prepared from 900 parts of Crylcoat 4642-3 or an equivalent polyester, 47 parts of Primid XL-552, 5 parts of Richfos 626, 3 parts of benzoin, 5 parts of Worlee Add 902, 5 parts of Licowax C Micropowder PM and 2 parts of Tinuvin. By means of gravimetric feeding, this premix is metered into a twin-screw extruder (e. g. ZSK 27), molten with a screw configuration that is suitable for powder coating production and then dispersed. Such configurations are known to the person skilled in the art. In the last third of the process section of the extruder, 5 parts of aluminum powder PCU 5000 are added by means of a twin-shaft side feeder and gravimetric feeding. The screw configuration downstream from the side feeder is exemplarily shown in FIG. 17. The temperatures inside the extruder are preferably kept at less than 120 C. Next, the liquid extrudate is cold-rolled and crushed in an impact pin mill in order to obtain ground powder coating (D50 less than 80 m).

(34) The size of the pigments (D50 or mean value) depends on the desired effect and can vary between 3 m and 130 m, preferably between 35 m and 90 m. The weight proportion of the effect pigments in relation to the total amount present in the transparent master batch can amount to between 1% and 40%, in particular between 2% and 10% by weight.

(35) The opaque, colored basic powder coating B is prepared in the same manner as described above and, in addition to the above raw materials, also contains color pigments and bulking agents, but no metallic/effect pigments.

(36) The following mixture may be considered as an exemplary formulation for the basic powder coating B: 680 parts of CRYLCOAT 4655-2, 36 parts of Primid XL-552, 5 parts of Worlee Add 902, 8 parts of Lanco Wax TF 1890, 18 parts of Powder Add 9083, 2 parts of Pigment Red 101, 10 parts of Pigment Brown 24, 7 parts of Pigment Black 7, 24 parts of titanium TS-6200 and 210 parts of Portaryte B 15.

(37) Subsequently, the two milled components (effect powder coating A and colored, opaque basic powder coating B) were mixed in a ratio of 20 to 80 by means of dry blending. The mixing is conducted in either a dry blend mixer or a bonding mixer.

(38) FIG. 17 shows an extruder screw which is fitted with mixing elements downstream from the point of addition via side feeder.

(39) The pigment platelets in the powder coating according to the present invention were only slightly sheared, bent or cut, so that their original effect (light reflection and sparkle effect) was maintained. In this manner it is, e. g., possible to determine the influence of the time of addition and the employed screw configuration based on micrographs of the extruder cooled melt (transparent powder coating melt containing dispersed metallic pigments).

(40) The micrographs of FIGS. 2 to 6 show the effects of various dispersion processes with high and low shear forces. For this purpose, aluminum pigments having a D50 of about 55 m were introduced by means of bonding, dry blending or extrusion into a dark powder coating (for better visual representation).

(41) FIG. 18 shows an incident light microscope image of a cured powder coating film at 200 magnification, wherein the pigment has been introduced into the powder coating according to the present invention by means of bonding; due to the low shear forces acting in the bonding mixer, the pigment is only slightly damaged.

(42) FIG. 19 shows, in comparison, an incident light microscope image of a cured powder coating film, also at 200 magnification, wherein the pigment has been introduced into the powder coating by means of extrusion; the pigment has been fed to the extruder directly with the premix; a large portion of the pigment was damaged (hammer effect).

(43) FIG. 20 also shows an incident light microscope image of a cured powder coating film at 200 magnification, wherein the pigment has likewise been introduced into the powder coating by means of extrusion, but added via a side feeder. Screw configuration and mixing elements were arranged as shown in FIG. 1; it is clearly visible that the pigment is only slightly sheared.

(44) FIG. 21 also shows an incident light microscope image of a cured powder coating film at 200 magnification, wherein the aluminum pigment has been admixed by means of the dry blending method. It is also clearly visible that the pigment is only slightly sheared.

(45) FIG. 22 finally shows an incident light microscope image of a cured powder coating film at 200 magnification, wherein the aluminum pigment has been introduced during the extrusion process via a side feeder arranged in the rear third of the extruder; the screw configuration featured conveying elements downstream from the side feeder inlet. Again, it is clearly visible that the pigment is only slightly sheared.

(46) Within the scope of the present invention it has been found that, by adding at least one pigment via at least one side feeder that is arranged at the end of the process section of the extruder, it is possible to reduce the shear forces to such an extent that the pigment is only insignificantly sheared and crushed. Experiments conducted with an aluminum silver dollar pigment (by Eckart, PCU 5000, D50 about 55 m) show that the average diameter of the effect pigments is only slightly changed compared to the average diameter of the original pigment (admixed as a dry blend). In order to determine the extent of effect, several micrographs were taken and the particles were measured. For comparison and easier visual evaluation of the influence of shear forces on the final effect of the powder coating, tests were carried out on black, high-gloss powder coating. In these tests, the pigments were once more either incorporated at the beginning of the extrusion process or during the extrusion process by means of a side feeder, whereupon the melt was cooled, ground, applied on metal sheets in the form of a powder coating and finally baked. For comparison purposes, the result obtained was evaluated visually and also by means of incident light microscopy. In addition, tests with respect to the introduction into a transparent coating by means of extrusion were carried out, which, at least in part, led to the object of the present invention. Measurements with respect to particle size were conducted in the cold-rolled powder coating chip and, on the other hand, on a sample sheet coated with said ground coating.

(47) From FIG. 25 is also obvious that many of the pigments no longer have their original round shape and only fragments thereof are discernible. Microscopic evaluations have shown thatwith addition at the inlet of the extruder, together with all other raw materialsthe effect pigments or the fragments thereof only retain about 50% of their original diameter in the finished extrudate or in the cured coating. If the pigments were metered through the side feeder and subsequently exposed to low shear forces (cf. the screw configuration in FIG. 17), the average diameter was changed only insignificantly. The measurement results are documented in the following table:

(48) TABLE-US-00001 Pigment master Pigment batch in master transparent, batch, Pigment in Pigment, Pigment, addition at side black HGL, Pigment in addition addition extruder feeder, addition black HGL, at via inlet, coating at extruder addition via extruder side Pigment coating onto inlet, side feeder, inlet, feeder, dry blend onto metal metal coated metal coated metal extrudate extrudate in black sheet sheet sheet sheet chip chip HGL 26.52 56.3 32 60.6 59.3 57.9 59.6 68.4 24.75 26.92 56.3 93.25 58.6 84.6 18.12 64.69 23.28 18.5 35.8 89.4 55.97 72.1 28.96 25.75 32.47 62.2 75.6 60 18.62 52.74 19.57 22 30.8 63.7 74 59.6 13.3 19.8 65.44 29.56 49.15 63.1 29.11 72.48 27.9 23.7 15.5 69.19 66.5 64 16.78 13.271 52.15 59.59 43 33.1 7.8 52.74 47.2 16.8 23.3 58.7 44.68 54.65 18.12 16.58 34.12 52.17 62.2 53.3 17.4 63.85 20.69 24.4 35.87 59.9 70.1 52.14 17.59 24.22 38.39 78.2 60.6 56.8 14.48 62.22 14.46 27.2 23.32 54.03 46.17 59.12 27.4 25.9 58.43 63.4 69.3 35.7 20.11 63.85 24.6 16.2 23.32 58.9 93.9 32.65 18.21 49.35 78.133 57.87 42.8 34.1 39 51.35 24.1 15.57 30.17 58.4 44.9 43.92 25.35 38.2 60.54 58.58 54.35 64.2 15.65 47.77 18.38 26.57 76.9 40.25 88.5 40.9 21.95 23.15 59.04 59.63 57.1 76.2 11.66 26.66 20.2 30.8 54.46 44.9 60.89 24.38 21.5 28.2 84.51 41.9 59.6 36.19 63.16 60.3 10.9 50.7 35.5 47.86 29.49 23.15 5701 56.9 67.27 35.385 35.18 18.5 32.6 57.63 47.4 57.63 23.37 21.4 92.2 82.15 23.15 22.02 24.2 19.1 48.15 60.5 27.5 33.04 22.1 19.7 44.6 13 20.2 32.3 59.7 49.26 37.9 54.5 66.26 14.93 27.7 31.2 56.72 66.1 20.94 52.75 92.58 26.63 16 63.7 92.29 56.7 77.88 24.06 57 19.7 31 Average 21.66 58.80 27.94 26.72 31.98 58.91 61.19 52.95 23.85 25.09 51.69 63.54 54.49 61.85

(49) TABLE-US-00002 Average of measurements Measured particle diameter in m Fed into extruder at the beginning 26.21 Fed into extruder via side feeder 57.85 Admixture via dry blending 58.17 D50 pigment according to TDS 55

(50) Some recordings and measurements are shown in FIGS. 23 to 29. From these Figures it is also clearly evident that the pigment particles are significantly damaged when introduced at the beginning of the extrusion process. FIGS. 23 to 25 show metal sheets coated with the finished milled powder.

(51) FIG. 23 shows a micrograph of a coating prepared with powder coating at 100 magnification, wherein the effect pigment has been admixed by means of dry blending (NO shear forces). The effect pigment particles have retained their original round or oval shape.

(52) FIG. 24 shows a micrograph of a coating prepared with the powder coating according to the present invention at 100 magnification, wherein the effect pigment has been introduced into the transparent powder coating during the extrusion process via the side feeder; the majority of pigment particles is still round/oval, there are only few fragments.

(53) FIG. 25 shows a micrograph of a coating prepared with a comparative powder coating in 100 magnification, wherein the effect pigment has been fed into the extruder at the beginning of the process and co-extruded. The particle shape is irregular and there are many small fragments.

(54) The photographs of FIGS. 26 through 29 show powder coating chips which were evaluated immediately after leaving the extruder and the cooling roll (pressing into wafers, cooling and mechanical crushing).

(55) FIG. 26 shows a micrograph of a powder coating chip as used in the present invention at 200 magnification, wherein the effect pigment has been admixed by feeding into the extruder via side feeder.

(56) FIG. 27 shows, in comparison, a micrograph of a comparative powder coating chip at 200 magnification, wherein the effect pigment has been fed into the extruder at the beginning of the process and co-extruded.

(57) FIG. 28 shows a micrograph of a master batch effect powder coating A (pigment in transparent powder coating) according to the present invention at 200 magnification, wherein the effect pigment has been admixed by feeding into the extruder via side feeder.

(58) FIG. 29 shows, in comparison, a micrograph of a comparative master batch (pigment in transparent powder coating) at 200 magnification, wherein the effect pigment has been fed into the extruder at the beginning of the process and co-extruded.

Examples

(59) TABLE-US-00003 TABLE 1 SI (sparkle intensity) values obtained at various measurement angles SI value Measurement angle (between light source 15 45 75 and measuring sensor) RAL 9007, glossy, bonded, TIGER 24.22 3.29 2.54 product No. 029/76018 RAL 9007, glossy, according to the 47.42 30.14 29.08 present invention Dark gray metallic, fine structure, 36.12 11.35 10.13 bonded, TIGER product No. 029/80848 Dark gray metallic, fine structure, 25.51 31.28 31.57 according to the present invention Gray metallic matte, bonded, TIGER 27.34 10.15 2.89 product No. 068/71558 Gray metallic matte, according to the 54.05 53.31 36.15 present invention