Laser additive and its use in polymer materials

Abstract

The present invention relates to pigments which comprise niobium-doped titanium dioxide as well as a layer encapsulating the niobium-doped titanium dioxide, to polymer materials containing same and to the use of said pigments as laser absorbing additive in products comprising at least one polymer material and said encapsulated niobium-doped titanium dioxide containing pigments.

Claims

1. Pigments comprising a particle containing niobium-doped titanium dioxide and a layer encapsulating the niobium-doped titanium dioxide containing particle, the encapsulating layer comprising at least a calcium compound wherein the calcium compound is CaO or a mixture of CaO with CaCO.sub.3 and/or CaTiO.sub.3.

2. Pigments according to claim 1, characterised in that the encapsulating layer in addition to the calcium compound contains at least one further metal oxide, wherein the metal is selected from the group consisting of Zr, Ce, Si, Al, Zn and V.

3. Pigments according to claim 1 wherein the percentual weight content of the at least one calcium compound in the encapsulating layer is at least 80% by weight, based on the weight of the encapsulating layer.

4. Pigments according to claim 1 wherein the pigments are subject to a thermal treating step under reducing conditions prior to the use thereof.

5. Pigments according to claim 1 wherein the pigments each consist of a core being composed of a niobium-doped titanium dioxide particle and of an encapsulating layer being located directly on top of the core.

6. Pigments according to claim 1 wherein the pigments each consist of a core being composed of a substrate particle having a layer of niobium-doped titanium dioxide directly located on the substrate particle, and of an encapsulating layer being located directly on top of the core.

7. Pigments according to claim 6, characterised in that the substrate particle consists of a silicatic material, of titanium dioxide, of titanium dioxide doped with Al, Si, Zr or Mn, of alumina, silica, carbon, graphite, iron oxide, barium sulfate and/or of a pearl pigment.

8. Pigments according to claim 1 wherein the niobium-doped titanium dioxide has a percentage molar proportion of niobium of 0.05 to 15%, based on the molar mass of titanium.

9. Pigments according to claim 1 wherein the encapsulating layer has a thickness in the range of from 0.5 to 1000 nm.

10. Pigment according to claim 5 wherein the percentual weight content of the encapsulating layer, based on the weight of the core, is in the range of from 1 to 30% by weight.

11. Pigments according to claim 1 wherein the pigments have a particle size in the range of from 0.01 to 100 nm.

12. A method of absorbing laser light comprising exposing pigments according to claim 1 within a polymer composition to laser light.

13. A method according to claim 12, wherein the pigments are present in a polymer composition in a proportion in the range of from 0.001 to 20% by weight, based on the total weight of the polymer composition.

14. A method according to claim 12 wherein the polymer composition comprises at least one polymer compound, the laser absorbing pigment, and one or more of solvents, fillers, additives and/or colorants.

15. A method according to claim 12, wherein the polymer compound is a thermoplastic, a thermoset, an elastomer or a silicone.

16. Polymer composition, comprising at least one polymer compound and a pigment according to claim 1.

17. Polymer composition according to claim 16, characterised in that the pigment is present in the polymer composition in a proportion of 0.001 to 20% by weight, based on the total weight of the polymer composition.

18. Polymer composition according to claim 16 wherein the polymer compound is a thermoplastic, a thermoset, an elastomer or a silicone.

19. Laser markable article consisting of a corpus having a surface, characterised in that the corpus or at least a part of the surface thereof comprises a polymer composition according to claim 16.

20. Laser markable article according to claim 19, characterised in that the corpus has a laser marking on the surface.

Description

EXAMPLE 1

(1) Nb-Doped TiO.sub.2 Particle with CaO-Encapsulating Layer (H.sub.2O.sub.2-Route)

(2) 1.6 l of deionized water are heated in a reaction vessel to a temperature of about 75? C. The pH of the solution is adjusted with HCl (35%) to 1.8. A solution of 8.83 g NbCl.sub.5 powder in 374 g HCl (35%) and a 1490 ml TiCl.sub.4 solution (416 g/l) is then slowly dropped into the starting solution while the pH is kept at 1.8 with NaOH (32%). After the reaction is accomplished, the pH is adjusted at 7.0 by adding NaOH (32%) and the temperature of the resulting dispersion is raised to 80? C. Then, an aqueous mixture of 25.27 g CaCl.sub.2*2H.sub.2O, 50.85 g deionized water and 98.3 g H.sub.2O.sub.2 (30%) is added while keeping the pH constant. The reaction is finalized within about 1.5 hours. Finally, the solids are filtered, washed with deionized water and dried at 105? C. for several hours, whereby Nb-doped titanium oxide hydrate powder coated with calcium oxide hydrate is obtained. The dried powder is calcined at 850? C. for 7 minutes in an electric furnace. Afterwards, the calcined powder is calcined again under reducing conditions (1% H.sub.2 gas) at 700? C. for 10 minutes.

(3) A pigment comprising a core particle of niobium-doped titanium dioxide and an encapsulating layer of calcium oxide is obtained.

EXAMPLE 2

(4) Nb-Doped TiO.sub.2 Particle with CaO Encapsulating Laver (Na.sub.2CO.sub.3-Route)

(5) 1.6 l of deionized water are heated in a reaction vessel to a temperature of about 75? C. The pH of the solution is adjusted with HCl (35%) to 1.8. A solution of 8.83 g NbCl.sub.5 powder in 374 g HCl (35%) and a 1490 ml TiCl.sub.4 solution (416 g/1) is then slowly dropped into the starting solution while the pH is kept at 1.8 with NaOH (32%). After the reaction is accomplished, the pH is adjusted at 7.0 by adding NaOH (32%) and the temperature of the resulting dispersion is raised to 80? C. Then, an aqueous mixture of 25.27 g CaCl.sub.2*2H.sub.2O, 246 g deionized water and 24.65 g Na.sub.2CO.sub.3 is added while keeping the pH constant. The reaction is finalized within about 1.5 hours. Finally, the solids are filtered, washed with deionized water and dried at 105? C. for several hours, whereby Nb-doped titanium oxide hydrate powder coated with calcium carbonate hydrate is obtained. The dried powder is calcined at 850? C. for 7 minutes in an electric furnace. Afterwards, the calcined powder is calcined again under reducing conditions (1% H.sub.2 gas) at 700? C. for 10 minutes.

(6) A pigment comprising a core particle of niobium-doped titanium dioxide and an encapsulating layer of calcium oxide is obtained.

COMPARATIVE EXAMPLE 1

(7) Nb-Doped TiO.sub.2 Particle without Encapsulating Layer

(8) 1.6 l of deionized water are heated in a reaction vessel to a temperature of about 75? C. The pH of the solution is adjusted with HCl (35%) to 1.8. A solution of 8.83 g NbCl.sub.5 powder in 374 g HCl (35%) and a 1490 ml TiCl.sub.4 solution (416 g/1) is slowly dropped into the starting solution while the pH is kept at 1.8 with NaOH (32%). After the reaction is accomplished, the pH is adjusted at 7.0 by adding NaOH (32%). Finally, the solids are filtered, washed with deionized water and dried at 105? C. for several hours. The dried powder is calcined under reducing conditions (4% H.sub.2 gas) at 710? C. for 30 minutes.

(9) A niobium-doped titanium dioxide particle is obtained.

(10) Evaluation of Laser Marking Properties:

(11) 0.06 g of the pigments according to examples 1 and 2 and comparative example 1 are mixed with 19.94 g of a PVC T-sol compound (product of Nippon Pigment Co.) under vacuum in a planetary mixer (ARV-310, Thinky Co.). The mixture is coated onto a 0.1 mm PET film and dried at 180? C. for 3 minutes. Each test piece has an overall thickness of about 0.5 mm. The concentration of the pigment in the coating composition is 0.3% by weight, based on the weight of the total coating composition.

(12) A further comparative sample (comp. ex. 2) is prepared, using Iriotec? 8825 (laser pigment of Merck KGaA, antimony-doped tin oxide on mica substrate) as laser absorbing pigment instead of the pigments according to the present invention. The content thereof is 0.3 weight % as well, based on the weight of the total coating composition.

(13) The coated plastic films are irradiated by a 1064 nm fiber laser (LP-V10U of Panasonic Sunx) under standard conditions to form a test grid.

(14) Maximum output: 15 W

(15) Pulse frequency: 20 KHz-100 KHz

(16) TABLE-US-00001 Laser marking property Marking darkness reactivity color Comparative example 1 excellent excellent bluish black Comparative example 2 good good brown Example 1 excellent excellent bluish black Example 2 excellent excellent bluish black

(17) The examples show that the pigments according to the present invention, when used as laser absorbing additives, exhibit the same excellent laser marking ability as the niobium-doped titanium dioxide particles not having an encapsulating layer thereon. The color of the laser marks is bluish black as desired. The laser marking ability is better than that of the commercial comparison product.

(18) Evaluation of Coloristic Properties of Markings and Test Samples

(19) Light Stability Test:

(20) 2 g of the pigments according to examples 1 and 2 and comparative example 1 are mixed with 18 g of a PVC T-sol compound (product of Nippon Pigment Co.) under vacuum in a planetary mixer (ARV-310, Thinky Co.). The mixture is coated onto a 0.1 mm PET film and dried at 180? C. for 3 minutes. Each test piece has an overall thickness of about 0.5 mm.

(21) 3 test pieces having the same size and shape are prepared. The color of the test pieces is measured by a color measuring instrument (CR-400, Konica Minolta Co.) The test pieces are arranged adjacent to each other on a sample plate. A Xenon lamp emitting artificial solar light (XC-500, Seric Co.) is arranged in a distance of 45.5 cm right above the test pieces. One half of each of the test pieces is then covered by an aluminum foil. The remaining area of each test piece not covered by the aluminium foil is then exposed to light from the Xenon lamp (30.000 lux, 30 minutes).

(22) The color difference between the part areas exposed to solar light and not exposed to solar light is then evaluated. The color difference is indicated as delta E (?E, calculated by the colorimeter by using the L*, a*b* values of the exposed and the non-exposed part of each test piece).

(23) Light Stability Test:

(24) TABLE-US-00002 Example ?E example 1 0.8 example 2 1.4 comparative 4.9 example 1

(25) The test shows that polymer compounds containing the present pigments do not exhibit a significant change in color due to the exposure of solar radiation in contrast to polymer compounds containing non-encapsulated niobium-doped titanium dioxide particles.

(26) Lightness of Test Samples and Markings:

(27) Samples are prepared corresponding to the procedure of the laser marking evaluation described above.

(28) The lightness value L* of the laser marking itself (must be as low as possible for obtaining dark markings) as well as the transparency of the respective test film (the higher the transparency, the better) is measured. In addition, the coloristic data (L*, a, b) of the test films containing the laser additive in the coating should be as neutral as possible.

(29) The colorimetric measurement is performed on a piece of 20 mm?20 mm each, marked with 15 W vanadate laser (Trumpf VectorMark 5), 80% power, speed 2000 mm/s, frequency 80 kHz, line distance 50 ?m (alternating mode). The colorimetric evaluation is performed with a Konica Minolta CR-400 color measuring instrument.

(30) The Following Results are Achieved:

(31) TABLE-US-00003 Material comp.1 comp.2 ex. 1 ex.2 L*-value laser marking 53.8 64.2 59.9 60.2 L*-value test film on 85.6 87.6 85.9 85.5 white background a-value test film ?1.1 ?0.6 ?1.0 ?1.1 b-value test film 3.0 5.2 3.3 3.1 L*-value test film on 49.4 46.2 46.7 45.1 black blackground Transparency 42.3 47.3 45.6 47.3 (calculated in %)

(32) Transparency of the test film is calculated as follows:
Transparency=[L*value(white background)?L*-value(black background)]/L-value(white background)?100%

EXAMPLES 3-5

(33) Laser Marking in Silicone Test Plates:

(34) Laser markings in silicone polymers may be obtained only by using laser marking pigments exhibiting an intrinsic laser activity, since silicone polymers are not capable to carbonize when exposed to laser light. The pigments according to the present invention are tested in silicone polymer plates. To this end, silicone plates of Silopren LSP 2530 are prepared, having a content of the present pigments according to example 1 of 0.1% by weight (ex. 3), 0.3% by weight (ex. 4) and 0.5% by weight (ex. 5), respectively, based on the weight of silicone plate. The silicone plates are marked with a 15 W vanadate laser (Trumpf VectorMark 5), 99% power, speed 1000 mm/s, frequency 16 kHz. A rectangle of several cm.sup.2 size is prepared in each case. The laser absorption rises with rising content of the laser absorbing pigment, leading to contrastful dark markings on a light background in good and excellent quality in examples 4 and 5.

(35) The L*-values of the laser markings and of the test plates over white and black background are measures similar to examples 1, 2 and comparative examples 1 and 2 as described above, except that silicon test plates containing the laser absorbing pigments are used instead of coated test films containing the laser absorbing pigments in the coating.

(36) The following results are achieved:

(37) TABLE-US-00004 Material ex. 3 ex. 4 ex. 5 L*-value laser marking 46.0 35.8 33.1 L*-value test plate on 76.8 75.7 76.0 white background L*-value test plate on 45.8 57.0 63.3 black blackground Transparency 40.3 24.7 16.8 (calculated in %)

(38) Each of the test plates exhibits a clearly visible dark laser marking, whereby the laser markings according to examples 4 and 5 are of an especially desired darkness with good contrast. In addition, the transparency of the test plate remains acceptable while the color of the test plate is light bluish white which is highly desirable.