Additive for laser-markable and laser-weldable polymer materials

Abstract

The present invention relates to an additive for laser-markable and/or laser-weldable polymer materials, and in particular to the use of pigments which comprise niobium-doped titanium dioxide as laser absorbing additive in polymer materials, to polymer materials which comprise a laser absorbing additive of this type and to a laser-marked or laser-welded product comprising at least one polymer material and niobium-doped titanium dioxide containing pigments as laser absorbing additive.

Claims

1. A process for laser marking of an article, comprising exposing to laser radiation an article containing a pigment comprising a niobium-doped titanium dioxide laser absorbing additive in a polymer composition, the percentage molar proportion of niobium being 0.3 to 15% based on the molar mass of titanium, the polymer composition comprising polyethylene, polypropylene, a polyamide, a polyester, a polyester-ester, a polyether-ester, polyphenylene ether, polyacetal, polyurethane, polybutylene terephthalate, polymethyl methacrylate, polyvinyl acetal, polystyrene, acrylonitrile-butadiene-styrene, acrylonitrile-styrene-acrylate, polycarbonate, a polyether sulfone, a polyether ketone, or polymer blends or copolymers thereof, a melamine resin, an epoxy resin, a silicone resin or a polysiloxane, wherein the niobium-doped titanium dioxide is subjected to calcination under reducing conditions in an N.sub.2/H.sub.2 atmosphere prior to use as a laser absorbing additive.

2. The process according to claim 1, wherein the pigment consists of the niobium-doped titanium dioxide.

3. The process according to claim 1, wherein the pigment comprises a substrate and a coating located thereon, and the niobium-doped titanium dioxide is present in the coating.

4. The process according to claim 3, wherein the substrate is natural mica, synthetic mica, talc, sericite, titanium dioxide, titanium dioxide doped with Al, Si, Zr or Mn, alumina, silica, carbon, graphite, iron oxide, barium sulfate and/or a pearl pigment and has a coating which comprises niobium-doped titanium dioxide.

5. The process according to claim 1, wherein the pigment has a particle size in the range of from 0.01 to 100 μm.

6. The process according to claim 1, wherein the pigment is present in the 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.

7. The process according to claim 1, wherein the polymer composition comprises at least one polymer compound and the laser absorbing additive, and optionally solvents, fillers, additives and/or colorants.

8. The process according to claim 1, wherein the polymer compound is a thermoset that is a polyurethane, a melamine resin, an epoxy resin or a polyester resin.

9. A polymer composition, comprising at least one polymer compound that is polyethylene, polypropylene, a polyamide, a polyester, a polyester-ester, a polyether-ester, polyphenylene ether, polyacetal, polyurethane, polybutylene terephthalate, polymethyl methacrylate, polyvinyl acetal, polystyrene, acrylonitrile-butadiene-styrene, acrylonitrile-styrene-acrylate, polycarbonate, a polyether sulfone, a polyether ketone, or polymer blends or copolymers thereof, a melamine resin, an epoxy resin, a silicone resin or a polysiloxane, and a laser absorbing additive, in a proportion of 0.001 to 20% by weight, based on the total weight of the polymer composition, where the laser absorbing additive is a pigment consisting of titanium dioxide which is doped with niobium and is subject to calcination under reducing conditions in an N.sub.2/H.sub.2 atmosphere, prior to use as a laser absorbing additive, where the percentage molar proportion of niobium is 0.3 to 15%, based on the molar mass of titanium.

10. The polymer composition according to claim 9, wherein the polymer compound is a thermoset that is a polyurethane, a melamine resin, an epoxy resin or a polyester resin.

11. A laser markable and/or laser-weldable article consisting of a corpus having a surface, wherein the corpus or at least a part of the surface thereof is composed of or comprises a polymer composition according to claim 9.

12. The laser markable and/or laser weldable article according to claim 11, wherein the corpus has a laser marking on the surface.

Description

EXAMPLE 1

(1) A solution of 2.8 g of NbCl.sub.5 powder in 125 ml of HCl (37%) is added to 474 ml of a 400 g/l TiCl.sub.4 solution in deionized water. The resulting mixture is added into 1600 ml of deionized water while keeping the pH controlled at a value of 1.8 at a temperature of about 75° C. for three hours. Thereafter, the solids are filtered, washed and dried in an oven at 105° C. for ten hours. The dried sample is filled in a crucible and calcined at 700° C. under N.sub.2/H.sub.2 (96%/4%) for 15 min. A pigment containing 1.00 mol % Nb relative to the mol mass of Ti is achieved.

EXAMPLES 2 to 4

(2) Example 1 is repeated with the amendment that the amounts of NbCl.sub.5 and HCl are adapted in order to achieve a pigment having a content of 0.05 mol % Nb in example 2 (0.14 g NbCl.sub.5, 6 ml HCl), 4.00 mol % Nb in example 3 (11.0 g NbCl.sub.5, 499 ml HCl) and 10.00 mol % Nb in example 4 (28 g NbCl.sub.5, 1247 ml HCl), respectively, in each case relative to the mol mass of Ti.

COMPARATIVE EXAMPLE 1

(3) Example 1 is repeated with the amendment that a solution of NbCl.sub.5 in HCl is not used, but the TiCl.sub.4 solution is solely added to the deionized water at a pH of 1.8 and further prosecuted as described above. A TiO.sub.2 containing pigment without any Nb content is thus obtained.

Evaluation of Laser Marking Properties

(4) Plastic plates having a size of 74×147 mm are produced by molding at 180° C. a polymer composition consisting of a mixture of a low density polyethylene (LDPE, product of Japan Polyethylene Corporation) and of a dry powder, the latter being composed of the pigment according to examples 1-4 as well as of the pigment of comparative example 1, and zinc stearate powder, in a weight ratio 8:2 (sample/zinc stearate), resulting in a content of the niobium-doped titanium dioxide pigment or alternatively, the titanium dioxide pigment of 0.3% by weight, based on the weight of the whole polymer composition, in the LDPE.

(5) 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 niobium-doped titanium dioxide. The content thereof in the test plate is 0.3 weight % as well, based on the weight of the whole polymer composition.

(6) The plastic plates are irradiated by a 1064 nm fiber laser (LP-V10U of Panasonic sunx) under standard conditions to form a test grid. Maximum output: 15 W Pulse frequence: 10-50 μs

(7) TABLE-US-00001 Laser marking property Marking darkness reactivity color Comparative example 1 average average grey Comparative example 2 good good brown Example 1 excellent excellent bluish black Example 2 good good bluish black Example 3 excellent excellent bluish black Example 4 excellent excellent bluish black

(8) Irradiation of the plastic plates by a 10.5 W vanadate laser (Trumpf VectorMark 5) at 99% power, speed 500-5000 mm/s, pulse 20-100 KHz and 50 μm line distance gives similar results by evaluation of the resulting test grids.

EXAMPLES 5-8

(9) Examples 1 to 4 are repeated with the proviso that the final calcination of the pigment is executed in an N.sub.2 atmosphere at 800° C.

COMPARATIVE EXAMPLE 3

(10) Comparative example 1 is repeated with the proviso that the final calcination of the pigment is executed in an N.sub.2 atmosphere at 800° C.

(11) The evaluation of the laser marking properties of examples 5-8 and comparative example 3 after irradiation with a 1064 nm fiber laser takes place in the same manner as described above for examples 1-4 and comparative examples 1 and 2.

(12) TABLE-US-00002 Laser marking property Marking darkness reactivity color Comparative example 3 poor poor grey Example 5 good good bluish black Example 6 average average bluish black Example 7 good good bluish black Example 8 good good bluish black

(13) Here as well, irradiation by a 10.5 W vanadate laser (Trumpf VectorMark 5) at 99% power, speed 500-5000 mm/s, pulse 20-100 KHz and 50 μm line distance gives similar results by evaluation of the resulting test grids.

Evaluation of Coloristic Properties of Markings and Test Plates

(14) In order to be able to compare the coloristic data achieved by the use of the niobium-doped titanium dioxide containing pigment as laser additive in the present invention with the prior art, it is reasonable to determine the lightness value L* of the marking itself (must be as low as possible for obtaining dark markings) as well as the transparency of the test plastic plate (the higher the transparency, the better the opportunity to color the plastic material in the desired color). In addition, the coloristic data (L*, a, b) of the test plate containing the laser additive should be as neutral as possible making sure that the content of the laser additive pigment does not hamper the neutral color of the test plate itself. The colorimetric measurement is performed on a block of 50 mm×30 mm marked with 10.5 W vanadate laser (Trumpf VectorMark 5), 99% power, speed 3000 mm/s, frequency 80 Hz, line distance 50 μm (alternating mode). The colorimetric evaluation is performed with a Minolta Chroma Meter CR-300.

(15) The following results are achieved:

(16) TABLE-US-00003 Material comp. 1 comp. 2 ex. 1 Concentration Nb 0 0 1.0 (mol %) L-value laser marking 56.4 47.2 42.2 L-value test plate on 78.8 72.7 71.8 white background a-value test plate −1.4 −0.3 −1.6 b-value test plate −0.8 2.2 −4.0 L-value test plate on 69.9 52.7 57.3 black blackground Transparency 11.3 27.5 20.2 (calculated in %)

(17) Transparency of the test plate is calculated as follows:
Transparency=[L*value(white background)−L*-value(black background)]/L-value(white background)×100%

(18) The test plate of example 1 exhibits a light color with high L*-values, indicating that the niobium-doped titanium dioxide in the plate content does not diminish the lightness of the plate significantly more than the comparative laser additive Iriotec®8825 (comp. ex. 2). In particular the b-value of the test plate indicates that the use of the laser additive pigments according to the present invention leads to a slight bluish color not only of the marking itself, but also of the test plate, which is more tolerable than the slight yellowish color of the test plate of comp. ex. 2.

(19) In addition, the laser marking of example 1 itself exhibits a lower L*-value than that of comp. ex. 2, indicating a darker color of the marking which is dark bluish-black instead of dark brown for comp. ex. 2. Although the absolute transparency of the test plate for comp. ex. 2 is not achieved, the test plate of example 1, corresponding to an article composed of the polymer composition according to the present invention, shows a transparency sufficiently high in order to allow coloration in all colors desired by the applicant of the newly presented laser absorbing additive.

EXAMPLE 9—LASER WELDING

(20) A plastic plate corresponding to the plastic plate of example 3 is used in order to check the laser welding performance. Said plastic plate is used for the laser absorbing bottom layer of the welded element. The top layer consists of a laser transparent plate of the same polyethylene material as used for the plate of example 3 but without additives. The laser transparent plate has the same size as the laser absorbing bottom layer plate and was produced under the same conditions on the injection moulding machine prior to the use thereof. For testing the laser welding performance, the 10.5 W vanadate laser (Trumpf VectorMark 5) is used in continuous wave mode (unpulsed). The laser beam is set up in a way that the focus lies 4 mm under the surface of the laser absorbing bottom layer plate which contains the niobium-doped titanium dioxide. The laser transparent plate is put in close contact to the laser absorbing bottom layer plate on top of the latter and is fixed at the edges by means of magnets. The maximum laser power of 100% is used and the speed of the laser beam is set to 20 mm/s. 1000 parallel lines with a length of 1 mm and a distance of 50 μm are lasered. With a progress of 1 mm/s a welding line is formed. The welding line is well defined and both plates are strongly bond to each other.