Laser-markable polymers and coatings

Abstract

The present invention relates to laser-markable polymers and coatings which are distinguished by the fact that they comprise tin/antimony oxide-coated spherical TiO.sub.2 particles of defined particle size as laser additive.

Claims

1. A method for the production of darkened laser-markings on a laser-markable polymer or on a laser-markable polymeric coating, which comprises: laser-treating the polymer or polymeric coating, which polymer or polymeric coating comprises a polymer and, in the polymer, a laser additive, which laser additive comprises spherical TiO.sub.2 particles which are coated on the surface with an antimony-doped tin dioxide layer (Sn,Sb)O.sub.2 and the TiO.sub.2 particles have a number weighted particle size of <15 m, measured at the D.sub.95 by means of laser diffraction, and wherein, in the resulting polymer or polymeric coating, the laser-treating results in reducing the TiO.sub.2 in the laser additive to Ti.sub.xO.sub.y, which results in a visibly darkened marking with a surface which is not roughened, where it was laser-treated.

2. The method of claim 1, wherein the content of antimony in the tin dioxide layer is 0.1-60 mol %, based on the tin dioxide.

3. The method of claim 1, wherein the laser additive has a number-weighted particle size of 0.05 m, measured at the D.sub.25 by means of laser diffraction.

4. The method of claim 1, wherein the laser additive is employed in a concentration of 0.005 to 30% by weight, based on the polymer or polymeric coating.

5. The method of claim 1, wherein the polymer is a thermoplastic, thermoset, elastomer or silicone.

6. The method of claim 1, wherein the polymer additionally comprises one or more coloured pigments and/or dyes.

7. The method of claim 1, wherein the content of antimony in the tin dioxide layer is 2-15 mol %, based on the tin dioxide.

8. A moulding composition, a product, a part or a film, which comprises a dark laser-marking on a polymer or polymeric coating thereof, which marking was produced by the method of claim 1.

9. A powder coating, which comprises a dark laser-marking thereon, which marking was produced by the method of claim 1.

Description

EXAMPLES

Example 1

(1) 100 g of spherical TiO.sub.2 (Kronos 2900, KRONOS Inc.) having a diameter D.sub.95 of 700-900 nm (measured using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. in 2 I of demineralised water with stirring. The pH of the suspension is adjusted to a value of 2.0 using 10% hydrochloric acid. A tin antimony chloride solution in hydrochloric acid, consisting of 264.5 g of 50% SnCl.sub.4 solution, 60.4 g of 35% SbCl.sub.3 solution ad and 440 g of 10% hydrochloric acid, is subsequently metered in slowly, during which the pH of the suspension is kept constant by simultaneous addition of 32% sodium hydroxide solution. When the addition is complete, the mixture is stirred for a further 15 min. The pH is subsequently adjusted to a value of 3.0 by addition of 32% sodium hydroxide solution, and the mixture is stirred for a further 30 min.

(2) The product is filtered off, washed, dried, calcined at a temperature of 500-900 C. for 30 min. and sieved through a 100 m sieve.

Use Examples

Example A1Laser Marking of Plastics

(3) 1 kg of PP granules (Metocene 648T, Basell) are wetted with 2 g of dispersion aid (Process-Aid 24, Colormatrix) in a drum mixer. 3 g of the laser additive from Example 1, 1 g of organic yellow pigment (PV Fast Yellow HG, Clariant) and 0.25 g of green pigment (PV Fast Green GNX, Clariant) are added and incorporated for 2 min in the drum mixer. The resulting mixture is compounded in a co-rotating twin-screw extruder with high shear at a jacket temperature of 200-220 C., shaped through a pelletising die to give a strand, cooled in a water bath and granulated by means of a rotating knife. The compound obtained is converted into tiles having the dimensions 60 mm90 mm1.5 mm (whd) on an injection moulding machine. The plastic tiles are then laser-marked using a pulsed YVO.sub.4 laser having a wavelength of 1064 nm and a maximum output power of 10.5 W. The test grid varies the speed between 500 and 5000 mm/s and the frequency between 20 and 100 kHz. Filled areas with a line spacing of 50 m and also line text are lasered. Stable dark laser markings are obtained up to a speed of 3000 mm/s. The line marking is very defined with accurate detail. The smooth surface of the marking confirms the reaction of the additive and less of the surrounding polymer.

Example A2Laser Marking of Plastics

(4) 3 g of additive from Example 1 are incorporated into PMMA analogously to Example A1instead of organic coloured pigments, 2 g of TiO.sub.2 Kronos 2220 are used. The plastic tiles are subsequently laser-marked using a pulsed YVO.sub.4 laser having a wavelength of 1064 nm and a maximum output power of 10.5 W. The test grid varies the speed between 500 and 5000 mm/s and the frequency between 20 and 100 kHz. Filled areas having a line separation of 50 m and in addition line script are lasered. Stable dark laser markings are achieved up to a speed of 5000 mm/s, which corresponds to the maximum marking speed of the laser.

Example A3Laser Marking of Silicone

(5) Liquid silicone rubber (LSR) is a two-component system which easily polymerises under the action of heat. The two liquid components are mixed in the ratio 1:1 to give the silicone rubber. In the example, an LSR type: KEG 2000/50 from Shin-Etsu is used. 6 g of the laser additive from Example 1 are added to 500 g of component 1 of the LSR and mixed vigorously. 500 g of component 2 are subsequently added and again mixed vigorously. This liquid mixture is poured into a mould and placed in a laboratory oven at 180 C. for 20 minutes for curing. After curing, the moulding is allowed to cool and laser-marked analogously to Example A1.

Example A4Laser Marking of Powder Coatings

(6) 560.5 g of Crylcoat 2689-0 (Allnex), 29.5 g of Primid XL-552 (Ems Chemie AG), 8.0 g of BYK 364P (BYK-Chemie GmbH), 2.0 g of Benzoin (DSM) and 400 g of Kronos 2160 (Kronos Titan GmbH) and 60 g of additive from Example 1 are mixed vigorously in a laboratory mixer for 5 min. The mixture obtained is extruded in a suitable extruder at temperatures between 70 and 100 C. The extrudate obtained is cooled, broken and ground. After addition of 2.0 g of Aeroxide Alu C (Evonik), the powder is sieved using a sieve, mesh width 125 m. The powder coating material obtained is applied to test metal sheets by means of the corona or tribo method and baked at 180 C. (specimen temperature) for 10 min.

(7) The coating on the test metal sheets is marked using an IR laser analogously to Example A1 and Example A2.