LASER-MARKABLE AND LASER-WELDABLE POLYMERIC MATERIALS

Abstract

The present invention relates to laser-markable and laser-weldable polymeric materials which are distinguished by the fact that they comprise at least one fluorine-doped tin oxide (FTO) as absorber.

Claims

1. Laser-markable and/or laser-weldable polymers, characterised in that they comprise at least one fluorine-doped tin oxide (FTO) as absorber.

2. Laser-markable and/or laser-weldable polymers according to claim 1, characterised in that the content of fluorine in the FTO is 1-15 mol % based on the tin oxide.

3. Laser-markable and/or laser-weldable polymers according to claim 1, characterised in that the FTO has a number-weighted particle size of <5 m, measured at the D.sub.90 by means of laser diffraction.

4. Laser-markable and/or laser-weldable polymers according to claim 1, characterised in that the FTO consists of aggregates of primary particles having a diameter of less than 100 nm.

5. Laser-markable and/or laser-weldable polymers according to claim 1, characterised in that the laser additive is used in concentrations of 0.01 to 1% by weight, based on the polymer.

6. Laser-markable and/or laser-weldable polymers according to claim 1, characterised in that the polymer is a thermoplastic, thermoset or elastomer.

7. Laser-markable and/or laser-weldable polymers according to claim 1, characterised in that the polymer additionally comprises one or more coloured pigments and/or dyes.

8. Process for the preparation of laser-markable and/or laser-weldable polymers according to claim 1, characterised in that the addition of the FTO is carried out simultaneously or successively by compounding, via a masterbatch or via pastes or by direct addition to the polymer, and optionally one or more additives are added and the polymer is then shaped under the action of heat.

9. (canceled)

10. Moulding compositions, semi-finished products and finished parts consisting of the laser-markable and laser-weldable polymer according to claim 1.

11. A method of producing moulding compositions, semi-finished products or finished parts, comprising subjecting to laser energy a polymer according to claim 1.

12. A method of producing an image on an article, comprising subjecting to laser energy an article comprising a polymer according to claim 1.

Description

EXAMPLES

Example 1

[0039] A powder mixture of 47.5 g of anhydrous tin(II) chloride, 22 g of sodium carbonate (anhydrous), 5 g of sodium fluoride and 43 g of sodium chloride are dry-ground in a ball mill with 3.2 kg of steel balls for 30 min. During this time, the tin(II) chloride reacts with sodium fluoride and sodium carbonate to give nanoscale fluorine-doped tin oxide. The mixture is then heated to 400 C. in a crucible, cooled and washed successively with hydrochloric acid and a number of times with water. The resulting pigment paste is dried at 110 C. and then ground to give a fine powder. The particle size of the pigment powder is determined with the aid of laser diffraction (Malvern 2000) and scanning electron microscopy. The average number-weighted particle size of the pigment particles is 560 nm, the D.sub.90=1.2 m, the size of the primary particles in the aggregates is on average 40 nm.

Example 2

Preparation of a Hydrophobic Finely-Divided Pigment Preparation

[0040] Fluorine-doped tin(II) oxide (FTO) from Example 1 is ground extremely finely in a bead mill with zirconium beads in a weakly acidic aqueous suspension (pH=2). The average particle size is 0.07 m (SEM). 100 ml of the approx. 20% suspension are admixed with 15 g of polymeric protective colloid (random lauryl methacrylate-hydroxymethyl methacrylate copolymer, molar mass about 5000). The mixture is emulsified by means of ultrasound or a high-pressure homogeniser.

[0041] The solvents are stripped off in vacuo. This gives a pasty residue which consists of finely divided FTO and protective colloid. 1 g of this preparation is mixed with 5 kg of PP granules (Metocene X50081, Basell). Samples of the mixture are converted into plates having a thickness of 15 mm by injection moulding. The plastic plates have a red colour; no particles are visible using an 8 magnifying glass. Following inscription using a 12 W Nd:YAG laser (SHT at 300 mm/s and 0.03 mm beam width; 40-90% lamp energy and a frequency of 5-15 kHz), the plates exhibit a pale inscription with high contrast.

Example 3

[0042] 1 kg of PP granules (Metocene 648T, Basell) are wetted with 2 g of dispersion aid (Process-Aid 24, Colormatrix) in a drum mixer. 5 g of the pigment from Example 1 and 1 g of organic green coloured pigment (PV Fast Green GG01, 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 250-260 C., shaped through a pelletising die to give a strand, cooled in a water bath and granulated by means of a rotating knife. The resulting compound is dried at 100 C. for 1 h and converted into plates having the dimensions 60 mm90 mm1.5 mm (whd) on an injection moulding machine. The plastic plates 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.

[0043] Filled areas with a line spacing of 50 m and also line text are lasered. Stable pale laser markings are obtained up to a speed of 3000 mm/s. The line marking is very defined with accurate detail and confirms the homogeneous distribution of the additive. No particles are visible under a 12 magnifying glass.

Example 4 (comparison):

[0044] Preparation of Tin Oxide without Fluorine Doping

[0045] The process according to Example 1 is used to prepare finely divided tin dioxide without F doping. For this purpose, a mixture of 47.5 g of anhydrous tin(II) chloride, 31 g of sodium carbonate (anhydrous) and 43 g of sodium chloride are dry-ground in a ball mill with 3.2 kg of steel balls for 30 min. The mixture is then heated to 400 C. in a crucible, cooled and washed successively with hydrochloric acid and a number of times with water. The resulting pigment paste is dried at 110 C. and then ground to give a fine powder. The average number-weighted particle size of the pigment particles is 630 nm, the D.sub.90=1.4 m. The pigment is introduced into the plastic as described in Example 3 and converted into plates. These are exposed to the laser as described. A weak, barely visible pale marking is obtained.

Example 5 (comparison)

Preparation of Fluorine-Doped Tin Oxide Having Relatively Large Particles

[0046] Fluorine-doped tin oxide is prepared in accordance with Example 1 of DE 40 06 044 A1 from tin(II) oxide and tin(II) fluoride. A brownish powder is obtained which, after grinding in a bead mill, has an average number-weighted particle size of 2 m and a D.sub.90=9 m. The resulting pigment is converted into plastic plates as described in Example 3 and exposed to the laser. This gives a dark marking that is irregular in fine elements and which, upon viewing with a 12 magnifying glass, consists of darkly marked dots. On exposure to a higher intensity, the surface becomes very roughened.