Method for the partial colouring of plastic parts

Abstract

The present invention relates to an improved method for the partial colouring, in particular for the coloured laser engraving, of plastic parts, in particular thermoplastic plastic parts, more particularly thermoplastic plastic parts, comprising a layer structure, and to the resulting partially coloured, preferably coloured and laser engraved, plastic parts, in particular thermoplastic plastic parts.

Claims

1. A process for partial coloring of plastic parts containing the steps of i) immersing a plastic part in a coloring bath, ii) optionally heating the coloring bath, iii) irradiating the plastic part from i) and optionally ii) with focused nonionizing electromagnetic radiation, wherein the partial coloring is effected substantially only at a site irradiated in step iii); wherein a wavelength range of the focused nonionizing electromagnetic radiation is chosen such that the coloring bath has a light permeability of ≥10% to ≤99%, determined according to ISO 13468-2; wherein the plastic part comprises at least one additive which has an absorption maximum in the wavelength range of the focused nonionizing electromagnetic radiation or wherein the plastic part is coated with at least one additive comprising a coating composition which has an absorption maximum in the wavelength range of the focused nonionizing electromagnetic radiation.

2. The process as claimed in claim 1, wherein the plastic part contains a thermoplastic plastic.

3. The process as claimed in claim 1, wherein step iii) is carried out using laser radiation having a wavelength range of from ≥0.70 μm to ≤1000 μm.

4. The process as claimed in claim 1, wherein the additive comprises at least one or more organic and/or inorganic IR absorbers.

5. The process as claimed in claim 1, wherein the additive comprises at least one or more inorganic IR absorbers selected from the group consisting of borides, tungstates, and mixtures thereof.

6. The process as claimed in claim 1, wherein the coloring bath comprises at least one colorant.

7. The process as claimed in claim 1, wherein the coloring bath comprises at least one dye selected from the group consisting of solvent dyes, disperse dyes, and mixtures thereof.

8. The process as claimed in claim 1, wherein an immersion depth of the plastic part in step i) is ≤120 mm.

9. The process as claimed in claim 1, wherein the coloring bath comprises: a) solvent and/or dispersant, and b) at least one colorant.

10. The process as claimed in claim 1, wherein steps i) to iii) are preceded or followed by an irradiation with focused nonionizing electromagnetic radiation as in step iii).

11. The process as claimed in claim 1, wherein the plastic part has a layer construction, wherein the layer construction comprises at least one layer of a thermoplastic plastic, wherein the at least one thermoplastic plastic forms at least one outer layer of the layer construction and comprises at least one additive which has an absorption maximum in the wavelength range of the employed focused nonionizing electromagnetic radiation or, wherein the at least one thermoplastic plastic forms at least one outer layer of the layer construction and the outer thermoplastic plastic is coated with at least one additive in the form of a coating composition which has an absorption maximum in the wavelength range of the employed focused nonionizing electromagnetic radiation.

12. The process as claimed in claim 1, wherein the plastic part has a layer construction, wherein the layer construction comprises at least one layer of a thermoplastic plastic, wherein the at least one thermoplastic plastic forms at least one outer layer of the layer construction and comprises at least one additive which has an absorption maximum in the wavelength range of the employed focused nonionizing electromagnetic radiation, and comprises at least one further layer of a thermoplastic plastic.

13. The process as claimed in claim 12, wherein at least one layer of a thermoplastic plastic or the at least one further layer of a thermoplastic plastic additionally contains at least one black pigment.

14. The process as claimed in claim 12, wherein the at least one further layer of a thermoplastic plastic additionally contains at least one black pigment.

15. A security document obtainable by the process as claimed in claim 1.

16. A method comprising utilizing an additive having an absorption in the wavelength range of the employed focused nonionizing electromagnetic radiation for production of color laser engraved plastic parts by the process as claimed in claim 1.

Description

EXAMPLES

(1) I. Composition of the Coloring Bath

(2) 69.31% by weight of water

(3) 0.99% by weight of Macrolex™ Blue 3R (colorant, from Lanxess AG Deutschland)

(4) 19.8% by weight of ethylene glycol butyl ether (EGBE), (solvent, The Dow Chemical Company)

(5) 9.9% by weight of diethylene glycol (DEG), (leveling agent, Merck KGaA)

(6) II. Process for Color Laser Engraving

(7) Laser irradiation was carried out using a Foba D84 NdYAG laser having a laser power of about 7.5 W, a laser frequency of 8 kHz in pulsed operation and a current of 8 A. The advance rate of the laser, the immersion depth and the temperature of the coloring bath for the examples which follow are reported in table 1.

(8) The films/the molding of the examples 1 to 3 were immersed in the coloring bath according to the specifications in table 1. The coloring bath comprising the film/the molding was placed on the workpiece carrier of a Foba D84S laser apparatus. The focus of the laser was tuned to the film surface. The immersion depth is reported in table 1. In the context of the present invention immersion depth is to be understood as meaning the penetration depth of the employed radiation into the coloring bath up to the surface of the plastic part onto which the partial coloring is to be applied. Irradiation with the laser beam was commenced.

(9) TABLE-US-00001 TABLE 1 Conditions of the color laser engraving Example 1 (V) Example 2 Example 3 Temperature of 40° C. 40° C. 40° C. coloring bath Immersion depth 1 mm 1 mm 1 mm Advancing rate 100 mm/s 100 mm/s 100 mm/s (V): Comparative example

Example 1—Comparison

(10) A plastics film Makrofol™ ID 4-4 opaque white made of polycarbonate and having a thickness of 200 μm from Covestro Deutschland AG was colored as described above under II.

(11) After removal of the plastic part from the coloring bath a blue coloring had formed in the path of the laser on the film. The regions of the film not irradiated with the laser were not significantly colored.

Example 2—Inventive

(12) A plastic film composite composed of two different polycarbonate films (film (a-1) and film (a-2)) was colored as described above under II.

(13) Film (a-1): Makrofol™ ID4-4 opaque white made of polycarbonate in a thickness of 300 μm from Covestro Deutschland AG.

(14) Production of film (a-2): Transparent polycarbonate film in a thickness of 100 μm.

(15) Masterbatch: Compounding of a Highly Concentrated IR Masterbatch

(16) The production of the masterbatch for the production of the film (a-2) was carried out with a conventional twin-screw compounding extruder (ZSK 32) at processing temperatures customary for polycarbonate of 250° C. to 330° C.

(17) A masterbatch having the following composition was compounded and subsequently granulated: 94.69% by weight of polycarbonate Makrolon™ 3108 from Covestro Deutschland AG 0.75% by weight of YMDS 874 IR absorber from Sumitomo 4.5% by weight of Makrolon™ 3108 powder from Covestro Deutschland AG 0.006% by weight (60 ppm) lamp black 101 (carbon black from Evonik-Degussa GmbH) having an average particle size of 95 nm
Production of Extrusion Film (a-2)

(18) The employed apparatus for producing the extruded film comprises: an extruder for extrusion of the layer containing at least one polycarbonate or with a screw of 60 mm in diameter (D) and a length of 33 D. The screw has a degassing zone; melt pump; crosshead; slot die of 450 mm in width; three-roller smoothing calendar with horizontal roller orientation, wherein the third roller can swivel by +1-45 relative to the horizontal; roller conveyor; thickness measuring means means for double-sided application of protective film; takeoff means; winding station.

(19) The granulate of the masterbatch was conveyed from the dryer into the filling hopper of the extruder. The material was melted and conveyed in the barrel/screw plasticizing system of the extruder. The melt passed from the slot die on to the smoothing calendar. The final shaping and cooling of the film was carried out on the smoothing calendar (consisting of three rollers). The surfaces were embossed using a textured steel roller (no. 6 side) and a textured silicone rubber roller (no. 2 side). The rubber roller used for texturing the film surface is described in U.S. Pat. No. 4,368,240 from Nauta Roll Corporation. The film was subsequently transported through a takeoff and then the film was wound up.

(20) Lamination of Films (a-1) and (a-2)

(21) Lamination was carried out on a Bürckle 50/100 lamination press. The films (a-1) and (a-2) were laminated with the following press settings:

(22) Heating zone: temperature 190° C., duration 8 minutes, pressure 60 N/cm.sup.2

(23) Cooling zone: temperature 38° C., duration 10 minutes, pressure 100 N/cm.sup.2

(24) After removal of the plastic film composite from the coloring bath an intensive blue coloring had formed in the path of the laser on the film. The regions of the film not irradiated with the laser were not significantly colored.

Example 3—Inventive

(25) The plastic part to be colored is a multilayered three-dimensionally molded plastic part produced by film insert molding (FIM) technology. The film composite from example 2 was molded in a three-dimensional mold by high-pressure molding. Forming was carried out on a Niebling HPF forming apparatus. The three-dimensionally formed film composite was placed in a plastic injection mold and subjected to film insert molding with Bayblend™ T65 from Covestro Deutschland AG on the white side of the film composite.

(26) The thus-produced molding was colored as described under 11.

(27) After removal of the plastic part from the coloring bath an intensive blue coloring had formed in the path of the laser on the film insert molded plastic part. The regions of the plastic part not irradiated with the laser were not significantly colored.

(28) The coloring in the path of the laser in inventive examples 2 and 3 was more intensive compared to example 1 where no IR absorber was present in the film.