METHOD FOR THE PARTIAL COLORING OF PLASTIC PARTS

Abstract

The invention relates to an improved method for the partial coloring, in particular for the color laser engraving, of plastic parts, in particular thermoplastic plastic parts, more particularly thermoplastic plastic parts that have a multi-layered structure, to the resulting partially colored, preferably color laser engraved, plastic parts, in particular thermoplastic plastic parts, and to a device for the partial coloring of plastic parts.

Claims

1.-11. (canceled)

12. A process for partial coloring, in particular color laser engraving, of plastic parts, preferably of thermoplastic plastic parts, very particularly preferably of thermoplastic plastic parts comprising a layer construction, comprising at least: i) producing a coloring layer b) on at least a partial area of a plastic part (A); ii) irradiating the plastic part (A) from i) with nonionizing electromagnetic radiation (C), wherein the partial coloring is effected substantially only at sites covered with the coloring layer b) in step i) or at sites irradiated in step ii), wherein a wavelength range of the nonionizing electromagnetic radiation (C) is chosen such that the coloring layer b) has a radiation permeability of ≥0.1% to ≤99%, preferably of ≥0.5% to ≤95%, particularly preferably of ≥0.9% to ≤93%, for a chosen radiation determined by the UV-VIS-NIR-MIR method according to DIN EN ISO/IEC 17025.

13. The process as claimed in claim 12, wherein the plastic part (A) comprises a layer construction, wherein the layer construction comprises at least one layer of a thermoplastic plastic.

14. The process as claimed in claim 13, wherein the layer construction comprises at least one layer comprising at least one thermoplastic plastic and at least one further layer comprising at least one thermoplastic plastic and at least one black pigment, preferably carbon black.

15. The process as claimed in claim 14, comprising irradiating with focused nonionizing electromagnetic radiation (C) as in step ii) in the absence of a coloring bath before step i) and/or after step ii).

16. A security document obtained by the process as claimed in claim 12.

17. An apparatus comprising a coloring bath (B), a sheet (D) comprising one or more radiation-decoupling materials and a radiation source (E) for producing focused nonionizing electromagnetic radiation (C), wherein the coloring bath (B) preferably has a temperature of ≤99° C. to ≥−60.0° C., more preferably ≤99° C. to ≥0.0° C., more preferably of ≤70° C. to ≥10° C., particularly preferably of ≤50° C. to ≥15° C., wherein the temperature may vary in a temperature range of 100° C. or remains constant upon startup of the apparatus and in that the focused nonionizing electromagnetic radiation (C) passes through the sheet (D) comprising one or more radiation-decoupling materials before impacting a plastic part (A).

18. The apparatus as claimed in claim 17, wherein the coloring bath (B) has a temperature of ≤99° C. to ≥−60° C., preferably of ≤99° C. to ≥0° C., more preferably of ≤70° C. to ≥10° C., particularly preferably of ≤50° C. to ≥15° C., wherein the temperature preferably remains constant upon startup of the apparatus.

Description

[0153] FIG. 1 shows a possible embodiment of the apparatus according to the invention for the partial coloring of two-dimensional plastic parts.

[0154] FIG. 2 shows a possible embodiment of the apparatus according to the invention for the partial coloring of three-dimensional plastic parts.

[0155] The reference numerals in FIGS. 1 and 2 are as follows:

A-1: Two-dimensional plastic part, preferably thermoplastic plastic part, particularly preferably thermoplastic plastic part comprising a layer construction
A-2: Three-dimensional plastic part, preferably thermoplastic three-dimensional plastic part
B: Coloring bath or coloring layer in liquid form
C: Focused nonionizing electromagnetic radiation
D: Sheet comprising one or more radiation-decoupling materials
E: Radiation source for producing focused nonionizing electromagnetic radiation
b: Immersion depth or color layer thickness

[0156] FIG. 1 shows a schematic diagram of a coloring bath B into which a two-dimensional plastic part A-1 is immersed such that at least one of its surfaces contacts the colorant present in the coloring bath B. Arranged above the surface of the two-dimensional plastic part A-1 arranged in the coloring bath B at a well-defined distance b, also known as immersion depth or the color layer thickness, is a sheet D comprising one or more radiation-decoupling materials. During the process according to the invention a radiation source for producing focused nonionizing electromagnetic radiation E is used to direct focused nonionizing electromagnetic radiation C onto the surface of the plastic part A-1 in order to undertake partial coloring of the plastic part A-1. The coloring bath B may have a discharge and a feed for the colorant, thus allowing continuous introduction of fresh colorant into the coloring bath B in order for example to maintain the coloring bath B at a substantially constant temperature. The radiation source E may be arranged movably in at least two dimensions with respect to the plastic part A-1 and the sheet D so that different regions on the surface of the plastic part A-1 may be irradiated.

[0157] In the alternative process according to the invention the sheet D is optional and the coloring bath B may be in contact with the plastic part A-1 in such a way that only parts of the surface of the plastic part A-1 are covered with colorant.

[0158] FIG. 2 shows a schematic diagram of an arrangement with a coloring bath B as shown in FIG. 1 which is suitable for irradiating a three-dimensional plastic part A-2. In contrast to the arrangement in FIG. 1, both the radiation source E and the sheet D are arranged movably with respect to the surface of the plastic part A-2 so that the radiation source E together with the sheet D are movable in three dimensions relative to the plastic part A-2, thus making it possible to undertake engraving on the three-dimensional plastic part A-2.

EXAMPLES

[0159] Film 1: Makrofol™ ID4-4 opaque white made of polycarbonate in a thickness of 300 μm from Covestro Deutschland AG. [0160] Film 2: Transparent polycarbonate film comprising IR absorber in a thickness of 100 μm was produced as follows:

Masterbatch: Compounding of a Highly Concentrated IR Masterbatch

[0161] The production of the masterbatch for the production of the film 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.

[0162] A master batch having the following composition was compounded and subsequently granulated: [0163] 94.69% by weight of polycarbonate Makrolon™ 3108 from Covestro Deutschland AG [0164] 0.75% by weight of YMDS 874 IR absorber from Sumitomo [0165] 4.5% by weight of Makrolon™ 3108 powder from Covestro Deutschland AG [0166] 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 2

[0167] The employed apparatus for producing the extruded film comprises: [0168] an extruder for extrusion of the layer containing at least one polycarbonate with a screw of 60 mm in diameter (D) and a length of 33 D. The screw has a degassing zone; [0169] a melt pump; [0170] a crosshead; [0171] a slot die of 450 mm in width; [0172] a three-roller smoothing calendar with horizontal roller orientation, wherein the third roller can swivel by +/−45° relative to the horizontal; [0173] a roller conveyor, [0174] thickness measuring means; [0175] means for double-sided application of protective film; [0176] a haul-off; [0177] a winding station.

[0178] 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 onto 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 disclosed in US-4 368 240 from Nauta Roll Corporation. The film was subsequently transported through a haul-off and then the film was wound up.

Lamination of Films 1 and 2 to Afford Laminate a and A′:

[0179] Lamination was carried out on a Bürckle 50/100 lamination press. Films 1 and 2 were laminated with the following press settings:

Preheating the press to 170-180° C.
Pressing for 8 minutes at a pressure of 15 N/cm.sup.2
Pressing for 2 minutes at a pressure of 100 N/cm.sup.2
Cooling the press to 38° C. and opening the press.

Composition of Coloring Bath for Examples 1 and 2

[0180] 69.31% by weight of water
0.99% by weight of Macrolex™ Blue 3R (dye, from Lanxess AG Deutschland)
19.8% by weight of ethylene glycol butyl ether (EGBE), (solvent, The Dow Chemical Company)
9.9% by weight of diethylene glycol (DEG), (leveling agent, Merck KGaA)

Composition of Coloring Solution for Producing Coloring Layer

[0181] 30% by weight of water
20% by weight of Macrolex™ Blue 3R (dye, from Lanxess AG Deutschland)
50% by weight of isopropanol.

Example 1 (Comparative)

[0182] The laminate A was placed (transparent side (film 2) facing upward) in the coloring bath (B) of the abovementioned composition.

[0183] 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 30 A. The advance rate of the laser, the immersion depth and the temperature of the coloring bath (B) are reported in table 1.

[0184] The coloring bath comprising the film was placed on the workpiece carrier of a Foba D84S laser apparatus. The laser (E) was focused onto 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.

TABLE-US-00001 TABLE 1 Conditions of the color laser engraving Temperature of coloring bath 40° C. Immersion depth 1 mm Advance rate 100 mm/s

[0185] After irradiation with the laser (E) the laminate A was withdrawn from the coloring bath and the quality of the laser engraving was subjected to visual assessment. The engraving was nonuniform in terms of color intensity and sharpness of the engraved image.

Example 2 (Inventive—According to the Process According to Claim 1 (Laminate A) and According to the Alternative Process (Laminate A′))

[0186] The laminate A (A-1) was placed (transparent side (film 2) facing upward) in the coloring bath (B) of the abovementioned composition. The laminate A′ was coated with a coloring layer by printing.

[0187] A glass sheet (D) made of silicate glass having a thickness of 3 mm was placed on the laminate A. Spacers were used to establish a distance of 1 mm (immersion depth) between the laminate A and the glass sheet (D). The coloring bath (B) was filled such that the top of the glass sheet (B) could remain free of coloring liquid.

[0188] The laminate A′ was clamped in a holder.

[0189] Laser irradiation was carried out using a Foba D84 NdYAG laser having a laser power of about 7.5 W and a laser frequency of 8 kHz for laminate A and 30 kHz for laminate A′ in pulsed operation and a current of 30 A. The advance rate of the laser, the immersion depth/color layer thickness (b) and the temperature of the coloring bath (B) are reported in table 2.

[0190] The laser (E) was focused through the glass sheet onto the film surface of laminate A′. In the context of the present invention immersion depth/color layer thickness (b) is to be understood as meaning the penetration depth of the employed radiation into the coloring bath (B)/into the coloring layer b) up to the surface of the plastic part onto which the partial coloring is to be applied. Irradiation with the laser beam was commenced.

TABLE-US-00002 TABLE 2 Conditions of the color laser engraving Temperature of the coloring 40° C. bath for laminate A/the coloring layer for laminate A′ Immersion depth/color layer 1 mm or 0.3 mm defined by thickness the distance between the laminate and the glass sheet or the thickness of the coloring layer Advance rate in process 100 or 50 mm/s according to claim 1 or according to alternative processes

[0191] After the irradiation with the laser the laminate A was removed from the coloring bath (B) or the unirradiated color layer was removed from laminate A′ in a water bath with the aid of a sponge. The quality of the laser engraving was subsequently subjected to visual inspection. Compared to example 1 the engraving of both laminate A and laminate A′ was markedly more uniform in terms of color intensity and sharpness of the engraved image.