Antimony free composition for laser marking thermoplastic compounds

Abstract

It has been found, that when co-absorbing substances are added to intrinsic laser-absorbing bismuthoxide, the marking performance with a Nd.YAG-laser is improved or at least kept at the same level by reducing the costs. It is suspected, that the co-absorbing additive is not simply adding a contrast to the polymer by carbonizing the surrounding polymer but helping the bismuthoxide to couple the laser radiation and to ease the color change of this additive. This so found effect helps to cheapen the replacement of antimony trioxide and therewith have a safer and more sustainable solution for the current and future technology of laser marking.

Claims

1. A laser-markable plastic comprising a thermoplastic polymer, bismuth oxide and a co-absorbing additive selected from the group consisting of platelet-shaped silicates and inorganic copper-, cobalt-, aluminum or iron-containing pigments, wherein the amount of the co-absorbing additive relative to the bismuth oxide is from 2 to 80 wt.-%.

2. The laser-markable plastic according to claim 1, wherein the amount of the co-absorbing additive relative to the bismuth oxide is from 10 to 30 wt.-%.

3. The laser-markable plastic according to claim 1, wherein the thermoplastic polymer is a thermoplastic polyurethane, acrylonitrile-butadiene-styrene, or other non-intrrinscally laser-markable polymer.

4. The laser-markable plastic according to claim 1, comprising from 0.2 to 5 wt.-% of bismuth oxide, relative to the total weight of the laser-markable plastic.

5. The laser-markable plastic according to claim 1, wherein the platelet-shaped silicates are phyllosilicates.

6. The laser-markable plastic according to claim 1, wherein the platelet-shaped silicates are selected from the group consisting of mica, talc, and kaolin.

7. The laser-markable plastic according to claim 1, wherein the particle size d.sub.50 of the bismuth oxide is from 0.5 to 20 microns.

8. A method for preparing the laser-markable plastic according to claim 1, comprising the step of dispersing the bismuth oxide and the co-absorbing additive into the thermoplastic polymer in a melt-mixing process.

9. Use of the laser-markable plastic according to claim 1, for labelling of industrial and consumer products, and plastic marks for the individual tagging of animals.

Description

EXAMPLES

[0033]

TABLE-US-00001 TABLE 1 Materials: Bismuth oxide, Bi.sub.2O.sub.3 “Varistor Grade” supplied by 5Nplus CAS No. 1304-76-3 Particle size d.sub.50 = 3.7 μm “Varistor Grade Fine” supplied by 5Nplus Particle size d.sub.50 = 1.6 μm “Submicron Grade” (chemically oxidized) supplied by 5Nplus Particle size d.sub.50 = 0.7 mm “Technical Grade” supplied by 5Nplus Particle size d.sub.50 = 7 μm Mica “Micafill 115” supplied by Alpha Calcit CAS No. 12001-26-2 Particle size d.sub.50 = 5 μm “Micafill 125” supplied by Alpha Calcit Particle size d.sub.50 = 7 μm “Micafill 145” supplied by Alpha Calcit Particle size d.sub.50 = 12 μm “Micro Mica” sipplied by Omya Particle size d.sub.50 = 10 μm “Iriotec 8800” supplied by Merck Particle size d.sub.50 50 = 6 μm Copper Hydroxy Phosphate Fabulase ®361 supplied by BUDENHEIM CAS No. 12158-74-6/235-285-2 IBERICA, S.L. Soc. en Comandita Particle size d.sub.50 = 3.5 μm Ultrafine aluminia on a PE-carrier Lasersafe ® 040 supplied by Eckart GmbH Iriotec ™ 8208 Encapsulated antimony trioxide on a polyolefinic carrier Antimony trioxide Sb.sub.2O.sub.3 Campine ® Z supplied by Campine CAS No. 1309-64-4 Particle size d.sub.50 = 8.0-13 μm TPU polymer Ellastollan ® 1185 A supplied by BASF CAS No. 25750-84-9 Masterbatch resin EBA (Lucofin ® 1400 MN supplied by Lucobit AG) CAS No. 9018-04-6

[0034] Several formulations as listed in Table 2 were prepared on a twin screw extruder “Leistritz ZSE 40” with a 27 mm screw diameter and an L/D ratio of 40 equipped with two gravimetric dosing systems and a side feeder was used. The so-called carrier resin was dosed via main feeder. The additive formulation that was premixed together with all other additives and antoxidants were dosed by using the side feeder. The strand coming from the die was cooled by a water bath and cut down to cylindrical shaped pellets by a strand pelletizer. All Masterbatches have been letdown together with 3% of a yellow color concentrate and diluted with commercially available TPU Elastollan 11 85A.

[0035] These so produced Masterbatches were diluted on a BOY 35 injection moulding machine to produce plaques made from thermoplastic urethane.

[0036] These so manufactured injection molded plaques contain areas of the surface that are structured and firm. This is especially important for the application of identification tag for domestic livestock, to avoid deflections when BAR-code scanners are applied.

Example 1

[0037] To test the effect of laser marking of the different formulation, these so equipped injection molded plaques are applied to a laser marking system. For the mentioned trials a device was used by company Trumpf with a Nd:YAG marking laser with a 20 W laser source (TruMark 3020).

[0038] To visualize the enhanced absorption of the thermoplastic compound, the plaque was marked with a so-called “test grid”. Herewith you vary the main laser marking parameters like marking speed and pulse frequency. The result is a matrix where you can see the effect of these different parameters. This helps you to find the optimal setting for the laser and shows the robustness of the system. The more parts of this test-grid show a good contrast the less sensible your system is for changes of laser settings. To prove the applicability of the test the bars were also marked letters and numbers as well as a BAR code with specific laser parameters, similar to the application of ear cattle tags.

[0039] To quantify the results numerical a filled circle was marked on 3 molded plaques each of the tested formulations. By using a spectrometer Datacolor SF600® PLUS-CT the brightness of the unmarked and the marked marked circle were marked and calculated to a delta L* value. The higher the negative delta L* value, the better is the marking contrast.

TABLE-US-00002 TABLE 2 Formulations of injection molded compounds for Delta L* values: TPU + Laser marking Co-absorbing MB resin + Delta L* MB No. additive additive color value 1 1% Bi.sub.2O.sub.3 0.2% Mica 98.8% −37.0 Varistor Grade Micafill 145 2 2% Iriotec 8208 — .sup. 98% −36.5 3 1% Bi.sub.2O.sub.3 0.2% Mica 98.8% −33.1 Technical Grade Iriotec ® 8800 4 1% Bi.sub.2O.sub.3 0.2% Mica 98.8% −23.6 Fine Grade Iriotec ® 8800 5 1% Bi.sub.2O.sub.3 0.2% Mica 98.8% −18.1 Submicron Grade Iriotec ® 8800 6 — —  100% 0.06 ± 0.02

Results Example 1

[0040] It has been found, that above mentioned formulation 1 shows an improvement in contrast and edge sharpness in comparison to formulation 2, which can be called as state of the art for laser marking, especially in TPU. This is proven by the higher delta L* values relatively to the amount of bismuth oxide when marked with the co-absorbant. This leads to a reduction of the mentioned mixture to achieve the same performance as achieved with pure bismuth oxide and in most cases a reduction of costs and color influence of the additive formulation.

[0041] It can also be recognized that formulation 1 and 3 performs better that formulation 4 and 5. This surprisingly leads to the conclusion that medium to bigger particle sized bismuth oxide absorbs the laser energy more efficient than smaller particle sizes.

Example 2

[0042] Different trials using the same way of making test-specimens as mentioned above, were measured by using a ColorLite sph900 device. This device is able to measure a so-called K-value (Light contrast value). Like the Delta L* value, the result gives an indication about the quality of the marking but does also recognize light reflectance. The lower the value, the better is the marking contrast.

[0043] The laser used for these trials was a Datalogic 50 Hz with fiber technology. Three different measurements were performed using 3 different laser marking speeds (1000 mm/s, 2000 mm/s, 3000 mm/s).

TABLE-US-00003 TABLE 3 Formulations of injection molded compounds for K values: K value Laser TPU + 1000 mm/s marking Co-absorbing MB resin + 2000 mm/s MB No. additive additive color 3000 mm/s K1 — —  100% 0.10 0.10 0.10 K2 2% Iriotec ® 8208 — .sup. 98% −0.62 −0.55 −0.53 K3 1.2% Sb.sub.2O.sub.3 — .sup. 99% −0.43 Campine ® Z −0.33 −0.34 K4 1% Bi.sub.2O.sub.3 — .sup. 99% −0.50 Varistor Grade −0.50 −0.46 K5 0.99% Bi.sub.2O.sub.3 0.01% Lasersafe ® .sup. 99% 0.51 Varistor Grade 040 −0.48 −0.53 K6 0.96% Bi.sub.2O.sub.3 0.04% Fabulase ® 330 .sup. 99% −0.54 Varistor Grade −0.48 −0.57 K7 1% Bi.sub.2O.sub.3 0.2% Micro Mica ® 98.8% −0.51 Varistor Grade −0.55 −0.57 K8 2% Bi.sub.2O.sub.3 0.4% Micro Mica ® 97.6% −0.54 Varistor Grade −0.59 −0.59 K9 1% Bi.sub.2O.sub.3 0.2% Micafill ® 125 98.8% −0.52 Varistor Grade −0.53 −0.58 K10 2% Bi.sub.2O.sub.3 0.4% Micafill ® 125 98.8% −0.56 Varistor Grade −0.62 −0.62 K11 1% Bi.sub.2O.sub.3 0.2% Micafill ® 145 98.8% −0.53 Varistor Grade −0.56 −0.56 K12 2% Bi.sub.2O.sub.3 0.4% Micafill ® 145 98.8% −0.60 Varistor Grade −0.62 −0.65
see also Diagram 1.

Results Example 2

[0044] It has been found, that above mentioned formulations K5-K12 show an improvement in contrast and edge sharpness in comparison to formulation K4. This was proven by the higher K values relatively to the amount of bismuth oxide when marked alone and with the co-absorbant. Formulation K2 and K3 can be called as benchmark. With the same amount of active ingredient, the contrast is comparable or even better with lower costs and without the content of antimony.

[0045] It can also be recognized that Mica, when used as a co-absorbant, shows different performance in respect to the particle size.