RU2772273C2 - Antimony-free composition for laser marking of thermoplastic compounds - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a plastic composition marked with laser that does not contain antimony. Laser-marked plastic contains thermoplastic polymer, bismuth oxide and co-absorbent additive selected from plate silicates. The amount of bismuth oxide is 0.5-5 wt.% relatively to the total weight of plastic. The amount of co-absorbent additive relatively to bismuth oxide is 5-40 wt.%. Thermoplastic polymer is thermoplastic polyurethane.

EFFECT: improvement of contrast and sharpness along the edge of laser marking is provided.

8 cl, 1 dwg, 3 tbl, 2 ex

Description

The present invention relates to a laser-markable plastic composition that does not contain antimony.

Many plastics applications require labeling of the end product. Whether it is food packaging, where an expiration date or manufacturer must be indicated, or electronic components, where a type description or serial number must be added. Today's consumers, as well as industry, want transparency and traceability throughout the value chain, especially when sustainable sourcing and production are required.

If it is necessary to mark thermoplastic plastics, non-contact laser marking technology is preferably used today. Unlike ink-based pad printing, laser marking is free from solvents and contacts and offers superior application flexibility and speed.

Various types of materials and laser technologies are available for laser marking.

For laser marking of plastics, the 1064 nm Nd:YAG system is commonly used because it is cheap and flexible. However, not all plastics interact with a laser with the same absorbance within the emitted wavelength. Therefore, in order to increase the markability of thermoplastics that are not inherently laser markable, such as polycarbonates, for example, laser markability enhancing additives are needed. Polymers such as polyolefins or thermoplastic urethanes need additional additives to ensure proper laser marking for contrast and edge sharpness. Laser marking additives are usually added to the polymer by diluting the additive or dye concentrate (masterbatch) into the polymer.

In general, laser marking additives operate in two different modes of action: self-acting and non-intrinsic additives.

Indirect additives absorb laser energy and transfer it to the surrounding polymer matrix. Depending on the response of the polymer, the polymer may carbonize, typically resulting in a brownish or greyish contrast on the polymer surface, or the polymer decomposes into short length molecules and monomers that tend to evaporate on the surface and generate foam. This results in a bright marking caused by different refractive indices at the interface between different solid phases. Laser marking can also result from both of these mechanisms.

Self-acting additives work by changing their own chemical structure. For example, the commonly used antimony trioxide Sb ₂ O ₃ is reduced to antimony Sb, which is dark in color to provide sufficient marking contrast. Self-acting laser marking additives should be dispersed within the polymer matrix with good uniformity so that edge sharpness is normally better than non-intrinsic additives.

However, there is a need to replace antimony trioxide used as a laser marking additive due to its toxic profile. It is classified as hazardous to health and the environment and must be labeled as hazardous to health in accordance with Regulation (EC) No 272/2008.

The use of laser marking additives for marking cattle ear tags is a particularly important aspect. Today, antimony trioxide is the additive of choice for marking such products. However, antimony trioxide does not have an environmentally friendly profile and therefore represents a potential replacement candidate for other solutions sought in the labeling field. Due to the lack of alternatives, antimony trioxide or additives containing antimony still constitute the majority of additives that are used for this purpose.

U.S. Patent No. 4,816,374 (Lecomte) discloses the use of antimony oxide as a laser absorptive agent in a polyurethane plastic material conforming to the French standard (number NF-T-54006) for surface mechanical damage due to friction for manufacturing and use. ear tags for farm animals. However, it is undesirable to use heavy metals such as antimony in thermoplastic compounds for health and safety reasons. Indeed, antimony is still being studied for the health problems it can cause in mammals.

US Pat. No. 6,214,917 (Linzmeier et al.) describes thermoplastic polyurethanes (TPU) as laser-markable plastics. TPUs contain pigments coated with tin dioxide, which coating is doped with antimony, arsenic, bismuth, copper, gallium, germanium or their respective oxides in an amount of 0.5-20 wt.%.

EP-0697433 B1 describes the use of copper salts for laser marking purposes. It is well known that, for example, copper hydroxyphosphate is highly effective for high contrast laser marking. However, for example, for ear tag applications, there is limited utility because copper hydroxyphosphate is able to react with animal feces, resulting in color changes.

EP-1190988B1 claims the use of bismuth-containing compounds as substitutes for antimony trioxide for the purpose of imparting absorbent properties for laser marking. However, the result is a decrease in contrast compared to Sb ₂ O ₃ and also an increase in cost.

DE-102014000359 A1 claims pigments based on bismuth compounds and their use, preferably as a laser absorbing additive, and a process for their preparation. However, the manufacture of such compounds is complex and expensive. To obtain a suitable replacement for antimony trioxide, the costs cannot be much higher.

Therefore, there is a need for an inexpensive, environmentally and toxicologically safe, laser-markable plastic that does not contain antimony and that provides good contrast after laser processing.

Surprisingly, it has been found that the addition of specific co-absorbent additives to intrinsically laser-marked bismuth oxide can enhance the result of laser marking, providing high contrast and edge sharpness, even though these added substances themselves have little or no effect. effect when used alone.

Therefore, the object of the invention is a laser-markable plastic containing a thermoplastic polymer, bismuth oxide and a co-absorbent additive selected from the group consisting of lamellar silicates and inorganic copper-, cobalt-, aluminum- or iron-containing pigments, in which the amount of coabsorbent additive relative to bismuth oxide is from 2 to 80 wt.%, preferably from 5 to 50 wt.%, more preferably from 10 to 40 wt.%, most preferably from 10 to 30 wt.%.

The bismuth oxide used in the present invention is preferably Bi ₂ O ₃ . The bismuth oxide used as the inherently laser active material may have any particle size, for example d ₅₀ between 0.5 and 25 microns. However, it has surprisingly been found that the technical grade particle size provides better delta L contrast values than fine or submicron grade material. Therefore, the preferred particle size d ₅₀ of bismuth oxide is 0.5 to 20 microns, more preferably 2 to 10 microns.

The amount of bismuth oxide relative to the total weight of the laser-marked plastic is preferably 0.2 to 5% by weight, more preferably 0.5 to 2.5% by weight, most preferably 0.75 to 2% by weight.

Suitable thermoplastic polymers suitable for the present invention are all thermoplastic polymers, preferably polyurethane, acrylonitrile butadiene styrene and other plastomeric polymers.

The co-absorbent additive is preferably a plate shaped silicate, eg phyllosilicate, eg selected from the group consisting of mica, talc and kaolin.

Preferred particle sizes d ₅₀ coabsorbent additives are from 1 to 20 microns, more preferably from 3 to 10 microns.

Without being bound by any theory, it is believed that the co-absorbent additive primarily functions to absorb the energy delivered by the laser system to provide more energy that can be absorbed by the bismuth oxide. In particular, phyllosilicates, which typically do not show contrast in laser marking, have an enhancing effect as a co-absorbent when used in conjunction with bismuth oxide.

Some laser marking additives, such as copper hydroxyl phosphate, which have serious disadvantages when used alone, do not show this disadvantage when used in combination with bismuth oxide and also improve the color change result of bismuth oxide.

Copper hydroxyphosphate, when used alone in ear tags, may come into contact with animal feces, resulting in severe discoloration due to the additive reacting with such a substance.

Also, the use of finely ground aluminum pigment is limited due to the strong gray color it creates. Also in this case, the bismuth oxide laser marking effect is improved by using a small amount of aluminum, which cannot affect the color cast.

Another object of the present invention is a process for the manufacture of a laser-markable plastic comprising the step of dispersing bismuth oxide and a co-absorbent in a thermoplastic polymer, expediently by a melt blending process, preferably on a twin screw extruder. This can be done by direct compounding or by using an additive masterbatch in the form of a pre-dispersed concentrate.

If a masterbatch is used, the resin can either be of the same thermoplastic polymer as the final polymer to be equipped, or it can be a different polymeric carrier, a so-called multipurpose carrier. Such a carrier is dispersed in the final polymer and can provide additional benefits such as increased compatibility with the additive formulation while providing improved dispersibility. Other benefits of using some of these multipurpose carriers may be improved mechanical properties compared to an additive filled polymer to be equipped. In addition, these polymers can achieve a higher concentration of additive that can be loaded into the additive and be more cost effective than the polymer of the application itself. EVA (ethylene vinyl acetate) or EBA (ethylene butyl acrylate) are examples of such resins.

In addition to the above additives according to the invention, other conventional additives such as UV stabilizers, antioxidants, waxes, processing aids and dyes, e.g. pigments, dyes, or both, can be added to provide a specific color for better contrast against laser marking.

The laser-markable plastic according to the invention can be used for marking industrial and consumer products, such as barcodes or serial numbers, and plastic labels for the individual marking of animals, such as ear tags.

Other uses are, for example, electrical and electronic components that must be labeled with waste disposal guidelines, batch numbers, certificates and other information. Also, any possible consumer product can be marked for decorative purposes. Laser marking of plastics is preferably performed using Nd-YAG lasers which emit a pulsed energy beam having a characteristic wavelength of 1064 nm. Inscription with a laser is performed by introducing a test sample into the beam path of said laser.

Examples

Table 1: Materials:

Bismuth oxide, Bi ₂ O ₃
CAS No.1304-76-3 "Grade Varistor" supplied by 5Nplus
Particle size d ₅₀ = 3.7 µm "Varistor grade shredded" supplied by 5Nplus
Particle size d ₅₀ = 1.6 µm "Submicron grade" (chemically oxidized) supplied by 5Nplus
Particle size d ₅₀ = 0.7 µm "Technical grade" supplied by 5Nplus
Particle size d ₅₀ = 7 µm Mica
C.A.S. No. 12001-26-2 "Micafill 115" supplied by Alpha Calcit
Particle size d ₅₀ = 5 µm "Micafill 125" supplied by Alpha Calcit
Particle size d ₅₀ = 7 µm "Micafill 145" supplied by Alpha Calcit
Particle size d ₅₀ = 12 µm "Micro Mica" supplied by Omya
Particle size d ₅₀ = 10 µm "Iriotec 8800" supplied by Merck
Particle size d ₅₀ = 6 µm Copper hydroxyphosphate
C.A.S. No. 12158-74-6/235-285-2 ^Fabulase® 361 supplied by BUDENHEIM IBERICA, SL Soc. en Comandita
Particle size d ₅₀ = 3.5 µm Ultra-thin aluminum oxide on PE carrier ^Lasersafe® 040 supplied by Eckart GmbH ^IriotecTM 8208 Encapsulated antimony trioxide on a polyolefin carrier Antimony trioxide Sb ₂ O ₃
C.A.S. No. 1309-64-4 Campine ^® Z supplied by Campine
Particle size d ₅₀ = 8.0 - 13 µm TPU polymer
C.A.S. No. 25750-84-9 ^{Ellastollan®} 1185 A supplied by BASF Resin Masterbatch
C.A.S. No. 9018-04-6 EBA (Lucofin ^® 1400 MN supplied by Lucobit AG)

Several compositions listed in Table 2 were prepared on a Leistritz ZSE 40 twin screw extruder with a screw diameter of 27 mm and an L/D ratio of 40, equipped with two gravimetric dosing systems, and using a side feeder. The so-called carrier resin was dosed through the main feeder. The additive composition, which had been pre-blended with all other additives and antioxidants, was dosed using a side dispenser. The thread emerging from the spinneret was cooled in a water bath and cut into cylindrical granules using a strand granulator. All dye masterbatches were produced with a 3% yellow concentrate and diluted with commercially available TPU Elastollan 11 85A.

These masterbatches thus produced were diluted on a BOY 35 injection molding machine to produce thermoplastic urethane plates.

These injection-molded plates contained structured and strong surface areas. This is especially important for livestock identification tag applications to avoid bias when using barcode scanners.

Example 1:

To test the laser marking effect of various compositions, these injection molded plates were used in a laser marking system. For the tests mentioned, a Trumpf Nd:YAG marking laser device with a 20 W laser source (TruMark 3020) was used.

To visualize the enhanced absorption of the thermoplastic compound, a so-called "test grid" was applied to the plate. In doing so, you change the basic parameters of laser marking, such as marking speed and pulse frequency. The result is a matrix in which you can see the effect of these different parameters. This will help you find the optimal settings for the laser and show the reliability of the system. The more parts of this test grid that show good contrast, the less sensitive your system is to changes in laser settings. To prove the applicability of the test, the columns were also marked with letters and numbers, as well as barcodes with specific laser parameters, similar to the use of bovine ear tags.

To quantify the numerical results, the 3 cast platinums of each of the tested compositions were marked with a solid circle. Using a Datacolor SF600® PLUS CT spectrometer, the brightness of the unmarked and marked circle was marked and calculated to a delta L* value. The higher the negative delta L* value, the better the marking contrast.

Table 2: Compositions of injection molded compounds for determining delta L* values:

MBNo. Additive for laser marking co-absorbent
additive TPU+
MB resin + dye Meaning
delta L* one ₁ % _Bi2O3
Grade Varistor 0.2% mica
Micafill 145 98.8% -37.0 2 2% Iriotec 8208 - 98% -36.5 3 ₁ % _Bi2O3
technical grade 0.2% mica
^Iriotec® 8800 98.8% -33.1 4 ₁ % _Bi2O3
small variety 0.2% mica
^Iriotec® 8800 98.8% -23.6 5 ₁ % _Bi2O3
submicron grade 0.2% mica
^Iriotec® 8800 98.8% -18.1 6 - - 100% 0.06 ± 0.02

results

Example 1:

The aforementioned Composition 1 was found to show an improvement in contrast and edge sharpness compared to Composition 2, which can be called state of the art in laser marking, especially in TPU. This is confirmed by the higher delta L* values relative to the amount of bismuth oxide when labeled with coabsorbent. This results in the reduction of said mixture to achieve the same performance as when using pure bismuth oxide and in most cases to reduce the cost and color impact of the additive composition.

It can also be recognized that Compositions 1 and 3 perform better than Compositions 4 and 5. This unexpectedly leads to the conclusion that medium to larger bismuth oxide particles absorb laser energy more efficiently than smaller particles.

Example 2:

Various tests using the same sample preparation method as mentioned above were carried out using the ColorLite sph900 device. This device can measure the so-called K value (light contrast value). Like the delta L* value, the result gives an indication of the quality of the marking, but also recognizes the light reflectance. The lower the value, the better the marking contrast.

These tests used a Datalogic 50 Hz laser with fiber optic technology. Three different measurements were made using 3 different laser marking speeds (1000 mm/s, 2000 mm/s, 3000 mm/s).

Table 3: Compositions of injection molded compounds for determining K values:

No. MB Additive for laser marking Co-absorbent additive TPU+
MB resin + dye K value
1000 mm/s
2000 mm/s
3000 mm/s K1 - - 100% 0.10
0.10
0.10 2% ^Iriotec® 8208 - 98% -0.62
-0.55
-0.53 K3 _1.2 % _Sb2O3
^Campine® Z - 99% -0.43
-0.33
-0.34 K4 ₁ % _Bi2O3
Grade Varistor - 99% -0.50
-0.50
-0.46 K5 0.99% Bi ₂ O ₃
Grade Varistor 0.01% ^Lasersafe® 040 99% 0.51
-0.48
-0.53 K6 0.96% Bi ₂ O ₃
Grade Varistor 0.04% ^Fabulase® 330 99% -0.54
-0.48
-0.57 K7 ₁ % _Bi2O3
Grade Varistor 0.2% Micro ^Mica® 98.8% -0.51
-0.55
-0.57 K8 ₂ % _Bi2O3
Grade Varistor 0.4% Micro ^Mica® 97.6% -0.54
-0.59
-0.59 K9 ₁ % _Bi2O3
Grade Varistor 0.2% ^Micafill® 125 98.8% -0.52
-0.53
-0.58 K10 ₂ % _Bi2O3
Grade Varistor 0.4% ^Micafill® 125 98.8% -0.56
-0.62
-0.62 K11 ₁ % _Bi2O3
Grade Varistor 0.2% ^Micafill® 145 98.8% -0.53
-0.56
-0.56 K12 ₂ % _Bi2O3
Grade Varistor 0.4% ^Micafill® 145 98.8% -0.60
-0.62
-0.65

The figure 1 also presents a diagram showing the K-values of the tested compounds.

results

Example 2:

The aforementioned compositions K5-K12 were found to show improvement in contrast and edge sharpness compared to composition K4. This was confirmed by the higher K values relative to the amount of bismuth oxide when labeled with it alone and together with the co-absorbent. Compositions K2 and K3 can be called reference. With the same amount of active ingredient, the contrast was comparable or even better at lower cost and without antimony.

It can also be recognized that mica, when used as a co-absorbent, exhibits different particle size characteristics.

Claims (8)

1. A laser-markable plastic containing a thermoplastic polymer, bismuth oxide and a co-absorbent additive selected from the group consisting of lamellar silicates, in which the amount of bismuth oxide is in the range from 0.5 to 5 wt.% in relation to the total weight of the laser-marked plastic , the amount of co-absorbent additive relative to bismuth oxide is from 5 to 40 wt.% and the thermoplastic polymer is a thermoplastic polyurethane. 2. The laser-markable plastic according to claim 1, wherein the amount of co-absorbent additive relative to bismuth oxide is 10 to 30% by weight. 3. Laser-markable plastic according to any one of paragraphs. 1, 2, containing from 0.5 to 2.5 wt.% bismuth oxide in relation to the total mass of the laser-marked plastic. 4. Laser-markable plastic according to any one of paragraphs. 1-3, in which the lamellar silicates are phyllosilicates. 5. Laser-markable plastic according to any one of paragraphs. 1-4, in which the lamellar silicates are selected from the group consisting of mica, talc and kaolin. 6. Laser-markable plastic according to any one of paragraphs. 1-5, in which the particle size d ₅₀ of bismuth oxide is from 0.5 to 20 microns. 7. A method of obtaining a laser-marked plastic according to any one of paragraphs. 1-6, which includes the step of dispersing bismuth oxide and a co-absorbent additive in a thermoplastic polymer during a melt blending process. 8. The use of laser-marked plastic according to any one of paragraphs. 1-6 for marking industrial and consumer goods and plastic tags for individual marking of animals.

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