POLYOLEFIN COMPOSITION PROVIDING IMPROVED CONTRAST OF LASER MARKS

Abstract

The present invention is directed to a polyolefin composition which provides improved contrast of laser marks. It is suitable for many applications where precise marking of a molded article made of a polyolefin composition is required, e.g. as outer layer of a wire or cable or in automotive applications. The polyolefin composition of the present invention comprises a polyolefin, carbon black in an amount of 0.25 to 1.0 wt % and an optical brightener in an amount of 0.001 to 0.1 wt %. The present invention is further directed to a molded article comprising the polyolefin composition of the present invention. Further on, the present invention is directed to the use of the polyolefin composition of the present invention as an outer layer of a cable. Finally, the present invention is directed to a method of inducing print on a molded article by laser printing.

Claims

1-15. (canceled)

16. A polyolefin composition comprising (A) a polyolefin, (B) carbon black in an amount of 0.25 to 1.0 wt % based on the weight of the polyolefin composition, and (C) an optical brightener in an amount of 0.001 to 0.1 wt % based on the weight of the polyolefin composition.

17. The polyolefin composition according to claim 16, wherein the polyolefin is selected from the group consisting of an ethylene homopolymer, an ethylene copolymer, a propylene homopolymer, a propylene copolymer, a blend of an ethylene homopolymer and an ethylene copolymer, and a blend of a propylene homopolymer and a propylene copolymer.

18. The polyolefin composition according to claim 17, wherein the ethylene copolymer is a copolymer of ethylene and a C.sub.3-C.sub.12-alpha-olefin.

19. The polyolefin composition according to claim 17, wherein the propylene copolymer is a copolymer of propylene and ethylene and/or a C.sub.4-C.sub.12-alpha-olefin.

20. The polyolefin composition according to claim 16, wherein the polyolefin is a high density polyethylene (HDPE).

21. The polyolefin composition according to claim 16, wherein the polyolefin is polypropylene.

22. The polyolefin composition according to claim 16, wherein the amount of carbon black is 0.25-0.75 wt % based on the weight of the polyolefin composition.

23. The polyolefin composition according to claim 16, wherein the amount of the optical brightener is 0.001 to 0.05 wt % based on the weight of the polyolefin composition.

24. The polyolefin composition according to claim 16, wherein the optical brightener is 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole).

25. The polyolefin composition according to claim 16, wherein said composition further comprises (D) a UV agent in an amount of 0.1 to 1.0 wt % based on the weight of the polyolefin composition.

26. A molded article comprising a polyolefin composition according to claim 16.

27. A molded article comprising a polyolefin composition according to claim 17.

28. The molded article according to claim 26, wherein the molded article is an outer layer of a cable.

29. A cable comprising an outer layer according to claim 28.

30. A method of inducing a print on a molded article according to claim 26, the method comprising inducing said print by laser radiation.

Description

EXAMPLES

1. Definitions/Measuring Methods

[0058] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

Density

[0059] Density is measured according to ISO 1183-1method A (2004). Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

Flexural Modulus

[0060] Flexural modulus was determined according to ISO 178:2010/Amd.1:2013.

Melt Flow Rate

[0061] Melt flow rate MFR.sub.2 of polyethylene was determined according to ISO 1133 at 190 C. under a load of 2.16 kg. Melt flow rate MFR.sub.2 of polypropylene was determined according to ISO 1133 at 230 C. under a load of 2.16 kg.

Light Intensity

[0062] Light intensity of the samples (squares) is determined as follows. The method is also described in general in the co-pending international patent application PCT/EP2019/065328.

[0063] Images were collected with a Keyence VHX-5000 microscope with objective 50, namely Z20:X50. Exposure time was fixed at 14 ms, which in this kind of microscopes univocally identifies the settings of the lighting to be used. In particular, the standard LED ring provided with the microscope was used. The images were collected in monochromatic manner, i.e. black&white, in order to have an image with a unique intensity value. A diffuser should not be used. The additional settings in the microscope software, e.g. contrast or sharpness increasers or amplifiers were all set off as this can change the images in an uncontrolled manner. For each setting of the laser printing, a square of 500500 pixels' was selected, well inside the printed area. The histogram of the distribution of the intensity was subsequently calculated, and treated with a median filter 3 in order to smoothen its shape. This distribution was fitted with a Gaussian curve, and the center of this Gaussian curve was recorded for each square.

2. Examples

[0064] The following materials and compounds are used in the Examples.

TABLE-US-00001 PE1 poly(ethylene-co-(1-butene)) copolymer having a density of 963 kg/m.sup.3, an MFR.sub.2 of 12 g/10 min, mixed with 39 wt % of carbon black (CB) PE2 bimodal high density polyethylene (HDPE) having a density of 944 kg/m.sup.3, an MFR.sub.2 of 1.7 g/10 min, a flexural modulus of 850 MPa, commercially available as Borstar HE6068 from Borealis AG Optical 2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole), brightener commercially available as Tinopal OB CO from BASF SE UV agent Tinuvin 783 FDE commercially available from BASF SE Antioxidant Irganox B225 commercially available from BASF SE Antistatic calcium stearate commercially available as Ceasit SW from agent Baerlocher GmbH

[0065] PE2 is used as base resin and contains already 0.2 wt % of the antioxidant, 0.15 wt % of the antistatic agent and 0.3 wt % of the UV agent.

[0066] Three samples were prepared using PE1 as the carbon black masterbatch (MB), wherein PE1 was compounded with the base resin PE2 in an amount such that the amount of carbon black in the final composition is 0.5 wt % for each of the three samples (see Table 1). In the sample of the comparative example CE1 no optical brightener is added. In the samples of the inventive examples IE1 and 1E2 optical brightener is added.

[0067] Compounding was implemented on ZSK 18 MEGAlab laboratory twin screw extruder under the following conditions: speed 200 rpm; melt temperature 175-190 C.; pressure 45-50 bar; output 5 kg/h. Plaques of size 150803 mm were produced from the resulting composition using injection moulding on Engel ES 700H/80V/700H/250 3K machine under following conditions: injection speed 11 mm/s; injection time 3.4 sec; switching pressure 66 bar; holding time during backpressure 15 sec; cooling time 20 sec; cycle time 45 sec; melt temperature 150 C.; mould temperature 50 C.

TABLE-US-00002 TABLE 1 Compositions of examples wt % Constituents CE1 IE1 IE2 PE2 98.75 98.74 98.745 PE1 1.25 1.25 1.25 Optical brightener 0.01 0.005 UV agent + + + Antioxidant + + + Antistatic agent + + + + indicates the presence of these compounds in PE2

[0068] Laser marking was carried out using Laser machine, SpeedMarker 700, 20 W Fiber laser. For marking, a frequency range of 20-100 kHz and a power varying between 5-70% of 20 W was used. Speed was kept constant at 2000 mm/s.

[0069] FIGS. 1-3 show the laser printed samples (laser pass: 2 passes). FIG. 1 shows CE1, FIG. 2 shows IE1, FIG. 3 shows IE2.

[0070] Each square represents a combination of frequency to power of the ranges indicated above. The samples are assessed visually by a human being. High contrast quality is achieved in the presence of the optical brightener in an amount of 0.01 wt % (FIG. 2, IE1), however, contrast quality is already good in the presence of the optical brightener in an amount of 0.005 wt % (FIG. 3, IE2). The samples according to the present invention have a brighter appearance and accordingly a higher contrast in view of the black background.

[0071] In addition, the light intensity of the samples is assessed by an objective measurement method as described above. The result is that the samples according to the present invention have a higher light intensity and accordingly a higher contrast in view of the black background. The results of light intensity for the squares with the highest light intensity of all three samples CE1, IE1, and IE2, respectively, are given in Table 2 below. The squares are numbered in Table 2 and the numbering is indicated in the corresponding FIGS. 4 to 6 which correspond to FIGS. 1 to 3 apart from indicating the numbering of the squares. Accordingly, FIG. 4 shows CE1, FIG. 5 shows IE1, FIG. 6 shows IE2.

TABLE-US-00003 TABLE 2 Measured light intensities of individual squares with highest light intensity Example/square no. Intensity CE1/64 143 CE1/65 139 CE1/95 139 IE1/21 173 IE1/22 179 IE1/23 181 IE2/17 172 IE2/25 178 IE2/26 172

[0072] Furthermore, the results of the objective measurement method are also indicated in FIGS. 7 and 8 for all squares. FIG. 7 shows a comparison of IE1 with CE1. FIG. 8 shows a comparison of IE2 with CE1. The points on graph with the highest light intensity are marked black.

[0073] What can be derived from these results is that the light intensity is higher in the inventive examples IE1 and IE2 compared to the comparative example CE1.