RoHS/WEEE Measurement of Hazardous Substances in Plastics

Transcription

1 HELMUT FISCHER GMBH + + CO. COKG INDUSTRIESTRASSE INDUSTRIESTASSE SINDELFINGEN - MAICHINGEN TEL TEL // FAX 0 FAX / / Application Report bn2005_01 RoHS/WEEE Measurement of Hazardous Substances in Plastics In the near future, two EU Guidelines with the objective of avoiding certain hazardous substances in electrical and electronic equipment will take effect. The Guideline 2002/95/EC, short RoHS (Restriction of certain Hazardous Substances), specifies that certain substances may no longer be used in new electrical and electronic equipment and the Guideline 2002/96/EC, short WEEE (Waste from Electrical and Electronic Equipment) controls handling of used equipment. In Germany, the two guidelines will be combined in one law. Currently, only the draft exists for this Elektround Elektronikgerätegesetz ElektroG [Electrical and Electronic Equipment Law], however, it is expected that it will take effect very soon with minor changes. The crucial section of the law is 5: It is prohibited to put on the market new electrical and electronic equipment that contains more than 0.1 percent in weight lead, mercury, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE) per homogeneous material or more than 0.01 percent in weight cadmium per homogeneous material. Sentence 1 does not apply to electrical and electronic equipment of categories 8 and 9 and not for electrical and electronic equipment that has been put on the market for the first time in a member nation of the European Union prior to July 1, Each manufacturer of electrical and electronic equipment must ensure that he adheres to these limits (exceptions 8 and 9 relate to medical instruments as well as monitoring and control instruments). Certainly, this section will be essentially identical in all other EU nations. Thus, manufacturers around the globe will have to deal with this situation. Even if many manufacturers themselves will not make measurements and instead will require guarantees from their suppliers, this nonetheless provides a great potential for us. Our competitors are certainly active in this field (Niton, Spectro, Oxford). The measurement problems In principle all substances mentioned by the law can be measured using XRF. However, for Cr and Br, the measurement yields the total content of Cr and Br in the sample and not the content of Cr (VI) or PBB and PBDE. However, this is sufficient for monitoring the limits: If the total content of Cr is below the limit, then the content of Cr (VI) is below the limit as well. This applies in the same fashion to the Br compounds. Only if the Cr or Br content exceeds the limit, additional analysis methods must be employed to determine the Cr (VI), PBB or PBDE content.

2 The limits refer to any homogeneous material that is present in the instrument. Essentially, the following groups of materials are of interest: 1. Plastics: In plastics, essentially all listed substances are used for various purposes (as stabilizers, coloring agents, flame inhibitors). In addition, synthetic materials are employed in many variations and in most cases, data concerning the composition are not available. Since plastics are used in electrical equipment in many places, this will certainly constitute the most important measurement application. 2. Solder: The measurement of lead in solder, or the verification that a product is lead-free is another important measurement application. Concerning this topic, there is an application report (vr0324) and a publication in the journal Galvanotechnik (Issue 4/2004). 3. Steel, aluminum and copper alloys: In these materials, Pb can be used as an alloy element. However, here the limits are significantly higher: 0.35% for steel, 0.4% for Al and 4% for copper alloys so that these measurements can be done without problems. 4. Cr passivation coatings: Previously, passivations used for corrosion protection on Zn/Fe or Al contained Cr (VI). XRF can only state whether Cr is present in the passivation or not. However, the detection of Cr (VI) in passivations is very elaborate so that the proof that passivations are free of Cr (VI) will most likely be the duty of the coating companies. This report will, therefore, present the possibility of measurements of hazardous substances in plastics. Measurements For the measurement, two problems arise due to the variety of uses of plastics: 1. Due to the low average atomic number (~ 6, with carbon as the main element), plastics generate a significant background from scattered x-rays. This background varies greatly and can influence the measurement of low concentrations significantly. 2. In most cases, the plastics have no saturation thickness, i.e., the thickness and density, or the mass per unit area of the sample influences the result. All measurements have been carried out using an XAN; Instrument settings: 50kV, Al filter, collimator 4, I = 500 (the count rate corresponds approximately to that of an XDAL with an coll. 3 and I = 1000). Figure 1 shows the spectra for four typical samples.

3 Plastic 2.7mm Rubber 2.4mm Plastic 1 mm Foam Figure 1: Spectra of four synthetic materials One can see different scatter spectra for different synthetic materials: The maximum is not at the same position and the high-energy range is shaped differently. If our default scatt spectrum is used in the application, the measurement results will depend greatly on the scatter spectrum of the sample, in particular for Cd. A shift of 100ppm can occur easily. For this reason, two scatter spectra that cover the differences in a good manner have been used for the application (Fig. 2). In addition, the software has been modified (beginning with Version 6.11) so that a polynomial of degree 7 is calculated automatically as an additional background spectrum when a scatter spectrum is loaded (so far, a polynomial of degree 2 is used). PE 1mm Al 1.5mm Figure 2: Scatter spectrum for 1mm polyethylene and 1.5mm Al.

4 An additional modification of the software was necessary to analyze layers with a fixed thickness. Until now, this was possible only if the layer had saturation thickness, i.e., when analyzing a solid sample. Beginning with Version 6.11, the composition of a layer can be determined as well if the thickness is fix and has a finite value. For example, it is possible to analyze a plastic with a thickness of 1mm. This value is provided in the DefMA. If the sample is thicker, the computed concentrations will be too high, if the sample is thinner, the computed concentrations will be too low. Results The following table shows the results for 13 different samples. For all samples, the calculation was done with a thickness of 1 mm. In addition, the elements Zn and Ti have been filtered, because they were contained in several samples. The listed values are mean values and standard deviations from 10 single readings with measuring times of 50 s. Measuring time 50s, calculation with 1 mm thickness Sample Pb / ppm Hg / ppm Cd / ppm Cr / ppm Br / ppm mq 1 Plastics 2.7mm 2 Plastics 1 mm 3 Rubber 2.4 mm 4 Plastics 0.6 mm 5 Adhesive tape 20 mm 6 Adhesive tape 0.23 mm 7 Foam 20 mm 8 Plastics 2.2mm 9 Foam 2.2 mm 10 Plastics 0.9 mm 11 Plastics 1.1 mm 12 Foam 10 mm 13 Plastics 1 mm 2.3 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Samples 5, 10 and 13 are conspicuous. Sample 5 exhibits a higher mq value and significant results for Hg and Cr; however, they are still far below the limit of 1000ppm. Sample 10 exhibits a significant value for Br also far below the limit. Sample 13 contains Cd, significantly above the limit and would, therefore, not be

5 admissible after 7/1/2006. The high mq value results from Se, which is contained in the sample and is not taken into account by the evaluation. The assumption of a sample thickness of 1mm is not met for most samples so that the concentration values are wrong for these samples. Lower concentrations are the result for all samples that are thicker than 1 mm. Only the thinner samples or samples with a low density are problematic. The following table shows the results of an evaluation of the same spectra, computed with a thickness of 0.2 mm. Measuring time 50s, calculation with 0.2mm thickness Sample Pb / ppm Hg / ppm Cd / ppm Cr / ppm Br / ppm mq 6 Adhesive tape 0.23 mm 7 Foam 20 mm 9 Foam 2.2 mm 12 Foam 10 mm 1.4 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± One can see that all final results are now higher and the standard deviations are increased. For Cd, the result with a standard deviation of about 30 ppm is no longer satisfactory. Thus, longer measuring times are required for thin materials or materials with a low density. It may also be advantageous to stack the material. The following table shows measurements with measuring times of 200s. Samples 3 and 10 have been calculated with 1mm and samples 6 and 12 with 0.2mm. Measuring time 200s, calculation with 1mm (samples 3, 10) and 0.2mm thickness (samples 6, 12) Sample Pb / ppm Hg / ppm Cd / ppm Cr / ppm Br / ppm mq 3 Rubber 2.4 mm 10 Plastics 0.9 mm 6 Adhesive tape 0.23 mm 12 Foam 10 mm 3.8 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

6 Summary The measurements show that a simple screening can be performed, i.e., a decision can be made, whether a part lies securely below the limit value or is in a critical range. Two applications are required (DefMA 60102, each time, the thickness of the coating must be adapted): An application for thick parts (thickness specified in the application ~ 0.5 1mm) and an application for thin parts or foam (thickness specified in the application ~ mm). Thick parts should be measured using a measuring time of s and thin parts using ~ 200s. Suitable limits should then be specified for the individual elements, e.g., 100ppm for Pb, Hg, Cr, Br and 30ppm for Cd. If the measurements are below all limits, the part passes. If one limit is exceeded, further investigation is required. This could mean: 1. Quantitative analysis using XRF. First, the set thickness or mass per unit area must be adjusted to the actual thickness or mass per unit area of the sample. In addition, a calibration will be required. However, the quantitative determination of Cr (VI), PBB and PBDE is not possible, even with a calibration. 2. Use of alternative chemical or physical analysis methods. 3. Inquiry at the supplier. We have the following argument for manufacturers of electrical and electronic equipment: To manufacture in conformity to RoHS, it must be ensured that specified limits are met. XRF can provide a simple and quick answer. A quantitative determination is possible, but needs a greater effort and it is in general not required. A quantitative analysis is carried out with more ease at the manufacturers of the source materials (e.g., plastic granules) for parts made of plastics, because the samples can be characterized well in their structure. B. Nensel, nensel@helmut-fischer.de