US008932512B2

(12) United States Patent (10) Patent No.: US 8,932,512 B2 Edler et al. (45) Date of Patent: Jan. 13, 2015

(54) POLYMERS HAVING A HIGH (58) Field of Classification Search ABSORPTION CAPACITY CPC ...... B29C 65/14: CO8K7/16; C08K9/02; ). CO8K7/OO (75) inventors: Eagle. The Piner USPC ...... 524/432, 430, 440; 156/272: 216/65; inzmeier, Gross-Zimmern (DE) 264/405, 482, 494,492, 319; 523/200, (73) Assignee: Merck Patent GmbH, Darmstadt (DE) See application file for523/216; complete 106/417, search 441,history. 442, 455 (*) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 (56) References Cited U.S.C. 154(b) by 602 days. U.S. PATENT DOCUMENTS (21) Appl. No.: 12/063,817 4,702.964. A 10/1987 Hirano et al. 5,529,744 A * 6/1996 Tindale ...... 264,532 (22) PCT Filed: Jul. 26, 2006 6,214,917 B1 * 4/2001 Linzmeier et al. . ... 524/430 6,376,577 B2 * 4/2002 Kniess et al...... 523,215 (86). PCT No.: PCT/EP2006/007385 2005/02531 17 A1* 11/2005 Pfaffet al...... 252/SOO 2006/0024476 A1 2/2006 Leland et al...... 428,137 S371 (c)(1), 2007/01294.75 A1* 6, 2007 Sakata et al...... 524,306 (2), (4) Date: Feb. 14, 2008 2007/0173581 A1* 7/2007 Hager et al...... 524/430 2007/O1997 29 A1 8/2007 Siegel (87) PCT Pub. No.: WO2007/019951 2007/0295689 A1* 12/2007 Clauss et al...... 216.65 PCT Pub. Date: Feb. 22, 2007 FOREIGN PATENT DOCUMENTS (65) Prior Publication Data DE 35 25545 A1 1, 1986 DE 238877 9, 1986 US 2010/O139855A1 Jun. 10, 2010 DE O238877 A1 9, 1986 O O WO WO 2005036563 A2 4, 2005 (30) Foreign Application Priority Data WO WO2O06042714 * 10/2005 Aug. 15, 2005 (DE) ...... 10 2005038 774 * cited by examiner (51) Int. Cl. Primary Examiner — James J Seidleck B29C 65/14 (2006.01) Assistant Examiner — Deve E Valdez CSK 7/16 (2006.01) (74) Attorney, Agent, or Firm — Millen, White, Zelano & CSK 9/02 (2006.01) Branigan, P.C. CSK 700 (2006.01) CSK 3/22 (2006.01) (57) ABSTRACT CSK 3/30 (2006.01) The present invention relates to polymers comprising absorp (52) U.S. Cl. tion pigments, which are distinguished by the fact that they CPC. C08K9/02 (2013.01); C08K 3/22 (2013.01); have high absorption in the near IR region, and to the use C08K 3/30 (2013.01); B29C 65/1416 (2013.01) thereof, in particular in thermoforming and in IR light weld USPC ...... 264/405; 524/430; 524/440,523/200; ing. 523/216; 106/417: 106/441; 106/442; 106/455; 264/482; 264/494; 264/492; 264/319 22 Claims, 1 Drawing Sheet U.S. Patent Jan. 13, 2015 US 8,932,512 B2

Temperature behaviour of film under the influence of an IR emitter

O 1OO 200 3OO 400 5OO 600 700 Time in Sec US 8,932,512 B2 1. 2 POLYMERS HAVINGA HIGH INFRARED region from 850 to 2500 nm, without changing the colour in ABSORPTION CAPACITY the visible region. Although the absorption pigment has very high absorption in the near IR, the pigment is itself virtually The present invention relates to polymers which are distin white and thus only influences the properties of the polymer, guished by the fact that they have high absorption in the near Such as colour and transparency, to an insignificant extent. IR region, and to the use thereof, in particular in thermoform Furthermore, the absorption pigment increases the thermal ing and in IR light . conductivity within the polymer matrix and accelerates poly The heating of plastics using IR radiation is widespread in merisation and curing processes. the area of thermoforming, Such as the deep drawing of plastic The invention therefore relates to polymers, preferably sheets and films, and the conditioning of preforms for stretch 10 , which comprise, as absorption pigment, pale blow moulding. However, this radiation is also employed for ortransparent particulate semiconductor materials or particu accelerating polymerisation and curing processes and the late Substrates coated with pale or transparent semiconductor welding of plastic parts. materials. The IR source used here are hot bodies which emit IR 15 Suitable pale or transparent semiconductor materials are radiation over a broad wavelength spectrum. The higher the preferably those which absorb in the near IR region, in par temperature of the radiating body, the higher also the emitted ticular in the region from 750 to 2500 nm. The particulate energy and the shorter the wavelength. The electromagnetic semiconductor materials are preferably spherical, needle spectrum of IR sources can be divided into three regions in shaped or flake-form particles or flake-form, spherical or accordance with their wavelength: needle-shaped Substrates coated with semiconductor materi als. The semiconductor materials are built up homogeneously IR type Wavelength (nm) Temperature C. from pale or transparent semiconductor materials or applied Short 1000-1500 1SOO-2700 as coating to a particulate Substrate. The semiconductor mate Moderate 1500-2SOO 750-1500 25 rials are preferably based on oxides and/or sulfides, such as, Long 3OOO-SOOO 200-7SO for example, indium oxide, antimony oxide, tin oxide, Zinc oxide, zinc sulfide, tin sulfide or mixtures thereof. More recent developments in emitter technology even Suitable semiconductor materials generally have particle reach wavelengths of up to 800 nm, i.e. as far as the region of sizes of 0.01 to 2000 um, preferably 0.1 to 100 um, in par visible light. 30 ticular 0.1 to 30 um. Since high-temperature emitters emit more energy, they The semiconductor materials either consist homoge represent the best heat source. However, most polymer neously of the said semiconductors or are particulate, prefer groups only exhibit good absorption in a range from 2900 to ably spherical, needle-shaped or flake-form substrates which 3700 and above 5500 nm. This means that the energy of very are mono- or multicoated with the said semiconductor mate effective high-temperature emitters cannot be utilised suffi 35 ciently for heating polymeric systems. rials. The substrates are preferably coated with only one layer. In the case of pigmented plastics, the situation is even more The substrates can be spherical, flake-form or needle complex, since the absorption and reflection of the pigment shaped. The shape of the particles is not crucial per se. In are now added. Black pigments have high absorption in the general, the particles have a diameter of 0.01-2000 um, par near infrared and therefore heat up very quickly in the short 40 ticularly 0.1-300 um and in particular 0.5-60 um. The particu wave IR. White pigments, by contrast, reflect visible light larly preferred substrates are spherical and flake-form sub very well, and this property is valid into the IR region. In the strates. Suitable flake-form substrates have a thickness case of pale colours, this results in a significant delay in between 0.02 and 5um, in particular between 0.1 and 4.5um. heating compared with black or dark colours. Owing to this The size in the two other dimensions is generally between 0.1 delay, it not only takes much longer until, for example, a pale 45 and 1000 um, preferably between 1 and 500 um and in par plastic sheet has reached the forming temperature necessary ticular between 1 and 60 um. for thermoforming, but the long dwell time may even result in The substrates are preferably natural or synthetic mica damage to the plastic Surface. flakes, SiO flakes, Al2O flakes, glass flakes, aluminium However, the absorption pigments known from the prior flakes, BiOCl flakes, SiO, beads, silica gel, kieselguhr, glass art, such as, for example, carbon black, all have the disadvan 50 beads, hollow glass beads, TiO, beads, polymer beads, for tage that they permanently colour the plastic. In addition, they example comprising or , or TiO2 have to be added in comparatively high concentrations and needles, or mixtures of the said Substrates. are frequently toxicologically unacceptable. The coating of the particulate substrates with the semicon The object of the present invention was to find a pale or ductor materials is either known or can be carried out by white plastic colouring which simultaneously has good 55 processes known to the person skilled in the art. The sub absorption in the near infrared region and can be carried out in strates are preferably coated by hydrolysis of the correspond a simple manner. The absorber material must exhibit pro ing metal salts, such as, for example, metal chlorides or metal nounced absorption and an adequate reaction in this specific Sulfates, metal alkoxides or carboxylic acid salts in aqueous NIR region. or conventional solvent solution. The absorber here should be easy to incorporate into the 60 In the case of the semiconductors with a homogeneous polymer system, have high transparency and only be structure and also in the case of the Substrates coated with one employed in low concentrations. or more semiconductor materials, the semiconductor material Surprisingly, it has now been found that the addition of preferably has a microcrystalline structure. absorption pigments based on finely divided pale or transpar Particularly preferred absorption pigments are flake-form ent semiconductor materials gives a polymer system which 65 or spherical tin oxide, antimony oxide, indium tin oxide (ITO) has high absorption in the near IR, in particular in the region and mica flakes coated with ITO, tin oxide orantimony oxide, from 750 to >2500 nm, very particularly preferably in the and mixtures of the said oxides. US 8,932,512 B2 3 4 Particularly preferred absorption pigments are transparent thalate (PET), polymethyl methacrylate (PMMA), polyvinyl or pale semiconductor materials having a powder resistance acetal, (PVC), polyphenylene oxide of <20 S2 m, preferably <5S2m. (PPO), polyoxymethylene (POM), polystyrene (PS), acry A particularly preferred absorption pigment is a tin oxide lonitrile-butadiene-styrene (ABS), acrylonitrile-styrene doped with antimony oxide or a substrate coated therewith, acrylate (ASA), acrylonitrile-butadiene-styrene (ABS), poly Such as, for example, a mica flake. carbonates (PC), polyether sulfones, polyurethanes (TPU) Preference is furthermore given to spherical SiO, particles and polyether ether ketones (PEEK), and copolymers, mix coated with antimony oxide-doped tin oxide. The particle tures and/or polymer blends thereof. Such as, for example, sizes of these preferred absorption pigments are preferably PC/ABS, MABS. Besides the thermoplastics and ther 1-2 um. 10 moelastic plastics, thermosets, elastomers, biopolymers Besides antimony, preferably antimony oxide, the ele (semisynthetic plastics or modified natural products) are fur ments of main group 3, 5 and 7 are suitable as dopant, pref thermore suitable. erably the halides, in particular chlorides and fluorides. The absorption pigment is incorporated into the polymer The doping is dependent on the semiconductor material system by mixing the plastic granules with the absorption employed and is generally 0.01-30% by weight, preferably 15 pigment and then shaping the mixture under the action of 0.1-25% by weight, in particular 1-16% by weight, based on heat. During incorporation of the absorption pigment, it is the semiconductor material. furthermore possible to add colour and/or effect pigments and Preferred mixtures are indium tin oxides with antimony optionally additives, such as, for example, adhesives, organic doped tin oxides and indium tin oxide with doped Zinc oxides. polymer-compatible solvents, stabilisers and/or surfactants It is also possible to add mixtures of two, three or more which are heat-stable under the working conditions, to the absorption pigments to the polymer system, where the mixing plastic granules. The polymer system according to the inven ratio is unlimited. The total concentration is dependent on the tion is generally prepared by charging a suitable mixer with polymer composition, but should not be greater than 30% by the plastic granules, wetting the latter with any additives and weight in the polymer system. then adding and mixing-in the absorption pigment. The pig Owing to the high absorption rate, the absorption pigment 25 mentation of the plastic with (in)organic colour, white, black is effective in the polymer system even in relatively low and/or effect pigments is generally carried out via a colour concentration of <1%. This also enables use in natural-co concentrate (masterbatch) or compound. loured plastics, to which it merely imparts a slight haze. The The resultant mixture can then be processed directly in an absorption pigment can be added in amounts of 0.1-30% by extruder or injection-moulding machine. The mouldings weight, preferably 0.3-20% by weight, based on the polymer 30 formed during processing exhibit a very homogeneous distri system. Taking into account efficacy and economy, the range bution of the absorption pigment. Thermoforming or IR from 0.3 to 10% by weight is particularly preferred. welding is subsequently carried out using a suitable IR light However, the concentration of the absorption pigment in SOUC. the polymer is dependent on the plastic employed. The low The invention also relates to a process for the preparation of proportion of absorption pigment changes the plastic system 35 the polymer system according to the invention having high insignificantly and does not influence its processability. absorption in the near infrared, characterised in that a poly The uniform distribution of the absorption pigment mer or plastic granules, preferably a , is (are) throughout the plastic matrix causes heating of the plastic mixed with the absorption pigment and optionally further material even in the interior of the material. A more uniform additives and then shaped under the action of heat. heat distribution over the entire cross section is thus obtained. 40 The polymers according to the invention are particularly Particularly in the case of thick-walled parts, this reduces the Suitable for thermoforming, Such as the deep drawing of formation of internal stresses during thermoforming of the plastic sheets and films, and the conditioning of preforms for plastic material, significantly shortens the warm-up time and stretch blow moulding, for example PET bottles. prevents damage to the plastic Surface. At the same time, the The injection stretch blow moulding of hollowware is car shortening of the heat-up time reduces the energy require 45 ried out starting from injection-moulded preforms, which ment, which is in turn associated with significantly lower have to be brought to the corresponding stretching tempera production costs. ture (for example 90-120° C. in the case of PET) before the Transparent thermoplastics comprising the said absorption actual stretch blow moulding operation. This is frequently pigments in pure colouring exhibit a slight haze, but retain carried out with the aid of a series of IR emitters, past which their transparency. The addition of 0.2 to 10% by weight, 50 the preforms are transported with rotation. The use of the preferably 0.5 to 3% by weight, of opaque pigments, such as, plastics according to the invention having high absorption for example, titanium dioxide, can, if required, completely compared with conventional plastics results in faster heating hide this haze, in particular in polyolefins. Furthermore, colo of the preforms. Depending on the cycle time of the blow rants, which allow colour variations of any type and at the moulding unit, either the cycle time can thus be reduced or same time ensure retention of the absorber performance, can 55 alternatively the length of the emitter Zone can be shortened. be added to the plastics. Suitable colorants are, in particular, In both cases, the energy costs per finished part are reduced. coloured metal oxide pigments and organic pigments and The absorption pigment enables the heating rates of the poly dyes. mer systems to be shortened to 10% of the original heat-up All known polymer systems, in particular thermoplastics time, depending on the pigment concentration, emitter power and thermoelastic plastics, as described, for example, in Ull 60 and geometry of the plastic (for example wall thickness). mann, Vol. 15, pp. 457 ff. Verlag VCH, can be doped with the The plastics according to the invention are furthermore absorption pigments. Suitable plastics are thermoplastics and eminently suitable for the welding of plastic parts by means of thermoelastic plastics, such as, for example, IR light. In a similar manner to laser welding, infrared light (PE, HDPE, LDPE), (PP), , poly welding uses a short-wave infrared radiation for melting of esters, polyester-esters, polyether-esters, polyphenylene 65 the join area. The radiation Source used is usually a halogen ether, polyacetals, polyalkylene terephthalates, in particular lamp having a light emission in the range 500-1500 nm. The polybutylene terephthalate (PBT) and polyethylene tereph light from the lamp is focused on a focal point by means of an US 8,932,512 B2 5 6 ellipsoidal reflector, enabling a light power of >3000 W/cm Example 2 to be achieved with a focal point diameter of about 2 mm. The process is suitable both for direct welding of parts and Comparison of Two Pearlescent Films with and also for welding in the transmission process, in which a without Addition of an IR-Absorbent Pigment transparent part is welded to an absorbent part. The use of the pale and transparent absorption pigment in the polymer Pearlescent films having a thickness of 350 um are pro matrix has the advantage that the two join partners can be duced from polypropylene (Sabic PP575 P) with the follow made the same colour, since it has virtually no effect on ing recipe: colours present. a) 99% of Sabic PP 575 P The polymer System pigmented in accordance with the 10 1% of Iriodin(R) 123 Bright Lustre Satin pearlescent pig invention can be used in all areas where thermoplastics have ment from Merck KGaA (a TiO-coated mica pigment) been employed to date. For example, mouldings of the plastic b) 98% of Sabic PP575 P according to the invention can be used in the electrical, elec 1% of Iriodin(R) 123 Bright Lustre Satin pearlescent pig tronics and motor vehicle industries. The plastic system ment according to the invention can also be employed in packaging 15 1% of IR absorption pigment analogous to Example 1 Film pieces measuring 5 cmx5 cm are cut out of these films (films) in the foods sector. Furthermore, the polymer system and irradiated using a quartz ceramic emitter having a power according to the invention can be used in the area of construc of 1000 watts at a distance of 30 cm. The temperature change tion and architecture, as well as sport and leisure. during the irradiation is recorded and plotted graphically The invention also relates to the use of the polymers (FIG. 1). according to the invention having high NIR absorption in the In both films, a temperature equilibrium becomes estab area of thermoforming and in the IR welding of plastic parts. lished after a certain irradiation time. This is about 13°C. or Further embodiments according to the invention are 20% higher in the case of the film comprising absorberthan in revealed by the examples and the claims. the comparison without absorber, with the film without 25 absorber reaching its equilibrium temperature of about 52°C. BRIEF DESCRIPTION OF DRAWINGS after an exposure time of 120 s, while this temperature is reached after only 60s in the case of the film comprising FIG. 1 shows temperature change during irradiation. absorber. The invention claimed is: The following examples are intended to explain the inven 30 1. A method of thermoforming a plastic part, comprising tion, but without limiting it. The percent data indicated are irradiating said plastic part with IR radiation followed by percent by weight. thermoforming said plastic part, wherein the plastic part is a thermoplastic orthermoelastic EXAMPLES polymer system having a high IR absorption in the 35 region of 750 to >2500 nm, comprising absorption pig Example 1 ments having a powder resistance of <20 S2 m, wherein the absorption pigments are pale or transparent spherical, flake-form or needle-shaped particulate semicon Comparison of Natural-Coloured, Unpigmented PP ductor materials or particulate Substrates coated with pale or with PP which is Natural-Coloured, but is Pigmented 40 transparent semiconductor materials, with Absorbent Pigment wherein the particulate Substrates are synthetic or natural mica flakes, SiO, flakes, Al-O flakes, glass flakes, alu Films having a thickness of 350 um are produced from minium flakes, BiOCl flakes, SiO, beads, silica gel, kiesel polypropylene (Sabic PP 575 P) with pigmenting by guhr, glass beads, hollow glass beads, TiO beads, polymer a) 0.1% 45 beads, TiO, needles or a mixture thereof, b) 0.3% wherein the particulate substrates have a diameter of 0.5 to 60 lm, of the absorption pigment (an antimony oxide-doped tin diox wherein the absorption pigments are present in an amount of ide having a particle size of about 1 um). 0.1 to 30% by weight, based on the polymer system, As comparison, a film without pigmentation is produced. 50 wherein the thermal conductivity of the thermoplastic orther Parts are shaped from these films using a thermoforming moelastic polymer System is increased compared to an oth machine from Illig (model KFG 37) with 90% of the maxi erwise identical thermoplastic or thermoelastic polymer sys mum emitter power. 10 Elstein FRS/2 emitters having a tem that does not contain said particulate semiconductor power of 200 W each are used. The maximum achievable materials or particulate Substrates coated with pale or trans temperature is 600° C. The heat-up time required for an 55 parent semiconductor materials. optimum result which is comparable between the individual 2. A method according to claim 1, wherein the absorption films is measured in each case: pigments are semiconductor materials which have a homo geneous structure comprising pale or transparent semicon ductor materials or are applied as coating to a particulate PP film natural (comparison) heat-up time: 18 sec 60 substrate. PP film comprising 0.1% of absorption pigment heat-up time: 17.5 sec PP film comprising 0.3% of absorption pigment heat-up time: 16 sec 3. A method according to claim 1, wherein the absorption pigments are semiconductor materials which have an oxidic or sulfidic structure. As the measurement values show, the concentration of 4. A method according to claim 1, wherein the absorption 0.1% already has a small measurable influence in this plastic 65 pigments are semiconductor materials which are built up on system. Even with 0.3%, however, a significant shortening of the basis of indium oxide, antimony oxide, tin oxide, Zinc the heat-up time by 2 sec, i.e. about 11%, can be achieved. oxide, Zinc sulfide, tin Sulfide or is a mixture of said materials. US 8,932,512 B2 7 8 5. A method according to claim 4, wherein the absorption 20. A method of thermoforming a plastic part, comprising pigments are semiconductor materials which are indium tin irradiating said plastic part with IR radiation followed by oxide (ITO). thermoforming said plastic part, 6. A method according to claim 1, wherein the absorption wherein the plastic part is a thermoplastic orthermoelastic pigments are particulate Substrates which are synthetic or 5 polymer system having a high IR absorption in the natural mica flakes. region of 750 to >2500 nm, comprising absorption pig 7. A method according to claim 1, wherein the absorption ments having a powder resistance of <20 S2 m, pigments are semiconductor materials which are doped. wherein the absorption pigments are particulate Substrates 8. A method according to claim 1, wherein the absorption coated with pale or transparent semiconductor materials, pigments are semiconductor materials which have an amor- 10 phous, crystalline or microcrystalline structure. wherein the particulate Substrates are synthetic or natural 9. A method according to claim 1, wherein the absorption mica flakes, SiO, flakes, Al-O flakes, glass flakes, alu pigments are present in an amount of 0.3 to 10% by weight, minium flakes, BiOCl flakes, SiO, beads, silica gel, kiesel based on the polymer System. guhr, glass beads, hollow glass beads, TiO, beads, polymer 10. A method according to claim 1, wherein the polymer is 15 beads, TiO, needles or a mixture thereof, selected from the group consisting of polyethylene (PE, wherein the particulate substrates have a diameter of 0.5 to 60 HDPE, LDPE), polypropylene (PP), polyamides, polyesters, lm, polyester-esters, polyether-esters, polyphenylene ether, poly wherein the absorption pigments are present in an amount of acetals, polyalkylene terephthalate, polymethyl methacrylate 0.1 to 30% by weight, based on the polymer system, (PMMA), polyvinylacetals, polyvinyl chloride (PVC), 20 wherein the thermal conductivity of the thermoplastic orther polyphenylene oxide (PPO), (POM), moelastic polymer System is increased compared to an oth polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), erwise identical thermoplastic or thermoelastic polymer sys acrylonitrile-styrene-acrylate (ASA), acrylonitrile-butadi tem that does not contain said particulate Substrates coated ene-styrene (ABS), (PC), polyether sulfones, with pale or transparent semiconductor materials. polyurethanes (TPU) and polyether ether ketones (PEEK), 25 21. A method according to claim 20, wherein the absorp and copolymers and mixtures thereof. tion pigments are present in an amount of 0.3 to 10% by 11. A method according to claim 1, wherein the polymer weight, based on the polymer system. system has been prepared by charging a mixer with plastic 22. A method of thermoforming a plastic part, comprising granules, wetting with optional additives, and mixing with irradiating said plastic part with IR radiation followed by absorption pigments, and optionally with further additives. 30 thermoforming said plastic part, 12. A method according to claim 1, wherein the absorption pigments are semiconductor materials which have particle wherein the plastic part is a thermoplastic orthermoelastic sizes of 0.01 to 2000 um. polymer system having a high IR absorption in the 13. A method according to claim 1, wherein the absorption region of 750 to >2500 nm, comprising absorption pig pigments are semiconductor materials which have particle 35 ments having a powder resistance of <20 S2 m, sizes of 0.1 to 30 um. wherein the absorption pigments are particulate Substrates 14. A method according to claim 1, wherein the particulate coated with pale or transparent semiconductor materials, semiconductor materials or particulate Substrates coated with wherein the particulate Substrates are synthetic or natural pale or transparent semiconductor materials are uniformly mica flakes, SiO flakes, Al-O flakes, glass flakes, alu distributed throughout the polymer system. 40 minium flakes, BiOCl flakes, SiO, beads, silica gel, kiesel 15. A method according to claim 1, which achieves deep guhr, glass beads, hollow glass beads, TiO beads, polymer drawing of plastic sheets or films, or the conditioning of beads, TiO, needles or a mixture thereof, preforms for stretch blow molding of articles. wherein the particulate substrates have a diameter of 0.5 to 60 16. A method according to claim 1, wherein the plastic part lm, is a thermoplastic polymer system. 45 wherein the absorption pigments are present in an amount of 17. A method according to claim 1, wherein the polymer 0.1 to <1% by weight, based on the polymer system, systemachieves uniform heat distribution over its entire cross section. wherein the thermal conductivity of the thermoplastic orther 18. A method according to claim 1, wherein the plastic part moelastic polymer System is increased compared to an oth is a thermoelastic polymer system. 50 erwise identical thermoplastic or thermoelastic polymer sys 19. A method according to claim 1, wherein the absorption tem that does not contain said particulate Substrates coated pigment is present in an amount of 0.1 to <1% by weight, with pale or transparent semiconductor materials. based on the polymer System. k k k k k