WO2012104006A1

WO2012104006A1 - Laser-markable and laser-weldable polymers

Info

Publication number: WO2012104006A1
Application number: PCT/EP2012/000066
Authority: WO
Inventors: Tetsuji Honjo; Satoru Kobayashi; Masahiko Yazawa; Kazuhisa AZUMA
Original assignee: Merck Patent Gmbh
Priority date: 2011-02-03
Filing date: 2012-01-09
Publication date: 2012-08-09

Abstract

The present invention relates to laser-markable and laser-weldable polymers which comprise, as absorber, a tungsten and/or phosphorus doped tin oxide or a substrate coated with a tungsten and/or phosphorus doped tin oxide.

Description

Laser-markable and laser-weldable polymers

The present invention relates to laser-markable and laser-weldable polymers which comprise, as absorber, a tungsten and/or phosphorus doped tin oxide or a substrate coated with tungsten and/or phosphorus doped tin oxide.

The identification marking of products is becoming increasingly important in almost every branch of industry. For example, it is frequently necessary to apply production dates, expiry dates, bar codes, company logos, serial numbers, etc. to plastics or plastic films. These markings are currently mostly executed using conventional techniques, such as printing, hot- stamping, other stamping methods or labelling. However, in particular for plastics, increasing importance is being attached to the contactless, very rapid and flexible method of marking with lasers. With this technique it is possible to apply graphic inscriptions, such as bar codes, at high speed, even to non-planar surfaces. Since the inscription is located within the plastics article itself, it is durably abrasion-resistant.

Many plastics, e.g. polyolefins and polystyrenes, have hitherto been difficult or impossible to mark with a laser. A CO₂ laser which emits infrared light in the region of 10.6 m brings about only very weak, hardly legible marking on polyolefins or polystyrenes, even using very high power. In the case of polyurethane elastomers and polyether ester elastomers, no interaction occurs with Nd-YAG lasers, but engraving occurs using C0₂ lasers. It is not permissible for the plastic to reflect or transmit all of the laser light, since there is then no interaction. Nor must excessively strong absorption take place, however, since in this case the plastics evaporate and all that remains is an engraving. The absorption of the laser beams, and therefore the interaction with the material, depends on the chemical structure of the plastic and on the laser wavelength used. It is often necessary to add appropriate additives, such as absorbers, in order to render plastics laser-inscribable.

As an absorbent resin composition for laser, the resin compositions that contain phthalocyanine-based compounds, cyanine-based compounds, aminium-based compounds, imonium-based compounds, squalium-based compounds, polymethine-based compounds, anthraquinone-based compounds, azo-based compounds and carbon black are known in JP-A 2004-148800.

In JP-A 2005-290087, in order to enhance sensitivity to the laser, a absorbent resin composition for laser is proposed in which copper phosphonate with an aromatic ring, metallic elements, salts, oxides, hydroxides, and the like are added. However, these compounds have inadequate sensitivity to laser light, and a large quantity of them must be added to obtain a problem-free bonding. Moreover, the addition of a large quantity of the composition can alter the basic physical properties of the resin molding itself and can lead to reduced mechanical strength and other drawbacks. Most of the above mentioned compositions also absorb light in the visible wavelength region, and severe coloration of the plastics is also cited as a drawback.

As an absorbent, tin-doped indium oxide (ITO) and antimony-doped tin oxide (ATO) coated on platelet inorganic substrates described in JP 3591654 have relatively high transparency and absorption for laser.

However, the resource and cost problems of ITO are particularly

significant. Also, the use of Sb contained in ATO is feared by the toxicity in human body and environmental problems. Especially, it is desirable not to contain Sb or other toxic metals from the view point of food package applications for example.

A powder of mixed oxides of tin and a transition metal selected from group consisting of niobium, tungsten, vanadium and chromium has been published in U.S. 2009-060572. When the powder absorbs YAG laser energy and converts it into heat, carbonization in the surrounding material occurs and results in the formation of a dark mark that contrasts to the remainder of the surrounding area. However, it is necessary to increase the additive amount of these mixed metals to obtain the acceptable markings. As a result, the color of powder become darker and can not result in the formation of dark markings that contrasts to the remainder of the surrounding area which is colored by addition of these powders. Consequently, the successful absorber should have high transparency or bright own color.

Transmission laser welding is an elegant technique which was developed for welding together materials such as polymers, like plastics. This is achieved by bringing two plastic elements into contact with one another, where one thereof is transparent to laser light and the other is opaque to laser light. The area of contact between the two plastic elements is then exposed to a laser beam. The laser beam passes through the transparent plastic element and is absorbed by the second, opaque plastic element. This causes the opaque plastic element to warm, so that the area of contact between the two plastic elements melts, resulting in the formation of a weld site. The lasers used are usually diode lasers or Nd:YAG lasers having wavelengths between 808-1100 nm. Most polymers are more or less transparent at this wavelength, meaning that the absorption property can be achieved by the addition of additives. The absorber used is usually carbon black. This exhibits very high absorption both in the visible and also in the IR region. Carbon black therefore only allows black as colour. Pale colours and transparent systems are impossible.

EP 1117502 B1 describes a method in which the absorber is applied in the interlayer. This method enables welding of polymers in all colours, even of transparent plastics. The disadvantage of this method is the additional application step of the absorber paste. The weld seam usually also tends to be on the surface. The NIR absorbers used here are of an organic nature and exhibit no or virtually no light scattering.

The organic absorbent for laser welding described in JP-A 2004-148800 generally has a narrow wavelength range of absorbance, and a relatively large amount thereof must be added to obtain adequate heat generation. The carbon black has high thermal stability and absorbance. However, the plastic turned to black color due to the absorbance in the wavelength region of visible light. It is undesirable when a transparent plastic is required. The additives used for laser marking, such as, for example, antimony, antimony oxide, conductive pigments and TiO2, generally allow colouring in pale colours. They are added to the formulations of the laser-absorbent side and thus facilitate transmissive laser welding without the intermediate step of application of a laser additive to the site to be welded. Weldability is possible, but is not of commercial interest owing to the long process times. Besides the speed, a disadvantage is that the absorption of these additives is lower than that in the case of carbon black. For example, T1O2 is a surface absorber and thus does not allow a large penetration depth of the laser radiation.

On use of more strongly absorbent additives for the laser-absorbent part in transmissive laser welding, the plastic may melt, but stable welding cannot be achieved.

In general, in order to achieve sharp markings with a high contrast and an easy welding in plastic by using the laser, it is necessary to add a suitable absorber which corresponds to the wavelength of the laser.

Besides CO2 lasers, Nd:YAG lasers are increasingly being used for the identification marking or welding of plastics by laser. The YAG lasers usually used give a pulsed energy beam with a characteristic wavelength of 1064 nm or 532 nm. The absorber material must have pronounced absorption in this specific NIR region in order to exhibit an adequate reaction during fast inscription procedures.

The object of the present invention is therefore to find laser-markable and laser-weldable polymers which when exposed to laser light can give a white marking with high contrast and at the same time enable good welding, even for pale colours, on exposure to laser light. The successful absorbent should therefore have a very pale inherent colour and/or only have to be employed in very small amounts. The objective of this invention is to find a laser marking and welding absorber which can be adapted to various industrial fields. Surprisingly, it has been found that the laser-markability and laser- weldability of polymers, in particular the contrast of marking can be improved by addition of an absorber selected from a tungsten and/or phosphorus doped tin oxide or a substrate coated with tungsten and/or phosphorus doped tin oxide, preferably a tungsten and phosphorus doped tin oxide (TPTO) or a substrate coated with tungsten and phosphorus doped tin oxide.

In comparison to the absorbers known from the prior art the markings and laser-weldings achieved by the use of the transparent TPTO or TPTO coated on substrate are significantly paler, and at the same time the energy densities are lower.

The present invention therefore relates to laser-markable and laser- weldable polymers characterised in that the polymer contains, as absorber, a tungsten and/or phosphorus doped tin oxide or a tungsten and/or phosphorus doped tin oxide coated on substrate.

The laser-weldability of polymers consisting of a laser-absorbent part and a laser-transparent part can be improved by addition of TPTO or a TPTO coated on substrate into a laser-absorbent part. The welding results achieved by the use of the TPTO powder are excellent compared to the absorbers known from the prior art.

TPTO and TPTO coated on substrates are characterized that they have the absorption at a certain wavelength corresponding to the YAG-laser. Additionally, TPTO is environment-friendly and harmless because it does not contain toxic elements and heavy metals. Thus, the application field is not limited.

By adding the TPTO powder in the range of 0.03 to 10 % by weight, based on the plastic resin, preferably from 0.05 to 2 % by weight, and in particular from 0.1 to 1 % by weight, a sharp laser-marking with high contrast and excellent laser-welding results can be achieved by the use of such small concentrations. The concentration of the laser absorber in the polymers is of course dependent on the polymer system used. The small proportion of TPTO or TPTO coated on substrates does not substantially alter the polymer system, and has no effect on its processability.

It is also possible for colorants to be added to the polymers, permitting any type of variation in colour and at the same time ensuring retention of the laser-marking. Suitable colorants are colour pigments, white pigments, black pigments, effect pigments and in particular coloured metal oxide pigments, and also organic pigments and dyes.

The proportion of the laser absorber in plastic molding applications for laser-marking and laser-welding is preferably from 0.05 to 10 % by weight, based on plastic articles, more preferably from 0.1 to 1 % by weight.

The proportion of the laser absorber in the plastic printing and in coating applications for laser-marking and welding is preferably from 1 to 50 % by weight, based on plastic films, more preferably from 3 to 10 % by weight.

In order to increase the strength of the weld seam and the welding speed, a scattering additive, such as, for example, Ti0₂, CaC03, MgC0₃ or other white pigments or fillers, etc., known to the person skilled in the art can optionally be added to the laser-transparent part. Depending on the polymer employed, the additive is used in amounts of < 2 % by weight, preferably≤ 0.5% by weight and particularly preferably≤ 0.3 % by weight.

Furthermore, an absorber can likewise be added in small amounts to the laser-transparent polymer part. The addition of a scattering absorber in the laser-transparent part generally increases the strength of the weld seam and allows faster welding. Suitable laser-scattering absorbers are conductive pigments, such as, for example, antimony, Sb₂O3, (Sn,Sb)0₂,

(Sn,Sb)0₂-coated mica, (Sn,Sb)0₂- and Si0₂-coated mica, Ti0₂-coated mica pigments, copper hydroxide phosphate and copper phosphate. Absorbers of this type are available, for example, from Merck KGaA under the trade name Lazerflair^®. The absorber is preferably added to the laser-transparent polymer part in amounts of 0.001 - 2 % by weight, in particular 0.01 - % by weight and very particularly preferably 0.05 - 0.5 % by weight, based on the polymer part. However, the proportion of absorber in the laser-transparent polymer part is always significantly smaller than in the laser-absorbent part. In general, the laser-absorbent part comprises a 2-20 times, preferably 5-10 times, larger amount of absorber than the laser-transparent part.

The laser-transparent part may comprise both a scattering absorber and a scattering additive. If the scattering absorber is copper hydroxide phosphate or copper phosphate, the absorber in the laser-transparent part and in the laser-absorbent part differs merely in the concentration. The total concentration of scattering absorber and scattering additive in the laser- transparent part preferably should not exceed 2 % by weight.

The concentration of the absorber(s) in the respective polymer part is, however, dependent on the plastic system employed. The small proportion of absorber changes the plastic system insignificantly and does not affect its processability.

The suitable substrates are inorganic materials preferably selected from the group of from T1O2, ZnO, BaS0₄, AI2O3, Si0₂, ZrO₂, glass, alkali titanate, natural or synthetic mica, phyllosilicates, such as talc, kaolin, wollastonite or sericite, and mixtures thereof. A preferred substrate is T1O2 in view of the whitish hiding power due to high refractive index. The crystal system of T1O2 can be selected from rutile, anatase, brookite or

amorphous. Especially, the preferred crystal system is rutile which is the same crystal system of the tin oxide.

The shape of the base substrates can be selected from grains, spheres, plates, needles, fibers, columns, rods, and mixtures thereof. Especially preferred are grain or sphere-shaped substrates to obtain a good and smooth surface of the plastic films. In terms of the size of the base substrates, the mean diameter is in the range of 0.01 to 100 pm, in particular 0.01 - 30 pm, especially preferred 0.05 - 5 pm.

The grain or sphere-shaped substrates have preferably a mean radius of 0.01 - 10 pm, in particular 0.01 - 1 pm, especially preferred 10 - 500 nm. These mean diameters of substrates are desirable at the half of wavelength of visible light, since the whitish hiding power can be obtained on black base materials.

In the case of plate, needle, fiber, column, rod-shaped substrates, the ratio of its long axis and short axis (i.e., long axis/short axis) ranges from 2 to 200, preferably 10 to 50. In the case of spheres (including oval spheres), the ratio of its long axis and short axis (i.e.; long axis/short axis) ranges from 1 to 10, preferably 1 to 5.

Preferred spherical base substrates are selected from the group of Ti0_2l ZnO, BaSO₄, glass, alkali titanate,

S1O2, Zr02 or mixtures thereof. Especially preferred base substrates are Τ1Ό2, alkali titanate and ZnO which have a whitish hiding power due to the high refractive index.

Preferred plate, needle, fiber, column and rod-shaped base substrates are selected from the group of natural or synthetic mica, talc, kaolin, sericite, glass, TiO₂, ZnO, BaSO₄, AI₂O₃, SiO₂, ZrO₂, alkali titanate, wollastonite or mixtures thereof. Especially preferred base substrates are TiO_2> alkali titanate and ZnO which have a whitish hiding power due to high refractive index.

The amount of TPTO on the substrates is in the range of 20 - 80 wt.%, in particular 20 - 60 wt.%, and most preferably in the range of 40 - 50 wt.%, based on the weight of the final absorber. The layer thickness of TPTO on the substrates is in the range of 10 - 200 nm, preferably 30 - 100 nm.

In most cases, higher amounts of TPTO do not provide any further formation of a dark marking, and the colour of powder becomes significantly darker. On the other hand, at smaller amounts of TPTO darker markings and higher contrast can be achieved.

In TPTO, the atomic ratio of tungsten and phosphorus to tin is preferably 0.1 - 30 at.%, in particular, 1 - 10 at.%. If the doping content of tungsten and phosphorus is less or more, the darker markings cannot be achieved.

Especially preferred are T1O2 particles (spherical, grain-shaped) having a mean radius of 150 - 500 nm which are coated with 30 - 50 wt.% of TPTO based on the weight of the final particles. In this case the layer thickness of the TPTO layer is preferably in the range of 10 - 100 nm.

Particularly preferred absorbers are

- TPTO powder

- SiO₂ substrate coated with TPTO

- TiO₂ substrate coated with TPTO.

A production process of TPTO powder or TPTO coated on substrates is not limited to a specific process. For example, these particles can be prepared by treating an aqueous solution or suspension of the substrates at an elevated temperature, preferably > 40 °C, preferably 40 - 90 °C, at a suitable pH, preferably pH =1 - 3, with an aqueous tin salt, phosphate and tungsten salt solution with stirring. The pH is held constant by

simultaneous titration with a base. The TPTO is deposited or coated on the substrates in the solution. The deposited particles or coated substrates are filtered off, washed, dried and calcined at temperatures of 600 - 1000 °C, preferably 800 - 900 °C, in air or nitrogen atmosphere, preferably in nitrogen atmosphere. It is often advisable to add anionic and/or nonionic surfactants to improve properties.

Suitable water-soluble tin and tungsten salts are selected from chlorides, sodium salt, sulfates and nitrates, especially preferred are chlorides. A suitable water-soluble phosphate is preferably phosphoric acid. The layer thickness of TPTO coated on substrates is the range from 5 to 500 nm, preferably from 10 to 200 nm, in particular from 20 to 150 nm.

All known plastic resins can be used in the laser marking and welding application. Suitable plastics are thermo and thermo setting plastics such as polyethylene (PE), polypropylene (PP), polyamide (PA), polyester, polyether, polyphenylene ether, polyacrylate, polyurethane (PU), polyoxymethylene (POM), polymethacrylate, polymethylmethacrylate (PMMA), polyvinyl acetate (PVAC), polyvinyl acetal (PVB), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylate (ASA), ABS graft polymer, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polycarbonate (PC), polyether sulfones, polyether ketone, thermopolymer polyurethane (TPU), thermopolymer elastomers (TPE), epoxy resin (EP), silicon resin (SI), unsaturated polyester resin (UP), phenolic formaldehyde resin (PF), urea formaldehyde resin (UF), melamine resin (MF) and copolymers thereof and/or mixtures thereof. The polymer can also be a copolymer or block copolymer, etc. Conventional additives may be present.

The incorporation of the absorber within the polymer like plastic, takes place by mixing the plastics pellets with the absorber and optionally with further additives and/or dyes and/or colorants, followed by shaping with exposure to heat. During incorporation of the dopant, the plastics pellets may, if desired, be treated with adhesion promoters, organic polymer- compatible solvents, stabilizers, dispersants and/or surfactants resistant to the operating temperatures used. The doped plastics pellets are usually produced by placing the plastics pellets in a suitable mixer, wetting these with any additives, and then adding and incorporating the dopant. The plastics are generally pigmented by way of a colour concentrate

(masterbatch) or compound. The resultant mixture may then be directly processed in an extruder or injection-moulding machine. The mouldings formed during the processing have a very homogeneous absorber distribution. Finally, the laser-marking or laser-welding with a suitable laser takes place. Also, the laser absorber of the invention is coated on the surface of the resin molding and films by a printing and coating method. At first, a laser absorbent is dispersed in any solvent and additive by using a bead mill, a ball mill, a sand mill, ultrasonic dispersion, or another method, and mixed with a binder resin. The obtained coating product is printed and coated on the surface of resin moldings and films. After the solvent is evaporated, the binder resin is cured by a prescribed method. Then, a thin plastic film contained a laser absorbent can be formed in which the particles are dispersed in a medium. The thickness of the coating film is not particularly limited, but a thickness range of about 1 to 100 pm is preferred. The printing and coating method is not particularly limited as far as the surface of the substrate can be evenly coated with the resin that includes the powder, and examples include screen printing, gravure printing, offset printing, bar coating, spray coating, dip coating, brush coating, and other methods. When the particles are directly dispersed in a binder resin, there is no need to evaporate the solvent after application on the substrate surface, and such a product is environmentally and commercially preferred.

The invention also provides a process for producing the laser-markable and laser-weldable polymers, characterized in that a polymer is mixed with the absorber and then shaped with exposure to heat.

The plastic is marked and welded with suitable laser radiation as follows.

The method of inscription by the laser is such that the specimen is placed in the path of a pulsed laser beam, preferably an Nd:YAG laser. Inscription by a CO₂ laser, e.g. by using a mask technique, is also possible. The desired results can also be achieved by other conventional types of laser whose wavelength is within the region of high absorption of the pigment used. The marking obtained is determined by the irradiation time (or number of pulses in the case of pulsed lasers) and by the power emitted by the laser, and also by the polymer system used. The power of the laser used depends on the particular application and can readily be determined by the skilled worker in any particular case. For the laser-marking, the laser used generally has a wavelength within the region from 157 nm to 10.6 pm, preferably within the region from 532 nm to 10.6 pm. Examples which may be mentioned here are a CO₂ laser (10.6 μιτι) and an Nd:YAG laser (1064 or 532 nm), and a pulsed UV laser. Excimer lasers have the following wavelengths: F₂ excimer laser: 157 nm, Arf excimer laser: 193 nm, KrCI excimer laser: 222 nm, KrF excimer laser: 248 nm, XeCI excimer laser: 308 nm, XeF excimer laser: 351 nm, and frequency-multiplied Nd:YAG laser: wavelength of 355 nm (frequency-tripled) or 265 nm (frequency-quadrupled). Particular preference is given to using Nd:YAG lasers (1064 or 532 nm) and C0₂ lasers. The energy densities of the lasers used are generally within the range from 0.3 mJ/cm² to 50 J/cm², preferably from 0.3 mJ/cm² to

10 J/cm².

When pulsed lasers are used, the pulse frequency is generally within the range from 1 to 30 kHz. Corresponding lasers which can be used in the process of the invention are commercially available.

The inscription with the laser is preferably carried out by introducing the article into the ray path of a pulsed laser, preferably of an Nd:YAG laser.

The laser welding is carried out by introducing the specimen into the ray path of a continuous wave laser, preferably an Nd:YAG or diode laser. The wavelengths are preferably between 808 and 1100 nm. Since most polymers are more or less transparent at these wavelengths, the absorption property is achieved by the addition of additives. Weldings using other conventional types of laser are also possible if they operate at a wavelength at which the absorber used exhibits high absorption. The welding is determined by the irradiation time and irradiation power of the laser and the plastic system used. The power of the lasers used depends on the respective application and can readily be determined by the person skilled in the art in the individual case.

The pigmented plastics of the invention can be used in any sector where conventional printing processes have hitherto been used to inscribe plastics. For example, mouldings made from the plastics of the invention may be used in the electrical industry, electronic industry or motor vehicle industry. With the aid of laser light, it is possible to produce identification markings or inscription markings even at locations to which it is difficult to gain access, for example, on cables, lines, decorative strips, or functional parts in the heating, ventilation or cooling sector, or on switches, plugs, levers or handles which consist of the plastics of the invention. It is also possible for the polymer system of the invention to be used for packaging in the food and drinks sector, or in the toy sector. The markings on the packaging are wipe- and scratch-resistant, resistant to downstream sterilization processes, and can be applied by the marking process in a manner which is hygienically clean. Complete label motifs can be applied durably to the packaging for a reusable system. Another important application sector for laser inscription is that of the marking of plastics to produce individual identification marking for animals, known as cattle tags or ear tags. The information specifically associated with the animal is stored via a barcode system. It can be called up again when required with the aid of a scanner. The inscription must be highly durable since some tags remain on the animals for a number of years.

Laser welding with the polymers doped in accordance with the invention can be carried out in all areas where conventional joining methods have hitherto been employed and where it has hitherto not been possible to employ the welding process owing to the laser-transparent polymers and pale colours. The laser-transmissive plastic welding process thus represents an alternative to conventional joining methods, for example high- frequency welding, vibration welding, ultrasound welding, hot-air welding or also the adhesive bonding of plastic parts.

The laser marking and laser welding of plastic articles or mouldings which consist of the polymer parts doped in accordance with the invention is thus possible.

The examples below are intended to illustrate the invention but not to restrict the same. The percentages given are by weight unless otherwise indicated. Examples

Example 1 : Process for the preparation of TPTO powder

2 I of deionized water is heated at 75 °C under stirring. The pH-value is adjusted to 1-3 by diluted HCI. Then, a 50 wt.% SnCI solution (429 ml) mixed with 10 g of 85 wt.% H₃P0₄ and a 4 wt.% Na₂W0₄ solution (215 ml) are simultaneously dropped to the suspension while maintaining the pH 1-

3 by addition of a 32 wt.% NaOH solution.

The obtained TPTO precursor particles are then filtered, washed with deionized water and dried at 105 °C. The dried powders are calcinated at 900 °C for 10 min. in an N2 gas atmosphere (less than 3 % of O₂).

Example 2: Process for the preparation of TPTO coated on TiO₂ powder

250 g of TiO₂ pigments (mean particle diameter: 0.3 - 0.5 pm) is dispersed in 2 I of deionized water, and the suspension is heated at 75 °C under stirring. The following process is shown in Example 1.

Example 3: Process for the preparation of TPTO coated on SiO₂ powder

250 g of SiO₂ particles (Fine grinding particles, mean particle diameter: 1 - 5 pm) is dispersed in 2 I of deionized water, and the suspension is heated at 75 °C under stirring. The following process is shown in Example 1.

Laser marking for plastics prepared by injection molding process

Plastic plates containing each an absorber according to Examples 1-3 are prepared. At first, 0.48 g of each absorber, 1.2 g of TiO₂ pigment and 0.42 g of zinc stearate are added to 300 g of granulate HDPE (High density poly ethylene, HI-ZEX™2100J of Mitsui Chemicals) and dispersed therein. Then, white plastic plates (145 mm x 75mm x 2mm in thick) are prepared by injection molding process. The injection is carried out under heating at 230 - 250 °C and 100 rpm as a screw rotation speed. As a comparative example, natural plastic plates without absorber are prepared by the same injection molding condition. Laser markings are conducted by Fiber laser marker (LP-V10 of Panasonic Electric Works SUNX, Wave length: 1064 nm) using laser with an output power of 12 W and pulse cycle of 40 ps. Black or dark brown markings are made on the plastic bodies by the action of laser irradiation using a scan speed of 500 mm/s. Also, the whiteness of prepared samples are evaluated by L* value in the L*a*b* color system as defined in JIS Z 8729. The L^* value is measured by using CHROMA meter (CR-400 from Minolta Co., Ltd.).

Table 1 shows the results of the laser marking experiments. These results indicate that the TPTO powder, TPTO coated on TiO₂ powder and TPTO coated on S1O₂ powder are highly suitable for the use as laser marking additive. The color of the plastics does not change significantly by addition of the inventive absorbers.

Table 1 : Marking Results

Laser marking for plastics prepared by printing process

Laminate films are prepared by the gravure printing process. At first, the absorbers according to Examples 1 and 2 are mixed with gravure printing inks and dispersed by mixers. Then, the layer structure of the films is prepared as follows:

Laser marking layer is printed on PET film with a thickness of 100 pm by the gravure printing press (180 Lines/inch, 25pm in cell depth).

Step 2:

Opaque colorant is printed on the laser marking layer by the gravure printing press according to Step 1. Step 3:

Sticker film (PET film with a thickness of 100 μ^ηι) is heat-sealed with above layers according to Steps 1 and 2.

Prepared ink formulations are composed as follows:

(Ink formulation)

- Gravure ink for Laser marking layer -

• Working samples: 10.25 g

• Fine Star R: 41.00 g (*Fine Star R: Urethane system gravure

binder/TOYO INK MFG. CO., LTD)

NF 102: 18.00 g (NF 102: Solvent for Fine Star R/ TOYO INK MFG. CO., LTD)

- Gravure ink for opaque colorant -

• Multilac White: 31.50 g (Multilac White: TiO2 dispersion/TOYO INK MFG. CO., LTD)

• Fine Star R: 27.00 g

NF 102: 14.00 g

The laser absorbers according to Examples 1 and 2 are tested at different concentrations as a powder weight concentration. Laser markings are conducted by using a standard YAG laser beam with varying pulse energies (ranging from about 1 to 7 W) and frequencies (ranging from about 1 to 45 kHz). The laser is radiated on the top of non-printed PET film. Then, a black or dark brown marking is made on the printed films by the action of laser marking. Scan speed is set at 500 mm/s. Also, the whiteness of prepared samples are evaluated by L^* value in the L*a^*b* color system as defined in JIS Z 8729. The L^* value is measured by using CHROMA meter (CR-400 from Minolta Co., Ltd.).

Table 2 shows the results of the laser marking experiments. These results indicate that the TPTO powder and TPTO coated on TiO₂ powder are highly suitable for the use as laser marking additive. The color of the inks does not change by addition of the inventive absorbers. Table 2: Marking Results

Laser welding for plastics prepared by injection molding process

The plastic plates containing each an absorber according to Examples 1-3 (= laser-absorbent part) are prepared. At first, 2.4 g of Example samples, 1.2 g of T1O₂ pigment and 0.7 g of zinc stearate are added to 300 g of granulate PP (polypropylene, NOVATEC MA-3 of Japan Polypropylene Co., Ltd.) and dispersed therein. Then, white plastic plates (145 mm x 75mm x 2mm in thick) are prepared by injection molding process. The injection is carried out under heating at 230 - 250 °C and 100 rpm as a screw rotation speed. Also, natural plastic plates without absorber (= laser- transparent part) are prepared by the same injection molding condition. Both plates are pinched each other by using a compression tools. As a comparative example, laser-transparent part are pinched each other by using a compression tools. A laser beam is irradiated over 4 cm along the width direction from laser-transparent part side as shown in Fig. 1. Laser welding is conducted by Fiber laser marker (LP-V10 of Panasonic Electric Works SUNX, Wave length: 1064 nm) using laser with an output power of 15 W and pulse cycle of 50 ps. As a result, the laser welding between the laser-transparent part and the laser-absorbent part could be achieved by 5 times of laser irradiation using a scan speed of 2 mm/s.

Table 3 shows the results of the laser welding experiments. These results indicate that the TPTO powder, TPTO coated on T1O₂ powder and TPTO coated on Si0₂ powder are highly suitable as laser welding additive. The color of the plastics does not change significantly by addition of the inventive absorbers. Table 3: Welding Results

Laser welding for plastics prepared by printing process

The plastic films for laser welding are prepared by gravure printing process (= laser-absorbent part). At first, the gravure inks each mixed with the absorbers according to Example 1 and Example 2 are coated on PET film with 100 pm in thick by gravure press (Screen ruling: 180 Lines/inch, Cell depth: 30 pm).

Prepared ink formulations are composed as follows:

(Ink formulation)

- Gravure ink for Laser marking layer -

• Working samples: 10.25 g

• Fine Star R: 41.00 g (^*Fine Star R: Urethane system gravure

binder/TOYO INK MFG. CO., LTD)

NF 102: 18.00 g (NF 102: Solvent for Fine Star R/ TOYO INK MFG. CO., LTD)

Another PET film with 100 pm in thick (= laser-transparent part) is piled up to the printing surface of Laser-absorbent part by using glass plates. As a comparative example, laser-transparent parts are piled up to each other by using glass plates. A laser beam is irradiated over 4 cm along the width direction from laser-transparent part side. Laser welding is conducted by Fiber laser marker (LP-V10 of Panasonic Electric Works SUNX, Wave length: 1064 nm) using laser with an output power of 15 W and pulse cycle of 50 ps. As a result, laser welding between laser-transparent part and laser-absorbent part could be achieved by a laser irradiation using a scan speed of 2 mm/s. Table 4 shows the results of the laser welding experiments. These results indicate that the TPTO powder and TPTO coated on TiO₂ powder have highly aptitude for laser welding additive. The color of the plastics does not change significantly by addition of the inventive absorbers.

Table 4: Welding results

^■Laser-transparent part : PP (Novatec MA-3)

■ Laser-absorbent part : PP + absorber

Claims

Patent claims

1. Laser-markable and laser-weldable polymers, characterized in that they comprise, as absorber a tungsten and/or phosphorus doped tin oxide or a substrate coated with tungsten and/or phosphorus doped tin oxide.

Laser-markable and laser-weldable polymers according to Claim 1 , characterized in that they comprise, as absorber, a tungsten and phosphorus doped tin oxide (TPTO) or a substrate coated with tungsten and phosphorus doped tin oxide (TPTO).

Laser-markable and laser-weldable polymers according to Claim 1 or 2, characterized in that the atomic ratio of tungsten and phosphorus to tin is 0.1-30 at%.

Laser-markable and laser-weldable polymers according to one or more of Claims 1 to 3, characterized in that a substrate coated with a TPTO layer contains 20-80 wt.% of TPTO based on the substrate.

Laser-markable and laser-weldable polymers according to one or more of Claims 1 to 4, characterized in that the substrate is selected from TiO₂, alkali titanate, ZnO, BaSO₄, AI₂O_3> SiO₂, ZrO₂, glass, natural mica, synthetic mica, talc, kaolin, sericite, wollastonite or mixtures thereof

Laser-markable and laser-weldable polymers according to one or more of Claims 1 to 5, characterized in that the substrate is SiO₂ or TiO₂.

Laser-markable and laser-weldable polymers according to one or more of Claims 1 to 6, characterized in that the substrates have a mean particle size of 0.1 - 10 μητι. Laser-markable and laser-weldable polymers according to one or more of Claims 1 to 7, characterized in that the proportion of absorber is from 0.03 to 10 % by weight, based on the polymer.

Laser-markable and laser-weldable polymers according to one or more of Claims 1 to 8, characterized in that the polymer is selected from polyethylene (PE), polypropylene (PP), polyamide (PA), polyester, polyether, polyphenylene ether, polyacrylate, polyurethane (PU), polyoxymethylene (POM), polymethacrylate,

polymethylmethacrylate (PMMA), polyvinyl acetate (PVAC), polyvinyl acetal (PVB), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylate (ASA), ABS graft polymer, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polycarbonate (PC), polyether sulfones, polyether ketone, thermopolymer polyurethane (TPU), thermopolymer elastomers (TPE), epoxy resin (EP), silicon resin (SI), unsaturated polyester resin (UP), phenolic formaldehyde resin (PF), urea formaldehyde resin (UF), melamine resin (MF) and copolymers thereof and/or mixtures thereof.

Laser-markable and laser-weldable polymers according to one or more of Claims 1 to 9, characterized in that the polymers also comprise colour pigments and/or white pigments and/or black pigments and/or effect pigments and/or pearlescent pigments and/or dyes.

Laser-weldable polymers according to one or more of claims 1 to 10 consisting of a laser-transparent part and a laser-absorbent part, which can be welded to one another by means of laser light, characterised in that the laser-absorbent part comprises, as absorber, a TPTO or a substrate coated with TPTO. ₁₂. Laser-markable and laser-weldable polymers according to one or more of Claims 1 to 11 , characterised in that the polymers are marked or welded using a diode laser or Nd:YAG laser.

13. Process for producing laser-markable and laser-weldable polymers according to one or more of Claims 1 to 10, characterized in that a polymer is mixed with the absorber and optionally with further additives and colors, and finally shaped with exposure to heat.

14. Use of the laser-markable and laser-weldable polymers according to one or more of Claims 1 to 10 as a material for producing mouldings which are marked with the aid of laser beams.

15. Use of the laser-weldable polymers according to one or more of Claims 1 to 10 for transmissive laser welding.

16. Mouldings consisting of the laser-markable or laser-weldable plastic according to one or more of Claims 1 to 10.