DE102009056093A1 - Intrinsic laser-markable pigment preparation, useful for laser marking of inorganic systems and organic polymers e.g. plastics or printing inks, comprises a reducible metal compound and a reducing agent, and has a specific particle size - Google Patents

Abstract

Intrinsic laser-markable pigment preparation comprises at least one reducible metal compound and a reducing agent, and has a particle size of 0.01-200 pm. Independent claims are also included for: (1) preparing the pigment, comprising partially or completely coating the reducible metal compound with the reducing agent, or vice versa; (2) an organic polymer comprising the intrinsic laser-markable pigment; and (3) preparing the laser-markable organic polymer, comprising incorporating the pigment in the polymer or polymer matrix by using an extruder.

Description

The present invention relates to an intrinsically markable laser pigment in the form of a preparation of a reducible metal compound, a process for its preparation and its use in inorganic systems, such as. As water glass or water glass based coatings, and organic polymers, in particular plastics, paints, automotive coatings, powder coatings, printing inks, paper coatings and pulps.

The labeling of assets by means of laser radiation is now a common technology in almost all industries. So z. As production data, batch numbers, expiration dates, barcodes, company logos, serial numbers, etc. are applied to plastics or plastic films.

• 1. Abtragen von Schichten unterschiedlicher Einfärbung Von Nachteil ist, dass es sich hier um ein sehr aufwendiges Verfahren handelt, welches nur in einem begrenzten Umfang anwendbar ist.
• 2. Carbonisierung einer organischen Matrix Dies ist das derzeit am häufigsten eingesetzte Verfahren. Die Carbonisierung wird dabei entweder durch Absorption der Laserstrahlung in der organischen Matrix selbst oder durch Absorption an zugesetzten Absorbern hervorgerufen. In beiden Fällen wird die Carbonisierung des Polymermaterials durch einen kurzzeitigen Hitzeschock hervorgerufen, welcher die umgebende Matrix verbrennt. Dabei ist das Vermögen der Matrix beim Verbrennen ausreichend Kohlenstoff zu bilden von entscheidender Bedeutung für das Markierergebnis. Somit hat das eingesetzte Polymer bzw. die Rezeptur der Matrix einen starken Einfluss auf das Markierergebnis. Diese Ab hängigkeit führt in der Regel zu umfangreichen Vorversuchen zur Ermittlung eines für die jeweilige Anwendung ausreichenden Markierergebnisses. Bei Änderungen in der Zusammensetzung und vielfach auch schon bei Schwankungen der Rohstoffqualität müssen die geeigneten Beschriftungsparameter stets erneut bestimmt werden.
• 3. Farbwechsel von zugesetzten Pigmenten Um der vorgenannten Abhängigkeit zu entgehen, wird seit längerem schon versucht Pigmente bzw. Additive zu entwickeln, welche bei Laserbeschuss selbst einen Farbwechsel durchführen (intrinsisch markieren). Solche Additive erzeugen eine Markierung nahezu unabhängig von der umgebenden Matrix. Sie sind daher in allen Kunststoffen einsetzbar. Auch in dünnen Schichten wie Beschichtungen, Lacken und Drucken sind Markierungen möglich ohne die Schichten signifikant zu schädigen. Produkte mit dieser Eigenschaft sind jedoch bisher entweder auf der Basis von Schwermetallverbindungen aufgebaut oder lediglich in der Literatur beschrieben ohne den Einzug in die industrielle Praxis gefunden zu haben.

The contrast required for a marking is preferably produced according to the following methods:

• 1. Removal of layers of different coloration The disadvantage is that this is a very complex process which can only be used to a limited extent.
• 2. Carbonation of an Organic Matrix This is currently the most commonly used process. The carbonation is caused either by absorption of the laser radiation in the organic matrix itself or by absorption on added absorbers. In both cases, the carbonization of the polymer material is caused by a brief heat shock which burns the surrounding matrix. The ability of the matrix to form enough carbon when burning is of crucial importance for the marking result. Thus, the polymer used or the formulation of the matrix has a strong influence on the marking result. This dependency usually leads to extensive preliminary tests for determining a marking result sufficient for the respective application. In the case of changes in the composition and in many cases even fluctuations in the quality of the raw materials, the appropriate labeling parameters must always be determined again.
• 3. Color change of added pigments In order to avoid the above-mentioned dependence, it has long been attempted to develop pigments or additives which themselves perform a color change upon laser bombardment (mark intrinsically). Such additives produce a label almost independent of the surrounding matrix. They are therefore suitable for use in all plastics. Even in thin layers such as coatings, lacquers and prints, markings are possible without significantly damaging the layers. However, products with this property have hitherto been constructed either on the basis of heavy metal compounds or merely described in the literature without having found their way into industrial practice.

It is therefore an object of the present invention to find an intrinsically marking additive for laser marking which, when exposed to laser light, gives very good marking results, in particular high-contrast and sharp markings, and at the same time is free from heavy metals and can be produced on an industrial scale.

It is also an object of the present invention to provide a method for producing an intrinsically-marking laser additive.

Another object of the invention is to demonstrate the use of such a laser additive.

Surprisingly, it has been found that finely divided metal compounds, which are reduced by the laser radiation to colored metal compounds of low oxidation state or up to the metal, are outstandingly suitable as intrinsically marking additives for laser marking. Particularly suitable are as color neutral oxides of metals, the latter should not be toxic to the universal applicability and also should not form toxic reaction products in the reduction.

The present invention is an intrinsically laser-markable pigment, which is characterized in that the pigment having a particle size of 0.01-200 microns in the form of a preparation containing one or more reducible metal compounds and a reducing agent.

The present invention likewise provides a process for the preparation of the intrinsically laser-markable pigment according to the invention, where one or more reducible metal compounds be partially or completely coated with a reducing agent or a reducing agent is coated with one or more reducible metal compounds partially or completely.

The present invention is also the use of the laser pigment according to the invention in organic polymers, in particular in plastics, plastic films, paints, automotive coatings, powder coatings, printing inks, paper coatings and pulps, and in inorganic systems, such as. As water glass or water glass based coatings.

The invention furthermore also relates to the inorganic systems and organic polymer systems which contain the laser pigment according to the invention.

Under the action of laser light, the polymer doped with the laser pigment according to the invention shows a dark mark with high contrast and pronounced edge sharpness on a light or colored background.

As advantageous with regard to the by-products formed during the reduction, metal oxides or metal oxide mixtures have been shown to be reducible metal compounds.

The metal oxides can be present in doped or undoped form.

A heavy metal-free metal oxide, which can be very well reduced to colored metal suboxides or to metal, for example, titanium dioxide, which may also be present in doped or undoped form.

It is known that titanium dioxide can be reduced under the action of hydrogen at elevated temperature to a stable, bluish black suboxide of the formula TiO _x , where x is less than 2 and greater than 1.

However, a laser pigment or laser additive is in its intended use within the polymer matrix, for. As a plastic, usually no mobile reactant as in the above-mentioned hydrogen reduction available. It is a reaction between solids. Therefore, the reactants must be in close contact with each other to form a sufficient amount of reaction product in the short exposure time of the laser bombardment, which is required for a high-contrast marking. This is achieved according to the invention by coating the reducible metal compound, preferably the metal oxide or metal oxide mixture, with a reducing agent or coating a reducing agent with a reducible metal compound, preferably a metal oxide or metal oxide mixture. Suitable reducing agents are either all substances which are readily oxidized and precipitate on the surface of a metal compound, preferably a metal oxide or metal oxide mixture, or which envelop themselves as particles with a reducible metal compound, preferably with a metal oxide or metal oxide mixture to let.

• 1. mindestens einer Metallverbindung, vorzugsweise einem Metalloxid oder einem Metalloxidgemisch, die sich leicht reduzieren lässt, und
• 2. mindestens einem Reduktionsmittel.

The laser pigment according to the invention consists essentially of two components:

• 1. at least one metal compound, preferably a metal oxide or a metal oxide mixture which is easy to reduce, and
• 2. at least one reducing agent.

Of importance here is that the metal compound with the reducing agent has a direct or intimate contact, for. Example by coating the metal compound with the reducing agent or by coating the reducing agent with the metal compound.

The material to be coated in each case is present in particulate form.

If the reducible metal compound is coated with a reducing agent, it is in the form of carrier-free particles or as a coating on a carrier. It is understood that not only in each case a single particle, but also a group of several particles can be coated simultaneously with the reducing agent, so that the laser pigment according to the invention both from a single coated particles as well as from a group of particles with the common coating form a pigment, can put together. The same applies if the reducible metal compound is present on a support (for example on a mica flake, as described below).

If the reducing agent is coated with a reducible metal compound, the reducing agent is in the form of particles, ie particulate.

If the reducible metal compound is a metal oxide, it is preferable to use titanium dioxide, and also B ₂ O ₃ , Fe ₂ O ₃ or SnO ₂ . Other suitable reducible metal compounds are in particular bismuth oxychloride, bismuth oxide, silver halides such. B. AgCl, but also zinc sulfide or tin oxalate.

The doped metal oxide used is preferably titanium dioxide doped with Al, Si, Zr, Mn or Sb.

Preferred metal oxide mixtures are SnO / SbO, (Sn, Sb) O ₂ or bismuth vanadate.

If the reducible metal compound in the form of carrier-free particles coated with a reducing agent, the particle shape of the metal compound plays only a minor role for the Markierergebnis. The metal compound can in principle be present in all known particle shapes, for. As platelets, spheres, fibers, cubes, rods, cuboids or as approximately isotropic granules irregular shape. Preferred are isotropic forms such as spheres and cubes, or irregularly shaped granules.

According to the invention, such carrier-free particles have a particle size (corresponding to the length of the largest axis) in the range from 1 nm to 1000 nm.

As the particle size increases, the hiding power of the (core) particles grows, because they scatter the light emitted with increasing size to an increased extent. Depending on the intended use of the laser additive according to the invention, d. H. Depending in particular on the type of materials to be laser-marked and the layer thickness of the layers containing the laser additives, different ranges of particle sizes from the above-mentioned particle size range are therefore preferred.

If only slight light scattering and, associated therewith, low hiding power of the reducible metal compound are desired, particle sizes in the range from 10 nm to <100 nm are particularly preferred.

If, on the other hand, a higher hiding power is allowed or desired, particle sizes in the range from 100 nm to 700 nm are particularly preferred.

Furthermore, the metal compound to be reduced can also be applied to a carrier or a mixture of different carriers. Suitable carrier materials are all carrier materials known to the person skilled in the art, in particular transparent or semitransparent, preferably platelet-shaped, substrates. Preferred carriers are phyllosilicates. Particularly suitable are natural and / or synthetic mica, talc, kaolin, platelet-shaped iron or aluminum oxides, glass, SiO ₂ , TiO ₂ , platelet-shaped mixed oxides, such as. FeTiO ₃ , Fe ₂ TiO ₅ , graphite platelets or other comparable materials. Preferably, mica flakes, glass flakes or graphite flakes are used. It is also possible to use mixtures of different carrier materials which are coated with the same or else with different metal compounds.

The support materials are preferably platelet-shaped substrates which generally have a thickness of 0.005-10 μm, in particular 0.05-5 μm. The expansion in the other two ranges is usually 0.01-100 .mu.m, preferably 0.1-50 .mu.m, and especially 0.1-20 .mu.m.

When the carrier material is coated with a layer of a reducible metal compound, in particular a metal oxide layer, the thickness of the layer is preferably 1-500 nm, in particular 5-400 nm and very particularly preferably 5-200 nm.

In a particularly preferred embodiment, the laser pigment according to the invention consists of a preparation of mica flakes which are coated with a reducible metal oxide, preferably a titanium dioxide, and a reducing agent. The thickness of the titanium dioxide layer here is preferably 10-200 nm, in particular 20-100 nm and very particularly preferably 40-60 nm.

In a further preferred embodiment, the laser pigment according to the invention contains platelet-shaped pigments which are based on glass platelets and are coated with a reducible metal oxide. Particular preference is given to glass platelets which are coated with titanium dioxide.

If a reducible metal oxide, as described above, is applied to a support, the proportion of metal oxide is 5-80 wt .-%, in particular 20-70 wt .-% and most preferably 40-60 wt .-%, based on the carrier material.

Suitable reducing agents are, in particular, those which can be readily or partially completely deposited on the surface of the metal compound to be reduced, in particular the metal oxide or the metal oxide mixture.

Particularly suitable reducing agents are in particular aminoplasts, preferably selected from the group consisting of melamine resin, urea resin, urea / melamine resin mixtures, but also polyamides, carbon, polyoxymethylene, polyacrylates, epoxy resins, polyurethanes, polyesters, casein derivatives, etc.

The ratio of metal compound, in particular metal oxide or metal oxide mixture, to reducing agent is generally 1-10: 1, in particular 2-8: 1 and very particularly preferably 3-6: 1.

In a preferred embodiment, the metal compound to be reduced, preferably the metal oxide or metal oxide mixture which is present in the form of carrier-free particles or as a coating on a carrier material, is partially or completely coated on its (its) surface with the reducing agent.

This embodiment is described below by way of example for titanium dioxide particles or for titanium dioxide-coated support materials, both of which are particularly preferably used as the metal compound to be reduced.

If titanium dioxide particles or titanium dioxide-coated support materials are coated, for example, with an aminoplast, preferably a melamine resin, urea resin, urea-formaldehyde resin, urea / melamine resin mixture or a polyamide, the resulting pigments are formed on irradiation of the organic or inorganic polymer system contains, with laser light, surprisingly similar reaction conditions as in the reduction of titanium dioxide with hydrogen in an annealing furnace. As a result, the titanium dioxide converts to a stable blue-black colored suboxide. It does not matter in which crystal modification the titanium dioxide (anatase or rutile) is present. Also stabilized TiO ₂ variations, such. B. with Al, Si, Zr, Mn, Sb, etc. stabilized (doped) TiO _{2 ,} as well as on one of the already previously named carrier coated titanium dioxide react analogously.

This reduction process of titanium dioxide can already take place under conditions in which the surrounding polymer matrix has not yet been damaged, for. B. carbonized is. Therefore, with a laser pigment according to the invention also markings in thin layers, such. As in finishes and prints and in paper and paper coatings, possible. The polymer matrix to be marked, for. As a plastic, as such, in principle requires no carbonizable portion for laser marking. Therefore, non-organic systems, such as inorganic systems such as water glass or coatings based on water glass, can also be marked with the pigment according to the invention.

The coating of the titanium dioxide particles with a reducing agent may, for example, be carried out by wet-chemically acid-catalyzed polycondensation of an aqueous solution of an aminoplast resin in the presence of dispersed titanium dioxide particles or dispersed pigments comprising titanium dioxide on a support material. The condensate of the aminoplast thereby becomes insoluble in the water and precipitates on the surface of the pure titanium dioxide or on the surface of the titanium dioxide-coated support material as a thin layer.

Analogously to the described coating of titanium dioxide particles or of titanium dioxide-coated support materials with a reducing agent, the coating of the abovementioned other reducible metal compounds also proceeds with a reducing agent and the reaction of the laser pigments produced in accordance with the invention under laser light.

For the reduction of the metal compound, in particular the metal oxide or metal oxide mixture, with the laser is an amount of 5-80 wt .-% reducing agent, based on the total pigment, in particular 10-50 wt .-%, and most preferably 10-30 Wt .-%, wherein the reducing agent is preferably an aminoplast.

In principle, no further additives are required for the function as a laser-sensitive pigment.

If the reducing agent does not have sufficient absorption of the laser, however, the addition or incorporation of an absorber into the laser pigment is frequently recommended. The absorber may be added to both the reducing agent and the metal compound to be reduced, preferably the metal oxide or metal oxide mixture (eg, the titanium dioxide), or evenly distributed in the laser pigment of the present invention in the reducing agent and the metal compound to be reduced.

Suitable absorbers are in particular all the specialist in the laser marking of plastics known absorber, preferably carbon black, conductive pigments, such as. Example, antimony, Sb / Sn mixed oxides, z. B. Sb ₂ O ₃ , (Sn, Sb) O ₂ , coated with (Sn, Sb) O ₂ mica flakes, iron compounds, eg. B. magnetite, molybdenum sulfide, molybdenum oxide, BiOCl, platelet-shaped, in particular transparent or semi-transparent, substrates, for. B. phyllosilicates, finely divided metal particles, eg. As tin, iron or aluminum, dyes, z. B. Nirsorb from Milliken, copper hydroxide or copper phosphates, z. B. Cu ₃ (PO ₄ ) ₂ .2Cu (OH) ₂ (CHP = libethenitol), basic copper diphosphate Cu ₃ (PO ₄ ) _2. Cu (OH) ₂ , copper pyrophosphate Cu ₂ P ₂ O ₇ .H ₂ O, 4CuO P ₂ O ₅ .H ₂ O, 5CuO, P ₂ O ₅ 3H ₂ O, 6CuO · P ₂ O ₅ · 3H ₂ O, 4CuO · P ₂ O ₅ · 3H ₂ O, 4CuO · P ₂ O ₅ · 1 , 2H ₂ O, 4 CuO · P ₂ O _5, 4CuO · P ₂ O ₅ · 1.5H ₂ O. It is also possible to use mixtures of said copper hydroxide and copper phosphate. In the case of the copper phosphates, the libethenite is particularly preferred.

Particularly preferred absorbers are selected from the group carbon black, antimony, Sb / Sn mixed oxides, with (Sn, Sb) O ₂ coated mica flakes, magnetite, molybdenum sulfide, molybdenum oxide, BiOCl, phyllosilicates and dyes.

In part, these are identical to the preferred metal compounds to be reduced described above. In such a case, the metal compound to be reduced also acts as an absorber at the same time. It is also possible to use mixtures of a laser-absorbing metal compound and another of the abovementioned absorbers. Of these, however, preference is given to various metal compounds to be reduced, in particular doped or undoped TiO ₂ , but also B ₂ O ₃ , SnO ₂ , Bi ₂ O ₃ , silver halides, zinc sulfide, zinc oxalate or bismuth vanadate, each in particulate form or as a coating on a support, or the reducing agent enveloping these metal compounds, mixed with one or more of the absorber described above.

The incorporation of suitable light absorbers into the laser pigment then supports the response to the laser bombardment and results in a stronger color change. For this purpose, even very small amounts of absorber are sufficient, which also do not or negligibly influence the color of the polymer.

The concentration of the absorber or of an absorber mixture depends on the reducing agent used. The proportion of additionally used absorber in the laser pigment according to the invention, if present, is generally 0.0001-5 wt .-%, preferably 0.001-2 wt .-% and in particular 0.01-1 wt .-% based on the reducing metal compound, in particular the metal oxide or metal oxide mixture.

In particular, for the case that the laser pigment according to the invention comprises a metal compound to be reduced, which is coated with a reducing agent and in the form of nanoparticle particles to 1000 nm particle size, in particular in the form of previously described carrier-free particles having a particle size of 10 to <100 nm , It is also advantageous if the pigment-forming preparation according to the invention additionally contains one or more protective colloids as further component.

The latter prevent agglomeration of these particularly finely divided particles from the metal compound to be reduced, if they are coated with the reducing agent. Since not a single, but rather several nanoparticle particles are enveloped together with the reducing agent and in this way a cluster is produced which represents the laser pigment according to the invention, it is the task of the protective colloids to uniformly distribute the nanoparticle particles from the metal compound to be reduced in the Ensure clusters. The clusters have a particle size of 0.01 to 20 .mu.m, preferably from 0.05 to 10 .mu.m, more preferably 0.05 to <10 .mu.m. In this way, a laser pigment according to the invention is obtained which has a particularly low hiding power because the nanoparticulate metal compounds distributed in the pigment virtually barely scatter irradiated visible light. At the same time, however, such a laser pigment is readily dispersible in the application medium. Such a laser pigment can therefore also be used for marking virtually transparent application systems or particularly thin coatings.

Suitable protective colloids are the classes of compounds known to the person skilled in the art for such purposes, in particular water-soluble polymers such as partially saponified polyvinyl acetate, polyvinyl alcohol, polyvinylpyrrolidone, cellulose ethers (Tylose) such as, for example, methylcellulose, hydroxyethylcellulose and hydroxypropylmethylcellulose, polyacrylates, starch, proteins, alginates, pectins or gelatin. Particularly preferred are cellulose ethers, in particular hydroxyethyl cellulose.

The protective colloids are added in small amounts of from 0.01 to 5%, preferably from 0.1 to 2%, based on the weight of the preparation. The size of the clusters can be adjusted in a targeted manner via the amount of the protective colloids used and, if appropriate, additionally available surfactants. Basically, the principle applies here that a larger amount of protective colloids leads to a reduced size of the clusters.

The laser pigment according to the invention, if it consists in the previously described form of clusters of nanoparticulate metal compounds to be reduced with a coating of a reducing agent, the application medium, ie the material to be lasered, in an amount of about 0.1 to 20 wt .-% , preferably from 0.1 to 5 wt .-%, and particularly preferably from 0.5 to 2 wt .-%, based on the weight of the material to be laser-marked added.

In a further preferred embodiment, the reducing agent with a reducible metal compound, in particular a metal oxide or metal oxide mixture, such as. As titanium dioxide, completely (coated) or partially coated.

If, for example, finely divided, oxidizable material, which may be both organic, inorganic, metallic or organometallic origin, such. As carbon black, sulfites, cellulose powder, plastic powder, plant seeds, etc. coated with a reducible metal compound, such as a metal oxide, the product of this sheath reacts under laser bombardment as well as coated metal oxide to suboxides or metals. In the case of titanium dioxide as a partner, the reaction product of a laser bombardment is a blue-black suboxide, which allows a very high-contrast laser marking.

In a preferred embodiment, carbon black dispersed in water is coated with TiO ₂ analogously to the processes known from pearlescent pigments. Advantageously, the annealing of the pigment so obtained to convert the hydroxide to the oxide with the exclusion of oxygen, so that the trapped soot does not burn. This can be achieved relatively easily by flooding the furnace with nitrogen. In this example, the carbon black acts both as an absorber and as a reducing agent. Should the reducing agent have no absorption of the laser, such as microfine plastic particles, ground organic material e.g. As flour, colorless inorganic reducing agents, the addition or incorporation of an absorber, as indicated above is recommended.

If a finely divided particulate reducing agent, as described above, coated with a metal compound to be reduced, the reducing agent advantageously has a particle size of 0.01 to 50 .mu.m, in particular from 0.1 to 20 microns.

The laser pigments according to the invention have particle sizes of 0.01-200 μm, preferably 0.01-100 μm, in particular 0.1-20 μm, so that they can be used universally for the laser marking of organic polymers and inorganic systems. The smaller particle sizes can be advantageously used in thin layers and coatings, while larger particles can also be used in plastic compositions.

To adjust the particle size required in each case, the laser pigments according to the invention can be subjected to grinding if necessary.

For the purposes of the present invention, the particle size is considered to be the length of the largest axis of the pigments. The determination of the particle size can, in principle, be carried out using any method familiar to the person skilled in the art for particle size determination. In a simple way, the particle size determination, depending on the size of the laser pigments, for example, by direct observation and measurement of a number of individual particles in high-resolution light microscopes, but better in electron microscopes such as the scanning electron microscope (SEM) or the high-resolution electron microscope (HRTEM), but also in the Atomic Force Microscope (AFM), the latter in each case with appropriate image evaluation software done. Advantageously, the determination of the particle size can also be carried out with measuring devices (eg Malvern Mastersizer 2000, APA200, Malvern Instruments Ltd., UK), which operate on the principle of laser diffraction. With These measuring instruments can be determined in the standard method (SOP) from a pigment suspension both the particle size and the particle size distribution in the volume. According to the present invention, the latter measuring method is preferred.

Analogously to the determination of the particle size of the laser pigments according to the invention, it is also possible to determine the particle size of the metal compound or of the reducing agent to be reduced, if these particles are particulate, as described above.

The laser pigments according to the invention can have different shapes. Depending on whether a particulate metal compound to be reduced or a metal compound to be reduced on a support is coated with a reducing agent, or whether a particulate reducing agent is coated with a metal compound to be reduced, and depending on the original shape of each compound to be coated the laser pigments of the invention generally in spherical form, egg shape, lens shape, sausage shape, etc before. It is self-evident in view of the manufacturing process that these forms need not be regular, but may also be deformed.

Particularly preferred intrinsically markable laser pigments according to the present invention are mentioned below: metal compound reducing agent absorber Titanium dioxide (pigment without carrier) melamine resin Carbon black, magnetite, (Sn, Sb) O ₂ Supported Titanium Dioxide (TiO ₂ Coated Mica Flake) melamine resin Carbon black, magnetite, (Sn, Sb) O ₂ Supported titanium dioxide (TiO ₂ coated glass plate) melamine resin Carbon black, magnetite, (Sn, Sb) O ₂ Titanium dioxide (pigment without carrier Urea-formaldehyde resin Carbon black, magnetite, (Sn, Sb) O ₂ Supported Titanium Dioxide (TiO ₂ Coated Mica Flake) Urea-formaldehyde resin Carbon black, magnetite, (Sn, Sb) O ₂ Supported titanium dioxide (TiO ₂ coated glass plate) Urea-formaldehyde resin Carbon black, magnetite, (Sn, Sb) O ₂ Titanium dioxide (pigment without carrier Melamine-formaldehyde resin Carbon black, magnetite, (Sn, Sb) O ₂ Supported Titanium Dioxide (TiO ₂ Coated Mica Flake) Melamine-formaldehyde resin Carbon black, magnetite, (Sn, Sb) O ₂ Supported titanium dioxide (TiO ₂ coated glass plate) Melamine-formaldehyde resin Carbon black, magnetite, (Sn, Sb) O ₂ Titanium dioxide (as a coating) Soot particles Carbon black, magnetite, (Sn, Sb) O ₂ Copper hydroxide particles Melamine-formaldehyde resin Carbon black, magnetite, (Sn, Sb) O ₂ Titanium dioxide (as a coating) Polyamide particles Carbon black, magnetite, (Sn, Sb) O ₂ Sb / Sn composite oxide pigment Melamine-formaldehyde resin Sb / Sn mixed oxide on carrier mica platelets Melamine-formaldehyde resin

The present invention also provides a process for the preparation of the above-described intrinsically laser-markable pigment according to the invention, wherein one or more reducible metal compounds are partially or completely coated with a reducing agent or a reducing agent is partially or completely coated with one or more reducible metal compounds.

The reducible metal compound can be present in the form of carrier-free particles or as a coating on a support. If a reducing agent is coated with a metal compound to be reduced, the reducing agent is also particulate in finely divided form.

The details of the process have already been described above with regard to the structure of the pigment according to the invention, in particular the example of titanium dioxide as the metal compound to be reduced. In this respect, reference is made to the statements there.

The present invention also provides the use of the above-described pigment according to the invention for the laser marking of inorganic systems and of organic polymers. Details on this have also been explained above.

In particular, an organic polymer system or an inorganic system which contains the intrinsically laser-markable pigment according to the invention is also an object of the present invention.

By adding the laser pigments according to the invention as additives, in particular in concentrations of 0.1 to 30 wt .-%, preferably 0.5 to 20 wt .-%, and most preferably from 1 to 10 wt .-%, based on the To be marked, preferably organic, polymer or polymer system, a significantly higher contrast is achieved in the laser marking of polymers than with the commercially available absorbers at comparable concentrations. The concentrations mentioned are not solely dependent on the desired contrast but also on the layer thickness of the feed medium. Thus, in printing and coating applications, significantly higher concentrations are required than in plastics to provide the laser beam with a sufficient number of pigment particles available.

However, the concentration of the laser pigment according to the invention in polymers or in polymer systems, preferably in thermoplastics, thermosets or elastomers, is also dependent on the polymer material used. The low proportion of laser pigment changes the polymer system insignificantly and does not affect its processability.

Furthermore, colorants can be added to the polymers which allow color variations of any kind and at the same time ensure retention of the laser marking. Suitable colorants are in particular colored metal oxide pigments as well as organic pigments and dyes which do not decompose during laser marking or do not react under laser light.

As polymeric materials for laser marking in particular all known plastics, in particular thermoplastics, furthermore thermosets and elastomers, are suitable, as they are, for. In the Ullmann, Vol. 15, p. 457 ff. , Verlag VCH. Suitable polymers are, for. Polyethylene, polypropylene, polyamides, polyesters, polyester esters, polyether esters, polyphenylene ethers, polyacetal, polyurethane, polybutylene terephthalate (PBT), polymethyl methacrylate, polyvinyl acetal, polystyrene, acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylic ester (ASA), polycarbonate , Polyethersulfone and polyether ketones and their copolymers, mixtures, and / or polymer blends, such as. PC / ABS, MARS.

The incorporation of the laser pigment of the invention into the polymer to be marked, preferably a plastic or a plastic film or a coating, for. As a paint, a paper or powder coating, an automotive paint or a printing ink is done by the polymer granules, the paint or the ink is mixed with the laser pigment and possibly deformed under heat. The addition of the laser pigment to the polymer may be simultaneous or sequential. If appropriate, adhesives, organic polymer-compatible solvents, stabilizers and / or surfactants which are temperature-stable under the working conditions can be added to the polymer, preferably a plastic granulate, during the incorporation of the laser pigment.

The production of a plastic granulate doped with the laser pigment generally takes place in such a way that the plastic granulate is introduced into a suitable mixer, wetted with any additives and then the laser pigment is added and mixed in. The pigmentation of the polymer is generally carried out via a color concentrate (masterbatch) or compound. The mixture thus obtained can then be processed directly in an extruder or an injection molding machine. The shaped bodies formed during processing show a very homogeneous distribution of the laser pigment. Subsequently, the laser marking takes place with a suitable laser.

The invention also provides a process for producing a polymer doped with the pigment according to the invention, wherein a polymeric material is mixed with the laser pigment according to the invention and the pigment is incorporated into the polymer or the polymer matrix by means of an extruder. Optionally, the resulting polymer composition is then deformed under the action of heat.

The inscription with the laser takes place in such a way that the specimen is brought into the beam path of a pulsed laser, preferably an Nd: YAG laser. Furthermore, a label with an excimer laser, z. B. a mask technique possible. However, they are also conventional with others Laser types that have a wavelength in a range of high absorption of the pigment used to achieve the desired results. The mark obtained is determined by the irradiation time (or pulse number in pulse lasers) and the irradiation power of the laser and the plastic system used. The power of the laser used depends on the particular application and can be determined in individual cases by the skilled person readily.

The laser used generally has a wavelength in the range of 157 nm to 10.6 μm, preferably in the range of 532 nm to 10.6 μm. For example, mention may be made here of CO ₂ lasers (10.6 μm) and Nd: YAG lasers (1064 or 532 nm) or pulsed UV lasers. The excimer lasers have the following wavelengths: F ₂ excimer laser (157 nm), ArF excimer laser (193 nm), KrCl excimer laser (222 nm), KrF excimer laser (248 nm), XeCl excimer laser (308 nm), XeF- Excimer laser (351 nm), frequency multiplied Nd: YAG lasers with wavelengths of 355 nm (frequency tripled) or 265 nm (frequency quadrupled). Particular preference is given to using Nd: YAG lasers (1064 or 532 nm) and CO ₂ lasers. The energy densities of the lasers used are generally in the range from 0.3 mJ / cm ² to 50 J / cm ² , preferably 0.3 mJ / cm ² to 10 J / cm ² . When using pulsed lasers, the pulse frequency is generally in the range of 1 to 60 kHz. Corresponding lasers which can be used in the process according to the invention are commercially available.

The use of the polymer doped with the laser pigment according to the invention can be carried out in all fields where hitherto customary printing processes for the inscription of plastics, plastic films, are used. For example, molding compounds, semi-finished products and finished parts of the polymer according to the invention can be used in the electrical, electronics and motor vehicle industries. The marking and labeling of z. As cables, wires, trim or functional parts in the heating, ventilation and cooling area or switches, plugs, levers and handles that consist of the inventively doped polymers can be marked even in hard to reach places with the help of laser light. Furthermore, the polymer system according to the invention can be used in packaging in the food sector or in the toy sector. The markings on the packaging are characterized by the fact that they are wipe and scratch resistant, stable in subsequent sterilization processes, and hygienically pure in the marking process can be applied. Furthermore, plastic corks z. B. for wine bottles, be labeled.

Complete label images can be permanently applied to the packaging for a reusable system. Furthermore, the polymer system according to the invention finds application in medical technology, for example in the labeling of petri dishes, microtiter plates, disposable syringes, ampoules, sample containers, supply hoses and medical collection bags or storage bags.

Another important field of application for laser marking are plastic brands for the individual marking of animals, so-called cattle tags or ear tags. A barcode system stores the information that is specific to the animal. These can be recalled when needed with the help of a scanner. The label must be very durable, because the mark sometimes remain on the animals for several years.

The laser marking of molding compounds, semi-finished products and finished parts which consist of polymers doped with the laser pigment according to the invention is thus possible.

The following examples are intended to illustrate the invention without, however, limiting it. The percentages given are percent by weight.

Examples

Coated with reducing agent metal oxide

Example 1:

100 g of rutile titanium dioxide pigment in the particle size range of 100-500 nm (RN 2900 from Kronos) are pasted into 150 g of water. 25 g of melamine resin (Madurit powder from Ineos) and 0.1 g of an aqueous carbon black dispersion having a carbon black content of 25% (Derussol N25 / L from Evonik) are stirred into this titanium dioxide suspension and the entire batch is stirred in a bead mill (bead mill attachment for Dissolver "Dispermat" Fa. Getzmann) dispersed. The ready-dispersed mixture is then heated to 70 ° C and adjusted to pH = 4 with about 30 ml of a 25% solution of p-toluenesulfonic acid. After a reaction time After 30 minutes, the batch is allowed to cool and then filtered through a suction filter. Drying takes place overnight at 180.degree.

The material thus obtained has one with a Mastersizer 2000 from Malvern Instruments Ltd. under standard conditions determined particle size of D ₉₅ = 20 microns and is incorporated by means of extruder 1% in polypropylene. This compound is then molded into 9 cm x 6 cm x 0.15 cm test plates on an injection molding machine. These plates are marked with a Nd: YAG laser test grid, which can be used to display a wide range of different laser settings with regard to laser energy, laser beam speed and laser pulse frequency.

The following laser settings are tested:
Diode pumped 12 W Nd: YAG laser from Trumpf. The test grid consists of filled squares with edge lengths of 4 and 2 mm. The energy is varied from 30% to 100% of the maximum power in increments of 10%. The writing speed is varied between 200 mm / s and 2000 mm / s and the frequency between 1 KHz and 60 KHz.

The additive from Example 1 shows a uniform black marking of excellent contrast over the entire spectrum of different laser parameters.

Example 2:

80 g of an aqueous urea-formaldehyde resin solution (Kaurit 210 liquid from BASF) with a content of 50% resin are diluted with 100 g of water. 0.02 g of carbon black FW 1 from Evonik are stirred into this solution. In a dissolver, 100 g of an anatase titanium dioxide pigment particle size 100-500 nm (Kronos 1171) stirred and then at elevated speed (of 2500 rev / min = about 8 m / s peripheral speed at a diameter of 60 mm of the dissolver disk) dispersed , The fully dispersed batch is then heated to 70 ° C and adjusted to pH = 4 with about 4 ml of a 25% citric acid solution. After a reaction time of 30 min, the mixture is allowed to cool and then filtered through a suction filter. Drying takes place overnight at 180.degree.

The material thus obtained has a particle size of D ₉₅ = 30 μm determined analogously to Example 1 and is stirred into a 10% strength aqueous solution of polyvinyl alcohol. With a doctor blade from a film is pulled, which has a layer thickness of 50 microns after drying. This film is marked with a Nd: YAG laser analogous to Example 1 with the test grid. The result also shows a high-contrast, black mark with almost constant blackening over a wide range of different laser parameters.

Example 3:

20 g of silver nitrate (AgNO ₃ ) are dissolved in 100 g of water. 50 g of kaolin having a particle size D ₉₅ = 30 μm are stirred into this solution and, by dropwise addition of 80 g of 10% strength NaCl solution with stirring, the silver is filled in as silver chloride (AgCl) onto the kaolin. Before the addition of 30 g of Madurit MW 116 (75% melamine-formaldehyde resin solution from Ineos), the suspension is adjusted to pH 8 with NaOH. Thereafter, the entire batch is heated to 70 ° C and acidified after reaching the temperature by slowly dropwise addition of 1 molar HCl to pH 3-4. After a reaction time of about 30 minutes, the whole is allowed to cool and filtered through a suction filter. Drying takes place overnight at 180.degree.

The material thus obtained has a particle size of D ₉₅ = 100 .mu.m determined analogously to Example 1 and is incorporated in polypropylene by means of an extruder at 0.5% strength. This compound is then molded into 9.0 cm x 6.0 cm x 0.15 cm test plates on an injection molding machine. On these plates is marked with a CO ₂ - laser at a wavelength of 10.6 microns and the variations in laser power and laser speed analogous to Example 1, the test grid. The laser bombardment reduces the silver chloride to finely divided elemental silver and the marking shows a high-contrast black over almost the entire bandwidth of the laser parameters.

Reductant coated with metal oxide

Example 4:

0.2 g of an aqueous carbon black dispersion having a primary particle size of 25 nm (Derussol A from Evonik) are diluted in 1.5 liters of water and adjusted to pH 2.2 with HCl. This suspension is stirred heated to 75 ° C. Subsequently, 400 g of TiCl ₄ solution are added dropwise, while maintaining the pH at 2.2 with NaOH. After cooling, the mixture is filtered off and dried at 180 ° C to constant weight. After drying, the material is annealed under nitrogen at 600 ° C.

The pigment thus obtained has a particle size of D ₉₅ = 10 μm determined in a manner analogous to Example 1 and is incorporated into polypropylene by means of an extruder. This compound is then molded into 9 cm x 6 cm x 0.15 cm test plates on an injection molding machine. On these plates are marked with a Nd: YAG laser test grid analogous to Example 1, with which a wide range of different laser settings in terms of energy of the laser, speed of the laser beam and frequency of the laser pulses can be displayed.

This gives a high-contrast dark mark in almost all laser settings contained in the test grid.

Example 5:

100 g of finely divided Vestosint 2159 polyamide powder from Evonik with a particle size of D ₅₀ = 11 μm is mixed with 100 g of a rutile titanium dioxide pigment stabilized for outdoor use with Al and Si with a TiO ₂ content of 92.5% and a particle size distribution of 100 to 500 nm (Kronos 2230 from Kronos Titan) and a proportion of 0.05 carbon black powder (FW 200 from. Evonik) mixed physically homogeneous and then by means of a suitable mechanical method, such as. As the Mechanofusion process of the company Nara, firmly and intimately connected by the action of large mechanical forces. The relatively large plastic particles remain as primary particles, while the much smaller pigment particles are incorporated by means of the mechanical energy of the process in the surface of the plastic. The laser pigment obtained has a particle size of D ₉₅ = 30 μm determined analogously to Example 1.

The laser marking of the material thus produced, after being incorporated at a concentration of 1% in a plastic, shows a dark and high-contrast marking, which is caused both by carbonization of the plastic and simultaneously by reduction of the titanium dioxide to a black suboxide.

Example 6:

50 g of an aqueous urea-formaldehyde resin solution (Kaurit 210 liquid from BASF.) Containing 50% resin with 5 g of carbon black (1%, aqueous carbon black dispersion, prepared from Derusol N25 / L the Fa. Evonik ), 50 g of a nanoparticulate titanium dioxide pigment (P25 from Evonik, average primary particle size 21 nm) and 50 g of a 0.4% solution of Tylose H20 mixed and dispersed in a dissolver. The ready-dispersed batch is then heated to 70 ° C, mixed with a further 100 g of a 0.4% Tyloselösung and adjusted to pH 3-4 with about 4 ml of a 10% strength oxalic acid solution. After a reaction time of about 30 minutes, the batch is allowed to cool and then filtered through a suction filter. Preferably, the filter cake is washed with deionized water. Drying takes place overnight at 180.degree.

The light gray powder thus obtained has a particle size of D ₉₅ = 1 μm, determined analogously to Example 1, and is stirred into a 10% strength aqueous solution of polyvinyl alcohol, so that a 1.5% strength dispersion is obtained. With a doctor blade from a film is pulled, which has a layer thickness of 50 microns after drying. This film, which contains no further pigments or dyes in addition to the laser pigment of the invention, shows only a slight haze. It is marked with the Nd: YAG laser analogous to Example 1 with the test grid. The result also shows a high-contrast, black mark with almost constant blackening over a wide range of different laser parameters.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Ullmann, Vol. 15, p. 457 et seq. [0077]

Claims (26)

Intrinsically laser-markable pigment, characterized in that the pigment is present as a preparation containing one or more reducible metal compounds and a reducing agent, and has a particle size of 0.01-200 microns. Pigment according to claim 1, characterized in that the reducible metal compound has direct and intimate contact with the reducing agent. Pigment according to claim 1 or 2, characterized in that the reducible metal compound is present as a carrier-free particles. Pigment according to claim 1 or 2, characterized in that the reducible metal compound is present as a coating on a support. Pigment according to one or more of claims 1 to 4, characterized in that the reducible metal compound is partially or completely coated with a reducing agent. Pigment according to one or more of claims 1 to 4, characterized in that the reducing agent is coated with a reducible metal compound partially or completely. Pigment according to one or more of claims 1 to 6, characterized in that the reducible metal compound is selected according to the criterion that it has a color change by a chemical reduction. Pigment according to one or more of claims 1 to 7, characterized in that the reducible metal compound is a doped or undoped metal oxide. Pigment according to one or more of claims 1 to 8, characterized in that the reducible metal compound is selected from the group TiO ₂ (rutile or anatase), B ₂ O ₃ , Fe ₂ O ₃ , SnO ₂ , BiOCl, Bi ₂ O ₃ , Silver halides. Pigment according to claim 8 or 9, characterized in that the metal oxide is doped or undoped titanium dioxide. Pigment according to one or more of claims 1 to 10, characterized in that the reducing agent is an aminoplast. Pigment according to one or more of claims 1 to 11, characterized in that the reducing agent is selected from the group melamine resin, urea resin, urea-formaldehyde resin, urea / melamine resin mixtures or polyamide. Pigment according to one or more of claims 4 to 12, characterized in that the carrier is selected from the group of mica flakes, silicon dioxide flakes, glass flakes, ceramic flakes, aluminum oxide flakes, iron oxide flakes or graphite flakes. Pigment according to claim 13, characterized in that the support is a mica flake or glass flake. Pigment according to one or more of claims 1 to 14, characterized in that the pigment additionally contains as further component one or more absorbers. Pigment according to claim 15, characterized in that the absorber is selected from the group carbon black, antimony, Sb / Sn mixed oxides, with (Sn, Sb) O ₂ coated mica flakes, copper hydroxide phosphate, copper phosphate, magnetite, molybdenum sulfide, molybdenum oxide, BiOCl, phyllosilicates , Dyes. Pigment according to one or more of claims 1 to 16, characterized in that the pigment additionally contains as further component one or more protective colloids. Pigment according to one or more of claims 3, 5 to 12 and 15 to 17, characterized in that the carrier-free particle has a particle size in the range of 1 nm to 1000 nm. Pigment according to claim 18, characterized in that the particle size is in the range of 10 nm to <100 nm. Process for the preparation of a pigment according to one or more of claims 1 to 19, characterized in that one or more completely coated one or more reducible metal compounds with a reducing agent or a reducing agent partially or completely coated with one or more reducible metal compounds. A method according to claim 20, characterized in that the reducible metal compound is present as a carrier-free particles or as a coating on a support and is coated with a reducing agent partially or completely. Use of the pigment according to one or more of Claims 1 to 19 for the laser marking of inorganic systems and of organic polymers. Organic polymer containing an intrinsically laser-markable pigment according to one or more of claims 1 to 19. Polymer according to claim 23, characterized in that the proportion of pigment according to one or more of claims 1 to 18 in the polymer 0.1-30 wt .-%, based on the polymer. Polymer according to claim 23 or 24, characterized in that the polymer is a plastic, a plastic film, a paint, an automotive paint, a powder coating, an ink or a paper coating. Process for the preparation of the laser-markable polymer according to one or more of Claims 23 to 25, characterized in that the pigment according to one or more of Claims 1 to 19 is incorporated into the polymer or the polymer matrix using an extruder.