EP2646514A1

EP2646514A1 - Pigments

Info

Publication number: EP2646514A1
Application number: EP11782052.2A
Authority: EP
Inventors: Reinhold Rueger; Matthias Kuntz
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2010-12-01
Filing date: 2011-11-02
Publication date: 2013-10-09
Also published as: DE102010052888A1; US20130248781A1; WO2012072173A1; KR20130138282A; CN103228742B; CN103228742A; JP6121908B2; KR101903206B1; US9403996B2; JP2014505120A

Abstract

The invention relates to semiconducting pigments based on plate-shaped substrates, which have a doped tin dioxide layer on the surface, and to the use of the pigments in dyes, paints, printing inks, plastics, security applications, floor coverings, films, formulations, ceramic materials, glasses, paper, for laser marking, in thermal protection, in dry preparations, in pigment preparations, and in particular as a varistor pigment.

Description

pigments

The present invention relates to semiconducting pigments based on platelet-shaped substrates which have a semiconductive layer on the surface and to the use of the pigments in paints, lacquers, printing inks, plastics, sensors, security applications,

Floor coverings, films, formulations, ceramic materials, glasses, paper, for laser marking, in thermal insulation, in

Dry preparations, in pigment preparations, as a photo semiconductor and in particular as a varistor pigment in functional materials for the

High Voltage Engineering.

Electrically conductive pigments are used today in various

Application areas used, such. for antistatic

Coatings, antistatic floor coverings, antistatic

Equipment of explosion-proof rooms or electrically conductive primers for the coating of plastics.

In these applications are low surface and

Volume resistances necessary to a reliable

to ensure electrical condition. Regarding the used

Therefore, there is a demand for the best possible pigments

Conductivity. Usually soot or graphite are used around the

Increase the conductivity of the dielectric materials. These substances meet the requirement of high conductivity, but have the

Disadvantage that they are black and thus always lead to the darkening of the staggered materials. This approach is therefore limited to dark to black applications and is not always practical because of this limitation.

Electrically conductive pigments based on transparent platelet-shaped substrates are known. These pigments are based on thin ones

Mica platelets coated with (Sn, Sb) O2, or with a sequence of layers of TiO ₂ / SiO ₂ / (Sn, Sb) O ₂ (eg Minatec.RTM ^® 31 CM or 30 CM of the Fa. Merck KGaA). Such pigments are z. In patents DE 38 42 330, DE 42 37 990, EP 0 139 557, EP 0 359 569, EP 0 743 654 and US Pat. No. 7,416,688 described. Such pigments are transparent, have a bright

Body color and have a high conductivity. With these pigments, light or transparent conductive coatings with surface resistivities kilohms ^* cm range are accessible. The values apply to DC voltage and low-frequency AC voltage.

Low resistance values are achieved in the pigmented materials when the pigment volume concentration in the

dielectric matrix is above the percolation threshold. The

Percolation threshold is the minimum concentration of conductive pigment in a dielectric in which continuous conductive paths can be formed. In this concentration range, the electrical resistance of the material changes by several orders of magnitude with small changes in the pigment volume concentration. Typically, this threshold is 10-20 vol.% Of pigment in the formulation. If the pigment volume concentration is below this threshold, the electrical resistance is essentially determined by the dielectric matrix material. Specific surface resistances of such materials in the form of paints or moldings are in a dry atmosphere

typically in the teraohm range.

Coatings or functional materials with resistivities in the range of 10 ⁸ to 10 ¹² ohm ^* cm are z. B. in high voltage engineering or in sensor elements of great interest.

Semiconducting functional materials with non-linear properties are used in electrical engineering to control the function of electrical components. An example of a non-linear property is a voltage-dependent resistor. Applications of this kind are z. For example, in Andreas Küchler "Hochspannungstechnik", Springer Verlag, 3rd edition, 2009 or in the ETG technical reports 110 and 112, 3rd ETG conference, Würzburg, 2008. Materials with voltage-dependent resistance are for example used as varistors.

Semiconducting coatings and tapes with voltage-dependent resistance are used for electric field control at high voltage Insulators used, for. As for resistive field control in cable sets. The prior art composites of silicon carbide and dielectric binders in the form of paints or tapes.

Here there is a constant need for improved material properties. In DE 19839285 it is proposed to use conductive pigments coated with antimony-doped tin oxide in bands for end corona protection in generators. In the invention, pigments are used with high conductivity, the dosages are in the

Percolation threshold. The pigments contain 12 to 15 mol% antimony in the antimony doped tin oxide, the resistance of the ribbons is set by the concentration of the pigments in the resin matrix.

Specific resistances in the range of 10 ⁸ to 10 ¹² ohm ^* cm are difficult to adjust with conductive pigments of high conductivity, however, because the preparations with pigment concentrations in the percolation threshold range must be formulated for the high resistances of the functional materials. In this concentration range, sudden changes in the electrical properties occur. Low concentration fluctuations, degree of crosslinking, residual solvent or water content or external parameters such as temperature can cause the resistance of the functional material to fluctuate by several orders of magnitude. A stable state can be set and maintained only with great effort. The method of accurately controlling high resistances in the dielectric material via low concentrations of conductive pigment is not practical in practice. There is therefore an urgent need for pigments with which semiconductive functional materials with readily adjustable and stable electrical properties are accessible.

The object of the invention is therefore to find semiconducting pigments with which semiconducting coatings and functional materials can be formulated which have specific resistivities in the range of 10 ⁸ to 10 ¹² ohm.cm and a defined voltage dependence of the resistance at pigment volume concentrations above the percolation threshold. Other objects of the invention are semiconducting Provide pigments with low intrinsic color, high mechanical stability and easy dispersibility.

Surprisingly, it has been found that pigments according to the present invention fulfill this requirement profile.

The pigments of the invention are distinguished from the conductive pigments of the prior art, in particular by a high resistance, by an adjustable nonlinearity of the resistor, their white body color, small particle size and good dispersibility. Compared to dark conductive pigments, the pigments of the present invention show significant advantages in applications requiring flexibility in the application system color (paints, plastics, inks). Thus, color and electrical conductivity can be combined in a very good manner, while the use of soot is always limited to dark colors.

Overall, however, could the demand for bright semiconducting

Pigments, especially white and semiconducting pigments with varistor properties, have not been fulfilled so far.

The present invention relates to a pigment based on a platelet-shaped substrate, characterized in that it has on the surface a conductive layer consisting of a doped tin dioxide layer, the molar ratio of tin: dopant = 99.99: 0.01 to 97: 3 amounts to.

Furthermore, the use of the pigment according to the invention is also an object of the present invention. The semi-conductive pigment with white body color is particularly suitable for use in paints, coatings, printing inks, plastics, sensors, eg. In a flat touch sensor, security applications, floor coverings, films, formulations, ceramic materials, glasses, paper, in

Dry preparations, in pigment preparations, as a photo semiconductor and particularly preferably as a varistor pigment in functional materials, in particular for high voltage engineering. Semiconducting or semiconducting pigments are in this

In contrast to conductive pigments, which have specific powder resistances of less than 100 KOhm ^* cm, preferably less than 1 KOhm * cm, the specific powder resistance of the semiconducting pigments is in the range of 100 KOhm ^* cm and 100 megohm * cm. The resistance range of a semiconducting pigment containing

Coating is in the lower resistance range of insulating materials with specific resistances in the mega- to teraohm range.

The semiconducting pigments according to the invention are based on

platelet-shaped substrates coated with a semiconducting layer. In principle, all transparent platelet-shaped substrates known to the person skilled in the art are suitable as platelet-shaped substrates. Particularly suitable substrates are selected from the group of TiO ₂ platelets, synthetic mica flakes, natural mica flakes, glass flakes, SiO ₂ flakes, talc, kaolin, sericite, Al ₂ O ₃ platelets, or mixtures thereof. Very particularly preferred substrates are natural or synthetic mica platelets, and also AI ₂ O ₃ platelets. Platelet-shaped semiconducting pigments have significant performance advantages over spherical pigments. With platelet-shaped semiconducting pigments, the desired electrical resistances of the materials can be achieved at significantly lower pigment volume concentrations than with spherical pigments.

The size of the base substrates is not critical per se and can be tailored to the particular application. As a rule, the platelet-shaped substrates have a thickness between 0.02 and 5 μm, in particular between 0.05 and 4.5 μm. The extent in the other two ranges is usually between 1 and 250 pm, preferably between 2 and 200 pm, and in particular

between 5 and 150 pm. Glass slides preferably have one

Layer thickness of <1, 0 pm, in particular <0.8 pm and completely

more preferably <0.5 pm. The shape factor of the platelet-shaped substrates, that is, the ratio of the longest axis of the

Particles to the thickness, is at least 4, preferably more than 10. The semiconductive layer is doped tin dioxide in the present invention.

The dopant is preferably a cation or an anion or a mixture of two or more cations or a mixture of at least one cation and at least one anion or a mixture of at least two anions.

Preferred cations are selected from the group of antimony, cobalt, tungsten, molybdenum, chromium, copper, titanium and iron, furthermore gallium, aluminum, indium, thallium, germanium, tin, phosphorus and arsenic.

Preferred anions are selected from the group fluorine, chlorine and phosphate.

In a particularly preferred embodiment is used as a semiconducting layer

Antimony doped tin dioxide,

Fluorine doped tin dioxide,

Chlorine-doped tin dioxide,

Tungsten doped tin dioxide,

Molybdenum doped tin dioxide,

Antimony and titanium doped tin dioxide,

Antimony and iron doped tin dioxide, or

Antimony and phosphorus doped tin dioxide used.

Particularly preferred is a semiconductive layer consisting of antimony-doped tin oxide. The molar ratio of tin to dopant, in particular antimony, in this preferred embodiment is 99.99: 0.01-97: 3, in particular 99.8: 0.2-99: 1.

The pigment according to the invention is preferably composed of 50-80% by weight of substrate and 20-50% by weight of semiconducting layer, wherein the sum of substrate and semiconductive layer gives 100 wt.%.

The pigment according to the invention particularly preferably consists of 50-80% mica and 20-50% by weight of the doped tin dioxide layer. The amount of tin dioxide depends on the specific surface of the substrate used.

Very particularly preferred pigments consist of mica platelets of particle size <15 .mu.m, coated with usually 35-50 wt.% Of doped tin dioxide based on the total pigment. If, on the other hand, the mica flakes have a particle size of 10-60 μm, the pigments preferably contain 20-35% by weight of tin dioxide, based on the total pigment.

The mica platelets can be both natural and synthetic mica.

The indication of the particle size refers to the d ₉₀ in a volume-weighted measurement by means of laser diffraction, z. B. determined with a Mastersizer 2000 Malvern. The average particle size d _{50 of} the particularly preferred pigments is in the range from 2 to 8 μm. Such pigments often show advantages in applications in terms of settling behavior, dispersibility and / or homogeneity of the coatings.

The layer thickness of the semiconductive layer is preferably 20-70 nm, in particular 30-40 nm.

The coating of the pigments according to the invention with a thin layer of a dielectric or further semiconducting material is often advantageous for setting higher resistances.

Particularly preferred is the application of a thin layer on the semiconductive layer of TiO ₂ , ZnO, Al ₂ O _3l Cr ₂ O ₃ or SiO ₂ . The layer thicknesses are generally <0.1 pm, preferably <0.05 pm. Preferably, the amount of the dielectric or semiconductive material with respect to the conductive layer is 0.5-5 wt%.

Particularly preferred pigments according to the invention have the following layer structure:

Substrate + SnO ₂ (doped)

Substrate + SnO ₂ (doped) + Ti0 ₂

Substrate + SnO ₂ (doped) + Si0 ₂

Substrate + SnO ₂ (doped) + ZnO

Substrate + SnO ₂ (doped) + Al ₂ O ₃

Substrate + SnO ₂ (doped) + Cr ₂ O ₃

Substrate + Si0 ₂ + Sn0 ₂ (doped)

Substrate + TiO ₂ + SnO ₂ (doped).

Very particularly preferred pigments according to the invention have the following structure:

Mica platelets + SnO ₂ (doped)

Mica platelets + Sn0 ₂ (doped) + Ti0 ₂

Mica platelets + Sn0 ₂ (doped) + Si0 ₂

Mica platelets + SnO ₂ (doped) + ZnO

Mica platelets + SnO ₂ (doped) + Al ₂ O ₃

Al ₂ O ₃ platelets + SnO ₂ (doped)

Al ₂ O ₃ platelets + SnO ₂ (doped) + TiO ₂

Al ₂ O ₃ platelets + SnO ₂ (doped) + SiO ₂

Al ₂ O ₃ platelets + SnO ₂ (doped) + ZnO

Al ₂ O ₃ platelets + SnO ₂ (doped) + Al ₂ O ₃ .

The doping in a preferred embodiment is preferably antimony oxide.

In a particularly preferred embodiment can be

produce low-Varistorpigmente, which preferably are based on mica flakes, in particular mica flakes having particle sizes of <5 ^μι η which, based on the substrate with 70 wt.% a semiconducting layer, preferably tin dioxide, are occupied, wherein the semiconductive layer with 1 wt.% Antimony, based on the semiconducting layer, is doped. In this way one obtains low-resistance

Varistor pigments that have a surface resistivity in a coating of 10 ⁸ ohms and a nonlinearity coefficient alpha of 4.5.

High-resistance pigments of the invention preferably consist of mica platelets with particle sizes <15 pm, which are based on the substrate with 70 wt.% First, with a semiconductive layer, preferably coated tin dioxide, wherein the semiconductive layer with 0.25 wt.% Antimony, based on the semiconducting layer is doped and subsequently has a TiO ₂ layer, the content of ΤΊΟ _{2 being} 1.4% by weight, based on the substrate. The resistivity of a coating containing this pigment is 10 ¹² ohms and the nonlinearity coefficient alpha is 4.

In the present application refers to the low-resistance

Resistance of a dielectric insulating material and is defined as follows: The specific resistance of a coating consisting of a binder and the semiconductive pigment in a

Pigment Volume Concentration (PVK) of 11 - 20% is 10 ⁷ to 10 ⁹ ohm * cm

In the present application, high resistance is defined as follows:

The resistivity of a coating consisting of a binder and pigment at a PVK of 12-20% is 10 ¹¹ to 10 ¹³ ohm.cm.

With the present invention, it is possible low-resistance and

targeted production of high-resistance pigments. If one mixes low-resistance and high-resistance pigments according to the invention, it is possible in one

Coating specifically to set the desired resistivity of the coating from 10 ⁸ to 10 ¹² ohms, without the

To change total pigment concentration. The walls are precisely adjustable and stable. Particularly preferred pigments of the present invention include mica platelets coated with an antimony-doped tin dioxide layer or mica platelets coated with an antimony-doped tin dioxide layer and a metal oxide layer, in particular a

Titanium oxide layer, coated.

By coating with titanium dioxide, the band gap of the

semiconducting Zinndioxids increases, whereby the pigment becomes whiter and the electrical conductivity decreases strongly because of the decreasing density of free charge carriers. This way are special

high-resistance semiconducting pigments accessible, the level of resistance alone via the doping, e.g. with antimony, is difficult to adjust.

Likewise provided by the present invention are processes for the preparation of the pigments of the invention, comprising

Coating of platelet-shaped substrates with a semiconducting layer and optionally with a subsequent metal oxide layer,

preferably titanium dioxide, characterized in that the coating of the platelet-shaped substrates with a semiconducting layer according to the coating methods known from the prior art,

preferably wet-chemical, takes place.

In the simplest embodiment of the process according to the invention, a layer of a doped metal oxide, metal hydroxide or metal oxide hydrate is applied to the platelet-shaped substrate from suitable precursors. In this case, the precursors for the metal oxide and the

Doping either separately, preferably continuously, or mixed together, i. together in a solution. Suitable precursors are the corresponding halides, nitrates, sulfates, phosphates or oxalates, preferably the corresponding halides are used. Such methods are e.g. described in DE 42 37 990, DE 38 42 330, EP 0 139 557, U.S. Pat. 7,416,688, the disclosure of which is hereby

Reference is included. The optimization of the application conditions lies in the area of expert know-how. Usually, in the case of wet coating, the substrates are suspended in water and admixed with one or more hydrolyzable metal salts at a pH suitable for the hydrolysis, which is chosen such that the metal oxides, metal hydroxides or metal oxide hydrates are precipitated directly on the platelets without it comes to Nebenfällungen. The pH is usually kept constant by simultaneous addition of a base or acid. The pigments are separated after application of the conductive layer, dried and usually calcined in air or under inert gas or reducing conditions, usually at temperatures of 300 to 900 ° C, preferably at temperatures of 650 to 850 ° C.

In a further embodiment of the method according to the invention, a layer of metal oxide or metal oxide hydrate is applied after the coating of the platelet-shaped substrates with a semiconducting layer. The application of the single or multiple layers can be carried out wet-chemically, by means of sol-gel method, CVD and / or PVD method. Preferably, a coating with a metal oxide is wet-chemically.

If desired, after application of the conductive or semiconducting layer, the pigments may be separated, dried and optionally calcined, to be resuspended to precipitate the metal oxide layer. In an alternative embodiment, all the desired layers can first be precipitated and subsequently calcined in their entirety.

The pigments according to the invention are suitable for a wide range of applications because of their advantageous properties.

The invention is therefore also the use of

pigments according to the invention in paints, varnishes, printing inks,

Plastics, in security applications, floor coverings, foils, formulations, ceramic materials, glasses, paper, in

Dry preparations, in sensors, as a photo semiconductor or in

Pigment preparations and as varistor pigment for electrical Field control in high voltage engineering, z. B. for the suppression of glow discharges in terminations of high voltage cables or cable glands.

In the case of formulations, the pigments of the invention are particularly suitable for formulations which are to have a defined low conductivity, e.g. conductive pastes. Of course, the pigments according to the invention in the formulations can also be combined with any type of raw materials and excipients. These include u.a. Oils, fats, waxes, film formers, preservatives and general application properties determining auxiliaries, such. Thickeners and rheological additives such as bentonites, hectorites, silicon dioxide, cocoa silicates, gelatin and / or surface-active auxiliaries, etc.

When the pigments are used in paints and coatings, all the fields of application known to the person skilled in the art are possible, such as, for example, Powder coatings,

Automotive coatings, printing inks for gravure, offset, screen or flexo printing as well as coatings in outdoor applications. For the production of printing inks, a variety of binders, in particular water-soluble types, are suitable, e.g. based on acrylates, methacrylates, polyesters, polyurethanes, nitrocellulose, ethylcellulose, polyamide, polyvinyl butyrate, phenolic resins, maleic resins, starch or polyvinyl alcohol. The paints may be water- or solvent-based paints, the selection of the paint components is subject to the general knowledge of the skilled person.

In addition, the pigments of the invention can be used in particular for the production of conductive films and plastics, e.g. for conductive films and disks, plastic containers and moldings for all applications known to those skilled in the art which require conductivity. Suitable plastics are all common ones

Plastics for the incorporation of the conductive according to the invention

Pigments, e.g. Duromeric or thermoplastic plastics. The

Description of possible applications and applicable

Plastics, processing methods and additives can be found, for example, in RD 472005 or in R. Glausch, M. Kieser, R. Maisch, G. Pfaff, J. Weitzel, Pearlescent pigments, Curt R. Vincentz Verlag, 1996, 83 ff., Whose

The disclosure content hereby includes.

The pigments of the invention are also suitable for use in blends with organic dyes, pigments and / or other conductive materials, such as carbon black, transparent and opaque white, colored and black pigments and platelet-shaped iron oxides, organic pigments, holographic pigments, LCPs (Liquid Crystal Polymers) and conventional transparent, colored and black luster pigments based on metal oxide-coated platelets based on mica, metal, glass, Al ₂ O ₃ , Fe ₂ O ₃ , SiO ₂ , etc. The pigments according to the invention can be mixed in any ratio with commercially available pigments and fillers become.

As fillers are e.g. natural and synthetic mica, nylon powder, pure or filled melamine resins, talcum, glasses, kaolin, oxides or hydroxides of aluminum, magnesium, calcium, zinc, BiOCl,

Barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, carbon, as well as physical or chemical combinations of these substances.

The pigments according to the invention are furthermore suitable for the preparation of flowable pigment preparations and dry preparations comprising one or more pigments according to the invention, binders and optionally one or more additives. Dry preparations are also to be understood as preparations which contain 0 to 8% by weight, preferably 2 to 8% by weight, in particular 3 to 6% by weight, of water and / or of a solvent or solvent mixture. The dry preparations are preferably in the form of pellets, granules, chips, sausages or briquettes and have particle sizes of 0.2-80 mm.

The present invention also provides the use of the pigment according to the invention in paints, varnishes, printing inks,

Plastics, sensors, security applications, floor coverings, films, formulations, ceramic materials, glasses, paper, for laser marking, in heat protection, in dry preparations, in Pigment preparations, as a photo semiconductor and as a varistor pigment in functional materials for high voltage engineering.

The following examples are intended to illustrate the invention without, however, limiting it.

Examples

Example 1: Low-resistance semiconductive pigment

In a 5 l stirred tank, 100 g of mica platelets with a maximum particle size of 15 pm are suspended in 2 l of water. At 75 ° C 590 g of a hydrochloric acid solution containing 120 g of SnC and 1, 09 g of SbC are added with stirring within 2 hours. The pH is kept constant by simultaneous addition of sodium hydroxide to pH = 2. After the addition is stirred at 75 ° C for half an hour. The pH is then adjusted to 4 with NaOH and the suspension is cooled to room temperature. The pigment is filtered off, washed salt-free with water, dried and calcined at 750 ° C. for 30 minutes. 170 g of pigment are obtained as an off-white powder. The content of antimony in the tin dioxide layer is 1 mol% based on the sum of Sn + Sb.

Example 2: High-resistance semiconducting pigment

In a 5 l stirred tank, 100 g of mica having a maximum particle size of <15 pm are suspended in 2 l of water. At 75 ° C 590 g of a hydrochloric acid solution containing 121 g of SnC and 0.273 g of SbC are added with stirring within 2 hours. The pH is kept constant by simultaneous addition of sodium hydroxide to pH = 1, 6 After completion of the addition, at pH = 2 nor 0.6 g of a 40 wt.% Salt Acid titanium oxychloride solution was added and stirred at 75 ° C for half an hour , The pH is then adjusted to 4 with NaOH and the suspension is cooled to room temperature. The pigment is filtered off, washed salt-free with water, dried and 30 Annealed at 750 ° C for a few minutes. This gives 171 g of pigment as a white glossy powder. The content of antimony in the tin dioxide layer is 0.25 mol% based on the sum of Sn + Sb.

Example 3 Production of a Partially Conductive Coating with a Voltage-Dependent Resistor for Electric Field Control

The pigment according to Example 2 is in an aqueous PU lacquer

(Binder: Bayhydrol UH 2952/1 from Bayer, Hardener Cymel 327 Resin from Cytec Industries, filler BaS0 ₄ , Blache Fixe micro, Sachtleben, 9% by weight based on the binder). The

Pigment mass concentration (proportion of pigment in the total solids content of the coating in% by weight) is 45%. Polypropylene sheets are coated with this paint, the paint is dried and baked at 140 ° C. This gives a whitish gloss lacquer layer, wherein the layer thickness of 40 μιτι amounts.

At this lacquer layer is with a spring tongue electrode and a high-voltage ohmmeter Gossen Metrawatt the

Surface resistance at measured voltages of 500 V to 5000 V measured. The electrode spacing is 1 cm, the resulting field strengths are in accordance with the applied measuring voltage between 500 V / cm and 5000 V / cm.

At 500 V, the resistivity is 1, 07 × 10 ¹² ohms, at the field strength 5000 V / cm the resistivity is 4 × 10 ¹⁰ ohms.

The experiment shows that the lacquer layer obtained a

having field strength-dependent resistance. Mixed dielectrics of this type with high, but field strength-dependent resistance, z. B. for

Suppression of glow discharges at end caps of

High voltage leading cables or cable glands can be used. Example 4: Mixing series with two pigments of different conductivity for setting resistances of a coating

Preparation of the nitrocellulose / acrylate varnish:

0.5 kg of collodion wool are dissolved in a mixture of 2.1 kg of n-butyl acetate and 1.5 kg of ethyl acetate. Subsequently, a solution of 0.65 kg of Acronal 700 L in 0.65 kg of ethyl acetate and 0.6 kg of toluene is stirred.

Subsequently, the viscosity of the paint is measured and optionally adjusted by addition of a mixture of 1.4 parts of n-butyl acetate and 1 part of ethyl acetate to a value between 1, 9 and 2.1 Pa · s.

In the o.a. Nitrocellulose / acrylate varnish, the pigments of Example 1 and 2 are stirred in different proportions of 0, 20, 40, 60, 80 and 100% proportion of the pigment of Example 2. Pigment (1) from Example 1 and pigment (2) from Example 2 always give 100%. In the sum of the two pigments, a pigment mass concentration of 57% is always set. The paints are used to coat PET films. The

dried layers have a thickness of 50 μιη. On the dried lacquer layers, the surface resistivity is determined after 2 days. The results are shown in the diagram below. The pigment volume concentration is about 17%.

Mixing curve of partially conductive pigments in the paint film

12.0

11, 0

<3>

_O

^• σ

c 10.0

(0

w

9.0

Ό

5

c

Φ 8.0

O

<Β

Έ 7.0

Φ

O 6.0

N

<D

Q.

(0 5.0

20% 40% 60% 80%

Percentage of pigment 2 in mixture of pigment 1 + 2

The tests show that in the resistance range of 3 × 10 ⁷ to 10 ¹¹ ohms covered by the two pigments, any resistance can be set without changing the PMK. This allows a much more accurate adjustment than the change in PMK.

Example 5:

In a thermally crosslinkable epoxy paint consisting of

- EPON ™ 3002 from Hexion, a novolac epoxy resin, 50% in

methyl ethyl ketone,

Benzyl alcohol (5% by weight, based on the resin),

- Dicyanamide (8 wt.% Based on the resin) and

- Urone 300, a urea derivative (3% by weight based on the resin) from Evonik be pigment according to Example 1 (50 wt.% Based on the resin) and a red iron oxide pigment (Tarox AM 200 from Titan Kogyo), 6 wt.% Based on the resin, stirred. The paint is used to coat glass plates. The lacquer layer is dried and in 2 stages, first at 80 ° C, then baked at 150 ° C, 30 minutes. This gives a shiny reddish-brown varnish layer.

At this lacquer layer as described in Example 3 described the

Surface resistance at measured voltages of 500 V to 5000 V measured.

At 500V the resistivity is 9.5 x 10 ⁸ ohms, at the 5000 volts / cm field strength the resistivity is 6 x 10 ⁷ ohms. The experiment shows that the lacquer layer obtained both a

field strength-dependent resistance as well as an attractive color for the observer.

Claims

claims

Pigment based on a platelet-shaped substrate, characterized in that it has on the surface of a layer consisting of a doped tin dioxide layer, wherein the molar ratio of tin: dopant = 99.99 .0.01 to 97: 3.

Pigment according to claim 1, characterized in that the

Molar ratio of tin: dopant = 99.8: 0.2 to 99: 1.

Pigment according to claim 1 or 2, characterized in that the doped tin dioxide layer is a semiconductive layer.

Pigment according to one or more of Claims 1 to 3, characterized in that the dopant is a cation or an anion or a mixture of two or more cations or a mixture of at least one cation and at least one anion or a mixture of at least two anions.

Pigment according to one or more of Claims 1 to 4, characterized in that the dopant is cations from the group consisting of antimony, cobalt, tungsten, molybdenum, titanium, iron, chromium, copper, aluminum, phosphorus and arsenic.

Pigment according to one or more of Claims 1 to 5, characterized in that the pigment consists of 50-80% by weight of substrate and 20-50% by weight of doped tin dioxide layer, the sum of substrate and doped tin dioxide layer being 100% by weight.

Pigment according to one or more of claims 1 to 6, characterized in that the substrate is selected from the group of TiO ₂ platelets, synthetic mica platelets, natural mica flakes, glass flakes, SiO ₂ platelets, sericite, kaolin, talc, Al ₂ O ₃ Platelets, or mixtures thereof.

8. Pigment according to one or more of claims 1 to 7, characterized in that the shape factor of the platelet-shaped substrates, the ratio of the longest axis of the particles to the thickness,> 4. 9. Pigment according to one or more of claims 1 to 8, characterized in that the substrate is a mica platelet.

10. Pigment according to one or more of claims 1 to 9, characterized in that the substrate is a mica platelet with a particle size <15 pm.

11. Pigment according to one or more of claims 1 to 10, characterized in that the tin dioxide is doped with Antimonkationen.

12. Pigment according to one or more of claims 1 to 11, characterized in that on the doped Zinndioxidschicht one or more oxide layers selected from the group TiO ₂ , ZnO, Al ₂ O ₃ ,

Cr ₂ O ₃ or SiO ₂ are located.

13. Pigment according to one or more of claims 1 to 12, characterized in that it is in the oxide layer is a TiO ₂ - layer.

14. Pigment according to one or more of claims 1 to 13, characterized in that the following layer structure is located on the substrate:

Substrate + SnO ₂ (doped)

Substrate + SnO ₂ (doped) + TiO ₂

Substrate + SnO ₂ (doped) + SiO ₂

Substrate + SnO ₂ (doped) + ZnO

Substrate + SnO ₂ (doped) + Al ₂ O ₃

Substrate + SnO ₂ (doped) + Cr ₂ O ₃

15. Pigment according to one or more of claims 1 to 14, characterized in that the pigment is constructed as follows: Mica platelets + Sn0 ₂ (doped)

Mica platelets + Sn0 ₂ (doped) + Ti0 ₂

Mica platelets + Sn0 ₂ (doped) + Si0 ₂

Mica platelets + SnO ₂ (doped) + ZnO

Mica platelets + SnO ₂ (doped) + Cr ₂ O ₃

Mica platelets + Sn0 ₂ (doped) + Al ₂ 0 ₃

Al ₂ O ₃ platelets + SnO ₂ (doped)

Al ₂ O ₃ platelets + SnO ₂ (doped) + TiO ₂

Al ₂ 0 ₃ platelets + Sn0 ₂ (doped) + Si0 ₂

Al ₂ O ₃ platelets + SnO ₂ (doped) + ZnO

Al ₂ O ₃ platelets + SnO ₂ (doped) + Cr ₂ O ₃

Al ₂ O ₃ platelets + SnO ₂ (doped) + Al ₂ O ₃ .

Process for the preparation of the pigment according to one or more of Claims 1 to 15, characterized in that the coating of the platelet-shaped substrate takes place with a doped tin dioxide layer, wet-chemically, by means of sol-gel processes, CVD and / or PVD processes.

A method according to claim 15, characterized in that the substrate plate is suspended in water and admixed with one or more hydrolyzable metal salts at a suitable pH for the hydrolysis, which is chosen so that the metal oxides,

Metal hydroxide or metal oxide hydrates are precipitated directly on the substrate platelets, without causing any precipitation, wherein the pH kept constant by simultaneous addition of a base or acid, and the pigment separated after the application of the doped Zinndioxidschicht, dried and optionally in air or calcined under inert gas or reducing conditions.

A method according to claim 16 or 17, characterized in that after the coating of the platelet-shaped substrates with a doped Zinndioxidschicht a layer of metal oxide or

Metal oxide hydrate is applied. Use of the pigment according to one or more of Claims 1 to 15 in paints, lacquers, printing inks, plastics, sensors, security applications, floor coverings, films, formulations, ceramic materials, glasses, paper, for laser marking, in thermal protection, in dry preparations, in pigment preparations, as a photo semiconductor and as a varistor pigment in functional materials.

Use of the pigment according to claim 19 as varistor pigment in functional materials for high voltage engineering.