EP3010979A1

EP3010979A1 - Transparent, electrically semiconducting interference pigments with high color strength

Info

Publication number: EP3010979A1
Application number: EP14728828.6A
Authority: EP
Inventors: Reinhold Rueger
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2013-06-17
Filing date: 2014-05-28
Publication date: 2016-04-27
Also published as: MX2015017041A; KR20160020549A; JP2016528316A; JP6608813B2; AU2014283735B2; WO2014202179A1; CN105308127B; CN105308127A; RU2658842C2; RU2016101117A; US20160137846A1; AU2014283735A1; US9850384B2

Abstract

The present invention relates to transparent, electrically semiconducting interference pigments with high color strength, and in particular platelet-shaped interference pigments, which have an oxygen-deficient ΤiΟ_2-Χ layer, to a method for producing said pigments and to the use of the pigments produced in this way.

Description

Transparent, electrically semiconductive interference pigments with high

color strength

The present invention relates to transparent, electrically semiconductive interference pigments with high color strength, and in particular to platelet-shaped interference pigments which contain an oxygen-deficient TiO ₂ -x layer, to a process for preparing such pigments and to the use of the pigments thus prepared.

In many applications of printing inks, paints, plastics, etc., it is desirable to be able to adjust the electrical properties of the materials specifically. This is done by using suitable additives such as fillers or pigments with corresponding electrical properties. Thus, for example, it is known to greatly increase the electrical conductivity of layers containing dielectric binders by the addition of conductive fillers or pigments.

In addition to carbon black, which has a high electrical conductivity, but also a dark coloration, transparent, colorless or light-colored electrically conductive pigments have recently been developed which enable bright, electrically conductive coatings, for example for floors. Such pigments are typically based on mica platelets and have layers of tin oxide doped with antimony or other dopants. They are described, for example, in the patents DE 3842 330, DE 42 37 990, EP 0 139 557, EP 0 359 569 and EP 0 743 654, and are described, inter alia, by Merck KGaA under the name Minatec® 31 CM or Minatec® 30 CM offered.

However, mica flakes which are coated with doped tin oxide layers can also be pigments with semiconductive properties if the doping is modified according to DE 10 2010 052 888. The pigments described there are achromatic and bright. They show a non-ohmic nice electrical behavior at high field strengths and can be used advantageously in field-controlling insulating materials.

Since the mica platelet-based pigments described above are bright and transparent, they can be combined in the application medium with various colorants, whereby the color design for the application medium can be variably interpreted. However, the addition of colorants can lead to undesirable interactions between coloring components and electrically conductive components in the application medium. Thus, electrically insulating colorants reduce the electrical conductivity of the electrically conductive additives, but the latter, in particular when used in relatively large amounts, influence the color location and the color intensity of the products by their intrinsic color and light scattering. Simply increasing the respective proportions of the components to produce desired color and conductivity effects is uneconomical and may also impair physical-mechanical properties, such as viscosity, adhesion, strength or elasticity, during processing and use of the compositions containing them Make preparations.

It is therefore desirable to have available pigments which have both attractive coloring and defined electrically conductive properties.

EP 0 632 821 discloses platelet-shaped colored interference pigments which have a charge on mica platelets which contains titanium dioxide, one or more titanium suboxides and one or more oxides of one or more metals and / or nonmetals. The coating is gradually different in composition over its thickness. The resulting pigments are colored and electrically conductive, but in addition to interference colors also have dark body colors and have Such a wide range of electrical conductivity that a targeted influence of the latter seems unlikely.

Interference pigments which contain various titanium suboxides and optionally also titanium oxynitrides are also described, for example, in the documents EP 0 332 071 and EP 0 735 115. These pigments have a blue interference color and a blue to blue-black body color.

In particular, however, the dark, brown, gray or blue-black body colors of the previously described pigments considerably limit their applicability in various application media in which transparent or translucent coatings are desired. The

Setting rich, clear interference colors while maintaining the transparency of the coating and the presence of reliable electrical characteristics is a major challenge that previously could not be overcome with the help of a single pigment.

In addition to coatings containing electrically conductive pigments with high electrical conductivity, which are used in particular for antistatic purposes, additives with attractive color are also required for applications in which an electrically semiconductive behavior is sufficient, for example for the antistatic finishing of coatings or for use in coatings certain safety products which are exposed to an electric field, where the additives contribute to the deflection of the electric field lines and thus to the machine readability of the safety products.

There is therefore still a need for transparent, electrically conductive interference pigments which have attractive colored interference colors and only slight, in particular no, body color (absorption color). dye) and whose electrical properties can be adjusted selectively in the semiconducting range.

Object of the present invention is to provide a transparent interference pigment with colored interference color and defined electrically conductive properties available, which has no or only a very low intrinsic absorption.

Another object of the present invention is to provide a process for producing the above-described pigments. In addition, an additional object of the invention is to demonstrate the use of such pigments.

The object of the present invention is achieved by a transparent, electrically semiconductive, platelet-shaped interference pigment containing a layer of TiO _2-x , where 0.001 - = x <0.05.

Furthermore, the object of the invention is achieved by a process for producing such a pigment, in which a transparent, platelet-shaped interference pigment, which consists of Ti0 ₂ , or which consists of a coated transparent, piättchenförmigen carrier, which on its outer surface a layer of TiO ₂ , is thermally treated in a gas phase with the addition of a reducing gas over a period in the range of 5 to 60 minutes, wherein the TiO _{2 is converted} to TiO _2-x and 0.001 <x <0.05.

The object of the present invention is also achieved by the use of the above-described interference pigment in paints, lacquers, printing inks, plastics, sensors, security applications, floor coverings, textiles, films, ceramic materials, Glasses, paper, for laser marking, in thermal insulation, as photosemiconductors, in pigment-containing formulations, pigment preparations and dry preparations.

The present invention is a transparent, electrically semiconductive, platelet-shaped interference pigment which contains a layer having the composition T1O2, where:

0.001. £ x <0.05. Such a composition is not a titanium suboxide, but rather an oxygen-deficient titanium dioxide. Since the formation of lower titanium oxides, titanium suboxides or Magneli phases such as TiO, Ti ₂ 0 ₃ , Ti ₃ 0 ₅ , Ti ₂ 0, Ti ₃ 0, Ti _e O or Ti _n 0 _2n -i always with an intrinsic absorption of these In accordance with the present invention, it is of particular importance that the layer consisting of TiO ₂ -x does not contain such lower titanium oxides, titanium suboxides or Magneli phases. Particularly preferred is a composition of TiO _2-x layer of TiOi, ₉₆ to TiOi gg, where: 0.01 <x <0.04.

The transparency T of interference pigments can be determined via brightness values L ^* of coatings which contain the interference pigments on black and white lacquer cards. The measurements are carried out in the CIEL * a * b ^* color space by means of a suitable measuring device, for example an ETA device (STEAG-ETA Optic GmbH, Inc.) The measurements are carried out at a body color angle of 45 90 ° above the coated black and white lacquer card. The determinable transparency T behaves inversely proportional to the hiding power and can according to the equation:

T = (L * 5 / go white ^- L * 45/90 / black) / 00

be determined. (Determination of the opacity DV according to Hofmeister (Colorimetric evaluation of pearlescent pigments, Congress "Mondial Coleur 85", Monte Carlo, 1985 pursuant to the equation DV = 100 / (L * _45/9 _{0 /} white - L ^* 45 / 9o / black) ) -

The interference pigments according to the invention have a transparency of> 0.35, preferably> 0.45 and in particular> 0.50, determined according to the aforementioned equation. The interference pigments according to the invention preferably have only a very slight and preferably no body color (absorption color). A measure of the body color is the above measurement of the inconvenience at an angle of 45 90 ° over the white lacquer card.

Since each body color reduces the reflection above white and thus reduces the available L ^* value and the interference pigments according to the invention may only have a very low to no body color, the L * value over white is 45 ° (= 4570 °) of the pigments according to the invention with a pigment application of 5 g / m ² at a value L ^* > 70 and thus very high.

When platelet-shaped pigments or support materials are referred to, when their outer shape corresponds to a flat structure having with its top and bottom two approximately parallel surfaces whose extension in length and width represents the largest dimension of the pigment or the support material. The distance between said surfaces, which represents the thickness of the plate, on the other hand, has a smaller extent.

The expansion of the pigments in length and width is between 2 and 250 μm, preferably between 2 and 100 μm, and in particular between 5 and 60 μm. It also represents the value commonly referred to as the particle size of the interference pigments. This is not critical as such, but a narrow particle size distribution of the interference pigments according to the invention is preferred. Especially preferred is a reduced fines content. The proportion of particles having a particle size below 10 μm is <5% by weight, based on the total weight of the pigments. The d ₉ o value is preferably in the range of 40 to 45 μιη.

The particle size and the particle size distribution can be determined by various commercially available methods. However, according to the invention, the laser diffraction method is preferably used in a standard method by means of a Malvern Mastersizer 2000, APA200 (product of Malvern Instruments Ltd., UK). This method has the advantage that particle size and particle size distribution can be determined simultaneously under standard conditions.

The particle size and the thickness of individual particles can also be determined with the aid of SEM (Scanning Electron Microscope) images. In these particles and geometric particle thickness can be determined by direct measurement. To determine average values, at least 1000 particles are evaluated individually and the results are averaged.

The thickness of the interference pigments is between 0.2 and 4 μιτι, in particular between 0.3 and 2.5 μητι.

The interference pigments according to the invention have a form factor (ratio of length or width to thickness) in the range from 2: 1 to 500: 1, preferably in the range from 20: 1 to 300: 1. As electrically semiconductive in the context of the present invention is a

Pigment is considered to have a specific powder resistance in the range of 0.1 to 00 megaohm ^* cm. The interference pigments according to the invention preferably have a specific powder resistance in the range from 1 to 80 megaohm ^* cm, in particular in the range from 10 to 60 MegaOhm ^* cm, on. The values given here refer to field strengths of up to 10 V / mm, whereby the field strength refers to the applied measuring voltage.

The measurement of the specific powder resistance is carried out in such a way that in an acrylic glass tube with a diameter of 2 cm, an amount of each 0.5 g of pigment by means of a weight of 10 kg with a metal die is pressed against a metal electrode. The electrical resistance R is measured on the pigments so compressed. From the layer thickness L of the compressed pigment, the resistivity p is given by the following relationship: p = R * -rr * (d / 2) ² / L (ohm ^* cm).

In a first, simplest embodiment, the transparent, platelet-shaped interference pigment according to the present invention consists of a platelet-shaped TiO ₂ -x particle with 0.001 <x <0.05 in the above-mentioned dimensions. In this case, TiO _2-x can be present both in the anatase and in the rutile modification. Starting materials for the preparation of such pigments are platelet-shaped TiO ₂ pigments, which are commercially available. Such TiO ₂ platelets can also be prepared according to the method described in WO 93/08237. However, the TiO ₂ pigments prepared analogously to this process should not contain any dissolved or undissolved colorants. They are produced from the corresponding, preferably inorganic, precursor material in a strip process, wherein the precursor is applied to the strip, converted with acid into the oxidic form or into the hydrated oxide, solidified and then removed from the strip. The resulting pigments may be used in dried form or after calcination in air at elevated temperatures. The geometric layer thickness of the platelets is set by means of the application quantity or wet layer thickness of the precursor layer, which is possible very precisely. The transfer of TiO ₂ in TiO _{2 ·} x according to the present invention will be described below.

Platelet-shaped pigments of ΤιΌ _2-χ with 0.001 <x <0.05 have, as well as the corresponding platelet-shaped TiO ₂ pigments, a high refractive index n in the range of n = 2.0 to 2.7. Therefore, they are in application media such as paints, paints and plastics whose base materials usually refractive indices in the range of 1, 3 to 1, 6, with appropriate alignment to form interference effects in a position. Due to the rather high refractive index differences between base materials (usually binders and auxiliaries) and platelet-shaped pigments and, depending on the respective thickness of the platelets, the pigments in the application media pigmented therewith can form clear interference colors. The oxygen deficit in the TiO ₂ -x layer, ie here, in the entire interference pigment, however, leads to a certain electrical conductivity, so that the interference pigment in addition to the interference color still has a specific powder resistance in the range of 0.1 to 100 MegaOhm ^* cm, whereby it shows a semi-conductive behavior in the application medium and also gives the application medium at sufficiently high pigment concentration such a semiconductive behavior. Carrier-free, crystalline Ti0 ₂ platelets, however, are comparatively complicated to produce in certain dimensions and, in particular, difficult to handle in further processes because their mechanical strength is low. Therefore, it is advantageous when used as a starting material for the present invention interference pigments platelet-shaped interference pigments having on a transparent support a layer of Ti0 _2, wherein the layer of TiO ₂ is present at least on the outermost surface of the support. This layer of TiO ₂ is converted according to the present invention into a layer of TiO _2-x with 0.001 <x <0.05, as will be described below. Preferably, therefore, the interference pigment according to the invention is formed such that the layer of Τϊθ _2-χ with the above restrictions for x is on a transparent, platelet-shaped carrier. In particular, the layer of ΤιΌ _2- um completely envelopes the platelet-shaped carrier.

In this case, the layer of Ti0 _2-x according to the present invention, the outermost, optically active inorganic layer on the platelet-shaped support. As optically active layers in interference pigments such layers are considered, due to their optical thickness (product of geometric thickness and Refractive index of the material) can provide an independent contribution to the interference color. This is the case for highly refractive materials (n> 1.8) from a geometric layer thickness of about 10 nm, for low-refractive materials (n <1, 8), however, only from a geometric layer thickness of about 20 nm.

The optically active layers do not include, for example, customary secondary coatings, which can be both inorganic and organic in nature and, if required, enable pigments to be incorporated better into the respective application media.

The transparent, platelet-shaped carriers used according to the invention are natural or synthetic mica platelets, platelets of kaolin, sericite or talc, glass platelets, borosilicate platelets, Al ₂ O ₃ platelets or mixtures of two or more of these.

Preference is given to using natural or synthetic mica.

In addition to a transparency in the sense described above are such

Platelets also colorless or almost colorless. Their extension in length and width, as in the case of the interference pigments according to the invention themselves, is in the range between 2 and 250 μm, preferably between 2 and 100 μm, and in particular between 5 and 60 μm. The thickness of the Carrier plate is in the range of 0.2 to 1, 5 μητι, in particular in the range of 0.3 to 1 μιτι.

In a preferred embodiment of the present invention, the interference pigment according to the invention consists of a platelet-shaped support and a layer of Ti0 _2- x enclosing the support, with x in the abovementioned ranges. The layer of TiO _2-x is present in crystalline form and can be present both in the anatase modification and in the rutile modification.

It is known to the person skilled in the art that a rutile modification of TiO _{2 can be promoted} by doping the layer with SnO ₂ or by undercoating a TiO ₂ layer with a layer of SnO ₂ . This also applies to the oxygen deficient Ti0 ₂ - _x layer according to the present invention. Advantageously, therefore, there is an additional layer of SnO ₂ between the transparent, platelet-shaped carrier and the layer of ΤιΌ _2-χ . In order to influence the rutilization of the layer of Ti0 _2-x , the layer of Sn0 _{2 is located} directly below the layer of Ti0 _2-x .

For the induction of a rutile crystal phase in the Ti0 _2-x layer, it is sufficient if an Sn0 ₂ layer with a very small layer thickness is present below the Ti0 _2-x layer. The geometric layer thickness of this Sn0 ₂ layer is therefore in the range of 0.5 to 15 nm, in particular of up to 10 nm, so that this layer also represents an optically non-active layer according to the above definition. Alternatively or in addition to such a Sn0 ₂ layer between Ti0 _2-x layer and support, the Ti0 _2-x layer may be doped in a preferred embodiment with 0.1 to 3 mol% Sn. TiO.sub.2 layers on support platelets, which are to be coated in such a manner as interference pigments, can be produced homogeneously and in good quality using layer thicknesses of up to about 170 nm by known processes. This interference colors II order are easy to produce. For particularly intense interference colors III. However, the simple increase of the layer thickness of the TiO ₂ layer by the simple application of larger amounts of material and prolonged time of occurrence of the titanium oxide hydrates on the support is not sufficient, since the TiO ₂ layer applied to the support with more than 170 nm of increasing layer thickness more porous and mechanical becomes more unstable.

In a particularly preferred embodiment of the present invention, therefore, the TiO ₂ -x layer consists of two or three sub-layers, the sub-layers of TiO _{2-x being} separated from one another by an intermediate layer of a transparent material having a refractive index n n <1.8 and the intermediate layer in each case has a geometric layer thickness d <15 nm. In this case, a system is formed on the platelet-shaped support, which consists of two partial layers with an intermediate layer or three partial layers with two intermediate layers, each with an outer, final partial layer of TiO _2-x .

Suitable materials for the intermediate layers are transparent, colorless materials with a refractive index n <1.8, which can be applied well to a layer of TiO ₂ -x. SiO ₂ , Al ₂ O ₃ , silicon oxide hydrate, aluminum oxide hydrate, MgF ₂ or mixtures of two or more of these are particularly suitable materials. Particularly preferably, the intermediate layer or the intermediate layers consists of SiO ₂ . Due to the small layer thickness of 0.5 to a maximum of 15 nm and the low refractive index, such layers belong to the optically non-active layers as defined above. They serve for the mechanical stabilization of the optically active TiO ₂ _-x layer and allow the construction of a high-quality TiO ₂ _-x layer in the range of interference dyeing III. Order. The total geometric thickness of TiO ₂ -x layers stabilized in this way can exceed clearly 170 nm and can reach a thickness of up to 350 nm.

As an example of a green III. Arrangement in the total layer thickness (300 nm) is therefore a division into 2 or 3 partial layers of TiO _2-x possible, of which (for a total of two partial layers of TiO _2-x with an intermediate layer), a partial layer has a geometric thickness of 160 nm and the second sub-layer has a geometric thickness of 140 nm, or a division into three sub-layers of TiO _2-x , each having a geometric thickness of 100 nm, with a total of two intermediate layers, which separate the sub-layers from each other.

However, an intermediate layer can also separate two TiO _2-x sublayers of the same geometric thickness from one another. This embodiment of the present invention is also preferred. The division of the TiO _2-x layer into partial layers has, in addition to the achievable higher color strength of the interference colors and the increase of the mechanical strength of the total layer of TiO _2-x , the further advantage that the electrical conductivity of the respective TiO _2-x partial layers differs can be designed. Since each sub-layer must be transferred separately from TiO ₂ in TiO ₂ -x, can be different by the respective

Designing the conditions for the required reduction reaction, the oxygen deficit in the individual sub-layers vary in strength. With reducing the oxygen deficit ^'of or close to the carrier TiO ₂ - partial layer (s) the transparency of the total pigment further increased without the Gesamtleitfähigleit of the interference pigment of the invention is greatly reduced, since the conductivity of the pigments substantially by the conductivity of the outer layer is determined. However, if the carrier-near Ti0 _2-x sublayers are not subjected to any reducing treatment, (1.

Partial layer of T1O2 on the support) x = 0. That is, it is one or two stoichiometric Ti0 ₂ layer (s) and only the outer, final partial layer of Ti02 _-X satisfies the condition 0.001 ^ x <0.05. Interference pigments of this construction show a particularly high transparency with simultaneously high color strength and semiconductive electrical properties. Particularly in the case of total layer thicknesses of the TiO ₂ -X layer of greater than 200 nm, this embodiment is particularly preferred.

Also in the above-described embodiments of the present invention, it is preferred if at least below the first Ti0 _2-x - layer on the support, ie between sub-layer and support, still a Sn0 ₂ layer is applied, which is configured as described above and which favors the rutile modification in the subsequent TiO _2-x sublayer. Preferably, such a Sn0 ₂ layer is below each TiO _2-x -

Partial layer applied. In addition, as an alternative or in addition to the SnO ₂ layer, one, two or each of the TiO ₂ -x sublayers may be doped with 0.1 to 2 mol% tin, which is particularly preferred. The total geometric thickness of the TiO ₂ -x layer on the carrier is according to the invention 50 to 350 nm, in particular 60 to 300 nm.

The geometrical thickness of the outer final TiO ₂ - _x sublayer on the support is 30 to 200 nm, preferably 50 to 150 nm. In all of the aforementioned embodiments according to the present invention, the rutile phase is preferred in the TiC layer. The present invention also provides a process for the preparation of the interference pigments according to the invention with high color intensity and electrically semiconductive behavior.

To produce these pigments, a transparent, platelet-shaped interference pigment which consists of TiO ₂ or which consists of a coated, transparent, platelet-shaped support which has a layer of TiO ₂ on its outer surface, in a gas phase with the addition of a reducing gas via a treating time ranging from 5 to 60 minutes thermally, wherein the TiO ₂ to ΤιΌ ₂ - is reacted _χ and 0.001 <x <0.05. Particularly preferably, x is set in the range 0.01 <x <0.04.

Starting material for the process according to the invention is a platelet-shaped interference pigment, which consists of TiO ₂ , or an interference pigment, which consists of a platelet-shaped support, which is coated at least on its outer surface with a TiO ₂ layer.

As TiO ₂ or TiO ₂ layer here also a material or a layer is referred to, which consists wholly or predominantly of titanium dioxide, because drying of the corresponding hydrated oxide layer without calcination does not always reliably leads to a titanium dioxide layer, but consist of titanium dioxide or a mixed composition of titanium dioxide and titanium dioxide hydrate. The applied and dried titanium dioxide layer can be subjected directly to the process according to the invention, but can also first be calcined at elevated temperature under air and, in a further step, treated according to the invention in a reducing manner. Interference pigments of Ti0 ₂ can be obtained commercially or, for example, also according to the previously described process according to WO

93/08237 are produced.

The production of interference pigments, which are coated on a carrier at least with an outer layer of TiO ₂ , takes place according to the customary processes for the preparation of interference pigments by means of preferably wet-chemical processes. These are, for example, in the publications DE 14 67 468, DE 19 59 998, DE 20 09 566, DE 22 14 545, DE 22 15 191, DE 22 44 298, DE 23 13 331, DE 25 22 572, DE 31 37 808 DE 31 37 809, DE 31 51 355, DE 32 11 602 and DE 32 35 017

described.

For this, the substrate platelets are suspended in water. The application of a TiO ₂ layer is preferably carried out analogously to that in US

3,553,001 described method. In this case, an aqueous titanium salt solution is slowly added to a suspension of the pigment to be coated, the suspension heated to 50 to 100 ° C and the pH in the range of 0.5 to 5.0 by simultaneous addition of a base, for example an aqueous ammonium hydroxide or an aqueous alkali hydroxide solution, kept almost constant. When the desired TiO ₂ layer thickness on the pigment platelets is reached, the addition of the titanium salt solution and the base is stopped. Since the addition of the titanium salt solution takes place so slowly that a virtually complete separation of the hydrolysis product takes place on the pigment platelets, virtually no precipitation occurs. The method is known as titration method.

If a layer of TiO _{2 is} applied, which is subdivided into a plurality of sublayers with intermediate layers of a low refractive index material, the application of the low refractive index layer, which is preferably an SiO ₂ layer (may consist of silicon dioxide, silicon dioxide hydrate or a mixture thereof), for example as follows:

For the application of a Si0 ₂ layer, a sodium or potassium water glass solution is usually used. The precipitation of a silicon dioxide or silicon dioxide hydrate layer takes place at a pH in the range from 6 to 10, preferably from 7 to 9.

Preferably, the carrier particles coated in advance with a layer consisting of TiO ₂ or ΤιΌ _2- χ are suspended in water and the suspension is heated to a temperature in the range from 50 to 100 ° C. The pH is adjusted in the range from 6 to 10 and kept constant by simultaneous addition of a dilute mineral acid, for example HCl, HNO ₃ or H ₂ SO ₄ . To this suspension is added a sodium or potassium waterglass solution. As soon as the desired layer thickness of S1O.sub.2 has been obtained on the coated substrate, the addition of the silicate solution is stopped and the batch is stirred for a further 0.5 hours.

Alternatively, a hydrolytic coating with S1O2 may also be accomplished using organic silicon compounds such as TEOS in an acid or base catalyzed process via a sol-gel reaction. Again, this is a wet-chemical process.

As the outermost optically active layer, a TiO ₂ layer is applied in each case.

The transfer of the Ti0 ₂ layer in Ti0 _2-x takes place according to the invention under slightly reducing conditions in the gas stream. To this is added a reducing gas and the pigments are thermally treated therein for a period of 5 to 60 minutes. If the starting pigment has a multilayer structure by dividing a TiO ₂ layer into two or three TiO ₂ partial layers with a respective interruption of these partial layers by an optically non-active intermediate layer of a low-refractive material, as described above, then the transformation of the TiO ₂ Sub-layers in Ti02- _X sublayers optionally in the way that each of the sub-layers is transferred separately into a Ti0 _2-x - layer, the composition of the condition 0.001 <x <0.05 is sufficient (occupancy with all other layers occurs then in each case after the reducing step), or the close to the carrier Ti0 layer ₂ -Teil- or the two near-carrier Ti0 ₂ -Teilschichten (1 and / or 2 i0 ₂ - partial layer on the support) may be subjected to reducing treatment, so that in these layers x is 0, while the outermost TiO ₂ sublayer of the starting pigment is subjected to the reducing treatment as described d and in this layer the condition 0.001 <x <0.05 applies. In terms of a high process economy, the latter variant of the method according to the invention is preferred if the resulting TiO ₂ -x layer as a whole should have a high geometric layer thickness (> 170 nm).

It is advantageous if the pigments are kept in motion during the reduction. The thermal treatment can take place, for example, in a gas-tight rotary kiln while passing the gas stream or in a fluidized bed reactor while passing the gas mixture through the fluidized bed.

According to the invention, it is of particular importance that in the reduction of TiO ₂ no lower titanium oxides, titanium suboxides or Magneli phases are formed. The reduction therefore takes place under very low reducing conditions. For example, the content of reducing gas in the gas mixture is reduced compared to generally customary reducing conditions. The proportion of reducing gas in the gas mixture is in the range of 0.05 to 10 vol.%, Based on the total volume of the gas mixture. The proportion of reducing gas is staggered depending on the reaction temperature.

The reaction temperature used in the invention is in the range of 400 ° C to 800 ° C and thus is also relatively moderate. The higher the reaction temperature is selected, the lower the proportion of reducing gas in the gas mixture must be according to the invention so that titanium suboxides are not formed. At a lower reaction temperature in the aforementioned range, on the other hand, the content of the reducing gas in the gas mixture can be set higher.

Thus, the proportion of reducing gas in the gas mixture at a reaction temperature of 400 ° C 5 to 10 vol.% While it at a

Reaction temperature of 800 ° C may only be in the range of 0.05 to <5 vol.%.

In particular, the following adjustments of reaction temperature and proportion of reducing gas in the gas mixture are preferred in detail

performed:

T <550 ° C, preferably <500 ° C: reducing gas content: 5-10% by volume, in particular 5-8% by volume,

T <650 ° C, preferably <600 ° C: reducing gas content: 2-5 vol.%,

T <750 ° C, preferably <700 ° C: reducing gas content: 1-2 vol.%,

T <800 ° C, reducing gas content: 0.05-1 vol.%.

In compliance with the above conditions for the reduction, it does not lead to the formation of titanium suboxides in the Ti0 ₂ layer, but only to form an oxygen deficit, so that the resulting layer has the composition Ti0 _2-x with 0.001 <x <0.05.

In the X-ray diffractogram of the corresponding pigment samples, only the respective crystal modification anatase and / or rutile can be found. As reducing gas, hydrogen, ammonia or hydrocarbon compounds having 1 to 4 carbon atoms (CiC ₄ ) can be used. These are known in the art as Reduziergase, but are usually used otherwise with a higher proportion in the gas stream. In particular, methane, ethylene or propanone are considered as C 1 -C ₄ -hydrocarbons. Suitable carrier gases are in particular nitrogen or argon, which represent the other constituents of the gas mixture. Forming gas (N ₂ / H ₂ ) with the small amount of hydrogen mentioned above is particularly preferably used.

The interference pigments according to the invention can also be obtained by annealing the starting pigments in vacuo. However, in this case, the reducing conditions and thus the final composition of the TiO ₂ -x layer are more difficult to control. For this reason, a reducing treatment in a vacuum is not preferred. After the thermal treatment, the obtained interference pigments are cooled or classified under the existing reducing conditions or under protective gas.

The present invention also relates to the use of the interference pigments of the invention in paints, coatings, printing inks, plastics, sensors, security applications, floor coverings, textiles, films, ceramic materials, glasses, paper, for laser marking, in thermal protection, as a photo semiconductor, in pigmented

Formulations, pigment preparations and dry preparations.

Due to their high Interferenzfarbstark and transparency, the pigments of the invention are well suited to be used only because of their color properties for pigmentation of application media of the aforementioned type. They will be in the same Way as usual interference pigments used. However, it is particularly advantageous that in addition to the attractive color properties they also have semiconductive electrical properties which make them particularly suitable for use in technical applications which require electrically semiconductive coatings, but which are also particularly suitable for use in various security products which occasionally require electrically conductive or semiconductive pigments in coatings to test for safety features. Such security products include, for example, banknotes, checks, credit cards, shares, passports, identity documents, driving licenses, tickets, tokens,

Tax stamps, etc., just to name a few.

When 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 large number of binders, in particular water-soluble but also solvent-containing types, e.g. based on acrylates, methacrylates, polyesters, polyurethanes, nitrocellulose, ethylcellulose, polyamide, polyvinyl butyrate, phenolic resins, melamine 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.

The pigments according to the invention can likewise be advantageously used for the production of electrically semiconductive plastics and films, and indeed for all applications known to those skilled in the art which require electrical semiconductivity. Suitable plastics are all common plastics, for example thermosets and thermoplastics. The pigments of the invention are subject to the same conditions as conventional pearlescent or interference pigments. Special features of the incorporation into plastics are therefore, for example, in R. Glausch, M. Kieser, R. Maisch, G. Pfaff, J. Weitzel, pearlescent pigments, Curt Vincentz Verlag, 1996, 83, et seq.

The pigments according to the invention are also suitable for the preparation of flowable pigment preparations and dry preparations which contain one or more pigments according to the invention, optionally further pigments or colorants, binders and optionally one or more additives. Dry preparations are also 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 pearlets, pellets, granules, chips, sausages or briquettes and have particle sizes of about 0.2 to 80 mm.

Due to their semiconductive properties, the interference pigments according to the invention can be used with particular advantage, for example in antistatic decorative surfaces. In addition to the electrical properties which can be readily controlled by the production process, the interference pigments according to the invention are transparent, without inherent absorption and high interference color strength, so that they are optimally usable for coloring otherwise transparent, dielectric layers in the previously described fields of application and not mixed with absorbing colorants or other effect pigments must be in order to give the application medium in addition to the semiconducting properties and an attractive color while maintaining the transparency of the application medium. The combination of optically attractive interference colors and semiconductive properties in a single pigment makes the interference pigments of the invention particularly suitable for use in security products. They have attractive gold, red, green, and blue interference colors that were previously considered semi-conductive Pigments were not available. Since the pigments according to the invention are non-absorbing effect pigments, they are easily and very advantageously combinable in security applications with interference pigments which have the same layer structure and the same coloring of the interference colors but instead of the TiO ₂ -x layer or the TiO ₂ _2-x- layers exclusively TiO ₂ layers have.

Thus, combined security features can be created, for example, consisting of two adjacent fields, one of which contains in one coating an interference pigment according to the present invention, while the adjacent field contains a conventional interference pigment of the same size, composition, layer structure and interference color in a coating with the only difference that none of the TiO ₂ layer (s) of the comparative pigment of the condition ΤΊΟ ₂ -Χ satisfies with 0.001 x <0.05, but consists of stoichiometric TiO ₂ . While the coloring and even the electron micrographs of the pigments in the first and second field are completely identical, both fields differ by their electrical properties, which in the field coated with the interference pigments according to the invention with detectors by, for example, measuring the electrical resistance of the layer or Identify microwave absorption as a hidden security feature.

The use of the interference pigments according to the invention is particularly preferably carried out in security products which are exposed to the influence of an electromagnetic field for their testing. In such an application, the interference pigments of the invention exhibit, for example, an attenuation or reflection of high-frequency electromagnetic fields and a targeted change in the electrical flux density in an otherwise dielectric coating in the electric field. This is also below the pigment concentrations Percolation threshold of the case. This is particularly advantageous when testing invisible security features for security products since the interference pigments according to the invention can be used, for example, for deflecting field lines in electric fields, whereby a local amplification of the electromagnetic field can be achieved (a so-called "hot spot") Help such hot spots, for example, electroluminescent substances can be brought to light.

The present invention therefore also relates to a security product which contains the interference pigments according to the invention.

The concentration of the interference pigments according to the invention in the respective application medium depends on the properties desired there with respect to coloring and electrical conductivity and can be selected by the person skilled in the art on the basis of customary formulations.

Although the interference pigments according to the invention have attractive optical and electrical semiconducting properties and can thus be used as the sole effect pigments in a wide variety of applications, it is of course possible and, depending on the intended use, also advantageous if required with organic and / or inorganic colorants and / or electrically conductive materials and / or other non-electrically conductive effect pigments. In addition, they can also be mixed with each other in different colors or with different semiconducting properties, if it results in benefits for the application. The mixing ratios are not limited, as long as the advantageous properties of the pigments according to the invention are not adversely affected by the added foreign pigments. The pigments according to the invention can be mixed in any ratio with customary additives, fillers and / or binder systems. The pigments according to the invention have optically attractive, colored interference colors of high color strength and electrically semiconductive properties, are transparent and almost free up to the area of the near infrared light or completely free of intrinsic absorption. In addition to the usual applications of semiconducting pigments, they are therefore particularly suitable for the generation of visible and invisible multiple security features in security applications.

The present invention will be explained below by way of example but not limited to these.

Examples:

Examples 1-3:

100 g of ground and classified mica (10-50 pm, d ₉₀ 25 pm) are suspended in 1900 ml of demineralized water. 100 ml of a solution of 0.75 g of concentrated HCl and 2.2 g of SnCl ₄ in water are slowly added to the suspension in an acidic medium at 75 ° C. with stirring. By simultaneous addition of sodium hydroxide solution, the pH is kept constant. Then it is still 30 min. stirred at 75 ° C, then at pH 1, 6 by slow addition of an aqueous TiCl ₄ solution (400 g / l TiCl ₄ ) and keeping the pH constant with 32% sodium hydroxide solution with Ti0 ₂ coated. The coating will after reaching the following

Canceled color endpoints:

Example 1: Gold

Example 2: red

Example 3: Blue

The mixture is then cooled to room temperature while stirring and the reaction mixture is neutralized. The resulting pigments are filtered through a suction filter, washed with water and dried at 140 ° C. The dried pigments are subjected to a thermal treatment under the conditions listed in Table 1.

Example 4:

Preparation of a pigment with optically inactive SiO ₂ intermediate layer: 100 g of ground and classified mica (10-50 μm, ₉₀ 25 μm) are suspended in 1900 ml of demineralized water. 100 ml of a solution of 0.75 g of concentrated HCl and 2.2 g of SnCl ₄ in water are slowly added to the suspension in an acidic medium at 75 ° C. with stirring. By simultaneous addition of sodium hydroxide solution, the pH is kept constant. Then it is still 30 min. stirred at 75 ° C, then at pH 1.6 by slow addition of an aqueous TiCl ₄ solution (400 g / l TiCl ₄ ) and keeping the pH constant with 32% sodium hydroxide solution

coated with TiO ₂ . At the color endpoint green II. Order, the addition is stopped, 30 min. stirred and the pH adjusted to 7.5 with sodium hydroxide solution.

Subsequently, an approximately 12% sodium silicate solution in water is metered in at pH 7.5 until a total of 2.5 g of SiO _{2 are} added. After that 15 min. stirred again with hydrochloric acid to a pH of 1, 6 and the addition of TiCl ₄ solution continued until the color endpoint green III. Order is reached. The mixture is then cooled to room temperature while stirring and the reaction mixture is neutralized. The resulting pigment is filtered through a suction filter, washed with water and dried at 140 ° C. The SiO ₂ intermediate layer is approximately 2/3 of the geometric TiO ₂ layer thickness. The obtained green interference pigment is subjected to a thermal reaction according to the conditions shown in Table 1.

Table 1:

Thermal treatment under reducing conditions Example Pigment Atmosphere Temperature Duration from Ex.

5 (Comp.) 1 air 750 ° C 30 min.

6 (Comp.) 2 air 750 ° C 30 min.

7 (Comp.) 3 air 750 ° C 30 min.

8 (Comp.) 4 air 750 ° C 30 min.

9 (Eleven) 1 N ₂ / H ₂ (5% H ₂ ) 500 ° C 30 min.

10 (Erf.) 2 N ₂ / H ₂ (5% H ₂ ) 500 ° C 30 min.

11 (Inventive) 3 N ₂ / H ₂ (5% H ₂ ) 500 ° C 30 min.

12 (Inventive) 4 N ₂ / H ₂ (5% H ₂ ) 500 ° C 30 min.

13 (Inventive) 2 N ₂ / H ₂ (5% H ₂ ) 500 ° C 10 min.

14 (Inventive) 2N ₂ / H ₂ (5% H ₂ ) 450 ° C 30 min

15 (Inventive) 2 N ₂ / H ₂ (5% H ₂ ) 550 ° C 30 min

16 (Erf.) 3 N ₂ / H ₂ (5% H ₂ ) 450 ° C 30 min

17 (Inventive) 2 N ₂ /2% C ₂ H ₄ 500 ° C 30 min

18 (Inventive) 2 N ₂ /2% C ₂ H ₄ 550 ° C 60 min

19 (Inventive) 3 N ₂ /2% C ₂ H ₄ 500 ° C 60 min

20 (Erf.) 2 N ₂ / 0.5% acetone 500 ° C 30 min

21 (Erf.) 2 N ₂ / H ₂ (1% H ₂ ) 750 ° C 30 min

22 (Erf.) 3 N ₂ / H ₂ (1% H ₂ ) 750 ° C 30 min

23 (Comp.) 3 N ₂ 750 ° C 30 min

Example 24:

Testing the electrical properties in the paint film:

The pigments obtained after the thermal treatment according to Table 1 are dispersed in NC lacquer (12% collodium / butyl acrylate in a solvent mixture). The coating preparation is used to coat PET films. The concentration of the pigments in the dry lacquer layer is 48.1% by weight, the layer thickness of the lacquer layer is 50 μm. After drying the lacquer layers, the surface resistance is measured using a spring tongue electrode (1 cm electrode distance, length 10 cm) Measuring voltage of 1000 V measured. The results are shown in Table 2. A comparison resist film without conductive pigment shows a resistivity of> 10 ¹² ohms.

Example 25:

Examination of coloristic properties:

Samples of the pigments according to Table 1 are dispersed in NC lacquer according to Example 24 (1, 7 wt.% Pigment in the paint). The paint is then coated with a wet film thickness of 500 μηι on black / white cardboard cards and dried. The dried layer has a thickness of 40 μm and a pigment mass concentration (PMK) of 12.3%. The maps are then measured with a spectrophotometer (ETA Optics Fa. Steag Optics) in reflection at the following angles:

45 90 ° over black and white and 75795 ° over black, where the angle 90 ° represents the perpendicular to the plane of the map.

The L ^* , a ^* , b ^* values are then determined from the raw data of the measurements. The L ^* value over white is a measure of the body color of the pigment. The values are also listed in Table 2.

Table 2:

Resistances and colorimetric values of the pigments

Example Color L ^* a ^* b ^* (s) L ^* 45790 ° (w) Resistance

5 (Comp.) Gold 152.0 / 6.8 / 76.0 85.8> 1 TOhm

6 (compare) red 123.7 / 56 / -7.2 85.6> 1 TOhm

7 (Comp.) Blue 104.4 / -11.9 / -85.9 88.6> 1 TOhm

8 (Comp.) Green 113.1 / -49.8 / 37.6 83.7> 1 TOhm

9 (Comp.) Gold 150.2 / 6.1 / 74.3 82.9 14 MOhm

10 (Erf.) Red 123.5 / 53.9 / -4.7 80.8 18 MOhm

Blue (blue) 102.7 / -9.6 / -86.8 79.5 20 MOhm

12 (Erf.) Green 111.9 / -47, 8 / 85.9 81, 9 45 MOhm

13 (comp.) Red 123,2 / 55, 5 / -5,5 83,7 33 MOhm 14 (Erf.) Red 124.3 / 54.0 / -4.8 80.0 27 MOhm

16 (Erf.) Blue 102.7 / -10.9 / -87.0 78.9 50 MOhm

17 (Erf.) Red 122.8 / 55.1 / -5.0 83.3 22 MOhm

21 (Erf.) Red 123.3 / 53.7 / - .5 81.0 14 MOhm

22 (Erf.) Blue 102.3 / -3.2 / -89.6 80.0 33 MOhm

23 (compare) purple 92.0 / 31.4 / -91, 6 87.1> 1 TOhm

Example 26 (comparison):

Strongly reduced pigment with dark body color:

The pigment of Example 3 (blue) is subjected to forming gas (5% H ₂ ) at 900

° C annealed for 45 minutes. This gives a pigment with a dark purple body color. The film is used to prepare and measure paint films and lacquer cards according to Examples 24 and 25. The resistance of the film is 9.8 MOhm, the L ^* value over white 32. The low L ^* value indicates the strong body color and high hiding power of the pigment. The electrical resistance of the paint film is only insignificantly lower than the resistances of the paint films with the transparent interference pigments according to the invention. For antistatic-dissipative coatings, all resistors are sufficiently low.

Example 27:

Determination of the oxygen deficit of the pigments:

With the aid of the thermal differential analysis, the mass change of pigment samples is determined. The pigment samples are heated on a balance under air at 10 ° C / min from room temperature to 1000 ° C. Up to 300 ° C the pigments lose their residual moisture. From 400 ° C, the reduced pigments increase in mass by reoxidation. From the mass increase from 400 ° C, the oxygen deficit is calculated.

The following pigments are investigated: Example 7 (Comp.) Increase: -0.1%

Example 11 (Invent.) Increase: 0.3%

Example 16 (Invent.) Increase: 0.12%

Example 26 (compare) Increase: 0.66%

The pigments contain about 48 wt.% TiO _2-x . Based on the Ti0 _2-x -

The weight gain in Example 11 is 0.625%, in Example 16 0.25% and in Example 26 1.33%. This results in the following

compositions:

Example 7: Ti0 ₂

Example 11: TiOi, 96

Example 16: TiOi.gs

Example 26: TiOi, 93

Claims

claims

A transparent, electrically semiconductive, platelet-shaped interference pigment containing a layer of TiO _2-x , where 0.001 -S x <0.05.

Interference pigment according to claim 1, characterized in that the layer of Τίθ2- _{χ is} on a transparent, platelet-shaped carrier.

Interference pigment according to claim 1 or 2, characterized in that the platelet-shaped support is natural or synthetic mica platelets, platelets of kaolin, sericite or talc, glass platelets, borosilicate platelets, Al ₂ O ₃ platelets or

Mixtures of two or more of these are.

Interference pigment according to one or more of Claims 1 to 3, characterized in that it comprises a platelet-shaped support and a layer of TiO ₂ enveloping the support. _x exists.

Interference pigment according to one or more of claims 1 to 3, characterized in that the layer of Τϊθ _2-χ consists of two or three sub-layers, wherein the sub-layers are each separated by an intermediate layer of a transparent material having a refractive index n, where n <1, 8 and the intermediate layer each has a geometric layer thickness d <15 nm, and wherein on the platelet-shaped support is a system of two partial layers with an intermediate layer or of three partial layers with two

Intermediate layers, each with an outer, final

Partial layer of Ti0 _{2-x is} formed.

6. interference pigment according to claim 5, characterized in that in all partial layers of TiO _2-x 0.001 <x <0.05.

7. interference pigment according to claim 5, characterized in that only in the outer, final partial layer of Ti0 _2-x 0.001 <x <0.05.

8. interference pigment according to one or more of claims 5 to

7, characterized in that the intermediate layer consists of SiO ₂ , Al ₂ 0 ₃ , silica hydrate, alumina hydrate, MgF _2> or mixtures of two or more of these.

9. interference pigment according to one or more of claims 2 to

8, characterized in that between the transparent, platelet-shaped support and the layer of Ti0 _{2-x is} an additional layer of Sn0 ₂ , wherein the layer of TiO _{2-x is} directly on the layer of SnO ₂ .

10. interference pigment according to one or more of claims 1 to

9, characterized in that the layer of ΤιΌ _2-χ is doped with 0.1 to 3 mol% Sn.

11. A process for producing an interference pigment according to claim 1, characterized in that a transparent, platelet-shaped interference pigment, which consists of TiO ₂ , or which consists of a coated, transparent, platelet-shaped support, which on one outer surface is a layer from TiO ₂ , is thermally treated in a gas phase with the addition of a reducing gas over a period in the range of 5 to 60 minutes, wherein the TiO _{2 is converted} to TiO ₂ -x and 0.001 <x <0.05.

12. The method according to claim 11, characterized thereby, that the

thermal treatment is carried out in a gas mixture having a proportion of the reducing gas of 0.05 to 10 vol .-%.

13. The method according to claim 11 or 12, characterized in that it is the reducing gas to hydrogen, ammonia or a hydrocarbon compound with C-i-C ^ and the gas mixture further contains nitrogen or argon.

14. The method according to claim 13, characterized in that it is the hydrocarbon compound is methane, ethylene or

Propanone is.

15. The method according to one or more of claims 11 to 14,

characterized in that the thermal treatment is carried out at a temperature in the range of 400 ° C to 800 ° C.

16. The method according to claim 15, characterized in that the proportion of reducing gas in the gas mixture at a temperature of 800 ° C 0.05 to <5 vol .-% and at a temperature of 400 ° C 5 to 10 vol.%.

17. Use of transparent, electrically semiconductive, platelet-shaped interference pigments according to one or more of claims 1 to 10 in paints, coatings, printing inks, plastics, sensors, security applications, floor coverings, textiles, films, ceramic materials, glasses, paper, for laser marking , in heat protection, as a photo semiconductor, in pigmented

Formulations, pigment preparations and dry preparations.

18. Use according to claim 17, characterized in that the interference pigments with organic and / or inorganic colorants and / or electrically conductive materials and / or non-electrically conductive effect pigments are used in the mixture.

19. Use according to claim 17 or 18, characterized in that the interference pigments are used in security products that are exposed to the influence of an electromagnetic field.

20. Security product containing interference pigments according to one or more of claims 1 to 10.