MXPA99002480A - Duct pigments - Google Patents

Abstract

The present invention relates to a pale or light, electrically conductive pigment, consisting of a substrate and an electrically conductive layer, formed of tin oxide that is adulterated or added with phosphorus and / or fluorine. An intermediate layer can be placed between the conductive layer and the substrate

Description

CONDUCTIVE PIGMENTS FIELD OF THE INVENTION The invention relates to electrically conductive pigments having a layer of tin oxide added or adulterated with fluorine and phosphorus, as a conductive layer, on a substrate.

BACKGROUND OF THE INVENTION In many sectors of the industry there is a need for conductive pigments which can be used, for example, to produce plastics, lacquers, coatings or fibers, or the like, which are electrically conductive or antis tartic or which can serve as a barrier against electromagnetic waves. Conductive carbon black is used for this purpose in large quantities and yet, due to its high absorption of light, it can not be used for pale or colored coatings. A further disadvantage is the strong absorption of the carbon black in the IR region, which in the case, REF. : 29586, for example, from solar irradiation leads to the heating, which is not undesired, of the coated articles. Therefore, for clear or pale conductive coatings, the use of metal oxides with added compounds has increased, especially tin oxide added with antimony. No. 5,472,640 describes conductive pigments in the form of lamellae: a lamellar substrate coated with one or more layers of metal oxide is coated with a conductive layer of tin oxide added with antimony, and between the conductive layer and the layer of metal oxide is a thin layer of SiO2. US 5 350 448 discloses a light, electrically conductive pigment consisting of a substrate in the form of lamellae and a tin and / or titanium dioxide added with a halogen, as the conductive layer. The specific resistance of the pigment is less than 25 kOcm. DE 44 35 301 discloses electrically conductive pigments having a layer of tin oxide added with phosphorus, as a conductive layer on a substrate. The specific resistance of the pigments is less than 10kOcm. The conductive pigments, clear or pale, of the prior art, have levels of electrical conductivity that fail to meet the stringent requirements of certain conductive coatings.

DESCRIPTION OF THE INVENTION The object of the present invention is to provide pale conductive pigments which have a better conductivity. This objective is achieved in accordance with the invention, through pale or clear conductive pigments, in which a substrate is coated with a conductive layer and which are characterized in that the layer consists of a layer of tin oxide added with phosphorus and / or fluorine. It is possible for an intermediate layer to be placed between the substrate and the conductive layer. This object is further achieved, according to the invention, by a process for preparing the pigments of the invention, suspending the substrate in water and dosing a solution of a hydrolysable tin salt, the aqueous solution of a phosphorus compound and / or the aqueous solution of a fluoride, maintaining the pH of the suspension of the substrate, constant, within a range of 1 to 5 by the simultaneous addition of an acid or a base, and separating the coated substrate, washing it, drying it, and calcining it in the absence of oxygen, at temperatures from 400 to 1100 ° C. This object is further achieved in accordance with the invention, by means of a process for preparing the pigments thereof, suspending the substrate in water and dosing the aqueous solution of a silicate, maintaining the pH constant and within a range of 4 to 10 by the simultaneous addition of acid, and then by dosing a solution of a hydrolysable tin salt, the aqueous solution of a phosphorus compound and / or the aqueous solution of a fluoride, the pH of the substrate suspension is kept constant within a range from 1 to 5 through the simultaneous addition of an acid or a base, and separating the coated substrate, washing it, drying it and calcining it in the absence of oxygen, at temperatures of 400 to 1100 ° C. This objective is further achieved, in accordance with the invention, by a process for preparing the pigments of the invention, by suspending the substrate in water and, followed by the addition of an agent for the formation of complexes, dosing it with a solution of a salt. of barium, keeping the pH constant within a range of 0 to 5 by the simultaneous metered addition of dilute sulfuric acid and sodium sulfate, and then adding a solution of a hydrolysable tin salt, the aqueous solution of a phosphorus compound and the aqueous solution of a fluoride, the pH of the suspension of the substrate is kept constant within a range of 1 to 5 through the simultaneous addition of acid or base, and separating the coated substrate, washing, drying and calcining in the absence of oxygen at temperatures of 400 to 1100 ° C. The invention further provides the use of the pigments of the invention for the pigmentation of paints, printing inks, plastics, lusters or varnishes for ceramics, and glasses and cosmetics. For these purposes they can also be used as mixtures with commonly commercial pigments, of which some examples are absorption pigments, organic and inorganic, pigments to create metallic effects and LCP pigments. As substrates, both spherical particles and lamellar particles or mixtures thereof can be used. All the materials for substrates, in the form of lamellae, known, such as metals, metal oxides, mica pigments and synthetic lamellae, can be coated by the process of the invention and can be easily coated with metal oxides. Examples of these materials are natural or synthetic mica, other substances such as talc, kaolin or sericite, or others, comparable materials such as iron oxide in the form of lamellae, aluminum flakes, bismuth oxychloride, or Si02, the glass or flakes of synthetic ceramics. Particularly preferred substrates are mica and lamellar pigments and also SiO2 flakes prepared in accordance with International Application WO 93/08237. These consist of a transparent, inorganic matrix, in the form of lamellae, preferably silica, which may include an insoluble colorant. To say, if a highly transparent conductive pigment is to be prepared, a substrate material in the form of lamellae whose matrix consists solely of silica is used. These conductive pigments are particularly suitable for producing transparent electrically conductive coatings or layers for clear electrodes. Alternately, if the requirement is for a clear or pale conductive pigment of high hiding power, insoluble colorants, examples of which are titanium dioxide particles, are incorporated into the transparent matrix. The advantage of this preferred substrate material is that a substrate material which is inherently high covering power can be used to prepare the pigment of the invention.

Since there is no need for high forces in the process, this is also remarkably convenient for coating pearlescent luster pigments. All common pearlescent luster pigments, such as micas coated with colorless or colorless metal oxides, such as Ti02, Fe2? 3, Sn02, Cr203, ZnO and other metal oxides, alone or in combination, can be used in one uniform layer or in successive layers. These pigments are known, for example, from German patents and patent applications 14 67 468, 19 59 998, 20 09 566, 2 14 545, 22 15 191, 2 44 298, 23 13 331, 25 22 572, 32 11 602 and 32 35 017 and can be obtained commercially, for example, under the tradename IriodinMK from MERCK KGaA, Darmstadt. The spherical particles may consist, for example, of Si02 or metal oxides, such as Fe20, Ti02, MgTi03, CaTi03, BaTi03, SrTi03, A1203 or BaS04, CaS04 or CaC03. The particles have an average diameter of less than 200 μm and, in particular, no greater than 50 μ. The lamellar substrates have an extension in the main dimension, less than 500 μm and, in particular, less than 250 μm and its thickness is less than 10 μm, preferably not more than 5 μm and, in particular, it is found in the interval of 0.1-1 μm. The ratio of the extension in the main dimension to the thickness (aspect ratio) of the lamellar substrates is greater than 3 and in particular greater than 5. The substrates to be coated may also consist of a mixture of spherical and lamellar-shaped particles, in which case the ratio of lamellar-shaped particles to spherical particles is preferably in the range of 80:20 to 2 --- 0: 80 and, in particular, It's 50:50. In a particular embodiment of the pigment, it is possible to have, between the substrate and the conductive layer, an intermediate layer of barium sulfate, silica or an insoluble silicate, such as aluminum silicate, which acts as a diffusion barrier between the substrate and the conductive layer.

The process used to apply the silica layer is as follows: a water-soluble silicate solution, preferably a solution of liquid sodium silicate, is dosed into a suspension of the substrate to be coated which is heated to a temperature from about 50 to 100 ° C, in particular from 70 to 80 ° C. By the simultaneous addition of strong hydrochloric acid at 10 ° the pH is kept constant at a value of 4 to 10, preferably 6.5 to 8.5. Following the addition of the silicate, the mixture is stirred for an additional 30 minutes. The silica layer applied in this manner would represent at least about 51, by weight, calculated as SiO¿ and based on the substrate, of the pigment. There are no upper limits, although it was found that an increase in conductivity can not be obtained through very thick layers of Si02. Therefore preference is given to silica layers of about 5-20% by weight, in particular about 10%. The barium sulfate layer is applied by the process described in US 5 380 360.

In this process, an agent for the formation of complexes, preferably citric acid, is added to a suspension of the substrate, which is heated to a temperature of about 50 to 95 ° C, in particular 60 to 80 ° C, and then the aqueous solution of the barium salt is dosed separately, and a solution of sodium sulfate containing sulfuric acid. The substrate coated with barium sulfate is then coated with adulterated tin oxide, in the manner described above. According to the invention, the barium sulfate content of the pigment is 0.1 to 50% by weight based on the pigment. This corresponds to a layer thickness of approximately 10 to 100 nm. The substrates are coated in accordance with known processes, suspending them in water and coating them first with silica, a barium silicate or sulfate, and then, at an elevated temperature and at an appropriate pH, by adding the solution of a water-soluble tin salt, a water-soluble phosphorus compound and / or a water-soluble fluoride, maintaining the pH within the appropriate range, by the simultaneous addition of an acid or base, if required. In the case of the pigment mode without an intermediate layer, the substrates are suspended in water and - preferably at elevated temperature and at an appropriate pH - the solution of a water soluble tin salt, of a phosphorus compound is added. - soluble in water and a fluoride, and the pH is maintained within the appropriate range through the simultaneous addition of an acid or base, if required.It is wise to use the bases that are readily available industrially such as for example the NaOH, KOH or ammonia, and as acids use dilute mineral acids, since the bases and acids only serve to alter the pH, their nature is not critical, and therefore other acids and bases can also be used. Suitable are 2 and 4-valent halides, sulfates or nitrates, preferably halides and especially chlorides, Particular preference is given to a tin salt solution consisting of SnCl 4 and SnCl2, in which the ratio of SnIV to Sn11 is in the range from 90:10 to 10:90, in particular from 80:20 to 60:40, and additional preference is given to solutions comprising only salts of Tin (IV). The tin salts can also be added in the solid form to the aqueous suspension of the substrate. Suitable phosphorus compounds are phosphorus trihalides, phosphoryl halides, phosphorus acids containing oxygen, and sodium phosphates. It is preferred to use the readily available and inexpensive phosphoric acid or sodium phosphate. Suitable fluorine compounds are the alkali metal fluorides and the ammonium fluoride, the latter being preferred. The conductive layer of tin oxide added with phosphorus and fluorine is applied to the substrate in an amount of 10 to 200% by weight, preferably 50 to 75% by weight, based on the substrate. Larger quantities are also possible, which do not cause any additional increase in conductivity. The ratio of fluorine to phosphorus, in the conductive layer, is from 10: 1 to 1: 100, in particular from 3:10 to 5: 100. The ratio of the sum of the two addition compounds, with respect to tin, is from 0.1: 100 to 10: 100, in particular from 1: 100 to 5: 100. If the content of phosphorus or fluoride is too low, it is impossible to achieve high conductivities, while with a too high phosphorus or fluorine content the conductivity drops drastically. If only phosphorus is used as an addition compound, its proportion in the conductive layer, relative to tin, is from 0.1 to 20 atomic%, preferably from 1 to 10 atomic% and, in particular, from 2 to 8 atomic%. If only fluorine is used as an addition compound, its proportion in the conductive layer is from 0.1 to 2.5% by weight, preferably from 0.5 to 1% by weight. The homogeneous, desired distribution of tin, fluoride and / or phosphorus in the conductive layer can be easily achieved by dosing the tin, fluoride and / or phosphorus compounds in water - either together in a solution, or in separate solutions - continuously and at a predetermined mixing ratio to the substrate suspension, at an appropriate pH of about 1 to 5 and an appropriate temperature of about 50 to 90 ° C in a form such that hydrolysis and deposition on the substrate is carried out directly in each case. Any acid or base can be used to precipitate the metal salts. The optimal concentrations and pH values can be determined by routine experiments. The pH, once established for precipitation, it is usually maintained through all the precipitation, to obtain uniform pigments. After finishing the coating, the pigments are separated from the suspension, washed, dried and calcined in the absence of oxygen, at temperatures of 400-1100 ° C, preferably 900-1000 ° C, for a time of 15 minutes up to 5 hours Depending on the choice of initial material and the thickness of the adulterated tin oxide layer, the pigments of the invention are yellowish, silver, pale gray or pale grayish brown. In addition to phosphorus and / or fluorine and tin oxide, the conductive layer may also comprise other metal oxides. For example, it may be advantageous to add other metal oxides such as alumina, iron oxide, zirconium oxide or chromium oxide, to the aforementioned outer layer, to increase the thermal and / or mechanical stability and / or to generate effects of specific colors. Since these additions generally increase the specific strength of the pigments, their mass proportion, in the outer layer, is preferably selected so that it is not too high and to be less than 25% by weight. Particular preference is given to pigments in which those additions represent less than 10% by weight and, in particular, less than 5% by weight. The tin oxide layer added with phosphorus and / or fluorine, provides the pigments of the invention with high conductivity. The specific resistance is in each case less than 1 Ocm. In general, levels lower than 300Ocm are obtained. To measure the specific resistance of the pigments, a small amount of the pigment -about 0.5 g- is compacted between two metal punches, in an acrylic glass tube having a diameter of 2 cm, with the aid of a weight of 10 Kg. . In this way the electrical resistance R of the pigments is measured. From the thickness L of the layer, of the compressed pigment, the specific resistance p is given by the ratio p • (d / 2) C = P. chm • cm] The pigments of the invention are remarkable not only for their high electrical conductivity but also for a color that can be optimized and for a covering power which can also be optimized in view of the respective application. Depending on their specific design the pigments of the invention can be used for a wide range of different applications such as for transparent electrodes for exciting liquid crystal displays, for example, for anti-static coatings, or for antistatic plastics, for floor coverings, etc. They are also used in paints, lacquers, printing inks and plastics. Therefore, the invention likewise provides formulations comprising the pigments of the invention. The pigments of the invention frequently meet the requirements arising during the respective applications, and in a better way than traditional pigments do, and in any case they represent a considerable enlargement of the grouping of those compounds that is available for the person experienced in the art. Accordingly, considerable economic significance is attached to the compounds of the invention. The possible uses listed for the pigments of the invention should be understood only as examples and are intended to illustrate the invention rather than limit it. Whatever the specific profile of the requirements for a particular application, however, the person skilled in the art can vary the properties of the pigments within a wide range and can use them in view of the respective application. The following examples are to illustrate the invention without limiting it.

E j emp lq 1 Suspend in 2 liters of water, 100 g of Si02 flakes (particle size of 1-40 μm). At a pH of 2.3, 200 ml of an aqueous solution consisting of 112 g of SnCl4"5H20, 15 g of SnCl2" 2H20, 50 ml of concentrated HCl, are metered into the suspension at a temperature of 75 ° C. 0.2 g of strong H3P04 at 85% and 4.0 g of NH4F. During hydrolysis the pH is kept constant by the addition of NaOH. After finishing the coating, the product is filtered with suction, washed with water, dried and calcined under nitrogen at a temperature of 1000 ° C for 30 minutes. The calcination provides a pale pigment having a specific dust resistance of 100 ohm »cm.

Example 2 Suspend, 100 g of mica having a particle size of 10-60 μm, in 2 liters of water, and the suspension is heated to 75 ° C.

Subsequently a pH of 1.8 is established and 1 g of citric acid monohydrate is added. This is followed by the simultaneous but separate addition of 11.8 g of Na2S04 and 1.3 g of concentrated H2S04 in 180 ml of water and 105 g of BaCl2 «2H20 in 300 ml of water, keeping the pH constant. After finishing the addition, the product is allowed to stand, the supernatant solution is decanted, and the system is completed with fresh water. This provides a mica coated with a BaS04 layer. This suspension is heated up to 75 ° C again and adjusted to a pH of 2.3. Subsequently, 200 ml of an aqueous solution consisting of 112 g of SnCl4.5H20, 15 g of SnCl2 »2H20, 50 ml of concentrated HCl, 0.2 g of 85% H3PO4 and 4.0 g of NH4F are metered into it. During hydrolysis the pH is kept constant by the addition of NaOH. After finishing the coating, the product is filtered off with suction, washed with water, dried and calcined under nitrogen at 1000 ° C for 30 minutes. The calcination provides a pale pigment having a specific powder resistance of 50 Ocm.

E j emp 1 o 100 g of mica (particle size 10-60 μ) are suspended in 2 liters of water, the suspension is heated to 75 ° C, and 400 ml of a solution are continuously added with stirring over a course of 4 hours. of hydrochloric acid containing 84.6 g of SnCl4 »5H20, 6 g of SnCl2 »2H: 0 and 100 ml of concentrated HCl. At the same time, a solution of NH4F (4.0 g of NH4F and 300 ml of H20) is metered into the mica suspension from another vessel over a period of 4 hours. Through the period of the reaction, the pH is kept constant at a value of 1.8, using 15% NaOH. Nitrogen is passed through the suspension during the reaction. The suspension is stirred at 75 ° C for 30 minutes and then allowed to stand for 10 hours. Subsequently the solid is separated by filtration, washed with about 20 ml of water until it is free of chlorides, and dried at 110 ° C. The resulting product is calcined at 500 ° C. This provides a pigment that has a specific powder resistance of 9000 ohm * cm.

E j us 4 50 g of Si02 flakes (particle size of 1-40 μm) are suspended in 2 liters of water. The suspension is dosed at 75 ° C and at a pH of 2.0, 200 ml of an aqueous solution consisting of 70 g of SnCl4 * 5H20, 12 g of SnCl2 * 2H20, 10 ml of concentrated HCl and 0.1 g of H3PO4 at 85%. During hydrolysis the pH is kept constant by the addition of NaOH. After finishing the coating, the product is filtered off with suction, washed with water, dried and calcined under nitrogen at 1000 ° C for 30 minutes. The calcination provides a slightly grayish, pale brown pigment, which has a specific powder resistance of 180 ohm * cm.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, which is clear from the present description of the invention. Having described the aforementioned, the property contained in the following is claimed as property:

Claims (16)

RE IVIND ICAC IONE S

1. A pale or light, electrically conductive pigment in which a substrate is coated with a conductive layer, characterized in that the conductive layer is a layer of tin oxide added or adulterated with phosphorus and / or fluorine.

2. The pigment according to claim 1, characterized in that an intermediate layer is placed between the substrate and the conductive layer.

3. The pigment according to claim 1 or 2, characterized in that the ratio of phosphorus and / or fluorine to tin is from 0.1: 100 to 10: 100.

4. The pigment according to at least one of claims 1 to 3, characterized in that the ratio of fluorine to phosphorus is from 10: 1 to 1: 100.

The pigment according to at least one of claims 1 to 4, characterized in that the content of tin oxide, relative to the substrate, is from 10 to 200% by weight.

6. The pigment according to at least one of claims 1 to 5, characterized in that the substrate is in the form of 1 to ini lias.

7. The pigment in accordance with the rei indication 6, characterized in that the substrate in the form of lamellae consists of mica, synthetic mica, flakes of Si02, glass flakes or ceramic flakes, or a pigment with pearl luster.

8. The pigment according to at least one of the rei indications from 1 to 5, characterized in that the substrate consists of spherical particles --- of A1203, BaS04 or Si02.

9. The pigment according to at least one of claims 1 to 8, characterized in that the substrate is a mixture of spherical particles and lamellar-shaped particles.

10. The pigment according to the rei indication 2, characterized in that the intermediate layer consists of barium sulfate, silica or another insoluble layer.

11. The pigment according to claim 10, characterized in that the intermediate layer is present in an amount from 5 to 20% by weight, based on the substrate.

12. A process for preparing the pigment according to the rei indication 1, characterized in that the substrate is suspended in water and the hydrolyzable tin salt solution, the aqueous solution of a phosphorus compound and / or the aqueous solution of a fluoride, dosed in the substrate suspended in the water, maintaining the pH of this suspension, constant, within a range of 1 to 5, by the simultaneous addition of an acid or a base, and the coated substrate is separated, washed, dried and it is calcined in the absence of oxygen, at temperatures from 400 to 1100 ° C.

13. The process for preparing the pigment according to claims 1 and 2, characterized in that the substrate is suspended in water and an aqueous solution of a silicate is dosed, keeping the pH constant within a range of 4 to 10 by simultaneous addition of acid, and then the solution of hydrolysable tin salt and the aqueous solution of a phosphorus compound and / or the aqueous solution of a fluoride, maintaining the pH, of the suspension of the substrate constant, are dosed thereto, a range of 1 to 5 by the simultaneous addition of an acid or a base, and the coated substrate is separated, washed, dried, and calcined in the absence of oxygen, at temperatures of 400 to 1100 ° C.

14. The process for preparing the pigment in accordance with the rei indications 1 and 2, characterized in that the substrate is suspended in water and, followed by the addition of a complexing agent, a solution of barium salt is dosed, maintaining the constant pH within a range of 0 to 5 by the simultaneous metered addition of dilute sulfuric acid and sodium sulfate, and then the solution of a hydrolysable tin salt and the aqueous solution of a phosphorus compound is dosed thereto. and / or the aqueous solution of a fluoride, maintaining the pH of the substrate suspension, constant, within a range of 1 to 5, by the simultaneous addition of an acid or a base, and the coated substrate is separated, It is washed, dried and calcined in the absence of oxygen, at temperatures of 400 to 1100 ° C.

15. The use of the pigment in accordance with the rei indications from i to 11 to pigment paints, printing inks, plastics and varnishes for ceramics and glass.

16. Paints, printing inks, plastics, cosmetics, and varnishes for ceramics and glasses, characterized in that they are pigmented with a pigment in accordance with the rei indications from 1 to 11.