DE19811693A1 - Light-colored, electroconductive pigment for use in lacquer, printing ink, plastics and glaze for ceramics and glass - Google Patents

Abstract

A light-colored, electroconductive pigment has a substrate with a conductive coating of tin oxide doped with phosphorus (P) and/or fluorine (F). Independent claims are also included for: (a) lacquers, printing inks, plastics and glazes for ceramics and glass pigmented with this pigment; and (b) three methods of producing the pigment.

Description

The invention relates to electrically conductive pigments that are considered conductive Layer on a substrate a tin oxide doped with fluorine and phosphorus have layer.

There is a need for conductive in many areas of technology Pigments with which, for example, electrically conductive, antistatic or plastics, paints, shielding electromagnetic waves, Coatings, fibers or the like can be produced. In Large quantities of conductive carbon black are used for this, however, because of its high light absorption not for light or colored coatings can be used. Another disadvantage is the strong absorption of Soot in the IR range, e.g. B. in the sun to a many times un desired heating of the coated objects leads.

For bright, conductive coatings, therefore, are increasingly doped Metal oxides, especially antimony-doped tin oxide, are used.

US Pat. No. 5,472,640 describes conductive platelet-shaped pigments in which a platelet-shaped substrate coated with one or more metal oxide layers is coated with a conductive layer of tin oxide doped with antimony, a thin SiO ₂ layer being present between the conductive layer and the metal oxide layer is ordered.

A bright, electrically conductive pigment is known from US Pat. No. 5,350,448. that of a platelet-shaped substrate and halogen-doped tin and / or Titanium dioxide exists as a conductive layer. For the specific Resistance of the pigment is given less than 25 kΩcm.  

DE 44 35 301 describes electrically conductive pigments as conductive Layer on a substrate a tin oxide layer doped with phosphorus exhibit. For the specific resistance of the pigments are less stated as 10 kΩcm.

The bright, conductive pigments from the prior art have values for the electrical conductivity, which meet the high requirements for be conductive coatings were not sufficient.

The object of the present invention is to use bright, conductive pigments to provide better conductivity.

This object is achieved according to the invention by bright, conductive Pigments, a substrate being coated with a conductive layer, which are characterized in that the conductive layer with a Phosphorus and fluorine doped tin oxide layer.

Furthermore, this object is achieved according to the invention by a Ver drive to the production of the pigments according to the invention by the Substrate suspended in water and a solution of a hydrolyzable Tin salt, the aqueous solution of a phosphorus compound and the aq solution of a fluoride, the pH of the Substrate suspension by simultaneous addition of acid or base in a range of 1 to 5 is kept constant, and the coated Substrate separated, washed, dried and at temperatures of 400 to 1100 ° C is calcined in the absence of oxygen.

The invention also relates to the use of the Invention appropriate pigments for pigmenting paints, printing inks, art fabrics, glazes for ceramics and glasses and cosmetics.  

Both platelet-shaped and spherical particles or mixtures thereof can be used as substrates. All known platelet-shaped carrier materials, such as. B. metals, metal oxides, mica pigments, synthetic platelets can be coated by the process according to the invention, which may already be coated with metal oxides. Examples include natural or synthetic mica, other layered silicates such as talc, kaolin or sericite or other comparable materials such as platelet-shaped iron oxide, aluminum platelets, bismuth oxychloride, SiO ₂ -, glass or synthetic ceramic flakes.

Mica and platelet-shaped pigments and SiO ₂ flakes, which are produced in accordance with international application WO 93/08237, are particularly preferred as substrates.

They consist of a transparent, inorganic platelet-shaped Matrix, preferably silicon dioxide, which ent a non-soluble colorant can hold. If, for example, a highly transparent conductive pigment to be produced, a platelet-shaped carrier material is inserted sets, whose matrix consists only of silicon dioxide. This conductive Pigments are particularly suitable for the production of electrically conductive capable clear coats or transparent electrode layers.

But if a bright, conductive pigment with high hiding power is used reaches, insoluble colorants, for example, in the transparent matrix wise titanium dioxide particles, incorporated. The advantage of this preferred Backing material is that one already for the production of pigment according to the invention from a carrier material with high Opacity can run out.  

Since no high gravitational forces are required in the process, the process is also outstandingly suitable for coating pearlescent pigments. All usual pearlescent pigments can be used, e.g. B. mica coatings with colored or colorless metal oxides, such as TiO ₂ , Fe ₂ O ₃ , SnO ₂ , Cr ₂ O ₃ , ZnO and other metal oxides, alone or in a mixture in a uniform layer or in successive layers. These pigments are e.g. B. from the 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 known and in Commercially available e.g. B. under the trademark Iriodin® from MERCK KGaA, Darmstadt.

The spherical particles can e.g. B. from SiO ₂ or metal oxides, such as. B. Fe ₂ O ₃ , TiO ₂ , MgTiO ₃ , CaTiO ₃ , BaTiO ₃ , SrTiO ₃ , Al ₂ O ₃ or BaSO ₄ , CaSO ₄ or CaCO ₃ exist.

The particles have an average diameter of less than 200 µm and in particular not more than 50 µm. Flaky substrates have an extension of less than 500 µm in the main dimension and in particular less than 250 µm, and the thickness is less than 10 µm, preferably not more than 5 µm and especially in the range from 0.1-1 µm. The ratio of the expansion in the main dimension aspect ratio is more for the platelet-shaped substrates than 3 and especially more than 5.

The substrates to be coated can also be made from a mixture of platelet-shaped and spherical particles exist, the Ratio flaky: spherical, preferably in the range 80:20 to 20:80 and especially 50:50.  

According to the invention, the substrate is suspended in water, and it is preferably at an elevated temperature and a suitable pH the solution of a water-soluble tin salt, a water-soluble one Phosphorus compound and a fluoride added, where appropriate by simultaneously adding an acid or base, the pH in the ge own area is held.

Expediently, one becomes the technically easily accessible bases, such as B. NaOH, KOH or ammonia, mineral acids diluted as acids use. Since the bases and acids only serve to change the pH value, their nature is not critical, so that other acids and bases are used can be.

Suitable tin salts are the 2 and 4-valent halides, sulfates or nitrates, preferably the halides and in particular the chlorides. A tin salt solution consisting of SnCl ₄ and SnCl ₂ is particularly preferred, the ratio Sn ^IV to Sn ^{II being} in the range 90:10 to 10:90, in particular 80:20 to 60:40, and solutions which contain only tin ( IV) contain salts. The tin salts can also be added in solid form to the aqueous substrate suspension.

Suitable phosphorus compounds are the phosphorus trihalides, Phosphoryl halides, the oxygen acids of phosphorus as well Sodium phosphates. Preferably the most accessible and affordable valuable phosphoric acid or sodium phosphate used.

Suitable fluorine compounds are alkali fluorides and ammonium fluoride, the latter being preferred.  

The conductive layer of phosphorus and fluorine doped tin oxide is in an amount of 10 to 200 wt .-%, preferably 50 to 75 wt .-%, be moved to the substrate applied to the substrate. Big amount of are also possible per se, but there will be no further increase in Conductivity achieved.

The ratio of fluorine to phosphorus in the conductive layer is 10: 1 to 1: 100, especially 3: 10 to 5: 100. The ratio of the sum both dopants to tin is 0.1: 100 to 10: 100, in particular 1: 100 to 5: 100.

If the phosphorus or fluoride content is too low, none can be obtained achieve high conductivities, while if the phosphor or fluoride content the conductivity decreases drastically.

The desired homogeneous distribution of tin and phosphorus in the lead capable layer can be easily achieved by the tin, Fluoride and phosphorus compounds in water either together in one solution or in three separate solutions continuously and in front determined mixing ratio of the substrate suspension at a suitable pH of about 1 to 5 and a suitable temperature from about 50 to 90 ° C are metered in such a way that one immediately Hydrolysis and deposition takes place on the substrate.

Any acid or base can be used to precipitate the metal salts. The optimal concentrations and pH values can be determined through routine attempts to be determined. Usually it is used once for precipitation maintain the set pH value throughout the precipitation by one unit to achieve pigments.  

After finishing the coating, the pigments from the Sus pension separated, washed, dried and at temperatures of 400-1100 ° C, preferably at 900-1000 ° C with exclusion of oxygen Annealed for 15 min to 5 h. Depending on the choice of the starting material and the The layer thickness of the doped tin oxide layer is that of the invention Pigments yellowish, silver-colored, light gray or slightly gray-brown.

In addition to phosphorus, fluorine and tin oxide, the conductive layer can also additionally contain other metal oxides. So it can e.g. B. be advantageous this outer layer to increase the thermal and / or mechanical stability, to create special color effects others Metal oxides such as As aluminum oxide, iron oxide, zirconium oxide or Add chromium oxide. Because of these additives the specific contradiction the pigments are generally increased, their mass fraction on the outer layer preferably not too high and less than 25 wt .-% selected. Pigments in which the like additives less than 10 wt .-% and in particular less than Make up 5% by weight.

The tin oxide layer doped with phosphorus and fluorine Pigments according to the invention impart a high conductivity. Of the specific resistance is in any case less than 1 kΩcm. In general values of less than 300 Ωcm are obtained.

To measure the specific resistance of the pigments, a small amount of about 0.5 g of pigment is pressed between two metal punches in an acrylic glass tube with a diameter of 2 cm using a weight of 10 kg. The electrical resistance R is measured from the pigments pressed in this way. The specific resistance ρ results from the relationship from the layer thickness L of the compressed pigment

The pigments according to the invention are not only distinguished by the high electrical conductivity by a with regard to each Application of opacity and color that can be optimized out. The pigments according to the invention can, depending on their specific Design for a whole range of different applications, such as about for transparent electrodes for control, z. B. of liquid crystal displays, for antistatic painting or for antistatic Plastics, flooring, etc. can be used. Furthermore, they are in Paints, varnishes, printing inks and plastics are used.

The invention therefore also relates to formulations which pigments according to the invention contain. The invention Pigments meet those that occur in the respective applications Requirements are often better than conventional pigments in any case a considerable broadening of what is available to the person skilled in the art Pools of such compounds. Thus, the invention Connections have a significant economic importance.

The enumerated applications of the invention Pigments are only to be understood as examples and are intended to be free from the invention explain without limiting it. However, that look like a special requirement profile for a specific application  may, the expert can the properties of the pigments in a wide Vary range and optimize with regard to the respective application.

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

example

100 g of SiO ₂ flakes (particle size 1-40 μm) are suspended in 2 l of water. At a pH of 2.3 at 75 ° C of the suspension 200 ml of an aqueous solution consisting of 112 g SnCl ₄ .5H ₂ O, 15 g SnCl ₂ .2H ₂ O, 50 ml conc. HCl, 0.2 g of 85% H ₃ PO ₄ and 4.0 g of NH ₄ F are metered in. During the hydrolysis, the pH is kept constant by adding NaOH. After completion of the assignment, the product is suctioned off, washed with water, dried and annealed at 1000 ° C. for 30 minutes under nitrogen. After annealing, a bright pigment is obtained which has a specific powder resistance of 100 ohm.cm.

Comparative Example 1 Fluoride doping

100 g of mica (particle size 10-60 µm) are suspended in 2 l of water, heated to 75 ° C and 400 ml of a hydrochloric acid solution containing 84.6 g of SnCl ₄ .5H ₂ O are continuously added with stirring , 6 g SnCl ₂ .2H ₂ O and 100 ml conc. Contains HCl. At the same time, an NH ₄ F solution (4.0 g of NH ₄ F in 300 ml of H ₂ O) is metered into the mica suspension from another vessel over 4 hours. The pH is kept constant at 1.8 with 15% NaOH during the entire reaction time. Nitrogen is passed over the reaction suspension during the reaction. The mixture is left to stir at 75 ° C. for 30 min and then to sit for 10 hours. The solid is then filtered off, washed with about 20 ml of water until free of chloride and dried at 110 ° C. The product thus obtained is calcined at 500 ° C. A pigment is obtained which has a specific powder resistance of 9000 Ohm.cm.

Comparative Example 2 Doping with phosphorus

50 g of SiO ₂ flakes (particle size 1-40 µm) are suspended in 2 l of water. At a pH of 2.0 at 75 ° C of the suspension 200 ml of an aqueous solution consisting of 70 g SnCl ₄ .5H ₂ O, 12 g SnCl ₂ .2H ₂ O, 10 ml conc. HCl and 0.1 g of 85% H ₃ PO _{4 were} added. During the hydrolysis, the pH is kept constant by adding NaOH. After completion of the occupancy, the product is filtered off, washed with water ge, dried and annealed at 1000 ° C for 30 min under nitrogen. After annealing, a light, light gray-brown pigment is obtained which has a specific powder resistance of 180 Ohm.cm.

Claims (11)

1. Bright, electrically conductive pigment, wherein a substrate is coated with a conductive layer, characterized in that the conductive layer is a tin oxide doped with phosphorus and fluorine. 2. Pigment according to claim 1, characterized in that the Ver Ratio of the sum of both dopants to tin 0.1: 100 to 10: 100 be wearing. 3. Pigment according to claim 1 or 2, characterized in that the The ratio of fluorine to phosphorus is 10: 1 to 1: 100. 4. Pigment according to one of claims 1 to 3, characterized in that the content of tin oxide based on the substrate 10 to Is 200% by weight. 5. Pigment according to one of claims 1 to 4, characterized in that the substrate is platelet-shaped. 6. Pigment according to claim 5, characterized in that the platelet-shaped substrate consists of mica, synthetic mica, SiO ₂ -, glass or ceramic flakes or a pearlescent pigment. 7. Pigment according to one of claims 1 to 4, characterized in that the substrate consists of spherical Al ₂ O ₃ -, BaSO ₄ - or SiO ₂ particles. 8. Pigment according to one of claims 1 to 7, characterized in that the substrate is a mixture of platelet-shaped and spherical particles. 9. A method for producing the pigment according to claim 1, characterized characterized in that the substrate is suspended in water and the Solution of a hydrolyzable tin salt, the aqueous solution of a Phosphorus compound and the aqueous solution of a fluoride metered in be, the pH of the substrate suspension being equal to timely addition of acid or base in a range from 1 to 5 is kept constant and the coated substrate is separated off, washed, dried and at temperatures from 400 to 1100 ° C is calcined in the absence of oxygen. 10. Use of the pigment according to claim 1 for pigmenting Varnishes, printing inks, plastics and glazes for ceramics and Glasses. 11. Formulations containing pigments according to claim 1.