JP5301366B2 - Method for producing conductive titanium oxide and method for producing conductive composition - Google Patents

Description

  The present invention relates to a conductive titanium oxide having high conductivity and excellent safety, and a method for producing the same.

  Titanium dioxide is widely used as a pigment, and when a conductive treatment is applied to titanium dioxide, it becomes a conductive filler having the function of a pigment. If this conductive filler is blended into a paint and applied to an insulating material, the insulating material can be provided with conductivity, design, concealment, etc., for example, a conductive primer for plastic compositions, etc. Has been applied. As such a conductive filler, conventionally, conductive titanium oxide coated with a conductive layer made of tin oxide doped with antimony has been used (Patent Document 1). However, in recent years, toxicity of antimony has become a problem, and conductive titanium oxide in which the surface of titanium dioxide columnar particles is coated with a conductive layer made of tin oxide doped with phosphorus (Patent Document 2), conductive titanium oxide doped with niobium (Patent Document 3), or conductive titanium oxide (Patent Document 4) that covers a conductive layer made of titanium dioxide doped with niobium has been proposed.

JP 61-141616 A International Publication WO2007 / 102490 Pamphlet JP 2007-320821 A JP 2008-4332 A

  In the present invention, a highly safe conductive titanium oxide having further improved conductivity is provided.

  As a result of intensive studies by the present inventors, it was found that conductive titanium oxide doped with niobium in titanium dioxide columnar particles having a specific size has excellent conductivity, and completed the present invention. It was.

  That is, a conductive material in which titanium dioxide columnar particles having a weight average major axis diameter of 7.0 to 15.0 μm and a weight average minor axis diameter of 0.25 to 1.0 μm are doped with niobium. Titanium oxide.

  According to the present invention, a conductive composition having excellent conductivity and high safety can be obtained.

  The present invention is a conductive titanium oxide having a weight average major axis diameter in the range of 7.0 to 15.0 μm and a weight average minor axis diameter in the range of 0.25 to 1.0 μm. The particles are doped with niobium. In the present invention, since the columnar particles of the substrate are large and the conductive titanium oxides are easily brought into contact with each other in the conductive composition, it is easy to secure an electrical conduction path, so that excellent conductivity is obtained. In addition, niobium used as a dopant is highly safe and has low color developability, so it does not significantly impair the whiteness of titanium dioxide and maintains excellent properties as a pigment such as easy toning. Yes.

In the present application, the “columnar particles” have a major axis diameter larger than the minor axis diameter, and include rod-shaped particles, needle-shaped particles, spindle-shaped particles, fibrous particles, and the like. The weight average major axis diameter and the weight average minor axis diameter were calculated by the following formulas by measuring the major axis diameter and minor axis diameter of 100 or more columnar particles by electron microscopy, and assuming that the columnar particles correspond to prismatic particles. Is. The preferable weight average major axis diameter is in the range of 8.0 to 14.0 μm, and more preferably in the range of 9.0 to 13.0 μm. On the other hand, the weight average minor axis diameter is preferably in the range of 0.3 to 0.8 μm. The axial ratio (weight average major axis diameter / weight average minor axis diameter) is not particularly limited as long as it is larger than 1, but it is preferably 3 or more because desired conductivity is easily obtained, and more preferably 5 to 40. More preferably, it is the range of 10-40. As for the particle size distribution, it is preferable that many columnar particles having a large long axis diameter are contained, and it is preferable that there are few columnar particles having a small long axis diameter. Such a particle size distribution can be represented by the content of columnar particles having a specific major axis diameter. Specifically, it is preferable that columnar particles having a major axis diameter of 10 μm or more are contained in an amount of 15% by weight or more of the whole, and the content of columnar particles having a major axis diameter of 5.0 μm or less is 40% by weight or less. It is preferable. A more preferable range of each is 25% by weight or more and 30% by weight or less, and a further preferable range is 35% by weight or more and 20% by weight or less.
Weight average major axis diameter = Σ (Ln · Ln · Dn ² ) / Σ (Ln · Dn ² )
Weight average minor axis diameter = Σ (Dn · Ln · Dn ² ) / Σ ( Ln · Dn ² )
(In the above formula, n represents the number of each measured particle, Ln represents the major axis diameter of the nth particle, and Dn represents the minor axis diameter of the nth particle.)

The doping amount of niobium is preferably 0.1 mol% or more as Nb with respect to Ti contained in the columnar particles because excellent conductivity can be obtained. Even if the doping amount exceeds 15% by weight, no further improvement in conductivity is observed, and on the contrary, the whiteness is significantly reduced. Therefore, the range of 0.1 to 15% by weight is more preferable. If the niobium doping amount is within this range, the whiteness (L value) of the powder color by the Hunter color system will be 65 or more. A more preferable dope amount is in the range of 0.1 to 10% by weight. In the present invention, as will be described later, by adjusting the reduction firing temperature, niobium can possibly be doped at a high concentration in the vicinity of the surface of the columnar particles, and in this case, a comparison of 0.1 to 3 mol% is possible. Even with a small amount of doping, a highly conductive titanium oxide having a powder resistance value of less than 10 ³ Ωcm is obtained. Here, niobium is “doped” means that niobium is in a solid solution state in the crystal lattice of the columnar particles, for example, by replacing part of the Ti sites of the columnar particles.

  Since the columnar particles of the substrate are doped with niobium, it is necessary to contain at least crystalline titanium dioxide, but some of them may be amorphous. However, it is preferable that the crystallinity is high because the doping state of niobium is easily controlled, such as doping with niobium at a high concentration in the vicinity of the surface as described above, and it is more preferable that the crystalline titanium dioxide is contained by 99% by weight or more. preferable.

  The surface of the conductive titanium oxide of the present invention may be coated with an organic compound or an inorganic compound as long as the conductivity is not impaired. Examples of inorganic compounds include oxides and hydrated oxides of aluminum, silicon, zirconium, and titanium, and examples of organic compounds include coupling agents, silicone oils, surfactants, polyols, and alkanolamines. These coating species may be used alone, or two or more may be laminated and coated, or may be coated as a mixture.

  Next, the present invention is a method for producing conductive titanium oxide, characterized by firing titanium dioxide columnar particles carrying a niobium compound on the surface in the presence of a reducing agent. The columnar particles can be obtained by a known method. For example, the columnar particles have a weight average major axis diameter in the range of 7.0 to 15.0 μm and a weight average minor axis diameter in the range of 0.25 to 1.0 μm. If particles are obtained, the method disclosed in Patent Document 2 is used. The method disclosed in Patent Document 2, that is, in the presence of titanium dioxide nuclei having an axial ratio of 2 or more and a weight average major axis diameter of the particles in the range of 3.0 to 7.0 μm, In this method, a titanium compound, an alkali metal compound and an oxyphosphorus compound are baked. Alternatively, commercially available titanium dioxide columnar particles having the weight average major axis diameter and the weight average minor axis diameter may be used. Although there is no restriction | limiting in the niobium compound to carry | support, If it is an oxide and / or a hydrous oxide of niobium, niobium is easy to dope into columnar particle | grains and it is preferable.

  In order to support the niobium compound on the columnar particle surface, first, a liquid medium containing titanium dioxide columnar particles is prepared. As the medium, water, an organic solvent such as alcohol, or a mixture thereof can be used, and industrially, it is preferable to use water or an aqueous medium mainly composed of water. After adding the columnar particles to the medium, wet pulverization may be performed using a vertical sand mill, a horizontal sand mill or the like according to the aggregation state of the columnar particles. Moreover, it is preferable to adjust the pH of the aqueous medium to 9 or more because the columnar particles are stably dispersed in water. If necessary, a dispersant such as a phosphoric acid compound such as sodium hexametaphosphate and sodium pyrophosphate, and a silicate compound such as sodium silicate and potassium silicate may be used. The solid content concentration of the columnar particles in the aqueous medium is in the range of 50 to 800 g / liter, preferably in the range of 100 to 500 g / liter.

  The hydrolyzable niobium compound is hydrolyzed in the prepared medium. Examples of hydrolyzable niobium compounds include salts such as niobium chloride and niobium oxychloride, alkoxides such as pentamethoxyniobium, and peroxoniobium obtained by dissolving metal niobium, niobium oxide, niobium hydroxide, etc. with hydrogen peroxide. The method of hydrolysis is appropriately selected from neutralization hydrolysis, heat hydrolysis and the like. When heating hydrolysis is used, it is preferable that the heating temperature is 70 ° C. or higher because hydrolysis easily proceeds, and if it is 100 ° C. or lower, a special apparatus such as a pressure vessel is not required, which is industrially preferable. When neutralization hydrolysis is used, after adding the hydrolyzable niobium compound to the medium, a neutralizer can be added, or the hydrolyzable niobium compound and the neutralizer can be added simultaneously. As the neutralizing agent, if it is a basic compound, hydroxides or carbonates such as alkali metals and alkaline earth metals, ammonium compounds such as ammonia, amines, etc., if acidic compounds, sulfuric acid, hydrochloric acid And inorganic acids such as acetic acid and formic acid.

  After loading the niobium compound, the columnar particles are solid-liquid separated from the medium, and dried and dry pulverized as necessary. For solid-liquid separation, for example, a filter press, a roll press, or the like can be used. For example, a band heater, a batch heater, or the like can be used for drying. For the dry pulverization, for example, an impact pulverizer such as a hammer mill or a pin mill, a pulverizer or the like, a grinding pulverizer, an airflow pulverizer such as a jet mill, or a spray dryer such as a spray dryer can be used.

  The columnar particles subjected to solid-liquid separation are fired in the presence of a reducing material, so that niobium is doped into the columnar particles. Reducing agents include hydrogen, ammonia, hydrazine and its hydrates, hydrazine compounds (hydrazine hydrochloride, hydrazine sulfate, etc.), low-order inorganic oxygen acids (sulfurous acid, nitrous acid, hyponitrous acid, phosphorous acid, phosphorous acid) Etc.) and hydrates thereof (such as hydrogen sulfite) or salts thereof (alkali metal salts such as sodium), hydrogen compounds (such as sodium borohydride), and the like can be used. Among these, hydrogen is preferable because of its high reducing power, and when hydrogen is used, it is preferably used as a mixed gas with an inert gas such as nitrogen, carbonic acid, and argon for safety. If the firing temperature is 500 ° C. or higher, niobium is easily doped, and even if it exceeds 1000 ° C., it is difficult to obtain further effects. In order to prevent sintering of the obtained conductive titanium oxide, 500 to 1000 ° C. It is more preferable to set the range. In the present invention, if the doping amount of niobium is in the range of 0.1 to 3 mol% and the firing temperature is in the range of 500 to 800 ° C., the niobium probably does not sufficiently diffuse to the center of the columnar particles, and the surface Conductive titanium oxide having excellent conductivity can be obtained even with the small doping amount because the doping is performed in the vicinity at a high concentration. As the baking equipment, known devices such as a rotary kiln and a tunnel kiln can be used. If the obtained conductive titanium oxide is sintered and agglomerated after firing, it may be pulverized using a flake crusher, hammer mill, pin mill, bantam mill, jet mill or the like, if necessary.

  Next, the present invention is a conductive composition, characterized by including the conductive titanium oxide. Examples of the conductive composition include a conductive coating composition and a conductive plastic composition. In the present invention, the conductive titanium oxide is preferably blended in the range of 10 to 200 parts by weight and more preferably in the range of 20 to 250 parts by weight with respect to 100 parts by weight of the solid component.

  In the case of a conductive coating composition, it is preferable that at least a binder and a solvent are blended. Examples of the binder include alkyd resins, acrylic resins, polyester resins, epoxy resins, amino resins, fluorine resins, modified silicone resins, urethane resins, vinyl resins, and the like. Examples of the solvent include nonaqueous solvents such as alcohols, esters, ethers, ketones, aromatics and aliphatic hydrocarbons, water, and mixed solvents thereof. The state of the conductive paint is not particularly limited, such as a dissolution type, an emulsion type, and a colloidal dispersion type. Furthermore, at least one selected from coloring agents, fillers, dispersants, plasticizers, curing aids, dryers, antifoaming agents, thickeners, emulsifiers, flow regulators, ultraviolet absorbers, antifungal agents and the like is incorporated. You may do it.

  In the case of a conductive plastic composition, examples of the plastic resin used include polyolefin resins (polyethylene, polypropylene, etc.), polyvinyl chloride resins, polystyrene resins, methacrylic resins, ABS resins, AS resins, polyvinylidene chloride resins, and polycarbonate resins. And thermoplastic resins such as polyethylene terephthalate resin and polyacetal resin, and thermosetting resins such as epoxy resin, unsaturated polyester resin, melamine resin, polyurethane resin, and silicone resin. Moreover, at least 1 sort (s) chosen from a coloring material, a filler, a stabilizer, a dispersing agent, a lubricant, antioxidant, a ultraviolet absorber, a flame retardant etc. can also be mix | blended as needed.

  Examples of the present invention are shown below, but these do not limit the present invention.

Example 1
Titanium dioxide columnar particles (weight average major axis diameter: 9.7 μm, weight average minor axis diameter: 0.51 μm, content of particles whose major axis diameter is less than 5 μm: 8.9 wt%, major axis diameter is 10 μm or more Particle content: 46.6% by weight) was dispersed in water to obtain an aqueous slurry having a TiO ₂ concentration of 16 g / liter. To this slurry, an ethanol solution of niobium chloride corresponding to 1 mol% as Nb was added to Ti contained in the columnar particles. After adding the niobium chloride solution, the slurry is heated to a temperature of 95 ° C. and hydrolyzed over 2 hours while maintaining the temperature of 95 ° C. to support the hydrous oxide of niobium on the surface of the columnar particles I let you. Thereafter, it was filtered, washed with water, and dried at 80 ° C. for 16 hours to obtain a dried product. The dried product was calcined in a reducing atmosphere at 700 ° C. for 3 hours in a reducing atmosphere using a mixed gas of nitrogen containing 25% hydrogen as a reducing agent, and the conductive titanium dioxide of the present invention. (Sample A) was obtained.

Example 2
In Example 1, conductive titanium dioxide (sample B) of the present invention was obtained in the same manner as in Example 1 except that the amount of niobium chloride added was equivalent to 7.5 mol% as Nb.

Comparative Example 1
In Example 1, instead of the columnar particles, commercially available titanium dioxide spherical particles (CR-EL (manufactured by Ishihara Sangyo), average particle size: 0.25 μm) were used in the same manner as in Example 1 for comparison. Conductive titanium dioxide (Sample C) was obtained.

Evaluation 1: Evaluation of powder resistance value 1 g of conductive titanium oxide (samples A to C) obtained in Examples 1 and 2 and Comparative Example 1 was molded into a cylindrical shape (18 mmφ) at a pressure of 4 MPa, and the direct current resistance was reduced. Measurement was performed using a digital multimeter (Model 3457A type: manufactured by Hewlett Packard), and the powder resistance value was calculated by the following equation. The results are shown in Table 1. The smaller the powder resistance value, the better the conductivity.
Powder resistance value = Measured value × Cylinder cross-sectional area / Cylinder thickness

Evaluation 2: Evaluation of powder color Conductive titanium oxides (samples A to C) obtained in Examples 1 and 2 and Comparative Example 1 were filled in a dedicated glass cell having an outer diameter of 35 mm, and a hunter table of molded products The L value and b value according to the color system were measured using a whiteness meter (NW-1 type: manufactured by Nippon Denshoku Industries Co., Ltd.). The results are shown in Table 1. The higher the L value, the better the whiteness.

  It can be seen that the conductive titanium oxide of the present invention has high conductivity and relatively high whiteness.

  The present invention is useful for conductive compositions, particularly for conductive primers.

Claims (3)

(1) Firing a titanium compound, an alkali metal compound, and an oxylin compound in the presence of a titanium dioxide nucleus crystal having an axial ratio of 2 or more and a weight average major axis diameter of 3.0 to 7.0 μm, A step of obtaining titanium dioxide columnar particles having a weight average major axis diameter of 7.0 to 15.0 μm and a weight average minor axis diameter of 0.25 to 1.0 μm;
(2) The hydrolyzable niobium compound is hydrolyzed in a liquid medium containing the obtained titanium dioxide columnar particles, the niobium compound is supported on the surface of the columnar particles, and then fired in the presence of a reducing agent. A method for producing conductive titanium oxide , comprising a step of doping niobium into the columnar particles . To Ti of the amount of supported niobium compound is included in the columnar particles, in the range of 0.1 to 3 mol% Nb, conductive titanium oxide according to claim 1, wherein the firing temperature is in the range of 500 to 800 ° C. Manufacturing method. A method for producing a conductive composition, comprising: obtaining a conductive titanium oxide by the method according to claim 1; and blending the obtained conductive titanium oxide in a binder and a solvent, or blending in a plastic resin.