JPH06299086A - Conductive barium sulfate filler and its production - Google Patents

Abstract

PURPOSE:To obtain a barium sulfate filler which itself has excellent whiteness or transparency, can be colored with a colorant with any desired hue, has conductivity stable against changes in both temperature and humidity, and is highly dispersible in a resin or the like. CONSTITUTION:The filler consists of a particulate core of barium sulfate and a coating film of tin oxide doped with niobium or tantalum. The core has a specific surface area of 0.1-150m<2>/g in an uncoated state, and the film contains 0.1-10wt.% (in terms of Nb or Ta based on tin oxide) niobium or tantalum and has a thickness of 2-80nm. The production process of the filler comprises combining a slurry containing barium sulfate particles with a solution containing a tetravalent tin compound to prepare a combined solution of a pH of 11-14, adding an acid solution of a pentavalent niobium compound or tantalum compound in an amount to give 0.1-10wt.%, based on the weight of the tin oxide, Nb or Ta atoms to the combined solution, adjusting the pH of the resulting solution to 1-5, separating the formed precipitate from the solution, drying the separated precipitate, and firing it in an inert atmosphere or a reducing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive barium sulfate filler and a method for producing the same, more specifically, it has excellent whiteness, is non-toxic, and has a conductivity that is stable against temperature changes. TECHNICAL FIELD The present invention relates to a conductive barium sulfate filler having high dispersibility in plastics, rubbers, resins, paints and fibers, and a method for producing the same.

[0002]

In some applications of plastics,
Their electrical insulation causes technical problems. The electrical insulation of plastics is particularly undesirable when electrical components need to be shielded from relatively large electromagnetic fields, such as with computer housings, or when discharged from charged components.
The electrical insulation of plastics also poses problems in the storage or transportation of high explosives or IC parts, the production of antistatic treated carpets or medical rubber products, or the production of conductive adhesives for metals.

It is known that polymers can be made electrically conductive by the addition of electrically conductive particles. As fine substances that can be mixed with plastics and paints to impart conductivity to them, metal particles, carbon black particles, particles made of semiconductor oxides such as zinc oxide or iodide (eg, copper iodide), antimony Etc. doped tin oxide powder, aluminum doped zinc oxide powder, tin doped indium oxide powder, tin oxide coated titanium oxide or aluminum oxide powder, and tin oxide coated glass fiber, titanic acid Materials such as alkali metal salt fibers and titanium oxide fibers are known.

When metal particles or carbon black particles are used, the polymer containing such additives becomes black and also has a conductivity of 10 which is generally required for antistatic properties.
It is difficult to control ⁴ to 10 ⁸ Ω / □, and these are often undesirable. The use of zinc oxide particles reduces the chemical resistance, increases the temperature / humidity change dependency, and has the undesirable consequence of varying electrical conductivity. With the use of copper iodide, the polymers containing it have a very low chemical stability, so that such polymers have only limited applications. Further, antimony-doped tin oxide powder is excellent in conductivity-providing property, but due to the antimony dope, it exhibits a bluish-black color tone, and thus there is a problem in whiteness, and there is concern about the toxicity of the antimony. Its use is limited.

Japanese Unexamined Patent Publication (Kokai) No. 56-157438 discloses a method for producing a powder mixture which can be added to plastic to make the plastic conductive. In the method of preparation, a solution containing SnCl ₄ and SbCl ₃ is added to a heated aqueous suspension of barium sulfate. Since the precipitation reaction is carried out in the acidic region, the result is a mixed powder of SnO ₂ powder and barium sulfate powder. However, the conductivity of plastics containing such mixed powder is unstable with respect to temperature changes. In addition, since the mixed powder has relatively poor dispersibility in plastic, a problem occurs when the mixed powder is uniformly dispersed in plastic.

The present inventors have previously found that conductive barium sulfate composed of BaSO ₄ particles coated with a SnO ₂ coating doped with Sb ₂ O ₃ (Japanese Patent Application No. 3-91557).
No. 4) and a granular core material made of barium sulfate, and a conductive barium sulfate filler (Japanese Patent Application No. 4-265396) consisting of a tin dioxide coating covering the surface of the core material. Has excellent conductivity imparting property, is stable against temperature change, and has high dispersibility in plastic, but due to its antimony dope, it has a bluish-black color tone, and therefore has a problem in whiteness. There is concern about the toxicity of the antimony, and in the latter case, there is no problem of toxicity, but it is not always stable against changes in humidity, thus limiting its use.

[0007]

As described above, the conductive barium sulfate filler according to the conventional technique and the previously proposed technique is applicable in any of whiteness, transparency, toxicity, cost, conductivity, dispersibility and the like. Limited or whiteness,
Any one of the transparency, conductivity, dispersibility, etc. was not always satisfactory.

In view of the above circumstances, the present inventors have found that the conductive barium sulfate filler without the above-mentioned drawbacks, that is, (1) the conductive barium sulfate filler itself is excellent in whiteness or transparency. When added to base materials such as paper, plastics, rubber, resins, paints, fibers, etc., they are not colored as in the case of using the conventional conductive barium sulfate filler, and are white or transparent. However, by adding a colorant, any desired color tone can be obtained, and (2) it does not contain harmful substances such as antimony, and (3) it is stable against changes in temperature and humidity. Having conductivity, (4) having high dispersibility in plastics, resins, etc., (5) adding conductive barium sulfate filler to base materials such as paper, plastics, rubber, resins, paints, fibers, etc. When The conductive coating coated on the surface of the conductive barium sulfate filler does not peel off to cause a loss of conductivity, and various studies are repeated for the purpose of providing a conductive barium sulfate filler. Was completed.

Another object of the present invention is to provide a manufacturing method capable of manufacturing the above conductive barium sulfate filler by a simple technical means.

[0010]

That is, the conductive barium sulfate filler of the present invention comprises a granular core material made of barium sulfate and a coating made of tin oxide doped with niobium or tantalum covering the surface thereof. The granular core material has a specific surface area of 0.1 to 150 m ² / g in an uncoated state, and the coating film contains 0.1 to 10 wt% as Nb or Ta based on the weight of tin oxide. It is characterized by containing niobium or tantalum and having a thickness of 2 to 80 nm.

In the method for producing the conductive barium sulfate filler according to the present invention, the specific surface area is 0.1 to 150 m ² /
A slurry containing barium sulfate particles of g at a concentration of 10 to 1000 g / l and a solution containing a tetravalent tin compound at a concentration of 1 to 95% by weight were mixed to prepare a mixed solution having a pH of 11 to 14. An acid solution containing a pentavalent niobium compound or a tantalum compound in the mixed solution is added with Nb based on the weight of tin oxide.
Alternatively, it is added in an amount of 0.1 to 10 wt% as Ta to adjust the pH of the liquid after the addition to 1 to 5, and the resulting precipitate is subjected to solid-liquid separation, dried, and inert atmosphere. It is characterized in that it is fired underneath or in a reducing atmosphere.

In the conductive barium sulfate filler of the present invention, the core material has a specific surface area of 0.1 to 1 in an uncoated state.
It is necessary to use barium sulphate particles which are 50 m ² / g. When the specific surface area is less than 0.1 m ² / g in the uncoated state, the conductivity per unit weight of the conductive barium sulfate filler becomes small, and therefore even if such particles are mixed in the resin matrix. A satisfactory antistatic effect cannot be obtained. Further, when the specific surface area thereof exceeds 150 m ² / g in an uncoated state, a coating substance necessary to achieve a desired conductivity (that is, a coating substance composed of tin oxide doped with niobium or tantalum). However, the cost is increased and the specific gravity is increased, and the amount added to the resin matrix must be increased in order to obtain the desired antistatic effect. If the specific surface area of the barium sulfate particles is 0.1~3m ² / g or 12~150m ² / g uncoated state, the conductive barium sulfate filler is transparent,
It is particularly desirable to use such filler particles for paints, and the paints become electrically conductive. The addition of the conductive barium sulfate filler does not adversely affect the hiding power of the added pigment. The barium sulfate used in the present invention may contain zinc sulfide which is an accompanying impurity.

In the conductive barium sulfate of the present invention,
The thickness of the niobium- or tantalum-doped tin oxide coating on the surface should be 2 to 80 nm, preferably 10 to 30 nm. The film thickness is 2
If it is less than nm, the conductivity of the coated barium sulfate particles is insufficient, and therefore, even if such particles are mixed into the resin matrix, a satisfactory antistatic effect cannot be obtained. Further, even if the thickness of the coating exceeds 80 nm, the effect commensurate with the increasing cost is not achieved and the cost increases. If the coating has a thickness of 10-30 nm,
The binding force between the coating and the barium sulfate particles becomes relatively strong, and the coating does not separate from the barium sulfate particles when the conductive barium sulfate filler of the present invention is kneaded in the resin.

In the conductive barium sulfate of the present invention,
The niobium or tantalum content in the coating must be 0.1 to 10% by weight as Nb or Ta, preferably 0.3 to 5% by weight, based on the weight of tin oxide. If the niobium or tantalum content is less than 0.1% by weight, the coated barium sulphate particles have insufficient electrical conductivity, so that even if such particles are incorporated into the resin matrix, a satisfactory antistatic effect is obtained. Can't get Further, when the niobium or tantalum content exceeds 10% by weight, not only the whiteness of the coated barium sulfate particles is lowered, but also the amount of niobium or tantalum present in the SnO ₂ lattice which does not form a solid solution is increased. The above-mentioned improvement in conductivity cannot be obtained, resulting in an increase in cost. When the content of niobium or tantalum in the coating is within the above-mentioned preferable range, the coating has an extremely high conductivity, so that the coating amount of the conductive barium sulfate (coating thickness) is changed to the weight of the conductive barium sulfate. It can have sufficient conductivity even if it is relatively low (thin) as a result, and as a result,
The cost of conductive barium sulfate can be relatively low.

In the production method of the present invention, a method of mixing a slurry containing barium sulfate particles and a solution containing a tetravalent tin compound to prepare a mixed solution having a pH of 11 to 14 includes barium sulfate particles. An alkaline solution was added to the slurry to adjust the pH of the slurry to about 11 to 14 and then mixed with a solution containing a tetravalent tin compound to adjust the pH to 11 to 14.
Or a method of preparing a mixed solution having a pH of 11 to 14 by mixing a slurry containing barium sulfate particles with an alkaline solution containing a tetravalent tin compound.

Examples of tetravalent tin compounds that can be used in the production method of the present invention include sodium stannate, ammonium stannate, potassium stannate, tin tetrachloride and the like. As the pentavalent niobium compound or tantalum compound, there are soluble compounds such as chlorides and fluorides.

The process according to the invention offers the advantage that the barium sulphate particles are completely covered by the niobium- or tantalum-doped tin oxide coating, which can be carried out easily and in a short time. The conductive particles exhibit high dispersibility in plastics, resins and the like.

The conductive barium sulfate filler of the present invention uses barium sulfate particles as a core material, and a thin film of tin oxide doped with niobium or tantalum is formed on the surface thereof. It does not generate a bluish black tone due to antimony dope and has excellent whiteness.The thin film of tin oxide has transparency and the refractive index of barium sulfate as the core material is similar to that of resin. Therefore, this conductive barium sulfate filler is used for paint, resin,
Less likely to impair their transparency even if mixed into plastics, let alone coloring, so that any desired color tone can be obtained by adding a colorant together with the conductive barium sulfate filler of the present invention, In addition, it is a conductive barium sulfate filler which has no toxicity problem due to antimony, has stable conductivity with respect to temperature changes and humidity changes, and has high dispersibility in resins.

The conductive barium sulfate filler of the present invention is
It can be mixed with paper, plastic, rubber, resin, paint, fiber, etc. to give them conductivity, so that, for example, a housing for prevention of electrostatic damage of precision electronic equipment, prevention of electrostatic disaster, dust prevention, etc. , Building materials, textiles, machine parts, etc. Further, the conductive barium sulfate filler of the present invention can be used as a charge adjusting agent for a conductive roller, a photosensitive drum, a toner, a gas sensor, and an electrode modifier for a battery in a copying machine.

[0020]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 100 g of barium sulfate particles having a particle size of 0.1 μm and a specific surface area of 20 m ² / g were dispersed in 1500 ml of water, the dispersion slurry was heated to 75 ° C., and then 25% sodium hydroxide was added. The pH of the slurry was adjusted to about 12 by dropping the aqueous solution. Then sodium stannate (containing 40% Sn) 1
An aqueous solution prepared by dissolving 96.9 g in 500 ml of warm water was added to the dispersion slurry, the liquid temperature was adjusted to 75 ° C., and the mixture was stirred for 30 minutes, and then 1.47 g of niobium pentachloride (Nb based on the weight of tin oxide was 0. An aqueous solution of 20% sulfuric acid in which 0.5% by weight) was dissolved was neutralized for 90 minutes until the pH of the solution became 2.5. The dispersion slurry was aged for 3 hours while maintaining the pH at 2.5 and the temperature at 75 ° C., then filtered, washed, dried,
The conductive barium sulfate filler of the present invention was obtained by firing at 450 ° C. for 2 hours in a nitrogen atmosphere. This conductive barium sulfate filler contained 49.8% by weight of tin as SnO ₂ . The volume resistivity of this conductive barium sulfate filler (the obtained conductive barium sulfate filler was pressure-molded at a pressure of 2 ton / cm ² to give a test piece, and the volume resistivity of the test piece was measured with a low resistance measuring instrument ( (Measured by Mitsubishi Petrochemical, Loresta AP)) and whiteness (color difference meter (manufactured by Suga Test Instruments, SM
-5 type) was used to measure L ^* . ) Was as shown in Table 1.

Examples 2 to 10 In the method of Example 1, the particle size of barium sulfate, the coverage of tin oxide, the type and addition amount of the niobium compound or tantalum compound used (as Nb or Ta based on the weight of tin oxide). %), The firing temperature, and the firing atmosphere were changed as shown in Table 1 to obtain a conductive barium sulfate filler of the present invention in the same manner as in Example 1. The volume resistivity and whiteness of these conductive barium sulfate fillers are shown in Table 1.

[0023]

[Table 1] The atmosphere in Examples 8 and 9 was 95 vol% N ₂ +.
It is 5 vol% H ₂ .

Example 11 Conductivity obtained by the same method as in Example 1 except that the conductive barium sulfate filler obtained in Examples 1 and 2 and the Nb compound in the method of Example 1 were not added. Barium sulfate filler (described as Nb-free in Table 2 below) was kept at a constant temperature and humidity (80 ° C., 90% RH) and 1
Leave it in the environment of 00 ℃, its volume resistivity (Ω · cm)
Was examined over time. The results are shown in Table 2.

[0025]

[Table 2] As is clear from the data in Table 2, the conductive barium sulfate filler of the present invention doped with niobium or tantalum can maintain stable conductivity even under the severe conditions as described above.

[0026]

The conductive barium sulfate of the present invention has (1)
Conductive barium sulfate filler itself has excellent whiteness or transparency, and paper, plastic, rubber, resin, paint,
When added to substrates such as fibers, they remain white or transparent without being colored as with the prior art conductive barium sulphate fillers, so add colorants Any desired color tone can be obtained by (2) does not contain harmful substances such as antimony, (3) has conductivity that is stable against temperature changes and humidity changes, and (4) plastics, It has high dispersibility in resin, etc., and (5) When the conductive barium sulfate filler is added to the base material such as paper, plastic, rubber, resin, paint, fiber, etc., the surface of the conductive barium sulfate filler is The conductive coating film is not peeled off to cause loss of conductivity.

Claims (6)

[Claims] 1. A granular core material made of barium sulfate and a coating made of tin oxide doped with niobium or tantalum, which coats the surface of the granular core material. It has a specific surface area of 150 m ² / g, and the coating has a Nb or Ta content of 0.1 to 0.1 based on the weight of tin oxide.
Contains 10% by weight of niobium or tantalum and 2
A conductive barium sulfate filler having a thickness of ˜80 nm. 2. The granular core material in an uncoated state is 0.1 to 10.
3m ² / g or 12~150m conductive barium sulfate filler according to claim 1, characterized in that it has a specific surface area of ² / g. 3. The conductive barium sulfate filler according to claim 1 or 2, wherein the coating has a thickness of 10 to 30 nm. 4. The conductive material according to claim 1, 2 or 3, wherein the coating film contains 0.3 to 5% by weight of niobium or tantalum as Nb or Ta based on the weight of tin oxide. Barium sulfate filler. 5. A slurry containing barium sulfate particles having a specific surface area of 0.1 to 150 m ² / g at a concentration of 10 to 1000 g / l, and a tetravalent tin compound at a concentration of 1 to 95% by weight. A mixed solution having a pH of 11 to 14 is prepared by mixing with a solution, and an acid solution containing a pentavalent niobium compound or a tantalum compound is added to the mixed solution with Nb or Ta based on the weight of tin oxide.
Is added in an amount of 0.1 to 10% by weight to adjust the pH of the liquid after the addition to 1 to 5, and the precipitate thus obtained is subjected to solid-liquid separation, dried, or under an inert atmosphere or The method for producing a conductive barium sulfate filler according to any one of claims 1 to 4, wherein the firing is performed in a reducing atmosphere. 6. A slurry containing barium sulfate particles having a specific surface area of 0.1 to 150 m ² / g at a concentration of 50 to 500 g / l, and a tetravalent tin compound at a concentration of 1 to 95% by weight. A mixed solution having a pH of 11 to 12 is prepared by mixing with a solution, and an acid solution containing a pentavalent niobium compound or a tantalum compound is added to the mixed solution in an amount of 0.3 to 5 as Nb or Ta based on the weight of tin oxide. % To adjust the pH of the solution after addition to 2-3, and the resulting precipitate is subjected to solid-liquid separation, dried, and calcined under an inert atmosphere or a reducing atmosphere. The manufacturing method according to claim 5, wherein: