JP2000080300A - Electroconductive calcium carbonate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the cheap subject material excellent in whiteness, good in optical characteristics and useful as an antistatic agent or an electroconductive material for a plastic, a coating material, a paper, a rubber, a sealant, a sol of polyvinyl chloride or the like by coating an electroconductive metal oxide on the surface of calcium carbonate. SOLUTION: This electroconductive calcium carbonate is obtained by suspending and mixing an electroconductive metal oxide (preferably tin oxide containing an activating agent such as antimony) with calcium carbonate (preferably in a needle shape) in an organic solvent to provide the calcium carbonate coated with the electroconductive metal oxide, and carrying out the heat treatment of the coated calcium carbonate at 100-600 deg.C, preferably in a reductive atmosphere. The electroconductive calcium carbonate has 1-1,000 pts.wt., preferably 10-30 pts.wt. electroconductive metal oxide based on 100 pts.wt. calcium carbonate on the surface of the calcium carbonate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to conductive calcium carbonate and a method for producing the same.
The present invention relates to a conductive calcium carbonate which is inexpensive, has excellent whiteness and good optical characteristics, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, in order to minimize dust and dirt in a clean room with the development of electro technology, inorganic antistatic fillers are particularly used. Inorganic antistatic materials are roughly classified into metal-based, carbon-based, and metal oxide-based materials. For example, antistatic pigments obtained by coating or complexing various kinds of pigments with the antistatic material are commercially available. Metal-based or carbon-based paints have aesthetic problems due to blackening of various pigments, and have poor optical properties, that is, inferior in total light transmittance and light diffusivity, so their use in applications where optical properties are required is limited. Problem. Further, there is a problem that the metal system has low oxidation resistance, and the carbon system has lower conductivity than the metal system. Therefore, development of a white conductive material using a metal oxide-based material free of these problems has been strongly desired.

As a metal oxide-based conductive material, conductive potassium titanate is known. However, potassium titanate is expensive, and a conductive material using the same is not sufficient in optical characteristics, and thus has a problem that its use in fields requiring optical characteristics is limited.

On the other hand, calcium carbonate has excellent whiteness,
Because it is inexpensive, it is widely used as an extender for rubber, plastics, paper, paints, etc., but since it is a perfect insulator and has chargeability, the aforementioned adhesion of dust and dirt is serious. It is a problem.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a conductive calcium carbonate having excellent whiteness and good optical characteristics, and a method for producing the same.

[0006]

Means for Solving the Problems In view of such circumstances, the present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by coating the surface of calcium carbonate with a conductive metal oxide, It has been found that a conductive calcium carbonate having excellent optical properties and good optical properties can be obtained, and the present invention has been completed.

That is, a first aspect of the present invention is to provide conductive calcium carbonate, which is characterized in that a surface of calcium carbonate is coated with a conductive metal oxide in an amount of 1 to 1000 parts by weight per 100 parts by weight of calcium carbonate. Content (Claim 1).

In a preferred embodiment, the conductive metal oxide is tin oxide.

In a preferred embodiment, the conductive metal oxide contains an activator (claim 3).

In a preferred embodiment, the activator is antimony (claim 4).

In a preferred embodiment, the shape of the calcium carbonate is acicular (claim 5).

A second aspect of the present invention is to obtain a calcium carbonate coated with a conductive metal oxide by suspending and mixing a conductive metal oxide and calcium carbonate in an organic solvent.
A method for producing conductive calcium carbonate, characterized by performing a heat treatment at 00 to 600 ° C. (claim 6).

In a preferred embodiment, a polar solvent is added to an organic solvent (claim 7).

In a preferred embodiment, the heat treatment is performed in a reducing atmosphere.

[0015]

Hereinafter, the present invention will be described in more detail. The conductive metal oxide used in the present invention is not particularly limited, and examples thereof include tin oxide, indium oxide, silica, titanium oxide, zinc oxide and the like. These may be used alone or in combination of two or more. Tin oxide is particularly preferred from the viewpoint of covering properties with calcium carbonate. From the viewpoint of coatability, it is desirable that the metal oxide particles have a certain particle size, usually from 0.001 to 10 μm, preferably from 0.01 to 1 μm. Particle size 0.001μm
When it is less than 10 μm, the conductive metal oxide particles tend to aggregate, while when it exceeds 10 μm, the metal oxide particles tend to peel off.

For the purpose of improving the conductivity, a trivalent or pentavalent metal can be contained as an activator for the metal oxide. The activator is appropriately selected depending on the type of the metal oxide. For example, in the case of tin oxide,
It is effective to use antimony or the like as an activator.
The amount of the activator is usually about 1 to 20 parts by weight based on 100 parts by weight of the conductive metal oxide. If the amount is less than 1 part by weight, the effect of the addition is not sufficient. On the other hand, if the amount exceeds 20 parts by weight, the charge balance is lost and the conductivity tends to be adversely affected.

The shape of the calcium carbonate used in the present invention is not particularly limited, and examples thereof include a cubic shape, a spherical shape, a spindle shape, and a needle shape. When kneading with a synthetic resin or the like, a needle-like shape which is easy to obtain an antistatic effect at a low content is suitable. Although the particle size of the acicular calcium carbonate is not particularly limited, it is usually preferable that the length is 2 to 100 μm and the aspect ratio is 4 or more.
No. 14 can be prepared.

Further, in order to enhance the adsorptivity of the conductive metal oxide, the BET specific surface area of calcium carbonate (by the nitrogen adsorption method) is usually 0.1 to 150 m ² / g, preferably 1 to 5 m ² / g.
0 m ² / g, more preferably from 3 to 10 m ² / g. B
When the ET specific surface area is less than 0.1 m ² / g, it may adversely affect the adsorptivity of the conductive metal oxide.
If it exceeds 0 m ² / g, not only the coating amount of the conductive metal oxide for achieving the predetermined conductivity is increased and the cost is increased, but also the specific gravity is increased, and the dispersibility in the synthetic resin or the like is increased. May have adverse effects.

In the present invention, the coating amount of the conductive metal oxide is usually 1 to 10 with respect to 100 parts by weight of calcium carbonate.
00 parts by weight, preferably 5 to 50 parts by weight, more preferably 10 to 30 parts by weight. If the amount is less than 1 part by weight, the surface of calcium carbonate cannot be uniformly coated with the metal oxide,
Therefore, it is difficult to develop sufficient conductivity.
If the amount exceeds 0 parts by weight, calcium carbonate having a low Mohs hardness is pressed, and not only can the shape and aspect ratio not be maintained, but also the metal oxide is liberated, so that sufficient coating cannot be performed.

In a preferred method for producing conductive calcium carbonate of the present invention, a conductive metal oxide and calcium carbonate are suspended and mixed in an organic solvent to coat the surface of the calcium oxide with the metal oxide. This is a method of performing heat treatment at ~ 600 ° C. In this case, after suspending the conductive metal oxide and calcium carbonate in separate organic solvents, by mixing both suspensions, the surface of calcium carbonate can be more uniformly coated with the metal oxide. Can be. The conductive metal oxide suspended in an organic solvent is not only more easily adapted to calcium carbonate than the conductive metal oxide suspended in an aqueous medium, but also has a high adsorption rate, so that the surface of the calcium carbonate has The oxide can be uniformly and strongly adsorbed and supported. The method for preparing the conductive metal oxide suspended in an organic solvent may be a conventional method such as a sol-gel method, or a method described in JP-A-59-6235.
As described in Japanese Patent Application Laid-Open No. H10-260, a method of preparing an oxide from chloride can be exemplified.

The organic solvent is not particularly limited.
Hydrophilic organic solvents such as ethanol, methanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and acetone are preferred, with 2-propanol being most preferred.

Preferred conditions for preparing the conductive calcium carbonate are as follows. (Solid concentration of material) Calcium carbonate suspension: 50 parts by weight or less (organic solvent 10
Conductive metal oxide suspension: 20 parts by weight or less (organic solvent 1)
(Per 00 parts by weight)

(Mixing conditions) Coating amount of conductive metal oxide: 1 to 1000 parts by weight (per 100 parts by weight of calcium carbonate) Mixing temperature: 5 to 97 ° C

The solid content concentration of the calcium carbonate suspension and the conductive metal oxide suspension is not particularly limited.
Per 100 parts by weight, calcium carbonate is 50 parts by weight or less,
The content of the metal oxide is preferably 20 parts by weight or less. If the solid content is higher than the above, the dispersibility of the prepared conductive calcium carbonate may be affected.

Specific mixing conditions include, in addition to the above-described amount of the conductive metal oxide coating, the temperature and the dropping time when the conductive metal oxide and calcium carbonate are suspended in separate organic solvents. Is mentioned. The temperature at the time of mixing is not particularly limited, but is usually 5 to 97 ° C, preferably 30 to 90 ° C.
° C, more preferably 50-80 ° C. 5 ℃
If it is less than 3, solidification or the like is likely to occur, and therefore, the selection of the organic solvent is likely to be restricted. On the other hand, when the temperature exceeds 97 ° C., the selection of the organic solvent tends to be restricted due to the boiling point and the like.

The dropping conditions are preferably to drop the conductive metal oxide suspension into the calcium carbonate suspension, and the dropping time is not particularly limited, but is usually 1 to 600 minutes. If the dropping time is less than 1 minute, the metal oxide tends to hinder uniform coating of the calcium carbonate surface,
On the other hand, if it exceeds 600 minutes, it takes a long time and the cost becomes industrially high.

In order to uniformly and firmly coat the conductive metal oxide on the calcium carbonate surface, a polar solvent having a higher dielectric constant than the organic solvent can be added to the organic solvent. The content of the polar solvent is not particularly limited, but is usually 0.1 to 50 parts by weight, based on 100 parts by weight of calcium carbonate,
Preferably it is 1 to 10 parts by weight. If the amount is less than 0.1 part by weight, the amount of the polar solvent added is not sufficient. On the other hand, if the amount exceeds 50 parts by weight, the potential balance is lost, and the coating property tends to be adversely affected. The organic solvent used in the present invention is not particularly limited as long as it is a polar solvent having a higher relative dielectric constant than the organic solvent used. For example, formamide, N-methylformamide, N-methylacetamide, N-methylpropionamide, carbonic acid Propylene, ethylene carbonate and the like can be mentioned, and these can be used alone or in combination of two or more.

The heat treatment is for making the conductive metal oxide conductive, and the temperature is usually 100 to 600.
° C, preferably 150 to 550 ° C, more preferably 2 ° C.
50-500 ° C. When the heat treatment temperature is lower than 100 ° C., the effect of making calcium carbonate conductive is small. On the other hand, when the temperature exceeds 600 ° C., calcium carbonate is rearranged into calcium oxide. Conducting the heat treatment in a reducing or neutral atmosphere can further improve the conductivity.

The conductive calcium carbonate of the present invention may contain, if necessary, one or more of dyes, pigments, fillers, surfactants, plasticizers, activators, dispersants, defoamers, and the like. It can also be contained. The conductive calcium carbonate of the present invention,
Other inorganic antistatic materials and organic antistatic materials such as cationic copolymers may be used in combination. Also,
For the conductive calcium carbonate of the present invention, if necessary, dyes, pigments, fillers, surfactants, plasticizers, activators,
It is also possible to add dispersants, defoamers and the like. The conductive calcium carbonate of the present invention is a plastics, paint, paper, rubber, sealant as an antistatic material or a conductive material,
It is used extensively in vinyl chloride sols and the like, as well as pigments or fillers.

[0030]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, which do not limit the present invention in any way. In the following description, the measurement of the volume resistance value and the powder whiteness was performed according to the following methods.

Volume resistance value: The powder was molded under pressure at a pressure of 2.0 t / cm ² , and the volume resistivity of the test piece was measured using a resistance meter (HP4140B, manufactured by Yokogawa Hewlett-Packard). did.

Powder Whiteness: The L value of the powder was measured using a powder whiteness meter (1001 DP, Nippon Denshoku Industries).

Example 1 1000 parts by weight of an aqueous solution of stannic chloride (15% by weight), 4 parts by weight of antimony trichloride, and 20 parts of hydrochloric acid (35% by weight)
0 parts by weight were mixed and dissolved to prepare a uniform aqueous solution. This aqueous solution is treated with ammonium hydrogen carbonate (NH ₃ 3% by weight).
The solution was dropped and mixed with 6000 parts by weight of the aqueous solution with stirring to produce a gelled tin oxide. The pH at this time was 7.5. The gelled tin oxide is washed with water and dehydrated, and benzyl-type cationic surfactant 15 is added to a 2-propanol (IPA) solution.
After the addition of parts by weight, the tin oxide gel was suspended, and the solid content concentration was 1
A tin oxide IPA suspension activated with 0% by weight of antimony was prepared.

Next, the major axis is 30 μm, the minor axis is 1 μm, and BE
Acicular aragonite-type calcium carbonate having a T surface area of 6 m ² / g (trade name: Wiscal A, manufactured by Maruo Calcium Co., Ltd.)
Was weighed, and an IPA solvent was added thereto to prepare a 10% by weight calcium carbonate IPA suspension. The temperature of the calcium carbonate IPA suspension was adjusted to 80 ° C., and then 250 g of the above 10% by weight tin oxide IPA suspension was added dropwise over 60 minutes. After stirring for 1 hour with a stirrer, the mixture was filtered and dried with filter paper (manufactured by Toyo Roshi Kaisha, Ltd .: 5C) according to a conventional method.
A calcium carbonate powder on which tin oxide fine particles were adsorbed and supported was obtained. Further, the calcium carbonate powder supporting the tin oxide was subjected to a heat treatment at 450 ° C. for 2 hours in a nitrogen (neutral) atmosphere to prepare a conductive calcium carbonate of the present invention.

Table 1 shows the volume resistivity and powder whiteness of the conductive calcium carbonate. In addition, X-ray analyzer (XRD)
As a result of observation with a transmission electron microscope (TEM), it was found that dislocation had occurred in calcite crystals maintaining the aspect ratio. In addition, it was confirmed that the tin oxide film uniformly covered the calcium carbonate surface, and free tin oxide fine particles did not exist. FIG. 1 shows a TEM photograph (× 40000) of untreated acicular calcium carbonate, and FIG. 2 shows a TEM photograph (× 40000) of the conductive calcium carbonate obtained in Example 1.

Example 2 In the same manner as in Example 1, except that 5 parts by weight of N-methylformamide was added as a polar solvent to 100 parts by weight of calcium carbonate in the suspension of calcium carbonate IPA, the present invention was repeated. Was prepared. Table 1 shows the volume resistivity and powder whiteness of the conductive calcium carbonate. Further, as a result of observation by XRD and TEM, dislocation was found to be a calcite crystal maintaining the aspect ratio. In addition, it was confirmed that the tin oxide film uniformly covered the calcium carbonate surface, and free tin oxide fine particles did not exist.

Example 3 The procedure of Example 2 was repeated, except that the reaction was carried out in a nitrogen (neutral) atmosphere under a nitrogen and hydrogen (reducing) atmosphere (N ₂ : H ₂ = 97: 3). An inventive conductive calcium carbonate was prepared. Table 1 shows the volume resistivity and powder whiteness of the conductive calcium carbonate. Further, as a result of observation by XRD and TEM, dislocation was found to be a calcite crystal maintaining the aspect ratio. In addition, it was confirmed that the tin oxide film uniformly covered the calcium carbonate surface, and free tin oxide fine particles did not exist.

Example 4 A conductive calcium carbonate of the present invention was prepared in the same manner as in Example 1, except that antimony trichloride was not contained. Table 1 shows the volume resistivity and powder whiteness of the conductive calcium carbonate. Also, X
As a result of observation by RD and TEM, dislocation was found in the calcite crystal maintaining the aspect ratio. In addition, it was confirmed that the tin oxide film uniformly covered the calcium carbonate surface, and free tin oxide fine particles did not exist.

Comparative Example 1 A conductive potassium titanate was prepared in the same manner as in Example 2, except that the needle-like aragonite-type calcium carbonate was changed to needle-like potassium titanate. Table 1 shows the volume resistivity and powder whiteness of the conductive potassium titanate. In addition, as a result of observation with a TEM, it was confirmed that the potassium titanate maintained the aspect ratio, but the coating property of tin oxide was somewhat poor, and free tin oxide was sparsely present.

Comparative Example 2 A conductive calcium carbonate was prepared in the same manner as in Example 2 except that the heat treatment temperature was changed to 800 ° C. Table 1 shows the volume resistivity and powder whiteness of the conductive calcium carbonate. In addition, as a result of observation by XRD and TEM, it was confirmed that the particles were dislocated to quick lime and that a large number of free tin oxide fine particles were present.

Comparative Example 3 100 g of the calcium carbonate used in Example 1 was weighed, and distilled water was added thereto to prepare a 10% by weight aqueous suspension. 10% by weight of carbon black powder (manufactured by Lion Akzo) was added to the aqueous suspension. After stirring with a stirrer for 1 hour, the mixture was filtered and dried according to a conventional method, and then calcium carbonate supporting carbon black was prepared. Table 1 shows the volume resistivity and powder whiteness of the conductive calcium carbonate. XR
As a result of observation with D and TEM, it was found to be an aragonite-type crystal having an aspect ratio of at least. Further, it was confirmed that carbon almost covered the calcium carbonate surface.

[0042]

[Table 1]

REFERENCE EXAMPLE 1 Table 2 shows the volume resistivity and powder whiteness of the metal oxide suspension prepared in Example 1, which was filtered and dried, and then heat-treated at 450 ° C. for 2 hours.

REFERENCE EXAMPLE 2 Table 2 shows the volume resistivity and powder whiteness of the metal oxide suspension prepared in Example 2 which was filtered and dried and then heat-treated at 450 ° C. for 2 hours.

Reference Example 3 Table 2 shows the volume resistivity and powder whiteness of the carbon black used alone in Comparative Example 3.

Reference Example 4 Table 2 shows the volume resistivity and powder whiteness of the calcium carbonate used alone in Examples and Comparative Examples.

Reference Example 5 Table 2 shows the volume resistivity and powder whiteness of potassium titanate used alone in Comparative Example 1.

[0048]

[Table 2]

Application Examples 1 to 4 and Comparative Application Examples 1 to 3 Using the conductive inorganic particle powders obtained in Examples 1 to 4 and Comparative Examples 1 to 3, a plastic composition for light diffusion was produced in the following manner. Was prepared, the composition was processed into a plate, and the optical properties and surface resistance (spring electrode contact method) of the plastic composition for light diffusion were evaluated by the following methods. Table 3 shows the results
It was shown to. As is evident from Table 3, the particles of Comparative Examples 1 to 3 are all inferior in optical characteristics, and the particles of Comparative Example 3 cause the molded product to be colored black and have an aesthetic problem.

<Method for Preparing Plastic Composition for Light Diffusion> Partial copolymer of methyl methacrylate (polymerization ratio: 18
%) To 100 parts by weight of Examples 1 to 4 and Comparative Examples 1 to 4.
10 parts by weight of each of the particles No. 3 was mixed and stirred at a high speed for 60 seconds with a Henschel mixer to sufficiently disperse the particles. Next, an extruder with a 65 mmφ vent and a die width of 60 mm
It was extruded into a sheet at a resin temperature of 250 ° C. with a 0 mm coat hanger die, and processed into a plate shape with a thickness of 2 mm from three polishing rolls. <Evaluation method> Total light transmittance: measured by an integrating sphere HTR meter according to ASTM D-1003-61T. Light diffusivity: Angles of 20 ° and 7 measured with a goniometer (HR-100, manufactured by Murakami Color Research Laboratory)
The value obtained by dividing the average of the light intensity transmitted at 0 ° by the light intensity transmitted at an angle of 5 ° was obtained as a percentage.

[0051]

[Table 3]

[0052]

The conductive calcium carbonate of the present invention does not impair the whiteness of the calcium carbonate and has good optical properties. Therefore, as the antistatic agent and the conductive material, plastics, paint, paper, rubber, sealant, It is useful in a wide variety of fields such as PVC sol. Further, according to the method for producing conductive calcium carbonate of the present invention, the conductive metal oxide dispersed in an organic solvent is not only more easily adapted to calcium carbonate as compared with the case where the conductive metal oxide is dispersed in an aqueous medium, but also has a higher adsorption rate. Therefore, the conductive metal oxide can be uniformly and strongly adsorbed and supported on the surface of the calcium carbonate.

[Brief description of the drawings]

FIG. 1 is a transmission electron micrograph (× 40000) of untreated acicular calcium carbonate.

FIG. 2 is a transmission electron micrograph (× 40000) of the conductive calcium carbonate obtained in Example 1.

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Claims (8)

[Claims] 1. A conductive metal oxide is coated on the surface of calcium carbonate in an amount of 1 to 1000 parts by weight based on 100 parts by weight of calcium carbonate.
Conductive calcium carbonate characterized by being coated by weight. 2. The conductive calcium carbonate according to claim 1, wherein the conductive metal oxide is tin oxide. 3. The conductive calcium carbonate according to claim 1, wherein the conductive metal oxide contains an activator. 4. The conductive calcium carbonate according to claim 3, wherein the activator is antimony. 5. The conductive calcium carbonate according to claim 1, wherein the shape of the calcium carbonate is acicular. 6. A calcium carbonate coated with a conductive metal oxide is obtained by suspending and mixing a conductive metal oxide and calcium carbonate in an organic solvent.
A method for producing conductive calcium carbonate, characterized by performing a heat treatment. 7. The method according to claim 6, wherein a polar solvent is added to the organic solvent. 8. The method according to claim 6, wherein the heat treatment is performed in a reducing atmosphere.