JP2559874B2 - Method for producing composite particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing composite particles having large saturation magnetization and high electrical conductivity, which are particularly preferably used for various fillers as functional particles and particles for magnetic fluid. Regarding

(Prior Art) Conventionally known as particles having both magnetic properties and conductivity are metal powders of iron, nickel and the like and magnetic powders of oxides of metals such as ferrite and magnetite.

Metal powders such as iron and nickel are easily oxidized, and fine powders may be ignited if left in the air, and are extremely difficult to handle. It is possible to disperse the metal powder in the binder, but the metal powder has a very large specific gravity,
It is difficult to disperse uniformly in a binder, especially plastic or rubber. In addition, the conductivity of metal oxides such as ferrite and magnetite is as low as 10 ^-9 S / cm.

As a method of imparting conductivity to magnetic powder, a method of imparting conductivity by attaching conductive fine particles to the surface of particles obtained by binding magnetic powder with a binder resin has been disclosed (JP-A-62-246075). Gazette). However, the particles produced by this method have a low electric conductivity of 10 ⁻⁴ S / cm or less, and further have a drawback that the conductive particles are separated during use.
Further, since the particle size is small, there is a drawback that secondary aggregation easily occurs.

(Problem to be Solved by the Invention) Therefore, an object of the present invention is to provide a production method capable of easily obtaining composite particles having a large saturation magnetization value and excellent conductivity.

(Means for Solving the Problems) As a result of intensive research to solve the above problems, the present inventors have found that the particle surfaces of magnetic particles composed of ferromagnetic fine particles having a specific particle diameter and a specific organic polymer. The present invention was found to find that the above problems can be solved by coating with a metal.

That is, the present invention has a number average particle diameter of 10 μm to 1000 μm by reacting and curing phenols and aldehydes in an aqueous medium in the presence of a suspension stabilizer of ferromagnetic fine particles and a basic catalyst, The content of ferromagnetic particles is
A method for producing composite particles having magnetism and conductivity, which comprises producing magnetic particles in an amount of 50 to 99% by weight and then coating the surfaces of the magnetic particles with a metal by a chemical plating method.

 Hereinafter, the present invention will be described in detail.

The number average particle diameter of the composite particles having magnetism and conductivity obtained in the present invention is 10 μm to 1000 μm. Particles with a number average particle size of less than 10 μm tend to agglomerate to 1000 μm.
Those which exceed the range have a problem that they have a low mechanical strength and are destroyed when dispersed in plastic or the like.

Furthermore, since the composite particles obtained in the present invention are spherical, they have excellent dispersible fluidity mechanical strength.

The composite particles obtained in the present invention are about 40 emu / g to 150
It preferably exhibits a saturation magnetization of emu / g and a saturation magnetization of 40e.
If it is less than mu / g, sufficient magnetic properties may not be obtained when used as a filler for plastics and magnetic particles for display materials. On the other hand, at present, no practically known ferromagnetic fine powder with a saturation magnetization of more than 150 emu / g is known.

The composite particles obtained in the present invention have a conductivity of 10 ^-3 to 10 ⁶ S / cm in a DC electric field of 1000 V / cm, and a conductivity of less than 10 ^-3 S / cm is a filler for plastics and When used as conductive particles for display materials, sufficient conductivity cannot be obtained. On the other hand, when the conductivity exceeds 10 ⁶ S / cm, the metal coating on the surface of the particles becomes too thick, the specific gravity of the particles increases, and when used as a filler for plastics,
Dispersibility deteriorates.

Furthermore, the content of the ferromagnetic fine particles in the composite particles obtained in the present invention is 50 to 99% by weight. When the content of the ferromagnetic fine particles is less than 50% by weight, the saturation magnetization value becomes small, and when it exceeds 99% by weight, the binding between the ferromagnetic fine particles due to the organic polymer binder becomes weak. Cheap. Considering the strength of the composite particles, it is preferably 97% by weight or less.

Ferromagnetic fine particles include magnetite, spinel ferrite such as gamma iron oxide, and metals (Mn, Ni, Z) other than iron.
(n, Mg, Cu, etc.), magnetoplumbite-type ferrite such as spinel ferrite, barium ferrite, etc., and fine particles of iron or alloy having an oxide layer on the surface can be used. The shape may be granular, spherical, or acicular. In particular, when high magnetization is required, ferromagnetic fine particle powder such as iron can be used, but considering chemical stability, magnetite,
It is preferable to use ferromagnetic fine powder of magnetoplumbite type ferrite such as spinel ferrite or barium ferrite containing gamma iron oxide. By appropriately selecting the type and content of the ferromagnetic fine particle powder, composite particles having a desired saturation magnetization can be obtained. For example, when trying to obtain a magnetization of 40 to 70 emu / g, magnetoplumbite type ferrite such as barium ferrite or spinel type ferrite may be used.
In order to obtain a high magnetization of about 100 emu / g, spinel ferrite containing magnetite or Zn may be used. Further, in order to obtain high magnetization of 100 emu / g or more, fine particles of iron or alloy having an oxide layer on the surface may be used.

The magnetic particles used in the present invention are composed of ferromagnetic fine particles and an organic polymer binder,
As the organic polymer binder used in the present invention,
The phenol resin described below is used.

In the present invention, any metal can be used as the metal coating the composite particles as long as it has conductivity. For example, nickel, silver, copper, gold, platinum, chromium, tin, zinc, etc. may be mentioned, but in order to obtain high conductivity with a plated layer as thin as possible, it is preferable to use nickel, silver, copper, gold, platinum. preferable.

The coating amount of the metal coating the surface of the composite particles is preferably 5 to 60% by weight or less based on the composite particles. More preferably, it is 15 to 40% by weight or less. If it is less than 5% by weight, insufficient and non-uniform coating tends to be formed, and if it exceeds 60% by weight, the specific gravity of the composite particles becomes large, and when used as a filler for plastics, the dispersibility in plastics deteriorates.

In the present invention, phenols and aldehydes are reacted in an aqueous medium in the presence of a basic catalyst in the presence of ferromagnetic particles and a suspension stabilizer.

Examples of phenols used here include phenol, m-cresol, p-tert-butylphenol,
Examples include alkylphenols such as o-propylphenol, resorcinol, and bisphenol A, and compounds having a phenolic hydroxyl group such as halogenated phenols in which a part or all of the benzene nucleus or the alkyl group is substituted with a chlorine atom or a bromine atom. , One or more of these are used.

Further, examples of aldehydes used in the method for producing composite particles in the present invention include formaldehyde and furfural in the form of either formalin or paraformaldehyde, and formaldehyde is particularly preferable. The molar ratio of aldehydes to phenol is 1
˜2 is preferable, and 1.1 to 1.6 is particularly preferable. When the molar ratio of aldehydes to phenols is less than 1, particles are difficult to be generated, or even if they are generated, curing of the resin is difficult to proceed, so that the strength of the particles to be generated tends to be weak. When the molar ratio of aldehydes to phenols is larger than 2, unreacted aldehydes remaining in the aqueous medium after the reaction tends to increase.

Next, as the basic catalyst used in the method for producing the composite particles in the present invention, the basic catalyst used in the usual production of resole resin is used. Examples thereof include aqueous ammonia, hexamethylenetetramine, and alkylamines such as dimethylamine, diethyltriamine, and polyethyleneimine. The molar ratio of these basic catalysts to phenols is preferably 0.02 to 0.3.

When reacting the phenols and aldehydes in the presence of a basic catalyst, the ferromagnetic particles to be coexisted are, as described above, magnetite, spinel ferrite containing gamma iron oxide, magnetoplumbite type ferrite such as barium ferrite. Fine particles of iron or an alloy having an oxide layer on its surface are preferred. The amount thereof is preferably 0.5 to 200 times the weight of phenols. Furthermore, as described above, it is more preferably 4 to 100 times in consideration of the saturation magnetization value of the produced composite particles and the strength of the particles.

Furthermore, the particle diameter of the ferromagnetic fine particles is 0.01 to
It is preferably 10 μm, and when considering the dispersion of fine particles in an aqueous medium and the strength of the resulting composite particles, it is
It is preferably from 05 to 5 μm.

Furthermore, as the suspension stabilizer used in the method for producing the composite particles in the present invention, carboxymethyl cellulose, a hydrophilic organic compound such as polyvinyl alcohol and a fluorine compound such as calcium fluoride, or a substantial amount of calcium sulfate or the like. Include insoluble inorganic salts in water,
One of these or two or more of them are used in combination.

The amount of such suspension stabilizer added is preferably 0.2 to 10% by weight, and more preferably 0.5 to 3.5% by weight, based on the phenols. When the amount of the suspension stabilizer added to the phenols is less than 0.2% by weight, amorphous particles tend to be formed. On the other hand, when the amount added exceeds 10% by weight, the surface of the composite particles is The amount of residual suspension stabilizer such as calcium fluoride tends to increase.

In addition, in order to add the substantially water-insoluble inorganic salts, the above-mentioned substantially water-insoluble inorganic salts may be directly added, and the substantially water-insoluble inorganic salts which are involved in the reaction may be added. Two or more kinds of water-soluble inorganic salts may be added so that For example, instead of the fluorine compound of calcium, at least one selected from the group consisting of sodium fluoride, calcium fluoride, ammonium fluoride and the like on one side of the water-soluble inorganic salt, and chloride, sulfate, nitrate of calcium on the other side. It is also possible to add at least one selected from the group consisting of to produce a fluorine compound of calcium during the reaction.

The reaction in the method for producing the composite particles in the present invention is
It is carried out in an aqueous medium, but the amount of water charged in this case is
For example, the solid content concentration of the carrier is preferably 30 to 95% by weight, and particularly preferably 40 to 90% by weight.

The reaction is carried out by gradually increasing the temperature with stirring at a temperature rising rate of 0.5 to 1.5 ° C./min, preferably 0.8 to 1.2 ° C./min.
The reaction is carried out at -90 ° C, preferably 83-87 ° C for 60-150 minutes, preferably 80-110 minutes. In such a reaction, a gelling reaction proceeds simultaneously with the reaction to form a gelled phenol resin matrix. React in this way
After gelation, the reaction product is cooled to 40 ° C. or lower to obtain an aqueous dispersion of spherical magnetic particles in which fine ferromagnetic particles are uniformly dispersed in a hardened phenol resin matrix.

Next, the aqueous dispersion is separated into solid and liquid by a conventional method such as filtration and centrifugation, washed and dried to obtain magnetic particles in which ferromagnetic fine particles are uniformly dispersed in the phenol resin matrix.

A known chemical plating method is used as the method for imparting the conductivity of the present invention, and the chemical nickel plating will be specifically described with reference to an example.

After degreasing 10 g of the magnetic particles in a 50 wt% methanol aqueous solution, 100 g of stannous chloride and 50 ml of hydrochloric acid were added with water to make 1000 ml, and the whole was immersed at 30 ° C. for 2 minutes for sensitization treatment. To do. Then 0.1 g of palladium chloride 0.1 g and 1 ml
Add 400 ml of water to the hydrochloric acid of to make the whole 400 ml in the activation bath 4
After treatment at 0 ℃ for 2 minutes, wash with water and wash with nickel chloride 3
0 g, 10 g of sodium hypophosphite and 10 g of sodium citrate were added to water to make 1000 ml, immersed in a bath at 60 ° C. for 60 minutes, washed with water, and dried to firmly and uniformly on the surface of the magnetic particles. Nickel can be attached to. In addition,
Since the magnetic particles used in the present invention have excellent plating properties, it is possible to directly immerse the magnetic particles in a plating bath without performing the above-mentioned pretreatment.

(Examples) Next, the present invention will be specifically described with reference to Examples.

The number average particle diameter in the present invention is an average value of values measured for 200 particles from an optical micrograph. Saturation magnetization is "vibrating sample magnetometer VSM-3S-15"
(Manufactured by Toei Industry Co., Ltd.) with an external magnetic field of 10 kOe.
"A" (manufactured by Yokogawa Hewlett-Packard). The shape of the composite particles is the scanning electron microscope S-800.
It is the result of observation by Hitachi.

Example 1 A spherical magnetite 400 having 50 g of phenol, 65 g of 37% formalin and an average particle diameter of 0.24 μm was placed in a three-necked flask of 1.
g, 28% ammonia water 7.8 g, calcium fluoride 1.0 g, and water 50 g with stirring, raised to 85 ° C in 40 minutes, reacted and hardened at the same temperature for 180 minutes, spherical magnetite and hardened phenol Magnetic particles composed of a resin were produced.

Next, the content in the flask was cooled to 30 ° C., 0.5 l of water was added, the supernatant was removed, and the lower spherical particles were washed with water and air-dried. Then, this is depressurized (5 mmHg
The following) was dried at 50 to 60 ° C. to obtain magnetic particles (hereinafter referred to as particles A).

The various properties of the obtained A are as shown in Table 1, and the shape thereof was spherical as shown in the scanning electron micrograph (× 1000) of FIG.

Example 2 Instead of 7.8 g of 28% aqueous ammonia as a basic catalyst,
Reaction, curing and post-treatment were carried out in the same manner as in Example 1 except that 4.5 g of hexamethylenetetramine was used to obtain magnetic particles (hereinafter referred to as particles B).

Various properties of the obtained magnetic particles are as shown in Table 1.

Example 3 450 g of polyhedral magnetite particles as ferromagnetic particles
Reaction, curing, and post-treatment were carried out in the same manner as in Example 1 except that was used to obtain magnetic particles (hereinafter referred to as particles C).

 The properties of the obtained magnetic particles are as shown in Table 1.

Example 4 300 g of spherical magnetite (average particle size of about 0.24 μm) and water
Reaction, curing and post-treatment were carried out in the same manner as in Example 1 except that 30 g was used to obtain magnetic particles (particle D). Various properties of the obtained magnetic particles are as shown in Table 1.

Example 5 After washing 10 g of each of the magnetic resin particles obtained in Examples 1 to 4 with a 50 wt% methanol mixed aqueous solution, water was added to 100 g of stannous chloride and 50 ml of hydrochloric acid to adjust the total amount to 1000 ml, and the temperature was adjusted to 30 ° C.
It was immersed for 2 minutes at the temperature of. Next, 0.2 g of palladium chloride and 2 ml of hydrochloric acid were added to water in a bath having a total volume of 800 ml,
After dipping at 40 ° C for 2 minutes and washing with water, nickel chloride 60g, sodium hypophosphite 20g and sodium citrate 20g, respectively
Water was added to the mixture to make the total volume 2000 ml, and the mixture was immersed in a bath at 60 ° C. for 60 minutes, washed with water and dried to obtain nickel-plated particles (particles E to H).

Various properties of the obtained particles are as shown in Table 1. Composite particle E coated with nickel obtained in Example 5
The state of the nickel coating in Fig. 2 is sufficient and uniform as shown in Fig. 2.

Example 6 Nickel plating was carried out in the same manner as in Example 5 except that 10 g of the magnetic particles of Example 1 were used and the time for immersion in a nickel chloride, sodium hypophosphite, or sodium citrate bath was 40 minutes. Particle I).

Example 7 30 g of silver nitrate was dissolved in 1500 ml of 0.5 wt% aqueous ammonia solution, and 30 g of the magnetic particles of Example 1 were stirred and dispersed. Next, 500 ml of a 2 wt% aqueous formaldehyde solution was added dropwise while continuing to stir slowly, silver plating was performed, followed by washing with water and drying (particle J). Various properties of the obtained particles are as shown in Table 1.

Example 8 Copper sulfate 25 g, Rochelle salt 100 g and sodium hydroxide 25 g
Water was added to prepare a solution having a total volume of 1000 ml, and 10 g of the magnetic particles obtained in Example 1 were dispersed. Then, 200 ml of a 5 wt% formaldehyde aqueous solution was added dropwise, followed by washing with water and drying to obtain copper-plated particles (particles K). Various properties of the obtained particles are as shown in Table 1.

(Effects of the Invention) The composite particles composed of the ferromagnetic fine particles whose surface is metal-coated and the organic polymer have a high magnetic susceptibility due to the high content of the ferromagnetic fine particles. In addition, since the surface of the particle is covered with metal, it has high conductivity.

Therefore, since the composite particles obtained in the present invention have a high magnetic susceptibility and a high electric conductivity, they are suitably used as particles for a magnetic fluid as a display material.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph (× 1000) showing the particle structure of the particle A obtained in Example 1, and FIG. 2 is the composite particle E coated with nickel obtained in Example 5 2 is a scanning electron micrograph (× 1000) showing the particle structure of

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01F 1/20 H01F 1/113

Claims (1)

(57) [Claims] 1. A number average particle diameter of 10 μm obtained by reacting and curing a phenol and an aldehyde in an aqueous medium in the presence of a suspension stabilizer of ferromagnetic fine particles and a basic catalyst.
To 1000 μm, the content of the ferromagnetic fine particles is 50 to 99% by weight, magnetic particles are produced, and then the surfaces of the magnetic particles are metal-coated by a chemical plating method. A method for producing the composite particle having.