JP2925602B2 - Conductive magnetic powder for electrostatic latent image developer and production method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a conductive magnetic powder for an electrostatic latent image developer, more specifically, an average particle diameter of 1 to 10 μm and a bulk density of 1.5 g / cm ^3. The present invention relates to a composite particle excellent in fluidity, wherein the content of the ferromagnetic fine particles is 80 to 99% by weight, and a method for producing the same.

[Conventional technology]

Conventionally, as a method of developing an electrostatic latent image, a developing method using a so-called one-component magnetic toner in which composite particles obtained by mixing and dispersing ferromagnetic fine particles in a resin without using a carrier is used as a developer. Widely known and widely used.

As the magnetic toner, a conductive magnetic toner in which a conductive material such as carbon is added in addition to ferromagnetic fine particles and a resin is generally known. In the developing method using the conductive magnetic toner, the magnetic toner is held on the non-magnetic sleeve by the magnetic force of the magnet roller, and when approaching the latent image, is charged to a charge having a polarity opposite to that of the latent image by electrostatic induction. Next, the magnetic toner charged to the opposite polarity overcomes the magnetic attraction, adheres to the latent image surface, and is developed.

The image developed using the conductive magnetic toner described above is
It has the drawback that it is difficult to electrostatically transfer it to other recording media. As a method of improving this drawback, a magnetic toner with a high electrical resistance of 10 ¹² Ωcm or more is used instead of conductive toner. There has been proposed a method of performing development by using.

However, it has been pointed out that the method of developing using the magnetic toner having high electric resistance improves transferability, but impairs developability.

Therefore, according to JP-A-56-142540, as a method for improving both transferability and developability, a mixture of a magnetic toner having a high electrical resistance and a magnetic powder having a smaller average particle size of the toner is used. It has been proposed to.

Various properties of the magnetic powder used in this method include an average particle diameter of 1 to 10 μm, and a softness that does not damage the roller when fixing the image with the roller, that is, in terms of bulk density. It is strongly demanded that it be about 1.5 g / cm ³ or less, and have a volume electric resistance of less than 10 ¹² Ωcm, especially 10 ⁹ Ωcm or less, and have excellent fluidity.

The fact that particles having an average particle diameter of 1 to 10 μm are required as magnetic powder is based on the fact that the average particle system of currently used one-component magnetic toners is 5 to 20 μm, -142540, `` The volume average particle diameter of the conductive magnetic particles is preferably about 1/5 to 4/5 of that of the magnetic toner, more preferably about 3/10 to 2/3. The reason is that the important point in the developer of the present invention is that the average particle diameter of the conductive magnetic particles 5b is smaller than that of the high electric resistance magnetic toner 5a. That is, if magnetic toner
When the magnetic particles 5b are larger than 5a, a small magnetic toner covers the periphery of the magnetic particles, and when the magnetic particles are large, the magnetic attraction force to the magnet 6 becomes stronger, so that the magnetic toner is carried in the surroundings. The magnetic particles are just removed from the electrostatic latent image, and white spots called white spots appear on the image. On the other hand, if the conductive magnetic particles are too small, it is not preferable. That is, if the particle diameter is too small, fine magnetic particles are strongly adsorbed around the magnetic toner by Van der Waals force, resulting in a structure similar to that of a conventional conductive magnetic toner in which the toner surrounding is made conductive. The electrotransfer property will be deteriorated. ".

Further, the electric resistance of the magnetic powder, the volume resistivity of the conductive powder of the present invention is 10 ⁹ Ωc
m and the high electrical resistance of the magnetic toner is defined as a volume electrical resistance of 10 ¹² Ωcm or more. As described in な る, the electric resistance is required to be smaller than that of the magnetic toner having a high electric resistance of 10 ¹² Ωcm or more, that is, less than 10 ¹² Ωcm, in particular, it is 10 ⁹ Ωcm or less. preferable.

Further, regarding the fluidity, it is known that the fluidity of the developer strongly controls the behavior of the developer in the developing machine and affects the charging characteristics of the developer. As a result, for example, when the fluidity is poor, it causes a problem that an image becomes uneven or in an extreme case, an image does not appear, and there is a strong demand for improving the fluidity of the magnetic powder.

Conventionally, as a magnetic powder, as described in Japanese Patent Application Laid-Open No. 56-159653, ferromagnetic fine particles are thoroughly washed with water and then rapidly dried while stirring in a dryer, or
Coagulated particles obtained by spraying an organic polymer substance or the like onto ferromagnetic fine particles while flowing them in a fluidized bed are known.

[Problems to be solved by the invention]

The average particle size is 1 to 10 μm, and the bulk density is 1.5 g / cm ³
Degree or less, and the volumetric electrical resistance is less than 10 ¹² Ωcm, and the magnetic powder excellent in fluidity is currently the most required, but according to the known method described above, any method Although it is possible to obtain coagulated particles having a bulk density of about 1.5 g / cm ³ or less, the fluidity is poor, and particularly,
The particle size is about 45 g / sec or less, and a large number of agglomerated particles having an average particle diameter of 10 μm or more are difficult to control, so that the particle size distribution is widened and cannot be used without classification.

In particular, in the case of the former method, the ferromagnetic fine particles are merely dried and agglomerated, so that the agglomeration is easily dislodged, and a large number of fine powders of 1 μm or less are mixed and the particle size distribution is expanded. This is the cause of further increase.

In the latter method, the formed aggregated particles are not easily loosened because the organic polymer substance as the binder is interposed between the ferromagnetic fine particles. There is a drawback that the ratio of the molecular substance increases, and as a result, the volume electric resistance becomes 10 ¹² Ωcm or more.

That is, the amount of the organic polymer substance contained in the magnetic powder is required to be a necessary minimum in consideration of the binding property and electric resistance between the ferromagnetic fine particles.

Hitherto, composite particles of ferromagnetic fine particles and an organic polymer substance such as a resin have been widely known.
As described in JP-A-59-31967, a predetermined amount of the ferromagnetic fine particles and the resin is obtained by mixing in a molten resin and then pulverizing, but the content of the ferromagnetic fine particles is Generally, the content is less than 80% by weight, and the content of the ferromagnetic fine particles cannot be further increased. Therefore, it is difficult to reduce the content of the resin to obtain composite particles having an electric resistance of less than 10 ¹² Ωcm. Met.

Therefore, the present invention has an average particle diameter of 1 to 10 μm, a bulk density of 1.5 g / cm ³ or less, and a high content of ferromagnetic fine particles, and excellent fluidity. It is an object of the present invention to obtain composite particles.

[Means for solving the problem]

The present inventor has an average particle diameter of 1 to 10 μm, a bulk density of 1.5 g / cm ³ or less, and a content of ferromagnetic fine particles as high as possible, and excellent fluidity. As a result of various studies on a method for obtaining composite particles, the present invention has been achieved.

That is, the present invention is composed of ferromagnetic fine particles having a surface subjected to hydrophobic treatment and a cured phenol resin, has an average particle diameter of 1 to 10 μm, and has a bulk density of 1.5 g / cm ³ or less, And the content of the ferromagnetic fine particles is 80 to 99% by weight.
Phenols and aldehydes are reacted and hardened in an aqueous medium in the presence of a magnetic powder for an electrostatic latent image developer composed of composite particles, and ferromagnetic fine particles and a basic catalyst. In producing composite fine particles composed of a hardened phenolic resin and a hardened phenol resin, a ferromagnetic material whose surface is subjected to a hydrophobic treatment is used as the ferromagnetic fine particles. It is composed of fine particles and a cured phenol resin, has an average particle size of 1 to 10 μm, a bulk density of 1.5 g / cm ³ or less, and a content of the ferromagnetic fine particles of 80 to 99% by weight.
This is a method for producing a conductive magnetic powder for an electrostatic latent image developer comprising composite particles.

[Action]

First, the most important point in the present invention is that when phenols and aldehydes are reacted and cured in an aqueous medium in the presence of ferromagnetic fine particles and a basic catalyst, the content of the ferromagnetic fine particles In the case where ferromagnetic fine particles whose surface is subjected to a hydrophobic treatment are used as the ferromagnetic fine particles for the reaction hardening, the average particle size of the formed composite particles can be increased. 1 to 10 μm in diameter
And the fluidity of the composite particles can be improved.

In the present invention, the content of the ferromagnetic fine particles is 80 to 99
% Of composite particles are obtained.

In the present invention, regarding the reason why the content of the ferromagnetic fine particles can be increased, the present inventor has proposed that the hardening reaction proceeds simultaneously with the reaction, so that the ferromagnetic fine particles are strongly bound with a small amount of phenol resin. I think that it can be.

The present inventors have adjusted the concentration of the ferromagnetic fine particles to less than 60% by weight so that the average particle size of the formed composite particles is 1 to 1.
Although a technology for controlling the particle size to 10 μm has already been developed, in the present invention, by using ferromagnetic particles whose surface has been subjected to a hydrophobic treatment, almost no restriction of concentration adjustment of the ferromagnetic particles is taken into account. , Average particle size is 1-10
The resulting composite particles have a size of μm.

In the present invention, composite particles having a flow rate of 0.45 g / sec or more are obtained.

Next, conditions for implementing the present invention will be described.

The average particle size of the composite particles according to the present invention is 1 to 10 μm. When it is less than 1 μm or more than 10 μm, it is not preferable as the conductive magnetic powder for an electrostatic latent image developer intended in the present invention. Since the particle size of the magnetic powder is closely related to the particle size of the magnetic toner used together, it may be appropriately selected from the range of 1 to 10 μm.

The bulk density of the composite particles according to the present invention is 1.5 g / cm ³ or less. When the bulk density is small, it is possible to give higher image quality. Further, since the bulk density is small and the fixing is performed with a roller, the roller and the like are not damaged.

The content of the ferromagnetic fine particles in the composite particles according to the present invention is 80 to 99% by weight. When the content is less than 80% by weight, the content of the insulating resin component is increased, and the electric resistance is 10 ¹² Ωcm.
The composite particles having a particle size of less than 10% cannot be obtained. If it exceeds 99% by weight, the bonding force between the ferromagnetic fine particles is weakened, the ferromagnetic fine particles are separated independently, and fine powder of less than 1 μm increases.

As the ferromagnetic fine particles used in the present invention,
Spinel ferrites such as magnetite and gamma iron oxide,
These include spinel ferrites containing one or more metals other than iron (Mn, Ni, Zn, Mg, Cu, etc.), magnetoplumbite ferrites such as barium ferrite, and iron and alloys having an oxide layer on the surface. Fine particle powder can be used. Further, an oxide of a metal (Mn, Ni, Zn, Mg, Cu, or the like) other than iron can be contained together with the ferromagnetic fine particles. The shape of the ferromagnetic fine particles may be granular, spherical, or acicular. Also,
By appropriately selecting the type and content of the ferromagnetic fine particles, 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 ferrite such as barium ferrite or spinel ferrite may be used, and further, to obtain a high magnetization of about 70 to 100 emu / g. In this case, spinel ferrite containing magnetite or Zn may be used. Further, in order to obtain a high magnetization of 100 emu / g or more, fine powder of iron or alloy having an oxide layer on the surface may be used.

The particle diameter of the ferromagnetic fine particles used in the present invention,
It is preferably about 0.01 to 0.3 μm. The amount is preferably 0.5 to 200 times the weight of the phenols. Further, as described above, the ratio is preferably 4 to 100 times in consideration of the saturation magnetization value of the composite particles to be generated and the particle strength.

The ferromagnetic particles whose surface in the present invention has been subjected to hydrophobizing treatment are prepared by simply mixing the ferromagnetic particles and the hydrophobizing agent, or by mixing the ferromagnetic particles and the hydrophobizing agent in an aqueous solvent. It can be obtained by any method such as a method of adsorbing the hydrophobizing agent on the particle surface by mixing.

As the hydrophobizing agent, titanate-based or silane-based coupling agents having a hydrophobic group, silylating agents, silicone oils, various surfactants, and the like can be used.

As titanate coupling agents having a hydrophobic group, isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, bis (dioctyl pyrophosphate)
Oxyacetate titanate, bis (dioctyl pyrophosphate) ethylene titanate, and the like, as a silane coupling agent having a hydrophobic group, include vinyltrichlorosilane, vinyltriethoxysilane, vinyltris (β-
Methoxyethoxy) silane and the like, as a silylating agent,
Hexamethyldisilazane, trialkylalkoxysilane, trimethylethoxysilane and the like, and silicone oils include dimethyl silicone oil and methyl hydrogen silicone oil.

As the surfactant, any commercially available surfactant can be used. However, a surfactant having a functional group capable of binding to a hydroxyl group present on the surface of the ferromagnetic fine particles is desirable. Or an anionic one is desirable.

The treatment with the hydrophobizing agent is preferably performed so that the degree of hydrophobicity of the ferromagnetic fine particles is 20 to 60%. If it is less than 20% by weight, the hydrophobization of the ferromagnetic fine particles is not sufficient, and the conductive magnetic powder excellent in fluidity, which is the object of the present invention, cannot be obtained. If it exceeds 60% by weight,
It becomes difficult to obtain the composite particles having an average particle diameter of 1 to 10 μm in the present invention in a high yield.

As the basic catalyst used in the present invention, a basic catalyst used in ordinary resol resin production is used. For example, ammonia water, hexamethylenetetramine,
Examples thereof include alkylamines such as diethylenetriamine and polyethyleneimine. The molar ratio of these basic catalysts to phenols is preferably 0.04 or more in consideration of the particle size of the resulting composite particles.

Examples of the phenols used in the present invention include, in addition to phenol, m-cresol, p-tert-butylphenol, o-propylphenol, resorcinol, alkylphenols such as bisphenol A, and part or all of benzene nuclei or alkyl groups. Compounds having a phenolic hydroxyl group, such as halogenated phenols substituted with a chlorine atom or a bromine atom, may be mentioned, of which phenol is most preferred.

Examples of the aldehyde used in the present invention include formaldehyde and furfural in any form of formalin or paraaldehyde, and formaldehyde is particularly preferred. The molar ratio of the aldehydes to the phenols is preferably from 1 to 4, and particularly preferably from 1.2 to 3 in consideration of the particle size of the obtained composite particles. When the molar ratio of the aldehyde to the phenol is less than 1, it is difficult to form the composite particles, and even if it is formed, the resin tends to have low strength. On the other hand, when the molar ratio of aldehydes to phenols exceeds 4, unreacted aldehydes remaining in the aqueous medium after the reaction tend to increase.

The reaction in the present invention is carried out in an aqueous medium.In this case, the charged amount of water is such that the concentration of the ferromagnetic fine particles is 35 to 95.
It is preferably adjusted to be 50% by weight, especially 50 to 90% by weight. If the amount is less than 35% by weight, it becomes difficult to obtain the composite particles having an average particle diameter of 1 to 10 μm in the present invention in a high yield. If it exceeds 95% by weight, it is difficult to obtain the desired composite particles.

The reaction in the present invention is carried out under stirring at a heating rate of 0.5 to 1.5 ° C.
/ min, preferably at 0.8-1.2 ° C / min, gradually raise the temperature, the reaction temperature is 79-90 ° C, preferably 83-87 ° C for 60-150 ° C.
The reaction is carried out for minutes, preferably 80 to 110 minutes. In such a reaction, a curing reaction proceeds simultaneously with the reaction to form a cured phenolic resin matrix. After reacting and curing as described above, the reaction product is cooled to 40 ° C. or lower, and an aqueous dispersion of composite particles in which ferromagnetic fine particles are uniformly dispersed in the cured phenol resin matrix is obtained.

Next, the aqueous dispersion is filtered, solid-liquid separated according to a conventional method such as centrifugation, and then washed and dried to obtain composite particles in which ferromagnetic fine particles are uniformly dispersed in a phenol resin matrix. .

In the reaction of the present invention, if necessary, a suspension stabilizer may be present. Examples of the suspension stabilizer include hydrophilic organic compounds such as carboxymethylcellulose and polyvinyl alcohol, fluorine compounds such as calcium fluoride, and water-insoluble inorganic salts such as calcium sulfate.

〔Example〕

Next, the present invention will be described with reference to Examples and Comparative Examples.

The average particle size in the following Examples and Comparative Examples is an average value of values measured for 200 particles from an optical microscope photograph. The bulk density was measured according to the method described in JIS K5101, and the saturation magnetization was measured using the vibration sample magnetometer VSM.
−3S-15 ”(made by Toei Kogyo Co., Ltd.
It is a value measured under e. The flow velocity is the composite particle 5
0 g was filled in a glass funnel (open part 75φ height 75mm, conical part inner diameter 6φ length 30mm length straight pipe part), the powder falling time (sec) when given a certain vibration was obtained, and the above composite particles were obtained. Of the powder was divided by the powder falling time.

Hydrophobicity, 0.2 g of ferromagnetic fine particles and 50 g of water were placed in a 50 cc Erlenmeyer flask, methanol was continuously added with stirring, and the ferromagnetic powder that had been liberated first began to precipitate,
The point of dispersion in the water-methanol mixed solution was defined as the end point. The amount of methanol used up to this point was determined, and the value was calculated by inserting it into the following equation.

Example 1 400 g of spherical magnetite having an average particle diameter of 0.24 μm was charged into a Henschel mixer, stirred well, and then a titanate-based coupling agent (Plenact TTS: manufactured by Ajinomoto Co., Inc.)
Add 2 g, raise the temperature to about 100 ° C, mix and stir well for about 30 minutes to treat.

Phenol 50g, 37% formalin 75g, hydrophobized magnetite 400g, 28%
Ammonia water 18g, water 150g (the concentration of ferromagnetic fine particles is 5
This corresponds to 7.7% by weight. ) Was added with stirring, raised to 85 ° C. in 40 minutes, reacted and cured at the same temperature for 180 minutes to produce composite particles composed of spherical magnetite and cured phenolic resin.

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 composite particles were washed with water and air-dried. Then, this was reduced under reduced pressure (5 mmH
g or less) to obtain spherical composite particles (hereinafter, referred to as composite particles A) dried at 50 to 60 ° C.

A scanning electron micrograph (× 1000) of the obtained composite particle A
0) is shown in FIG. 1 and its characteristics are shown in Table 2.

Examples 2 to 7, Comparative Example 1 Various types of ferromagnetic fine particles, type and amount of hydrophobizing agent, type and amount of basic catalyst, amount of phenols, amount of aldehydes, and amount of water varied Except that the composite particles were prepared in the same manner as in Example 1 (hereinafter, the composite particles obtained in Examples 2 to 7 and Comparative Example 1 were sequentially subjected to composite particles B to H).
That. ) Got.

The main production conditions at this time are shown in Table 1, and various properties of the composite particles are shown in Table 2.

Usage Example 25 parts by weight of each of the composite particles A to H obtained in the above Examples 1 to 7 and Comparative Example 1 were added to a commercially available magnetic toner 10
0 parts by weight to prepare a developer. Next, Example 1
Using a developer containing each of the composite particles A to G obtained in Nos. 1 to 7, using an electrophotographic copying machine using Se as a photoreceptor, a clear copy image without any white spots was obtained. was gotten. On the other hand, in each of the developers containing the composite particles H of Comparative Example 1, white spots called white spots were observed.

[Effect of the Invention] The magnetic powder according to the present invention is, as shown in the above-described embodiment,
The average particle diameter is 1 to 10 μm, the bulk density is 1.5 g / cm ³ or less, and the electric resistance is less than 10 ¹² Ωcm due to the increased content of the ferromagnetic fine particles. In particular, since it is a composite particle having a flowability of 10 ⁹ Ωcm or less and improved ferromagnetic fine particles, the most required electrostatic latent image developer at present. Suitable as conductive magnetic powder for use.

Further, according to the method of the present invention, it is easy to control the average particle diameter of the composite particles to be produced, so that classification is not required, and composite particles having an average particle diameter of 0.1 to 10 μm are obtained in high yield. This is extremely useful industrially and economically.

The magnetic powder according to the present invention is used not only for electrostatic latent image developers but also for general applications as magnetic composite particles, that is, toners, paints, coloring agents such as inks, column fillers, and the like. It can be expected to be used in many fields such as radio wave absorbers and vibration dampers.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph (× 10000) showing the particle structure of the composite particles according to the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 9/083 G03G 9/107

Claims (2)

(57) [Claims] Claims: 1. A ferromagnetic fine particle whose surface has been subjected to a hydrophobic treatment and a cured phenol resin, having an average particle diameter of 1 to 10 μm, a bulk density of 1.5 g / cm ³ or less, and Conductive magnetic powder for an electrostatic latent image developer comprising composite particles having a content of the ferromagnetic fine particles of 80 to 99% by weight. 2. A composite particle comprising a ferromagnetic fine particle and a phenol resin cured by reacting and curing a phenol and an aldehyde in an aqueous medium in the presence of a ferromagnetic fine particle and a basic catalyst. 2. The method for producing a conductive magnetic powder for an electrostatic latent image developer according to claim 1, wherein the ferromagnetic fine particles are formed by using ferromagnetic fine particles whose surface is subjected to a hydrophobic treatment.