JPH0486749A - Magnetic carrier for electrophotography - Google Patents

Abstract

PURPOSE:To provide the carrier which has a small bulk density, large saturation magnetization and can be controlled in electrostatic charge quantity by consisting this carrier of ferromagnetic fine particles and a cured phenolic resin and coating the particle surfaces of specific composite particles with one or >= 2 kinds of the resins selected from an epoxy resin, etc. CONSTITUTION:This carrier consists of the feromagnetic fine particles and the cured phenolic resin and has 10 to 1000 mum number average particle size and <= 2.0 g/cm<3> bulk density. In addition, the particle surface of the composite particles having 80 to 99 wt.% content of the ferromagnetic fine particles are coated with one or >= 2 kinds of the resins selected from the epoxy resin, polyester resin, styrene resin, silicon resin, and fluororesin. This carrier has the small bulk density and has the large saturation magnetization as the content of the magnetic particles in high. In addition, the electrostatic charge quantity is freely controllable by the kinds, etc., of the resin, with which the particle surfaces of the composite particles are coated.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention has a particle surface having a small bulk density, a large saturation magnetization, and a controlled amount of charge. The present invention relates to a magnetic carrier for electrophotography consisting of composite particles of ferromagnetic fine particles and hardened phenol resin coated with one or more resins selected from the group consisting of resins, silicone resins, and fluororesins. .

[Conventional technology]

In electrophotography, selenium, OPC (organic semiconductor)
Using a photoconductive material such as , α-5i, etc. as a photoreceptor, an electrostatic latent image is formed by various means, and this latent image is subjected to VRT using a magnetic brush development method or the like in a manner opposite to the polarity of the latent image. Generally, a method is adopted in which toner is attached by electrostatic force and visualized.

In this development process, carrier particles called carriers are used to apply an appropriate amount of positive or negative electricity to the toner by triboelectric charging, and by using magnetic force, the toner is transferred through a developing sleeve containing a built-in magnet. The toner is conveyed to a development area near the surface of the photoreceptor where a latent image has been formed.

In recent years, as copying equipment has become faster, more continuous, and more sophisticated, there has been a strong demand for improved characteristics of carriers used therein.

That is, the primary characteristics of the carrier are that it has a small bulk density (and a large saturation magnetization).

If the bulk density of the carrier is large, a large driving force is required for agitation in the developing machine, resulting in significant mechanical wear and tear, resulting in so-called spent toner, deterioration of the chargeability of the carrier itself, and damage to the photoreceptor. Therefore, it is strongly required that the bulk density be small.

In addition, if the saturation magnetization is small, the magnetic adhesion of the carrier to the developing sleeve will be weak, causing the carrier to easily scatter from the developing sleeve and adhere to the photoreceptor. requested.

Regarding the amount of charge, toner is required to have an appropriate amount of charge that is compatible with the developing equipment in order to form a clear image. It is strongly required that the amount of charge of the carrier, which has the role of imparting , can be freely controlled as desired.

This fact is explained in Japanese Patent Application Laid-Open No. 60-458, ``The role of the carrier during development is to impart accurate triboelectric charging properties and appropriate charges to the toner, and to re-electrostatically charge the toner adhering to the image area.'' The objective is to remove the particles by suction and form a clear image.''

Conventionally, as magnetic carriers, iron powder carriers, ferrite carriers, binder type carriers (resin particles in which magnetic fine particles are dispersed), etc. have been developed and put into practical use.

[Problem to be solved by the invention]

Although there is currently a demand for magnetic carriers with low bulk density, large saturation magnetization, and a controlled amount of charge, a magnetic carrier that satisfactorily satisfies these characteristics has not yet been obtained. Not yet.

That is, iron powder carriers have flake-like, sponge-like, and spherical shapes, but have a true specific gravity of 7 to 8,
The bulk density is also as high as 3 g/d to 4 g/d.

In addition, the ferrite carrier is spherical and has a true specific gravity of 4.
．． 5 to 5.5, and the bulk density is about 2 g/cj to 3 g/cd, so the weight, which is a drawback of iron powder carriers, can be solved to some extent, but the rotation of the developing sleeve or the magnet in the sleeve It is not yet sufficient to support large numbers of high-speed copying machines, high-speed laser beam printers for general-purpose computers, and the like.

Binder-type carriers have a small bulk density of less than 28 mm, but as described in Japanese Patent Publication No. 59-24416, after melting and mixing magnetic fine powder and insulating resin, Since it is manufactured by cooling and pulverizing the mixture, the content of fine magnetic powder is 8.
It has a low magnetization value of 0% by weight or less.

Therefore, the technical object of the present invention is to obtain a magnetic carrier having a low bulk density, a large saturation magnetization, and a controlled amount of charge.

[Means to solve problems]

The above technical problem can be achieved by the present invention as follows.

That is, the present invention is composed of ferromagnetic fine particles and hardened phenol resin, has a number average particle diameter of 10 to 1000 μm, has a bulk density of 2.0 g/d or less, and has the ferromagnetic The particle surface of the composite particle having a content of 80 to 99% by weight of body fine particles is coated with one or more resins selected from epoxy resin, polyester resin, styrene resin, silicone resin, and fluorine resin. This is a magnetic carrier for electrophotography consisting of:

[For production]

First, the most important point in the present invention is that it is made of ferromagnetic fine particles and hardened phenol resin, has a number average particle diameter of 10 to 1000 μm, and has a bulk density of 2.0 g/c.
j or less, and the content of the ferromagnetic fine particles is 8.
0 to 99% by weight of the particle surface of the composite particles is coated with one or more resins selected from epoxy resins, polyester resins, styrene resins, silicone resins, and fluorine resins. Magnetic carriers for electrophotography have a large saturation magnetization due to their low bulk density and high content of magnetic particles. The fact is that the amount of charge can be freely controlled depending on the type, etc.

The magnetic carrier according to the present invention will be explained below.

First, the number average particle diameter of the composite particles consisting of ferromagnetic fine particles and hardened phenol resin in the present invention is 10 μm.
m to 1000 μm. Number average particle size is 10
If the diameter is less than 1000 μm, it is difficult to eliminate carrier adhesion to the photoreceptor, whereas if the diameter is less than 1000 μm,
It becomes impossible to obtain a clear image. In particular, when seeking high image quality, the range is preferably from 30 μm to 200 μm, and more preferably from 30 μm to 100 μm.

Next, the bulk density of the composite particles in the present invention is 2.0
It is below God. There is no particular restriction on the lower limit of bulk density, but
Practically, it is about 1.0 g/cj. A carrier with a low bulk density can be expected to provide higher image quality. It is thought that the bulk density of the carrier corresponds to the bulk density of the so-called "ears" of the carrier when they are formed along the lines of magnetic force on the developing sleeve.
It is thought that if the value is low, the ears can move softly and freely, resulting in high image quality.

Further, the composite particles in the present invention have a curved particle surface, and include spherical particles, elliptic spherical particles, flat disk-shaped particles, and irregular particles with complicated curved surfaces. Since both have curved particle surfaces, the contact area between carrier particles is small and they exhibit excellent fluidity. Among these, spherical particles are preferable because they have the best fluidity, have less shape distortion, and tend to have high particle strength.

Furthermore, the content of the ferromagnetic fine particles in the composite particles of the present invention is 80% by weight to 99% by weight. When the content of the ferromagnetic fine particles is less than 80% by weight, the saturation magnetization value becomes small, and when it exceeds 99% by weight, the binding between the ferromagnetic fine particles by the phenol resin tends to become weak. Considering the strength of the composite particles, the content is preferably 97% by weight or less. In the present invention, the reason why the content of ferromagnetic fine particles can be increased in this way is not clear, but since the curing reaction proceeds at the same time as the reaction, a small amount of phenol resin is used to firmly bind the ferromagnetic fine particles to each other. It is presumed that this is because it is possible to

Such composite particles in the present invention have a particle size of about 40 eg+
It has a saturation magnetization of u/g to 150 emu/g. 40
If the value is less than emu/g, the carrier tends to adhere to the photoreceptor, while if it exceeds 150 emu/g, it is difficult to obtain a value since no practical ferromagnetic fine powder is known. The saturation magnetization of conventionally known ferrite carriers is said to be about 70 esu/g at most (
“Fundamentals and Applications of Electrophotographic Technology J” published by Corona Publishing, 1988
In the case of the composite particles of the present invention, a large saturation magnetization of 70 emu/g or more can be easily obtained by increasing the content of fine ferrite powder.

Examples of ferromagnetic particles include magnetite, spinel ferrite such as gamma iron oxide, metals other than iron (Mn, Ni
Magnetobrambite-type ferrite such as spinel ferrite and barium ferrite containing one or more types of Zns, Mg, Cu, etc.), fine particle powder of iron or alloy having an oxide layer on the surface can be used. Its shape may be granular, spherical, or acicular; in particular,
If high magnetization is required, ferromagnetic fine particles such as iron can be used, but in consideration of chemical stability, magnetite, magnetoblanbite-type ferrite such as spinel ferrite containing gamma iron oxide, barium ferrite, etc. By appropriately selecting the type and content of the ferromagnetic fine particle powder, it is possible to obtain composite particles having a desired saturation magnetization. For example, when trying to obtain a magnetization of 40 to 70 e■u/H, magnetoblanbite ferrite such as barium ferrite or spinel ferrite may be used, and a high magnetization of about 70 to 10100 e/g may be used. If desired, magnetite or spinel ferrite containing Zn may be used. Furthermore, 1
When trying to obtain high magnetization of 0100e/g or more,
Fine particle powder of iron or alloy having an oxide layer on the surface may be used.

As the resin coating the particle surface of the composite particles, one or more resins selected from well-known epoxy resins, polyester resins, styrene resins, silicone resins, and fluororesins can be used. The amount of charge can be changed mainly by changing the type of resin.

The coating amount of the resin is 0.05% by weight or more based on the composite particles. If it is less than 0.05% by weight, the coating tends to be insufficient and non-uniform, and the amount of charge aimed at in the present invention cannot be achieved. It becomes difficult to control freely.

Moreover, if the amount of coating is too large, the content of ferromagnetic fine particles in the composite particles decreases, making it impossible to obtain a large magnetization value. Preferably it is 0.1 to 10% by weight.

Below, a method for manufacturing a magnetic carrier according to the present invention will be explained.

First, in the method for producing composite particles of the present invention,
Phenols and aldehydes are reacted in an aqueous medium in the presence of a basic catalyst, ferromagnetic particles, and a suspension stabilizer.

In addition to phenol, the phenols used here include alkylphenols such as -cresol, P-tert-phytylphenol, 0-propylphenol, resorcinol, and bisphenol A, and part or all of the benzene nucleus or alkyl group. Examples include compounds having a phenolic hydroxyl group such as halogenated phenols in which is substituted with a chlorine atom or a bromine atom, and among these, phenol is most preferred. When a compound other than phenol is used as the phenol, it may be difficult to form particles, or even if particles are formed, they may have an irregular shape, so phenol is most preferable from the viewpoint of shape.

The aldehydes used in the method for producing composite particles of the present invention include formaldehyde in the form of formalin or paraformaldehyde, furfural, and the like, with formaldehyde being particularly preferred. The molar ratio of aldehydes to phenol is 1
-2 is preferable, and 1.1-1.6 is especially preferable. If the molar ratio of aldehydes to phenols is less than 1, particles tend to be difficult to form, or even if they are formed, the strength of the particles tends to be weak because it is difficult for the resin to harden. When the molar ratio of aldehydes to phenols is greater than 2, the amount of unreacted aldehydes remaining in the aqueous medium after the reaction tends to increase.

Next, as the basic catalyst used in the method for producing composite particles according to the present invention, a basic catalyst used in normal production of resol resins is used. For example, ammonia water,
Examples include hexamethylenetetramine and alkylamines such as dimethylamine, diethyltriamine, and polyethyleneimine.

The molar ratio of these basic catalysts to phenols is 0
．． 02 to 0.3 is preferable.

When the phenols and aldehydes are reacted in the presence of a basic catalyst, the ferromagnetic particles to be allowed to coexist include magnetite, spinel ferrite containing gamma iron oxide, and magnetobrambite ferrite such as barium ferrite. A fine powder of iron or alloy having an oxide layer on its surface is preferable. The amount is preferably 0.5 to 200 times the weight of the phenols. moreover,
As mentioned above, in consideration of the saturation magnetization value of the composite particles to be produced and the strength of the particles, it is more preferable that it is 4 to 100 times as large.

Furthermore, the particle diameter of the ferromagnetic fine particles is 0.01
It is desirable that the mist is ~10 μm, and in consideration of the dispersion of the fine particles in the aqueous medium and the strength of the composite particles produced, it is preferably 0.05 μm to 5 μm.

Furthermore, the suspension stabilizers used in the method for producing composite particles in the present invention include carboxymethyl cellulose,
Examples include hydrophilic organic compounds such as polyvinyl alcohol, fluorine compounds such as calcium fluoride, and inorganic salts that are substantially insoluble in water such as calcium sulfate.
Considering the dispersion of ferromagnetic fine particles inside the phenolic resin matrix, calcium fluoride is preferable. When a suspension stabilizer other than calcium fluoride is used, depending on the conditions, it may be difficult for the ferromagnetic particles mentioned above to disperse into the phenolic resin matrix, and particles with irregular shapes tend to be produced. .

The amount of suspension stabilizer added is as follows:
It is preferably 0.2 to 10% by weight, more preferably 0.5 to 3.5% by weight. If the amount of suspension stabilizer added to the phenols is less than 0.2% by weight,
There is a tendency for irregularly shaped particles to be produced, while when the amount added is 1
When the amount exceeds 0% by weight, the amount of suspension stabilizer such as calcium fluoride remaining on the surface of the composite particles tends to increase.

In addition, to add inorganic salts that are substantially insoluble in water,
Substantially water-insoluble inorganic salts as described above may be added directly, or two or more water-soluble inorganic salts may be added such that such substantially water-insoluble inorganic salts are produced during the reaction. It's okay.

For example, instead of a fluorine compound of calcium, one of the water-soluble inorganic salts is at least one selected from the group consisting of sodium fluoride, calcium fluoride, ammonium fluoride, etc., and the other is a chloride, sulfate, or nitrate of calcium. At least one member selected from the group consisting of: may be added to generate a fluorine compound of calcium during the reaction.

The reaction in the method for producing composite particles in the present invention is carried out in an aqueous medium, and in this case, the amount of water charged is preferably such that the solid content concentration of the carrier is, for example, 30 to 95% by weight. In particular, it is desirable that the content be 60 to 90% by weight.

The reaction was carried out at a temperature increase rate of 0.5 to 1.5°C/in under stirring.
, preferably 0.8 to 1.2°C/win, and the reaction temperature is 70 to 90°C, preferably 83 to 8°C.
React at 7°C for 60-150 minutes, preferably 80-110 minutes. In such a reaction, a gelation reaction proceeds simultaneously with the reaction, and a gelled phenolic resin matrix is formed. After reacting and gelling in this manner, the reactant is cooled to below 40°C to obtain an aqueous dispersion of spherical composite particles in which ferromagnetic fine particles are uniformly dispersed in a hardened phenolic resin matrix. It will be done.

Next, the aqueous dispersion is separated into solid and liquid by conventional methods such as oven treatment or centrifugation, and then washed and dried.The ferromagnetic fine particles are uniformly dispersed in the phenolic resin matrix, and the particle surfaces are curved. Composite particles having a shape are obtained.

The resin coating the composite particles in the present invention is one or more resins selected from epoxy resins, polyester resins, styrene resins, silicone resins, and fluororesins.

Epoxy resins include bisphenol A epoxy resins and novolak epoxy resins, and polyester resins are obtained by condensation polymerization of polyols such as ethylene glycol and triethylene glycol with dicarboxylic acids such as maleic acid and itaconic acid. Styrene resins include styrene-acrylic copolymers such as polystyrene and styrene-butyl acrylate, styrene-butadiene copolymers, styrene-maleic anhydride copolymers, etc.; silicone resins include styrene-maleic anhydride copolymers, etc.; Silicone resins such as curable silicone resins and room temperature curable silicone resins, silicone oils, or silane coupling agents are used as fluororesins, such as polytetrafluoroethylene, polyvinylidene fluoride, and tetrafluoroethylene-ethylene copolymers. Containing resin etc. can be used.

Coating with the resin in the present invention can be done by a well-known method, for example, a method of spraying the resin onto the composite particles using a spray dryer, a method of dry mixing the composite particles and the resin using a Henschel mixer high-speed mixer, etc. Any method may be used, such as a method of impregnating the composite particles into a solvent containing a resin.

[Example] Next, the present invention will be specifically explained by using Examples and Comparative Examples.

Note that the number average particle diameter in the present invention is the average value of values measured for 200 particles from optical micrographs. The bulk density was measured according to the method described in JIS K5101, and the saturation magnetization was measured using a “vibrating sample magnetometer VSM-3S”.
-15J (manufactured by Toi Kogyo ■) using an external magnetic field of 10
It is shown as a value measured under kOe.

The charge amount of the composite particles whose particle surfaces are coated with resin is 95 parts by weight of the composite particles and commercially available toner CL.
Blow off 20 g of a mixture with 5 parts by weight of C-200 Black (product name) (manufactured by Canon ■) using a charge measuring device MO.
The value is expressed as a value per g based on the value A [μC] measured using DEL TB-200 (manufactured by Toshiba Chemical ■).

Further, the charge amount of the toner in the above mixture was similarly calculated as a value per g from the above A [μC].

The shape of the composite particles is the result of observation using a scanning electron microscope S-800 (manufactured by Hitachi).

<Generation of composite particles> Examples 1 to 3; Example 1 If 50 g of phenol was added to the Mitsuro flask, 37
% formalin 65g, spherical magnetite 400g with an average particle size of 0.24μm, 28% ammonia water 7.8g,
Calcium fluoride 1. Add Og and 50g of water with stirring, raise the temperature to 85°C in 40 minutes, and heat to 180°C at the same temperature.
The mixture was reacted and cured for minutes to produce composite particles consisting of spherical magnetite and cured phenolic resin.

Next, the contents in the flask were cooled to 30°C and 0°5!
After adding water, the supernatant liquid was removed, and the spherical particles in the lower layer were further washed with water and air-dried. Next, this was heated under reduced pressure (5
m@Hg or less) at 50 to 60'C to obtain composite particles (hereinafter referred to as composite particles A).

The properties of the obtained composite particles A are as shown in Table 2, and the shape is shown in the scanning electron micrograph (X6
00), it had a spherical shape.

Example 2 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 instead of 7.8 g of 28% aqueous ammonia as the basic catalyst.
Composite particles (hereinafter referred to as composite particles B) were obtained.

The properties of the obtained composite particles are shown in Table 2,
Moreover, the shape was spherical as a result of scanning electron microscopy observation.

Example 3 Polyhedral magnetite particles 450 as ferromagnetic fine particles
Composite particles (hereinafter referred to as composite particles C) were obtained by performing the reaction, curing, and post-treatment in the same manner as in Example 1, except that g was used.

The properties of the obtained composite particles are shown in Table 2,
Moreover, the shape was spherical as a result of scanning electron microscopy observation.

Coating with resin> Examples 4 to 9; Example 4 Composite particles A1 were placed in a Henschel mixer under a nitrogen stream.
and 30 g of a styrene resin (Himer 5B-75; manufactured by Sanyo Chemical Co., Ltd.) were added to the solution, and the temperature was raised to 120° C. with stirring, and the mixture was stirred at the same temperature for 1 hour.

The coating with the styrene resin was found to be uniform and dense as a result of observation using a scanning electron photomicroscope.

Table 1 shows the properties of the composite particles coated with the obtained styrene resin.

The amount of coating with the styrene resin was calculated from magnetization measurements, and was 2.9% by weight based on the composite particles.

Examples 5 to 9 Composite particles coated with a resin were obtained in the same manner as in Example 4, except that the type of composite particles, the type of resin, and the mixing amount were varied. Table 3 shows the main conditions and characteristics at this time.

For reference, the amount of charge of the toner is also listed in Table 3.

〔Effect of the invention〕

A composite of ferromagnetic fine particles and phenol resin, the particle surface of which is coated with one or more resins selected from epoxy resin, polyester resin, styrene resin, silicone resin, and fluororesin according to the present invention In a magnetic carrier made of particles, due to the small bulk density of the composite particles and the high content of ferromagnetic fine particles as described above, the magnetic carrier exhibits as large a magnetization value as possible, and Since the amount of charge can be freely controlled by coating with resin, it is suitable as a magnetic carrier for electrophotography.

[Brief explanation of drawings]

FIG. 1 is a scanning electron micrograph (X 600) showing the particle structure of the composite particles obtained in Example 1.

Claims (1)

[Claims] (1) It consists of ferromagnetic fine particles and hardened phenolic resin, has a number average particle diameter of 10 to 1000 μm, and has a bulk density of 2.0 g/cm^2 or less, and the ferromagnetic fine particles have a The particle surface of the composite particle having a content of 80 to 99% by weight is coated with one or more resins selected from epoxy resin, polyester resin, styrene resin, silicone resin, and fluororesin. A magnetic carrier for electrophotography characterized by: