JP2779976B2 - Magnetic carrier for electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a resin composition having a low bulk density, a large saturation magnetization, and a controlled charge amount on the surface of an epoxy resin, polyester resin, or styrene. The present invention relates to a magnetic carrier for electrophotography comprising composite particles of ferromagnetic fine particles coated with one or more resins selected from a series of resins, silicon resins and fluororesins and a cured phenol resin. .

[Conventional technology]

In electrophotography, a photoconductive substance such as selenium, OPC (organic semiconductor), α-Si is used as a photoreceptor, and an electrostatic latent image is formed by various means. In general, a method in which a toner charged in a direction opposite to the polarity of a latent image is attached by electrostatic power to visualize the image.

In this development step, carrier particles called carriers are used, and an appropriate amount of positive or negative electricity is applied to the toner by triboelectric charging, and through a developing sleeve containing a magnet by utilizing a magnetic force, The toner is transported to a developing area near the surface of the photoconductor on which the latent image has been formed.

With the approximation, high speed, continuity, and high performance of copying machines, there is a strong demand for improved characteristics of carriers used therein.

That is, as the characteristics of the carrier, the bulk density is small,
In addition, it has a large saturation magnetization.

When the bulk density of the carrier is large, a large driving force is required for stirring in the developing machine, so that mechanical wear is large, so-called spent, deterioration of chargeability of the carrier itself, and damage of the photoconductor. Therefore, a low bulk density is strongly required.

Further, when the saturation magnetization is small, the magnetic adhesion of the carrier to the developing sleeve is weakened, and there is a problem that the carrier is easily scattered from the developing sleeve and adheres to the photoreceptor. Has been requested.

Speaking of the charge amount, the toner is required to have an appropriate charge amount suitable for the developing device in order to form a clear image, but in order to impart a desired charge amount to the toner, the charge amount is required. It is strongly required that the charge amount of the carrier having the role of imparting the color can be freely controlled as desired.

This fact is based on the fact that the role of the carrier during development is described in JP-A-60-458: (1) The toner is provided with accurate triboelectric charging characteristics and an appropriate charge, and the toner adhering to the image area is again electrostatically charged. And removing it by suction to form a clear image. "

Conventionally, as a magnetic carrier, an iron powder carrier, a ferrite carrier, a binder type carrier (resin particles in which magnetic fine particles are dispersed) and the like have been developed and put into practical use.

[Problems to be solved by the invention]

A magnetic carrier having a low bulk density, a large saturation magnetization, and a controlled charge amount is the most required at present, but a magnetic carrier that sufficiently satisfies these characteristics has not yet been obtained.

That is, iron powder carriers include flakes, sponges, and spheres, but have a true specific gravity of 7 to 8 and a bulk density of 3 g / cm ³ to 4 g / cm ^3. .

The ferrite carrier is spherical, and its true specific gravity is
4.5 from is about 5.5, since the bulk density is about 3 g / cm ³ from 2 g / cm ^3, but the weight is a disadvantage of the iron powder carrier may to some extent overcome the rotational speed of the magnet in the developing sleeve or the sleeve However, it is not enough to support a high-speed copier or a high-speed laser beam printer of a general-purpose computer.

The binder-type carrier, albeit one 2 g / cm ³ and less than the bulk density is small, as described in JP-B-59-24416, after the melt mixing a magnetic fine powder and an insulating resin, It is manufactured by cooling and pulverizing the molten mixture, so the content of magnetic fine powder is 80% by weight.
The following are few, and the magnetization value is low.

Accordingly, an object of the present invention is to provide a magnetic carrier having a low bulk density, a large saturation magnetization, and a controlled charge amount.

[Means for solving the problem]

The technical problem can be achieved by the present invention as described below.

That is, the present invention comprises a phenol resin cured by reacting ferromagnetic fine particles and aldehydes with phenols using a molar ratio of 1 to 2 to react,
Number average particle diameter is 10 ~ 1000μm, bulk density is 2.0g / c
m ³ or less, and the content of the ferromagnetic fine particles is 80
An electrophotograph comprising the surface of the composite particles of up to 99% by weight coated with one or more resins selected from epoxy resins, polyester resins, styrenic resins, silicon resins and fluororesins. Magnetic carrier.

[Action]

First, the most important point in the present invention is that the ferromagnetic fine particles and the aldehyde are mixed in a molar ratio of 1 to 2 with respect to the phenol.
Phenolic resin cured by reacting in the range of, the number average particle diameter is 10 to 1000 μm, the bulk density is 2.0 g / cm ³ or less, and the ferromagnetic fine particles The surface of the composite particles having a content of 80 to 99% by weight is one of a resin selected from an epoxy resin, a polyester resin, a styrene resin, a silicon resin and a fluororesin.
The magnetic carrier for electrophotography consisting of being coated with one or more species has a low bulk density, and has a large saturation magnetization due to a high content of magnetic particles, and This is a fact that the charge amount can be freely controlled depending on the type of resin coated on the particle surface of the composite particles.

Hereinafter, the magnetic carrier according to the present invention will be described.

First, the number average particle diameter of the composite particles composed of the phenol resin cured by reacting the ferromagnetic fine particles and the aldehyde with the phenol in the present invention in a molar ratio of 1 to 2 is 10 μm. From 1000 μm. When the number average particle diameter is less than 10 μm, it is difficult to eliminate the adhesion of the carrier to the photoreceptor. On the other hand, when it exceeds 1000 μm, a clear image cannot be obtained. In particular, when high image quality is required, 30 μm to 20 μm
The range is preferably 0 μm, more preferably 30 μm to 1 μm.
It is in the range of 00 μm.

Next, the bulk density of the composite particles in the present invention is 2.0 g / c
m ³ or less. The lower limit of the bulk density is not particularly limited, but is practically about 1.0 g / cm ³ . Those having a low bulk density can be expected as carriers that provide higher image quality. The bulk density of the carrier is determined by the current "spike" of the carrier along the lines of magnetic force on the sleeve.
It is considered that this corresponds to the bulk density of the panicle. If the value is low, the panicle can be moved freely and freely, and as a result, high image quality can be obtained.

Further, the composite particles in the present invention have a curved surface on the particle surface, and may be spherical, elliptical, flat disk-shaped, or even with a complicated curved surface. In each case, since the particle surface has a curved surface shape, the contact area between the carrier particles is small and excellent fluidity is exhibited. Of these, the spherical shape has the best fluidity, the particles have less shape distortion, and the particle strength tends to be high.
preferable.

Furthermore, the content of the ferromagnetic fine particles of the composite particles in the present invention is from 80% by weight to 99% by weight. When the content of the ferromagnetic 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 particles by the phenol resin tends to be 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 the ferromagnetic fine particles can be increased in this way is not clear, but since the curing reaction proceeds simultaneously with the reaction, the ferromagnetic fine particles are firmly fixed with a small amount of phenol resin. It is estimated that it is possible.

Such a composite particle in the present invention has a particle size of about 40 emu / g.
From 150 emu / g. At less than 40 emu / g, the carrier tends to adhere to the photoconductor, while 150 emu / g
A value exceeding / g is difficult to obtain because no practical powder is known as ferromagnetic fine powder. Conventionally, the saturation magnetization of a well-known ferrite carrier is at most about 70 emu / g (Corona Co., Ltd., “Basic and Application of Electrophotography”, p. 481, 1988), but in the case of the composite particles in the present invention, By increasing the content of the ferrite fine powder, a large saturation magnetization of 70 emu / g or more can be easily obtained.

Ferromagnetic fine particles include magnetite, spinel ferrite such as gamma iron oxide, and metals other than iron (Mn, Ni, Z
n, Mg, Cu, etc.), spinel ferrite, magnetoplumbite type ferrite such as barium ferrite, etc., and fine powder of iron or alloy having an oxide layer on the surface. The shape may be any of a granular shape, a spherical shape, and a needle shape. In particular, when high magnetization is required, ferromagnetic fine particles such as iron can be used, but in consideration of chemical stability, magnetite,
It is preferable to use ferromagnetic fine particles of magnetoplumbite ferrite such as spinel ferrite or barium ferrite containing gamma iron oxide. 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-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 or so, 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.

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, silicon resins, and fluororesins can be used, and the charge amount is changed mainly by changing the type of the resin. be able to.

The coating amount of the resin is 0.05% by weight or more based on the composite particles. If the resin amount is less than 0.05% by weight, the coating tends to be insufficient and non-uniform, and the charge amount intended in the present invention is freely controlled. It becomes difficult. On the other hand, if the coating amount is too large, the content of the ferromagnetic fine particles in the composite particles decreases, and a large magnetization value cannot be obtained. Preferably it is 0.1 to 10% by weight.

Hereinafter, a method for producing a magnetic carrier according to the present invention will be described.

First, in the method for producing composite particles according to 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.

As the phenols used here, in addition to phenol, m-cresol, p-tert-butylphenol,
Alkyl phenols such as o-propylphenol, resorcinol, bisphenol A, and compounds having a phenolic hydroxyl group such as halogenated phenols in which a part or all of a benzene nucleus or an alkyl group is substituted with a chlorine atom or a bromine atom are exemplified. Of these, phenol is most preferred. When a compound other than phenol is used as the phenol, particles may be difficult to form, or even if particles are formed, the particles may have an irregular shape. Therefore, phenol is most preferable in consideration of shape.

Examples of the aldehyde used in the method for producing composite particles according to the present invention include formaldehyde and furfural in either form of formalin or paraformaldehyde, and formaldehyde is particularly preferred. The molar ratio of aldehydes to phenol is
1-2 are preferable, and especially preferable are 1.1-1.6. If the molar ratio of the aldehydes to the phenols is less than 1, particles are hardly generated, or even if they are formed, the curing of the resin is difficult to progress, so that the strength of the generated particles tends to be weak. If the molar ratio of aldehydes to phenols is greater than 2, unreacted aldehydes remaining in the aqueous medium after the reaction tend 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 ordinary production of a resol 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 from 0.02 to 0.3.

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

Furthermore, the particle diameter of the ferromagnetic fine particles is 0.01 to
It is preferably 10 μm, taking into account the dispersion of the fine particles in an aqueous medium and the strength of the composite particles to be formed, which is 0.
It is preferably from 05 to 5 μm.

Further, the suspension stabilizer used in the method for producing composite particles according to the present invention includes carboxymethyl cellulose, a hydrophilic organic compound such as polyvinyl alcohol, a fluorine compound such as calcium fluoride, and a substantial compound such as calcium sulfate. Inorganic salts and the like which are insoluble in water can be mentioned, but calcium fluoride is preferable in consideration of the dispersion of the ferromagnetic fine particles inside the phenol resin matrix.
When a suspension stabilizer other than calcium fluoride is used, the ferromagnetic particles described above may be difficult to disperse inside the phenolic resin matrix depending on the conditions,
Irregular shaped particles tend to form.

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

In order to add the inorganic salts substantially insoluble in water, the inorganic salts substantially insoluble in water as described above may be directly added, or the inorganic salts substantially insoluble in water during the reaction. May be added to produce two or more water-soluble inorganic salts. For example, in place of a fluorine compound of calcium, one of water-soluble inorganic salts is at least one selected from the group consisting of sodium fluoride, calcium fluoride, and ammonium fluoride, and the other is calcium chloride, sulfate, and nitrate. And at least one member selected from the group consisting of the above may be added to generate a fluorine compound of calcium during the reaction.

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

During the reaction, the temperature is gradually increased at a rate of 0.5 to 1.5 ° C./min, preferably 0.8 to 1.2 ° C./min under stirring, and the reaction temperature is increased to 70 ° C.
The reaction is carried out at 9090 ° 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, and a matrix of the gelled phenol resin is formed. In this way the reaction
After the gelling, the reaction product is cooled to 40 ° C. or lower to obtain an aqueous dispersion of spherical composite particles in which ferromagnetic fine particles are uniformly dispersed in a hardened phenol resin matrix.

Next, the aqueous dispersion is filtered, solid-liquid separated according to a conventional method such as centrifugation, and then washed and dried.The ferromagnetic fine particles are uniformly dispersed in the phenol resin matrix,
Composite particles having a curved surface are obtained.

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

Examples of the epoxy resin include bisphenol A-based epoxy resins and novolak-based epoxy resins, and examples of the polyester resin include polyols such as ethylene glycol and triethylene glycol and dicarboxylic acids such as maleic acid and itaconic acid, which are obtained by condensation polymerization. Polyester resins and the like, as styrene resins, styrene-acryl copolymers such as polystyrene and styrene-butyl acrylate, styrene-butadiene copolymer, styrene-
Maleic anhydride copolymers and the like, as a silicon resin, a silicone resin such as a heat-curable silicone resin or a room temperature-curable silicone resin, a silicone oil or a silane coupling agent, and a fluorine resin as polytetrafluoroethylene, Fluorine-containing resins such as polyvinylidene fluoride and tetrafluoroethylene-ethylene copolymer can be used.

The coating with the resin in the present invention is performed by a known method, for example, a method of spraying the resin to the composite particles using a spray dryer, a method of dry-mixing the composite particles and the resin using a Henschel mixer, a high-speed mixer, or the like. Or a method of impregnating the composite particles into a solvent containing a resin.

〔Example〕

Next, the present invention will be specifically described with reference to examples and comparative columns.

In addition, the number average particle diameter in the present invention 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 a vibrating sample magnetometer VSM-31-15.
The values were measured using an external magnetic field of 10 kOe using a Toei Kogyo Co., Ltd.

The charge amount of the composite particles whose particle surfaces are coated with resin is 95 parts by weight of the composite particles and a commercially available toner CLC.
200 mg of a mixture with 5 parts by weight of -200 Black (trade name) (manufactured by Canon Inc.) is blow-off charge amount measuring machine MODEL TB
-200 (manufactured by Toshiba Chemical Corporation)
Converted value from [μc] to g Indicated by

Similarly, the charge amount of the toner in the mixture is calculated from the above-mentioned A [μc] by a conversion value per g. The value calculated as

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

<Formation of Composite Particles> Examples 1 to 3; Example 11 In the three-necked flask of Example 1, 50 g of phenol, 65 g of 37% formalin, and spherical magnetite 400 having an average particle diameter of 0.24 μm were placed.
g, 28% ammonia water 7.8g, calcium fluoride 1.0g, water 5
0 g was added with stirring, the temperature was raised to 85 ° C. in 40 minutes, and the reaction was carried out and cured at the same temperature for 180 minutes to produce composite particles composed of spherical magnetite and the cured phenol resin.

Next, the content in the flask was cooled to 30 ° C., water was added at 0.5, the supernatant was removed, and the spherical particles in the lower layer were washed with water and air-dried. Then, this was reduced under reduced pressure (5 mmH
g or less) to obtain composite particles (hereinafter, referred to as composite particles A).

Various properties of the obtained composite particle A are as shown in Table 2, and the shape thereof is shown in the scanning electron micrograph (×
As shown in (600), it was spherical.

Example 2 Instead of 7.8 g of 28% aqueous ammonia as a basic catalyst,
The 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 composite particles (hereinafter, referred to as composite particles B).

Various properties of the obtained composite particles are as shown in Table 2, and the shape thereof was determined by observation with a scanning electron microscope.
It was spherical.

Example 3 450 g of polyhedral magnetite particles as ferromagnetic fine particles
The reaction, curing and post-treatment were carried out in the same manner as in Example 1 except for using, to obtain composite particles (hereinafter, referred to as composite particles C).

Various properties of the obtained composite particles are as shown in Table 2, and the shape thereof was determined by observation with a scanning electron microscope.
It was spherical.

<Coating with Resin> Examples 4 to 9; Example 4 Composite particles A were placed in a Henschel mixer under a nitrogen stream.
1 kg and 30 g of a styrene-based resin (Hymer SB-75; manufactured by Sanyo Chemical Co., Ltd.) were added, and the temperature was increased to 120 ° C. while stirring.
The mixture was stirred at the same temperature for 1 hour.

As a result of observation with a scanning electrophotographic microscope, the coating with the styrene resin was uniform and dense.

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

The amount of coating with the styrene resin was 2.9% by weight with respect to the composite particles as a result of calculation based on the measurement of magnetization.

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 the composite particles, the type of the resin, and the mixing amount were variously changed. Table 3 shows the main conditions and various characteristics at this time.

 Table 3 also shows the charge amount of the toner for reference.

[Effect of the Invention] A ferromagnetic fine particle and a aldehyde, wherein the particle surface according to the present invention is coated with one or two or more resins selected from an epoxy resin, a polyester resin, a styrene resin, a silicon resin and a fluororesin. In a magnetic carrier composed of composite particles with a phenolic resin cured by reacting the phenols with phenols in a molar ratio of 1 to 2, the bulk density of the composite particles is small as described above. ,
And, due to the high content of ferromagnetic fine particles,
It is suitable as a magnetic carrier for electrophotography because it shows a magnetization value as large as possible and the charge amount can be freely controlled by coating with a resin.

[Brief description of the drawings]

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

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuo Fujioka 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Toda Kogyo Co., Ltd. (72) Yoshiaki Echigo 23, Uji Kozakura, Uji-shi, Kyoto Unitika Central Research Laboratory Co., Ltd. (72) Inventor Tsutomu Sakaida 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Central Research Laboratory Examiner Kenji Hara (56) References JP-A-63-228174 (JP, A) 63-241565 (JP, A) JP-A-58-136052 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/10

Claims (1)

(57) [Claims] 1. A phenol resin which is cured by reacting ferromagnetic fine particles and aldehydes with phenols in a molar ratio of 1 to 2 to form a phenol resin, and having a number average particle diameter of 10 to 1000 μm. In addition, the bulk density is 2.0 g / cm ³ or less, and the particle surface of the composite particles in which the content of the ferromagnetic fine particles is 80 to 99% by weight is an epoxy resin, a polyester resin, a styrene resin, A magnetic carrier for electrophotography, wherein the magnetic carrier is coated with one or more resins selected from a silicon resin and a fluorine resin.