JP2004151639A - Magnetic carrier for electrophotographic developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic carrier for electrophotographic developer, capable of forming a picture with no fogging and unevenness of picture. <P>SOLUTION: The magnetic carrier for electrophotographic developer is made of composite particles having an irregular shape of average particle size 10∼100μm which consists of planar magneto-plumbite type ferrite particle powder, particulate ferromagnetic iron compound particle powder and phenol resin. The total amount of the planar magneto-plumbite type ferrite particle powder and the particulate ferromagnetic iron compound particle powder which are included in the composite particles is 80∼99wt.%, the average particle size of planar magneto-plumbite type ferrite particle powder is 1.0∼3.0μm and the particle size ratio (ra/rb) of the average particle size (ra) of the planar magneto-plumbite type ferrite particle powder to the average particle size (rb) of the particulate ferromagnetic iron compound particle powder is 3.0-10.0. <P>COPYRIGHT: (C)2004,JPO

Description

【００９０】
【表２】

【００９１】
各実施例で得られた電子写真現像剤用磁性キャリアの粒子形状はいずれも、不定形であった。また、１万枚後の耐刷評価においても、良好な画像結果が得られた。比較例１で得られた電子写真現像剤用磁性キャリアは、図３に示す通り、球状の滑らかな表面を呈していた。
【００９２】
【発明の効果】
本発明に係る電子写真現像剤用磁性キャリアは、粒子形状が不定形であるので、滑らかなスリーブ上でのスリップが抑制され搬送性に優れているから、低温定着化に対応した良好な画像を得ることができる。
【図面の簡単な説明】
【図１】発明の実施の形態で得られた電子写真現像剤用磁性キャリアである。（２０００倍）
【図２】発明の実施の形態で得られた電子写真現像剤用磁性キャリアである。（５００倍）
【図３】比較例１で得られた電子写真現像剤用磁性キャリアである（２０００倍）。
【図４】電子写真現像剤用磁性キャリアのスパチュラ角と平均粒子径との関係を示すグラフである（●：実施の形態及び実施例、□：比較例）。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic carrier for an electrophotographic developer, and provides a magnetic carrier for an electrophotographic developer capable of forming an image free from fog and image unevenness.
[0002]
[Prior art]
As is well known, in electrophotography, a photoconductive substance such as selenium, OPC (organic semiconductor), α-Si, or the like is used as a photoreceptor, and an electrostatic latent image is formed by various means. Generally, a method is used in which a toner charged in a direction opposite to the polarity of a latent image is attached by electrostatic force using a brush developing method or the like to visualize the image.
[0003]
In this development step, a developer comprising a toner and a carrier is used, and carrier particles called a carrier apply an appropriate amount of positive or negative electricity to the toner by frictional charging, and use a magnetic force to form a magnet. The toner is conveyed to a development area near the surface of the photoconductor on which the latent image has been formed, through a built-in development sleeve.
[0004]
In recent years, the electrophotographic method has been widely used in copiers and printers, and it is desired that the electrophotographic method can handle various documents such as fine lines, small letters, photographs, and color originals. 2. Description of the Related Art As copiers and printers have higher functions, higher image quality, and higher speed, there is a demand for improvements in various characteristics as a developer used.
[0005]
In particular, high reliability is required for the carrier as the image becomes higher and the operation speed is increased. Therefore, it is necessary to extend the life of the carrier so that the charging performance of the carrier can be maintained for a long time.
[0006]
Conventionally, as a carrier used in the electrophotography, a ferrite carrier, an iron powder carrier, and a binder type carrier in which magnetic particle powder is dispersed in a binder resin are known.
[0007]
Ferrite carriers and iron powder carriers are usually used by coating the particle surface with a resin, but it is difficult to say that the adhesion between the particle surface and the coating resin is good, and the coating resin gradually peels off during use. This causes a change in the chargeability, resulting in problems such as image disturbance and carrier adhesion.
[0008]
On the other hand, a method of obtaining a binder-type carrier by kneading and grinding magnetic particles and a binder resin and a method of polymerizing magnetic particles and a resin are known. The magnetic carrier obtained by the kneading and pulverizing method is disclosed in Japanese Patent Application Laid-Open No. Hei 10-232512, "[0005] However, when a binder type carrier is used in combination with the above-described negatively charged toner, the following problems occur. ... A problem arises that sufficient chargeability for the negatively charged toner cannot be obtained even though a sufficient amount of the surface magnetic powder is confirmed, because the dispersibility of the magnetic powder in the binder resin is poor. This is considered to be due to the fact that the magnetic powder becomes uniform and is mixed during the production, or that the magnetic powder is agglomerated and contained in the carrier. When the content of the magnetic powder is increased in order to increase the particle size, the free magnetic powder easily adheres to the carrier particles due to a large difference in particle diameter from the carrier particles. Although it is difficult to remove easily by classification, if the accuracy of the classification process is increased by increasing the number of times of classification, etc., the problem due to the inclusion of the fine powder component can be solved. When the image is formed in a high-temperature and high-humidity (H / H) environment using such a carrier, the density of the image is reduced. There is also a problem that unevenness occurs. "(Page 2, Column 2, Lines 15 to 40), there is a problem that the content of the magnetic powder cannot be increased or the magnetic powder is released.
[0009]
However, the binder type carrier composed of spherical composite particles composed of magnetic particles and phenolic resin obtained by a method of polymerizing magnetic particles and a resin (for example, JP-A-2-220068) is the ferrite carrier. Compared with iron powder carriers, the adhesiveness to the coating resin is several times better, and the problem of peeling of the coating resin during use hardly occurs.
[0010]
In order to reduce the environmental load required in recent years, toners also tend to be fixed at a low temperature. The low-temperature fixing toner can be fixed more easily than the conventional toner.On the other hand, when a plurality of sheets are copied, the toner is fused to the unevenness on the sleeve, and the sleeve is contaminated. This causes a reduction in image density and fogging. This problem is solved by providing appropriate irregularities on the sleeve.
When the sleeve is used, the binder type carrier of the spherical composite particles has a smooth particle surface, so that the magnetic carrier slips on the sleeve having a smooth surface, and it is hard to say that the transportability is sufficient. The developer could not be uniformly attached. Therefore, fog and image unevenness are likely to occur.
[0011]
Therefore, there is a strong demand for a binder-type magnetic carrier capable of obtaining a good image in which fogging and image unevenness hardly occur even on a sleeve having a smooth surface.
[0012]
In a binder type magnetic carrier, a magnetic carrier using magnetic particles having a coercive force of less than 23.8 kA / m (300 Oe) and magnetic particles having a coercive force of 23.8 kA / m (300 Oe) or more as magnetic particle powder (Patent Document 1) 1) A magnetic carrier using magnetic particles having a spinel structure and magnetic particles having a magnetoplumbite structure as a magnetic particle powder (Patent Literature 2). Hard magnetic particles and soft magnetic particles are used as magnetic particles. And a magnetic carrier containing magnetite or soft ferrite and barium ferrite or strontium ferrite as magnetic particle powders (Patent Document 4).
[0013]
[Patent Document 1]
JP-A-6-11906
[Patent Document 2]
JP-A-6-35231
[Patent Document 3]
JP-A-10-268575
[Patent Document 4]
JP 2000-137352 A
[0014]
[Problems to be solved by the invention]
Patent Document 1 discloses a binder type magnetic carrier using magnetic particles having a coercive force of less than 23.8 kA / m (300 Oe) and magnetic particles having a coercive force of 23.8 kA / m (300 Oe) or more as magnetic particle powder. However, the particle shape of the magnetic carrier is not taken into consideration, and it is difficult to say that the transportability is sufficient.
[0015]
Patent Document 2 mentioned above discloses a binder-type magnetic carrier using spherical Cu-Zn ferrite as magnetic particles having a spinel structure and plate-like strontium ferrite particles as magnetic particles having a magnetoplumbite structure. However, no consideration is given to the particle shape of the magnetic carrier, and it is difficult to say that the transportability is sufficient.
[0016]
Patent Document 3 mentioned above describes a binder-type magnetic carrier using hard magnetic particle powder and soft magnetic particle powder. However, since the shape of the magnetic carrier is spherical, the spatula angle is low and the transportability is low. It is hardly enough.
[0017]
Patent Document 4 mentioned above describes a binder-type magnetic carrier using Cu-Zn ferrite and strontium ferrite particles, but does not consider the particle shape of the magnetic carrier and has sufficient transportability. It is hard to say.
[0018]
Accordingly, the present invention prevents the magnetic carrier from slipping on a sleeve having a smooth surface by making the shape of the magnetic carrier irregular, and causes fog and image unevenness by forming a uniform developer layer. It is a technical task to obtain a good and difficult image.
[0019]
[Means for Solving the Problems]
The technical problem can be achieved by the present invention as described below.
[0020]
That is, the present invention provides a magnetic carrier for an electrophotographic developer comprising amorphous composite particles having an average particle diameter of 10 to 100 μm comprising plate-like magnetoplumbite ferrite particles, granular ferromagnetic iron compound particles, and phenol resin. Wherein the total amount of the plate-like magnetoplumbite-type ferrite particles and the granular ferromagnetic iron compound particles contained in the composite particles is 80 to 99% by weight, and the plate-like magnetoplumbite-type ferrite particles The average particle diameter of the powder is 1.0 to 3.0 μm, and the average particle diameter (ra) of the plate-like magnetoplumbite ferrite particle powder and the average particle diameter (rb) of the granular ferromagnetic iron compound particle powder Has a particle size ratio (ra / rb) of 3.0 to 10.0.
[0021]
Further, the present invention is the magnetic carrier for an electrophotographic developer, wherein the relationship between the spatula angle and the average particle diameter of the magnetic carrier for an electrophotographic developer satisfies the following expression.
y ≧ −0.33x + 48
y: Spatula angle of magnetic carrier (°)
x: average particle diameter of magnetic carrier (μm)
[0022]
Further, the present invention is the magnetic carrier for an electrophotographic developer, wherein the particle surface of the magnetic carrier for an electrophotographic developer is coated with a silicone resin or a fluorine-based resin.
[0023]
Hereinafter, the present invention will be described in detail.
[0024]
First, the magnetic carrier for an electrophotographic developer according to the present invention will be described.
[0025]
The plate-like magnetoplumbite ferrite particles in the present invention are strontium ferrite particles and barium ferrite particles, and preferably strontium ferrite particles.
[0026]
The average particle size (average plate surface diameter: ra) of the plate-like magnetoplumbite-type ferrite particles in the present invention is 1.0 to 3.0 µm. When the average particle size is less than 1.0 μm, the plate-like magnetoplumbite-type ferrite particle powder becomes smaller relative to the composite particles, and amorphous composite particles cannot be obtained. If it exceeds 3.0 μm, composite particles of 100 μm or more are formed, which is not preferable as a magnetic carrier. More preferably, it is 1.0 to 2.0 μm.
[0027]
The plate-like ratio (average particle diameter / average thickness) of the plate-like magnetoplumbite ferrite particles in the present invention is preferably 1.3 or more. When the plate-like ratio is less than 1.3, the shape becomes similar to the granular particles, and amorphous composite particles cannot be obtained.
[0028]
Examples of the granular ferromagnetic iron compound particles in the present invention include magnetite particles, maghemite particles, and the like. The particle shape is spherical, hexahedral, octahedral or the like, preferably spherical.
[0029]
The average particle diameter (rb) of the granular ferromagnetic iron compound particles in the present invention is preferably from 0.1 to 1.0 μm, more preferably from 0.1 to 0.7 μm.
[0030]
In the present invention, the average particle diameter (ra) of the plate-like magnetoplumbite ferrite particles and the average particle diameter (rb) of the granular ferromagnetic iron compound particles are 3.0 (ra / rb). １10.0. When the particle size ratio is less than 3.0, amorphous composite particles cannot be obtained. If the particle size ratio exceeds 10.0, composite particles having a non-uniform composition depending on the particle size are not preferable. More preferably, it is 3.0 to 8.0.
[0031]
The ratio of the plate-like magnetoplumbite-type ferrite particles and the granular ferromagnetic iron compound particles in the present invention is 30 to 30% based on the total amount of the plate-like magnetoplumbite-type ferrite particles and the granular ferromagnetic iron compound particles. It preferably contains 90% of granular ferromagnetic iron compound particles. If it is less than 30%, it is not preferable in terms of magnetic properties as a magnetic carrier. If it exceeds 90%, amorphous composite particles cannot be obtained. More preferably, it is 50 to 90%.
[0032]
The total content of the plate-like magnetoplumbite-type ferrite particles and the granular ferromagnetic iron compound particles in the magnetic carrier is 80 to 99% by weight based on the magnetic carrier. If it is less than 80% by weight, the resin content increases, and large particles are easily formed. If it exceeds 99% by weight, the resin content is insufficient and sufficient strength cannot be obtained. More preferably, it is 85 to 99% by weight.
[0033]
The magnetic carrier for an electrophotographic developer according to the present invention is amorphous. By having such a structure, the flow rate is increased, and the transportability of the magnetic carrier is improved.
[0034]
The average particle size of the magnetic carrier for an electrophotographic developer according to the present invention is 10 to 100 μm, when the average particle size is less than 10 μm, secondary aggregation is easy, and when it exceeds 100 μm, the mechanical strength is weak, In addition, a clear image cannot be obtained. More preferably, it is 20 to 70 μm.
[0035]
In the magnetic carrier for an electrophotographic developer according to the present invention, the relationship between the spatula angle y and the average particle diameter x preferably satisfies the following expression. By satisfying the following relational expression, slipping on the sleeve becomes difficult, and the transportability of the magnetic carrier is improved.
[0036]
y ≧ −0.33x + 48
y: Spatula angle of magnetic carrier (°)
x: average particle diameter of magnetic carrier (μm)
[0037]
The bulk density of the magnetic carrier for an electrophotographic developer according to the present invention is 2.5 g / cm. ³ The following is preferred, and more preferably 1.0 to 2.0 g / cm ³ It is. The specific gravity is preferably from 2.5 to 5.2, and more preferably from 2.5 to 4.5.
[0038]
The magnetic carrier for an electrophotographic developer according to the present invention has an electric resistance of 1 × 10 ⁸ ~ 1 × 10 ^Fifteen Ωcm, preferably 1 × 10 ⁹ ~ 1 × 10 ^Fifteen Ωcm.
[0039]
The saturation magnetization value of the magnetic carrier for an electrophotographic developer according to the present invention is 20 to 80 Am ² / Kg (20-80 emu / g), more preferably 40-80 Am ² / Kg (40-80 emu / g).
[0040]
In the magnetic carrier for an electrophotographic developer according to the present invention, the surface of the composite particles is preferably coated with a silicone resin or a fluorine resin. By coating the particle surface with the resin having a low surface energy, spent toner can be suppressed.
[0041]
Although the coating resin used is not particularly limited, a condensation reaction type silicone resin is preferable as the silicone resin, and a polyfluorinated acrylate resin, a polyfluorinated methacrylate resin, a polyfluorinated vinylidene resin, and a polytetrafluoroethylene are preferable as the fluororesin. Resins, polyhexafluoropropylene resins and copolymers of combinations of the above resins are preferred.
[0042]
The coating amount of the carrier with the resin in the present invention is 0.1 to 5.0% by weight based on 100% by weight of the composite particles. When the coating amount is less than 0.1% by weight, it is difficult to sufficiently coat the coating, and uneven coating occurs. On the other hand, when the content exceeds 5.0% by weight, the surface becomes smooth, so that the transportability is not improved. Preferably it is 0.5 to 3.0% by weight.
[0043]
Next, a method for producing the magnetic carrier for an electrophotographic developer according to the present invention will be described.
[0044]
The magnetic carrier for an electrophotographic developer according to the present invention comprises phenols and aldehydes in an aqueous medium, in the presence of a basic catalyst, in the presence of plate-like magnetoplumbite-type ferrite particles and granular ferromagnetic iron compound particles. Then, the phenols are reacted with the aldehydes to obtain the phenols.
[0045]
Examples of the phenols used in the present invention include, in addition to phenol, alkylphenols such as m-cresol, p-tert-butylphenol, o-propylphenol, resorcinol and bisphenol A, and a benzene nucleus or a part or all of the alkyl group is a chlorine atom. And compounds having a phenolic hydroxyl group, such as halogenated phenols substituted with a bromine atom, and phenol is most preferred in view of the shape.
[0046]
Examples of the aldehyde used in the present invention include formaldehyde and furfural in either form of formalin or paraaldehyde, with formaldehyde being most preferred.
[0047]
The aldehydes preferably have a molar ratio of 1.0 to 4.0 with respect to the phenols. If the molar ratio of the aldehydes to the phenols is less than 1, it is difficult to form particles or harden the resin. Since the particles hardly progress, the strength of the obtained particles tends to be weak. If it exceeds 4.0, unreacted aldehydes remaining in the aqueous medium after the reaction tend to increase. More preferably, it is 1.2 to 3.0.
[0048]
As the basic catalyst used in the present invention, a basic catalyst used in ordinary production of a resol resin can be used. Examples thereof include aqueous ammonia, hexamethylenetetramine, and alkylamines such as dimethylamine, diethyltriamine, and polyethyleneimine. Particularly, aqueous ammonia is preferable. The molar ratio of the basic catalyst to phenols is preferably 0.05 to 0.7. If it is less than 0.05, the curing does not proceed sufficiently and granulation becomes difficult. If it exceeds 0.7, it affects the structure of the phenolic resin, resulting in poor granulation properties, making it difficult to obtain particles having a large particle diameter.
[0049]
The plate-like magnetoplumbite type ferrite particles and granular ferromagnetic iron compound particles used in the present invention are desirably subjected to lipophilic treatment on the particle surfaces in advance.
[0050]
The lipophilic treatment is performed by treating a plate-like magnetoplumbite type ferrite particle powder or a granular ferromagnetic iron compound particle with a coupling agent such as a silane coupling agent or a titanate coupling agent, or in an aqueous solvent containing a surfactant. A preferred method is to disperse plate-like magnetoplumbite-type ferrite particles or granular ferromagnetic iron compound particles and adsorb a surfactant on the particle surface.
[0051]
Examples of the silane coupling agent include those having a hydrophobic group, an amino group, and an epoxy group. Examples of the silane coupling agent having a hydrophobic group include vinyl trichlorosilane, vinyl triethoxysilane, and vinyl tris (β- Methoxy) silane. As the silane coupling agent having an amino group and an epoxy group, the silane coupling agent having an amino group and the silane coupling agent having an epoxy group may be used.
[0052]
As the titanate coupling agent, isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, or the like may be used.
[0053]
As the surfactant, a commercially available surfactant can be used, and one having a plate-like magnetoplumbite-type ferrite particle and a granular ferromagnetic iron compound particle or a functional group capable of binding to a hydroxyl group having on the particle surface. The ionicity is preferably cationic or anionic.
[0054]
The object of the present invention can be achieved by any of the above-mentioned treatment methods, but treatment with a silane coupling agent having an amino group or an epoxy group is preferable in consideration of the adhesiveness to a phenol resin.
[0055]
The treatment amount of the coupling agent or surfactant is preferably 0.1 to 10% by weight based on the plate-like magnetoplumbite ferrite particles or the granular ferromagnetic iron compound particles.
[0056]
When reacting the phenols and aldehydes in the presence of a basic catalyst, the amounts of the plate-like magnetoplumbite-type ferrite particles and the granular ferromagnetic iron compound particles to be coexisted are plate-like magnetoplumbite-type ferrite particles, granular It is preferably 75 to 99% by weight based on the total amount of the ferromagnetic iron compound particles, phenols and aldehydes, and more preferably 78 to 99% by weight in consideration of the strength of the magnetic carrier to be generated.
[0057]
Although the reaction in the present invention is carried out in an aqueous medium, the solid content in the aqueous medium is preferably adjusted to 30 to 95% by weight, particularly preferably to 60 to 90% by weight. .
[0058]
The reaction solution to which the basic catalyst has been added is heated to a temperature range of 60 to 95 ° C., reacted at this temperature for 30 to 300 minutes, preferably 60 to 240 minutes, and cured by performing a polycondensation reaction of the phenol resin.
[0059]
At this time, in order to obtain spherical composite particles having a high sphericity, it is desirable to slowly raise the temperature. The heating rate is preferably from 0.5 to 1.5 ° C / min, more preferably from 0.8 to 1.2 ° C / min.
[0060]
After the curing, the reaction product is cooled to 40 ° C. or lower, and the plate-like magnetoplumbite-type ferrite particles and the granular ferromagnetic iron compound particles are dispersed in the cured phenol resin binder, and the composite has an amorphous shape. An aqueous dispersion of the particles is obtained.
[0061]
The aqueous dispersion containing the composite particles is separated into a solid and a liquid by a conventional method of filtration and centrifugation, and then washed and dried to obtain a desired electrophotographic developer magnetic carrier.
[0062]
In addition, when coating the resin on the particle surface of the composite particles, a method of spraying the resin onto the composite particles using a well-known spray dryer, a Henschel mixer, a high-speed mixer, etc. It may be performed by a method of dry mixing, a method of impregnating the composite particles in a solvent containing a resin, or the like.
[0063]
As the toner used in combination with the carrier of the present invention, a known toner can be used. Specifically, a resin having a binder resin and a colorant as main constituents, and if necessary, a release agent, a magnetic substance, a fluidizing agent, and the like can be used. In addition, a known method can be used as a method for producing the toner.
[0064]
BEST MODE FOR CARRYING OUT THE INVENTION
A typical embodiment of the present invention is as follows.
[0065]
The average particle diameter of the particle powder was measured by a laser diffraction type particle size distribution analyzer LA500 (manufactured by Horiba, Ltd.) and expressed as a value on a volume basis. The particle morphology of the particles was observed with a scanning electron microscope (S-800, manufactured by Hitachi, Ltd.).
[0066]
The saturation magnetization was indicated by a value measured using a vibration sample magnetometer VSM-3S-15 (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of 795.8 kA / m (10 kOe).
[0067]
The spatula angle was indicated by a value measured with a powder tester PT-N type (manufactured by Hosokawa Micron Corporation).
[0068]
The true specific gravity was indicated by a value measured with a multi-volume densitometer (manufactured by Micromeritics).
[0069]
The electric resistance value (volume specific resistance value) was indicated by a value measured with a high resistance meter 4329A (manufactured by Yokogawa Hewlett-Packard).
[0070]
For image evaluation, DocuPrint C2220 was modified and used. The carrier was changed to the carrier of the present invention to perform image formation, and a printing durability test of 10,000 sheets was performed.
[0071]
The fog of the printed image was evaluated in the following four stages.
A: Very good.
：: good.
Δ: acceptable level.
×: Bad.
[0072]
The density unevenness of the printed image was evaluated in the following four grades.
A: Very good.
：: good.
Δ: acceptable level.
×: Bad.
[0073]
<Production of spherical composite particles>
After charging 240 g of plate-like strontium ferrite particle powder (average particle diameter 1.5 μm) into a 500 ml flask and sufficiently stirring, 2.4 g of a silane coupling agent (trade name: KBM-403 manufactured by Shin-Etsu Chemical) was added. The temperature was raised to about 100 ° C., and the mixture was thoroughly mixed and stirred for 30 minutes to obtain plate-like strontium ferrite particles powder coated with a coupling agent.
[0074]
400 g of spherical magnetite particle powder (average particle diameter: 0.3 μm) was charged into a separately prepared 500 ml flask, stirred sufficiently, and then 6.0 g of a silane coupling agent (trade name: KBM-403 manufactured by Shin-Etsu Chemical) was added. The temperature was raised to about 100 ° C. and mixed and stirred well for 30 minutes to obtain spherical magnetite particle powder coated with a coupling agent.
[0075]
Next, 45 g of phenol, 62 g of 37% formalin, 80 g of the lipophilic plate-like strontium ferrite particles powder, 320 g of the lipophilic spherical magnetite particles powder, 320 g of 28% ammonia water 13 g and 50 g of water were added, the temperature was raised to 85 ° C. in 40 minutes with stirring, and the mixture was reacted and cured at the same temperature for 180 minutes. The particle size ratio between the plate-like strontium ferrite particles and the spherical magnetite particles was 5.0.
[0076]
Next, the content in the flask was cooled to 30 ° C., the supernatant was removed, and the lower layer precipitate was washed with water and air-dried. Next, this is dried at 150 to 180 ° C. under reduced pressure (5 mmHg or less) at 150 to 180 ° C., and a magnetic carrier for an electrophotographic developer comprising spherical composite particles in which spherical magnetite particles and plate-like strontium ferrite are bound with a phenol resin as a binder 330 g were obtained.
[0077]
The magnetic carrier for an electrophotographic developer obtained here had an amorphous shape as shown in FIG.
[0078]
The magnetic carrier for an electrophotographic developer obtained here has an average particle diameter of 35 μm, a spatula angle of 50 °, and a bulk density of 1.89 g / cm. ³ , Specific gravity 3.85, saturation magnetization value 70.1 Am ² / Kg, electric resistance 3.2 × 10 ⁹ Ω · cm.
[0079]
In the printing durability test of the obtained magnetic carrier for electrophotographic developer and the toner, fog was ◎ and density unevenness was ◎.
[0080]
[Action]
An important point in the present invention is that, in the binder-type magnetic carrier, the plate-like magnetoplumbite-type ferrite particles having a large average particle diameter are used, and the particles of the plate-like magnetoplumbite-type ferrite particles and the granular ferromagnetic iron compound particles are used. By specifying the diameter ratio, the particle shape of the magnetic carrier is irregular.
[0081]
A spherical binder-type carrier having a smooth particle surface has a poor transportability due to slip on a smooth sleeve corresponding to a low-temperature fixing toner. In the present invention, it is possible to increase the spatula angle and suppress slippage by making the particle shape of the magnetic carrier amorphous. As a result, it is considered that an image without fog and density unevenness could be obtained.
[0082]
【Example】
Next, examples and comparative examples will be described.
[0083]
Examples 1-4 and Comparative Examples 1-5
Type and amount of plate-like magnetoplumbite-type ferrite particles and granular ferromagnetic iron compound particles, type and amount of lipophilic treatment agent, amount of phenol, amount of formalin, amount of basic aqueous ammonia water and water A magnetic carrier was obtained in the same manner as in the embodiment of the invention except that the amount was variously changed.
[0084]
The production conditions at this time are shown in Table 1, and various characteristics of the obtained magnetic carrier and the results of printing durability evaluation are shown in Table 2.
[0085]
<Production of resin-coated magnetic carrier>
Example 5
Type and amount of plate-like magnetoplumbite-type ferrite particles and granular ferromagnetic iron compound particles, type and amount of lipophilic treatment agent, amount of phenol, amount of formalin, amount of basic aqueous ammonia water and water Spherical composite particles were obtained in the same manner as in the embodiment of the invention except that the amount was variously changed.
[0086]
Next, 300 g of the spherical composite particles and 4.8 g of a silicone resin (KR-251: manufactured by Shin-Etsu Chemical Co., Ltd.) were added as solids in a Henschel mixer under a nitrogen stream, and the temperature was increased to 120 ° C. with stirring. The mixture was stirred at a temperature for 1 hour to form a resin coating layer made of a silicone resin.
[0087]
Table 1 shows a method for producing a magnetic carrier having the obtained resin coating layer, and Table 2 shows properties and printing durability evaluation results of the obtained magnetic carrier. The coating of the particle surface with the silicone resin was uniform.
[0088]
Example 6
Type and amount of plate-like magnetoplumbite type ferrite particles and granular ferromagnetic iron compound particles, type and amount of lipophilic treatment agent, amount of phenol, amount of formalin, amount of ammonia water as basic catalyst, amount of water Resin-coated spherical composite particles were obtained in the same manner as in Example 5, except that the amount and the resin coating amount were variously changed. The production conditions at this time are shown in Table 1, and various properties of the obtained resin-coated spherical composite particles and the results of printing durability evaluation are shown in Table 2.
[0089]
[Table 1]

[0090]
[Table 2]

[0091]
The particle shape of the magnetic carrier for an electrophotographic developer obtained in each example was indefinite. Also, in the printing durability evaluation after 10,000 sheets, good image results were obtained. The magnetic carrier for an electrophotographic developer obtained in Comparative Example 1 had a spherical smooth surface as shown in FIG.
[0092]
【The invention's effect】
Since the magnetic carrier for an electrophotographic developer according to the present invention has an irregular particle shape, the slip on a smooth sleeve is suppressed and the transportability is excellent, so that a good image corresponding to low-temperature fixing can be obtained. Obtainable.
[Brief description of the drawings]
FIG. 1 is a magnetic carrier for an electrophotographic developer obtained in an embodiment of the present invention. (2000 times)
FIG. 2 is a magnetic carrier for an electrophotographic developer obtained in an embodiment of the present invention. (500 times)
FIG. 3 is a magnetic carrier for an electrophotographic developer obtained in Comparative Example 1 (2000 times).
FIG. 4 is a graph showing a relationship between a spatula angle and an average particle diameter of a magnetic carrier for an electrophotographic developer (●: embodiment and example, □: comparative example).

Claims (3)

A magnetic carrier for an electrophotographic developer comprising amorphous composite particles having an average particle diameter of 10 to 100 μm comprising plate-like magnetoplumbite type ferrite particles, granular ferromagnetic iron compound particles, and a phenol resin. The total amount of the plate-like magnetoplumbite-type ferrite particles and the granular ferromagnetic iron compound particles contained in the body particles is 80 to 99% by weight, and the average particle size of the plate-like magnetoplumbite-type ferrite particles is 1.0 to 3.0 μm, and the particle diameter ratio (ra) between the average particle diameter (ra) of the plate-like magnetoplumbite ferrite particles and the average particle diameter (rb) of the granular ferromagnetic iron compound particles. / Rb) is from 3.0 to 10.0. The magnetic carrier for an electrophotographic developer according to claim 1, wherein the relationship between the spatula angle and the average particle size of the magnetic carrier for an electrophotographic developer satisfies the following expression.
y ≧ −0.33x + 48
y: Spatula angle of magnetic carrier (°)
x: average particle diameter of magnetic carrier (μm) 3. A magnetic carrier for an electrophotographic developer, wherein the particle surface of the magnetic carrier for an electrophotographic developer according to claim 1 or 2 is coated with a silicone resin or a fluorine-based resin.

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