JPH0299973A - Carrier for electrophotographic development - Google Patents

Abstract

PURPOSE:To provide the carrier which is utilizable even to a contactless magnetic brush developing method and can reproduce high-grade images by using magnetic particles consisting of a specific compsn. as nuclei, coating the circumference with a synthetic resin layer contg. a charge control agent and specifying the polymn. of both. CONSTITUTION:The magnetic particles consisting of the compsn. contg., by molar ratio, 40 to 50% Fe2O3, 15 to 35% MgO, 10 to 25% ZnO, 1.0 to 5.0% CuO, and 1.0 to 7.0% MnO2 are used as the nuclei and the circumference thereof is coated with the synthetic resin layer contg. the charge control agent; in addition, the weight of the charge control agent is so determined as to attain 0.1 to 5wt% of the weight of the resin component in the synthetic resin layer. As a result, the short magnetic brush of a uniform napping state is easily obtd. and the contact of the magnetic brush with an electrotatic latent image forming body is obviated. The destruction of the image formed on the image holding body is obviated. The high-quality image is maintained over a long period of time in this way by using the carrier for the developer of the contactless development method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a carrier for electrophotographic development, and more specifically to a two-component developer which can also be used in a non-contact magnetic brush development method. It's about career.

(Prior Art) The most widely used developing method for electrophotography at present is the magnetic brush developing method. This magnetic brush development method uses a two-component developer in which a magnetic carrier and a non-magnetic toner are stirred and mixed. This method is characterized in that a magnetic brush is brought into contact with a photoconductor that holds the electrostatic latent image, and only the toner is electrostatically attracted to the latent image to form a visible image. Magnesium-zinc ferrite materials have generally been used as magnetic carriers in this type of developer, as seen in, for example, Japanese Patent Application Laid-Open No. 123549/1983.

(Problems to be Solved by the Invention) As described above, the conventional magnetic brush development method utilizes the magnetism generated when a magnetic roll is rotated in order to bring the magnetic brush into contact with the photoreceptor and attract toner to the latent image surface. The smudged brush impedes faithful visualization of the latent image, causing scratched or blurred characters, brush marks, and the like.

In order to prevent this, a non-contact magnetic brush development method may be considered in which the amount of contact between the magnetic brush and the electrostatic latent image holder is extremely small, or there is no contact between the magnetic brush and the electrostatic latent image holder.

However, in conventional carriers, the magnetic brushes tend to become long due to the large magnetizing force, and it is difficult to uniformly shorten the brush lengths even if the length of the brushes is regulated to be small using the ear trimming regulating blade. There is also a method of weakening the magnetic force of the magnetic roll in order to shorten the magnetic brush, but this approach is impractical because it involves problems such as changing the design of the roll itself and reducing developer transportability.

Similarly, when a conventional carrier is used in a developing method that uses a magnetic brush in a non-contact manner, part of the magnetic brush comes into contact with the latent image holder, causing image defects and making the latent image visible with fidelity. It was extremely difficult to visualize it.

This invention was made in view of the above-mentioned problems, and its purpose is to enable use in non-contact magnetic brush development, and to extremely improve the latent image written on the latent image carrier. To provide an electrophotographic developing carrier capable of faithfully developing and reproducing high-quality images over a long period of time.

(Means for Solving the Problems) In order to achieve the above-mentioned object, in the carrier for electrophotographic development according to the present invention, F e 20 a is 40% by molar ratio.
~50%, MgO 15-35%, ZnO 10-2
5%, CuO 1.0-5.0%.

The core is a magnetic particle having a composition of 1.0 to 7.0% M n O2, and the core is coated with a synthetic resin layer containing a charge control agent, and the weight of the charge control agent is is 0.1 to 5 νt% of the resin component in the synthetic resin layer.

The molar ratio was determined as described above based on numerous experiments, and is based on the following reasons.

Fe2O8 is 40 to 50 mo1%> The present invention is first characterized in that the Fe2O3 content is less than 50 mo1% and a relatively large amount of M g 02 component is included. In this way, if the Fe2O3 component is 40Ilo1% or more, if it is less than 40Ilo1%, the magnetic roll
The connection of carrier particles on the sleeve becomes weaker,
This is because when the magnetic roll is rotated at high speed, the carrier is disconnected due to centrifugal force, causing the carrier to scatter from the sleeve. Also, 50mo1% is less than 50II101%.
This is because the specific resistance of the carrier particles decreases, and the carrier is easily guided to the electrostatic latent image carrier by charge injection from the sleeve, inducing carrier adhesion to the surface of the printed paper.

<MgO is 15 to 35 mo1%> MgO component is 1%
5mo1% or more is 15n+.

This is because if it is less than 1%, the specific resistance of the carrier particles becomes small and carrier adhesion is induced. Also 35mo1
% or less, if it is more than 35 mo1%, the density of the carrier particles will be small, and when forming a film using the fluidized bed coating method, the carrier particles will be too light, making it difficult to obtain a fluid state suitable for coating. To become.

<ZnO is 10 to 25 ino1%> The ZnO component is 10 mo1% or more.
This is because if the amount is less than %, the residual magnetization of the carrier becomes large and the fluidity of the developer decreases, resulting in an increase in the stirring torque of the developer and making it difficult to maintain a uniform toner concentration. Also, 25mo1% or less is 25n
If the amount is more than +o1%, the magnetizing force of the carrier particles becomes weaker,
This is because scattering occurs from the magnetic roll sleeve.

<CuO is 1.0 to 5.0 mo1%> The reason why the CuO component is set to 1.0 mo1% or more and 5.0 mo1% or less is because otherwise the sintering reaction of the raw material will be uneven, and the particle surface will not be smooth. This is because the properties cannot be maintained and it becomes difficult to obtain a coating layer without unevenness or pinholes during coating.

<MnO2 is 1, 0-7, Onoo1
%>Mn The reason why the O2 component is set to 1.0IIlo1% or more is that if it is less than 1.0IIlo1%, the specific resistance of the carrier particles tends to change during the sintering reaction. 7゜0
7. IIlo should be 1% or less. This is because if O+eo exceeds 1%, it becomes difficult to obtain the necessary strength for the carrier particles, and destructive development of the carrier particles occurs when the developer is stirred, making it difficult to maintain a stable image over a long period of time.

The charge control agent contained in the synthetic resin layer coated around the magnetic particles having a predetermined composition is 0.1% of the resin component.
~5wt%> By coating the ferrite carrier material with a synthetic resin containing a charge control agent in a specific ratio, it is possible to obtain a developer with excellent image stability over a long period of time.

Then, the weight of the charge control agent is 0.1 to 0.1 to the weight of the coating layer resin.
The reason why the content is 5wt% is that if it is less than 0.1vt%, the frictional charging force with the toner particles will be weak, and when the magnetic roll is rotated at high speed and the developer is conveyed to the surface of the electrostatic latent image carrier, the toner will be transferred to the carrier surface. This is because they may be released from the water and contaminate the area around the developing device, or they may adhere to non-printing areas during development, staining the paper surface and reducing the resolution of printing. The reason why the amount is set to be 5 wt % or less is that if it is more than 5 wt %, the amount of triboelectric charging increases with the length of the developer stirring time, resulting in a decrease in image density.

As the coating resin containing this charge control agent, acrylic resin, styrene/acrylic copolymer resin, epoxy resin, polyester resin, butadiene resin, melamine resin, fluororesin, butyral resin, and cellulose resin are used, and these resins can be used alone. However, it is also possible to use a mixture of several types.

(Function) As mentioned above, FeO, MgO, Zn0゜CuO
, MnO2 at a predetermined molar ratio is used as a carrier, it becomes possible to easily obtain a short magnetic brush with uniform spikes. When this is used in a non-contact development method, a brush with longer than necessary bristles is not formed, so the magnetic brush does not come into contact with the electrostatic latent image holder.

Furthermore, even if they come into contact, the brush is soft and will not destroy the latent image (image formed on the latent image holder), making it possible to develop the latent image with great fidelity.

Furthermore, if the carrier is coated with a predetermined synthetic resin layer and used as a developer for non-contact development, high quality images can be maintained for a long period of time.

In addition, when the resin-coated ferrite particles shown above are used as a carrier in a non-contact development method, it is possible to maintain high quality images for a long period of time, and they are particularly excellent as a second developing carrier in a two-color development method. be effective. In other words, the two-color development method is a method in which development is performed twice at the same time in the first development section and the second development section in one recording process, and the characteristics required of the carrier for the second development are visualized in the first development. It is possible to superimpose the developed images in the second developing section without destroying them. This carrier fully satisfies this characteristic, and even with respect to color mixing that occurs when the toner released during the first development mixes into the second development area, the toner for the first development is negative, and the toner for the second development is Due to the effect of positively charging each toner, when the first development toner is mixed in, the charge of that toner is neutralized and prevented from contributing to development, so a two-color recorded image without color mixture can be easily obtained. .

(Example) Hereinafter, preferred embodiments of the present invention will be described.

*Example-1 Fe20345II01%, Mg029mo1%, 2n
020mol%, Cu03mol%, MnO23m
.

A mixed raw material having a composition of 1% was calcined at 900°C.

This was ground in a ball mill, dispersed in an aqueous solution containing a binder and a dispersant, and spray-dried as a slurry in hot air to obtain pellets of about 50 μs.

Further, this pellet was sintered at 1250° C. and then classified to obtain spherical ferrite having an average particle size of 40 μs. Next, add 100g of styrene/acrylic resin to 1i [solvent 2000c]
After completely dissolving the charge control agent in c, 1 g of the charge control agent was uniformly dispersed in this solution to prepare a coating agent solution. This was uniformly spray-dried onto 10 grains of spherical ferrite rice grains using a Wurster type fluidized bed coating device to obtain a resin-coated carrier.

7vt% polyester toner was added to this carrier and mixed in a ball mill for 10 minutes, and the toner specific charge of this developer was measured and found to be 14 μC/g.

Next, when this developer was installed in a commercially available laser printer and initial printing was performed, the resulting image had excellent fine line reproducibility and gradation, and no image defects were observed.

In addition, when the black solid area was measured with an optical reflection densitometer, 1
．． An image density of 4 was obtained. Furthermore, with this developer, 5 consecutive
When a 10,000-sheet printing test was conducted, the images obtained were no different from the images obtained initially.

*Example-2 Fe20a47mol%, Mg030+o
1%, 2no19+ool%, Cur1.5mol
%, MnO22,5io1% was prepared in the same manner as in Example-1 to obtain a spherical ferrite material having an average particle size of 404. Next, epoxy resin 1
After completely dissolving 00g in 2000cc of organic solvent, 1.5g of the charge control agent was uniformly dispersed in this solution to prepare a coating agent solution. This was uniformly spray-dried onto 10 kg of the above-mentioned spherical ferrite material using a Wurster type fluidized bed coating apparatus to obtain a resin-coated carrier.

10% by volume of polyester toner was added to this carrier and mixed in a ball mill for 10 minutes, and the toner specific charge amount of this developer was measured and found to be 15 μC/g.

Next, when this developer was installed in a commercially available laser printer and initial printing was performed, the resulting image had excellent fine line reproducibility and gradation, and no image defects were observed.

In addition, when the black solid area was measured with an optical reflection densitometer, 1
．． An image density of 4 was obtained. Furthermore, with this developer, 5 consecutive
When a 10,000-sheet printing test was carried out, the images obtained were no different from those obtained initially.

*Example-3 Fe20349s+ol%, Mg033mol%,
2no15wo1%, Cur1.5go1%1M n
Example of a mixed raw material with a composition of 1% O21.5so-
A spherical ferrite material having an average particle size of 40 μs was obtained by using the same method as in Example 1. Next, styrene/acrylic resin 50
After completely dissolving 1,500 cc of an organic solvent, 0.3 g of a charge control agent was uniformly dispersed in this solution to obtain a coating agent solution. This was placed in a stirrer together with the above ferrite material, and stirred and dried to obtain a resin-coated carrier.

8vt% polyester toner was added to this carrier and mixed in a ball mill for 10 minutes, and the toner specific charge amount of this developer was measured and found to be 15 μC/g.

Next, when this developer was installed in a commercially available laser printer and initial printing was performed, the resulting image had excellent fine line reproducibility and gradation, and no image defects were observed.

In addition, when the black solid area was measured with an optical reflection densitometer, 1
．． An image density of 4 was obtained. Furthermore, with this developer, 5 consecutive
When a 10,000-sheet printing test was carried out, the images obtained were no different from those obtained initially.

Comparative Example-1 Fe 20 a 30 mol %, Mg040so
l%, 2n010mol%, Cu017mol%
A mixed raw material having a composition of 3 mo1% of MnO2 was prepared in the same manner as in Example-1, and the average particle size was 40j.
A spherical ferrite material J was obtained. Next, 100 g of styrene/acrylic resin was completely dissolved in 2000 cc of organic solvent, and then 1 g of charge control agent was uniformly dispersed in this solution to prepare a coating agent solution. This was uniformly spray-dried onto 10 kg of the above ferrite material using a Wurster type fluidized bed coating apparatus to obtain a resin-coated carrier. 7vt% polyester toner was added to this carrier and mixed in a ball mill for 10 minutes, and the toner specific charge amount of this developer was measured and found to be 14 μC/t.

Next, when this developer was mounted on a commercially available laser printer and initial printing was performed, the resulting image was defective due to carrier adhesion on the paper surface.

*Comparative example-2 F e 20 a 45 mol %, Mg029+o
l%, 2n020+ol%, Cu03sol%,
Mn023a.

A mixed raw material having a composition of 1% was prepared in the same manner as in Example-1 to obtain a spherical ferrite material with an average particle size of 40 μs. Next, add 100g of styrene/acrylic resin to 20g of organic solvent.
After completely dissolving the charge control agent in 0.00cc of
g was uniformly dispersed in this solution to prepare a coating agent solution. This was uniformly stirred and dried on 10 kg of the above ferrite material using a Wurster type fluidized bed coating device to obtain a resin-coated carrier. 5wt% polyester toner was added to this carrier and mixed in a ball mill for 10 minutes, and the toner specific charge of this developer was measured to be 11μ.
C/g.

Next, when this developer was installed in a commercially available laser printer and initial printing was performed, fogging occurred in the non-printing areas and the resulting image was defective.

*Comparative example-3 Fe20a65 mol%, MgO15io
A mixed raw material having a composition of 1% Cu, 1% 2n01.5ao, and 1% Cu05o+o was prepared in the same manner as in Example-1 to obtain a spherical ferrite material with an average particle size of 40 μs. Next, 50 g of epoxy resin was completely dissolved in 2000 cc of an organic solvent, and then 0.5 g of a charge control agent was uniformly dispersed in this solution to obtain a coating agent solution.

This was placed in a stirrer together with the above spherical ferrite material, and stirred and dried to obtain a resin-coated carrier. 1 for this career
2 wt % polyester toner was added and mixed in a ball mill for 10 minutes, and the toner specific charge of this developer was measured and found to be 18 μC/g.

Next, when this developer was installed in a commercially available laser printer and initial printing was performed, the resulting image had scratches and smearing on the characters, and a large amount of carrier had adhered to the paper surface. After that, printing was stopped to protect the equipment.

Consideration when using the carrier of the present invention in two-color development method> The results when the carriers in the above Examples and Comparative Examples were used as the second development carrier in the two-color development method are shown in the table below.

As shown in the table, in Examples 1 to 3, sufficiently good image quality was obtained as a two-color development method, but in Comparative Examples, it became unusable.

*1...Carrier adhesion to the paper surface *2...Fog on non-printing areas *3...Carrier adhesion fire (effects of the invention) As described above, the carrier for electrophotographic development according to the present invention For example, it exhibits the effect of developing the latent image written on the latent image holder extremely faithfully.

Furthermore, if a coating layer made of predetermined components is formed on the surface, high-quality images can be reproduced over a long period of time.

That is, when the magnetic carrier material of the present invention is used in an electrophotographic two-component developer, it becomes possible to easily obtain high-quality images.

In particular, when this carrier is used in a two-color development method, the above effects are excellent.

Claims (1)

[Claims] In molar ratio, Fe_2O_3 is 40% to 50%, MgO is 1
5~35%, ZnO 10~25%, CuO 1.0~
5.0%, MnO_2 is 1.0 to 7.0% as a core, and the core is coated with a synthetic resin layer containing a charge control agent, and the charge control agent A carrier for electrophotographic development, characterized in that the weight of the agent is 0.1 to 5 wt% of the resin component in the synthetic resin layer.