JP2621351B2 - Career - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a carrier for an electrostatic latent image developer, particularly to a binder type carrier.

2. Description of the Related Art Conventionally, a magnetic brush of a magnetic developer is formed on the surface of a developing sleeve by a magnetic force, and the magnetic brush is slid in contact with a surface of a photoreceptor functioning as an electrostatic latent image carrier and the electrostatic brush carried on the surface. As a developer for visualizing a latent image, an average particle diameter of 10
A magnetic carrier composed of iron powder particles of about 0 to 200 μm,
A mixture with an insulating toner having an average particle size of about 10 to 20 μm has been used. However, with this developer, the magnetic attraction force between the carrier particles during formation of the magnetic brush is too strong, so that the ears of the magnetic brush are hard, and the carrier particles aggregate on the developing sleeve in a chain or fin. In addition to causing troubles such as generation of white stripes, etc., since the volume specific electric resistance of the carrier itself is generally low at 10 ⁶ Ωcm or less, if the toner concentration in the developer decreases due to continuous use, etc., The charge on the electrostatic latent image carrier escapes through the carrier and the latent image is disturbed, resulting in image loss or the like,
There is a problem that the carrier adheres to the image portion of the electrostatic latent image carrier due to charge injected from the developing sleeve. In addition, when the carrier adheres to the electrostatic latent image on the photoreceptor, the surface of the photoreceptor is damaged because the carrier particles are hard.

On the other hand, as a means for solving the drawbacks of a carrier composed of a magnetic substance alone such as iron powder, a binder type carrier having an average particle diameter of 5 to 30 μm in which magnetic substance fine powder is dispersed in an insulating material such as a resin is known. It is proposed in Japanese Patent Laid-Open Publication No. 54-66134 and is put to practical use. This type of binder-type carrier has low magnetization in a magnetic field of about 1000 gauss in a general developing device, and can form soft spikes, providing excellent images without white streaks caused by the carrier. It has advantages that can be obtained. However, this type of binder-type carrier not only raises the problem of heat generation of the developing sleeve but also requires the use of a motor with a large torque when performing high-speed development, which has been recently required, and reduces the cost of the developing device. There was a drawback that it became expensive. That is, a developing device that uses a developer containing a binder-type carrier usually forms a magnetic brush with the developer by rotating a magnet disposed in a developing sleeve, and at the same time, removes the ears. It is desired that the developer be transported by being rotated on the surface of the developing sleeve. However, when the rotation of the magnet is low in response to the change in the magnetic pole accompanying the rotation of the magnet, uneven development is likely to occur, and this uneven development increases the developing speed (moving speed of the electrostatic latent image carrier). The rotation speed of the magnet needs to be as high as possible to prevent this. Generally, the rotation speed of the magnet is set in the range of 100 to 2500 rpm, but in the case of performing high-speed development, it is necessary to increase the speed corresponding to the moving speed of the electrostatic latent image carrier. Since the eddy current generated in the developing sleeve increases, the higher the speed of development, the higher the heat generation of the developing sleeve and the higher the rotational driving load, and a motor having a large torque must be used. It is. Some commercially available electrophotographic copiers employ a developing device that not only rotates the magnet at high speed but also rotates the developing sleeve in an auxiliary manner. I couldn't.

A method in which the magnet is fixed and only the developing sleeve is rotated (hereinafter, referred to as a developing sleeve rotating method) does not cause a problem due to the rotation of the magnet. Therefore, it is conceivable to obtain an image without white stripes due to magnetic aggregation by using a binder type carrier used in a magnet rotation system in a development sleeve rotation system, and also to eliminate a disadvantage associated with the magnet rotation. Even if a developer containing a binder-type carrier that can be used in a magnet rotation system is simply used for a development sleeve rotation system, a large amount of the carrier adheres to the non-image area on the surface of the electrostatic latent image carrier, and in practical use, It has been experienced that a great trouble occurs, and the attempt has not yet been put to practical use.

Problems to be Solved by the Invention As described above, although the binder type carrier has an excellent point, since the magnetic force is inferior to that of a normal iron powder or ferrite powder carrier, the transportability of the developer is deteriorated. Not suitable for ultra-high-speed development of 100 sheets or more of A-4 size paper per minute,
Further, when the charge amount of the toner is increased, there is a problem that the amount of carrier attached to the photoreceptor increases.

In contrast, simply increasing the ratio of the magnetic powder to the binder resin to increase the magnetic force will cause the volume specific electrical resistance of the carrier to drop sharply, and the binding force will become weak and brittle, so the carrier will have a smaller diameter during use. As described above, the carrier adheres to the image area as described above, and thus cannot be put to practical use.

In consideration of only the electric resistance, when the volume specific electric resistance of the carrier is as low as 10 ⁸ to 10 ¹² Ω · cm, the insulating property of the toner is used to increase the toner content in the developer. In general, the edge effect cannot be obtained properly even if the volume resistivity of the developer is increased, and when the content of the toner in the developer is reduced, the carrier due to the injected charge is reduced. Is not preferred because a large amount of is not adhered.

Another technical problem of the present invention is to obtain a sharp image with an appropriate edge effect and to prevent carriers from adhering to the image portion on the surface of the electrostatic latent image carrier due to charges injected from the developing sleeve. Preventing, preventing charge accumulation due to frictional charging of the carrier, stabilizing the chargeability given to the toner, and preventing deterioration of the carrier,
For example, the life of the carrier may be extended.

Means for Solving the Problems The present invention provides a binder type carrier comprising at least a binder resin and a magnetic powder, wherein the magnetic powder has a particle size distribution ratio D ₄ / D _{1 of} 1.70 to 4.00 (D ₄ is a weight average diameter, D 4 ₁ means a length average diameter), the magnetic powder is contained in a proportion of 200 to 900 parts by weight with respect to 100 parts by weight of the binder resin, and the carrier has an electric conductivity of 10 ¹² Ω · cm or more. The present invention relates to a carrier having resistance.

The binder resin that can be used in the present invention includes a bisphenol-type polyester, that is, bisphenol A to which ethylene oxide or propylene oxide is added.
May be used as an alcohol component, and a divalent carboxylic acid, a trivalent carboxylic acid, a dicarboxylic acid having a side chain having 4 to 20 carbon atoms, or the like subjected to a condensation polymerization reaction. As the component, those containing ethylene glycol as a main component, those using rosin glycidyl ester, and the like can be used. In addition, not only polyester resin but also styrene-acrylic copolymer resin and the like can be used, and all have a viscosity at 100 ° C. of 10 ⁵
What is ~ 10 ⁷ cps is good. This is because if the viscosity during kneading is too high, the wettability with the magnetic powder is deteriorated, and if the viscosity is too low, the dispersibility of the magnetic powder is deteriorated and aggregation occurs.

The magnetic powder that can be used in the present invention is not particularly limited as long as it is a magnetic material having a specific volume resistivity of 10 ⁷ Ω · cm or more. Among them, ferrite is preferred.
Specifically, as ferrite, for example,
General formula described in 19055: (Wherein M represents at least one atom selected from the group consisting of Mn, Ni, Co, Mg, Cu, Zn, and Cd, and 0.5 ≦ x
≦ 1,0.1 ≦ y ≦ 0.571. ) And the like. Other than these, there are magnetites such as FeO and Fe ₂ O ₃ and metals containing ferromagnetism such as iron, nickel and cobalt, or alloys and compounds thereof.

The magnetic powder used in the present invention has a primary particle diameter of 0.05 to 5 μm, preferably 0.1 to 1 μm, more preferably 0.1 to 0.5 μm as a length average diameter.

More preferably, the average particle size of the carrier is set in the range of 15 to 100 μm in terms of weight average particle size in order to more completely prevent the aggregation of the carrier and the prevention of adhesion to the electrostatic latent image carrier.

When the weight average particle diameter of the carrier is less than 15 μm, aggregation of the carrier, carrier adhesion to the electrostatic latent image carrier is likely to occur,
In addition, the flowability of the carrier is deteriorated, and if it exceeds 100 μm, brush unevenness occurs as in a normal iron powder carrier, and a clear image cannot be obtained.

The magnetic powder used in the present invention is further 1.70 or more and 4.00
The following particle distribution ratio is preferable.

In the present specification, the particle diameter distribution ratio is a value obtained by taking a photograph of a magnetic powder with a transmission electron microscope, measuring the particle diameter of 200 to 400 particles from the photograph, and calculating the particle diameter by the following formula.

[Where the length average diameter (D ₁ ) and weight average diameter (D ₄ ) ( _Di is the particle size of one particle) ( _Di is as defined above). The particle size distribution ratio (D ₄ / D ₁ ) is a sign indicating the spread of the particle size, and D ₄ / D ₁ becomes larger as the distribution becomes wider.

When the particle size distribution ratio is smaller than 1.70, the distribution of the particle size is narrow, and the magnetic powder cannot be packed in the carrier in the closest packing.When the magnetic powder ratio is high, the magnetic powder is exposed on the carrier surface, and the electric resistance is reduced. Carrier development becomes remarkable. Also,
If the particle size distribution ratio is greater than 4.00, the proportion of coarse particles becomes extremely large, so that a large number of magnetic powders consisting only of coarse particles are present in the carrier, which is developed by the carrier. In addition, since the binding force is weak and brittle, it is broken during use, and these small-diameter carriers are developed.

By the way, the particle size distribution can be measured by various methods, but the reference distribution differs depending on the measuring method. For example,
Particle size measured from photographs measured with an optical microscope or electron microscope, etc. is a number-based distribution, that determined by a light transmission method is an area-based distribution, and that of a coulter counter or laser diffraction method is a volume-based distribution. And weight sedimentation method are called weight-based distribution. The particle size distribution of the present invention is not particularly limited to these measurement methods, and different measurement methods do not mean that they are not included in the present invention. Accordingly, the carrier of the present invention can be manufactured by selecting a measuring method depending on the possessed device and the like.

Recently, the use of a coulter counter for toner used in electrophotography has been generalized because it is simple and has good reproducibility, and there is no dependence on a measuring instrument when a reference sample is used. In the case of a very small particle size, a material that is easily magnetized, or a material having a large specific gravity, the measurement reproducibility is poor, and it is impossible to measure with a Coulter counter.

In particular, in the case of magnetic particles like the product of the present invention, if the particle size is relatively small and is influenced by magnetism to some extent, the particles will aggregate and the true particle size cannot be measured. Therefore, it is preferable to measure the particle diameter by reading from a photograph measured with an electron microscope or directly connecting to an image processing device or the like.

In order to obtain a magnetic powder having a large particle diameter distribution ratio (D ₄ / D ₁ ) as in the present invention, two magnetic powders pulverized by a usual method are used.
It is easiest to mix seeds or more in any proportion, but it is also possible to increase the particle size distribution ratio by over-milling a relatively large magnetic material with a mill such as a ball mill or jet mill. It is possible.

The carrier of the present invention can be obtained by sufficiently heating and mixing the binder resin and the magnetic powder at a predetermined mixing ratio, cooling, and then pulverizing and classifying.

The magnetic powder and the binder resin are mixed at a ratio of 200 to 900 parts by weight of the magnetic powder to 100 parts by weight of the binder resin. This is because if the magnetic powder is less than 200 parts by weight, sufficient magnetic force cannot be obtained.
If the amount exceeds 00 parts by weight, the carrier becomes brittle.

Conventionally, when the magnetic powder is highly filled (700 parts by weight or more of the magnetic powder with respect to 100 parts by weight of the resin), the carrier becomes brittle and the volume resistance is too low to be used. This is because a magnetic powder having a single particle diameter or a narrow particle diameter distribution is used, so that the surface area of the filled magnetic powder becomes large, and the oil absorption increases accordingly, so the binder becomes large. This is because the binding force of the resin becomes small and the carrier becomes brittle. At the same time, the dispersibility of the magnetic powder also deteriorates, so that the volume-specific electric resistance is considered to decrease.

However, the magnetic powder having a wide distribution of particle diameters of the magnetic powder as in the present invention is dispersed in the binder in the form of closest packing. Compared with a conventional carrier using magnetic powder, the electric resistance of the magnetic powder can be maintained in a preferable range and a large amount of magnetic powder can be contained. As a result, the magnetic force increases, the effective surface area of the magnetic powder decreases, and the brittleness of the carrier can be prevented. Generally, a carrier having an electric resistance of 10 ¹² Ωcm or more is preferable as the carrier of the magnetic powder, but according to the present invention, even if the magnetic powder is highly filled, it is possible to prepare a carrier having a preferable electric resistance. It becomes possible.

After the carrier of the present invention is subjected to ordinary pulverization and classification to make the particle diameter uniform, the surface is further treated with fine powder such as silica, titanium oxide, and aluminum oxide to modify the surface; ) Heat treatment;

 Hereinafter, the present invention will be described with reference to examples.

Example Synthesis of binder resin (1) Bisphenol A / propylene oxide adduct 735
g-bisphenol A ethylene oxide adduct 285 g-terephthalic acid 255 g-n-dodecyl succinic acid 345 g-dibutyltin oxide 0.07 g.
A stainless steel stirrer, down-flow condenser and nitrogen inlet were fitted. The contents are heated at 275 ° C with a mantle heater.
And reacted in a nitrogen stream. When the flow of water stopped, 80 g of trimellitic acid was added, and the reaction was further proceeded. When the acid value reached 9 mgKOH / g, the reaction was stopped by cooling. The obtained polyester had an acid value of 9 mgKOH / g and a hydroxyl value of 18 mgKOH / g.

In addition, from viscosity measurement with a flow tester, Tm: 123
° C, η ₁₀₀ : 2 × 10 ⁶ poise, −d (log η) / dT: 4.2 × ₁
0 ² , moisture absorption: 0.72% The resin obtained as described above is referred to as a binder resin (1).

Synthesis of binder resin (2) ・ Styrene 750g ・ N-butyl acrylate 200g ・ Methacrylic acid 6g ・ Benzoyl peroxide 10g ・ Toluene 1000g
A stainless steel stirrer, down-flow condenser and nitrogen inlet were fitted. The contents were heated to 70 ° C. with a mantle heater and reacted in a nitrogen stream for 6 hours. After completion of the reaction, toluene was distilled off under reduced pressure to obtain a solid resin. The obtained copolymer resin has an acid value of 40 mgKOH / g, a glass transition point of 64 ° C., and a viscosity measurement with a flow tester of Tm: 124.
° C, η ₁₀₀ : 3 × 10 ⁶ poise, −d (log η) / dT: 4.2 × 10 ²
Met. The resin obtained as described above is referred to as a binder resin (2).

Preparation of toner (i) (-) parts by weight of chargeable toner (toner A) • polyester resin (softening point 126 ° C, glass transition point 62 ° C, acid value 12) 100 • carbon black 5 (MA # manufactured by Mitsubishi Kasei Kogyo KK) 8) ・ Charge control agent 2 (manufactured by Orient Chemical Co., Ltd .; Bontron S-34) The above materials are sufficiently mixed by a ball mill, then melt-kneaded by a twin-screw extruder, cooled, and then finely pulverized by a jet mill. After that, it was classified with a zigzag classifier and the average particle size was 1
(−) Chargeable toner of 2.5 μm was obtained (referred to as toner A). (Ii) (+) parts by weight of (+) chargeable toner (toner B) styrene-n-butyl methacrylate resin 100 (softening point 124 ° C., glass (Transition point 61 ° C) ・ Carbon black 5 (manufactured by Mitsubishi Chemical Corporation; MA # 8) ・ Charge control agent 4 (manufactured by Orient Chemical Industries; Bontron-01) To obtain a (+) chargeable toner having an average particle diameter of 13.2 μm (referred to as toner B).

(Iii) White toner White toner In the above-mentioned (+) chargeable toner, carbon black is used as 30 parts by weight of titanium oxide (manufactured by Ishihara Sangyo Co., Ltd.), and the charge control agent Bontron N-01 is used as colorless quaternary ammonium. A 13.4 μm white toner was obtained and used in place of salt, Bontron P-51 (manufactured by Orient Chemical Industries, Ltd.).

Carrier production method The polyester resin (binder resin (1)) and styrene / acrylic resin (binder resin (2)) are used, and the following compositions are sufficiently mixed, heated and kneaded using a twin-screw extruder, and then cooled. After crushing and classifying, a carrier having an average particle diameter of 55 to 65 μm was obtained.

Carrier composition The magnetic powder used for carrier preparation is Zn-based ferrite, which is fired and granulated, finely pulverized with a jet pulverizer, and then sieved with different sieves, and the following particle size distribution ratio ( D ₄ / D ₁ ) was obtained. Magnetic powder D ₁ (μm) D ₄ / D ₁ A 0.75 1.53 B 0.05 1.72 C 12.13 1.85 D 0.76 1.71 E 8.86 1.76 F 1.80 3.62 G 4.13 4.25 parts by weight・ Binder resin (1) or 100 ・ Binder resin (2) ・Carbon black 2 (Mitsubishi Kasei Kogyo Co., Ltd .: MA # 8) Silica 1.5 (Nippon Aerosil Co., Ltd .: Aerosil # 200) Zn-based ferrite x parts by weight (predetermined amount shown in Table 1)
(Maximum magnetization: 72 emu / g, Hc: 110, volume specific electric resistance 3 × 10
⁸ Ω · cm) The specific volume resistance of the carrier in Table 1 was measured by placing a sample on a metal circular electrode so as to have a thickness of 1 mm and a diameter of 50 mm.
95.4 g, an electrode having a diameter of 20 mm, a guard electrode having an inner diameter of 38 mm, and an outer diameter of 42 mm were mounted, and the resistance value one minute after the application of a DC voltage of 500 V was read and converted into the volume specific resistance of the sample.
The measurement environment was a temperature of 25 ± 1 ° C. and a relative humidity of 55 ± 5%. The measurement was repeated five times, and the average was taken.

Evaluation Carrier development in image area Carrier development in image area was performed using a developer using the above-mentioned positively-charged white toner in an environment of 23 ° C and 45% with a copying machine EP-470Z (manufactured by Minolta Camera Co., Ltd.). To determine the presence or absence of carriers in the solid image. The symbol of carrier development on the image area indicates the following.

A: No development was observed and no color turbidity was observed.

Δ: When the toner concentration becomes low, carrier development starts,
The color became cloudy.

X: Carrier development was slightly observed, and color turbidity was observed.

XX: Carrier development was severe and a gray image was formed.

Color turbidity The color turbidity of 10K sheets after printing was examined in order to determine whether the carrier was lost and small pieces were formed during the printing, and whether the white toner was turbid. The evaluation was performed by ranking as follows. ◎, ×, xx are the same rank for the carrier phenomenon.

Developer transportability The developer transportability is determined by using the carrier and toner A shown in Table 1.
8% by weight to prepare the developer, system speed 4
The T-character reproducibility chart shown in FIG. 1 was drawn using a high-speed copying machine of 0 cm / s, and evaluated from the T-character reproducibility.

A: No difference in density between part a and part b.

:: A slight difference in density was observed between the portions a and b, but hardly distinguishable.

Δ: Difference in density is conspicuous in part a and part b.

X: Extremely bad.

Carrier Adhesion Carrier adhesion was measured using a developer prepared by mixing and preparing the carrier shown in Table 1 and the aforementioned toner B at a ratio of 8 wt% using a copying machine EP-470Z manufactured by Minolta Camera Co., Ltd. The carrier is scattered around the frame, especially between lines of a resolution chart or the like, or on a white background. A: No adhesion (both on the copying machine and the photoconductor).

：: Slightly recognized on the photoreceptor, but not recognized on the transfer paper at all.

Δ: Slightly recognized on transfer paper.

×: Very noticeable on transfer paper.

Charge Amount Each carrier and toner A or toner B were mixed at a ratio of 90:10, and the charge amount after 10 minutes at normal temperature and normal humidity (23 ° C., 45%) was measured.

Fog after printing endurance When a printing endurance test of 10K sheets was performed with a copying machine at a system speed of 40 cm / sec using a developer prepared by mixing and preparing the carrier and toner A shown in Table 1 at a ratio of 8 wt%. The state of fog was examined.

Rank 5 Fog on the ground is hardly observed.

4 Very slight background fog is recognized, but there is no problem.

3 There is some fog on the background, but there is no practical problem.

2 The toner scattered considerably on the background, and fog was recognized at a glance.

 1 Very bad fog.

Effects of the Invention The carrier of the present invention is highly filled with magnetic powder, has a strong magnetic force, and has a high electric resistance. Therefore, high-speed followability is good,
It is effective for good image formation with no carrier adhesion and no turbidity or fogging of color images.

[Brief description of the drawings]

FIG. 1 is a view showing a copy image in which a T-character reproducibility chart is drawn.

Claims (1)

(57) [Claims] In a binder type carrier comprising at least a binder resin and a magnetic powder, the magnetic powder has a particle size distribution ratio D ₄ / D _{1 of} 1.70 to 4.00 (D ₄ is a weight average diameter, D ₁ is a length average diameter) Wherein the magnetic powder is contained in a proportion of 200 to 900 parts by weight with respect to 100 parts by weight of the binder resin, and the carrier has an electrical resistance of 10 ¹² Ω · cm or more. And career.