JPS6242163A - Developer for developing electrostatic charge image - Google Patents

Abstract

PURPOSE:To obtain a high image density and resolution, good reproducibility of medium contrast and an image having high quality without ground fogging by mixing a specific ferrite carrier and electric charge type magnetic toner at a specific ratio and executing development. CONSTITUTION:The ferrite carrier is the sintered body composed of a suitable metallic oxide and tervalent iron oxide and the concrete compsn. is exemplified by Ba-Ni-Zn ferrite, Mn-Zn ferrite, etc. and has the property values preferably ranging 55-75emu/g saturation magnetization (sigmas), 10<6>-10<10>OMEGA.cm volume resistivity at D.C. 100v/cm and 74-105mum average grain size distribution. The electric charge type magnetic toner is required to have 10-10muc/g electrostatic charge quantity in absolute value and is required to have >=10<14>OMEGA.cm volume resistivity in the electric field of D.C. 4,000v/cm. Such magnetic toner is prepd. by mixing a resin for fixing, magnetic powder and electric charge controlling agent at a suitable ratio. The developer is obtd. by mixing the above-mentioned ferrite carrier and the above-mentioned magnetic toner and the mixing ratio thereof is required to be made 60-90:40-10wt.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a dry developer used for developing an electrostatic latent image formed on the surface of an image carrier, and particularly relates to a dry developer used for developing an electrostatic latent image formed on the surface of an image carrier. Electrostatic image developer 1 (related to).

(Prior art) In the electrophotographic method, an electrostatic latent image is formed on the surface of an image carrier, this still image is developed to obtain a toner image, and this toner image is directly fixed or the toner image is transferred. After being transferred onto a member, it is fixed to obtain a final image. Magnetic brush development is usually used to develop electrostatic latent images. The developer used in magnetic brush development has traditionally been a magnetic carrier such as iron powder or ferrite powder, a resin, and a colorant. A two-component developer, which is a mixed powder with a non-magnetic toner containing Both are frictionally charged to charge the toner to a predetermined polarity so that only the toner adheres to the surface of the image carrier, which has the advantage of being easy to transfer due to the use of insulating toner.

On the other hand, a one-component magnetic toner mainly consisting of a developer, resin, and magnetic powder is also used.

A developing method using magnetic toner is described in Japanese Patent Publication No. 56-27, for example.
As noted in Japanese Patent Application No. 05, a method is known in which conductive magnetic toner is held on a conductive sleeve and the toner is attached to the surface of the image carrier by electrostatic induction. Since it is electrically conductive, it can be applied to the so-called CPC method in which the toner image is directly fixed after development, but cannot be applied to the so-called PPC method in which the toner image obtained by development is transferred to the transfer sheet 1 and then fixed.

Therefore, in order to facilitate transfer, a developing method using insulating magnetic toner was proposed. For example, JP-A-53-3113
No. 6 discloses a method in which a non-magnetic sleeve holding insulating magnetic toner is moved at high speed to pre-charge the toner before development. However, even with this method, since uncharged magnetic toner is difficult to charge, the surface potential of the photoreceptor must be set several hundred volts higher than normal, which reduces the lifespan of the photoreceptor. Therefore, a charged magnetic toner has been proposed in which a charge donor is added to a magnetic toner to charge the toner to a predetermined polarity before development. (Unexamined Japanese Patent Publication No. 55-48754, 5
No. 7-45555, No. 57-45556゜ No. 55-45
(Refer to various publications such as No. 557) When this charged magnetic toner is used, the toner is charged to the same degree as a two-component developer due to frictional charging between the toners, between the toners and the sleeve, or between the toner and the doctor blade. It became possible to develop images using the surface potential of the body.

Although the two-component developer and the charged magnetic toner have advantages as described above, they also have the following disadvantages.

In the case of two-component developers, good images can be obtained in terms of image density and resolution changes, but there is generally a problem in that the reproducibility of halftones is poor. On the other hand, in the case of charged magnetic toner,
As the amount of charge on the toner increases, the frictional electrification of the toner particles also increases, making it easier for the toner to coagulate on the sleeve, causing clumped toner to accumulate on the doctor blade, resulting in insufficient development due to insufficient toner on the sleeve. Streaks may occur.

Therefore, a developer containing a mixture of a magnetic carrier and a magnetic toner was proposed.
(See Nos. 162563 and 59-216149) (Problems to be Solved by the Invention) Even if the developer is a mixture of a magnetic carrier and a magnetic toner containing a charging material, if the magnetic carrier is iron powder (t ￥f
(Refer to the example of Japanese Patent Publication No. 56-106249), the problem arises that the reproducibility of halftones is insufficient.

When a ferrite carrier is used as a carrier (Japanese Patent Application Laid-open Nos. 59-162563 and 59-216149)
is effective in preventing charged agglomeration of toner, but if the particle size of the carrier is small, carrier adhesion tends to occur on the surface of the photoreceptor. It is an object of the present invention to provide a developer for developing electrostatic images that can obtain high-quality images without being accompanied by.

(Means for Solving the Problems) The developer for developing electrostatic images of the present invention comprises a ferrite carrier having a saturation magnetization of 55 to 75-/1 and a volume resistivity of 106 to 1010 Ω·m, and a ferrite carrier having a volume resistivity of 1,014 Ω·m. and a charged magnetic toner having a volume resistivity of 10 to 60 μe in absolute value.
It is characterized by having a charge amount of /l.

In the present invention, the ferrite carrier is a sintered body of a suitable metal oxide and trivalent iron oxide, and specific compositions include Ba-Ni-Zn ferrite, Mn-Z
n ferrite, Ni-Zn ferrite, Ln-Zn
7 z light, Cu Zn7 elite, Cu-Zn-
Examples include kneeling ferrite, NIg Zn 7 ferrite, and the like. Such a ferrite carrier is produced by calcining raw materials mixed at an appropriate blending ratio for 0.5 to 5.0 hours, pulverizing them to an average particle size of 2.0 μm or less, and granulating them to a predetermined particle size.
The product can then be produced by firing at a temperature of 1250° C. to 1650° C. for 3 to 5 hours, followed by crushing and classification.

The physical properties of the ferrite carrier are determined by the conditions of use, but under normal development conditions 1, for example, the development speed is 50 to 50%.
At 200 m/sec, the magnetic force of the magnet roll is 50 m/sec.
0 to j000G (value on the sleeve), when the developer transport speed is 10 to 800 y/sec, the saturation magnetization (, σS) is 55 to 75 emu/g, D, C100
The volume resistance in v/cm is 106 to 1010Ω・saw,
The average particle size distribution is preferably in the range of 74 to 105 μm.

When C3 is less than 55 emu/g, the carrier easily separates from the sleeve and adheres to the surface of the photoreceptor during conveyance, and when C8 is greater than 75 emu/g, the conveyance due to the magnetic force of the carrier is strong. If the image becomes too thick, streaks will appear in the image with solid black areas.

If the particle size of the carrier is small, the carrier will adhere to the surface of the photoreceptor, while if the particle size is large, the image will tend to become rough. Therefore, the particle size distribution is preferably in the range of 74 to 105 μm, but even if the content of particles smaller than 74 μm and larger than 105 μm is not necessarily zero, as long as both are 10 weight or less, there is no practical problem. Does not occur.

When the volume resistivity exceeds 10 10 Ω·m, the developability deteriorates, and when the volume resistivity is less than 10 6 Ω·a, carrier tends to adhere to the surface of the photoreceptor. The volume resistance of the carrier can be adjusted by various methods.
As proposed in No. 1985, a method of performing appropriate heat treatment after firing and crushing is effective.

In the present invention, any 7° C. light carrier having the above-mentioned physical properties can be used, but Ba--Ni--Zn type ferrite carrier is particularly suitable from the viewpoint of image quality.

In the present invention, the charged magnetic toner needs to have a charge amount of 10 to 60 μc/g in absolute value in order to obtain a good image. That is, if the amount of charge is less than 10 .mu.c/g, the force of adhesion to the electrostatic charge image becomes too strong, making it easy to cause sagging, while if it exceeds 30 .mu.c/g, the image density decreases. A more preferable range of the amount of charge is 15 to 2511 c/? It is. 1. In order to obtain good transferability, it is necessary that the t1 toner has a volume resistivity of 1014 Ω·m or more in an electric field of C4000v/crn.

Such magnetic sleeve toner is produced by mixing a fixing resin, magnetic powder, and charge control agent in an appropriate ratio, and then pulverizing the mixture.

It can be manufactured by a known method such as a spray drying method. It is also possible to add a fluidity modifier (for example, fine silica powder) and/or a resistance modifier (for example, carbon black) inside and/or on the surface of the toner particles.

The above-mentioned fixing resin may be appropriately selected depending on the fixing method (for example, see Japanese Patent Application Laid-Open No. 57-97545).
For example, in the case of a hot roll fixing method, styrene/acrylic copolymers, styrene/butadiene copolymers, polyester resins, epoxy resins, and mixed resins thereof may be used.

As the magnetic powder, alloys or compounds containing ferromagnetic elements such as ferrite, magnetite, iron, cobalt, nickel, etc. can be used, but in order to incorporate them into the toner, the average particle size should be 0.1 to 3 μm. I would like something like this. The amount contained in the toner is 10 to 70
A range of 10 to 10 cm is appropriate. If it is less than 10 Jt%, the magnetic force of the toner decreases and it becomes easy to separate from the sleeve.
If it exceeds 0 weight, the volume resistivity will decrease because it is itself conductive, and the fixing performance will also be poor. The more preferable content is 2
It is 0 to 55% by weight.

As the charge control agent, known dyes or pigments can be used. Examples include nigrosine dyes that have positive triboelectric charging properties, nigrosine dyes modified with higher fatty acids, and metal-containing (Cr) azo dyes that have negative triboelectric charging properties. The content of this charge control agent is determined depending on the amount of charge of the toner, but it may generally be in the range of 1 to 10 times.

The developer of the present invention is obtained by mixing the above-mentioned ferrite carrier and the above-mentioned magnetic toner, and it is necessary that the mixing ratio of the two be 60-90:40-10 by weight.

If the blending amount of the ferrite carrier is less than 60% by weight, that is, if the toner concentration exceeds 40% by weight, the toner tends to scatter9, and the amount of spent toner increases, shortening the life of the carrier. If the blending amount of the carrier exceeds 90% by weight, the carrier tends to aggregate and carrier adhesion tends to occur.

When using the developer of the present invention, it is desirable to set the following development conditions.

The developer conveyance method is not particularly limited, but a method in which at least the sleeve is rotated is desirable in order to prevent magnetic aggregation of the carrier. Therefore, in addition to a method in which only the sleeve is rotated, a method in which the sleeve and the magnet roll are rotated in the same direction (Japanese Patent Publication No. 57-12148) or in opposite directions is also included.

The development gap (the gap between the photoreceptor and the sleeve at the development position) must be 1.0 mm or less to ensure the contact width between the magnetic brush and the photoreceptor, and the magnetic brush makes soft contact with the photoreceptor. It is desirable that the deafness be 0.3 or more. The preferred range is 0.4 to 0.64. Further, the doctor gap may be set to be equal to the development gap.

In the present invention, the magnetic properties of the ferrite carrier are measured using a vibrating sample magnetometer (Model VSM-3 manufactured by Toei Kogyo). The volume resistance of the ferrite carrier and magnetic toner is small for the sample (several tens of mf).
6.05 Kakuφ(
Filled in a Teflon (trade name) insulating cylinder with cross-sectional area = 0.073i), and D-C2 under a pressure of 0.1 to 9.
The resistance of the carrier in an electric field of 00v/cy is D, C4D.
The resistance of the toner was measured using an electric field of OOvkn, and the volume resistivity was calculated. For the measurement, an insulation resistance meter (Model 4629A) manufactured by Yokotsu-Hieredbackard was used. The particle sizes of the carrier and toner were measured using a particle size analyzer (Coulter Counter Model TA-I manufactured by Coulter Electronics). Toner charge amount can be measured using a blow-off triboelectric charge meter (
The test was carried out using Toshiba Chemical TB-200 model).

(Examples) Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Ba015%, Zn025%, Ni010% in molar ratio.

Each raw material was weighed so that the Fezes content was 60%, and dry mixed in a ball mill. The obtained mixed powder was calcined at a temperature of 900°C for 2 hours (7. Then, the temporary phosphorus powder was put into the ball mill again and crushed into particles with a particle size of 1 μm or less. ○The obtained crushed pre-settling binder was added. granulated by a spray drying method, sintered in air at a temperature of 1600°C for 2 hours, and then granulated with N
2 + 02 atmosphere (0! concentration 20%) at a temperature of 800°C for about 6 minutes and then classified to obtain particles with a particle size of 74~
10μ (4.5% by weight of particles less than 74μm, 105μ
The ferrite carrier (A1
) was obtained.

In addition, under the same conditions as above except that the classification conditions were changed, a ferrite carrier (A2) with a particle size of 7 to 105 μm and a particle size of 7
A ferrite carrier (A5) with a diameter of 4 to 149 μm was obtained.

48 parts by weight of styrene-butadiene copolymer (Pryolide 85B, manufactured by Dou-Year), 50 parts by weight of magnetic powder (EPT-500, manufactured by Toda Kogyo), and 2 ffii parts of a negative charge control agent (Bondron E-81, manufactured by Orient Chemical Co., Ltd.) 0.6 parts by weight of hydrophobic silica fine powder (Nippon Aeromol Oku Aerosil R972) was externally added to a toner with an average particle size of 13 μm, and the volume resistance was 5 × 100 × 1, and the charge amount was 11.
A negatively charged magnetic toner (AI > 8 μC/liter) was obtained.

Each of the three types of ferrite carriers and the charged magnetic toner were mixed at a weight ratio of 60:40 to prepare six types of developers shown in Table 1.

Image evaluation was performed using the above developer under the following conditions.

Peripheral speed 150w! After uniformly charging the Se drum rotating with IAec to +720■ with a corona charger, a semiconductor laser (HL-1400, newly manufactured by Hitachi, oscillation wavelength 780 m, output 5 m
An electrostatic charge image was formed by dividing exposure of W). For development, a stainless steel sleeve with an outer diameter of 62 mm is rotated at 500 m/sec in the opposite direction to the Se drum in the developing section, and 8-pole symmetrical magnetization is applied with an outer diameter of 29 and 5 m, and a magnetic force of 1000 G is applied on the sleeve. 100 Or, p in the opposite direction to the sleeve.

m, and the development gap and doctor grab were both set to 0.5 mm [2. The toner images obtained from the plastic images 1 to 1 were transferred onto plain paper by corona discharge, and then heated at a roll temperature of 180°C, an inter-roll pressure of 1 ky,
Heat roll fixing was performed under the condition of double width 4.0 bleaching. The evaluation results are also shown in Table 1.

Table 1 From Table 1, when using a ferrite carrier (flat size 1) within the particle size distribution range of the present invention (7), a high quality image with high image density and resolution and no background fog due to toner scattering was obtained. Ferrite carriers outside the range of particle size distribution (
It can be seen that when A 2,3) is used, carrier adhesion or images become rough.

Example 2 Other than 1J where heat treatment conditions (Ot once) were changed, implementation f511
Manufactured under the same conditions as 1. The particle size is 74-10571. '
s60 emu/g, and four types of ferrite carriers (flat 4 to 7) with different volume resistivities were used. However, 1～,
Only samples No. 1 and 17 were not subjected to heat treatment.

The volume resistance is 5 x 106Ω for flat 4 and 1 x 10 for A5.
6Ω・-1A6 is 9X106Ω・σ'N71; 7 is <
It was 109Ω·on.

Each of these ferrite carriers and the charged magnetic toner of Example 1 were mixed at a heavy Jti ratio of 60:40 to obtain 4
Types of developers (B-1 to Is-4) &r,l! I
I did it.

Image evaluation was carried out under the same conditions as in Example 1 using the above developer No. 113 under conditions 1'. The results are shown in Table 2.

Table 2 From Table 2, carrier adhesion occurs when the resistance of the carrier is lower than the range of the present invention (B-1), but if it is within the range of the present invention, there is no carrier adhesion and a good image is obtained. You can see what you can get.

Example 3 NiO+ ZnO+ Fe! ds in various ratios and treated under substantially the same conditions as in Example 1 to obtain 5.
Various types of ferrite carriers were obtained.

Table 3 In addition, Li Or Zn O + Few Os were blended in various ratios and treated under substantially the same conditions as in Example 1 to obtain two types of ferrite carriers shown in Table 4.

Table 4 Five types of developers (C-1 to C-5) were prepared by combining each of these ferrite carriers and the charged magnetic toner of Example 1 at a weight ratio of 60:40. Image evaluation was performed under the same conditions as in Example 1 using these developers. The results are shown in Table 5.

Table 5 From Table 5, when the saturation magnetization (σS) of the carrier is higher than the range of the present invention (C-5, C-5>, the resolution is decreased and peeling streaks occur in the black solid image, but it is within the range of the present invention). It can be seen that a good image can be obtained within the range.

Example 4 The ferrite carrier (A1) of Example 1 was mixed with each of seven types of charged magnetic toners having different charge amounts in a total weight ratio of 60:40 to form a hepapolar developer (D-1). ~D-7)
adjusted. These charged magnetic toners had the same composition as in Example 1 except that the content of the negative charge control agent and the content of the magnetic powder were changed.

Image evaluation was performed under the same conditions as in Example 1 using each of the above developers. The results are shown in Table 6.

Table 6 From Table 6, when the charge amount of the toner is lower than the range of the present invention (D-1), capri occurs, and when it is higher than the range of the present invention (D-6, D-7), the image density is Although the image quality decreases, it can be seen that good images can be obtained within the range of the present invention.

Example 5 Five types of developers (E-1 to E-5) were prepared by varying the mixing ratio of the ferrite carrier (A1) of Example 1 and the negatively charged magnetic toner of Example 1. Image evaluation was performed under the same conditions as in Example 1 using these developers. The results are shown in Table 7.

Table 7 From Table 7, when the carrier composition is less than the range of the present invention (E-1, E-2), soil burrs occur, and when it is more than the range of the present invention (E-5), carrier adhesion occurs. It occurs, but
It can be seen that good images can be obtained within the scope of the present invention.

(Effect of the invention)

Claims (3)

[Claims] (1) Saturation magnetization of 55-75 emu/g and 10^6-1
It consists of a ferrite carrier having a volume resistivity of 0^1^0 Ω·cm and a charged magnetic toner having a volume resistivity of 10^1^4 Ω·cm or more, and the absolute value of the ferrite carrier and the magnetic toner is 10 A developer for developing an electrostatic image, characterized by having a charge amount of ~30 μc/g. (2) Ferrite carrier and magnetic toner are 60 to 90
The developer for developing an electrostatic image according to claim 1, wherein the developer is mixed at a weight ratio of: :40 to 10. (3) The developer for developing electrostatic images according to claim 1, wherein the ferrite carrier has an average particle size distribution of 74 to 105 μm.