JPS62294259A - Developer for electrostatic charge image - Google Patents

Abstract

PURPOSE:To improve the quality of a developer for electrostatic charge images by mixing a magnetic carrier contg. iron oxide and having specific satd. magnetization and volume resistivity and an electric charge type magnetic toner contg. magnetic powder and having specific coercive force and volume resistivity. CONSTITUTION:The magnetic carrier is formed by incorporating at least the iron oxide such as magnetite or ferrite therein. The satd. magnetization of the magnetic carrier is specified to 50-80emu/g and the volume resistivity thereof to 10<3>-10<12>OMEGA.cm. The electric charge type magnetic toner is prepd. by mixing 5-50wt% magnetic toner, resin for fixing and electric charge controlling agent. The coercive force of the charge type magnetic toner is specified to <150Oe and the volume resistivity to >=10<14>OMEGA.cm. Such magnetic carrier and magnetic toner are mixed at 90-30:10-70 by weight to prepare the developer for electrostatic charge images. Since the magnetic carrier contg. at least the iron oxide and the magnetic toner contg. the magnetic powder at the low ratio and having the low coercive force are mixed, the high-quality image is obtd.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] 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 The present invention relates to a developer for developing electrostatic images comprising a magnetic carrier and a magnetic toner.

[Conventional technology]

In electrophotography, an electrostatic latent image is formed on the surface of an image carrier, this electrostatic latent image is developed, and the resulting toner image is directly fixed, or the toner image is transferred onto a transfer member and then fixed. to obtain the final image features. Electrostatic latent images are usually developed by magnetic brush techniques.

Developers used in the magnetic brush development method include iron powder,
Two-component developers, which are mixed powders of a magnetic carrier such as ferrite powder and a non-magnetic toner in which a colorant or the like is dispersed in a resin, are often used. In the magnetic brush development method using a two-component developer, carrier and toner are mixed at a predetermined ratio (usually 3 to 3).
The toner is mixed with a toner tlA degree of about 5%, and the toner is charged to a predetermined polarity by frictional charging with the carrier, so that only the toner adheres to the surface of the image carrier. When using a two-component developer, it is easy to obtain faithful images because the toner has a distinct charge, but in order to achieve stable development, strict control of the toner concentration and means of mixing the carrier and toner are required. It is necessary to provide it in the developing device.

In contrast, it has been proposed to use a one-component developer consisting of a magnetic toner whose main components are resin and magnetic powder without using a carrier, and recently, insulating magnetic toner is often used from the viewpoint of transferability. . However, JP-A-53-31136
The uncharged magnetic toner disclosed in the above issue can be developed equally well even if the polarity of the charged latent image is positive or negative, but since the toner is difficult to charge, the surface potential of the image carrier is set higher than usual. This poses a problem in terms of the life of the photoreceptor.

Therefore, in order to make the toner easier to charge, a charged magnetic toner to which a charge donor is added has been proposed.

Charged magnetic toner is charged to the same degree as a two-component toner by contact with a sleeve or doctor blade and by contact between toners, and therefore can be developed with a normal surface potential of a photoreceptor. However, when a one-component developer made of charged magnetic toner is used, the toner tends to be charged and aggregated on the sleeve, and the agglomerated toner is deposited on the doctor blade, causing streaks of insufficient development on the sleeve due to insufficient toner. There is.

These shortcomings should be solved (for example, Japanese Patent Application Laid-Open No. 59-16
A developer in which a magnetic carrier and an rJ electromagnetic toner are mixed as disclosed in Japanese Patent No. 2563 and No. 59-216149 has been proposed and put into practical use.

When developing electrostatic latent images using the magnetic brush method using this developer, iron oxides such as ferrite and magnetite are used as the main carrier rather than iron powder carriers, in terms of image quality (particularly midtone reproducibility) and carrier life. A carrier is used.

Further, as the amount of toner increases, the toner tends to scatter, and on the other hand, as the amount of carrier increases, carrier adhesion tends to occur, so the toner concentration is set in the range of 10 to 70%.

[Problem that the invention seeks to solve]

An advantage of the developer containing the above magnetic carrier and charged magnetic toner is that the image quality is stable (equivalent to a two-component developer) even when a large number of copies (50,000 to 150,000) are made. In addition, in a one-component developer consisting only of magnetic toner, if the content of magnetic powder is less than 50% by weight, the image;
Since the magnetic strength decreases, it is necessary to add 50% by weight or more of magnetic powder, which is insufficient in terms of fixing properties. On the other hand, since the above developer contains a carrier, high image density can be obtained even if the amount of magnetic powder is less than 50% by weight.
Therefore, fixing performance can also be improved.

However, even the above-mentioned developer is not fully satisfactory in terms of image density and sharpness of image quality, and further improvement of image quality is desired.

Therefore, an object of the present invention is to provide a developer for developing electrostatic latent images that can obtain images of higher quality than conventional ones.

[Means for solving problems]

The developer for developing electrostatic latent images of the present invention contains at least iron oxide, and has a saturation oxidation of 50 to 80 emu/g and 103 to 1 emu/g.
A charged magnetic toner containing a magnetic carrier having a volume resistivity of 0'2 Ω·cIII and 5 to 50% magnetic The magnetic carrier and the magnetic toner are mixed in a weight ratio of 90 to 30:10 to 70.

In the present invention, the monovalent carrier is magnetite (pe
30n) or ferrite ((MO) l-x F
ezO3x, where M is a monovalent or divalent metal, and X is 50~
80 mol%] of iron oxide. The specific composition of the ferrite carrier is:
Mn-Zn ferrite, Ni-Zn ferrite, Ba-
Ni-Zn ferrite, I, 1-Zn ferrite, C
u-Zn ferrite, Cu-Zn-Mg ferrite,
Examples include Mg-Zn ferrite.

The physical property values of the magnetic carrier are appropriately determined depending on the usage conditions, but under normal conditions, that is, the development speed is 50 to 200 x
*/sec, the magnetic force on the sleeve is 500~1200G
In this case, it is desirable to set as follows.

If the saturation magnetization (σ,) is less than 50 emu/g, the carrier will easily separate from the sleeve and adhere to the image carrier, and if it exceeds 70 emu/g, the conveying force will be too strong and scratches will occur in the black edges. Therefore, it is set in the range of 50 to 70 emu/g. If the volume resistivity is less than 103 Ω·G, it will easily adhere to the surface of the image carrier, and if it exceeds 10”Ω·cm, the developability will deteriorate, so a range of 103 to IQ+2Ω·G is preferable.The particle size is If the particle size is too small, it tends to adhere to the surface of the image carrier, and if it is too large, the image becomes rough, so the average particle size is preferably in the range of 40 to 100 μm.

Magnetic toner has an absolute value of 5 to 3 to obtain a good image.
It is desirable to have a charge amount of 0 μc/g. That is, if the amount of charge is less than 5 μc/g, soil blurring tends to occur, while if the amount of charge is more than 30 pc/g, the image density will decrease. If the volume resistivity is too low, the transferability will deteriorate, so it is necessary to set the volume resistivity to 10'4 Ω·1 or more. Further, when the coercive force (tile) is 1500e or less, the image density is greatly improved and the image sharpness is also improved. However, if the coercive force is less than 3008, poor conveyance will occur on the sleeve. Therefore, the range of coercive force is 30 to 150e.

The reason why image quality improves when the coercive force is 1500e or less is as follows. Because the coercive force is weak, the toner chain is easily broken (the toner is more likely to be developed faithfully to the latent image).

Such a magnetic toner can be produced by mixing a fixing resin, magnetic powder, and charge control agent in an appropriate ratio, and using a known method such as a powder grinding method or a spray drying method. In addition, a fluidity modifier (for example, fine silica powder) or a resistance adjuster (for example, carbon bra,
) may be added.

The fixing resin described above may be appropriately set depending on the fixing method. (For example, see JP-A No. 57-97545) - For example, in the case of a hot roll fixing method, styrene-acrylic copolymer, styrene-butadiene copolymer, polyester resin, epoxy resin, or a mixture of two or more thereof Examples include resins that are

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 is about 0.1 to 3 μm. particles are good. Since the coercive force of toner is determined by the type of magnetic powder, it is necessary to use magnetic powder whose toner coercive force falls within the above-mentioned range. Of course, the magnetic powder is not limited to one type, and two or more types may be mixed. The amount contained in the toner needs to be 50% by weight or less from the viewpoint of fixing properties, and on the other hand, it needs to be 10% by weight or more from the viewpoint of transportability, so it is set in the range of 10 to 50% by weight. .

As the charge control agent, known dyes or pigments can be used. Specifically, nigrosine dyes having positive triboelectric charging properties and metal-containing (Cr) azo dyes having negative triboelectric charging properties may be mentioned. The content for this charge control is determined depending on the amount of charge of the toner, but it may generally be in the range of 0.1 to 5%.

In the developer of the present invention, the mixing ratio of the magnetic carrier and the magnetic toner is preferably 30 to 90,770 to 10 by weight. If the amount of the magnetic carrier is less than 30% by weight, the amount of toner becomes too large and the toner tends to scatter, and the amount of spent toner increases, resulting in a shortened carrier life.

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 in order to prevent magnetic agglomeration of the carrier, it is preferable to at least rotate the sleeve, and more preferably, the magnetic roll is rotated in the opposite direction to the sleeve at an angle of 2 to 10 degrees from the sleeve. It is a method that rotates twice as fast. The circumferential speed of the sleeve is 150 to 500
A range of 1/sec is preferred.

The development gap is preferably 1.0 mm or less to ensure a contact width between the magnetic brush and the image carrier, and 0.3 mm or less so that the magnetic brush comes into soft contact with the image carrier. The doctor gap may be set equal to the development gap.

The developer of the present invention is the same as a normal two-component developer in that it is a mixed powder of a magnetic carrier and a toner, but it is different in that a magnetic toner is used as the toner, and therefore it has a magnetic brush shape. There will be a big difference.

FIGS. 1 and 2 schematically show magnetic brushes using the developer of the present invention and a conventional two-component developer, respectively. Both figures show that in the two-component developer, the toner 2' is electrostatically adhered to the surface of the carrier 1 almost uniformly, whereas in the developer of the present invention, the magnetic toner is absorbed by the magnetic attraction force of the magnet. Since the image is also reflected, it can be seen that the magnetic toner 2 is concentrated and adhered to the vicinity of the contact area between particles of the carrier 1.

When the developer of the present invention is used, the magnetic brush takes on such a configuration, so that the contact between the magnetic toner and the image carrier is stable, and good development can be performed. In both figures, 3 indicates a non-magnetic sleeve and 4 indicates a magnet.

In the present invention, the magnetic properties of the magnetic carrier and the magnetic toner are values measured using a vibrating sample magnetometer (Model VSM-3 manufactured by Toei Kogyo Co., Ltd.). The volume resistivity of the magnetic carrier and magnetic toner is determined by weighing a small amount (several tens of mg) of the sample and using an improved dial gauge with an inner diameter of 3.05mm (cross-sectional area of 0).
．． 073 cIA) Fill in a Teflon (trade name) insulating cylinder, apply a load of 0.1 kg, D,
C, the resistance of the carrier in an electric field of 100 V/am, D, C
, the resistance of the toner was measured in an electric field of 4 kV/cm, and the volume resistivity was calculated. For the measurement, an insulation resistance meter (Model 4329A) manufactured by Yokogawa Hewless Packard was used. The particle size of the carrier and magnetic 1-ner was measured using a particle size analyzer (Coulter Counter Model TA-II manufactured by Coulter Electronics).
It was measured by The charge amount of the toner was measured using a blow-off triboelectric charge meter (Toshiba Chemical Model TL3-200).
The measurement was performed using a ferrite carrier (KBN-100 manufactured by Hitachi Metals) at a toner concentration of 5%.

〔Example〕

EXAMPLES The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

Example 1 Molar ratio of Ba015%, Zn025%, Ni010%,
Each raw material was weighed so that the FezO content was 360%, dry mixed in a ball mill, and calcined at a temperature of 900° C. for 2 hours.

This calcined powder was put into the ball mill again and pulverized into particles having a particle size of 1 μm or less. (obtained) A binder was added to the crushed powder, granulated by the spray drive method, sintered at a temperature of 1300°C for 2 hours, and classified to give an average particle size of 100 μm and σs.
A ferrite carrier with a volume resistance of 60 emu/g and a volume resistance of 5×10 3 Ω·cm was obtained.

The magnetic toner is made of styrene-acrylic copolymer (M, -
10,000, M, = 6,000) 58 parts by weight, 40 parts by weight of magnetic powder, and charge control agent (each Cr azo dye) 2
parts by weight were mixed, kneaded at 200°C, cooled and solidified, then pulverized, 0.5 parts by weight of pulverized hydrophobic silica fine powder was added, heat treated at 120°C, and then classified. Here, five types of magnetic powder (No,
Magnetic toners 1 to 5) were obtained.

All of these magnetic l/ners have an average particle size of 13 μm.
, volume resistance is lXl0"5Ω・IJ, charge amount is -I8μ
c/g. The above ferrite carrier and each magnetic toner were mixed at 60:
Five types of tn developers were prepared by mixing at a double star ratio of 40. Image evaluation was performed using these developers under the following conditions.

A Se drum rotating at a circumferential speed of 150 mm/sec was uniformly charged to +720 cm using a corona charger and then exposed to light to form an electrostatic latent image. For development, a stainless steel sleeve with an outer diameter of 32III was heated at 300 r in the opposite direction to the Se drum in the developing section.
A magnet roll with an outer diameter of 29.3 mm and 8-pole symmetrical magnetization and a magnetic force of 100 OG was placed on the sleeve at 120° r, p, in the opposite direction to the sleeve.
The developing gear and doctor gap were set to 0.6 mm and 0.4 u, respectively. The developed toner image was corona-transferred onto plain paper, and then heat roll fixing was performed under the conditions of a roll density of 180° C., an inter-roll pressure of 1 kg/CrR, and a nip width of 4.0 fins.

The image evaluation results are shown in Table 1.

From Table 1, it can be seen that 1Hc is a magnetic toner within the scope of the present invention (ll
With k12-4), a good image can be obtained, but with 1! l.

It can be seen that a magnetic toner with a high +IIc decreases the image density, and a magnetic toner with a low +IIc causes fogging.

Example 2 In the magnetic toner of Example 1, +ilc was used as the magnetic powder.
Five types of magnetic toners (11m6 to 11hlO) were manufactured using magnetite having a particle diameter of 1200e and varying the blending amount. Table 2 shows the composition and characteristics of these toners.

The ferrite carrier of Example 1 and each of the above magnetic toners were mixed at a weight ratio of 80:20 to prepare five types of developers. Image evaluation was performed under the same conditions as in Example 1 using these developers.

Table 3 From Table 3, high-quality images can be obtained using the magnetic toners of the present invention (Nos. 7 to 9), but capri occurs when using a magnetic toner with a small content of magnetic powder (No. 6). It can be seen that when a magnetic toner (IlhlO) containing a large amount of magnetic powder is used, the fixing performance is lowered.

〔Effect of the invention〕

As described above, the present invention ((K agent) is a mixture of a magnetic carrier containing at least iron oxide and a magnetic toner having a small content of magnetic powder and a low coercive force. High quality images can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the form of a magnetic brush using the developer of the present invention, and FIG. 2 is a diagram showing the form of a magnetic brush using a conventional two-component developer. Figure 1 Figure 2

Claims (1)

[Claims] (1) Contains at least iron oxide, 50 to 80 emu/
containing a magnetic carrier having a saturated oxidation of 100 g and a volume resistivity of 10^3 to 10^1^2 Ω cm and a magnetic powder of 5 to 50% by weight, with a coercive force of less than 150 Oe and a volume resistivity of 10^1^4 Ω
- A charged magnetic toner having a volume resistivity of cm or more, and the magnetic carrier and the magnetic toner have a volume resistance of 90 to 3 cm.
A developer for developing electrostatic latent images, characterized in that the components are mixed at a weight ratio of 0:10 to 70.