JPS59162563A - Mangetic developer for developing electrostatic latent image - Google Patents

Abstract

PURPOSE:To obtain an excellent image free of background fogging without generating any white stripe in a solid-state image by mixing and using magnetic toner with specific coercive force and a ferromagnetic carrier with specific mean particle size. CONSTITUTION:The toner is formed containing resin and magnetic particulates and has >=60 Oe coercive force, and the carrier is a ferromagnetic carrier with about 15-45mum mean particle size and mixed with the toner at a 90:10-60:40 weight ratio. This toner with the coercive force mixes with the carrier excellently and the magnetic flocculation of the carrier which may cause the formation of a white stripe does not occur; and the formation of a magnetic brush is made soft, so excellent image quality is obtained. Further, the carrier made of the ferromagnetic material has intense magnetism and never sticks to a nonimaged part of an electromagnetic latent image even when its amount of electrostatic charge increases, so that no background foggong occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a magnetic developer for developing an electrostatic latent image, specifically, an insulating toner is triboelectrically charged by a carrier, and a developing sleeve is charged by rotation of a magnet as necessary. With rotation, a magnetic developer consisting of toner and magnetic carrier forms a magnetic brush and is transported magnetically.
The present invention relates to a two-component magnetic developer used in the so-called magnetic brush development method, in which an electrostatic latent image carried on the surface of an electrostatic latent image carrier is developed by rubbing it on the surface of the carrier.

Conventionally, this type of magnetic developer has an average particle size of 100~
A developer is known that is made by mixing a magnetic carrier made of iron powder or the like with a diameter of about 200 μm and an insulating toner with an average particle size of about 10 to 20 μm. Unless the mixing ratio is kept constant with high precision, high-quality developed images cannot be stably obtained - and since the appropriate mixing ratio range is narrow, it is difficult to maintain the appropriate mixing ratio during use. In addition, due to long-term use, toner adheres to the carrier surface and the carrier deteriorates, making it necessary to periodically replace the developer with a new one, which requires a large amount of maintenance work and is uneconomical. In addition, there were other drawbacks such as fogging and smearing easily occurring in the developed image and the resolution of the image being low. For this reason,
In recent years, as a developing agent that has improved these drawbacks, Japanese Patent Application Laid-open No. 3/1983 (1989-3: ll'0) has proposed a developer in which fine magnetic powder is dispersed in a binder resin instead of an iron powder carrier. Developers using insulating magnetic particles with a particle size of about 5 to 40 μm as carriers have been proposed.

This developer was developed based on the recognition that some of the above-mentioned drawbacks could be improved by reducing the particle size of the carrier itself. Note 1. When iron powder or the like is reduced in particle size to about 25 to 60 μm and used as a carrier, the magnetic attraction force generated between the carriers during magnetic brush formation becomes strong, and each carrier is attached to the magnetic brush carrier. It is not practical because it aggregates in chains or fins, which impedes the conveyance of the developer and causes problems such as white streaks in solid developed images. For this reason,
In the proposed developer, so-called binder-type magnetic particles, which are made by dispersing fine magnetic powder such as fine iron powder in a binder resin, are used as carriers. Therefore, the magnetic attractive force between the carriers is weakened, and aggregation of the carriers on the magnetic brush carrier is prevented, and soft brush ears are formed, resulting in a developed image of good quality. becomes. However, in this developer, the magnetization of the magnetic carrier is weakened by the presence of resin as a binder, so if a toner with a high charge amount is used, the charge amount of the carrier itself will decrease due to frictional charging with the toner. As a result, the electric attractive force acting on the carrier (the force attracted to the non-image area of the electrostatic latent image carrier) increases, and the carrier is particularly attracted to the electric field reversal area around the image on the surface of the electrostatic latent image carrier. The phenomenon of adhesion of the toner may also occur, which often causes the problem of forming a base fog in the developed image and deteriorating the image quality of the developed image.

The present invention has been made in view of the above-mentioned problems, and it is possible to obtain developed images of extremely good quality without causing white streaks or background fog in solid developed images. The purpose of this invention is to provide a developer that can be used. The gist is that in a magnetic developer for developing electrostatic latent images consisting of an insulating toner and a magnetic carrier, the toner is composed of a resin and a magnetic fine powder and has a magnetic coercive force of approximately 60 Oe or more. toner, while the carrier has an average particle size of 15 to 45
The present invention is a ferromagnetic carrier having a diameter of .mu.m, in which the carrier and the toner are mixed at a weight ratio of 90:10 to 60:40.

That is, the present invention has the advantages of a carrier made of ferromagnetic material, specifically, it has strong magnetization and does not adhere to the non-image area of the electrostatic latent image carrier even if the amount of charge increases, and the underlying fogging is prevented. While taking advantage of the advantage of not generating magnetic flux, we are solving problems caused by too large magnetization. Specifically, the carriers themselves aggregate due to the strong magnetic attraction force generated between each carrier, which adversely affects the magnetic transportability of the developer. The problem of white streaks and the like occurring in a solid developed image is solved by increasing the toner ratio and using a magnetic toner having a specific coercive force.

Here, the reason why a magnetic toner having a coercive force of about 6 o Oe or more is used as an insulating toner is that if the toner does not have magnetism, the miscibility of the toner with the ferromagnetic carrier is extremely poor and the two will separate. This is because, while the above-mentioned white streaks are generated due to carrier aggregation, the triboelectric charging properties of the toner are also deteriorated, and as a result, significant toner scattering occurs. Furthermore, even though the carrier is magnetic, if its coercive force is less than about 60 oersted, the miscibility of the toner with the carrier will not be sufficiently improved, and the white streaks will likely occur due to agglomeration of the carrier. , approximately 6o Oersted or more, the mixing property is sufficiently improved, magnetic agglomeration of carriers is prevented, and a soft magnetic brush is formed. This is because the above problem can be actually solved.

Also, the mixing ratio of carrier and toner is 90:1 by weight.
0-60:40, preferably 85:15-70:30
The reason for this is that if the toner mixing ratio is less than 1Qwt%, even a magnetic toner having the above-mentioned coercive force cannot be expected to be sufficiently effective in preventing magnetic aggregation of carriers and furthermore the generation of the above-mentioned white streaks. Also, significant charge injection from the developing sleeve to the carrier occurs - the carrier is likely to be electrostatically attracted to the surface of the photoreceptor, resulting in scratches on the surface of the photoreceptor. .

On the other hand, if it exceeds 40 W [%, the triboelectric charging properties of the toner itself will deteriorate, resulting in toner scattering, background fogging, etc.

Furthermore, the average particle size of the ferromagnetic carrier is 15 to 45 μm.
Preferably, the average particle size is 30 to 40 μm.
If the thickness is less than 5 μm, the magnetic force of the carrier becomes weak, making it difficult to prevent the carrier from adhering to the surface of the photoreceptor, resulting in scratches on the surface of the photoreceptor. On the other hand, if the diameter exceeds 45 μm, the magnetic force of the carrier becomes stronger, making it easier for the developer to be magnetically aggregated on the developing sleeve, causing white streaks etc. to occur in the solid developed image. This is because the chargeability of the toner in the developer is deteriorated, and base fog etc. occur due to toner scattering and the like.

The insulating toner in the magnetic developer according to the present invention contains a resin as a binder and magnetic fine powder, and also contains a colorant and, if necessary, a charge control agent, etc., as in the case of insulating toners commonly used in the past. However, the content of the magnetic fine powder is preferably 5 to 35 W[%] based on the total toner. This is because it is difficult to produce a toner with sufficient magnetic force when the magnetic fine powder is less than 5 wt%, and when the magnetic fine powder is less than 5 wt%,
If it exceeds %, the development itself will be adversely affected, specifically, the density of the developed image will decrease. As the magnetic fine powder, fine powders of various magnetic substances conventionally used in developers may be used. However, as the material for the ferromagnetic carrier, ferromagnetic materials such as ferrite, iron powder, and magnetic iron oxide are particularly suitable. The particle shape of the magnetic fine powder is preferably an amorphous shape with an uneven surface. Further, as the binder resin, various resins conventionally used in developers, such as polystyrene, styrene-acrylic resin, acrylic resin, and epoxy resin-fluororesin, may be used.

On the other hand, as a developing device in which the developer is magnetically conveyed to the developing area by rotating a magnet, there is
Various other developing devices are known, including those disclosed in Japanese Patent Application Laid-open No. 935 and Japanese Patent Application Laid-Open No. 55-32073, but are not limited to these types of developing devices.
A developing device in which a developing sleeve containing a magnet (magnetic roller) is fixed, or a developing device in which the developing sleeve is rotated in the same direction or in the opposite direction as the magnet,
The magnetic developer according to the present invention can be used. The magnetic developer according to the present invention exhibits particularly excellent effects when used in combination with each of the above-mentioned developing devices.

Examples of the present invention will be described below.

Example 1 3000y of a mixture of 63.3 wt% ferric oxide with an average particle size of 0.5 μm, 25.9 wt% zinc oxide with an average particle size Q, 11Lm, and 10.8 wt% nickel oxide with an average particle size of 13 μm and water 1195F to form a slurry, and to this slurry, polymethacrylic acid sodium salt and Durban 7 (trade name, manufactured by R.T. Pandelbilt) were added.
After adding and mixing about 98 g of 5W% aqueous solution, spray drying with an atomizer, and then baking in air at 1190°C for 2 hours to obtain a ferrite carrier with an average particle size of 34.572 m (composition: (NiO) o, 3 (ZnO)0.7(Fe20
3). , 8. ) was obtained.

Also, this is separately commercially available styrene/acrylic resin 1
00 parts by weight, 4 parts by weight of negatively chargeable dye T RH (trade name, manufactured by Kageya Kagaku Co., Ltd.) and 20 parts by weight of magnetite KBC-100L (trade name, manufactured by Kanto Denka Co., Ltd.) as magnetic fine powder at 150°C. The mixture was kneaded using three rolls, cooled, and then crushed and classified to obtain an insulating toner having an average particle size of 11 μm. The coercive force of this toner was 60 oersted.

The carrier and toner were mixed in a weight ratio of 90:10 and
An insulating toner having an average particle size of 11 μm and a coercive force of 110 oersted was obtained using the same composition and method except that manetite, E'1) T-100 (trade name, manufactured by Toda Kogyo Co., Ltd.) was used in place of L. This toner is mixed with the carrier obtained in the actual flow side 1 at a weight ratio of 10:90 to form a magnetic developer CB).
was prepared.

Example 3 In Example 1, WBC-10O as magnetic fine powder
An insulating toner with an average particle size of 11 μm and a coercive force of 200 oersted was mixed with the carrier for 10 to :90 weight ratio to prepare a magnetic developer (C).

Example 4 In Example 1, WBC-10O as magnetic fine powder
An insulating toner with an average particle size of 11 μm and a coercive force of 350 oersted was obtained using the same composition and method except that magnetite, MTA-740 (trade name, manufactured by Toda Kogyo Co., Ltd.) was used in place of L, and this was mixed with the carrier and :90 weight ratio to prepare a magnetic developer (D).

Comparative Example 1 In Example 1, KBC-100 as magnetic fine powder
The average particle size was 11 μm using the same composition and method except that iron powder, MGMC (trade name, manufactured by Nippon Tetsuko Co., Ltd.) was used instead of L.
- An insulating toner having a coercive force of approximately 0 oersted was obtained, and this was mixed with the carrier at a weight ratio of 10:90 to prepare a magnetic developer (E).

Comparative Example 2 100 parts by weight of the styrene/acrylic resin used in Example 1, 4 parts by weight of TRH, and carbon black MA#8
(trade name, manufactured by Mitsubishi Chemical Industries, Ltd.) by the same method as in Example 1 to obtain an insulating toner (non-magnetic) with an average particle size of 11 μm, and add this to the carrier at a weight ratio of 10:90. A magnetic developer (F) was prepared by mixing.

Each developer is loaded into a developing device (a device in which a magnetic roller rotates in the opposite direction to the developer conveying direction and a developing roller rotates in the same direction) in a toner image transfer type electrophotographic copying machine, and copies are made. Table 1 shows the results of examining the image quality of the copied image restored by repeating the operation. In the above-mentioned developing device, the developing device 3 is arranged in parallel with the photosensitive drum with a small gap therebetween, and contains a magnetic roller that rotates at high speed. Here, the developing sensor 1 is rotated at a low speed in the opposite direction to the Ct photoconductor, and the magnetic roller therein is rotated at the same speed in the opposite direction to the developing sleeve. ≦ Applied. Further, in this developing device, the developer is mixed and agitated by a baguette roller, and the toner and carrier are mutually charged by friction and supplied onto the circumferential surface of the developing sleeve. By the way, conditions 6 for developing an electrostatic latent image in the copying machine are as follows.

[Development conditions]

Magnetic % Roller rotation speed -1, OOOrPm Developing sleeve rotation speed: 60 rPIN electrostatic latent image maximum potential: +400
V Development bias voltage: +100V As is clear from the results in Table 1, when a small particle size ferromagnetic carrier is used in combination with a non-magnetic toner (developer F), white streaks and undercoat fogging occur. If the coercive force is small (developer E) when used in combination with a magnetic toner, white streaks will occur although background fogging can be prevented. It can be seen that the combination with toner can simultaneously prevent the occurrence of white streaks and background fog. Regarding this copying experiment, it was also separately confirmed that the developers according to the present invention (Developers A to D) were able to obtain very sharp and good copied images compared to those obtained by commercially available copying machines. has been done.

Example 5 Using the ferrite carrier and insulating toner prepared in Example 1, magnetic developers (A, G-J) were prepared by varying their mixing ratio as shown in Table 2. A copying experiment identical to the copying experiment described above was conducted using a developer and the quality of the resulting copied image was examined. The results are shown in Table 2.

Table 2 As is clear from the results shown in Table 2, when the toner mixing ratio is 5W (%), white streaks occur, while at 60 W (%), the triboelectric charging properties of the toner deteriorate and the toner does not have enough charge. Since the toner cannot be retained and top-press fog occurs due to toner scattering, it is found that the appropriate toner mixing ratio is in the range of approximately 10 to 4 Q wt%.In addition, regarding this copying experiment,
In this range, especially when developer H is used, not only will there be no white streaks or background fog, but there will be no carrier adhesion to the non-image areas of the electrostatic latent image, and the image density will be very high. It has also been separately confirmed that sharp and good quality copied images can be obtained.

Example 6 According to the same method as in Example 1, ferrite carriers having the average particle diameter shown in Table 3 were obtained. Then, each carrier was mixed with the toner obtained in Example 1 at a toner mixing ratio of 1.
0w% developers (K, N) were prepared, and a copying experiment identical to the copying experiment described above was conducted using each developer, and the image quality of the resulting copied images was examined. The results are shown in Table 3.

As is clear from the results in Table 3 and Table 1, when used in combination with a toner having a coercive force of 60 degrees or more, good image quality is obtained when the carrier particle size is at least in the range of 15 to 45 μm. It can be seen that the following can be obtained. Note that when the average particle size of the carrier exceeds 45 μm (developer N), white streaks occur because the magnetization of the carrier itself becomes too strong as the particle size increases, causing the carrier to form on the developing sleeve. This is thought to be because magnetic aggregation is more likely to occur, making it difficult for the carrier to move following the rotation of the magnetic roller, and as a result, the conveyance of the developer itself is inhibited. Also, from this, the conventionally used mutton particle size 1
It is said that the ferromagnetic carrier of 00 to 20011 m is unsuitable as a carrier in a magnetic developer used in a developing device in which the developer is magnetically conveyed to a developing area by rotation of a magnet. Further, regarding this experiment, it has been separately confirmed that within the above range, especially when developer M is used, a developed image of very good quality can be obtained.

Comparative Example 3 Styrene-acrylic tree used in Example 1/+=100
Weight parts and macnetite RB-BL2 used in Example 3
Part by weight of Q'O is kneaded with three rolls, and after cooling, pulverization,
It was classified to obtain a so-called binder type magnetic carrier having an average particle size of 11 μm. Example 1 of this binder type magnetic carrier
A developer (0-R) was prepared by mixing with the insulating toner obtained in the mixing ratio shown in Table 4, and a copying experiment identical to the above copying experiment was conducted using each developer. I checked the image quality. The results are shown in Table 4.

Table 4 As is clear from the results in Table 4, when the developer using the binder-type magnetic carrier has a low toner mixing ratio, there is no white streak or background fog due to toner scattering, resulting in good copied images. However, because the potential of the electrostatic latent image to be developed is relatively low at +400μ, the density of the copied image is low, and the adhesion of carrier to non-image areas is unavoidable, and the image density is low. It can be seen that when the toner mixing ratio is increased in order to increase the toner content, the amount of carrier adhesion increases rapidly, and in any case, it is difficult to obtain good results.

Claims (1)

[Claims] (1) A magnetic developer for developing an electrostatic latent image consisting of an insulating toner and a magnetic carrier, wherein the toner contains a resin and a magnetic fine powder and has a coercive force of 60 Oe or more. , on the other hand, the carrier is a ferromagnetic carrier with an average particle size of 15 to 45 μm, and the carrier and the toner have a weight ratio of 90:10 to
A magnetic developer for developing electrostatic latent images, characterized in that the mixture is mixed at a ratio of 60:40.