JPH08262803A - Carrier for developing electrostatic latent image - Google Patents

Abstract

PURPOSE: To attain satisfactory electrostatic charge of a toner even when a toner having a small particle diameter is used so as to form a high quality image and to stably carry out satisfactory image formation by using a 1st carrier holding magnetic powder stuck to the surface and having a specified average particle diameter and a specified saturation magnetization or below and a 2nd carrier having a specified average particle diameter and a specified saturation magnetization or below. CONSTITUTION: This carrier contains a 1st carrier holding magnetic powder stuck to the surface and having 80-150μm average particle diameter and <=50emu/g saturation magnetization and a 2nd carrier having 30-50μm average particle diameter and >=55emu/g saturation magnetization. The reason for 80-150μm average particle diameter of the 1st carrier is that the flowability of a developer cannot be satisfactorily improved in the case of <80μm and the charging property to a toner is deteriorated in the case of >150μm. The reason for <=50emu/g saturation magnetization of the 1st carrier is that the flowability of a developer and the reproducibility of thin lines are adversely affected in the case of >50emu/g. A carrier having 90-100μm average particle diameter and 45-50emu/g saturation magnetization is preferably used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic latent image developing device used for developing an electrostatic latent image formed on an image bearing member such as a photoconductor in an image forming apparatus such as a copying machine or a printer. The present invention relates to a carrier, and more particularly to a binder type electrostatic latent image developing carrier in which magnetic powder is dispersed in a resin.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, when developing an electrostatic latent image formed on an image bearing member such as a photoconductor, a toner and a carrier are used as developers. The mixture was widely used.

As the carrier to be mixed with the toner in this way, in addition to the ones in which powders of iron, ferrite and the like are used as they are, there are binder type ones in which these magnetic powders are dispersed in a resin. Was known.

Here, a carrier using iron, ferrite or the like as it is generally has a high magnetic strength, the ears of a magnetic brush formed become hard, white streaks are generated in a black solid image, and a photo original or the like. There is a problem such as streak unevenness when developing the halftone image of the above, and because such a carrier generally has a low volume specific electric resistance, when the toner concentration in the developer is lowered, the image bearing is carried. Charges on the body flow through the carrier, and there is a problem that an image formed by the carrier is lost, and the charge is injected from the developing sleeve to attach the carrier to the image carrier.

For this reason, in recent years, a binder type carrier in which magnetic powder is dispersed in a resin as described above has been receiving attention.

On the other hand, in order to form a high quality image in the image forming apparatus such as the copying machine or the printer, in recent years, a toner having a small particle diameter has been gradually used.

However, when the toner having such a small particle size is used, the specific surface area of the toner per unit volume is increased, which lowers the fluidity of the developer composed of the toner and the carrier, and the charge of the toner. There was a problem that the start up of was worse.

Here, in order to improve the rising of the charge in the toner, conventionally, a carrier with a small particle size has been used, but when a carrier with such a small particle size is used, development is performed. The fluidity of the developer cannot be improved, and on the contrary, the fluidity of the developer tends to be further deteriorated. Further, the carrier having such a small particle diameter is attached to the image carrier to form an image on the carrier. Fogging occurs,
There is a problem that the image carrier is damaged by the attached carrier.

Further, in the prior art, Japanese Patent Laid-Open No. 58-14 has been used.
As disclosed in Japanese Laid-Open Patent Publication No. 0753, it has been proposed to use a carrier having a small particle size and a carrier having a large particle size in combination in order to improve the fluidity of the developer.

However, in the case of the binder type carrier in which the magnetic powder is dispersed in the resin as described above, when the carrier having a large particle size is contained as described above, the specific surface area of the entire carrier decreases, and the toner There is a problem that the number of charging points for charging the toner is reduced and the toner cannot be sufficiently charged.

[0011]

SUMMARY OF THE INVENTION The present invention is directed to electrostatic latent image development used for developing an electrostatic latent image formed on an image bearing member such as a photoconductor in an image forming apparatus such as a copying machine or a printer. It is an object of the present invention to solve various problems as described above in a carrier for use.

That is, in the present invention, when the binder type carrier in which the magnetic powder is dispersed in the resin is used, even if the toner having a small particle size is used in order to obtain a high quality image, the developer is used. It is an object of the present invention to prevent the fluidity of the toner from being lowered, to promptly rise the charge of the toner, and to sufficiently charge the toner so that good image formation can be stably performed. .

[0013]

According to the present invention, in order to solve the above problems, in a binder type electrostatic latent image developing carrier in which magnetic powder is dispersed in a resin, the average particle size is 80-150 μm, saturation magnetization 50e
A first carrier having a mu / g or less and having magnetic powder adhered to the surface and a second carrier having an average particle size of 30 to 50 μm and a saturation magnetization of 55 emu / g or more are used.

In the electrostatic latent image developing carrier of the present invention, the first carrier has an average particle size of 80 to 150 μm.
The saturation magnetization at m of 50 emu / g or less is used because when the average particle size is small, the fluidity of the developer cannot be sufficiently improved, while when the average particle size is too large, This is because the chargeability to the toner is deteriorated, and when the saturation magnetization is larger than 50 emu / g, the fluidity of the developer and the reproducibility of fine lines are adversely affected, and the average particle size is preferably 90 to 100 μm. , Those having a saturation magnetization of 45 to 50 emu / g should be used.

Further, in fixing the magnetic powder to the surface of the first carrier, the first carrier should have an appropriate resistance value and the first carrier should have a sufficient charge point. Therefore, as the above-mentioned magnetic powder, generally, those having a specific surface area of 8 to 12 m ² / g, preferably those having a specific surface area of 8 to 10 m ² / g are used. 50 to 20 relative to 100 parts by weight of binder resin used for one carrier
It is preferably used in the range of 0 parts by weight.

When fixing the magnetic powder to the surface of the first carrier as described above, the magnetic powder is pushed into the surface of the first carrier by using a mechanofusion system such as Ongmill (manufactured by Hosokawa Micron Co., Ltd.). In this way, the resin surface in the first carrier is heated and melted by using a heat treatment system in the air flow such as fusion or by using a suffusing system (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the magnetic powder is made into the carrier particles. To be fused to the surface of. From the viewpoint of improving the yield of the first carrier, it is preferable to use the above mechanofusion system.

Further, in order to further improve the fluidity of the developer and suppress the deviation of the developer and the generation of agglomerates, the residual magnetization of the first carrier is 10 emu /
It is preferable to use g.

On the other hand, the second carrier has an average particle size of 3
The reason why the magnetic material having a saturation magnetization of 0 to 50 μm and a saturation magnetization of 55 emu / g or more is used is that if the average particle diameter of the second carrier is too large, the charging stability with respect to a toner having a small particle diameter deteriorates, and a fine wire or a half wire is used. When the average particle size is too small, the fluidity of the developer deteriorates, and when the saturation magnetization is less than 55 emu / g, carrier adhesion to the image carrier easily occurs, while the reproducibility of a toned image decreases. This is because the saturation magnetization is preferably 60 to 65 em.
Use u / g.

When the first carrier and the second carrier are contained, the particle size is generally small in order to improve the fluidity of the developer and the charging performance for the toner and prevent the carrier from adhering. The content of the second carrier is 30 to 70% by weight, preferably 30 to
Adjust to 50% by weight.

Here, as the binder resin in each of the first and second carriers, for example, polystyrene resin, poly (meth) acrylic resin, styrene-acrylic copolymer resin, polyolefin resin, polyester resin are used. Resins, epoxy resins and the like can be used.

On the other hand, the magnetic powder used for each of these carriers is, for example, a metal such as iron, nickel or cobalt,
These metals and zinc, antimony, aluminum, lead,
Alloys or mixtures with metals such as tin, bismuth, beryllium, manganese, selenium, tungsten, zirconium, vanadium, mixtures with metal oxides such as iron oxide, titanium oxide, magnesium oxide, ferromagnetic ferrite, magnetite and mixtures thereof. Can be used.

In each of the above-mentioned first and second carriers, the magnetic powder contained in the binder resin as described above is dispersed in the binder resin so that the magnetic powder is uniformly dispersed. The primary particle diameter is 5 μm or less, preferably 2 μm or less, more preferably 0.1 to 1 μm.

Further, in order to adjust the first and second carriers so as to have the above-mentioned magnetic characteristics, the amount of magnetic powder contained in the binder resin of each carrier is as follows: 250 to 350 parts by weight with respect to 100 parts by weight of the binder resin, in the case of the second carrier,
The range is 600 to 750 parts by weight with respect to 100 parts by weight of the binder resin.

In the first and second carriers of the present invention, in order to uniformly disperse the magnetic powder in the binder resin, a dispersant such as carbon black, silica, titania or alumina is used. May be contained, and the amount of the dispersant contained is preferably in the range of 0.01 to 3% by weight based on the carrier.

In producing each of the above carriers, for example, a binder resin and magnetic powder are heated and mixed at a predetermined mixing ratio, cooled, and then pulverized and classified, or a binder resin is used as a solvent. The magnetic powder can be dispersed in a resin solution dissolved in the solution, and then spray-dried.

The toner used in combination with the electrostatic latent image developing carrier of the present invention has a volume average particle size of 9 μm or less, preferably 4 to 9 μm in order to obtain a highly delicate image. Use a toner with a small particle size. As such a toner, a toner manufactured by a known method can be used, for example, a toner manufactured by a suspension polymerization method, a pulverizing method, a microcapsule method, a spray drying method, a mechanochemical method, or the like. Can be used.

[0027]

In the carrier for developing an electrostatic latent image according to the present invention, as a binder type carrier in which magnetic powder is dispersed in resin, a carrier having an average particle size of 80 to 150 μm and a saturation magnetization of 50 emu / g or less is used. Since the first carrier to which the magnetic powder is fixed and the second carrier having an average particle size of 30 to 50 μm and a saturation magnetization of 55 emu / g or more are used together, these carriers have sufficient fluidity. As a result, the toner can be stably charged even when a toner having a small particle size is used, and the carrier is less attached to the image carrier.

Further, in the electrostatic latent image developing carrier according to the present invention, since the magnetic powder is adhered to the surface of the first carrier having a large particle size as described above, the charge points on the first carrier are increased. However, the toner having a small particle size can be sufficiently charged.

[0029]

EXAMPLES The electrostatic latent image developing carrier according to the examples of the present invention will be specifically described below, and comparative examples will be given. The electrostatic latent image developing carriers of the examples of the present invention are excellent. However, the present invention is not particularly limited to what is shown in the embodiments.

Here, in obtaining the carriers of Examples and Comparative Examples, three kinds of carriers a, b and c having large particle diameters and one kind of carrier d having small particle diameters were manufactured as follows. .

(Production of Carriers a and b) In producing these carriers, the specific surface area is 7.4 m ² / g.
And ferrite powder having a particle size of about 0.5 μm (manufactured by TDK:
MFP-2) 300 parts by weight, polyester resin (Kao Corporation: Tuffton NE1110) 100 parts by weight, carbon black (Lion Yushi Co., Ltd .: Ketjen Black)
2 parts by weight of silica (manufactured by Nippon Aerosil Co., Ltd .: # 200)
At a ratio of 1.5 parts by weight, these materials were mixed in a Henschel mixer, the mixture was melted and kneaded with a pressure kneader, the kneaded product was cooled, and coarsely pulverized with a feather mill, Further, after finely pulverized with a jet mill and classified with an air classifier, it was heat treated with a suffusing system (manufactured by Nippon Pneumatic Mfg. Co., Ltd.) to obtain carrier particles having an average particle size of 90 μm.

The specific surface area is 9.6 m with respect to 100 parts by weight of the binder resin in the carrier particles.
Add 100 parts by weight of ferrite powder with a small particle size of ² / g,
After mixing these, in the carrier a, this mixture is subjected to heat treatment for 10 minutes by an Ong mill (manufactured by Hosokawa Micron Co., Ltd.) so that the frictional heat becomes about 90 ° C., and the above-mentioned ferrite is added to the surface of the carrier particles. The powder was fixed, and in the carrier b, the temperature was 500 ° C., the carrier air was 8 nl / h, and the hot air was 0.3 g with respect to 3000 g of the mixture by the above suffusion system.
Heat treatment was performed under the condition of Nm ³ / min to fix the above ferrite powder on the surface of the above carrier particles.

(Manufacture of Carrier c) In manufacturing this carrier c, the above-mentioned carrier a,
Only the addition amount of ferrite powder in the material in b is 40
Change to 0 parts by weight, other materials are the same as carriers a and b, and this material is mixed, kneaded, pulverized, classified and heat treated in the same manner as in the case of carriers a and b, and the average particle size is A carrier c having a size of 90 μm was obtained. In this carrier c, ferrite powder was not fixed to the surface.

(Manufacture of Carrier d) In manufacturing the carrier d, the above carriers a and b are used as materials.
The amount of ferrite powder added to the material in
By changing to parts by weight, the other materials are the same as the carriers a and b, and this material is mixed, kneaded, crushed, classified and heat treated in the same manner as the case of the carriers a and b, and the average particle diameter is 40 μm. The obtained carrier d was

Next, the saturation magnetization and the residual magnetization (strength of the external magnetic field 1) in the carriers a to d manufactured as described above.
KOe) was measured and a dynamic current value was obtained, and the results are shown in Table 1 below. The saturation magnetization and the residual magnetization were measured by using a direct current magnetization characteristic automatic recording device (TYPE-3257 manufactured by Yokogawa Hokushin Electric Co., Ltd.). Regarding the dynamic current value, as shown in FIG. 1, each carrier 3 is placed on the sleeve roller 2 in which the magnet roller 1 is provided and the magnetic flux density is 1000 gauss.
g, the gap between the sleeve roller 2 and the electrode tube 4 is set to 1 mm, and the magnet roller 1 is set to 5 mm.
While rotating at 0 rpm, a bias voltage of 500 V was applied from the power supply 5, and the current value flowing through the carrier 3 to the electrode tube 4 was measured by the ammeter 6, and this was shown as a dynamic current value.

[0036]

[Table 1]

Next, the above carriers a to d were used to obtain the carriers of Examples 1 to 6 and Comparative Examples 1 to 4.

(Examples 1 to 3) In these examples, the carrier a having a large particle size, in which the ferrite powder is adhered to the surface, and the carrier d having a small particle size are used in combination. Carrier d is 30
% By weight, 40% by weight of carrier d in Example 2,
In Example 3, 50% by weight of the carrier d was contained.

(Examples 4 to 6) In these examples, the carrier b having a large particle size, in which the ferrite powder is adhered to the surface, and the carrier d having a small particle size are used in combination. Carrier d is 30
% By weight, in Example 5, 40% by weight of carrier d,
In Example 6, 50 wt% of the carrier d was contained.

(Comparative Examples 1 and 2) In Comparative Example 1, only the carrier c having a large particle size in which the ferrite powder is not adhered to the surface is used, and in Comparative Example 2, only the carrier d having a small particle size is used. I decided to use it.

(Comparative Examples 3 and 4) In these Comparative Examples, the carrier c and the carrier d were used in combination. In Comparative Example 3, the carrier d was 30% by weight, and in Comparative Example 4, the carrier d was used. The content of d was 40% by weight.

Next, the above Examples 1 to 6 and Comparative Examples 1 to 4
For each carrier, the residual magnetization, the saturation magnetization and the dynamic current value were determined in the same manner as described above, and the results are shown in Table 2 below.

In consideration of the fact that the carrier is deteriorated in both the direction in which the amount of charge of the toner is increased and the direction in which the amount of charge of the toner is decreased by use, the above Examples 1 to 6 and Comparative Examples 1 to 1 are taken into consideration.
For each carrier of No. 4, the variation range of the toner charge amount in the case of deterioration in the direction of increasing the toner charge amount and the deterioration in the direction of decreasing the toner charge amount was examined, and the results are shown in Table 2 below. Indicated.

Here, in order to obtain a deteriorated carrier in the direction of increasing the charge amount of the toner, 1.5 mg of Teflon resin fine particles (TFO-V manufactured by Central Glass Co., Ltd.) was added to 10 g of each of the above carriers. Was mixed and stirred by a roll mill at 120 rpm for 5 hours, and when a carrier deteriorated in the direction of decreasing the charge amount of toner was obtained, CC was added to each carrier 10 g.
1.5 mg of A (manufactured by Orient Chemical Co., Ltd .: S-34) was added, and these were mixed and stirred by a roll mill at 120 rpm for 12 hours.

A commercially available copying machine (Minolta: D
Using the toner having a particle size of 8 μm used in i30),
This toner is added to the carrier deteriorated in the direction of increasing the charge amount of the toner as described above, and the toner concentration is 3% by weight.
The obtained toner is obtained, and 10 g of the developer is stirred by a roll mill at 120 rpm for 60 minutes to measure the charge amount of the toner by this carrier, while the above toner is deteriorated in the direction of decreasing the charge amount of the toner. In addition to the above, a developer having a toner concentration of 7% by weight is obtained, 10 g of the developer is stirred by a roll mill at 120 rpm for 3 minutes, and the charge amount of the toner by the carrier is measured. The difference is shown in Table 2 as the change width of the charge amount.

[0046]

[Table 2]

As a result, as the content of the carrier d having a small particle diameter increases, the residual magnetization, the saturation magnetization, and the dynamic current value increase, while the change amount of the toner charge amount decreases. Further, in Examples 1 to 6 in which the carrier a or b having a large particle size in which the ferrite powder is fixed to the surface and the carrier d having a small particle size are combined, the ferrite powder having a particle size in which the particle size is not fixed to the surface is obtained. Compared with a comparative example in which a large carrier c and a carrier d having a small particle diameter are combined, the variation range of the charge amount of the toner is generally small, and the variation when the content of the carrier d varies. It was running low.

Next, the above Examples 1 to 6 and Comparative Examples 1 to 4
The above toner having a particle diameter of 8 μm is added to each carrier to prepare respective developers having a toner concentration of 4 to 5% by weight, and these developers are respectively put on a commercially available copying machine (manufactured by Minolta: D
i30) is used for continuous copying of 10,000 sheets to measure the amount of carrier contained in the toner collected by the cleaning device (carrier recovery amount), and to determine the background fog state at the time of toner replenishment and The presence or absence of unevenness of the developer and agglomerates in the developing device was examined, and the results are shown in Table 3 below. Regarding the carrier recovery amount, the toner and the carrier recovered by the cleaning device are roasted to obtain the content of the carrier. When the content of the carrier is 0 to 80 mg / thousand, it is O, and 80 to 120 m.
△ for g / 1000 sheets, × for 120 mg / 1000 sheets or more
Indicated by. Regarding background fogging, toner was continuously replenished in a low-humidity environment with a humidity of 30% to perform copying, and the state of fogging in the white image area was examined. When almost no fogging occurred, ◎, and a little fogging occurred. If there is no problem in quality, it is indicated by ◯, if fogging occurs but there is no problem, the limit level is indicated by Δ, and if there is much fogging and there is a problem in quality, x is indicated. Further, regarding the presence or absence of the deviation of the developer or the agglomerate in the developing device, the presence or absence of the agglomerate or the developer is visually inspected. Some cases are indicated by x.

[0049]

[Table 3]

As a result, the comparative example 1 using only the carrier c having a large particle diameter and the comparative example 2 using only the carrier d having a small particle diameter have practical problems, while the carrier having a large particle diameter. Each of the carriers of Examples 1 to 6 and Comparative Examples 3 and 4 in which the above and a carrier having a small particle size were combined had no problem in practical use. In particular, like each carrier of Examples 1 to 6, the ferrite powder was When the carrier a or b having a large particle size fixed to the surface was used, the chargeability to the toner was higher than that of each carrier of Comparative Examples 3 and 4 using the carrier c having a large particle size in which the ferrite powder was not fixed to the surface. And the occurrence of background fogging during toner replenishment is further suppressed.

[0051]

As described above in detail, when the carrier for electrostatic latent image development according to the present invention is used, the developer exhibits sufficient fluidity even when a toner having a small particle size is used. In addition, the adhesion of the carrier to the image carrier is reduced, and the charge of the toner rises quickly so that the toner is sufficiently charged and stable image formation without background fog can be stably performed. became.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram showing a state of measuring a dynamic current value in a carrier.

[Explanation of symbols]

 3 career

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Takenaka, Kouji Takenaka 2-33-1 Azuchi-cho, Chuo-ku, Osaka, Osaka International Building Minolta Co., Ltd. (72) Hiroshi Shibano 2-3, Azuchi-cho, Chuo-ku, Osaka No. 13 Osaka International Building Minolta Co., Ltd.

Claims (1)

[Claims] 1. A binder type electrostatic latent image developing carrier in which magnetic powder is dispersed in a resin, having an average particle size of 80 to 150 μm, a saturation magnetization of 50 emu / g or less, and magnetic powder on the surface. A carrier for electrostatic latent image development, comprising: a fixed first carrier; and a second carrier having an average particle size of 30 to 50 μm and a saturation magnetization of 55 emu / g or more.