JPH0540367A - Electromagnetic latent image developing carrier - Google Patents

Abstract

PURPOSE:To provide the electrostatic latent image developing carrier of a binder type which is formed by dispersing magnetic powder into a resin, is uniformly dispersed with this magnetic powder in the resin by the sufficient mixing of the magnetic powder with the resin, has high electric resistance, and is less fluctuated in compsn. CONSTITUTION:This electrostatic latent image developing carrier is obtd. by mixing and agitating at least the resin and the magnetic powder in a mixing machine and kneading, pulverizing and classifying this mixture. The magnetic powder and the resin are mixed and agitated by an agitating member 20 provided in this mixing machine while the sticking of the magnetic powder to the inside wall 11 of the mixing machine is prevented by a sticking suppressing means 30.

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 carrier used for developing an electrostatic latent image in an image forming apparatus such as a copying machine or a printer, and more particularly to a resin containing magnetic powder. The present invention relates to a dispersed binder type electrostatic latent image developing carrier.

[0002]

2. Description of the Related Art Conventionally, in image forming apparatuses such as copying machines and printers, when developing an electrostatic latent image formed on a photoconductor, a mixture of toner and carrier has been widely used as a developer. It was used.

As the carrier for developing the electrostatic latent image mixed with the toner, iron, ferrite or the like is used as it is, or a binder type carrier in which powders of these magnetic materials are dispersed in a resin. Was known.

Here, since a carrier using iron, ferrite or the like as it is generally has a low resistance, when the carrier is used for development, the carrier adheres to the photoconductor to form an image. There is a problem that defects occur and the surface of the carrier becomes spent of toner, and when the above carrier is used, the ears of the magnetic brush formed during development are generally hard, and photographic originals, etc. There was a problem such as streak-like unevenness when developing the halftone image.

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

Here, in producing such a binder type carrier, generally, a resin and magnetic powder are mixed and stirred by a Henschel mixer or the like, and the mixture thus mixed and stirred is kneaded, pulverized and classified. I was trying to manufacture.

However, when the binder type carrier is manufactured in this way, the magnetic powder is poorly dispersed when the resin and the magnetic powder are mixed, and the magnetic powder is mixed with the resin in a solidified state and manufactured. Some carriers contained magnetic powder in a solidified state and some contained no magnetic powder, resulting in variations in the composition of the obtained carrier.

When the magnetic powder is contained in the carrier in the solidified state as described above, the electric resistance of the carrier becomes low, and when the carrier is used for development, the above-mentioned iron and As in the case of the carrier in which ferrite is used as it is, there is a problem in that the carrier adheres to the photoconductor and a defect occurs in the formed image.

Further, if the carrier composition varies as described above, the toner is not uniformly charged, and there is a problem in that an image formed by this causes background fogging.

Further, in recent years, in the image forming apparatus such as the copying machine and the printer as described above, high speed image formation and high image reliability are demanded, and the optical system is changed from a conventional analog exposure system to a laser. Since it has been changed to one capable of forming a sharp electrostatic latent image such as a light emitting diode, it has been desired to increase the magnetic force of the carrier used for development.

However, in the binder type carrier as described above, if the amount of the magnetic powder added to increase the magnetic force is increased, the magnetic powder is not sufficiently mixed with the resin as described above, so that the magnetic powder is not formed. When it is further hardened, it is contained in the carrier, and the electrical resistance of the carrier decreases accordingly, and when developing in a high electric field, breakdown occurs and the image formed is defective. In addition to this, there is a problem that the photoreceptor is damaged by this.

[0012]

The present invention solves the above problems in an electrostatic latent image developing carrier used for developing an electrostatic latent image in an image forming apparatus such as a copying machine or a printer. This is an issue.

That is, according to the present invention, in the binder type electrostatic latent image developing carrier in which the magnetic powder is dispersed in the resin as described above, the magnetic powder is sufficiently mixed with the resin,
It is an object of the present invention to provide a carrier for electrostatic latent image development, in which magnetic powder is uniformly dispersed in a resin, which has a high electric resistance and a small variation in composition.

[0014]

According to the present invention, in order to solve the above problems, at least a resin and a magnetic powder are mixed and stirred in a mixer, and the mixture is kneaded, pulverized and classified. In the obtained electrostatic latent image developing carrier, magnetic particles are mixed and stirred with a resin by a stirring member provided in the mixer while suppressing adhesion of the magnetic powder to the inner wall of the mixer by the adhesion suppressing means. I did so.

The resin used in the carrier for developing an electrostatic latent image according to the present invention is an acrylic resin having a polar group such as a carboxyl group, a hydroxyl group, a glycidyl group or an amino group, for example, methacrylic acid or acryl. Acrylic acid type monomers such as acids, maleic acid, itaconic acid; hydroxy group monomers such as hydroxy polypropylene monomethacrylate and polyethylene glycol monomethacrylate; amino group monomers such as dimethylaminoethyl methacrylate; glycidyl methacrylate etc. lower alkyl acrylate The thing copolymerized with ester and / or styrene etc. can be used.

The above-mentioned resins include polyester resins such as ethylene glycol, triethylene glycol, 1,2-propylene glycol and 1,4-butanediol, and dicarboxylic acids such as
Examples thereof include polyester resins obtained by condensing maleic acid, itaconic acid, malonic acid, etc., and thermoplastic resins such as epoxy resins. Resin production conditions such as temperature, type or amount of catalyst, reaction time or chain transfer. It is also possible to use a resin having different properties obtained by changing the addition of an agent or a crosslinking agent, or a mixed resin thereof.

On the other hand, in the electrostatic latent image developing carrier according to the present invention, as the magnetic powder to be mixed with the above resin, a magnetic material having a volume specific electric resistance of 10 ⁷ Ω · cm or more is preferably used. For example, ferrite, magnetite composed of FeO.Fe ₂ O _3, or
Metals containing ferromagnetism such as iron, nickel and cobalt, alloys and compounds thereof, etc. can be used, but are not particularly limited to these.

As the magnetic material used for the above magnetic powder, it is particularly preferable to use ferrite, and examples of this ferrite include ferrite represented by the following general formula [Chemical formula 1].

[0019]

[Chemical 1]

In the above [Chemical formula 1], M is M
n is at least one atom selected from the group consisting of Ni, Co, Mg, Cu, Zn and Cd, and 0.5 ≦
x ≦ 1, 0.1 ≦ y ≦ 0.571.

When mixing the resin and the magnetic powder as described above, if the amount of the magnetic powder is small, sufficient magnetization cannot be obtained in the magnetic field, while if the amount of the magnetic powder is too large, the production Since the carrier is brittle, the magnetic powder is usually mixed in a proportion of 200 to 900 parts by weight with respect to 100 parts by weight of the resin.

Considering the magnetic property of the carrier, when the magnetic flux density Bm is larger than 7,000 gauss, the brush of the magnetic brush becomes too hard at the time of development. On the other hand, when the magnetic flux density Bm is smaller than 1000 gauss, the magnetic field in the magnetic field is increased. Since a sufficient amount of magnetization cannot be obtained with, the magnetic flux density B of the carrier
The m (Gauss) is set within the range of 1000 ≦ Bm ≦ 7000, preferably 2000 ≦ Bm ≦ 3000.

When mixing the resin and the magnetic powder, a mixer as shown in FIGS. 1 and 2 can be used.

Here, in the mixer shown in FIG. 1, the lower portion of the mixing chamber 10 for mixing the magnetic powder with the resin has a hemispherical shape.
The upper part was formed into a cylindrical shape. Further, as the stirring member 20 for mixing the magnetic powder with the resin in the mixing chamber 10,
The rotating shaft 21 provided with a plurality of stirring blades 22 was used.

Here, when mixing the magnetic powder with the resin by the stirring member 20 in the mixing chamber 10, the rotating shaft 21 of the stirring member 20 is tilted by a predetermined angle from the lower part of the mixing chamber 10 which is hemispherical. So that the stirring blades 22 provided on the rotating shaft 21 are inclined at a required angle in the mixing chamber 10. Then, the rotating shaft 21 is rotated by the motor 23 via the belt 24 and the pulley 25, whereby the stirring blade 22 is rotated in the mixing chamber 10 in a state inclined at a required angle, and the stirring blade 22 causes the magnetic powder to rotate. Was mixed with the resin in the mixing chamber 10.

Further, in this mixer, as a sticking restraint means 30 for restraining the magnetic powder from sticking to the inner wall 11 of the mixing chamber 10, a cylindrical rotation through which the rotary shaft 21 of the stirring member 20 is inserted. An arc-shaped first scraping member 31 corresponding to the internal shape of the lower part of the mixing chamber 10 is attached to the shaft 31a so that the first scraping member 31 is brought into close contact with the inner wall 11 of the lower part of the mixing chamber 10. In addition, the second scraping member 32 in the shape of a groove corresponding to the internal shape of the upper part of the mixing chamber 10 is attached to the rotary shaft 32a extending from the upper part of the mixing chamber 10 into the mixing chamber 10. The second scraping member 32 is attached to the inner wall 1 above the mixing chamber 10.
I made it close to 1.

Then, the rotary shaft 31a to which the first scraping member 31 is attached is rotated by the motor 31b via the belt 31c and the pulley 31d, and the first scraping member 31 is moved to the inner wall 11 below the mixing chamber 10. The second scraping member 32 is rotated in close contact with the second scraping member 32.
The rotating shaft 32a to which is attached is rotated by the motor 32b via the belt 32c and the pulley 32d so that the second scraping member 32 is brought into close contact with the inner wall 11 of the upper part of the mixing chamber 10 to rotate, and The magnetic powder adhering to the lower and upper inner walls 11 is removed by the first and second scraping members 31 and 32 of the inner wall 1 of the mixing chamber 10.
I tried to scrape it from 1.

In this mixer, while the magnetic powder adhering to the inner wall 11 at the lower and upper portions of the mixing chamber 10 is scraped off by the first and second scraping members 31 and 32 as described above, the magnetic powder is removed. When the resin and the stirring blades 22 of the stirring member 20 are mixed, the magnetic powder is mixed into the mixing chamber 1
The magnetic powder is mixed with the resin in a state of being crushed into a state of primary particles and sufficiently dispersed without sticking to the inner wall 11 of No. 0 and solidifying on the surface of the resin. It became evenly dispersed and adhered.

In this mixer, since the stirring blade 22 is rotated in the mixing chamber 10 in a state of being inclined at a required angle as described above, the stirring blade 22 mixes the magnetic powder with the resin. At that time, the stress applied to the magnetic powder and the resin was reduced.

The mixer shown in FIG. 2 is substantially the same as the mixer shown in FIG. 1, but in this mixer, the mixing chamber 10 for mixing the magnetic powder with the resin is formed into a spherical shape. At the same time, as the adhesion suppressing means 30 for suppressing the adhesion of the magnetic powder to the inner wall 11 of the mixing chamber 10, a cylindrical rotating shaft 33a having the rotating shaft 21 of the stirring member 20 inserted therethrough.
A ring-shaped scraping member 33 having a ring shape corresponding to the internal shape of the mixing chamber 10 was attached to the above, and the scraping member 33 was brought into close contact with the inner wall 11 of the mixing chamber 10.

Also in this mixer, the rotating shaft 33a to which the scraping member 33 is attached is rotated by the motor 33b via the belt 33c and the pulley 33d, and the scraping member 31 is moved to the inner wall of the mixing chamber 10. The magnetic powder adhering to the inner wall 11 of the mixing chamber 10 was scraped off by the scraping member 33.

In the mixer shown in FIGS. 1 and 2, the scraping members 31, 32, 32 as described above are used as the sticking suppressing means 30 for suppressing the adhesion of the magnetic powder to the inner wall of the mixing chamber 10. Although 33 is provided, the adhesion suppressing means 30 is not limited to the above-described one, and the magnetic powder adheres to the inner wall 11 of the mixing chamber 10 by vibrating the inner wall 11 of the mixing chamber 10, for example. It is also possible to use an ultrasonic vibrator or the like that suppresses the noise. In addition, the operating conditions of the scraping members 31, 32, and 33 described above need to be appropriately set according to the types and amounts of these samples so that samples such as magnetic powder do not adhere to the inner wall 11 of the mixing chamber 10. is there.

Then, while suppressing the adhesion of the magnetic powder to the inner wall 11 of the mixer by the adhesion suppressing means 30 as described above, the magnetic powder is mixed and stirred with the resin by the stirring member 20 provided in the mixer. After that, the mixture is kneaded, pulverized and classified by a conventionally known method.

Here, in the case where a mixture of magnetic powder and resin is kneaded as described above, and this is pulverized and classified to obtain an electrostatic latent image developing carrier, the average particle size of the carrier is too small. When the carrier agglomerates, the fluidity of the carrier deteriorates, or the carrier easily adheres to the photoreceptor, the average particle size is too large, as in the case of a usual iron powder carrier, etc. Therefore, the average particle size of the carrier is preferably in the range of 15 to 100 μm in terms of the weight average particle size.

After pulverizing and classifying as described above, in order to modify the surface of the carrier, further surface treatment with fine powder of silica, titanium oxide, aluminum oxide or the like, or heat treatment. Etc. may be performed.

[0036]

In the electrostatic latent image developing carrier according to the present invention, when at least the resin and the magnetic powder are mixed and stirred in the mixer as described above, the magnetic powder adheres to the inner wall of the mixer. While suppressing by the suppressing means, the magnetic powder is mixed and stirred with the resin by the stirring member provided in the mixer, so that the magnetic powder does not adhere to the inner wall of the mixer and harden, and the magnetic powder is sufficiently mixed. It will be mixed with the resin in the state of being dispersed.

When the magnetic powder thus thoroughly mixed with the resin is kneaded, pulverized, and classified to produce a carrier for developing an electrostatic latent image, the obtained electrostatic latent image is obtained. Also in the latent image developing carrier, the magnetic powder is uniformly dispersed in the resin, and the electrostatic latent image developing carrier having high electric resistance and less variation in composition can be obtained.

[0038]

EXAMPLES The electrostatic latent image developing carrier according to the examples of the present invention will be specifically described below, and the electrostatic latent image developing carriers according to the examples of the present invention will be compared with the electrostatic latent image developing carrier of the comparative example. The electrostatic latent image developing carrier is revealed to be excellent.

Example 1 In this example, a polyester resin (softening point 123 ° C., glass transition point 65 ° C.)
100 parts by weight and magnetic powder (Toda Kogyo Co., Ltd., EPT-10
00) 600 parts by weight and carbon black (Mitsubishi Kasei Co., Ltd., MA # 8) 3 parts by weight were mixed and stirred by the mixer shown in FIG.

Here, when the above raw materials are mixed and stirred by the mixer of FIG. 1, of the stirring blades 22 provided on the stirring member 20, the tip portion of the stirring blade 22 having the longest blade length. So that the peripheral speed is 40 m / sec, the stirring blades 22 are rotated by the rotating shaft 21, and the first and second scraping members 31, 3 are also rotated.
No. 2 performs normal rotation and reverse rotation with respect to the rotation direction of the stirring blade 22 every 10 seconds, and these scraping members 31 and 32 are rotated at a rotation speed of 50 rpm.

Then, the first and the second which rotate in this way
While scraping off the magnetic powder and the like adhering to the inner wall 11 of the mixing chamber 10 by the scraping members 31 and 32, the raw materials are mixed in the mixing chamber 10 for 5 minutes by the stirring blades 22 rotating as described above. I did it.

Then, the mixture as described above is mixed with 2
Melt and knead using an extrusion kneader set to a temperature of 00 ° C., cool the kneaded product, and pulverize with a jet mill,
Further, classification was performed using a classifier to obtain a binder type carrier having an average particle size of 50 μm.

The volume resistivity of the carrier of Example 1 was measured to be 6.3 × 10 ^14.
It was Ω · cm. When measuring the volume resistivity, the carrier was placed on a metal circular electrode so that the thickness was 1 mm, and the pressure was 400 g from the upper part.
The counter electrode was pressed at / cm ² , a voltage of 600 V was applied between the circular electrode and the counter electrode, and the volume resistivity was calculated based on the resistance value after 30 seconds.

(Comparative Example 1) In this comparative example, a Henschel mixer was used to mix and stir the raw materials in Example 1 described above, and the raw materials were mixed and stirred at a peripheral speed of 18 m / sec for 5 minutes. In the same manner as in Example 1 except for the above, a binder type carrier having an average particle size of 50 μm was obtained. The volume resistivity of the carrier of Comparative Example 1 was measured in the same manner as in Example 1 above, and was 4.7 × 10 ¹¹ Ω · cm, which is larger than that of the carrier of Example 1 above. Was significantly lower.

Next, for each carrier of Example 1 and Comparative Example 1 described above, a positively chargeable toner having an average particle size of 9 μm and composed of styrene-n-butyl methacrylate resin, carbon black and nigrosine dye was used. Weight ratio is 95: 5
Example 1 and Comparative Example 1
A two-component developer using each carrier of was prepared.

When the charge amount of the toner in these two-component developers was measured, the charge amount was +1 in the two-component developer using the carrier of Example 1 above.
6.2 μC / g, and in the two-component developer using the carrier of Comparative Example 1, the charge amount was +16.8.
It was μC / g, and the difference between the charge amounts was small.

Next, the above-mentioned two-component developer using each carrier of Example 1 and Comparative Example 1 was used in a commercially available copying machine (EP-4301, manufactured by Minolta Camera Co., Ltd.) to obtain a data quest standard chart. I made a copy.

As a result, when the two-component developer containing the carrier of Example 1 was used, carrier adhesion to the photoconductor was not observed in both the image area and the non-image area, and there was little background fog. A good image was obtained.

On the other hand, when the two-component developer containing the carrier of Comparative Example 1 was used, the adhesion of the carrier to the image area was conspicuous, and the case of using the carrier of Example 1 and charging as described above were compared. Despite the small difference in the amount, a large amount of background fogging occurred in the formed image.

Example 2 In this example, a polyester resin (softening point 123 ° C., glass transition point 65 ° C.)
100 parts by weight and magnetic powder (Toda Kogyo Co., Ltd., EPT-10
00) 550 parts by weight and carbon black (Mitsubishi Kasei Co., Ltd., MA # 8) 3 parts by weight were mixed and stirred using the mixer shown in FIG.

Here, when the above raw materials are mixed and stirred by this mixer, of the stirring blades 22 provided on the stirring member 20, the tip of the stirring blade 22 having the longest blade length is used. The stirring blades 22 are rotated by the rotary shaft 21 so that the peripheral speed becomes 38 m / sec, and the first and second scraping members 31,
The scraping members 31 and 32 are rotated at a rotational speed of 50 rpm so that the stirrer 32 performs normal rotation and reverse rotation with respect to the rotation direction of the stirring blade 22 every 10 seconds, and the inner wall 11 of the mixing chamber 10 is rotated. The above raw materials were mixed for 5 minutes by the respective stirring blades 22 while scraping off the adhered magnetic powder and the like by these scraping members 31, 32.

Then, the mixture as described above is mixed with 1
Melt and knead using an extrusion kneader set to a temperature of 95 ° C., cool the kneaded material, and then crush with a jet mill,
Further, classification was performed using a classifier to obtain a binder type carrier having an average particle size of 40 μm.

Then, the volume resistivity of the carrier of Example 2 was measured in the same manner as in Example 1 above, and it was 2.3 × 10 ¹⁴ Ω · cm.

(Comparative Example 2) In this Comparative Example, a Henschel mixer was used to mix and stir the raw materials in Example 2, and the Henschel mixer was used to stir and mix the raw materials for 5 minutes at a peripheral speed of 18 m / sec. In the same manner as in Example 2 except for the above, a binder type carrier having an average particle size of 40 μm was obtained. The volume resistivity of the carrier of Comparative Example 2 was measured to be 2.1 × 1.
It was 0 ¹² Ω · cm, and the volume resistivity was significantly lower than that of the carrier of Example 2 above.

Next, for each carrier of Example 2 and Comparative Example 2, the average particle size composed of polyester resin, carbon black and chromium complex salt type charge control agent was 10
The negatively chargeable toner having a particle size of μm was mixed in a weight ratio of 94: 6 to prepare a two-component developer using each carrier of Example 2 and Comparative Example 2.

When the charge amount of the toner in these two-component developers was measured, the charge amount in the two-component developer using the carrier of Example 2 was -1.
It is 4.3 μC / g, and the charge amount of the two-component developer using the carrier of Comparative Example 2 is −14.4.
It was μC / g, and the difference between the charge amounts was small.

Next, a commercially available laser beam printer (SP-34 manufactured by Minolta Camera Co., Ltd.) was used for each of the above two-component developers using the carriers of Example 2 and Comparative Example 2.
0) was used to print a mixed pattern of characters and graphics.

As a result, when the two-component developer containing the carrier of Example 2 was used, carrier adhesion to the photoconductor was not recognized in both the image area and the non-image area, and there was little background fog. A good image was obtained.

On the other hand, when the two-component developer containing the carrier of Comparative Example 2 was used, carrier adhesion to the image area was conspicuous, and as in the case of using the carrier of Example 2 as described above, charging was performed. Despite the small difference in the amount, a large amount of background fogging occurred in the formed image.

(Example 3) In this example, the amount of the magnetic powder (EPT-1000 manufactured by Toda Kogyo Co., Ltd.) added in Example 1 was set to 800 parts by weight, and otherwise the above Example. In the same manner as in the case of 1, a binder type carrier having an average particle size of 55 μm was obtained.

(Comparative Example 3) In this comparative example, the amount of the magnetic powder (EPT-1000 manufactured by Toda Kogyo Co., Ltd.) added in Comparative Example 1 was set to 800 parts by weight. In the same manner as in the case of 1, a binder type carrier having an average particle size of 55 μm was obtained.

For each carrier of Example 3 and Comparative Example 3, an electric field of 8000 V / cm was applied between the circular electrode and the counter electrode electrode in the same manner as in the case of measuring the volume resistivity. It was applied.

As a result, the breakdown did not occur in the carrier of Example 3 above, but the breakdown occurred in the carrier of Comparative Example 3 above.

[0064]

As described above in detail, in the electrostatic latent image developing carrier according to the present invention, when at least the resin and the magnetic powder are mixed and stirred in the mixer, the magnetic powder is deposited on the inner wall of the mixer. While suppressing the adhesion by the adhesion suppressing means, the stirring member provided in the mixer is used to mix and stir the magnetic powder with the resin, so that the magnetic powder does not adhere to the inner wall of the mixer and harden. , The magnetic powder comes to be mixed with the resin in a sufficiently dispersed state, and when this mixture is kneaded, pulverized, and classified, the magnetic powder is uniformly dispersed in the resin and has a high electric resistance and a composition. It is now possible to obtain a carrier for developing an electrostatic latent image with less variation.

As a result, when the electrostatic latent image developing carrier according to the present invention is used for the development, the carrier is not adhered to the photosensitive member and the formed image is free from defects. Further, since there is no variation in the composition of the carrier, the toner is uniformly charged, and the background fog does not occur in the formed image.

Further, in the electrostatic latent image developing carrier according to the present invention, the magnetic powder is sufficiently dispersed as described above even when the amount of the magnetic powder added to increase the magnetic force is increased. It will be mixed with the resin in such a state that even if development is carried out under a high electric field using a laser, a light emitting diode, etc., the breakdown will occur as in the conventional case, and the formed image will have defects. It no longer occurs and the photoreceptor is not damaged.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of one mixer used for mixing a resin and magnetic powder in a carrier for developing an electrostatic latent image according to the present invention.

FIG. 2 is a schematic explanatory view of another mixer used for mixing resin and magnetic powder in the electrostatic latent image developing carrier according to the present invention.

[Explanation of symbols]

 10 Mixing chamber 11 Inner wall 20 Stirring member 30 Adhesion suppressing means

Claims (1)

[Claims] 1. An electrostatic latent image developing carrier obtained by mixing and agitating at least a resin and magnetic powder in a mixer, kneading, pulverizing and classifying the mixture, and magnetic powder on the inner wall of the mixer. A carrier for electrostatic latent image development, characterized in that magnetic powder is mixed and stirred with a resin by a stirring member provided in the mixer while suppressing the adhesion of the toner by an adhesion suppressing means.