JPH0373966A - Production of dry coating carrier - Google Patents

Abstract

PURPOSE:To efficiently produce a coating carrier for dry processing by subjecting the powder of magnetic material particles to a dry coating treatment stage, then separating the powder to the powder of a specific small diameter and the powder of a specific large diameter. CONSTITUTION:The stage for separating the powder of the magnetic material particles to the small-diameter component having <=50mum average grain size and the powder of the large-diameter component having an average grain size of >=2 times the average grain size of this small-diameter component after the dry coating treatment stage is added. Thus, mechanical impact power is efficiently imparted to the fine particles of the resin for coating stuck to the small-diameter component via the large-diameter component and the time required for production of the carrier having the good coating layers is shortened regardless of the grain sizes.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a carrier constituting a developer used in electrophotography, electrostatic recording, electrostatic printing, etc.
In detail, it is a dry coating carrier that includes a dry coating process in which a powder of magnetic particles and a powder of fine coating resin particles are mixed and a mechanical impact force is applied to the mixture to coat the surface of the magnetic particles with a coating resin. Regarding the manufacturing method.

[Conventional technology]

A two-component developer consisting of a toner and a carrier is known as a developer used in electrophotography, etc., but coated carriers are preferred because of their excellent durability and triboelectric charging properties. is preferably used.

Conventionally, the method for manufacturing such a coating carrier is as follows: (1) A coating solution prepared by dissolving a coating resin in a solvent is spray-coated onto the surface of magnetic particles using a fluidized bed, and then dried. Method for obtaining coating carrier (fluidized bed spray coating method), (2)
A method for obtaining a coating carrier by immersing magnetic particles in a coating solution prepared by dissolving a coating resin in a solvent, and then drying the coating to obtain a coating carrier (dip coating method), (3) Coating resin A known method is to apply a coating liquid prepared by dissolving the magnetic material in a solvent onto the surface of magnetic particles, and then sinter the resin to obtain a coated carrier (sintered coating method).

However, with the techniques (1), (2) and (3) above,
Since both methods are so-called wet coating methods using a coating liquid, they have the essential problem that magnetic particles tend to granulate during the coating process, resulting in a low carrier yield.

Under these circumstances, a dry coating method has recently been proposed (see Japanese Patent Laid-Open No. 62-235959).

This dry coating method involves mixing powder of magnetic particles and powder of fine coating resin particles, applying mechanical impact repeatedly to this mixture, and coating the surface of the magnetic particles with coating resin. This is a method for obtaining carriers, and since no coating liquid is used, granulation of magnetic particles is prevented, and it is expected that the yield of carriers will be high.

On the other hand, recently, in order to improve the quality of copied images, small-diameter carriers with an average particle diameter of 50 uH or less are often required.

[Problem to be solved by the invention]

However, as a result of repeated experiments by the present inventor, when applying the conventional dry coating method to produce small carriers with an average particle size of 50μ or less, it is difficult to achieve an efficient coating process. It turned out to be.

In other words, in the dry coating process, the powder of magnetic particles and the powder of fine coating resin particles are mixed, and a mechanical impact force is applied to the mixture to coat the surface of the magnetic particles with the coating resin. Whether or not a coating layer is formed depends largely on the magnitude of the mechanical impact force applied to the resin particles attached to the surface of the magnetic particles. However, when the diameter of the carrier becomes small, it becomes difficult to apply mechanical impact force to the resin particles, and as a result, in order to obtain a carrier with a good coating layer, it is necessary to carry out coating treatment over a considerable period of time. As a result, a problem occurred in which production efficiency was greatly reduced.

The present invention has been made based on the above circumstances, and its object is to provide a method that can efficiently produce a dry coated carrier having a good coating layer.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a powder of magnetic particles and a powder of fine coating resin particles are mixed, and a mechanical impact force is applied to the mixture to coat the surface of the magnetic particles with the coating resin. In the method for producing a dry coating carrier including a dry coating treatment step, the powder of the magnetic particles has a small diameter component having an average particle diameter of 50 uM or less, and an average particle diameter of at least twice the average particle diameter of the small diameter component. After the dry coating process, a step of separating the powder into small-diameter powder and large-diameter powder is added.

In other words, as will be understood from the explanations of Examples and Comparative Examples to be described later, in the case of a powder of magnetic particles having only a small diameter component with an average particle size of 50 nm or less, coating particles attached to the magnetic particles are It takes a long time to form a good coating layer when mechanical impact force is applied to resin fine particles, but if the average particle size is a certain value, that is, twice or more of the average particle size of the small-sized component, It was discovered that by having a large-diameter component with a large diameter, mechanical impact force can be efficiently applied to the coating resin fine particles attached to the small-diameter component via the large-diameter component, and the result is a good result. This greatly reduces the time required to manufacture a carrier with a coating layer.

The reason why a good coating layer is formed even on small-diameter components by such a short dry coating process is that there are large-diameter components as well as small-diameter components in the magnetic particle powder, and these are mixed together with the coating resin fine particles. When stirred and mechanical impact force is applied, the large-diameter component sufficiently and uniformly applies mechanical impact force and shear force to the coating resin fine particles attached to the small-diameter component, and the surface of the small-diameter component is This is thought to be because a smooth coating layer with sufficient strength is formed.

Moreover, as a result of applying a sufficient mechanical impact force to the small-diameter components, the small-diameter components are not granulated, and small-diameter carriers can be obtained in a high yield in the subsequent separation step.

After the dry coating process, we added a step to separate small-diameter powder and large-diameter powder, resulting in a small-diameter carrier and a large-diameter carrier, which can be combined with toner to suit the purpose. A developer can be prepared.

Here, in the present invention, the average particle size refers to the particle size distribution measuring device rsRAMKIIJ (manufactured by Micro Trabuku Co., Ltd.).
The weight average particle diameter measured by

In the dry coating process, specifically, magnetic particles are formed of a small diameter component having an average particle diameter of 50 nm or less and a large diameter component having an average particle diameter twice or more of the average particle diameter of the small diameter component. and powder of fine coating resin particles having an average particle size of, for example, about 1 μm or less, are put into a mixing device, mixed and stirred, and the fine coating resin particles are electrostatically applied to the surface of the magnetic particles. After adhering to the surface of the magnetic particles to form a so-called clathrate layer of fine resin particles, a uniform and continuous coating layer is formed on the surface of the magnetic particles by repeatedly applying mechanical impact force by stirring to the surface of the clathrate layer. Form.

The average particle diameter of the small-diameter component is 50 microns or less, preferably 8 to 40 microns. In addition, the average particle size of the large diameter component is more than twice the average particle diameter of the small diameter component, and is defined based on the relationship with the small diameter component, but from a practical point of view, it is 60 to 150 μm.
Preferably within the stomach.

If the average particle size of the large-diameter component is less than twice the average particle size of the small-diameter component, the mechanical impact force on the large-diameter component is reduced, so that good coating is achieved not only for the small-diameter component but also for the large-diameter component. It becomes difficult to form layers efficiently.

In addition, from the viewpoint of efficiently forming a good coating layer on the small-diameter component and increasing the yield of small-diameter carrier, the mixing ratio of the small-diameter component and the large-diameter component was determined to be 50% by weight of the entire powder of magnetic particles. 80% by weight is preferably small diameter components. Note that if the proportion of the small diameter component exceeds 80% by weight, the mechanical impact force applied to the small diameter component may decrease, making it difficult to form a good coating layer.

From the viewpoint of preventing granulation and forming a good coating layer, the mixing ratio of the magnetic particle powder and the coating resin fine particle powder is 100% of the magnetic particle powder (total of small-diameter component and large-diameter component). It is preferable that the powder of coating resin fine particles is 0.5 to 20 parts by weight based on the weight part. If the proportion of the powder in the coating resin fine particles is too small, it may be difficult to form a good coating layer.

On the other hand, if the proportion of the powder in the coating resin fine particles is too large, the magnetic particles are likely to be bonded by the coating resin fine particles, which may cause a granulation problem.

Regarding the mode of mixing the small-diameter component, the large-diameter component, and the powder of fine resin particles for coating, for example, the small-diameter component and the large-diameter component are mixed first, and then the powder of fine resin particles for coating is added to the mixture. A mode of mixing, or mixing a large-diameter component and a powder of coating resin fine particles, and mixing a small-diameter component and a powder of coating resin fine particles,
Then mix these mixtures further! Mr. s etc. can be employed.

As a means for mixing the powder of magnetic particles and the powder of fine resin particles for coating and applying a mechanical impact force to the mixture,
For example, a rotary vane type mixing/stirring device, a container rotating type mixing/stirring device, etc. can be used.

Here, the circumferential speed of the mixing and stirring tank of the rotary vane type mixing and stirring device or the container rotation type mixing and stirring device is preferably 6 to 15 m/sec from the viewpoint of applying a suitable mechanical impact force. If this circumferential speed is too low, the mechanical impact force is too small and there is a risk that a good coating layer cannot be formed. If the circumferential speed is too high, the mechanical impact force is too large and the magnetic particles may be crushed or deformed. There is a risk that this may occur.

In addition, in the process of mixing the powder of magnetic particles and the powder of fine coating resin particles to form an inclusion layer of fine coating resin particles, from the viewpoint of preventing agglomeration of the fine coating resin particles, the coating resin does not soften. Preferably, it is carried out at temperature.

On the other hand, the step of repeatedly applying mechanical impact force to the clathrate layer of fine coating resin particles after forming the inclusion layer is preferably carried out by heating at a temperature at which the coating resin slightly softens.

Here, as the magnetic particles, commonly used particles such as ferrite and magnetite can be used.

. Further, as the coating resin, polymethyl methacrylate, styrene-acrylic copolymer resin, silicone resin, fluororesin, etc. can be used.

After undergoing the dry coating process as described above, the small-diameter powder and the large-diameter powder are separated using a sieve or the like. That is, in the treated product obtained through the dry coating process, there are both small-diameter powder with a particle size distribution corresponding to the small-diameter component and large-diameter powder with a particle size distribution corresponding to the large-diameter component. Therefore, these are separated using a sieve or the like to obtain a small-diameter coated carrier and a large-diameter coated carrier.

Both the small-diameter coated carrier and the large-diameter coated carrier obtained in this way have a good coating layer, exhibit stable performance as a carrier over a long period of time, and have excellent durability. .

These large-diameter coating carriers and small-diameter coating carriers are combined with toner to form a developer, and a developer using a small-diameter coating carrier in particular forms a high-quality copy image. Is possible.

〔Example〕

Examples of the present invention will be described below along with comparative examples, but the present invention is not limited to these embodiments.

In addition, in the following, "parts" represent "parts by weight".

Example 1 50 parts of a small-diameter component consisting of spherical ferrite (magnetic particles) powder with an average particle size of 3 On, 50 parts of a large-diameter component consisting of spherical ferrite powder with an average particle size of 120μ, and an average particle size of 4 parts of powder of polymethyl methacrylate fine particles (fine resin particles for coating) having a particle size of 0.1n are charged into a rotary blade type mixing and stirring device, and the mixing and stirring tank is heated at room temperature at a circumferential speed of 1.
The mixture was mixed and stirred for 15 minutes by rotating at 0 m/sec.

Subsequently, the mixing tank was heated to 70°C and the circumferential speed was 10 m.
The mixture was mixed and stirred for 20 minutes by rotating at a speed of 0.000000000000 seconds.Then, the treated material in the mixing stirring tank was taken out and separated into small diameter powder and large diameter powder using a 200 mesh sieve. The average particle size of the small diameter carrier 1A that passed through the sieve was 3 (In
The average particle size of the large-diameter carrier 1B remaining on the sieve was 120/JM.

Example 2 In Example 1, 80 parts of the small diameter component and 20 parts of the large diameter component were used.
A small-diameter carrier 2A and a large-diameter carrier 2B were obtained in the same manner except that the parts were changed.

Example 3 In Example 1, 65 parts of the small diameter component and 35 parts of the large diameter component were used.
A small-diameter carrier 3A and a large-diameter carrier 3B were obtained in the same manner except that the parts were changed.

Example 4 Same as Example 1 except that the small diameter component was changed to 50 parts of spherical ferrite powder with an average particle size of 12 μm and the large diameter component was changed to 50 parts of spherical ferrite powder with an average particle diameter of 8 OnM. A small diameter carrier 4A and a large diameter carrier 4B were obtained.

Example 5 In Example 1, the small diameter component was made into 50 parts of spherical ferrite powder with an average particle diameter of 4 On, and the large diameter component was made into 50 parts of spherical ferrite powder with an average particle diameter of 8 On.
A small diameter carrier 5Δ and a large diameter carrier 5B were obtained in the same manner except that 50 parts of On spherical ferrite powder was used.

Comparative Example 1 100 parts of a small-diameter component consisting of spherical ferrite powder with an average particle size of 30 μm and 4 parts of powder of polymethyl methacrylate fine particles (fine resin particles for coating) with an average particle size of 0.1 μm were mixed into a rotary blade. The mixture was placed in a type mixing stirrer, and mixed and stirred for 15 minutes by rotating the mixing tank at a circumferential speed of 10 m/sec at room temperature.

Subsequently, the mixing tank was heated to 70°C and the circumferential speed was 10 m.
Although the mixture was mixed and stirred for 20 minutes by rotating at a speed of /second, a sufficient resin coating layer could not be formed. For this reason, mixing and stirring were continued for an additional 40 minutes.

Next, the treated material in the mixing stirring tank was taken out and the granulated material was separated using a 200 mesh sieve, and the average particle size was 3 On.
A coated carrier 1a was obtained.

Comparative Example 2 Mixing and stirring were carried out in the same manner as in Example 1 except that the large-diameter component was changed to 50 parts of spherical ferrite powder with an average particle size of 50 μm, but a sufficient resin coating layer could not be formed. could not. Therefore, mixing and stirring at 70° C. was continued for another 40 minutes to obtain a small diameter carrier 2a and a large diameter carrier 2b.

The dry coating treatment time and coating carrier yield in the above Examples 1 to 5 and Comparative Examples 1 to 2 are summarized in Table 1 below.

In addition, each of the obtained coated carriers was observed using a scanning electron microscope to examine the presence or absence of granulation and the surface condition of the coating layer. The results are shown in Table 1 below.

As understood from Table 1, according to the examples of the present invention, a coated carrier having a good coating layer can be produced in a short time and with a high yield.

On the other hand, in Comparative Example 1, since the powder of the magnetic particles consists only of small diameter components, it is difficult to form a good coating layer if the dry coating treatment time is the same as in the example, and the dry coating treatment It takes a long time. There is also the problem of generation of granules.

In Comparative Example 2, the average particle diameter of the large-diameter component is less than twice the average particle diameter of the small-diameter component, so the mechanical impact force on the large-diameter component is reduced, and the performance is good not only for the small-diameter component but also for the large-diameter component. It is difficult to form a coating layer efficiently.

Example 6 100 parts of a small component consisting of spherical ferrite powder with an average particle size of 30 μM and styrene with an average particle size of 0.3 μM.
10 parts of powder of acrylic copolymer resin fine particles (resin fine particles for coating) are charged into a rotary vane type mixing agitator,
The mixing tank was rotated at a circumferential speed of 10 m/sec at room temperature to perform mixing and stirring for 15 minutes to obtain a preliminary mixture.

On the other hand, apart from the above, 100 parts of a large-diameter component consisting of spherical ferrite powder with an average particle size of 120μ, and fine styrene-acrylic copolymer resin particles (fine coating resin particles) with an average particle size of 0.1AII were added. The powder 1 was charged into a rotary vane type mixing and stirring device, and the mixing and stirring tank was rotated at a circumferential speed of 8 m/sec at room temperature to perform mixing and stirring for 15 minutes to obtain a premix.

Next, these two types of preliminary mixtures are charged into a rotary vane type mixing and stirring device, and the mixing and stirring tank is heated to 70°C to increase the circumferential speed IQm.
The mixture was mixed and stirred for 20 minutes by rotating at a speed of /second.

Next, the treated material in the mixing stirring tank was taken out and separated into small-diameter powder and large-diameter powder using a 200-mesh sieve. The average particle size of the small carriers 6A that passed through the sieve was 3 On, and the average particle size of the large carriers 6B that remained on the sieve was 1 On.
It was 207/Il.

In this Example 6, the dry coating treatment time was 50 minutes (15+15+20), and the yield of the coated carrier was 96% for the small diameter carrier 6A and 96% for the large diameter carrier 6B.
was 98%. Furthermore, when the small diameter carrier 6A and the large diameter carrier 6B were observed using a scanning electron microscope, no granulation was observed and the surface condition was smooth.

Next, in order to investigate the performance of each coating carrier obtained in the above Examples and Comparative Examples, each coating carrier and toner for an electrophotographic copying machine rU-Bix6040J (manufactured by Konica ■) were mixed at a toner concentration of 5% by weight. Each developer was prepared by mixing them in the following proportions, and a test was conducted to form a copy image using the above-mentioned copying machine, and fogging, toner scattering, and durability were evaluated.

For the evaluation of "fogging", the relative density of the white background area is measured using a "Sakura Densitometer" (manufactured by Konica ■), and when the relative density is less than 0.05, it is "O", and when it is 0.05 or more, it is "O". was marked as "×".

The evaluation of "toner scattering" was made by visually observing the inside of the copying machine, and the case where almost no toner scattering was observed was evaluated as "○", and the case where a large amount of toner scattering was observed was evaluated as "X".

"Durability" was evaluated by measuring the relative density of the white background using a "Sakura Densitometer" (manufactured by Konica ■), and checking the number of copies when the relative density of the solid image became 1/10 or less. .

As can be understood from Table 2, the developers using the small diameter carriers IA to 6A obtained in the Examples of the present invention can produce stable images over a large number of times without fogging or toner scattering. can be formed.

On the other hand, according to the developer using coating carrier 1a obtained in Comparative Example 1, the powder of magnetic particles consists only of small diameter components, so if the dry coating processing time is the same as in the example, Since a clear coating layer is not formed, it is inferior in terms of fogging, toner scattering, and durability.

According to the developer using the coating carrier 2a obtained in Comparative Example 2, the average particle size of the large diameter component was less than twice the average particle diameter of the small diameter component, so a good coating layer was not formed. It is inferior in terms of fogging, toner scattering, and durability.

Further, when similar actual photography tests were conducted on the developers using the large diameter carriers 1B to 6B obtained in Examples 1 to 6, good results were obtained.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the powder of magnetic particles includes a small diameter component having an average particle diameter of 50 nm or less,
Since the large-diameter component has an average particle diameter twice or more of the average particle diameter of the small-diameter component, a dry coated carrier having a good coating layer can be efficiently produced.

Claims (3)

[Claims] (1) A dry coating carrier that includes a dry coating process in which magnetic particle powder and coating resin fine particle powder are mixed and mechanical impact is applied to the mixture to coat the surface of the magnetic particle with coating resin. In the manufacturing method, the powder of magnetic particles consists of a small diameter component having an average particle diameter of 50 μm or less, and a large diameter component having an average particle diameter of at least twice the average particle diameter of the small diameter component,
A method for producing a dry-coated carrier, which comprises adding a step of separating the powder into small-diameter powder and large-diameter powder after the dry-coating process. (2) The method for producing a dry coated carrier according to claim 1, wherein the average particle size of the large diameter component is 60 to 150 μm. (3) The ratio of small diameter component to large diameter component is 50:50 to 80:
3. The method for producing a dry coated carrier according to claim 1 or 2, wherein the carrier is 20.