JP2003029468A - Electrophotographic developing carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resin coated carrier showing steep rising of electrification, keeping stable resistance characteristics and having excellent durability. SOLUTION: The electrophotographic developing carrier consists of soft ferrite particles the surface of which is coated with a resin coating layer. The resin coating layer is subjected to mechanical surface treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for electrophotographic development comprising soft ferrite particles having a surface coated with a resin and a method for producing the same.

[0002]

2. Description of the Related Art A carrier (electrophotographic developing carrier) used as a developer for a two-component type electronic copying machine is required to have various characteristics (magnetic characteristics, triboelectrification, durability, fluidity, etc.). However, in the case of a carrier whose surface is coated with resin (resin-coated carrier), it is possible to maintain the original purpose of resin coating, that is, prevention of spent (prevention of fusion of toner on the carrier surface) for a long period of time. It is essential that the resin coating layer does not change the frictional electrification property (charging property) and that the electrical property (static resistance value) is stable.

Various proposals have been made for prescriptions for improving these charging characteristics and resistances, for example, Japanese Patent Application Laid-Open No. Hei 4
No. 40472 and Japanese Unexamined Patent Publication No. 7-104522 describe methods for achieving low resistance by reducing the film thickness, and Japanese Unexamined Patent Publication No. 4-93954 discloses forming an uneven film on the surface of carrier particles. Then, a method of exposing the convex portion has been proposed. Japanese Patent Application Laid-Open No. 6-222619 teaches that a change in charge amount over time can be suppressed by setting the surface of particles of a ferrite carrier serving as a core to a surface porosity of 10% by volume or less. In the publication, the occupancy ratio of the convex resin film is 55 of the total area of the carrier.
It is taught that if the resin film portion of the convex portion is made thin, the resistance is low and the durability is excellent.

[0004]

The charging characteristics and resistance characteristics of the resin-coated carrier are greatly affected by the type of resin and its film thickness. It is possible to adjust the characteristics.
For example, the charging characteristics and resistance may change depending on the surface condition of the ferrite particles, which are the particle nuclei, and the coating treatment conditions. In order to stably develop the required certain characteristics, the manufacturing conditions should be strictly controlled. There must be. On the other hand, the required characteristic values are often different depending on the model and function of the electrophotographic copying machine, and it is important to understand the conditions for obtaining the predetermined charging characteristics and resistance. .

Among them, the charging characteristic is required to have a steep rise of charging. This is because it is essential for an electrophotographic copying machine, especially a high-speed copying machine, that the electrostatic amount (charge amount) generated when the resin-coated carrier is mixed with the toner reaches a value close to the saturation value from the initial stage of mixing.

On the other hand, there is a strong demand for a longer life of the carrier as an electrophotographic developer, and as a countermeasure against this, thickening of the resin coating layer has been planned. However, the particles may be associated with each other or bonded to each other to form a carrier in which two or more particles are adhered to each other, the resin film may be damaged by the disintegration, or a carrier in which excessive resin fragments are attached to the surface of the resin layer may be formed. When such a carrier is used in an electrophotographic copying machine, minute resin pieces may float due to agitation in the developing device, or exposed cores may be bonded to each other, resulting in charging failure or fixing failure (offset). It will have an adverse effect.

Therefore, an object of the present invention is to obtain a carrier having stable charging characteristics and resistance characteristics even if the manufacturing history is slightly different, and in particular, the rising of charging is sharp and continuous. The object is to obtain a resin-coated carrier that maintains stable resistance characteristics for use, reaches a saturation value in the initial stage of mixing with toner, and has excellent durability.

[0008]

According to the present invention, a mechanical surface treatment in which a compressive stress acts on the resin coating layer is performed by colliding soft ferrite particles having resin coating on their surfaces with each other. A carrier for electrophotographic development is provided. That is, there is provided an electrophotographic developing carrier comprising soft ferrite particles having a resin coating layer on the surface thereof, wherein the resin coating layer is subjected to a mechanical surface treatment. .

As the mechanical surface treatment, it is preferable to perform a polishing treatment in which soft ferrite particles having a resin coating layer are caused to collide with each other so that compressive stress is uniformly applied to the resin coating layer. Then, this polishing treatment is preferably performed after the coating resin layer is cured.

At that time, it is preferable that the core material made of soft ferrite is coated with 0.5 to 4.0 parts by weight of resin with respect to 1000 parts by weight, before the mechanical surface treatment. The carrier resistance is R ₁ [Ω · c
m], the same resistance value after mechanical surface treatment is R ₂ [Ω · cm]
Then, it is desirable that the relationship of 1.0 <R ₁ / R ₂ <50.0 is established.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a carrier for electrophotography in which the surface of soft ferrite particles is coated with resin.
Various soft ferrite particles can be applied. For such ferrite, the raw materials are mixed so that the target composition is obtained, and calcination, pulverization, drying, granulation, firing, crushing,
It can be manufactured through various classification steps.

Taking, for example, the production of MnO-MgO-Fe ₂ O ₃ type ferrite, Mn, Mg and F in the raw materials
The raw materials in the form of carbonates, hydroxides or oxides are weighed and mixed so that the composition ratio of e corresponds to the intended composition ratio of ferrite, mixed well, and then 600 to 1 in a heating furnace.
Calcination is performed by heating to a temperature of 000 ° C. in the atmosphere and holding for 1 to 5 hours. As a result, the raw materials prepared in the form of carbonates or hydroxides become substantially lumps in the form of oxides, and volatile components and non-metallic inclusions are decomposed and removed by evaporation. The obtained calcined product is cooled and then crushed to a size of about 1 μm by a crusher, for example, a vibration mill, and then water is added to make a coarse slurry of about 70%, which is wet crushed by a ball mill or the like. As a result, a slurry of finely pulverized calcined powder is obtained. If necessary, a dispersant such as polycarboxylic acid is added to the calcined powder slurry, and then the mixture is spray-dried by a spray dryer or granulated by a pelletizer.
Dry to 500 μm spherical pellets and dry.

Next, the above granulated product is fired to obtain ferrite. By controlling the atmosphere of this firing process, it is possible to obtain soft ferrite having the intended saturation magnetization. For example, when carrying out a firing treatment in which a calcined powder having an oxide composition substantially equivalent to the ferrite composition is held at a temperature sufficient for actually firing the ferrite, for example, 1150 to 1200 ° C. for at least 60 minutes, other conditions When the oxygen partial pressure in the atmosphere is continuously changed from air to nitrogen gas while maintaining constant, the saturation magnetization continuously rises following it, so to obtain the intended saturation magnetization, The obtained oxygen partial pressure may be adopted.

The fired product obtained by firing the ferrite is crushed by a crusher, and the crushed powder is classified or sieved to obtain a carrier having an appropriate particle size. This gives a MnO-MgO-Fe ₂ O ₃ based soft ferrite spherical particles having an average particle diameter uniform.

Next, the surface of the soft ferrite particles (carrier core) thus obtained is coated with a resin, and various kinds of resin can be applied, for example, acrylic resin, styrene resin, styrene resin. Acrylic resin, olefin resin (polyethylene, chlorinated polyethylene, polypropylene, etc.), polyester resin (polyethylene terephthalate, polycarbonate, etc.), unsaturated polyester resin (vinyl chloride resin, polyamide resin, polyurethane resin, epoxy resin) Examples thereof include resins, silicone resins, fluorine resins (polytetrafluoroethylene, polychlorotrifluoroethylene, vinylidene fluoride, etc.), phenol resins, xylene resins, diallyl phthalate resins and the like.

To perform resin coating, it is common to dilute the above resin in a solvent and coat the surface of the carrier core. Any solvent may be used as long as each resin is soluble. Toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, methanol, etc. can be used as a solvent in the case of a resin soluble in an organic solvent. Water is used for resin or emulsion type resin.

To coat the surface of the carrier core with a resin diluted with a solvent, a dipping method in which the carrier core is immersed in the liquid and stirred, a spraying method in which the liquid is sprayed onto the carrier core, and a brush for brush coating are applied. A coating method or the like can be applied, and the solvent is dried after applying the liquid. Although such a coating method can be said to be a wet method, a method in which a resin powder is adhered to the carrier core surface by a dry method without using a solvent can also be adopted.

In any case, it is preferable to bake the resin adhered to the surface of the carrier core particles by baking, and use a fixed or fluid type electric furnace, a rotary electric furnace, a burner furnace or the like to perform an external heating method. Alternatively, it can be baked by an internal heating method. Baking with a microwave is also possible. The baking temperature differs depending on the resin, but it must be above the melting point or above the glass transition point. With thermosetting resins or condensation type resins, it is necessary to raise the temperature to a temperature at which curing is sufficiently advanced.

The case of forming a film of a carrier core with a silicone resin will be specifically described as an example. The silicone resin is diluted with toluene, and this solution and the carrier core are placed in a vessel of an agitator and agitated. As a result, for example, the silicone resin is applied by the dipping method so that the proportion thereof is 3% by weight. At that time, a curing agent is added according to the type of resin used. After stirring and mixing, the solvent is dried and removed (for example, heat treatment at 130 ° C. for 30 minutes). Then, it is hardened while being heated and stirred (for example, it is heated in an oil bath and heated at 190 ° C. for 30 minutes while being stirred). Then, the resin is baked using an oven or a tunnel furnace (for example, 160 to 280 ° C. × 3 hours). As a result, a resin-coated carrier product is obtained.

The resin-coated carrier thus obtained is combined with the toner in this state to form a two-component electrophotographic developer, and even if the resin is firmly baked on the surface of the ferrite core. In some cases, further improvement is required in terms of charging characteristics, resistance, and durability. According to the present invention, by polishing the resin-coated carrier product, specifically, by subjecting the resin coating layer of the product to a mechanical surface treatment in which a compressive stress acts, more specifically, By polishing the particles that make the particles of this product collide with each other,
It was found that the above-mentioned properties of the product were improved.

[0021] In addition to the electron microscope week explained, FIG. 5 (a) ~ (c) is MnO-MgO-Fe ₂ O ₃ carrier core (without resin coating used in the examples below
The spherical particles of the soft ferrite) were photographed at different magnifications, and it can be seen that they are spherical particles having an average particle diameter of 50 μm. Particles (Comparative Example 1) obtained by coating and baking this carrier core with a fluorine-acrylic resin (coating amount: 1.0 wt%) are shown in FIGS. 6 (a) and 6 (b). FIGS. 6A and 6B are images of the same particle, with the applied voltage changed. (A) is 5.0 KV and (b) is 1.5 V. As shown in both figures of FIG. 6, the coated particles have incomplete surface coating, and exposed portions of the carrier core are observed in places.

7 (a) and 7 (b) show the particles (particles of Example 1) in which the amount of resin was increased to completely cover the surface of the core and further subjected to polishing treatment, as in the case of FIG. The images were taken with different applied voltages. As shown in both figures of FIG. 7, it can be seen that the incomplete portion of the coating disappears and the coating is uniform. As described in the embodiment, the toner has a steep rise in charging when mixed with toner and exhibits stable resistance characteristics.

That is, when a resin is attached to a surplus more than completely covering the surface of the carrier core and an appropriate mechanical surface treatment is applied to the resin coating layer so that compressive stress acts, as shown in FIG. It was clarified that the film changed to a solid and continuous film, and the charging property and resistance property were improved and the durability was also improved.

Similarly, in the silicone resin coating as well, the coated particles described in Comparative Example 2 described later are shown in FIG.
As shown in (b), the situation in which the coating is incomplete can be seen as shown in FIG. Example 4 as opposed to Comparative Example 2
As shown in FIG. 9, the particles with the increased coating resin amount and the polishing treatment are shown in FIGS. 9 (a) and 9 (b). However, in FIGS. 8 to 9, (a) is an image at an applied voltage of 5.0 KV, and (b) is an image at 1.5 V. It can be seen that the particles of FIG. 9 have a more complete coating than the particles of FIG. That is, the one in FIG. 9 in which the amount of resin is increased and the polishing treatment is applied compared to the one in FIG.
As shown in Examples described later, the rising of charging becomes steep and there is no difference in surface partial resistance.

In the polishing treatment, it is preferable to polish the particles so that the compressive stress acts evenly on the coating layer. In order to make such compressive stress act uniformly, the particles are collided with each other. It is even more advantageous.
In practice, it is desirable to use a polishing method in which the resin-coated product is placed in a fluidized stirrer to give a motion in which particles collide randomly.

The present invention will be further described below with reference to examples.

[0027]

EXAMPLES Example 1 so that the ferrite composition of _{MnO · MgO · Fe 2 O 3} , MnCO as Mn source
₃ , Mg (OH) ₂ as Mg source, Fe ₂ as iron source
O ₃ is respectively MnCO ₃ : 25 mol%, Mg (OH)
_2:25 mol%, Fe ₂ O _3: mixed at a ratio of 50 mole% was subjected to raw material mixing.

The above mixed powder was heated in a heating furnace at 900 ° C. for 3 hours in the atmosphere to be calcined. After cooling the obtained calcined product, it was pulverized to a size of approximately 1 μm with a vibration mill, and a dispersant (trade name: San Nopco SN Dispersant 5468) was added together with water at a ratio of 1% by weight to the dry powder to form a slurry. A slurry having a concentration of 70% was prepared. This slurry was loaded into a wet ball mill and wet-milled, and the obtained suspension was supplied to a spray dryer to obtain a granulated product composed of dry particles having an average particle size of about 80 μm.

This granulated product was loaded into a firing furnace and was placed in a mixed gas in which the oxygen concentration in nitrogen gas was adjusted to about 2 vol.%.
It was baked at 00 ° C. for 3 hours. The fired product was crushed by a crusher and then sieved to obtain a spherical soft ferrite powder having a particle size of about 50 μm. The saturation magnetization of this ferrite powder is 6
It was 2 emu / g.

The spherical particles thus obtained have an average particle size of 50.
The Mn.Mg-based soft ferrite powder having a μm and a saturation magnetization of 62 emu / g is hereinafter referred to as “carrier core”.

Fluorine resin 50 wt.% And acrylic resin 5
A coating resin solution prepared by dissolving a mixed resin component of 0 wt.% In toluene was prepared, and the coating resin solution and the carrier core were charged into a container of an agitator at a predetermined ratio, and each particle was added to the resin solution. Each of the carrier core particles was coated with the coating resin in such a manner that the total amount of the coating resin was 1.5% by weight with respect to the total amount of the carrier core by a method of mixing and stirring while soaking for a predetermined time.

This coating powder was loaded into a fixed heating device, and 2
The resin was cured by heating and holding at 50 ° C. for 4 hours to obtain a resin coating carrier. The resin coating carrier product at the stage of this curing treatment is called "primary product B".

This primary product B was put in a container of the same stirrer used for coating the resin liquid, and subjected to a polishing treatment in which it was stirred at room temperature for 3 hours. The amount of static charge and static resistance of the obtained polished product were measured, and the results are shown in Table 1. Table 1 also shows the measured values of the above-mentioned "carrier core" and "primary product B".

To measure the amount of charge, 9.5 g of carrier powder for measurement and 0.5 of toner were put in a 100 cc plastic container,
Rotate the plastic container at 100 rpm for a total of 20 minutes using a ball mill, collect samples from 1, 3, 5, 10 minutes in the middle and the last 20 minutes, and use a charge amount measuring device to measure the charge amount at each time ( μC / g) was measured. To measure the resistance value, accurately measure the carrier powder for measurement on an insulating pipe.
The sample was filled with g and the specific resistance of the filled sample was measured by the electrodes installed above and below the pipe.

Example 2 Example 1 was repeated except that the temperature and time of the polishing treatment for the primary product B were “120 ° C. × 3 hours”. The charge amount, the resistance value and the actual copying property of the obtained carrier powder were measured in the same manner as in Example 1, and the results are also shown in Table 1.

[Example 3] Example 1 was repeated except that the temperature and time of the polishing treatment for the primary product B were "room temperature x 3 hours + 120 ° C x 3 hours". The charge amount, the resistance value and the actual copying property of the obtained carrier powder were measured in the same manner as in Example 1, and the results are also shown in Table 1.

Comparative Example 1 The procedure of Example 1 was repeated, except that each carrier core particle was coated with the coating resin so that the total amount of the coating resin was 1.0% by weight with respect to the total amount of the carrier core. , Primary products with different (small) coating amount were obtained. The charge amount, resistance value, and actual copying characteristics of this primary product (resin-coated product not subjected to polishing treatment: this is referred to as "primary product A") were measured. The results are also shown in Table 1.

Example 4 The same carrier core as obtained in Example 1 was coated with silicone resin as follows. First, a resin solution prepared by dissolving a silicone-based resin in toluene is prepared, and the resin solution and the carrier core are charged in the same stirrer container as in Example 1, and the carrier core is immersed in the resin solution for a predetermined time. While mixing and stirring, each carrier core particle was coated with a coating resin so that the total amount of the resin was 3.5% by weight with respect to the total amount of the carrier core. The obtained coating powder was loaded into a fixed heating device and heated and held at 230 ° C. for 4 hours to cure the resin to obtain a resin coating carrier. The resin coating carrier product at the stage of this curing treatment is called "primary product D".

This primary product D was put into a container of the same stirrer used for coating the resin liquid, and subjected to a polishing treatment of stirring at room temperature for 3 hours. The electrification amount, static resistance and actual copying characteristics of the obtained polished product were measured, and the results are also shown in Table 1. Table 1 also shows the measured values of the "primary product D".

Example 5 Example 4 was repeated except that the temperature and time of the polishing treatment for the primary product D were “120 ° C. × 3 hours”. The charge amount, the resistance value and the actual copying property of the obtained carrier powder were measured in the same manner as in Example 1, and the results are also shown in Table 1.

Example 6 Example 4 was repeated except that the temperature and time of the polishing treatment for the primary product D were “room temperature × 3 hours + 120 ° C. × 3 hours”. The charge amount, the resistance value and the actual copying property of the obtained carrier powder were measured in the same manner as in Example 1, and the results are also shown in Table 1.

Comparative Example 2 The procedure of Example 4 was repeated, except that each carrier core particle was coated with the coating resin so that the total amount of the coating resin was 2.5% by weight with respect to the total amount of the carrier core. , Primary products with different (small) coating amount were obtained. The charge amount, resistance value, and actual copying characteristics of this primary product (resin-coated product not subjected to polishing treatment: this is referred to as "primary product C") were measured. The results are also shown in Table 1.

[0043]

[Table 1]

As can be seen from the results in Table 1, with respect to the charge amount, the polished products of Examples 1 to 3 (fluorine-acrylic type) are already charged to a state close to the saturation value in 1 minute of stirring. I understand. On the other hand, in the case of the primary product B which is not polished, it takes about 3 minutes of stirring to obtain the same charge amount. This behavior is shown in FIG. 1, and it can be seen that in Examples 1 to 3, the rise of charging (slope until reaching saturation) is steeper than that of the primary product B. In addition,
The carrier core without resin coating does not have sufficient charge,
The primary product A (Comparative Example 1), which has a small coating amount even when coated, also has a low charge amount.

Similarly, the samples of Examples 4 to 6 are charged to a saturation value in about 1 to 3 minutes, whereas the primary product D not polished takes about 5 minutes to obtain the same amount of charge. ing. Figure 2
This behavior is shown in Fig. 5, but it can be seen that the polished product has a sharper rise in charging than the unpolished primary product D. The primary product C (Comparative Example 2) having a small coating amount has a low absolute charge amount.

When the polishing treatment is carried out after the resin coating as described above, the particles are quickly charged even if the stirring time with the toner is short, but this changes into a state in which the form of the coating film of each particle is suitable for charging. It is shown that. If the resin film is left unpolished, there are some cracks or parts that are easily peeled off. However, if the particle surfaces are sufficiently polished by collision of particles, a solid and continuous film is formed. It is suspected that it was because of this.

On the other hand, when looking at the resistance value, the polishing effect is more apparent. The results of Table 1 are shown in FIG.
The relationship between the applied voltage and the static resistance value of the acrylic coated product is summarized and shown. However, in the primary product B which is not polished, the resistance value is greatly changed when the applied voltage is changed. No. 3 does not show much change. Similarly, FIG. 4 shows a silicone-based coated product, but in this case, it has a high resistance value and exhibits substantially insulating properties.

As a result of the improvement of the charging property and the conductive property by the polishing treatment, as shown in the results of Table 1, the polishing products of Examples 1 to 6 were also subjected to the carrier pulling and the actual copying properties. No toner scattering occurs, and it has excellent durability.

[0049]

As described above, according to the present invention,
The charging characteristics and resistance characteristics required for resin-coated carriers have been improved, making it possible to obtain high-quality electrophotographic images with good durability.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a stirring time and a charge amount when a resin-coated carrier according to the present invention is stirred with a toner, in comparison with that of a comparative example.

FIG. 2 is a view showing a relationship between a stirring time and a charge amount when a resin-coated carrier of another example according to the present invention is stirred with a toner, in comparison with that of a comparative example.

FIG. 3 is a diagram showing static resistance values measured by changing an applied voltage to a resin-coated carrier according to the present invention in comparison with those of a comparative example.

FIG. 4 is a view showing static resistance values of other resin-coated carriers according to the present invention in comparison with those of a comparative example.

FIG. 5 is an electron micrograph (SEM image) of a carrier core used in Examples.

FIG. 6 Resin coated carrier particles (without polishing treatment:
Electron micrograph (SEM image) of Comparative Example 1 / Primary Product A)
Is.

FIG. 7 is an electron micrograph (SEM image) of carrier particles (Example 1) which were subjected to polishing treatment after the amount shown in FIG. 6 was completely coated with an increased amount of coating resin.

FIG. 8 is an electron micrograph (SEM) of another resin-coated carrier particle (without polishing treatment: Comparative Example 2 / primary product C).
Image).

FIG. 9 is an electron micrograph (SEM image) of carrier particles (Example 4) obtained by polishing the carrier particles shown in FIG.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomohide Iida             7 Doki Sakae-cho, Okayama City, Okayama Prefecture Dowa Iron Powder Works             Business F-term (reference) 2H005 BA01 BA06 BA11 BA15 CB04                       DA10 EA01

Claims (6)

[Claims] 1. An electrophotographic developing carrier comprising soft ferrite particles having a resin coating layer on the surface thereof, wherein the resin coating layer is subjected to a mechanical surface treatment. Carrier. 2. The carrier for electrophotographic development according to claim 1, wherein the mechanical surface treatment is a treatment in which soft ferrite particles having a resin coating layer are made to collide with each other. 3. The carrier for electrophotographic development according to claim 1, wherein the mechanical surface treatment is performed on the cured resin coating layer. 4. A core material 100 made of soft ferrite.
4. The electrophotographic developing carrier according to claim 1, which is coated with 0.5 to 4.0 parts by weight of resin based on 0 parts by weight. 5. When the resistance value of the carrier before the mechanical surface treatment is R ₁ [Ω · cm] and the resistance value after the mechanical surface treatment is R ₂ [Ω · cm], 1. The electrophotographic developing carrier according to claim 1, 2, 3 or 4, wherein a relationship of 0 <R ₁ / R ₂ <50.0 is established. 6. An electrophotographic developer comprising the carrier according to claim 1 and a toner.