JP3133854B2 - Method for producing resin-coated carrier for electrophotographic developer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carrier for an electrophotographic developer used in a copying machine or a printer, and the like.
And an electrophotographic developer using the carrier obtained by the production method.

[0002]

2. Description of the Related Art A two-component developer used in electrophotography comprises a toner and a carrier. The carrier is a carrier material that is mixed and stirred with the toner in the developing box, gives a desired charge to the toner, carries the charged toner to the electrostatic latent image on the photoconductor, and forms a toner image. The carrier remains on the magnet roll, returns to the developing box again, is mixed and stirred again with new toner, and is used repeatedly.

[0003] Accordingly, it is required that the carrier be constantly provided with desired charging characteristics during use.

[0004] In recent years, resin-coated carriers in which the surface of a carrier core material is coated with various resins have been widely used in order to improve the durability and environmental resistance of many carriers.

However, the conventionally used developer causes various inconveniences on images due to collision between carriers due to agitation or friction between the development box and the carrier. One of the problems is that the toner fuses to the carrier surface due to frictional heat during stirring and consumes the toner, so-called "spent formation", and as a result, the charge amount distribution between the toner and the carrier is widened. . For this reason, toner scattering and fogging occur during the life test of the developer, so-called "during printing". In the case of a resin-coated carrier, the resin of the outermost layer of the resin coated at the time of printing is missing,
When the inner resin layer is exposed, the charge amount between the toner and the carrier varies. In particular, under high-temperature and high-humidity conditions, toner scattering and fogging are likely to occur similarly to the above. Furthermore, when printing is performed, the resin layer is lost, and the core material is exposed, so that the carrier resistance changes, and the initial image cannot be maintained. As a result, at present, the life of the developer eventually ends.

When a resin-coated carrier is used, there is a tendency that the above-mentioned spent and the like with toner tend to be reduced as compared with a carrier which is not coated with a resin. On the other hand, when a resin-coated carrier is used, resin coating is performed. In this case, so-called granulation occurs in which the resin adheres the carrier core materials to each other. As a result, the carrier granulated by agitation in the developing box separates into one particle and one particle, so that the fluidity during printing changes, causing fluctuations in toner concentration, toner scattering due to over toner, and a decrease in toner concentration. As a result, the image density is lowered, and defects on the image such as carrier adhesion are often caused.

Various resin-coated carriers have been known for improving durability. For example, a carrier in which the surface of a carrier core material is coated with a fluoropolymer-based resin has been proposed (Japanese Patent Application Laid-Open No. Sho 54-126040). This product had stable charging characteristics at the initial stage, but the fluidity of the developer changed over a long period of use, and the image density was insufficient. In addition, carrier adhesion increases,
For this reason, the photoreceptor was damaged, and as a result, a defect on an image was caused. As a result, the life as a comprehensive evaluation was short.

[0008] Many proposals have also been made for silicone resins and the like (JP-A-57-78552). Such a carrier coated with a silicone resin or the like has an advantage that the spent is hard to occur due to low surface energy, but the charge level gradually decreases,
Fog and toner scattering occurred, and as a result, the life as a developer was short.

In recent years, as described above, the carrier is required to have durability, and finally, there is a demand for maintenance-free developer. However, there is a problem that the life of the carrier is still short, and as a result, it is difficult to extend the life of the developer. Also, the resin-coated carrier has a problem that the resin coating cost is still high.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems of the prior art, and has excellent durability, environmental resistance which does not change the chargeability with toner, and production. It is an object of the present invention to provide a method for producing a resin-coated carrier for an electrophotographic developer, which has good properties and is economically advantageous, and an electrophotographic developer using the carrier obtained by the production method.

[0011]

Means to be Solved by the Invention Here, the present inventors
As a result of studying what factors of the carrier contribute to the above-mentioned problems, it has been found that occurrence of peeling of the resin coating layer and granulation of the resin-coated carrier are the most significant factors. As a result of further research, during the production of a resin-coated carrier, it was found that it was largely due to the method of heating the resin after coating the resin on the carrier core material,
The present invention has been completed.

That is, the method of manufacturing a resin-coated carrier for an electrophotographic developer according to the present invention is characterized in that the surface of a carrier core material as a dielectric is coated with a resin as a dielectric and then baked by microwave heating. And

Hereinafter, the contents of the present invention will be described in detail. The carrier core material used in the present invention may be a dielectric material, and examples thereof include ferrite, magnetite, and ceramics.
u-Zn ferrite. Therefore, metals such as iron and copper cannot be used because they are non-dielectric. The average particle size of the carrier core material is preferably about 15 to 200 μm, more preferably 20 to 150 μm. If the average particle size is less than 15 μm, carrier adhesion becomes excessive, and if it exceeds 200 μm, the image density of the solid portion becomes insufficient.

In the present invention, a desired resin is coated on the surface of the carrier core material which is such a dielectric.

The resin used in the method of the present invention is not particularly limited, and examples thereof include a fluororesin, a silicone resin, an acryl-styrene resin, an alkyd resin, a polyolefin resin, a polyester resin and an epoxy resin. Blend system.

Further, when typical examples are given, examples of the fluorine resin include polyvinylidene fluoride and vinylidene fluoride-tetrafluoroethylene copolymer. As the silicone resin, room-temperature-curable and heat-curable silicone resins are used in the form of silicone varnish. Also, various silane coupling agents having a low degree of polymerization can be used as the silicone-based material. Examples of the acrylic-styrene resin include an acrylic resin alone, a styrene resin alone, and a copolymer resin of an acrylic monomer and a styrene monomer. The acrylic resin referred to here is a homopolymer of acrylic acid or methacrylic acid or a copolymer with other components, a homopolymer of acrylic acid or methacrylic ester having a functional group or other components. Examples thereof include copolymers or those obtained by introducing a thermosetting resin such as a melamine resin or an isocyanate compound into each of these polymers. Among these resins, an acrylic resin is most preferable in consideration of the adhesiveness to the carrier core material.

The coating amount of such a resin is preferably 0.05 to 10.0% by weight based on the total amount of the carrier, and particularly preferably 0.1 to 10.0% by weight.
1-7.0% by weight is preferred. If it is less than 0.05% by weight, a uniform coating layer cannot be formed on the carrier surface, and if it exceeds 10% by weight, the coating layer becomes too thick,
Even if baking is performed by microwave heating, granulation of particles becomes remarkable.

For adjusting the charge and the resistance of the resin-coated carrier obtained by the production method of the present invention, it is also possible to add a conductive substance, for example, carbon black, to each of the above-mentioned resins as required. .

In the present invention, the resin is generally diluted with a solvent and the resin is applied to the surface of the carrier core material. The solvent used here may be any solvent that is soluble in each resin such as toluene, xylene, cellosolve butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and methanol. In addition, a method of coating the resin diluted with a solvent on the surface of the carrier core material is applied by an immersion method, a spray method, a brush application, a kneading method or the like, and thereafter, the solvent is volatilized.

The resin can be coated on the surface of the carrier core material by a dry method instead of a wet method using such a solvent.

Next, in the present invention, the resin which is a dielectric material coated on the surface of the carrier core material is baked to the carrier core particles by microwave heating. It is necessary to set the temperature higher than the temperature at which the resin is cured by the microwave heating, and for this purpose, it is necessary to adjust the microwave irradiation time. The irradiation time is generally 30 seconds to 1
0 minutes. If the time is less than 30 seconds, the heat generation is insufficient and the adhesion between the carrier core material and the resin is weak. If the irradiation is performed for 10 minutes or more, the temperature becomes too high, and the resin is decomposed.

Here, the microwave heating is a heating method using an electromagnetic wave having a frequency in a range of 300 MHz to 30 GHz, and among them, 915 ± 25 MHz
And a frequency of 2450 ± 50 MHz are preferably used,
More preferably, a frequency of 2450 ± 50 MHz is used. Note that these two types of frequencies are internationally defined.

In this way, the resin is coated and baked on the surface of the carrier core material, and then cooled to obtain a resin-coated carrier.

[0024]

Conventionally, a heating method for coating a resin on a carrier core material employs flame, hot air, a burner, an electric heater, steam or the like by combustion, and these coat the outer surface of the resin with heat rays from outside the resin. Heat, heat conduction inside,
That is, an external heating method of heating up to the carrier core material has been adopted.

On the other hand, the present invention employs an internal heating method by high-frequency heating, that is, a method in which the object to be heated itself becomes a heating element to perform heating. Thereby, since the heat is uniformly transmitted from the inside of the resin to the carrier core material, the adhesion of the resin layer to the carrier core material is improved. Furthermore, resin coating baking can be performed in a short time by performing the microwave heating method.

Accordingly, the carrier manufactured by using the conventional heating device has a long baking time and a high manufacturing cost, whereas the baking time is significantly reduced in the above-described present invention, and the manufacturing cost is high. The cost is low and the productivity is excellent.

[0027]

EXAMPLES Hereinafter, the present invention will be specifically described based on examples and the like.

Example 1 Cu-Zn ferrite particles ("F-
150 ”, average particle size 80 μm, saturation magnetization 65 emu /
g) was used as a carrier core material. On the other hand, acrylic
Styrene resin 88wt% and melamine resin 12wt%
Is dissolved in a toluene solvent, and the carrier core material is coated on the carrier core material using a fluidized bed so that the amount of the resin is 3.0% by weight based on the total amount. Microwave irradiation and baking were performed to obtain a resin-coated carrier coated with the above resin. At this time, the temperature of the carrier was 150 ° C.
Table 1 summarizes these characteristics, conditions, and the like.

Using this resin-coated carrier and toner,
The developer was prepared, and the image of the resin-coated carrier was evaluated by a printing test of 100,000 sheets using a commercially available copying machine. The toner used here is a commercially available black toner having a toner concentration of 4.5% by weight.

The image evaluation is carried out on the initial stage of image density, fogging on the image, carrier adhesion, toner scattering and after printing of 100,000 sheets, and on the environmental fluctuation of charge, the fluctuation of carrier resistance and the amount of spent. The overall evaluation was made. Table 2 shows the results. In Table 2, ◎ indicates very good, ○ indicates good, Δ indicates slightly poor, and × indicates poor. These evaluation methods are shown below.

[Evaluation of Carrier Image] Image Density (ID) A copy was made under appropriate exposure conditions, and the image density was evaluated. The image density of the solid portion was measured with a Sakura densitometer and ranked.

Fogging on Image For fogging on an image, toner fog on a white background image was evaluated and ranked.

Carrier adhesion Like the toner fog on the image, the carrier adhesion level on a white background image was evaluated and ranked.

Toner Scattering An unfavorable toner scattering state, such as toner scattering degree which becomes a stain on the copy paper and a charged charger stain, was evaluated and ranked.

Environmental Charge Variation The charge amount (QLL) of the developer after storage for 24 hours in an environment of 10 ° C. and 15% and the charge amount (QHH) of the developer after storage for 24 hours in an environment of 30 ° C. and 85% are shown. Then, the difference (ΔQ) was calculated, and ranking was performed to evaluate the environmental change of charging. ΔQ = QLL-QHH (μc / g)

Carrier Resistance Fluctuation The specific resistance (R ₁ ) of the carrier at the initial stage and the specific resistance (R ₂ ) of the carrier after printing 100,000 sheets have been obtained, and the difference (△
R) was obtained by calculation, and ranking was performed to evaluate the carrier resistance fluctuation. ΔR = R ₁ -R ₂ (Ωcm)

Spent Amount Spent amount was evaluated by measuring the amount of toner (spent amount) adhered to the carrier after printing for 100,000 sheets after printing and performing ranking.

Comprehensive Evaluation Each image evaluation (image density, fog on the image, carrier adhesion, toner scattering, charge environment fluctuation, carrier resistance fluctuation, amount of spent) of the 100,000-sheet printing test was comprehensively evaluated. Ranking was performed.

Example 2 Cu-Zn ferrite particles ("FL" manufactured by Powdertech Co., Ltd.)
−100 ”, average particle diameter 120 μm, saturation magnetization 55 emu
/ G) was used as a carrier core material. On the other hand, a silicone resin (SR-2411; manufactured by Toray Dow Corning Silicone Co., Ltd.) was added to the above carrier core material in the same manner as in Example 1 so that the above resin was 1.0% by weight based on the total amount. Coating, and further using a microwave heating device,
A microwave of 2450 MHz was irradiated for 6 minutes and baked to obtain a resin-coated carrier coated with the above resin. At this time, the temperature of the carrier was 200 ° C. Table 1 summarizes these characteristics, conditions, and the like.

Using this carrier and the toner used in Example 1, the developer was adjusted to a toner concentration of 4.0% by weight.
Using a commercially available copying machine, printing durability was evaluated under the same conditions as in Example 1. Table 2 shows the image evaluation at that time.

Example 3 Cu-Zn ferrite particles ("F-
1030 ", average particle diameter 100 μm, saturation magnetization 65 emu
/ G) was used as a carrier core material. On the other hand, fluorine-
An acrylic resin (polyvinylidene fluoride: acrylic styrene resin = 1: 1 mixed resin) was prepared in the same manner as in Example 1.
The above resin is coated on the carrier core material so that the total amount of the resin becomes 0.3% by weight, and further irradiated with microwaves of 2450 MHz for 4 minutes using a microwave heating device, and baked to cover with the resin. Got a career. At this time, the temperature of the carrier was 170 ° C. Table 1 summarizes these characteristics, conditions, and the like.

Using this carrier and the toner used in Example 1, the developer was adjusted to a toner concentration of 4.0% by weight.
Using a commercially available copying machine, printing durability was evaluated under the same conditions as in Example 1. Table 2 shows the image evaluation at that time.

Example 4 Cu-Zn ferrite particles ("F-
150 ”, average particle size 80 μm, saturation magnetization 65 emu /
g) was used as a carrier core material. On the other hand, acrylic
Styrene resin 88wt% and melasin resin 12wt%
Is dissolved in a toluene solvent, and the carrier core material is coated on the carrier core material using a fluidized bed so that the total amount of the resin is 8.0% by weight based on the total amount. Microwave irradiation and baking were performed to obtain a resin-coated carrier coated with the above resin. At this time, the temperature of the carrier was 150 ° C. Table 1 summarizes these characteristics and conditions.

COMPARATIVE EXAMPLE 1 Except that the baking of the resin was carried out by heating in an electric furnace at 150 ° C. for 60 minutes instead of the microwave heating at 2450 MHz for 3 minutes, the resin was manufactured using the same materials and conditions as in Example 1. A coated carrier was obtained. Table 1 summarizes these characteristics, conditions, and the like.

Using this carrier and the toner used in Example 1, the developer was adjusted to a toner concentration of 4.5% by weight.
Using a commercially available copying machine, printing durability was evaluated under the same conditions as in Example 1. Table 2 shows the image evaluation at that time.

COMPARATIVE EXAMPLE 2 Except that the baking of the resin was carried out by heating in a thermostatic chamber at 200 ° C. for 120 minutes instead of the microwave heating at 2450 MHz for 6 minutes, the resin was manufactured using the same materials and conditions as in Example 2. A coated carrier was obtained. Table 1 summarizes these characteristics, conditions, and the like.

Using this carrier and the toner used in Example 1, the developer was adjusted to a toner concentration of 4.0% by weight.
Using a commercially available copying machine, printing durability was evaluated under the same conditions as in Example 1. Table 2 shows the image evaluation at that time.

Comparative Example 3 Except that the baking of the resin was carried out by heating in an electric furnace at 170 ° C. for 90 minutes instead of the microwave heating at 2450 MHz for 4 minutes, the resin was manufactured using exactly the same materials and conditions as in Example 3. A coated carrier was obtained. Table 1 summarizes these characteristics, conditions, and the like.

Using this carrier and the toner used in Example 1, the developer was adjusted to a toner concentration of 4.0% by weight.
Using a commercially available copying machine, printing durability was evaluated under the same conditions as in Example 1. Table 2 shows the image evaluation at that time.

COMPARATIVE EXAMPLE 4 Except that the baking of the resin was carried out by heating in an electric furnace at 150 ° C. for 60 minutes instead of microwave heating at 915 MHz for 3 minutes, the resin was manufactured using exactly the same materials and conditions as in Example 4. A coated carrier was obtained. Table 1 summarizes these characteristics, conditions, and the like.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

The resin-coated carrier obtained according to the present invention as described above performs internal heating using microwaves during baking after resin coating, whereby the adhesion between the carrier core material and the resin is strengthened, It is durable because it hardly causes the toner to spend on curing and has little peeling or falling off of the resin coating layer on the carrier surface. In addition, the resin-coated carrier can have a stable charging performance even in environmental fluctuations. Therefore, the developer using such a resin carrier can greatly improve the life and image characteristics. Further, the production method of the present invention is excellent in economy and productivity because the heating time is short as described above.

Continuation of the front page (72) Inventor Toshio Honjo 217 Toyo, Kashiwa-shi, Chiba Powder Powder Co., Ltd. (56) References JP-A-3-220564 (JP, A) JP-A-2-33159 (JP, A (58) Fields surveyed (Int. Cl. ⁷ , DB name) G03G 9/10

Claims (4)

(57) [Claims] 1. A method for producing a resin-coated carrier for an electrophotographic developer, comprising coating the surface of a carrier core material, which is a dielectric, with a resin, which is also a dielectric, and baking by microwave heating. 2. An electrophotographic developer using the carrier obtained according to claim 1. 3. The surface of a carrier core material which is a dielectric,
A method for producing a resin-coated carrier for an electrophotographic developer, which is obtained by irradiating microwaves for 30 seconds to 10 minutes as a condition for baking by microwave heating after coating with a resin which is also a dielectric. 4. An electrophotographic developer using the carrier obtained according to claim 3.