JP2899863B2 - Manufacturing method of electrophotographic carrier - 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 an electrophotographic carrier, and more particularly to a method for producing an electrophotographic carrier comprising composite particles of magnetic fine particles and a polyurethane resin.

[0002]

2. Description of the Related Art With the spread of electrophotography, plain paper copiers, laser beam printers,
The performance of full-color copying machines and the like has been improved, and the speed, image quality, and definition have been increasing.

In the electrophotographic method employed in the above apparatus, toner charged to a polarity opposite to the polarity of the latent image is attached to an electrostatic latent image obtained by various means using a magnetic brush or the like. A developing method for obtaining a visible image is generally used.

In this development step, carrier particles called "carriers" are used. The carrier is mixed with the toner to frictionally charge the toner particles to give an appropriate charge to the toner, and to form a magnetic brush on a developing sleeve containing a magnet by utilizing the magnetic force of the carrier. Thereby, it has a function of transporting the toner particles onto the electrostatic latent image.

Conventionally known carriers include metal carriers such as iron powder carriers and ferrite carriers, and binder type carriers (resin particles in which magnetic particles are dispersed).

[0006]

Among the above metal carriers, iron powder carriers and ferrite carriers are particularly often used. These carriers are obtained by granulating and classifying metal powder so as to have a specific particle size distribution. Since metal powder is used, the true specific gravity is large and the bulk specific gravity (apparent specific gravity) is relatively large, being about ³ to 4 g / cm ³ .
For this reason, when agitating in the developing machine, a large driving force is required, and mechanical abrasion is large. As a result, inconveniences such as generation of so-called spent toner, deterioration of the carrier itself, and damage to the photoconductor are easily caused.

On the other hand, a binder type carrier is obtained by melting and kneading a magnetic powder and a resin. As the resin used,
Homopolymers such as polystyrene, polyacrylate, polymethacrylate, polyacrylonitrile, polyether, polyvinyl chloride, thermoplastic polyester, and vinyl resins, copolymer resins combining two or more of those monomers, modified acrylic resins, phenol resins, And a melamine resin. Conventional resin
Since these resins are contained as a main component, the bulk specific gravity is smaller than that of the carrier composed of the above-mentioned metal components, and is usually 3 g / cm ³ or less. Therefore, since it is smaller than that of the iron powder carrier and ferrite carrier,
The above disadvantages are unlikely to occur.

However, in order to adopt a manufacturing method in which the magnetic powder and the resin are melt-kneaded, if the amount of the magnetic powder is 80% by weight or more with respect to 100% by weight of the resin, the viscosity of the hot-melt kneaded material increases. Can not be sufficiently kneaded. Conversely, if the content of the magnetic powder is set to 80% by weight or less so that kneading can be sufficiently performed, a carrier having a sufficient magnetic force cannot be obtained. In addition, since the particles are formed into fine particles by pulverization, the shape of the particles becomes irregular. As a result, there was a problem that the fluidity was low and stirring was not sufficiently performed.

As a method for improving the shape of the carrier,
JP-A-59-31967 describes a method of spheroidizing by pulverizing and then treating with hot air. In addition, a spray dry method is known. The spray drying method is a method of dissolving a resin used as a binder in an organic solvent, adding and dispersing a magnetic powder, and performing spray granulation drying to obtain carrier particles. With this method, spheroidization is easy, but voids in the particles are likely to occur due to evaporation of the organic solvent. Furthermore, it is not suitable for an industrial production method, such as requiring a large amount of solvent recovery equipment.

[0010] As for the method of increasing the content of the magnetic powder, no solution has yet been found. further,
As the performance of full-color copiers and the like has improved, there has been a demand for smaller particle diameters and sufficient surface strength.

However, an electrophotographic carrier satisfying these requirements has not yet been provided. The present invention satisfies such a demand and has an object to provide an electrophotographic carrier having a small bulk specific gravity, a large magnetizability, a spherical shape and a small particle size, and a method for producing the same.

[0012]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have arrived at a method of manufacturing an electrophotographic carrier according to the present invention. That is,
Production of an electrophotographic carrier comprising magnetic powder and a polyurethane resin as main components, wherein an isocyanate and an alcohol are reacted in an aqueous medium in the presence of a magnetic powder and a suspension stabilizer. It has been found that the above objects can be achieved by the method.

Hereinafter, the method for producing the electrophotographic carrier of the present invention will be described in detail. First, a suspension stabilizer is added to an aqueous medium, and then an aqueous dispersion medium is obtained (Step 1). In this step 1, a dispersing aid can be added in addition to the above compounds. Next, magnetic powder, alcohols, and isocyanate are added to the obtained aqueous dispersion medium (Step 2). Next, the mixture is heated with stirring to react the alcohol with the isocyanate to produce a polyurethane resin (Step 3). The obtained mixture is classified to obtain particles having a desired diameter, and dehydrated and dried (Step 4). From such a process, an electrophotographic carrier composed of a magnetic powder and a polyurethane resin can be obtained.

Examples of the suspension stabilizer used in the above step 1 include organic compounds such as carboxymethylcellulose and polyvinyl alcohol, and poorly water-soluble inorganic fine particles such as calcium sulfate and calcium phosphate.
Examples of the aqueous dispersion medium include water, distilled water, and ion-exchanged water. The suspension stabilizer is 100% by weight of an aqueous dispersion medium.
Is preferably 0.2 to 20% by weight, and 0.5 to 5% by weight.
% Is more preferred. When the amount of the suspension stabilizer is less than 0.2% by weight, the suspension stabilizer cannot function as a suspension stabilizer. When the amount is more than 20% by weight, the suspension stabilizer is sufficiently removed from the obtained carrier particles. It is not preferable because it is difficult.

As the magnetic powder used in step 2, fine particles of magnetite, ferrite, or iron or alloy having an oxide layer on the surface can be used. The shape is not limited, and may be any shape such as a granular shape, a stadium, and a needle shape.
The size is 1 of the average particle diameter of the finally obtained carrier.
/ 10 or less is preferable. If greater than 1/10,
It is not preferable because it may be difficult to control the particle size distribution of the carrier. However, such a case can be solved by taking further measures such as classification.
By appropriately selecting the type and content of the magnetic powder, a carrier having a desired saturation magnetization can be obtained.

As the alcohols, both aromatic polyhydric alcohols and aliphatic polyhydric alcohols can be used. Specific examples include polyhydric alcohols such as hydroxyquinol, resorcinol, bis (4,4'-hydroxyphenyl) diphenylmethane, and aliphatic polyhydric alcohols such as glycerin and ethylene glycol. As the above isocyanate, both aromatic isocyanate and aliphatic isocyanate can be used. Specific examples include diphenylmethane-4,4'-diisocyanate, polyphenylene polyphenyl polyisocyanate, hexamethylene diisocyanate, and the like. When a dispersion aid is used, for example, sodium dodecyl sulfate, sodium benzenesulfonate and the like can be exemplified.

The amount of the alcohol added is 10
The amount is preferably 5 to 125 parts by weight based on 0 part by weight. The amount of isocyanate added is determined in relation to the amount of alcohol, and is preferably in the range of 2: 1 to 1:10. When a dispersing agent is used, it is preferably added at a ratio of 0.01 to 0.5% by weight based on 100% by weight of the aqueous dispersion medium.

The heating temperature and the heating time in the above step 3 are arbitrarily determined depending on the reactivity of the isocyanate. In step 3, the alcohols react with the isocyanate to produce a polyurethane resin.

In the step 4, after obtaining particles comprising a magnetic powder and a polyurethane resin and having a desired diameter, the aqueous dispersion medium is removed and the particles are dried to obtain the electrophotographic carrier of the present invention. . Various methods can be employed to dry the particles, such as using a centrifugal dehydrator.

According to the method for producing an electrophotographic carrier of the present invention comprising the above steps, a polymerization reaction of a polymer serving as a binder component proceeds on the surface of the magnetic powder, and the binder phase efficiently binds the magnetic powder. Therefore, the magnetic powder can be contained in a high ratio.

According to the method of manufacturing an electrophotographic carrier according to the present invention, a carrier having a number average diameter in the range of 10 μm to 1000 μm, particularly 30 μm to 200 μm can be obtained. One method is to use a toner having a small particle diameter to obtain a high quality and high definition image when high image quality is required. A small particle size carrier having a large specific surface area is desirable for the small particle size toner carrier. This is because a small particle size carrier having a large specific surface area increases the toner transportability in the developer and can obtain a higher image density.

Further, according to the production method of the present invention, a spherical carrier can be obtained. Since the contact area between the spherical carrier particles is small, even under stirring of the developer, the number of contact points between the carriers is small, and there is no convex portion which is entangled with each other.
Further, since the surface is smooth, even when the number average diameter of the carrier is processed to a relatively small particle diameter, excellent fluidity is exhibited.

[0023]

Next, the electrophotographic carrier of the present invention will be described more specifically. <Example 1> Water 1000 was placed in a 5 L separable flask.
g, tricalcium phosphate dispersion (manufactured by Taihei Chemical Co., Ltd., trade name: TCP-10, 10% by weight slurry) 10
00 g was added and stirred sufficiently. Further, 0.8 g of sodium dodecyl sulfate, which is a dispersing aid, and resorcinol 120
g was added and dissolved. Further, after adding 400 g of magnetic powder (spherical magnetite having an average particle diameter of 0.2 μm) and 40 g of diphenylmethane-4,4′-diisocyanate, a dispersing machine (trade name: Homomixer manufactured by Tokushu Kika Kogyo Co., Ltd.) (M type) at 3,000 rpm for 5 minutes. After removing the disperser, a turbine-type stirrer having a diameter of 100 mmφ was installed instead, and the flask was heated at 80 ° C. for 7 hours in a water bath while stirring at 150 rpm, and further heated to 90 ° C. The temperature was maintained for one hour. After cooling to room temperature, the contents of the flask are
Transfer to a 0 L stainless steel container, add 8000 g of water and 20 g of concentrated nitric acid to dissolve and remove the dispersant, and add
Stirred for minutes. After removing most of the water by a centrifugal dehydrator, the carrier was dried by a vacuum dryer until the water content became 0.3% or less, to obtain an electrophotographic carrier.

<Example 2> In Example 1, 40 g of diphenylmethane-4,4'-diisocyanate was used, whereas a polyvalent isocyanate compound (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name: Millionate MR-200) ) 1
20 g were used. Otherwise in the same manner as in Example 1, an electrophotographic carrier of this example was obtained.

Example 3 In a 5 L separable flask, 1500 g of water and 1500 g of a tricalcium phosphate dispersion (TCP-10, manufactured by Taihei Chemical Industry Co., Ltd.) were added and sufficiently stirred. Further, as a dispersant, sodium dodecyl sulfate 1.
2 g and resorcinol 120 g were added and dissolved. Otherwise, an electrophotographic carrier was obtained in the same manner as in Example 1.

Comparative Example 1 200 g of polyurethane resin
And 1000 g of the magnetic powder used in Example 1, and an electrophotographic carrier of this comparative example was obtained by a conventional melt-kneading method.

The following items were measured for the resin carriers obtained in the above Examples and Comparative Examples. (1) Particle size distribution (%) 80 or more, 100, 145, 200, 250, 350,
And a sieve having a mesh size of 350 mesh or less, and the percentage of each carrier falling from the sieve was measured.
(2) Apparent specific gravity (g / cm ² ) Measured by a method according to JIS Z-2504. (3) Flowability (sec / 50 g) Measured by a method according to JIS Z-2502. (4) Saturation magnetization, remanence magnetization, and coercive force Each was measured in a 500 Oe magnetic field environment using a vibration measurement type magnetometer (trade name: VSM-P7, manufactured by Toei Industry Co., Ltd.). . (5) Shape The obtained carrier was observed with an optical microscope. (6) Mixing ratio of polyurethane resin and magnetic powder 200 g of the obtained carrier was burned in a nitrogen atmosphere at a temperature of 55 ° C for 4 hours to burn the polyurethane resin and other additives. The weight of the remaining component, magnetic powder, was measured.

(7) Mechanical Strength Each carrier is stirred for 6 hours using a device modified so that a developing unit of a commercially available copying machine is detached and an agitating mechanism is driven by an external driving device, and a particle diameter before and after the agitation is obtained. The change in distribution was examined. As a result, it was confirmed that the particle size distribution of the carrier particles obtained by the production method of this example hardly changed from that before stirring. Table 1 shows the measurement results.

[0029]

[Table 1]

As is evident from Table 1, all the carriers obtained by the method for producing an electrophotographic carrier according to the present example have a true spherical shape, and the fluidity and apparent specific gravity are satisfactory as a magnetic carrier. Was something. Also,
The saturation magnetization was 52 to 54 esu / g. This value is
This is a necessary and sufficient value for forming a magnetic brush. On the other hand, the carrier in Comparative Example 1 has an irregular shape,
It was confirmed that the fluidity was poor.

The method of manufacturing a carrier according to the present embodiment is as follows.
In the presence of a magnetic powder and a suspension stabilizer in an aqueous medium,
The isocyanate is reacted with the alcohol, and the magnetic powder and the binder resin are not melt-kneaded. For this reason, magnetic powder can be added to polyurethane resin at a high ratio. Further, since a solvent that must be evaporated is not used, voids are hardly generated in the particles. further,
Since a large amount of solvent recovery equipment is not required, it is suitable as an industrial production method.

[0032]

The process for producing an electrophotographic carrier according to the present invention comprises the steps of: preparing an electrophotographic carrier in an aqueous medium in the presence of a magnetic powder and a suspension stabilizer;
A production method comprising a magnetic powder and a polyurethane resin as main components, wherein an isocyanate is reacted with an alcohol. The magnetic powder can be contained in a sufficient ratio to the polyurethane resin as the binder resin. Therefore, according to the method for producing an electrophotographic carrier of the present invention, it is possible to provide an electrophotographic carrier having a low bulk specific gravity and a high magnetizability.

According to the production method of the present invention, the reaction between the isocyanate and the alcohol proceeds on the surface of each magnetic powder, so that the magnetic powder can be contained in a sufficient ratio to the binder resin. Therefore, according to the production method of the present invention, a magnetic carrier having a sufficient magnetic force can be obtained. Furthermore, according to the production method of the present invention, since a binder resin is synthesized in an aqueous medium, an organic solvent is not used.
Therefore, a carrier having excellent fluidity can be obtained because of having a true spherical shape. Also, since a large amount of solvent recovery equipment is not required, it is suitable as an industrial production method.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-197211 (JP, A) JP-A-6-295102 (JP, A) JP-A-6-295103 (JP, A) 167150 (JP, A) JP-A-6-102707 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/10

Claims (1)

(57) [Claims] 1. An electronic device comprising a magnetic powder and a polyurethane resin as main components, wherein an isocyanate and an alcohol are reacted in an aqueous medium in the presence of a magnetic powder and a suspension stabilizer. Manufacturing method of photographic carrier.