JP3017660B2 - Electrophotographic carrier and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a binder type carrier,
That is, the present invention relates to an electrophotographic carrier comprising composite particles of a magnetic powder and a resin and a method for producing the same.

[0002]

2. Description of the Related Art In electrophotography, a toner charged to a polarity opposite to the polarity of a latent image is adhered to an electrostatic latent image obtained by various means using a magnetic brush or the like to form a visible image. Is generally used. In this development step, carrier particles called carriers are used. The carrier frictionally charges the toner by mixing with the toner, gives an appropriate charge to the toner, and uses a magnetic force of the carrier to form a magnetic brush on a developing sleeve in which a magnet is mounted, thereby forming an electrostatic brush. It has a function of conveying toner onto the latent image. Conventionally, as an electrophotographic carrier, an iron powder carrier, a ferrite carrier, and a binder type carrier (resin particles in which magnetic powder is dispersed) are known. Of these, the iron powder carrier and the ferrite carrier have a large true specific gravity, and therefore have a relatively large apparent specific gravity (bulk specific gravity). Therefore, when agitating in a developing machine, a large driving force is required, and mechanical abrasion is required. large. Therefore, there has been a problem that generation of so-called spent toner, deterioration of the carrier itself, and damage to the photoconductor are easily caused.

[0003] On the other hand, a binder-type carrier is usually manufactured by a method in which a magnetic powder and a resin are melt-kneaded and then pulverized. Since the carrier has an apparent specific gravity of 3 g / cm ³ or less, the above problem does not occur when an iron powder carrier or a ferrite carrier is used. However, if the content of the magnetic powder is hot melt kneaded at 80% by weight or more with respect to the resin in order to obtain sufficient magnetic properties required for the carrier, sufficient kneading cannot be performed due to an increase in the viscosity of the kneaded material. The obtained carrier had a problem that the dispersibility of the magnetic powder was poor and the content of the magnetic powder was different depending on the individual carrier particles. Therefore, the content of the magnetic powder of the conventional binder type carrier is as small as 80% by weight or less, and there is a problem that a sufficient magnetic force cannot be obtained. Further, since the particles are formed into fine particles by pulverization, the shape of the particles becomes irregular, so that problems such as low fluidity and difficulty in stirring in a developing machine have occurred. Regarding the shape, see, for example,
As described in Japanese Patent No. 31967, there is a method of spheroidizing by pulverizing and then treating with hot air. However, even if the shape can be improved, it does not contribute to an increase in the content of the magnetic powder at all. As another manufacturing method of the binder type carrier, a spray drying method is known. That is, this is a method of dissolving a resin used as a binder in an organic solvent, further adding and dispersing magnetic powder, and then performing spray granulation drying to obtain particles.
With this method, it is easy to make the shape of the carrier spherical, but it is easy to generate voids in the particles due to evaporation of the solvent, and the carrier has poor fluidity and has a problem in triboelectric charging with the toner. there were. In addition, there is a problem as an industrial production method, for example, a large amount of solvent recovery equipment is required. By the way, with the spread of electrophotography, the applied technologies such as plain paper copier, laser beam printer,
It is desired that the performance of full-color copying machines and the like be improved, and that higher speed, higher image quality, and higher definition be achieved. With the improvement in performance, a carrier having a higher function is also required for an electrophotographic carrier. The requirements include small apparent specific gravity, spheroidization, large magnetizability, small particle size, and sufficient surface strength. However, as is clear from the above prior art, no electrophotographic carrier satisfying those requirements has been provided yet.

[0004]

SUMMARY OF THE INVENTION The present invention meets such a demand and is intended for a binder type electrophotographic material having a small apparent specific gravity, a large magnetic ratio, and a small particle diameter. A carrier and a method for manufacturing the carrier are provided.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have reached the present invention. That is, the present invention relates to a resin 1 obtained by a polymerization reaction of an isocyanate, a phenol and an aldehyde.
An electrophotographic carrier comprising 4 to 100 parts by weight of a magnetic powder with respect to parts by weight, and a method for producing the same, comprising: preparing an isocyanate, a phenol, an aldehyde, and a magnetic powder in an aqueous medium. A method for producing an electrophotographic carrier, comprising dispersing, heating and stirring to carry out suspension polymerization, followed by dehydration and drying.

Hereinafter, the present invention will be described in detail. The electrophotographic carrier of the present invention is a binder type carrier containing a resin obtained by a polymerization reaction of an isocyanate, a phenol and an aldehyde, that is, a polyurethane resin and a phenol resin as a binder. There is no particular limitation on the structure of the isocyanate, phenols and aldehydes, but aromatic isocyanates and aliphatic isocyanates can be used as the isocyanate, for example, diphenylmethane-4,4'-diisocyanate. Isocyanate, polyphenylene polyphenyl polyisocyanate, hexamethylene diisocyanate and the like can be mentioned. In addition, phenols such as cresol, butylphenol, propylphenol, and aliphatic substituted phenols such as resorcinol can be used, among which phenol and resorcinol are most preferred. As the aldehyde, formaldehyde, furfural and the like can be used, but formaldehyde is preferred. In the electrophotographic carrier of the present invention, the magnetic powder may be contained in a ratio of 4 to 100 parts by weight based on 1 part by weight of the resin obtained by the polymerization reaction of the isocyanate, the phenol and the aldehyde. It is necessary, and preferably 40 to 100 parts by weight of magnetic powder per 1 part by weight of the resin. In this case, when the content of the magnetic powder is less than 4 parts by weight, the saturation magnetization value becomes small and the magnetic properties required for an electrophotographic carrier cannot be obtained. On the other hand, when it exceeds 100 parts by weight, the binding force of the resin is small, the strength of the carrier particles is reduced, and the particles are easily broken at the time of stirring in the developing machine.

As the magnetic powder that can be used in the present invention, magnetite, ferrite, or fine particles of iron or alloy having an oxide layer on the surface can be used. Its shape is
It may be granular, spherical, or acicular. The size of the magnetic powder is preferably at least 1/10 or less of the average particle diameter of the carrier. If it is larger than 1/10, it may be difficult to control the particle size distribution of the carrier. However, in that case, it can be solved by using means such as classification. By appropriately selecting the type and content of the magnetic powder, a binder-type carrier having a desired saturation magnetization can be obtained. Generally, in a copying machine or a printer, one method of using a toner having a small particle diameter is to obtain a high-quality and high-definition image. As a carrier for such a small particle size toner, a small particle size carrier having a large specific surface area is desirable,
In addition, the increase in the specific surface area increases the transportability of the toner in the developer, so that a higher image density can be obtained. Therefore, the number average particle diameter of the carrier for electrophotography of the present invention,
10 μm to 1000 μm is preferable, and particularly when high image quality is required, a small particle size carrier having a large specific surface area of 30 μm to 200 μm is preferable. Since the electrophotographic carrier of the present invention is obtained by a suspension polymerization method, its shape is spherical. Therefore, since the contact area between the carrier particles is small and the surface is smooth, excellent fluidity is exhibited even in a carrier having a relatively small particle diameter. Furthermore, having a spherical shape has the advantage that even under stirring of the developer, the number of contact points between the carriers is small, and there are no convex portions that are entangled with each other, so that the particle strength is high.

Next, a method for producing an electrophotographic carrier according to the present invention will be described. First, an isocyanate, phenols, aldehydes, and magnetic powder are added to an appropriate amount of water or an ion-exchanged aqueous medium to which other additives such as a suspension stabilizer are added, and dispersed using a disperser. I do. Then
The obtained mixture is further stirred while being heated at a temperature of 50 to 95 ° C., and the mixture is reacted to carry out suspension polymerization. By adjusting the stirring time and the stirring speed, particles having a desired diameter are obtained. After the reaction is completed, the carrier is cooled to room temperature, dehydrated using a centrifugal dehydrator or the like, and dried to obtain the electrophotographic carrier of the present invention. As the suspension stabilizer, organic compounds such as carboxymethyl cellulose and polyvinyl alcohol, and poorly water-soluble inorganic fine particles such as calcium sulfate and calcium phosphate can be used. The amount of the suspension stabilizer is preferably from 0.2 to 20% by weight, more preferably from 0.5 to 5% by weight, based on the aqueous medium. The binder phase containing the magnetic powder is dispersed in the aqueous medium,
The mixing ratio between the binder phase containing the magnetic powder and the aqueous medium at the time of dispersion is preferably from 2: 1 to 1:10 by weight, more preferably from 1: 2 to 1: 5. The charging ratio is 1: 1
When the particle diameter is smaller than 0, the particle diameter of the obtained particles is, for example, 10 μm.
If the particle size is too small, the particle size of the obtained particles is too large, the dispersibility of the suspension stabilizer is reduced, and it is difficult to obtain particles by the aggregation of the binder phase in an aqueous medium. Is not preferred. The carrier for electrophotography obtained by the production method of the present invention can contain 100 parts by weight of magnetic powder based on 1 part by weight of the resin. The reason why the content can be increased in the production method of the present invention is that the polymerization reaction of the polymer serving as the binder component proceeds on the surface of the magnetic powder, and the binder phase efficiently binds the magnetic powder. is there.

[0009]

Next, the present invention will be described specifically with reference to examples and comparative examples. <Example 1> Water 1000 was placed in a 5 L separable flask.
g of tricalcium phosphate dispersion (TCP-10, manufactured by Taihei Chemical Industry Co., Ltd.) and stirred well. Further, 0.8 g of sodium dodecyl sulfate, 60 g of resorcinol, 60 g of phenol, and 70 g of a 37% aqueous formaldehyde solution were added and dissolved. Further, 400 g of magnetic powder (spherical magnetite having an average particle diameter of 0.2 μm) and 40 g of diphenylmethane-4,4′-diisocyanate were added.
Disperser (Homomixer M type, manufactured by Tokushu Kika Kogyo Co., Ltd.)
For 5 minutes at 3000 rpm. Next, the disperser was removed, and a turbine type stirrer having a diameter of 100 mm was installed instead. 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. and heated for 1 hour. Then, suspension polymerization was carried out. After cooling to room temperature, the contents of the flask were transferred to a 10 L stainless steel container, and 8000 g of water and 20 g of concentrated nitric acid were added, followed by stirring for 30 minutes. After removing most of the water with a centrifugal dehydrator, the carrier for electrophotography of the present invention was obtained by drying with a vacuum dryer until the water content became 0.3% or less. 200 g of this electrophotographic carrier was heated to 55
The resin was burned by burning in a nitrogen atmosphere at 4 ° C. for 4 hours, and the weight of the magnetic powder as the remaining component was measured. As a result, the mixing ratio of the resin and the magnetic powder was 1:90. <Example 2>Diphenylmethane-4,4'- in Example 1
An electrophotographic carrier of the present invention was obtained in the same manner as in Example 1, except that 120 g of a polyvalent isocyanate compound (Millionate MR-200, manufactured by Nippon Polyurethane Industry Co., Ltd.) was used instead of 40 g of diisocyanate. As a result of obtaining the mixture ratio of the resin and the magnetic powder in the same manner as in Example 1, the result was 1:
90.

<Example 3> In Example 1, 1500 g of water in a 5 L separable flask was added to a dispersion of tricalcium phosphate (TCP-10, manufactured by Taihei Chemical Industry Co., Ltd.).
Was changed to 1500 g and the carrier for electrophotography of the present invention was obtained in the same manner as in Example 1 except that sodium dodecyl sulfate was changed to 1.2 g. The mixture ratio between the resin and the magnetic powder was determined in the same manner as in Example 1, and as a result, it was 1:90. <Comparative Example 1> In Example 1, 6 g of resorcinol was used,
6 g of phenol, 15 g of aqueous formaldehyde solution,
An electrophotographic carrier for comparison was obtained in the same manner as in Example 1, except that 1 g of diphenylmethane-4,4'-diisocyanate was used. The mixture ratio of the resin and the magnetic powder was determined in the same manner as in Example 1, and as a result, it was 1: 200. <Comparative Example 2> In Comparative Example 1, 250
g, phenol 250 g, formaldehyde aqueous solution 500 g, diphenylmethane-4,4'-diisocyanate 200 g, and a comparative electrophotographic carrier was obtained in the same manner as in Example 1. The mixture ratio between the resin and the magnetic powder was determined in the same manner as in Example 1, and the result was 1: 2. <Comparative Example 3> 100 g of a polyurethane resin, 100 g of a phenol resin, and 1000 g of magnetic powder (spherical magnetite having an average particle diameter of 0.2 μm) were melted and kneaded with a kneader, and then pulverized with a pulverizer to obtain an electrophotograph for comparison. For a carrier. The mixture ratio of the resin and the magnetic powder was determined in the same manner as in Example 1, and as a result, it was 1: 5.

The characteristics of the following items were measured for the carriers obtained in Examples 1 to 3 and Comparative Examples 1 to 3, and the results are shown in Table 1. (1) Particle size distribution (%) 100 mesh, 145 mesh, 200 mesh, 2
The mixture was passed through sieves of 50 mesh and 350 mesh, and the remaining amount on each of the sieves was indicated by% by weight. (2) Apparent specific gravity (g / cm ³ ) 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 Vibration measurement type magnetometer (Toei Kogyo Co., Ltd., product name: VS
(M-P7 type) under a magnetic field of 500 Oe. (5) Shape Observed with an optical microscope.

[0012]

[Table 1]

As is clear from the results in Table 1, the electrophotographic carrier of the present invention has a small apparent specific gravity and a high fluidity,
The carrier had sufficient and sufficient saturation magnetization for forming a magnetic brush as an electrophotographic carrier. On the other hand, the carrier for electrophotography of Comparative Example 1 has a large apparent specific gravity and a low fluidity because the ratio of the magnetic powder is too large, and the carrier for electrophotography of Comparative Example 2 has a small ratio of the magnetic powder so that the electrophotographic carrier is small. Saturation magnetization, which is a magnetic property required as a carrier for lasers, could not be obtained. Further, since the carrier for electrophotography of Comparative Example 3 was indefinite in shape, the apparent specific gravity was large and the fluidity was low. Further, for the purpose of determining the mechanical strength of the carriers obtained in Examples 1 to 3, and Comparative Examples 1 to 3,
The carrier was stirred for 6 hours using a device modified so that the developing unit of a commercially available copying machine was removed and the stirring mechanism was driven by an external driving device, and the change in particle size distribution before and after stirring was examined. As a result, the carrier for electrophotography of the present invention showed almost no change in the particle size distribution.
When the particle size of the carrier shown in was measured by sieving after stirring, 95% or more of the particles passed through a 250 mesh sieve. This is presumed to be due to the fact that the carrier particles were broken during the stirring due to the small amount of the binder resin component.

[0014]

The carrier for electrophotography according to the present invention can contain a larger amount of magnetic powder in a resin than a conventional binder type carrier, so that the apparent specific gravity is small and a large saturation magnetization can be obtained. Can be. Further, since the shape is spherical, the fluidity is excellent, and excellent mechanical strength is exhibited. Further, according to the method for producing an electrophotographic carrier of the present invention, it becomes possible to contain a larger amount of magnetic powder in a resin than in a conventional production method, and to synthesize the resin in an aqueous medium, Since no solvent is used and a large amount of solvent recovery equipment is not required, the method is excellent as an industrial production method.

Claims (2)

(57) [Claims] 1. An electrophotographic carrier comprising 4 to 100 parts by weight of a magnetic powder per 1 part by weight of a resin obtained by a polymerization reaction of an isocyanate, a phenol and an aldehyde. 2. A process for producing an electrophotographic carrier, comprising dispersing an isocyanate, a phenol, an aldehyde and a magnetic powder in an aqueous medium, stirring and heating to carry out suspension polymerization, followed by dehydration and drying. Method.