JPH0594048A - Binder type carrier and its production - Google Patents

Abstract

PURPOSE:To obtain a binder-type carrier in which a magnetic powder exists only in the center part without providing a coating layer excellent in electric insulation. CONSTITUTION:A carrier compsn. containing a hydrophobic monomer and a magnetic powder showing <63 degree contact angle with the hydrophobic monomer is subjected to suspension polymn. in a water-base solvent. By suspending the carrier compsn. in the water-base solvent, the magnetic powder having such characteristics as mentioned above becomes present only in the center part of drops. Thus, the obtd. binder-type carrier has no magnetic powder on the surfaces of resin particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder type carrier obtained by a polymerization method and a method for producing the same, and more particularly to a binder type carrier used for a developer for electrophotography and a method for producing the same.

[0002]

2. Description of the Related Art In a binder type carrier in which magnetic powder is dispersed in resin particles, if the magnetic powder is exposed on the surface of the carrier, the electric resistance of the carrier cannot be increased. In order to increase the number, a large number of carriers have been proposed in which an electrically insulating coat layer is further provided on the surface of binder type carrier particles (for example,
JP-A-58-121046).

However, since the charging characteristics of the binder type carrier obtained by such a method are influenced by the resin forming the coat layer, the electric characteristics of the binder type resin, which is one of the characteristics of the binder type carrier, causes the carrier characteristics to change. The advantage of being able to control the charging characteristics of is not utilized. Also,
Since a process for providing the coat layer is required, the productivity is poor and the cost is disadvantageous.

Instead of providing a coat layer, a method of increasing the electric resistance of the carrier by treating the binder type carrier particles with an acid to dissolve and remove the magnetic powder exposed on the surface of the carrier is disclosed. Although proposed in Japanese Patent No. 185656, such a method has a drawback that the carrier has poor moisture resistance and the number of steps is further increased.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and its object is to eliminate the step of providing an electrically insulating coating layer, and A binder type carrier capable of increasing the electric resistance of the carrier and a method of manufacturing the same are provided.

[0006]

The binder type carrier of the present invention is a binder type carrier in which magnetic powder is dispersed in spherical resin particles formed by a polymerization method, and the magnetic powder is the resin particles. Exists only in the central portion of the resin particles, and the surface portions of the resin particles are formed of the same resin as the resin in the central portions of the resin particles, thereby achieving the above object.

The method for producing a binder type carrier of the present invention comprises suspension-polymerizing a carrier composition containing a hydrophobic monomer and a magnetic powder having a contact angle with the hydrophobic monomer of 63 ° or less in an aqueous medium. The above object is achieved thereby.

The above-mentioned resin particles are spherical particles formed by a polymerization method, and as the resin forming the resin particles, known thermoplastic resins can be mentioned. For example, polystyrene, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride ester copolymer, polyethylene, polypropylene, etc. Can be given. Furthermore, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin and waxes can also be mentioned. These compounds may be used alone or in combination of two or more.

The magnetic powder dispersed in the resin particles may be a substance that is extremely strongly magnetized in that direction by a magnetic field, and examples thereof include metals such as iron, cobalt and nickel; ferrite, magnetite and hematite. An alloy or compound containing an element exhibiting ferromagnetism such as iron, cobalt, or nickel; an alloy containing no ferromagnetic element but exhibiting ferromagnetism by appropriate heat treatment,
Examples thereof include Heusler alloys containing manganese and copper, such as manganese-copper-aluminum or manganese-copper-tin. These compounds may be used alone or in combination of two or more.

In particular, when the binder type carrier is manufactured according to the method of the present invention, the contact angle with the hydrophobic monomer needs to be 63 ° or less, and the magnetic powder satisfying this condition is used. Since the magnetic powder has a contact angle with the hydrophobic monomer of more than 63 ° and about 90 °, in order to obtain a magnetic powder with a contact angle with the hydrophobic monomer of 63 ° or less, for example, It is preferable to surface-treat.

An organic solvent such as toluene, magnetic powder and a lipophilic surface treatment agent such as trimethoxyphenylsilane are mixed and stirred at a predetermined temperature for a predetermined time to adsorb the surface treatment agent on the surface of the magnetic powder. Next, the treated magnetic powder is filtered and dried to obtain a powdery magnetic powder.

In the present invention, the contact angle of the magnetic powder with the hydrophobic monomer is measured by the capillary rise method.

In the binder type carrier of the present invention, the magnetic powder is present only in the central portion of the resin particle, and the magnetic powder is not present in the surface portion of the resin particle. The absence of magnetic powder on the surface of the resin particles means that the magnetic powder is not exposed on the surface of the resin particles. Further, it is preferable that a surface layer having a thickness of about 0.1 to 10 μm, in which no magnetic powder is present, is formed on the surface of the resin particles.

The magnetic powder may be the largest in the center of the resin particles and may be gradually decreased toward the surface of the resin particles, or the magnetic particles are almost uniformly present within a predetermined radius of the resin particles, The magnetic powder may be reduced as it goes beyond the radius toward the surface of the resin particles.

In the binder type carrier of the present invention, the surface portion of the resin particle needs to be formed of the same resin as the resin in the central portion of the resin particle. That is, the binder type carrier of the present invention has a uniform resin composition as a whole.

The content of the magnetic powder is preferably 20 to 80% by weight based on the binder type carrier. When the content of the magnetic powder is less than 20% by weight, the magnetic attraction force of the developing sleeve is weakened, carrier adhesion to the photoconductor, developer spillage from the developing machine and the like occur. On the other hand, the content of magnetic powder is 8
If it exceeds 0% by weight, the binding effect of the resin cannot be sufficiently obtained and the carrier is cracked. In addition, the dispersion of the powder such as the magnetic powder becomes poor, and a homogeneous resin cannot be obtained. The particle size of the magnetic powder is preferably 0.01 to 5 μm.

The hydrophobic monomer contained in the carrier composition used in the method for producing the binder type carrier of the present invention may be any one which can be subjected to suspension polymerization, and examples thereof include styrene, chlorostyrene and vinylstyrene. Styrenes; mono-olefins such as ethylene, propylene, butylene, isobutylene; vinyl acetate, propylene vinyl,
Vinyl esters such as vinyl benzoate and vinyl butyrate; methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate. Α-methylene aliphatic monocarboxylic acid esters such as; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether; vinyl methyl ketone,
Examples thereof include vinyl ketone such as vinyl hexyl ketone and vinyl isopropenyl ketone. These compounds may be used alone or in combination of two or more.

In particular, the hydrophobic monomer is styrene 50
Contains more than weight% and has a solubility in water of 2g / 100g
The following are preferred.

The above carrier composition may contain a known thermoplastic resin in addition to the above monomers. For example, polystyrene, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride ester copolymer, polyethylene, polypropylene, etc. Can be given. Furthermore, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin and waxes can also be mentioned.

When the binder type carrier is manufactured according to the method of the present invention, the content of the resin is preferably 20 to 80% by weight based on the binder type carrier.

When a binder type carrier is used as a one-component developer, the carrier composition usually contains carbon black as a colorant, and if necessary, other colorants, charge control agents, offset preventing agents and the like. You may contain an additive.

Examples of the colorant include aniline blue, chalco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green, lamp black and rose bengal. These colorants may be used alone or 2
You may use together 1 or more types.

The charge control agent may be a charge control agent known per se in order to adjust the chargeability of the toner, such as naphthenic acid, salicylic acid, octylic acid, higher fatty acids, resin acids of manganese, iron and cobalt. Nickel, lead,
A metal soap which is a metal salt of zinc, cerium, calcium, etc .; a metal-containing azo dye; a pyrimidine compound; a metal chelate of alkylsalicylic acid, a nigrosine dye, an ammonium compound, etc. are used.

Examples of the offset preventing agent include, for example,
Various waxes such as low molecular weight polyethylene, low molecular weight polypropylene, and paraffin wax; olefin polymers having 4 or more carbon atoms; fatty acid amide; silicone oil and the like.

In order to manufacture a binder type carrier, first, the carrier composition containing the magnetic powder, the hydrophobic monomer and the polymerization initiator is suspended and granulated in an aqueous medium. The particle size of the generated droplets of the carrier composition is preferably 30 to 150 μm. Here, since the contact angle of the magnetic powder to the hydrophobic monomer is 63 ° or less, the magnetic powder exists in the state of being aggregated in the central portion of the generated droplet, and the carrier excluding the magnetic powder is present on the surface portion of the droplet. The composition is present. When the magnetic powder having a contact angle with the hydrophobic monomer of more than 63 ° is used, the magnetic powder comes to exist on the surface of the droplet as described above, and it is impossible to obtain a binder type carrier having high electric resistance. . Next, the temperature of the aqueous medium containing the droplets is raised to polymerize the hydrophobic monomer. The polymerization temperature may be the decomposition temperature of the above-mentioned polymerization initiator, typically 5
It is 0 ° C to 100 ° C. Then, the polymer is filtered and washed to obtain a binder type carrier.

The above aqueous medium is usually water to which a small amount of suspension stabilizer is added, and alcohol or the like may be added. Known suspension stabilizers such as tricalcium phosphate and sodium dodecylbenzene sulfonate are used.

[0027]

Since the magnetic powder exists only in the central portion of the resin particles, the magnetic powder does not exist near the surface of the resin particles, and a binder type carrier having high electric resistance can be obtained. In addition, the resin particles are spherical particles formed by the polymerization method, and the surface portion is formed of the same resin as the resin in the central portion, so that the charging characteristics of the binder type carrier can be changed by the electrical characteristics of the binder resin. Can be controlled.

Further, in the method for producing the binder type carrier of the present invention, the central portion of the droplet in the aqueous medium has weak polarity, and the droplet is slightly hydrophilic near the interface with the aqueous medium. When another material is added to such a droplet, the material is present in the droplet if it is lipophilic, and in the center of the droplet if the material is hydrophobic, and vice versa. If the material is hydrophilic, it is unevenly distributed so that it exists near the interface of the droplets. And whether the magnetic powder exists in the center of the droplet,
The present inventors have found that the condition for determining whether the droplets are present on the surface portion is that the contact angle with the hydrophobic monomer is 63 °. That is, by suspending in a water-based medium using magnetic powder having a contact angle with the hydrophobic monomer forming the droplet of 63 ° or less, the magnetic powder is present only in the center of the droplet. By polymerizing these droplets, a binder type carrier having no magnetic powder on the surface can be obtained.

[0029]

EXAMPLES The present invention will be specifically described below based on examples.

Examples 1 and 2 and Comparative Examples 1 to 5 (A) Surface Treatment of Magnetic Powder As magnetic powder, ferrite powder strontium ferrite (SrO.6Fe ₂ O ₃ , manufactured by Nippon Benai) was used.

Toluene, the above magnetic powder, and a predetermined amount of trimethoxyphenylsilane shown in Table 1 as a surface treatment agent were mixed and stirred at 20 ° C. for 5 hours to allow the surface treatment agent to be adsorbed on the surface of the magnetic powder. It was Then, the treated magnetic powder was filtered and dried to obtain a powdery magnetic powder.

The contact angle of this magnetic powder with the hydrophobic monomer was measured by the capillary rise method.

A mixture of styrene / butyl methacrylate = 80/20 (parts by weight) was used as the hydrophobic monomer.

Table 1 shows the relationship between the concentration of the surface treatment agent and the contact angle of the obtained magnetic powder.

[0035]

[Table 1]

(B) Production of Binder Type Carrier The following carrier materials were mixed to obtain a carrier composition.

Next, the above carrier composition was added to a dispersion prepared by adding 40 parts by weight of tricalcium phosphate and 0.5 parts by weight of sodium dodecylbenzenesulfonate to 600 parts by weight of distilled water, and adding the TK homomixer (special machine). (Kaika Kogyo) Rotation speed 6500 rpm using a mixer with modified legs for high viscosity
And stirred for 12 minutes.

The obtained suspension was transferred to a separable flask, and under a nitrogen atmosphere, the temperature was 80 ° C. and the rotation speed was 250 rp.
The polymerization was completed by reacting for 5 hours with stirring at m.
After the completion of the polymerization reaction, the polymer was filtered, treated with a dilute acid, washed with water and dried to obtain a carrier. [Carrier material] Styrene 80 parts by weight Butyl methacrylate 20 parts by weight Magnetic powder of ~ shown in Table 1 100 parts by weight 2,2'-Azobis- (2,4-dimethylvaleronitrile) 6 parts by weight (C) Binder type carrier Evaluation method of each binder type carrier obtained above is DC-2585
Common toner (manufactured by Mita Kogyo Co., Ltd.) to prepare a developer having a toner / developer ratio of 8%. Plain paper copier DC-2585
(Manufactured by Sanda Kogyo Co., Ltd.) was used to evaluate each charging characteristic. The results are shown in Tables 2 and 3. The conductivity of the binder type carrier was measured by forming a press film from the carrier composition and measuring the AC electric conductivity of the press film at a frequency of 1 KHz.

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

According to the present invention, the electric properties of the carrier can be enhanced without the need to provide a coat layer as in the prior art, and therefore the binder having improved charging property, rising of charging, durability and environment resistance. The mold carrier can be obtained with high productivity and at low cost, and the charging characteristics of the carrier can be controlled by the binder resin.

Claims (2)

[Claims] 1. A spherical spherical binder type carrier in which magnetic powder is dispersed in resin particles formed by a polymerization method, the magnetic powder being present only in the central portion of the resin particles, The surface portion of the binder carrier is formed of the same resin as the resin in the central portion of the resin particles. 2. A binder type carrier characterized by suspension polymerizing a carrier composition comprising a hydrophobic monomer and a magnetic powder having a contact angle with the hydrophobic monomer of 63 ° or less in an aqueous medium. Manufacturing method.