JPH0723968B2 - Magnetic toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic toner used in a method for developing a latent image.

The toner for such purpose is for forming and recording an image, and for example, in electrophotography, starting from U.S. Pat.No. 2,297,691, JP-B-42-23910, and JP-B-43-43. As described in, for example, Japanese Patent No. 24748, many methods are known, and generally, a photoconductive substance is used to form an electric latent image on a photoreceptor by various means, and then the latent image is formed. The image is developed with toner, the toner image is transferred to a transfer member such as paper, if necessary, and then fixed by heat, pressure, a superheated pressure roller or solvent vapor,
A copy is to be obtained. As a method of developing using a toner, various methods have been conventionally proposed, for example, a magnetic brush method described in U.S. Pat.No. 2,874,063, a cascade development method described in the same 2,618,552, Further, in addition to the powder cloud method described in the specification of No. 2,221,776, a fur brush developing method, a liquid developing method and the like are known. Among these developing methods, a magnetic brush method, a cascade method, a liquid developing method, and the like, which use a developer mainly composed of a toner and a carrier, have been widely put into practical use. All of these methods are excellent methods in which a good image can be obtained relatively stably, but on the other hand, they have the common problems associated with the component developers such as deterioration of the carrier and fluctuations in the mixing ratio of the toner and the carrier. In order to avoid such a problem, various developing methods using a one-component developer consisting of only toner have been proposed, but among them, many are excellent in the method of using a developer consisting of magnetic toner particles. For example, the so-called induced development method described in JP-B-37-491 is well known.

In this method, a toner having conductivity and magnetism is attached to a sleeve containing a magnet to form a magnetic brush of toner, and the magnetic brush is brought into contact with an electrostatic latent image carrier to develop the latent image with the toner. To do. In this developing method, when the magnetic brush is opposed to the electrostatic latent image due to the toner having conductivity, the electrostatic latent image is induced with electric charges of opposite polarities, and thus the toner with the electric charges induced. The latent image is developed based on the electric attraction between the electrostatic latent images. Further, an insulating magnetic toner is attached to a sleeve containing a magnet to form a magnetic brush of the toner, the toner is charged by friction with the sleeve, and the magnetic brush is brought into contact with or close to the electrostatic latent image carrier. There is also known a method of developing a latent image with toner. For example, the developing method is described in detail in JP-A-49-17739 using an encapsulated magnetic toner and JP-A-50-45639 using an insulating magnetic toner.

In the developing method using these one-component type developers, since the developer does not contain a carrier, it is not necessary to adjust the mixing ratio of the carrier and the toner, and the stirring operation for sufficiently uniformly mixing the carrier and the toner is required. Since there is no particular need, there is an advantage that the entire developing device can be configured simply and compactly. Further, there is an advantage in that there is no inconvenience such as deterioration of developed image quality due to deterioration of the carrier with time. In these magnetic toners, a large amount of magnetic fine particles as a magnetic material is generally dispersed in the binder resin, but the dispersibility of the magnetic fine particles in the binder resin is poor and it is difficult to obtain a uniform dispersion. . That is, even if it is obtained that has been dispersed to some extent through a sufficient kneading step,
In the subsequent pulverization step, breakage occurs at the interface between the magnetic fine particles and the binder resin, resulting in the presence of the magnetic fine particles on the toner surface, resulting in a decrease in electrical resistance and a decrease in moisture resistance. Further, there is a difference in the content of the magnetic fine particles among the toner particles, and the hiding power becomes uneven. On the other hand, a method for producing a polymerized toner by a suspension polymerization method has been proposed in order to overcome the problems caused in the toner by the pulverization method. In the suspension polymerization method, a monomer composition in which a polymerizable monomer, a magnetic substance, a polymerization initiator and, if necessary, a crosslinking agent, a charge control agent, a colorant, and other additives are uniformly dissolved or dispersed, is dispersed and stabilized. The toner particles having a desired particle diameter are obtained by dispersing them in an aqueous phase containing an agent using a stirrer and simultaneously performing a polymerization reaction. Since this suspension polymerization method does not include a mechanical pulverization step, there is no inconvenience due to pulverization as seen in the pulverization method, but since the monomer composition containing magnetic fine particles is dispersed in the aqueous phase, In the dispersion / polymerization step, generally hydrophilic magnetic fine particles are present on the surface of the toner particles, which causes the same problem as the pulverization method.

In order to improve the dispersibility of the magnetic fine particles in the polymerizable monomer and the binder resin, treatments for various magnetic fine particles have been proposed. For example, a magnetic powder is treated with an aliphatic compound (see JP-A-50-139745), a treatment with a silane coupling agent (see JP-A-54-127329), a titanium coupling agent (see JP-A-55- Japanese Patent No. 26519) has been proposed. However, these treatments still have to be improved in that the magnetic fine particles are uniformly dispersed in the polymerizable monomer monomer and the binder resin, and the bond strength between the magnetic fine particles and the binder resin is further improved. Is desired. Further, the silane coupling agent and the titanium coupling agent also generate impurities due to hydrolysis, which may adversely affect the characteristics of the toner.

An object of the present invention is to provide a magnetic toner that solves the above problems.

An object of the present invention is to provide a magnetic toner having a high image density and capable of obtaining a clear image.

Another object of the present invention is to provide a magnetic toner having a good fixing property and excellent developability.

A further object of the present invention is to provide a spherical magnetic toner in which the particle size can be easily controlled and the particle size is uniform.

The present invention is to provide a magnetic toner that has good fluidity and does not cause aggregation.

The above object is achieved by the following configurations.

The present invention relates to a magnetic toner containing a polymer and a magnetic material which have two or more vinyl groups at their ends and are crosslinked with a crosslinking agent having two or more urethane bonds in the molecule.

The crosslinked polymer used in the present invention contains a crosslinker having two or more vinyl groups at the terminals and two or more urethane bonds (-NHCOO-) in the molecule upon polymerization of the polymerizable monomer. It is a polymer crosslinked by

One specific example of the magnetic toner containing a polymer and a magnetic material crosslinked with a crosslinking agent having two or more vinyl groups at the end and two or more urethane bonds in the molecule of the present invention is a magnetic material. In a magnetic polymerization toner obtained by suspension-polymerizing a polymerizable monomer composition containing a monomer in an aqueous phase, during polymerization of the polymerizable monomer, the polymerizable monomer composition has two or more vinyl groups at the terminal and has a urethane bond in the molecule ( Examples of the magnetic toner include a polymer crosslinked by allowing a crosslinking agent having two or more —NHCOO—) to coexist.

By using the cross-linking agent, in the suspension particles immediately after the initiation of polymerization, hydrogen is present between the polar groups such as amino groups and carboxyl groups constituting the urethane bond contained in the cross-linking agent and the magnetic fine particles as the magnetic substance. It is considered that affinity such as binding or electric attraction is generated, and as a result, the dispersibility of the magnetic fine particles in the suspended particles is improved. That is, the obtained toner particles are those in which magnetic particles are not localized and are uniformly dispersed. On the other hand, as shown in Comparative Example 1 to be described later, for example, a polymer using a cross-linking agent containing no polar group such as divinylbenzene does not have good affinity with the magnetic fine particles, and therefore the toner particles are magnetic. The fine particles are likely to be localized, resulting in insufficient image quality and density in the image.

In addition, since the cross-linking agent containing these polar groups used in the present invention has two or more vinyl groups at the terminals, it has one or more bifunctional or more conventionally proposed terminal vinyl groups. Compared with a monomer containing a monofunctional polar group that only has, the viscosity at the beginning of the polymerization is the same and the granulation property at the time of suspension is not so different, but the thickening effect is large as the polymerization proceeds. ,
The retention of the magnetic fine particles in the toner particles is improved, the stability of the toner particles is increased, the reaction time is shortened, and a toner having a sharp viscosity distribution is obtained.

Typical examples of the above-mentioned cross-linking agent used in the toner according to the present invention include the following.

When the amount of these cross-linking agents used is large, the melting temperature of the toner rises, and the cross-linking agent does not melt sufficiently at a normal fixing temperature, resulting in poor fixability. On the other hand, when the amount used is small, the dispersibility of the magnetic fine particles is poor, and the blocking resistance and durability are also poor. Therefore, the amount of the crosslinking agent used is 0.1 to 30% by weight, preferably 0.5 to 15% by weight, based on the total amount of the monomers.
It is more preferable to use 0.7 to 10% by weight.

The polymerizable monomer applicable to the present invention is a monomer having a double bond, for example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p
-Methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, p Styrene and its derivatives such as -n-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene; ethylene, propylene, butylene, isobutylene, etc. Ethylenically unsaturated monoolefins; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, vinyl fluoride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate; methyl methacrylate, methacrylic acid Ethyl, propylmethacrylate, n-butylmethacrylate, isobutymethacrylate Α-methylene aliphatic monocarboxylic acid esters such as tyl, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate; Methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, acrylic acid Acrylic esters such as phenyl; Vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether; Vinyl methyl ketone, vinyl hexyl ketone, methyl isop Vinyl ketones such as penyl ketone; N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone; vinyl naphthalenes; acrylic acid or methacrylic acid such as acrylonitrile, methacrylonitrile and acrylamide. There are derivatives. Among them, styrene, acrylic acid ester, methacrylic acid ester, and a mixture thereof are preferable.

Further, a polymer may be added during the polymerization to polymerize the monomer.

The magnetic fine particles as the magnetic substance that can be used in the present invention include
A substance that is magnetized when placed in a magnetic field is used, and examples thereof include powders of ferromagnetic metals such as iron, cobalt, nickel, and powders of alloys and compounds such as magnetite, hairtite, and ferrite. Particles having a particle size of 0.05 to 5 μ, preferably 0.1 to 1 μ are used. The content of the magnetic fine particles is 15 to 80% by weight, preferably 30 to 70% by weight, based on the weight of the toner. These magnetic fine particles may be treated with a hydrophobizing agent such as the above-mentioned silane coupling agent or titanium coupling agent, or an appropriate reactive resin. In this case, depending on the surface area of the magnetic fine particles and the density of hydroxyl groups existing on the surface, sufficient dispersibility can be obtained with a treatment amount of 5% or less, and the physical properties of the toner are not adversely affected.

In the present invention, a method of suspending a monomer composition containing a polar polymer at the time of polymerization in an aqueous phase in which a dispersant having an opposite charge to the polar polymer is dispersed and polymerizing is a toner particle size. It is particularly preferable for making the distribution sharp. That is, the cationic or anionic polymer contained in the polymerizable monomer composition is the oppositely charged anionic or cationic dispersant dispersed in the aqueous phase and the particle surface to be the toner in the process of polymerization. It attracts electrostatically and prevents the particles from coalescing by covering the surface of the particles with a dispersant and stabilizes them.At the same time, the polar polymer added at the time of polymerization gathers on the surface layer of the particles that become toner, so it looks like a kind of shell. The resulting particles are pseudo capsules. This polar polymer with a relatively high molecular weight is used to impart excellent blocking properties, developability and abrasion resistance to the toner particles, while having a relatively low molecular weight inside to contribute to the improvement of fixing properties. By polymerizing the toner, it is possible to obtain a toner that satisfies the contradictory requirements of fixing property and blocking property. The polar polymer and the oppositely-charged dispersant which can be used in the present invention are exemplified below.

(I) As the cationic polymer, a polymer of a nitrogen-containing monomer such as dimeteraminoethyl methacrylate or diethylaminoethyl acrylate, or a copolymer of styrene, an unsaturated carboxylic acid ester or the like and the nitrogen-containing monomer is used. is there.

(Ii) Anionic polymers include nitrile monomers such as acrylonitrile, halogen-containing monomers such as vinyl chloride, unsaturated carboxylic acids such as acrylic acid, unsaturated dibasic acids, and unsaturated dibasic acids. There are anhydrides, polymer cyclized rubbers of nitro monomers, and the like.

(Iii) As the anionic dispersant, a water-soluble polymer such as partially saponified vinyl acetate polymer or Aerosil # 20
There are colloidal silica such as 0, # 300 (manufactured by Nippon Aerosil Co., Ltd.).

(Iv) Examples of the cationic dispersant include aluminum oxide, magnesium hydroxide, hydrophilic finely-charged silica powder such as aminoalkyl-modified colloidal silica, and the like.

If necessary, a charge control agent, a colorant, and a fluidity modifier may be added to the toner. The charge control agent and the fluidity modifier may be mixed (externally added) with the toner particles and used. As the charge control agent, there are metal-containing dyes, nigrosine, etc., as the colorant, conventionally known dyes and pigments can be used, and as the fluidity modifier, there are colloidal silica, fatty acid metal salts and the like. . For the purpose of increasing the amount, a filler such as calcium carbonate or fine powder silica may be blended in the toner in an amount of 0.5 to 20% by weight. Further, in order to prevent aggregation of the toner particles and improve the fluidity thereof, a fluidity improver such as Teflon fine powder may be added. Further, for the purpose of improving the releasability at the time of fixing with a heat roll, waxes generally used as a releasing agent such as a hydrocarbon compound and carnauba wax may be added to the toner.

For example, in the case of a hydrocarbon compound, since it is hydrophobic and has a low molecular weight, it is difficult to mix with a polar polymer, so that it is hard to come out on the surface and is pushed into the toner. Then, the toner comes out from the inside at the time of fixing and remarkably improves the fixability and the offset property.

The hydrocarbon compound used in the present invention is, for example, paraffin having 20 or more carbon atoms, polyolefin, and the like, for example, paraffin wax (Nippon Petroleum), paraffin wax (Nippon Seiwa), microwax (Japan Petroleum), micro Crystalline Wax (Nippon Seiwa), PE-130 (Hoechst), Mitsui Highwax 110P (Mitsui Petrochemical), Mitsui Highwax 220P (Mitsui Petrochemical), Mitsui Highwax
660P (Mitsui Petrochemical) and the like, with paraffin being particularly preferred.

As the polymerization initiator, any suitable polymerization initiator, for example, azobisisobutyronitrile (AIBN), benzoyl peroxide, methyl ethyl ketone peroxide, isopropyl peroxycarbonate, quinene hydroperoxide, 2,4-dichlorylbenzoyl The monomers can be polymerized using peroxide, lauroyl peroxide and the like. Generally, about 0.5-5% by weight of monomer of initiator is sufficient.

The suspension method is a method in which a monomer composition in which a polymerization initiator, a magnetic substance, a monomer, an additive and the like are uniformly dissolved or dispersed is usually stirred in an aqueous phase containing a suspension stabilizer, that is, a continuous phase. Disperse using a machine, homomixer, homogenizer, or the like. Preferably, the stirring speed and time are adjusted so that the droplets of the monomer have the desired size of toner particles (generally 30 μm or less), and thereafter the state is maintained substantially by the action of the dispersion stabilizer. The stirring may be performed to such an extent that the particles are prevented from settling. The polymerization temperature is set to 50 ° C. or higher, generally 70 to 90 ° C. to carry out the polymerization. After completion of the reaction, the produced toner particles are recovered by an appropriate method such as washing, filtration, decantation, centrifugation and the like, and dried.

Suitable dispersion media used in the present invention include, for example, any suitable stabilizer, such as polybutynyl alcohol,
Gelatin, methyl cellulose, methyl hydropropyl cellulose, ethyl cellulose, sodium salt of carboxymethyl cellulose, polyacrylic acid and salts thereof, starch, gum alginate, zein, casein,
It is possible to use those in which the aqueous phase contains tricalcium phosphate, takule, barium sulfate, bentonite, aluminum hydroxide, ferric hydroxide, titanium hydroxide, sodium hydroxide and the like.

This stabilizer is stabilized in a continuous phase in an amount, preferably about
Used within the range of 0.1 to 10% by weight. However, those that remain on the surface of the polymerized toner particles after the polymerization and are difficult to remove reduce the moisture resistance of the toner, so that it is better to avoid using them.

In order to finely disperse the inorganic dispersant, it is possible to use a surfactant in the range of 0.001 to 0.1% by weight, but when it is used, it is preferable to keep it to the minimum amount. As the surfactant for promoting the intended action of the dispersion stabilizer, sodium dodecylbenzene sulfonate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium allylalkyl polyether ether sulfonate, sodium eulenate , Sodium laurate, sodium caprate, sodium caprylate, sodium caproate, potassium stearate,
Potassium oleate, 3,3-disulfonediphenylurea-4,4-diazo-bis-amino-8-nephtole-6-
Sodium sulfonate, ortho-carboxybenzene-
Examples thereof include azo-dimethylaniline, 2,2,5,5-tetramethyl-triphenyltan-4,4-diazo-bis-β-naphthol-di-disulfonate, and the like.

A water-soluble monomer simultaneously undergoes emulsion polymerization in water, and the resulting suspension polymer is contaminated with small emulsion-polymerized particles.Therefore, a water-soluble polymerization inhibitor, such as a metal salt, is added to carry out emulsion polymerization in the aqueous phase. It is also good to prevent. In addition, glycerin, glycol or the like may be added to water in order to reduce the viscosity of the medium and prevent the particles from coalescing. It is also possible to use salts such as NaCl, kCl, and Na ₂ SO ₄ in order to reduce the solubility of the easily soluble monomer in water.

Hereinafter, the present invention will be described in more detail based on examples.

Example 1. The above formulation was heated to 70 ° C. in a container to dissolve / disperse it.
This is mixed for about 5 minutes in a container equipped with a mixing device having high shearing force such as TK homomixer (made by Tokushu Kika Kogyo) while maintaining at 70 ° C., and 6 g of azobisisobutyronitrile is further added. A monomer composition was prepared by adding and dissolving.

On the other hand, 2 flasks in which 4 g of Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.) were dispersed in water were heated to 70 ° C., the above-mentioned monomer composition was charged, and the mixture was stirred at 7,000 rpm for 20 minutes. The mixture was further stirred at a low rotation speed to complete the polymerization. After removing the dispersant, it was filtered, washed with water, and sufficiently dried to obtain a magnetic toner. The magnetic toner had an average particle size of 11μ and had a sharp particle size distribution with very little coarse powder and fine powder. The magnetic particles were well distributed in the toner particles, and the appearance was a black toner.

0.4g of Nipsyl ER (manufactured by Nippon Silica) was added to 100g of the magnetic toner to prepare a developer. Commercially available copying machine PC-20 (made by Canon)
When an image was printed using, a good image was obtained, and the offset property and the fixing property were also good. No deterioration in image quality or density was observed in the durability test.

Comparative Example-1 Instead of the cross-linking (1) used in Example 1, the same amount of divinylbenzene was used as a cross-linking agent to carry out polymerization to obtain an average particle size.
11 μ of toner was obtained. Some of the obtained toners did not contain a magnetic substance, and the particle size distribution was broader than that of the toner of Example-1. Therefore, classification was performed using an air classifier to obtain an equivalent distribution. Of toner. When images were formed using this toner in the same manner as in Example 1, the image quality and density were inferior to those in Example 1.

Example 2 Polymerization reaction of the above formulation in a container in the same manner as in Example 1,
A formal blue magnetic color toner having an average particle diameter of 12 μ was obtained. This toner had good dispersibility of magnetic particles and had a sharp particle size distribution. When an image was formed in the same manner as in Example 1, it was a good image, and the offset property and the fixing property were also good. No deterioration in image quality or density was observed in the durability test.

Comparative Example 2 Polymerization was carried out using divinylbenzene instead of the crosslinking agent (1) used in Example 2 to obtain a toner having an average particle size of 13 μ. Since there were toner particles containing no magnetic substance and the toner had a broad particle size distribution, classification was performed to obtain a toner having the same distribution as in Example 2. When images were formed using this toner in the same manner as in Example 1, deterioration in image quality and density was observed during the durability test.

Example 3 The above formulation was heated to 70 ° C. in a container to dissolve / disperse it.
This is mixed for about 5 minutes in a container equipped with a mixing device having high shearing force such as TK homomixer (made by Tokushu Kika Kogyo) while maintaining at 70 ° C., and 6 g of azobisisobutyronitrile is further added. Added and dissolved.

On the other hand, 2 flasks in which 10 g of aminoalkylsilane-treated silica was dispersed in water were heated to 70 ° C., the above monomer system was charged, and the mixture was stirred at 7,000 rpm for 20 minutes. The mixture was further stirred at a low rotation speed to complete the polymerization. After removing the dispersant, filtration,
After washing with water and drying, a toner was obtained. This toner had an average particle size of 10 μm, had a sharp particle size distribution, and had a black appearance. To 100 g of the magnetic toner thus obtained, 0.4 g of TARANOX 500 (manufactured by Tarco) was added to prepare a developer.
When images were printed using a commercially available copying machine NP-270RE (manufactured by Canon Inc.), the images were good, and the offset property and fixing property were also good. No deterioration in image quality or density was observed in the durability test.

Example 4 The above formulation was heated to 70 ° C. in a container to dissolve / disperse it.
This is mixed for about 5 minutes while maintaining at 70 ° C in a container equipped with a mixer having high shearing force such as TK homomixer (made by Tokushu Kika Kogyo), and further 6 g of azobisisobunaronitrile is added. Added and dissolved.

On the other hand, 2 flasks in which 10 g of aminoalkylsilane-treated silica was dispersed in water were heated to 70 ° C., the above monomer system was charged, and the mixture was stirred at 7,000 rpm for 20 minutes. The mixture was stirred at a lower rotation speed to complete the polymerization. After removing the dispersant, filtration, washing with water and drying were carried out to obtain a toner. This toner had an average particle size of 10 μm, had a sharp particle size distribution, and had a black appearance. 100 g of this toner will be added to the taranox 500
(Tarco Co.) 0.4 g was added to obtain a developer. Commercial copying machine
When an image was printed using NP-270RE (manufactured by Canon Inc.), the image was good, and the offset property and fixing property were also good. No deterioration in image quality or density was observed in the durability test.

Claims (1)

[Claims] 1. A magnetic toner comprising a polymer and a magnetic material which have two or more vinyl groups at their ends and are crosslinked with a crosslinking agent having two or more urethane bonds in the molecule.