JPH0727279B2 - Method of manufacturing toner for electrophotography - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an electrophotographic toner using a suspension polymerization method.

(Prior Art) In electrophotography, after uniformly charging the photoreceptor,
A photo-image based on the original image is exposed on the photoconductor to eliminate or reduce the charge in the light-irradiated portion to form an electrostatic latent image on the photo-conductor on the basis of the photo original, and then a developer containing toner. To visualize the toner image. This visualized toner image is generally transferred to a suitable transfer member and fixed to form a so-called copy.

The developer used in the above-mentioned process is basically composed mainly of a colorant for developing the electrostatic latent image and a binder for fixing the image on the transfer body. They are roughly classified into so-called wet (liquid) developers and dry developers.

Dry developers can be further divided into two-component developers and one-component developers. The former consists of carrier and toner, and the latter consists of toner only. In other words, a two-component type developer obtains a toner having a polarity opposite to that of the electrostatic charge image necessary for developing the electrostatic charge image on the photoconductor by frictional charging of the carrier and the toner. A one-component developer is one that is charged by friction between other members or by friction with other members in the developing device.

Conventionally, such a toner for a dry developer is generally prepared by melting and kneading a coloring agent such as carbon black and / or a magnetic powder such as magnetite into a thermoplastic resin to form a dispersion, and then using a suitable crushing device. It has been manufactured by a method of mechanically applying an impact force to pulverize the dispersion into a desired particle size, and if necessary, classifying the dispersion to obtain a toner (hereinafter, this method is referred to as a pulverization method). .

Such a method not only requires a large amount of energy for melt-kneading and pulverizing, but also the manufactured toner inevitably has many drawbacks.

In particular, when a desirable resin is used in the melt-kneading step and the pulverizing step, for example, when a resin that easily melts is used, aggregation (caking) during storage of toner, fogging due to toner filming on the photoconductor, etc. In addition, when a resin that is easily pulverized is used, the toner is pulverized into a fine toner in the developing device, which causes image fog and in-machine stain.

In addition, the colorant dispersed in the resin appears on the pulverized toner surface, which reduces the triboelectric charge amount in a high humidity state and causes the colorant to fall off in the developing machine. And the undesired phenomenon such as the contamination of the surface of the photosensitive member.

In order to solve the drawbacks of such a crushing method, Japanese Patent Publication No. 43-1079
Japanese Patent Laid-Open Publication No. 9-1987 proposes a method for producing completely spherical toner particles by spray drying an emulsion obtained by an emulsion polymerization method.

Further, as a method for producing a toner using a polymerization method in order to solve the drawbacks of the pulverization method, a method for producing a toner by a suspension polymerization method is disclosed in JP-B-51-14895 and JP-A-57-53756. Proposed. When the suspension polymerization method is used, a spherical toner is obtained.

(Problems to be Solved by the Invention) The toner obtained by using the suspension polymerization method solves some of the drawbacks of the toner obtained by the pulverization method.
Since the obtained toner particles are spherical, the cleaning property is poor.

Therefore, the present invention solves such problems in the conventional suspension polymerization method, is excellent in cleaning property, and is excellent in image density, resolution, gradation property, charge stability, blocking property, and dry type. An object of the present invention is to provide a method for producing an electrophotographic toner suitable for development.

(Means for Solving Problems) The present invention is to suspend and disperse a polymerizable monomer, a colorant and / or a magnetic powder and an oil-soluble polymerization initiator in water containing an inorganic or organic dispersant, and In the method for producing an electrophotographic toner, which comprises the step of subjecting a toner to turbid polymerization, a foamable azo-based polymerization initiator is added to a polymerizable monomer in an amount of 0.01 to 0.01 as a part of the oil-soluble polymerization initiator. 1% by weight is used, and the temperature is kept at a temperature 20 to 80 ° C. higher than the glass transition temperature of the main resin component obtained during the above-mentioned step until the polymerization conversion reaches 80% by weight or more and until the completion of the polymerization or after the completion of the polymerization. The present invention relates to a method for producing an electrophotographic toner, which comprises foaming the toner particles to obtain porous particles.

Polymerization of the polymerizable monomer in the present invention is carried out by suspending and dispersing the polymerizable monomer in an aqueous medium containing a suspension dispersant.

At the time of this polymerization, a colorant and / or a magnetic powder and a polymerization initiator are present. In addition, a charge control agent, a fluidity improver, a toner property improver such as a cleaning property improver, a dispersion aid for assisting suspension / dispersion, and a chain transfer agent can be appropriately present. Further, a foaming polymerization initiator for making the particle surface porous is used as a part of the polymerization initiator.

As a method for suspending and dispersing the polymerizable monomer in the aqueous medium, the polymerizable monomer, the dispersant and the aqueous medium may be simultaneously stirred and mixed, and the dispersant is dissolved or uniformly dispersed in the aqueous medium. The polymerizable monomer may be added and mixed with stirring.

Stirring and mixing in the above suspension dispersion may be carried out at a relatively high speed using an ordinary stirrer, but it is preferable to carry out stirring by high speed shearing using a homomixer or the like.
This is also the case when the colorant and / or the magnetic powder and the toner property improving agent used as necessary are dispersed in the polymerizable monomer.

Polymerization is carried out after the above-mentioned suspension dispersion, or while performing the suspension dispersion.
It is preferably carried out at a temperature of 120 ° C, particularly preferably at a temperature of 50 to 90 ° C.

After the polymerization rate reaches 80% by weight or more, preferably 95% by weight,
20 from the glass transition temperature of the main resin component that can give a polymerization system
The foaming treatment is carried out by keeping the temperature high at -80 ° C for 1 to 5 hours.
When the polymerization rate is less than 80% by weight, the system becomes unstable due to the generated N ₂ gas, and coalescence and agglomeration of particles occur.
Further, unless the temperature is higher than the glass transition temperature by 20 ° C. or more, the resin is not sufficiently softened and foaming is insufficient, and at a temperature higher than 80 ° C. above the glass transition temperature, coalescence and agglomeration of particles occur. This foaming treatment may be performed after the completion of polymerization.

The polymerization is preferably carried out until the rate of polymerization reaches 99% by weight or more, and particularly preferably 99.9% by weight or more. If the polymerization rate is low and the amount of residual monomer is high, the toner properties, especially the storage stability, tend to be poor.

The polymer obtained by polymerization preferably has a weight average molecular weight of 50,000 or more. If the molecular weight is too small, the cleaning properties and blocking resistance are likely to decrease.

Further, the obtained polymer preferably has a glass transition point of 30 to 90 ° C, and particularly preferably 50 to 80 ° C. If the glass transition point is too low, blocking resistance tends to decrease, and if it is too high, fixability tends to decrease. The glass transition point can be adjusted mainly by selecting the polymerizable monomer used.

By such polymerization, particles of about 3 μm or less are obtained.

Next, the materials used for the polymerization will be described.

Examples of the polymerizable monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-
Ethylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-
Styrene and its derivatives such as nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, n-methoxystyrene, n-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, ethylene, propylene, Ethylene unsaturated monoolefins such as butylene and isobutylene, vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide and vinyl fluoride, vinyl acetate,
Vinyl propionate, vinyl benzoate, vinyl acetate and other vinyl esters, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate,
Propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, α-chloromethyl acrylate, methyl methacrylate, ethyl methacrylate, methacryl Propyl acid, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimetal aminoethyl acrylate, dimethylaminoethyl methacrylate, Α-Methylene aliphatic monocarboxylic acid esters such as diethylaminoethyl acrylate and diethylaminoethyl acrylate, acrylonitrile, methacrylonitrile, acrylamide, methacryl Amides, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and other acrylic acid or methacrylic acid derivatives, and in some cases, acrylic acid, methacrylic acid,
Maleic acid and fumaric acid can also be used. Further, vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and methyl isopropyl vinyl ketone, N-vinyl pyrrole, N-
One or a combination of two or more of N-vinyl compounds such as vinylcarbazole, N-vinylindole and N-vinylpyrrolidone and vinylnaphthalene salts can be used. Among these polymerizable monomers, styrene or styrene derivative
When it is used in an amount of 40 to 100% by weight, the fixing property becomes very excellent when the toner is copied on paper by an electrophotographic copying machine.

Further, as the polymerizable monomer of the present invention, a compound having two or more polymerizable double bonds, which serves as a crosslinking agent, can be partially used. For example, aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene and their derivatives, ethylene glycol dimethacrylate, diethylene glycol dimemethacrylate, triethylene glycol diacrylate, dimethylol propane triacrylate and other diethylenic carboxylic acid esters, N, N -Divinyl compounds such as divinylaniline, divinyl ether and divinyl sulfite, and compounds having three or more vinyl groups can be used alone or as a mixture. The amount of the crosslinking agent used is 0 to 20% by weight based on the total amount of the polymerizable monomers.
Is preferable, and particularly preferably 0 to 5% by weight.

The aqueous medium used in the present invention is used in an amount of 80 to 500% by weight, preferably 100 to 200% by weight, based on the obtained polymer particles. If it is less than 80% by weight, it is difficult to keep the dispersion system stable, and if it exceeds 500% by weight, it is not preferable in terms of productivity.

In the present invention, as the dispersant, a sparingly soluble inorganic salt, a water-soluble polymer or the like is used.

As the poorly soluble inorganic salt, generally well-known ones can be used. For example, there are calcium phosphate, hydroxyapatite, magnesium phosphate, magnesium pyrophosphate and the like.

The sparingly soluble inorganic salt is preferably used in the range of 1.0 to 20% by weight based on the aqueous medium. If the amount of the poorly soluble inorganic salt is too small, the oil droplets coalesce during the polymerization to increase the particle size,
It is not possible to obtain polymer particles having a preferable particle size as a toner. Further, if the amount of the poorly soluble inorganic salt is too large, the viscosity of the medium becomes too high, and it becomes difficult to uniformly stir the entire medium.

Further, an anionic surfactant is often present as a dispersion aid together with the poorly soluble inorganic salt. As the anionic surfactant, generally known ones can be used, and examples thereof include sodium alkylbenzene sulfonate, sodium α-olefin sulfonate, sodium alkyl sulfonate and the like.

Anionic surfactant is 0.0001 to 0.02 in the aqueous medium.
Used in the weight% range. At doses outside this range,
It is difficult to function as a dispersion aid.

The water-soluble polymer, partially saponified polyvinyl alcohol, alkyl cellulose, hydroxyalkyl cellulose, carboxyalkyl cellulose, polyacrylamide, polyvinylpyrrolidone, sodium polyacrylate, etc., these are 0.5 to 10 wt% to the aqueous medium. %
It is preferably used, particularly preferably 1 to 5% by weight. When the amount of the water-soluble polymer is too small, it is impossible to obtain polymer particles having a preferable particle size, as in the case of the hardly soluble inorganic salt. On the other hand, if the amount of the water-soluble polymer is too large, the viscosity will be too high or the emulsion will be easily emulsified.

Examples of the foamable azo-based polymerization initiator include azobisisobutyronitrile, azobisdimethylvaleronitrile,
There are azo-based polymerization initiators such as azobiscyclohexanecarbonitrile, but azo-based polymerization initiators are highly toxic, and N ₂ gas generated during polymerization destabilizes the polymerization system, so use it in large amounts. It is not possible. Therefore, in order to complete the polymerization reaction, it is used in combination with an organic peroxide such as benzoyl peroxide, tert-butyl peroxide, tert-butyl peroxy 2-ethylhexanoate or acetyl peroxide. The amount of organic peroxide is 0.05 to 10 relative to the total amount of polymerizable monomers.
It is preferably used in weight percent. The azo-based polymerization initiator is used in an amount of 0.01 to 1% by weight based on the total amount of the polymerizable monomers, and 0.01 to 0.5% by weight based on the total amount of the charged polymerizable monomers before the foaming process. It is preferable to control the temperature during the polymerization so that it remains. This control can be determined by the decomposition rate of the azo polymerization initiator and the polymerization temperature.

Examples of the chain transfer agent include alkyl mercaptans such as t-dodecyl mercaptan, lower alkyl xanthogens such as diisopropyl xanthogen, carbon tetrachloride, carbon tetrabromide, etc., and used in an amount of 0 to 2% by weight based on the polymerizable monomer. Preferably.

Examples of the colorant preferably used in the present invention include pigments and dyes, for example, various carbon blacks, nigrosine dyes (CINo.50415), aniline blue (CINo.50405), and chalco oil blue (CINo.azoec).
Blue 3), Chrome Yellow (CINo.14090), Ultramarine Blue (CINo.77103), DuPont Oil Red (CINo.26105), Orient Oil Red # 330.
(CINo.60505), Quinoline Yellow (CINo.4700
5), Methylene Blue Chloride (CINo.52015), Phthalocyanine Blue (CINo.74160), Malachite Green Oxalate (CINo.42000), Lamp Black (CINo.77266), Rose Bengal (CINo.45435),
Oil black, azo oil black and the like can be used alone or in combination. These colorants may be used in any amount, but for the purpose of obtaining the required concentration and for economic reasons, the amount thereof should be about 1 to 30% by weight, preferably 5 to 15% by weight in the toner. Used in various proportions.

As the pigment or dye, those subjected to various treatments for the purpose of increasing the dispersibility in the polymerization reaction system or the toner of the present invention may be used. Examples of the treatment include treatment with a nigrosine dye (CI No. 50415) using an organic acid such as stearic acid and maleic acid.

Among these colorants, various carbon blacks such as furnace black, channel black, thermal black, acetylene black and lamp black are particularly preferable for the toner of the present invention. Further, the carbon black may be surface-treated. The surface treatment includes, for example, an oxidation treatment using various oxidizing agents such as oxygen, ozone and nitric acid, a surface adsorption treatment with an organic acid ester such as dibutyl phthalate and dioctyl phthalate.

When carbon black is used as the colorant, it is preferable to use grafted carbon black. The grafted carbon black is obtained by polymerizing the above polymerizable monomer in the presence of carbon black by a method such as bulk polymerization or solution polymerization. The polymer component of the grafted carbon black is preferably 50% by weight or less based on the grafted carbon black,
30% by weight or less is preferable. Grafted carbon black is preferred because it has excellent dispersion stability during emulsion polymerization, but when the amount of the polymer component is too large, when dispersed in the polymerizable monomer, the viscosity tends to be too high, Workability is reduced. The amount of grafted carbon black used is preferably determined by the amount of carbon black component.

The magnetic powder is used when producing a magnetic toner, which can also serve as a colorant. Preferred magnetic powders are, for example, iron such as magnetite and ferrite, or oxides or compounds of elements exhibiting ferromagnetism such as nickel and cobalt. These magnetic powders have a particle size of 0.01-3μ
The powder of m is preferable, and the surface of the magnetic powder may be treated with a resin, a titanium coupling agent, a silane coupling agent, a higher fatty acid metal salt or the like. These magnetic substances are contained in the toner in an amount of 20 to 80% by weight, preferably 30%.
~ 70 wt% can be included. You may use it as a coloring agent in the quantity below this.

The offset preventive agent is used as necessary. The anti-offset agent is present in the system in various forms during polymerization,
It can be contained in the toner as a product. Alternatively, it can be added later to the toner of the present invention in which no offset inhibitor is present. As the offset preventing agent, various natural waxes such as carnauba wax, hydrogenated castor oil, and low molecular weight olefin polymers are used in the present invention, but low molecular weight olefin polymers are preferably used. As this low molecular weight olefin polymer, a polymer of olefin or a copolymer of olefin and a monomer other than olefin and having a low molecular weight is used. Here, examples of the olefin include ethylene, propylene, butene-1 and the like, and examples of the monomer other than the olefin include acrylic acid ester and methacrylic acid ester. As the low molecular weight olefin monomer, for example, polyalkylene described in JP-A-55-153944, low molecular weight olefin copolymer described in JP-A-50-93647 should be used. You can

The molecular weight of the low molecular weight olefin polymer that can be used in the present invention may be that included in the concept of low molecular weight in ordinary polymer chemistry, but generally it is a weight average molecular weight (Mw).
It is from 1000 to 45000, preferably from 2000 to 6000.

The low molecular weight polyolefin polymer that can be used in the present invention,
Those having a softening point of 100 to 180 ° C, particularly 130 to 160 ° C are preferable.

The amount of the low molecular weight olefin polymer that can be used in the present invention is not particularly limited, but it is preferably in the range of 0 to 30% by weight, and preferably 1 to 30% by weight based on the weight of the toner. . If the amount of the low molecular weight olefin polymer is too small, the effect of preventing offset due to the addition of the low molecular weight olefin polymer will not be exhibited, and if it exceeds 30% by weight, gelation or the like may occur during the polymerization reaction.

Furthermore, a fluidity improver, a cleaning improver, etc. can be used if necessary. These can be present in the polymerization reaction system and in the product toner,
The product toner is preferably externally added afterwards. These contents are 0 to 3% by weight based on the toner of the present invention.
Is preferred. As the fluidity improver, silane,
There are titanium, aluminum, calcium, magnesium and oxides of magnesium and those obtained by subjecting the above oxides to a hydrophobic treatment with a titanium coupling agent or a silane coupling agent, and examples of the cleaning property improver include zinc stearate, lithium stearate and There are metal salts of higher fatty acids such as magnesium laurate or aromatic acid esters such as pentaerythritol benzoate.

In the present invention, the charge amount and charge polarity of the product toner can be freely adjusted by selecting the polymerizable monomer and the colorant, but the present invention is used to adjust the charge amount and charge polarity to desired values. It is also possible to use a charge control agent in combination with the colorant in the above toner.

As the charge control agent suitably used in the present invention, azo dyes such as Spiron Black TRH and Spiron Black TPH (manufactured by Hodogaya Chemical Co., Ltd.), p-fluorobenzoic acid, p-nitrobenzoic acid, 2,4- Examples thereof include aromatic acid derivatives such as di-t-butylsalicylic acid and tin compounds such as dibutyltin oxide and dioctyltin oxide. These are preferably used in an amount of 0 to 5% by weight based on the polymerizable monomer.

After the polymerization, the product is subjected to centrifugal dehydration, further washed, dried and, if necessary, classified to obtain toner particles.

Here, washing is preferable in order to completely remove the dispersant attached to the particles, whereby the charging stability and blocking property can be improved. The washing is preferably carried out with an aqueous solution of hydrochloric acid or the like having a pH of 1 to 3 in the case of a sparingly soluble inorganic dispersant, and with hot water at 40 to 100 ° C. in the case of a water-soluble polymer.

The toner obtained by the present invention has various development processes,
For example, the cascade development method described in U.S. Pat.No. 2,618,552, the magnetic brush method described in U.S. Pat.No. 2,874,065, the powder cloud method described in U.S. Pat.No. 2,221,776, and the U.S. patent number 3,
No. 166,432, a touchdown developing method, a so-called jumping method described in JP-A-55-18656, a so-called microtoning method using a magnetic toner manufactured by a powder method as a carrier, and a magnetic toner. It is possible to use a so-called bipolar magnetic toner method or the like in which a necessary toner charge is obtained by frictional charging between the two.

Further, the toner obtained by the present invention can be used in various fixing methods such as so-called oilless and oil coating heat roll method, flash method, oven method and pressure fixing method.

Further, various cleaning methods such as a so-called fur brush method and a blade method can be applied to the toner obtained by the present invention.

(Function) Since the toner obtained by the conventional suspension polymerization has a true spherical shape, when it is attached to the photoconductor, the contact area with the photoconductor is larger than that of the amorphous toner obtained by the pulverization method. , Adhesive is large and cleaning failure occurs.

The toner according to the present invention has a rough particle surface due to N ₂ gas generated when the azo-based polymerization initiator decomposes and has a rough surface, so that the contact area with the photoconductor is reduced and good cleaning properties are exhibited. Furthermore, since the surface area is large, the rise of charging is quick.

(Examples) Next, the present invention will be described in detail based on examples, but the present invention is not limited thereto.

Hereinafter,% means% by weight. Further, in the following, the molecular weight of the polymer was determined by gel permeation chromatography using a calibration curve of standard polystyrene. The polymerization rate was determined by gas chromatography.
It was determined by measuring the amount of unreacted monomer using paraxylene as a standard substance.

Example 1 (1) Grafted carbon paste in a stainless beaker 3 (using graft carbon GP-E-2 (manufactured by Ryoyu Kogyo Co., Ltd.) containing 40% of styrene monomer) 10
To 0 g, styrene 400 g as a polymerizable monomer, butyl acrylate 120 g, benzoyl peroxide 12 g, azobisisobutyronitrile 0.6 g and tert-dodecyl mercaptan 0.6 g as a chain transfer agent were mixed, and a high-speed shear disperser (special Kika Kogyo Co., Ltd., TK homomixer) was mixed and dispersed at 3000 rpm for 30 minutes.

Next, 650 g of ion-exchanged water, 650 g of hydroxyapatite (trade name: Super Tight, manufactured by Nippon Kagaku Co., Ltd.) and 0.024 g of sodium dodecylbenzenesulfonate (trade name: Neoperex No. 25, manufactured by Kao Atlas Co., Ltd.) are added. ,
Further high-speed shearing disperser (made by Tokushu Kika Kogyo Co., Ltd.) 10,000r
Dispersion was performed for 30 minutes at pm to obtain a suspension.

Next, the suspension was transferred to a three-necked four-separable flask equipped with a stirrer, a nitrogen inlet, a thermometer, and a condenser, and the temperature of the flask was adjusted to 80 ° C. under a nitrogen stream to carry out polymerization for 5 hours. The polymerization rate at this time was 95%. continue,
The temperature was raised to 95 ° C., foaming treatment was performed for 2 hours, and cooling was performed to obtain a slurry. The polymerization rate at this time was 99.5% or more. Also, the weight average molecular weight (Mw) of the polymer powder is 80,000,
The number average molecular weight (Mn) was 25,000.

After the slurry was centrifugally dehydrated, it was washed twice with a 1N HCl solution, and further washed twice with ion-exchanged water. Then, it was dried in a dryer at 30 to 35 ° C. to obtain a toner. When the particle size of the obtained toner was measured with a Coulter counter, the particle size was 2 to 50 μm and the average particle size was 14 μm. Furthermore, when the glass transition point (Tg) was measured by a differential scanning calorimeter, it was 73 ° C. When this toner was further classified to 5 to 25 μm with a zigzag classifier (100MZR, manufactured by Alpin Co.), the yield was 85% of that before classification.

Also in the following Examples and Comparative Examples, the particle diameter and the average particle diameter were measured with a Coulter counter, the glass transition point was measured with a differential scanning calorimeter, and the classification was performed with a zigzag classifier.

When the toner after classification was observed with a scanning electron microscope at a magnification of 4000 times, the surface was porous and rough.

Example 2 The procedure of Example 1 was repeated except that 3.0 g of azobisisobutyronitrile was used.

The polymerization rate before heating at 95 ° C was 96%, and the final polymerization rate was 99.5% or more. The obtained polymer component had a weight average molecular weight (Mw) of 73,000 and a number average molecular weight (Mn) of 21,000.
The average particle size, Tg, and surface condition did not change.

Example 3 The procedure of Example 2 was repeated, except that the foaming treatment after polymerization was carried out in an autoclave at 120 ° C. The polymerization rate before heating at 95 ° C was 96%, and the final polymerization rate was 99.5% or more.
The molecular weight of the polymer in the obtained toner, the average particle size of the toner, the Tg, and the surface state did not change.

Example 4 The same operation as in Example 3 was carried out except that 3 g of azobiscyclohexanecarbonitrile was used instead of azobisbutyronitrile. The polymerization rate before heating at 95 ° C was 91%, and the final polymerization rate was 99.5% or more. The weight average molecular weight (Mw) of the obtained toner was 80,000 and the number average molecular weight (Mn) was 27,000. The average particle size, Tg, and surface condition did not change.

Comparative Example 1 The procedure of Example 2 was repeated except that azobisisobutyronitrile was not used. The polymerization rate before raising the temperature to 95 ° C is 93
%, And the final polymerization rate was 99.5% or more. The molecular weight, average particle size and Tg were the same as in Example 1, but the surface of the particles was smooth.

Comparative Example 2 Instead of the foaming treatment at 95 ° C in Example 1, 5 ° C at 80 ° C was used.
The same procedure was performed except that the temperature was kept warm for a while. The polymerization rate before raising the temperature to 95 ° C was 95%, and the final polymerization rate was 99.5% or more.
The obtained toner had the same molecular weight, average particle size, and Tg as in Example 1, but the surface of the particles was smooth.

Comparative Example 3 Styrene / butyl methacrylate = 70/30 (weight ratio) by solution polymerization using toluene as a solvent, molecular weights Mw70000 and Mn3000
A polymer of 0 was prepared, desolvation was performed under reduced pressure, and toluene was removed to form a white solid.

Carbon black 50g, phthalocyanine copper 10g, low molecular weight polypropylene (trade name VISCOL 5
20P of 50P (manufactured by Sanyo Chemical Industry Co., Ltd.) was kneaded with a two-roll and pulverized with a jet mill to obtain a toner.

Using the classified toners obtained in Examples 1 to 4 and Comparative Examples 1 to 3, a plain paper copying machine (u-Bix1600, manufactured by Konishi Roku Photo Co., Ltd.) using a commercially available insulating carrier was used. hand,
The electrophotographic toner properties were tested. However, each toner was subjected to external addition treatment of hydrophobic silica (R-972 manufactured by Nippon Aerosil Co., Ltd.) and zinc stearate as fluidity improvers by 0.6% and 0.1% to the toner, respectively.
The test results are shown in Table 1.

The electrophotographic characteristics of Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated as follows.

(A) Resolution: Electrophotographic Society Test Chart No. 1 was used and each developer was used to make a copy on plain paper. It was compared and evaluated whether the copied image could be read in detail.

(B) Image density: The density of the black portion of the copied paper was measured by a densitometer and judged in the same manner as the resolution.

Gradation: Similar to the resolution,
The evaluation was made using the shaded area divided into 11 levels.

(C) Cleanability: Each of the prepared developers was continuously copied under the conditions of a temperature of 30 ° C. and a humidity of 80% RH using a copying machine, and the number of copies until the cleaning failure occurred was evaluated.

(D) Blocking property: Examples 1 to 4 and Comparative Examples 1 to 1
The toner prepared in No. 3 was allowed to stand for 72 hours under the conditions of 50 ° C. and 95% humidity, and it was judged whether or not the toner was blocked. ◎: Very good ○: Excellent Δ: Slightly inferior ×: Inferior evaluated.

(E) Charge stability: Each of the prepared developers was agitated by a copying machine, the charge amount was measured at regular intervals, and judged by the change in the charge amount. ◎: Very good ○: Excellent △ : Slightly inferior x: Inferior

(Effects of the Invention) According to the present invention, the dry development which is excellent in the resolution, the image density, the gradation, the charging stability, the blocking property, and particularly the cleaning property by using the suspension polymerization method. It is possible to obtain a toner suitable for electrophotography.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideki Kajiwara 4-13-1, Higashimachi, Hitachi, Ibaraki Prefecture Yamazaki Plant, Hitachi Chemical Co., Ltd. (56) Reference JP-A-57-154253 (JP, A) JP-A-58-37651 (JP, A) JP-A-56-107148 (JP, A) JP-A-56-116044 (JP, A)

Claims (1)

[Claims] 1. A step of obtaining a toner particle by suspension-dispersing a polymerizable monomer, a colorant and / or a magnetic powder and an oil-soluble polymerization initiator in water containing an inorganic or organic dispersant, and carrying out suspension polymerization. In the method for producing an electrophotographic toner, including 0.01 to 1% by weight of a foamable azo-based polymerization initiator with respect to a polymerizable monomer as a part of the oil-soluble polymerization initiator, , After the polymerization conversion rate reaches 80% by weight or more until the completion of the polymerization or after the completion of the polymerization, the toner particles are foamed by keeping them at a temperature 20 to 80 ° C. higher than the glass transition temperature of the main resin component obtained. A method for producing an electrophotographic toner, characterized in that the particles are fine particles.