JP2002207309A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method whereby a high quality image having excellent gradation can be obtained and high transfer efficiency can be ensured even in a high light area. SOLUTION: In the method for forming an image by forming on a developing sleeve (developer carrier) 109 a magnetic brush of developer 107 containing at lest toner and carrier, by developing an electrostatic latent image, formed on the photoreceptor drum (image carrier) 111, by the use of toner, and by transferring the toner onto a recording medium, the volume average particle diameter of the toner is 2 to 6 μm, and a ratio (Dv/Dn) between the volume average particle diameter (Dv) and number average particle diameter (Dn) is 1.00 to 1.20. In addition, the photoreceptor drum 111 is an electrophotographic photoreceptor and a dot distribution electrostatic latent image is formed by exposing the photoreceptor drum 111 with a flux of light modulated by a signal whose pulse width is modulated in accordance with the density of the recorded image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method for transferring a developed image obtained by developing an electrostatic latent image using a developer containing at least a toner and a carrier onto a recording medium.

[0002]

2. Description of the Related Art There is known an image forming method in which an electrophotographic photosensitive member is scanned and exposed by a laser beam modulated according to a recorded image signal to form a dot distribution electrostatic latent image. Among them, the so-called pulse width modulation (PWM) method of modulating the width of a driving pulse current of a laser (that is, the duration time) according to the density of an image to be recorded has a high recording density or a high resolution and a high gradation. It is possible to obtain the nature.

On the other hand, as a direction in which high resolution is aimed from the side of the developer, a method of reducing the particle size of the toner or reducing the magnetic force of the carrier is known.

[0004]

There is a limit in reducing the particle size of a toner as a means for achieving high image quality in a usual pulverized resin toner. It comes from two issues: manufacturing and performance.

[0005] As a problem in production, a classifying operation is included in the production process of a normal pulverized toner, and a sharp reduction in classification efficiency or a high precision of classification conditions is required as the particle size of the toner is reduced. Come.

Another problem with performance is that in the conventional particle size distribution of the pulverized toner, there are many toners (fine powders) having a smaller particle size than the average particle size, so that handling (cleaning, etc.) of the toner becomes difficult. It is mentioned.

Further, when a dot distribution electrostatic latent image is formed on a photoreceptor by using the PWM method, and a reversal development is performed with a magnetic brush of a two-component developer opposed to the photoreceptor, a highlight portion on a recording paper is reduced. It was found that it was difficult to obtain gradation. When the cause was examined, the following was found.

That is, when a latent image in a low density portion is formed by a normal dot distribution latent image, when viewed microscopically, the latent image on the photosensitive member is not a broad latent image like an analog latent image, but is a local dot. It has a two-dimensional distribution of latent images. And
When trying to reproduce low density, the dot latent image becomes dull,
The maximum contrast V ₀ (the difference between the non-exposed portion potential and the minimum potential in the absolute value in the dot-shaped latent image) gradually decreases. For example, when trying to reproduce an image having a reflection density of about 0.2, the V ₀ of the dot-like latent image at that time is 150 V to
It will be about 00V.

On the other hand, in the case of reversal development in which toner adheres to a light-exposed portion of a photoreceptor, the DC voltage component of the vibration developing bias potential is absolutely higher than the surface potential of the non-exposed portion (non-image portion) in order to prevent fogging. Since the value is set lower by 100V to 200V, the potential difference Vcont between the potential of the light exposure portion of the dot-shaped latent image and the DC voltage component of the developing bias when V0 is 150V to 200V is ₀ to 50V. . This is a very unstable contrast depending on whether the toner adheres to the photoconductor side or remains on the developer carrier side. In this region, the toner having a particularly high charge amount is selectively developed on the photoconductor.

Among toners having a normal particle size distribution, many toners having a high charge amount have a small particle size (fine powder), and it is known that a difference occurs in the toner particle size distribution to be developed depending on the contrast of development.

As mentioned above, the developing method based on the PWM method is excellent in image gradation. However, this is the image gradation related to development, and a high-definition image can be conventionally obtained on a photoreceptor. Have been.

However, it has been found that when the toner particle size is reduced, the gradation of the highlight portion on the transfer paper is gradually not obtained, and it becomes difficult to transfer the toner image adhered to the photoreceptor. This is attributable to the toner particle diameter and the adhesive force between the toner and the photoreceptor. Generally, in order for toner to be transferred, it is necessary that the Coulomb force due to a potential difference acting between the photosensitive member and the transfer paper overcomes the resultant force such as a mirror image force or an intermolecular force between the toner and the photosensitive member.

However, it has been found that when the particle size of the toner is reduced, the ratio of the intermolecular force to the Coulomb force is increased, which is considered to be the cause of significantly lowering the transfer efficiency.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object thereof is to obtain a high-quality image with excellent gradation and high transfer efficiency even in a highlight portion. It is an object of the present invention to provide an image forming method capable of performing the above.

[0015]

In order to achieve the above object, the present invention provides a method for forming a magnetic brush on a developer carrying member in which a developer containing at least toner and a carrier forms a magnetic brush. In an image forming method in which an electrostatic latent image is visualized with toner and the toner is transferred onto a recording medium, the volume average particle diameter of the toner is 2 to 6 μm, and the volume average particle diameter (Dv) and the number average particle diameter (Dn)
n) is 1.00 to 1.20, and the image bearing member is an electrophotographic photosensitive member, and the electrophotographic photosensitive member is a light beam modulated by a pulse width modulated signal corresponding to the density of a recorded image. Is exposed to form a dot distribution electrostatic latent image.

When an image is displayed using the above means,
It was found that an image with good gradation was obtained. The present inventors conducted a detailed study on this result, and found the following.

That is, in the image forming method of the PWM method, the charge amount distribution needs to be broad in order to obtain image gradation. This is because the potential distribution of the electrostatic latent image in the highlight portion is not a well type but shows a Gaussian distribution, and the toner having a relatively large charge amount is selectively developed, and the gradation of the highlight portion is obtained. Therefore, a wide distribution from a large charge amount to a small charge amount is required.

In general, toner having a high charge amount has a small particle diameter in many cases. As a means for achieving high image quality, when a toner having an average toner particle diameter of 2 to 6 μm is used,
In a normal particle size distribution, transferability is significantly deteriorated due to an attractive force due to an intermolecular force between a toner having a fine particle size side of the average particle size and the electrostatic latent image carrier, and a gradation characteristic which is a feature of the PWM method is obtained. Disappears. This is because the intermolecular force, which is considered to hinder transfer, is superior to the electrostatic force, which is a driving force for transfer, and transfer is likely to be difficult.

Since the fine particle toner used in the present invention has a sharp particle size distribution, the intermolecular force which is considered to hinder transfer depending on the particle size can be made substantially constant, and the transfer property can be improved. I have. Further, the charge amount of the particles is inversely proportional to the first power to the second power of the particle size, and the charge amount rapidly increases with the finer particles. Therefore, when the average particle size is 2 to 6 μm, the charge amount is maintained while maintaining the transferability. Can be broadened.

As described above, by combining the PWM method with the fine particle toner having a sharp particle size distribution, the fine dot reproducibility (high image quality) by the fine particle size toner and the highlight on the transfer paper by the development without the particle size selectivity can be obtained. It is possible to obtain a high-quality image that is compatible with the reproducibility (high gradation) of the part.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The particle size of the toner used in the method of the present invention is 2 to 6 μm in terms of volume average particle size. When the particle size is smaller than 2 μm, it is difficult to remove the toner adhered on the photosensitive drum by a normal cleaning method, which causes image stains. In addition, when forming fine dots on the photosensitive drum, if the particle size exceeds 6 μm, the dot shape becomes distorted and a sufficiently high image quality cannot be obtained.

The ratio of the volume average particle diameter to the number average particle diameter (Dv / Dn) of the toner which can be used in the method of the present invention is defined as 1.00 to 1.20. When the particle size distribution index is 1.00, it can be said that the particle size distribution is completely monodisperse. If the particle size distribution index exceeds 1.20, the particle size distribution becomes broad, the toner on the fine particle side selectively adheres to the image area in the highlight area, the transferability is reduced, and the image gradation property is reduced. cause.

The toner that can be used in the method of the present invention is produced by polymerizing in a hydrophilic solvent in which a monomer is dissolved and a polymer of the monomer is not dissolved.

The monomers that can be used in polymerizing the toner used in the method of the present invention include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-phenylstyrene and p-methylstyrene.
Styrene and its derivatives such as chlorostyrene, ethylenically unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene, methyl methacrylate, ethyl methacrylate, propyl methacrylate and n-methacrylic acid
-Methylene aliphatic monocarboxylic acid esters such as -butyl, isobutyl methacrylate, etc., methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate And acrylates such as 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate and phenyl acrylate. These monomers can be used alone or as a mixture.

As the dispersant that can be used when polymerizing the toner used in the method of the present invention, various polymer compounds and copolymers can be mentioned. As such a polymer, specifically, for example, polystyrene, polyhydroxystyrene, polyhydroxystyrene-acrylate copolymer, hydroxylstyrene-vinyl ether or vinyl ester copolymer, polymethyl methacrylate, phenol novolak resin, cresol Novolak resin, styrene-acryl copolymer, vinyl ether copolymer, specifically, for example, polymethyl vinyl ether, polyethyl vinyl ether, polybutyl vinyl ether, polyisobutyl vinyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, styrene-butadiene Copolymer, ethylene-vinyl acetate copolymer, vinyl chloride, polyvinyl acetal, cellulose, cellulose acetate, cellulose nitrate, alkylated cellulose Scan, hydroxyalkylated celluloses, specifically hydroxymethyl cellulose, hydroxypropyl cellulose, saturated alkyl polyester resins, aromatic polyester resins, polyamide resins, polyacetal, polyethylene carbonate resin,
Or a mixture thereof, or a copolymer that can be formed by using a monomer that forms the above-described polymer compound in any ratio, and is preferably satisfactorily dissolved in a reaction solvent, and And those having no affinity for the resulting polymer compound.

Examples of the initiator that can be used when polymerizing the toner used in the method of the present invention include known polymerization initiators. Specifically, for example, azo compounds such as 2,2-azobisisobutyronitrile, 2,2-azobis (2,4-dimethylvaleronitrile), peroxides such as benzoyl peroxide and methyl ethyl ketone peroxide; Examples include nucleophilic reagents such as alkali metals, metal hydroxides, Grignard reagents, protonic acids, metal halides, and stable carbonium ions. The concentration of the polymerization initiator is preferably from 0.1 to 20% by weight, more preferably from 0.1 to 10% by weight, based on the monomer.

Known chain transfer agents can be used as the chain transfer agent that can be used when polymerizing the toner used in the method of the present invention.

Examples of the colorant that can be used when polymerizing the toner used in the method of the present invention include, in addition to carbon black, an organic colorant, for example, C.I. I. Direct Red 1, C.I. I. Basic Red 1, C.I.
I. Modant Red 30, C.I. I. Direct Blue 1, C.I. I. Direct Blue 2, C.I. I. Acid Blue 15, C.I. I. Basic Blue 3, C.I. I. Basic Blue 5, C.I. I. Modant Blue 7, C.I.
I. Direct Green 6, C.I. I. Basic Green 4, C.I. I. Dyes such as Basic Green 6, Cadmium Yellow, Mineral First Yellow, Navel Yellow, Naphthol Yellow S, Hansa Yellow G,
Permanent yellow NCG, tartrazine lake, molybdenum orange GTR, benzidine orange G, cadmium red 4R, watching red calcium salt,
Brilliant Carmine 3B, Fast Violet B,
Pigments such as methyl violet lake, cobalt blue, alkali blue lake, Victoria blue lake, quinacridone, rhodamine lake, phthalocyanine blue, fast sky blue, pigment green B, macalite green lake, final yellow green G, and the like.

As the reaction solvent used in the method of the present invention, a solvent in which a polymerization product precipitates as the polymerization proceeds, for example, methanol, ethanol,
1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tertiary butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol Tert-pentyl alcohol, 1-hexanol, 2-methyl 1-pentanol, 4-methyl-2-pentanol, 2-ethylbutanol, 1-heptanol, 2-heptanol, 3-heptanol, 2-octanol, 2- Linear or branched aliphatic alcohols such as ethyl 1-hexanol,
Pentane, 2-methylbutane, n-hexane, cyclohexane, 2-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, heptane, n-octane, isooctane, 2,2,3-trimethylpentane,
Decane, nonane, cyclopentane, methylcyclopentane, methylcyclohexane, ethylcyclohexane, p
-In addition to aliphatic hydrocarbons such as menthane and bicyclohexyl, aromatic hydrocarbons, halogenated hydrocarbons, ethers, fatty acids, esters, sulfur-containing compounds, and mixtures thereof can be mentioned.

For the purpose of controlling the chargeability of the toner of the present invention, a charge control agent can be added. As the charge control agent, any of a positive charge control agent or a negative charge control agent can be used. Specifically, for example, a nigrosine dye, a triphenylmethane dye, a quaternary ammonium salt,
Amine or imine compounds and polymers, salicylic acid,
Alternatively, mention may be made of metal compounds of alkyl salicylic acid, metal-containing monoazo dyes, polymers having a carboxylic acid or sulfonic acid functional group, humic acids such as nitrohumin, and salts.

In the toner used in the method of the present invention, a known surface modifier may be externally added for various purposes such as improvement of fluidity, improvement of image quality, and prevention of damage to the photoreceptor. For example, vinylidene fluoride fine powder, resin fine powder such as polytetrafluoroethylene fine powder, zinc stearate, calcium stearate, fatty acid metal salts such as lead stearate, aluminum oxide, titanium oxide, metal oxides such as zinc oxide, Examples include finely divided silica such as wet-process silica and dry-process silica, or those obtained by subjecting such silica to a surface treatment with a silane coupling agent, a titanium coupling agent, silicon oil, or the like.

When forming the fine particle toner used in the method of the present invention, fine particles are generated as the reaction proceeds.
The obtained fine particles are repeatedly washed with a reaction solvent or another suitable solvent. At this time, a separating means such as a centrifugal separator may be used to improve the washing efficiency. After washing, the obtained toner is filtered, dried and crushed to obtain fine particles, and a predetermined additive is appropriately added to obtain a toner used in the method of the present invention. At this time, a spraying method such as spray drying can be used as the separation and drying means.

As the carrier used in the method of the present invention, known carriers can be used, and the particle size is 10 μm in number average particle size.
~ 50 μm is preferred. When the particle size is less than 10 μm, a carrier adhesion phenomenon such that the carrier is developed on the photoreceptor is likely to occur. On the other hand, if the particle diameter exceeds 50 μm, a surface area for one-to-one sufficient frictional charging of the fine particle toner cannot be obtained, and uncharged or opposite-polarized charging may occur, which may cause problems such as image fogging. is there.

Further, the core material of the carrier that can be used in the method of the present invention includes magnetic metals such as iron, nickel and cobalt and alloys thereof or alloys containing rare earth elements, hematite, magnetite, manganese-zinc ferrite, Nickel-zinc ferrite, manganese-magnesium ferrite, soft ferrite such as lithium ferrite,
Examples thereof include iron-based oxides such as copper-zinc-based ferrite and mixtures thereof. In addition, other iron-based alloys,
For example, iron-silicon, iron-aluminum, iron-silicon-aluminum, permalloy, and the like can be used. Preferably, it is a ferrite, and the ferrite particles are made of the periodic table IA, IIA, III | A, IVA, V
A, VIA, IB, IIB, IVB, VB, VIB, VIIB, VI
A carrier containing at least one element selected from the group IIB and containing less than 1% by mass of other elements can be used. The carrier can be manufactured by a manufacturing method such as a sintering method or an atomizing method. If necessary, the magnetic material particle size distribution may be sharpened and granulated, or a sintering temperature, a heating rate, and a heating holding time. By controlling such factors, a carrier core having desired magnetic characteristics can be manufactured.

The core most preferably used in the method of the present invention is a magnetic material-dispersed resin carrier obtained by dispersing a magnetic material in a resin. In a system using a small particle size toner as in the method of the present invention, it is necessary to increase the specific surface area of the carrier in order to sufficiently charge each toner. A magnetic particle-dispersed resin carrier can be made into a small particle size carrier depending on the production method, which is a more preferable form for the present invention. Examples of the magnetic material used in the magnetic material dispersion type carrier include ferromagnetic metals such as iron, cobalt, and nickel; irons such as ferrite, magnetite, and hematite; and alloys containing ferromagnetic elements such as nickel and the like or And the like.

As a method for producing a carrier used in the method of the present invention, a method of directly mixing and polymerizing a monomer, a magnetic iron compound and a non-magnetic metal oxide to obtain a carrier core can be mentioned. Although a general suspension polymerization method can be used, it can be more preferably produced by a polymerization method using a hydrophobized magnetic powder as a dispersant. At this time, as a monomer used for the polymerization, a general thermoplastic resin may be used, but phenols and aldehydes are more preferably used. Specifically, as a method of manufacturing a carrier core using a cured phenolic resin,
Phenols and aldehydes are added to the above-mentioned magnetic iron compound, non-magnetic metal oxide, dispersion stabilizer and the like in an aqueous medium in the presence of a basic catalyst, and polymerized to obtain composite particles. Here, as the phenols used, besides phenol, alkylphenols such as m-cresol, p-tert-butylphenol, o-propylphenol, resorcinol and bisphenol A can be preferably used. It can be more preferably used in terms of graininess, cost and the like.

Further, as a more preferable method for producing the magnetic material-dispersed carrier core of the present invention, it is preferable to use a crosslinked binder in order to increase the strength of the carrier core or to coat the coating resin better. good. For example, in a kneading and pulverization type, a crosslinking component is added during melt-kneading and crosslinking is performed during kneading, or in a direct polymerization type, a resin is crosslinked during polymerization to obtain a core, or a monomer containing a crosslinking component is used. Methods can be mentioned.

The carrier used in the method of the present invention can be used as it is as the core material, but it can also be obtained by coating an appropriate coat resin in accordance with the charge amount of the toner. The coating amount of the coating material used in the method of the present invention is in the range of 0.5% by weight to 10% by weight, and most preferably in the range of 0.6% by weight to 5% by weight.

If the coating amount is less than 0.5% by weight, it becomes difficult to sufficiently coat the carrier core material, and the control of the toner charge amount by the coating resin cannot be sufficiently exhibited.
If the content exceeds 15% by weight, the specific resistance can be kept in a desired range because the amount of resin coating is too large. However, the fluidity is deteriorated, and the durability of a large number of copies deteriorates. This is not preferred in terms of point.

As the coating resin that can be used in the method of the present invention, an insulating resin can be suitably used. Here, the insulating resin used may be a thermoplastic resin or a thermosetting resin. Specifically, for example, as the thermoplastic resin, polystyrene, polymethyl methacrylate, styrene-acrylic acid Acrylic resin such as copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, vinyl chloride, vinyl acetate, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin, polyvinyl alcohol, Polyvinyl acetal, polyvinylpyrrolidone, petroleum resin, cellulose, cellulose acetate, cellulose nitrate, methylcellulose, hydroxymethylcellulose, hydroxymethylcellulose, cellulose derivatives such as hydroxypropylcellulose, novolak resin, low Amount of aromatic polyester resin such as polyethylene, saturated alkyl polyester resin, polyethylene terephthalate, polybutylene terephthalate, polyarylate, polyamide resin, polyacetal resin, polycarbonate resin, polyether sulfone resin, polysulfone resin, polyphenylene sulfide resin, polyether ketone resin Can be mentioned.

Specific examples of the curable resin include a phenol resin, a modified phenol resin, a maleic resin, an alkyd resin, an epoxy resin, an acrylic resin, and the like.
Specifically, for example, maleic anhydride, unsaturated polyester obtained by polycondensation of terephthalic acid-polyhydric alcohol, urea resin, melamine resin, urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine-guanamine resin, Examples include acetoguanamine resin, griptal resin, furan resin, silicone resin, polyimide, polyamideimide resin, polyetherimide resin, and polyurethane resin. The above-mentioned resins can be used alone or in combination. Further, a thermoplastic resin may be mixed with a curing agent or the like and cured to be used.

As a method for preferably producing a coated carrier used in the method of the present invention, a method of spraying a coating resin solution while floating and flowing a carrier core material to form a coating film on the surface of the core material, and a spray drying method. No. These coating methods are particularly suitable for coating a resin core using a thermoplastic resin.

As another coating method, the resin-coated carrier of the present invention can be produced by another coating method such as gradually evaporating the solvent while applying a shearing stress. As such a method, specifically, a method of crushing the carrier fixed after the solvent volatilizes at or above the glass transition point of the coating resin and curing the coating while applying shear stress,
It can also be produced by a crushing method.

Hereinafter, the PWM method used in the method of the present invention will be described.

FIG. 3 is a circuit block diagram showing one example of the pulse width modulation circuit, and FIG. 4 is a timing chart showing the operation of the pulse width modulation circuit.

In FIG. 3, 1 is a TTL latch circuit for latching an 8-bit digital image signal, 2 is a level converter for converting a TTL logic level to a high-speed ECL logic level, and 3 is a converter for converting an ECL logic level to an analog signal. D
/ A converter.

4 is an ECL comparator for generating a PWM signal, 5 is a level converter for converting an ECL logic level to a TTL logic level, 6 is a clock oscillator for oscillating a clock signal 2f, and 7 is substantially synchronized with the clock signal 2f. A triangular wave generator 8 for generating an ideal triangular wave signal is a 1/2 frequency divider that generates an image clock signal f by dividing the clock signal 2f by 1/2. Thereby, the clock signal 2f
Has a period twice as long as the image clock signal f. In order to operate the circuit at high speed, ECL is used everywhere.
A logic circuit is provided.

The operation of the circuit having such a configuration will be described with reference to the timing chart of FIG.

The signal a indicates the clock signal 2f and the signal b indicates the image clock signal f, which is related to the image signal as shown. Also, inside the triangular wave generator 7, in order to keep the duty ratio of the triangular wave signal at 50%,
The triangular wave signal c is generated after once dividing the frequency of the clock signal 2f by １ ／. Further, this triangular wave signal c is ECL
The signal is converted to a level (0 to -1 V) and becomes a triangular wave signal d.

On the other hand, the image signal is from 00h (white) to FFh
(Black), for example, at 256 gradation levels. The symbol "h" indicates hexadecimal notation. The image signal e indicates the ECL voltage level obtained by D / A converting some image signal values. For example, the first pixel indicates a voltage of FFh of the highest density pixel level, the second pixel indicates a voltage of 80h of the halftone level, the third pixel indicates a voltage of 40h of the halftone level, and the fourth pixel indicates a voltage of 20h of the halftone level. The comparator 4 generates a PWM signal having a pulse width (time length) corresponding to the pixel density to be formed by comparing the triangular wave signal d with the image signal e. The pulse width corresponding to the low density pixel becomes narrower.

Then, this PWM signal is converted into a TTL level of 0 V or 5 V to become a PWM signal f, which is input to the laser driver circuit 6. By changing the exposure time per pixel corresponding to the PWM signal value obtained in this way, it is possible to obtain 256 gradations with one pixel. Note that h in FIG. 4 indicates the laser beam exposure area shape of the photoconductor corresponding to each drive pulse width. The area shape of each dot latent image substantially corresponds to this exposure area shape. In FIG. 4, the horizontal axis represents time for the signal waveforms a to g, and the horizontal axis represents distance in the beam scanning direction for h.

Hereinafter, various measuring methods used in the present invention will be described.

A specific example of the measurement of the particle size of the toner used in the method of the present invention will be described. 0.1 to 5 ml of a surfactant (alkylbenzene sulfonate) is added to 100 to 150 ml of pure water, and 2 to 20 mg of a measurement sample is added thereto. The electrolytic solution in which the sample is suspended is subjected to dispersion treatment for 1 to 3 minutes with an ultrasonic disperser,
Laser Scan Particle Size Distribution Analyzer CIS-100
(Manufactured by GALAI) to measure the particle size distribution and the like. In the present invention, particles of 0.5 μm to 60 μm were measured, and the number average particle diameter (Dn) and volume average particle diameter (Dv) were determined by computer processing.

In the method of measuring the particle size of the carrier used in the present invention, the particle size of the carrier is randomly extracted by 300 or more using an optical microscope, and the size of the carrier is measured by an image processing analyzer Luzex3 manufactured by NIRECO CORPORATION. The diameter was measured as the carrier particle diameter, and the number average particle diameter was calculated.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.

<Example> (Example of developer preparation) A cyan toner is used as a toner.

Methanol 90 parts by weight Polyvinylphenol 5 parts by weight Styrene 25 parts by weight n-butyl acrylate 5 parts by weight Azobisisobutyronitrile 2 parts by weight Copper phthalocyanine pigment 1.5 parts by weight Chromium complex salt of di-tert-butylsalicylic acid 1 0.0 parts by weight After thoroughly mixing and dissolving the above materials, a thermometer,
The reactor was fitted with a stirring device and a reflux condenser, and the reactor was purged with nitrogen. The reactor was heated to 65 ° C. under a nitrogen stream and reacted for 15 hours.

The obtained reaction product was filtered, and the filtrate was diluted with methanol, sufficiently stirred, and then filtered again. This operation was repeated several times. The obtained residue was sufficiently dried with a vacuum dryer to obtain polymer particles.

100 parts by weight of the above fine powder and 1.2 parts by weight of the hydrophobicized titanium oxide fine powder were mixed with a Henschel mixer to prepare a negatively chargeable cyan toner. At this time, the volume average particle diameter (Dv) was 3.7 μm, and Dv /
Dn was 1.08.

Next, a method for producing a carrier will be described.

Phenol 10% Formaldehyde 6% (Formaldehyde about 40%, Methanol about 10%, rest is water) Magnetite (particle size 0.24 μm) 36% α-Fe ₂ O ₃ 48% The above materials and a basic catalyst 28 % Ammonia water, calcium fluoride as a polymerization stabilizer, and water were placed in a flask, and the temperature was raised to and maintained at 85 ° C. over 40 minutes while stirring and mixing, followed by reaction and curing for 3 hours. Thereafter, the mixture was cooled to 30 ° C., and after adding 0.5 l of water, the supernatant was removed.
The precipitate was washed with water and air-dried. Then, this was reduced under reduced pressure (5
(Hg mmHg or less) at 50 to 60 ° C. to obtain a spherical carrier core in which magnetite and hematite are combined with a phenol resin as a binder.

The surface of the obtained core particles was coated with a thermosetting silicone resin by the following method.

That is, a 10% by weight carrier coating solution was prepared using toluene as a solvent so that the coating resin amount was 1% by weight. The solvent was volatilized while continuously applying shear stress to the coating solution to coat the carrier.
The coated carrier particles are cured at 250 ° C. for 1 hour,
After crushing, the particles were classified with a 100-mesh comb to obtain carrier particles. The number average particle size of the obtained carrier particles is ヽ 0 μm.
m.

(Comparative Example of Preparation of Developer) 100 parts by weight of a proboxylated bisphenol and fumaric acid 5 parts by weight of a polyester resin obtained by condensation 5 parts by weight of a copper phthalocyanine pigment These were sufficiently preliminarily mixed, and then melt-kneaded. After cooling, the mixture was roughly pulverized to a particle size of about 1 to 2 mm using a hammer mill. Next, it was pulverized by a pulverizer using an air jet method. Further, the obtained finely pulverized product was classified using an elbow jet classifier to obtain a negatively charged cyan powder.

A cyan toner was prepared by mixing 100 parts by weight of the above fine powder and 0.8 parts by weight of the hydrophobicized titanium oxide fine powder using a Henschel mixer. At this time, the volume average particle size (Dv) was 3.9 μm, and Dv / Dn was 1.42.

Next, a method for producing a carrier will be described.

A carrier core was prepared in the same manner as in the above-described developer preparation example, and the coating resin was prepared in the same manner as in the developer preparation example, except that a styrene acrylic resin and a fluororesin were used in a 7: 3 blend. Was done.

(Results of Examination of Example) The toner and carrier prepared as described above were mixed so that the toner concentration was 4.0% by weight, and the mixture was shaken at 250 rpm with a good shaker.
The mixture was shaken for a minute to obtain a developer.

The charge amount distribution of the toner was measured with an E-SPART analyzer (manufactured by Hosokawa Micron Corporation).
The result as shown in FIG. 1 was obtained. The horizontal axis in FIG. 1 indicates the toner specific charge (Q / M), and the vertical axis indicates the particle diameter. Each dot in the graph corresponds to one toner.

Comparing the example with the comparative example, it can be seen that both of the toner charge amount distributions are broad. Since the particle size distribution of the toner of the example is very sharp, it can be seen that most of the toner is concentrated around 3.5 μm.

On the other hand, in Comparative Example, since the particle size distribution was wide,
It can be seen that there are many toners having a high charge amount of μm or less.

This developer was placed in a developing device, and an image was formed using a modified full-color laser copying machine CLC-500 manufactured by Canon. In FIG. 5, the distance between the developing sleeve 109 and the developer regulating member 114 is 600 μm, and the distance B between the developing sleeve 109 and the electrostatic latent image carrier is 500 μm. The development nip at this time was 4.7 mm.
The peripheral ratio between the developing sleeve 109 and the photosensitive drum 111 is 1.75: 1, and the developing condition is a rectangular wave having an alternating electric field of 2 kV (peak-to-peak voltage) and a frequency of 2 kHz, and a developing bias of -470 V. Set.

Further, the toner development contrast (Vcont)
The voltage was 350 V and the fog removal voltage (Vback) was 100 V.
The primary charging of the photosensitive drum 111 was -560V.
Under these developing conditions, the digital latent image on the photosensitive drum 11 is developed, and observation of the developed image on the photosensitive drum 111 and V
The measurement of the toner concentration on the transfer paper with respect to vcont was performed.
In the untransferred image formed on the photosensitive drum 111, the same amount of toner was observed in both the example and the comparative example. The image density after the transfer was as shown in FIG. The developer of the example has excellent image reproducibility in the highlight portion compared to the comparative example, and the density rises from the low contrast portion, indicating that the transferability of the highlight portion is excellent.

[0075]

As is apparent from the above description, according to the present invention, it is possible to achieve both high image quality and high transfer efficiency by making the toner finer, and to obtain a high quality image with high gradation. it can.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a toner charge amount distribution in a developer.

FIG. 2 is a diagram illustrating image density on transfer paper.

FIG. 3 is a block diagram illustrating a configuration of a PWM circuit.

FIG. 4 is a diagram showing a signal waveform of a PWM method.

FIG. 5 is a sectional view of a developing device.

[Explanation of symbols]

 9 Semiconductor laser 101 Developing unit 106 Toner storage chamber 107 Developer 108 Stirring screw 109 Developing sleeve 110 Conveyor screw 111 Photosensitive drum 112 Developing unit 113 Magnet 114 Developer regulating member

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/09 G03G 9/10 351 F-term (Reference) 2H005 AB06 BA02 BA06 EA05 FA02 2H031 AC08 BA05 BA08 BA09 CA10 DA03 2H073 AA01 BA03 BA13 BA43 CA03

Claims (5)

[Claims] 1. A developer containing at least a toner and a carrier forms a magnetic brush on a developer carrier, and an electrostatic latent image formed on the image carrier is visualized by toner. Wherein the volume average particle diameter of the toner is 2 to 6 μm and the ratio (Dv) between the volume average particle diameter (Dv) and the number average particle diameter (Dn) is
/ Dn) is 1.00 to 1.20, and the image bearing member is an electrophotographic photosensitive member, and the electrophotographic photosensitive member is formed by a light beam modulated by a pulse width modulated signal corresponding to the density of a recorded image. An image forming method comprising exposing a body to form a dot distribution electrostatic latent image. 2. The image forming method according to claim 1, wherein the toner is polymerized in a hydrophilic solvent in which a monomer is dissolved and a polymer of the monomer is not dissolved. 3. The carrier according to claim 1, wherein the carrier is a magnetic carrier and has a particle size of 10 to 50 μm.
The image forming method as described in the above. 4. The image forming method according to claim 1, wherein the carrier is a resin-coated carrier. 5. The image forming method according to claim 1, wherein a vibration bias voltage is applied to said developer carrier.