JPH09305026A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method in which mechanical pressure applied to developer is reduced so as to hardly damage the developer and by which the initial characteristic of the developer is stably held even in the case of repeatedly using the developer. SOLUTION: In this image forming method; toner on a developer carrier 1 is made to fly onto an electrostatic latent image carrier 3 by a magnetic brush 2 so as to develop an electrostatic latent image 4. In the method, carrier for developing the electrostatic latent image satisfying a shape coefficient SF1 in an expression I and a shape coefficient SF2 in an expression II is used, and the moving direction of the developer carrier 1 is the same as the moving direction of the latent image carrier 3, then circumferential speed ratio between the developer carrier and the latent image carrier is adjusted within 0.5 to 1.8, so that the image is developed. The expression I: SF1 =(maximum length)<2> ×100π/4, provided that 100<=SF1 <=145 is set. The expression II: SF2 =(peripheral length of projected image)<2> ×100/(4π), provided that 100<=SF2 <=120 is set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming an image by a magnetic brush developing method using a two-component developer composed of a carrier for developing an electrostatic latent image and a toner.

[0002]

2. Description of the Related Art Conventionally, in a copying machine, a laser beam printer or the like, an image is formed by the Carlson method. The image forming method is to develop an electrostatic latent image formed on a photoconductor by an optical means with a developer, transfer it to a recording medium such as recording paper, and then fix it to the recording medium with heat or pressure. To do. At that time, since the photoconductor is repeatedly used, it is necessary to remove the toner remaining on the photoconductor after the transfer.
A cleaning device is installed.

The developing methods used for developing the electrostatic latent image include a one-component developing method using only toner and a two-component developing method using toner and carrier. In the two-component developing method, the toner is triboelectrically charged by agitating the toner and the carrier. Therefore, the triboelectric charge amount of the toner can be controlled to a considerable extent by selecting the characteristics of the carrier and the agitation conditions, so that the reliability of the image quality is improved. High and excellent.

As the developing method, there are a magnetic brush developing method, a cascade method and the like, but recently, the magnetic brush developing method is preferably used. The magnetic brush development method is a method in which the developer is conveyed to the development area by the magnetic force on the developer carrying roll, and the toner is attached to the electrostatic latent image to perform the development.

[0005]

Here, the developing machine is mainly composed of the developer carrying roll, a layer regulating member for controlling the amount of the developer conveyed to the developing area, and an auger for stirring the developer. ing. The developer and the additional toner are agitated by this auger to frictionally charge the toner. However, as a result of a detailed investigation, the inside of the developing device (pre-nip portion) of the layer regulating member and the layer regulating member and the developer carrying roll are separated. It was found that the toner was also triboelectrically charged on the developer carrying roll after passing through the gap (nip portion).

In the pre-nip portion, at least a larger amount of developer than the amount of the developer passing through the nip portion is conveyed by the developer carrying roll, and the developer is divided into the developer passing through the nip portion and the developer not passing through. The developer that cannot pass through the nip portion is subjected to pressure by the newly conveyed developer even while staying in the pre-nip portion, and the toner is further frictionally charged.

On the other hand, the developer that has passed through the nip portion is erected by a magnetic force to form a magnetic brush, and this magnetic brush rubs against the surface of the latent image carrier to attach toner to the electrostatic latent image. And develop. In this rubbing portion, the toner is frictionally charged.

However, since this triboelectric charging is performed by a physical external force such as contact or collision between the toner and the carrier, it inevitably damages both the toner and the carrier. For example, in a toner, an external additive added to the surface of the toner is embedded in the toner or a toner component is dropped. In addition, the carrier is contaminated with the toner constituent components including the external additive, and in the resin-coated carrier, the carrier coat component is worn or destroyed. These damages cause the initial characteristics of the developer to become unmaintainable as the number of times of copying increases, which may cause background fog, stains inside the machine, and fluctuations in image density.

In view of the above, the present invention solves the above problems, reduces the mechanical pressure on the developer and reduces damage to the developer, and maintains the initial characteristics of the developer even when the developer is repeatedly used. An object of the present invention is to provide an image forming method that can be stably held.

[0010]

The present invention has succeeded in solving the above-mentioned problems by adopting the following configuration. (1) In the image forming method of developing the electrostatic latent image by flying the toner on the developer carrying body onto the electrostatic latent image carrying body with a magnetic brush, the shape factor SF ₁ of the following formula (1) and the following formula The electrostatic latent image developing carrier satisfying the shape factor SF ₂ of (2) is used, and the moving direction of the developer carrying body is the same as the moving direction of the latent image carrying body, and the developer carrying body and the latent image carrying body are carried. An image forming method comprising: developing by adjusting a peripheral speed ratio with a body in a range of 0.5 to 1.8. SF ₁ = (maximum diameter length) ² × 100π / 4 (1) 100 ≦ SF ₁ ≦ 145 SF ₂ = (perimeter of projected image) ² × 100 / (4π) (2) 100 ≦ SF ₂ ≦ 120

(2) The image forming method as described in (1) above, wherein the carrier has a resin coating layer. (3) When the weight average particle diameter of the carrier is D ₅₀ ,
65 carriers within the range of 0.8 × D _{50 to} 1.2 × D ₅₀
The image forming method as described in (1) or (2) above, wherein the content is at least wt%. (4) The image forming method as described in any one of (1) to (3) above, wherein fine particles are dispersed in the resin coating layer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram for explaining the image forming method of the present invention. An electrostatic latent image 4 on a photoconductor roll 3, which is an electrostatic latent image carrier, is developed by a developer layer 2 (magnetic brush) carried on the roll 1 of the developer carrier to form an image 5. . At that time, the rotation directions of the developer carrying roll 1 and the photoconductor roll 3 are the directions shown by the arrows in the figure. Higher image quality can be obtained than when the rotation direction is opposite to that of FIG.

In the present invention, the peripheral speed ratio of the developer carrying roll to the photoconductor roll is set to a low level of 0.5 to 1.8. If the peripheral speed ratio is less than 0.5, the toner conveyance amount becomes too small, and the development density tends to decrease. If the peripheral speed ratio exceeds 1.8, excessive collision of toner and carrier and mechanical pressure that causes damage to them tend to be applied to the developer. The peripheral speed ratio is preferably in the range of 0.7 to 1.6.

In the present invention, when it is desired to supplement the toner conveyance amount, it is preferable to apply an AC bias, usually 1 to 4 kV, toward the developing region in addition to the DC bias. AC bias 1.4 to 2.5 is particularly preferable.
kV is applied toward the development area. The frequency at this time is selected in the range of 1 to 10 kHz.

In the present invention, the shape factor of the carrier constituting the two-component developer was determined by the following measuring method. That is,
It is based on a statistical method called image analysis, which can quantitatively analyze the area, the maximum length of the carrier image, the shape, etc. of a carrier image captured by an optical microscope with high accuracy. An image analyzer (manufactured by Nippon Regulator Co., Luzex 500)
0).

As is clear from the formula (I), SF ₁ is obtained by multiplying the value obtained by squaring the major axis of the carrier particle diameter by the area of the carrier particle by π / 4, and then multiplying it by 100. It is a numerical value, and the closer the carrier particle shape is to a sphere, the more 100
It becomes a value close to, and conversely, the longer it becomes, the larger the value becomes. In other words, the difference between the maximum length and the minimum length of the carrier represents the distortion of the carrier.

As is clear from the formula (II), SF ₂
Is a value obtained by dividing the value obtained by squaring the perimeter of the projected image of the carrier particles by the particle area of the carrier, multiplying by 1 / 4π, and multiplying by 100, and the shape of the carrier particles is a sphere. The closer to, the closer the value is to 100, and the more complex the surrounding shape, the larger the value. In other words, it expresses the carrier surface area (unevenness). For a perfect sphere, SF ₁ = SF ₂ = 100.

By adjusting the peripheral speed ratio of the developer carrying roll 1 to the photoconductor roll 3 in the range of 0.5 to 1.8, the mechanical force is reduced, and the contact between the toner and the carrier and the charge. Exchange is reduced, for example, the charging speed of the toner added in the developing machine becomes slow. Then, in the range of the peripheral speed ratio, the carrier shape factor SF ₁ = 100 to
When 145 and in the range of SF ₂ = 100 to 120, carrier fluidity is enhanced, charge exchange due to contact with toner is promoted, and the toner charge amount can be promptly brought to an appropriate charge amount level.

However, under the range of the peripheral speed ratio, when the range deviates from the range of SF ₁ , the stability of the charge amount, the stability of the image, the fog preventing property, etc. are not sufficient. Even when it deviates from the range of SF ₂ , it becomes impossible to sufficiently secure the same characteristics as SF ₁ . The rounder the carrier, the better the fluidity of the carrier, and the same is true for the developer mixed with the toner. Therefore, the contact probability between the toner and the carrier also increases as the shape of the carrier becomes rounder, so that the carrier is quickly charged.

In the carrier of the present invention, 65% by weight or more of the carrier is in the range of 0.8 × D _{50 to} 1.2 × D ₅₀ when the weight average particle diameter is D _50. Is preferred. When the amount of the small particle size carrier less than 0.8 times D ₅₀ increases, the fluidity of the carrier itself deteriorates and the magnetic force per unit decreases, so that the movement on the developing sleeve deteriorates. As a result, it may be difficult to obtain the fluidity of the developer, which is the object of the present invention. On the other hand, when the number of large particle size carriers exceeding 1.2 times D ₅₀ increases, the carrier surface area per carrier unit decreases, and it becomes difficult to convey the required amount of toner to the developing area. It may not be possible to obtain a high image density. The weight average particle diameter D ₅₀ is the value of the average particle diameter (μm) calculated from the mesh of the sieve when the carrier is passed through a predetermined sieve and the weight of the carrier remaining on the sieve is 50% by weight of the whole. Say.

The toner used in the present invention comprises at least a colorant and a binder resin. As the binder resin, styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, propylene, butylene and isoprene;
Vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl acetate; methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate. Α-methylene aliphatic monocarboxylic acid esters such as butyl methacrylate and dodecyl methacrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether; vinyl methyl ketone, vinyl hexyl ketone,
Examples thereof include homopolymers and copolymers of vinyl ketones such as vinyl isopropenyl ketone.

As typical binder resins, polystyrene, styrene / alkyl acrylate copolymer, styrene / alkyl methacrylate copolymer, styrene / acrylonitrile copolymer, styrene / butadiene copolymer,
Styrene / maleic anhydride copolymer, polyethylene, polypropylene and the like can be mentioned. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, waxes and the like can be mentioned. Among these, polyester is particularly effective. For example, a linear polyester resin comprising a polycondensate containing bisphenol A and a polyvalent aromatic carboxylic acid as main monomer components can be preferably used.

As the colorant for the toner particles, carbon black, nigrosine, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, Lamp black, rose bengal,
CI Pigment Red 48: 1, CI Pigment Red
122, CI Pigment Red 57: 1, CI Pigment
Representative examples include Yellow 97, CI Pigment Yellow 12, CI Pigment Blue 15: 1, CI Pigment Blue 15: 3 and the like.

The toner used in the present invention contains, in addition to the binder resin and the colorant, one or more fixing aids such as wax as an internal additive for improving the fixing property and a charge control agent for adjusting the charge. You may add.

Further, in order to further improve the long-term storage stability, fluidity, developability and transferability of the toner, inorganic powder and / or resin powder may be added to the toner surface. Examples of the inorganic powder include carbon black, silica, alumina, titania and zinc oxide, and examples of the resin powder include PMM.
Examples thereof include spherical particles of A, nylon, melamine, benzoguanamine, fluororesins, and the like, and further, amorphous powders such as vinylidene chloride and fatty acid metal salts. The amount added to the surface is 0.5 to 4% by weight, preferably 0.5 to 3
A weight percent range is suitable.

Further, the above surface-added powder can be used after being subjected to a desired surface treatment. The average particle size of the toner particles used in the present invention is smaller than about 30 μm,
A range of 4 to 20 μm is preferable.

The toner used in the present invention is produced by a known method. For example, as a dry method, a kneading / crushing method,
The wet method can be prepared by a suspension polymerization method, an interfacial polymerization method, or a liquid drying method. The kneading at this time can be performed using a known heating kneader, and specifically, a three-roll type, a single screw type, a twin screw type, a Banbury mixer type and the like can be used.

The toner crushing device includes, for example, Micronizer, Ulmax, Jet-o-mizer, KTM (Krypton), turbo mill, I type jet mill and the like. After the crushing step, a hybridization system (manufactured by Nara Machinery Co., Ltd.),
Mechano Fusion System (made by Hosokawa Micron),
It is also possible to adopt a Kryptron system (made by Kawasaki Heavy Industries, Ltd.) or the like.

In the present invention, the carrier particles are about 10
Those having an average particle size of less than 0 μm, preferably 30 to 60 μm can be used. As the carrier core material used in the present invention, at least one or more kinds of core materials selected from iron powder, ferrite, magnetite, and other known core materials can be selected. Depending on the conditions, it is preferable to use ferrite particles in order to reduce the developing torque.

Next, an example of producing ferrite particles used as a carrier core material will be shown. As a raw material, a metal oxide whose particle size was adjusted to 10 μm or less in advance was used in a molar ratio of Fe ₂ O ₃ : MgO: Z.
nO: MnO ₂ : CuO = 50: 25: 20: 1: 4 was prepared, mixed with a Henschel mixer or the like, and then pre-sintered in a kiln at 900 ° C. for 3 hours. The powder produced by the quasi-spinelization reaction by the preliminary sintering is mixed with water and pulverized with a ball mill for 10 hours. To this aqueous solution, a binder (polyvinyl alcohol) and a dispersant are added by several% by weight to obtain a slurry solution. The slurry is granulated and dried, and the granulated pellets are fired in an electric furnace at 1300 ° C. for 4 hours to obtain a ferrite powder composed of appropriate primary particles. This is sieved to remove coarse powder and fine powder to obtain carrier core particles having desired particle size and electric resistance.

The crystal growth of the primary particles at the time of sintering causes depressions on the bonding surface of the primary particles, and the generation ratio affects the shape factor. Therefore, a carrier having a desired shape factor can be obtained by controlling various properties such as the properties of raw materials, additives, calcination, calcination, and pulverization. In particular, if the firing temperature is increased, it tends to be spherical. Specifically, it is preferable to fire at a temperature of 1200 ° C. or higher.

The carrier core is suitable because a resin-coated carrier having the surface covered with a resin is excellent in charge imparting durability. The resin coating amount is 0.2 to 5% by weight, preferably 0.3 to 3% by weight, based on the whole carrier particles. If it is less than 0.2% by weight, the durability of charge imparting by the resin coat cannot be sufficiently obtained, and if it is more than 5% by weight, the production yield is lowered, resulting in an increase in the cost of producing the carrier, which is not preferable.

The resin for the carrier film may be silicone resin, fluororesin, acrylic resin, polyolefin resin, polyvinylidene chloride resin, phenol resin, epoxy resin, amino resin, polyamide resin, if necessary.
One kind or two or more kinds of polyester resin, polyurethane resin, polycarbonate resin and the like can be used. The shape factor of the carrier coated with resin on the surface of the core material varies from the shape factor of the core material itself depending on the properties of the resin to be coated, the coating method, and the coating amount. Is an important factor that greatly affects the shape factor of.

The shape factor of the resin-coated carrier is
It can be controlled by forming the coat layer by a dry method. Specifically, it can be controlled by changing the particle size of the fine powder and the melting conditions in the manufacturing method in which the resin fine powder is adhered and then heated and melted.

The type of fine powder is not particularly limited, but specifically, polyolefin resins such as polyethylene and polypropylene; polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, poly Polyvinyl resins such as vinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone, and polyvinylidene resins; vinyl chloride / vinyl acetate copolymers; styrene / acrylic acid copolymers; straight silicone resins composed of organosiloxane bonds or modified products thereof. Fluorine resin such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene; polyester; polyurethane; polycarbonate; phenol resin; Acid-formaldehyde resins, melamine resins, benzoguanamine resins, urea resins, amino resins such as polyamide resins; epoxy resin can be used.

The average particle size of these fine powders is from 0.05 to
Those having a thickness of 5 μm, preferably 0.05 to 2 μm are suitable. The shape may be crushed or spherical. The shape factor of the carrier can be controlled not only by the particle size of the fine powder, but also by the coating conditions of the carrier.

[0037]

EXAMPLES Production of Resin Coated Carrier (Resin Coated Carrier 1) Core Particles (Cu—Mg Ferrite Particles, Weight Average Particle Diameter D ₅₀ = 45 μm, SF ₁ = 140, SF ₂ = 117) 100 Parts by Weight Styrene / methacryl Methyl acid copolymer (copolymerization molar ratio = 6: 4, weight average molecular weight 100,000) 0.8 parts by weight Toluene 10 parts by weight The above raw materials were placed in a vacuum degassing type kneader, and the temperature was 10 ° C.
After stirring for 1 minute, the temperature was raised to 100 ° C. and the pressure was reduced to distill toluene off to obtain Resin Coated Carrier 1. This carrier is an image analyzer (made by Nippon Regulator Co., Ltd.,
The shape factor according to Luzex 5000) was measured, and the results are shown in Table 1.

(Resin Coated Carrier 2) Core Particles (Cu—Mg Ferrite Particles: Same as Example 1) 100 parts by weight Styrene-methyl methacrylate copolymer (same as Example 1) 2 parts by weight Carbon Black (Cabot Manufactured by Regal 330) 0.05 parts by weight Toluene 10 parts by weight The above raw materials are put in a vacuum degassing type kneader, and the temperature is 60 ° C.
After stirring for 1 minute, the temperature was raised to 100 ° C., the pressure was reduced, and toluene was distilled off to obtain a resin-coated carrier 2. In addition, carbon black was added to styrene / methyl methacrylate resin as a coating resin, diluted with toluene and dispersed in a sand mill for use.

(Resin Coated Carrier 3) Resin coated carrier 1 is the same as the resin coated carrier 1 except that the core particles are changed to Cu-Mg type ferrite particles having an average particle diameter of 60 μm and shape factors SF ₁ = 130 and SF ₂ = 110. Coated carrier 1
A resin-coated carrier 3 was obtained in the same manner as.

(Resin-coated carrier 4) Resin-coated carrier 1 is the same as resin-coated carrier 1 except that the core particles are changed to Cu-Zn ferrite particles having an average particle diameter of 40 μm and shape factors SF ₁ = 140 and SF ₂ = 115. Coated carrier 1
Resin coated carrier 4 was obtained in the same manner as in.

(Resin-coated carrier 5) Resin-coated carrier 1 is the same as resin-coated carrier 1 except that the core particles are changed to Cu-Zn ferrite particles having an average particle diameter of 48 μm and shape factors SF ₁ = 140 and SF ₂ = 115. Coated carrier 1
A resin-coated carrier 5 was obtained in the same manner as.

(Resin-Coated Carrier 6) Resin-coated carrier 1 is the same as the resin-coated carrier 1 except that the core particles are changed to Cu—Zn ferrite particles having an average particle diameter of 35 μm and shape factors SF ₁ = 145 and SF ₂ = 118. Coated carrier 1
A resin-coated carrier 6 was obtained in the same manner as in.

(Resin-coated carrier 7) In the resin-coated carrier 1, the coating resin was dry pulverized into particles having an average particle size of 1 μm, and the core particles and the resin particles were put into a horizontal rotary blade type mixer and horizontally. A resin-coated carrier 7 was obtained by mixing and stirring at a temperature of 30 ° C. for 20 minutes under the condition that the peripheral speed of the rotor was 8 m / s, then heating to a temperature of 110 ° C. and stirring for 40 minutes.

(Resin-coated carrier 8) Resin-coated carrier 1 is the same as resin-coated carrier 1 except that the core particles are changed to Cu-Zn ferrite particles having an average particle size of 50 μm and shape factors SF ₁ = 150 and SF ₂ = 123. Coated carrier 1
A resin-coated carrier 8 was obtained in the same manner as in.

(Resin-coated carrier 9) Resin-coated carrier 1 is the same as the resin-coated carrier 1 except that the core particles are changed to Cu-Zn ferrite particles having an average particle diameter of 50 μm and shape factors SF ₁ = 143 and SF ₂ = 123. Coated carrier 1
A resin-coated carrier 9 was obtained in the same manner as.

(Resin Coated Carrier 10) A resin coated carrier 10 was obtained in the same manner as the resin coated carrier 7 except that the particle size of the resin for coating was changed to 2.5 μm.

Toner Production (Magenta Toner Particles) Linear polyester resin 100% by weight (linear polyester obtained from terephthalic acid / bisphenol A ethylene oxide adduct / cyclohexandimethanol; Tg = 62 ° C., Mn = 4,000 , Mw = 35,000, acid value = 12, hydroxyl value = 25) Magenta pigment (CI Pigment Red 57) 3% by weight The above raw materials were kneaded with an extruder and pulverized with a dry pulverizer, and then winded. By using a type classifier, fine particles and coarse particles were classified to obtain magenta toner particles having D ₅₀ = 8 μm.

(Black Toner Particles) Linear Polyester Resin (Same as Magenta Toner) 100% by Weight Carbon Black (Cabot Co., Mogul L) 6% by Weight The above raw materials are kneaded with an extruder and a volume pulverization type pulverizer is used. After pulverization, the toner was classified into fine particles and coarse particles with an air classifier to obtain black toner particles having D ₅₀ = 9 μm.

(Cyan Toner Particles) Styrene-n-butyl methacrylate copolymer 97% by weight (copolymerization ratio: 70/30, Mn = about 7,000, Mw = about 40,000) Cyan pigment (β-type phthalocyanine: CI Pigment Blue 15: 3) 3% by weight The above raw materials are kneaded with an extruder, pulverized with a pulverizer that uses a combination of surface pulverization and volume pulverization, and then classified into fine and coarse particles with a wind classifier, and D Cyan toner particles of ₅₀ = 8 μm were obtained.

(Preparation of Toner Composition) 100 parts by weight of each of the above-mentioned magenta toner particles, black toner particles and cyan toner particles was prepared, and silica (manufactured by Nippon Aerosil Co., Ltd.,
R812) 0.5 parts by weight, Titania (Taika Co., M
0.8 parts by weight of T500B) was added and mixed by a high-speed mixer to obtain toner compositions 1, 2, and 3.

(Preparation of Developer) Toner Compositions 1 to 1 above
3 and the resin-coated carriers 1 to 10 were combined as shown in Tables 1 to 4, 7 parts by weight of the toner composition was added to 100 parts by weight of the carrier, and the mixture was mixed in a tumbler shaker mixer for evaluation. Used as a developer.

Examples 1 to 7 Resin coated carrier 1
7 and toner composition 1 were applied to a modified electrophotographic copying machine (A-Color 630, manufactured by Fuji Xerox Co., Ltd.), and the peripheral speed ratio of the developer carrying roll to the photoconductor was set to 0.7. Then, a copy test was performed on 10,000 sheets in an environment of medium temperature and humidity (22 ° C., 55% RH).

The obtained image was free from fluctuations in image density and scumming as a whole, and a stable image was obtained. Initial charge,
The amount of charge after copying 1,000 sheets and the amount of charge after copying 10,000 sheets were measured and are shown in Table 1 together with the fog on the copy. In addition,
Charge amount is charge spectrograph method (CGS method)
Is a value obtained by image analysis of. The solid density is measured by a spectrophotometric densitometer (X-Rite
404). It is desirable that this concentration be in the range of 1.45 to 1.35.

[Examples 8 and 9] In Example 1, resin coated carrier 1, toner composition 2 and toner composition 3 were used.
A copy test was conducted in the same manner as in Example 1 except that the developer was replaced with. In each of Examples 8 and 9, there was no background stain, a high-density high-quality image was obtained from the initial stage, and a stable image was obtained. Further, 10,000 copies were continuously copied, but almost no change in image quality was observed. The results for the amount of charge and upper fog are shown in Table 1.

Comparative Examples 1 to 3 The same copy test as in Example 1 was carried out except that the resin coated carriers 8 to 10 were changed. In each of Comparative Examples 1 to 3, there was background stain, and in-machine stain was also recognized. The amount of charge is
Measurements were made at the initial stage and after copying 1,000 sheets, and the fog on the copy is listed in Table 1.

[0056]

[Table 1]

[Examples 10 to 18] In Examples 1 to 9, the peripheral speed ratio of the developer carrying roll to the photosensitive member was 1.4.
The same copy test as in Example 1 was carried out except that the above was changed to. The images obtained in Examples 10 to 18 were stable images without fluctuations in image density or background stains. The initial charge amount, the charge amount after copying 1,000 sheets, and the charge amount after copying 10,000 sheets were measured and are shown in Table 2 together with the fog on the copy.

[Comparative Examples 4 to 6] Comparative Examples 4 to 6 were the same as Example 1 except that the resin coated carriers 8 to 10 were changed and the peripheral speed ratio of the developer carrying roll to the photosensitive member was changed to 1.4. A similar copy test was performed. In each of Comparative Examples 4 to 6, there was background stain, and in-machine stain was also recognized. The charge amount was measured at the initial stage and after copying 1,000 sheets, and is shown in Table 2 together with the fog on the copy.

[0059]

[Table 2]

Comparative Examples 7 to 18 Same as Example 1 except that the peripheral speed ratio of the developer carrying roll to the photosensitive member was changed to 0.4 in Examples 1 to 9 and Comparative Examples 1 to 3. A copy test was conducted. In the obtained image, the charge amount of the developer using the resin coated carriers 1 to 7 was stable,
The image density was generally low, and an image of poor quality was obtained. Further, in the developer using the resin coated carriers 8 to 10,
When copying 10,000 sheets, there was background stain, and stain inside the machine was also recognized.
The charge amount is shown in Table 3.

[0061]

[Table 3]

[Comparative Examples 19 to 30] In Comparative Examples 7 to 18, the peripheral speed ratio of the developer carrying roll to the photosensitive member was 2.
The same copy test as in Example 1 was performed except that the number was changed to 4. For all the developers, the charge amount was gradually decreased, and the obtained images had background stains, and images of poor quality were obtained. The charge amount is shown in Table 4.

[0063]

[Table 4]

[0064]

According to the present invention, by adopting the above constitution, the charging speed of toner particles is improved, the charge distribution range is narrow, and a stable charge amount is maintained even when continuously used for a long time. , It became possible to obtain a stable copy image. In addition, since the shape factor of the carrier is in a specific range, the flowability of the carrier is high, the chances of contact charging with the toner are increased, and uniform charging and a developer with a high charging speed are obtained, and the peripheral speed ratio is Is lower than that of the prior art, peeling of the coating layer of the carrier, less wear, and less toner impaction on the carrier, so that the charge imparting ability of the carrier can be maintained for a long time.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an image forming method of the present invention.

Claims (3)

[Claims] 1. An image forming method of developing an electrostatic latent image by causing toner on a developer carrying body to fly onto the electrostatic latent image carrying body with a magnetic brush, and a shape factor SF ₁ of the following formula (1) and An electrostatic latent image developing carrier satisfying the shape factor SF ₂ of the following formula (2) is used, and the moving direction of the developer carrying member is the same as the moving direction of the latent image carrying member. An image forming method comprising: developing by adjusting a peripheral speed ratio with an image carrier within a range of 0.5 to 1.8. SF ₁ = (maximum diameter length) ² × 100π / 4 (1) 100 ≦ SF ₁ ≦ 145 SF ₂ = (perimeter of projected image) ² × 100 / (4π) (2) 100 ≦ SF ₂ ≦ 120 2. The image forming method according to claim 1, wherein the carrier has a resin coating layer. 3. The carrier in the range of 0.8 × D _{50 to} 1.2 × D ₅₀ is 65% by weight or more, where D ₅₀ is the weight average particle diameter of the carrier. Claim 1
Or the image forming method described in 2.