JP3009436B2 - Development method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method used for a developing device such as a copying machine or a printer, and more particularly, to a two-component developer comprising a toner and a carrier. The present invention relates to a developing method that can obtain a high-density and high-quality image by using a developing method and that can reduce the size of a developing device.

(Prior Art) In the field of electrophotography, two-component magnetic developers are widely used as a means for developing an electrostatic latent image.
The two-component developer usually consists of toner particles containing a colorant and magnetic carrier particles, and is agitated during development. The toner and the carrier are frictionally charged by stirring, and the toner is attracted to the carrier surface by the charging. The developer in such a state is supplied onto a developing sleeve having a magnet therein, and is formed on a magnetic brush by suction of the internal magnet.
The developer is transported by the sleeve in this state, and is sent to the photoconductor having the electrostatic latent image.

The developer rubs against the photoreceptor surface as a magnetic brush, and the charged toner moves to the electrostatic latent image surface by a Coulomb force based on a potential difference from the electrostatic latent image surface to form a toner image. On the other hand, the magnetic carrier is attracted by the magnet in the sleeve and remains as it is on the sleeve. The toner image on the surface of the electrostatic latent image is transferred and fixed to a transfer paper or the like at the subsequent stage, and an image is formed.

In a two-component developer, the necessary conditions for obtaining a sufficient image density, no toner scattering, and maintaining these characteristics for a long period are determined by the compatibility between the toner and the carrier. As a general trend,
When the toner density is high, a high image density can be obtained, but the triboelectricity of the toner tends to be insufficient, the ability to bond with the carrier is reduced, and the toner enters and exits in the developing device becomes more intense. Some tendency is recognized. For this reason, in the conventional two-component developing method, although the toner density is suppressed to a lower level, the developing efficiency generally tends to be low and the density of a solid portion or the like is low.

To prevent this drawback, Japanese Patent Application Laid-Open No. 62-63970 discloses that an alternating electric field is formed between a drum and a sleeve, and the volume occupied by the magnetic carrier per volume between the drum and the sleeve is 1.5 to 30. It is proposed to be in the range of%.

(Problems to be Solved by the Invention) If the charging characteristics between the toner and the carrier in the two-component developer are sufficient, even when the toner concentration is high, the image density is high and the toner scattering is low. As expected, this is nearly impossible to achieve with commercial toners and development methods. That is, in toner production, defective toner particles that do not contain or contain a small amount of the charge control agent are necessarily generated at a certain probability, and the charge control agent is also used during development by mechanical force inside and outside the developing device. Is lost or toner particles having a reduced content occur at a certain frequency. Further, since uncharged toner particles for which the necessary charging was temporarily not obtained due to a change in the area ratio of the original or a change in the environment are included, toner scattering is inevitably generated. This leads to contamination inside the copying machine and contamination of the copy.

In another invention, the present inventors have found that in a developer using a two-component developer composed of a magnetic carrier and a toner, there is a key point in the flow state of the developer passing through the development area, and in relation to this flow state, It has been found that by setting the development conditions within a certain range, toner scattering can be effectively prevented even when a toner having a relatively high toner concentration and containing defectively charged particles is used. However, although optimal as a measure against such defective charged particles as proposed above, the developer in the development area, that is, the development nip portion has a small degree of freedom, so that the developer strongly hits the photoreceptor, and In some cases, after-sweep tends to occur and the image may be degraded. For this reason, lowering the carrier saturation magnetization,
Although there is a method of lowering the magnetic strength of the magnet roll in the developing sleeve, carrier pulling is seen to occur in such a simple method.

Also, digital copiers, which are becoming mainstream recently, perform halftone reproduction using a laser dot array. The quality of this image depends on how to prevent toner scattering around the dots (scattering around the dot image). Is an issue.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-density developing method which enables a high-density image without sweeping an image while preventing carrier pulling.

Another object of the present invention is to provide a high-density developing method capable of forming high-quality halftone images such as dot portions by transferring toner only to the latent image portions of finely formed dot portions. It is in.

In recent years, with the development of a full-color developing system that requires a plurality of developing devices, it has been desired to reduce the size of the developing device. The development of a developing device that does not cause pulling is urgent.

Thus, the object of the invention is also to reduce the size of the sleeve,
An object of the present invention is to provide a developing method capable of obtaining a high density image.

(Means for Solving the Problems) According to the present invention, a two-component developer comprising a magnetic carrier and a toner is supplied onto a developing sleeve having a magnet therein, and the developer is supplied to the developing sleeve. A developing method for developing an electrostatic latent image formed on the photosensitive drum by conveying the photosensitive drum in the form of a magnetic brush to a developing area between the photosensitive drum and rubbing the surface of the photosensitive drum; In the above, the photoconductor drum and the developing sleeve have a DS distance between 0.04 and 0.16, which indicates an interval at a position where they are closest to each other.
cm, the toner concentration in the developer is set in the range of 3 to 8% by weight, and the developer is contained per unit area of the developing sleeve.
An amount of 0.06 to 0.25 g / cm ² is supplied onto the developing sleeve, and the magnetic brush of the developer is supplied to the developing area after being cut to a height of 0.6 to 1.6 mm, and the following formula: M × (T / D × 1 / ρt + C / D × 1 / ρc) ÷ H (1) In the formula, M is a supply amount (g / cm ² ) of the developer per unit area of the sleeve, and H is , The DS distance (cm), T / D is the toner concentration weight fraction in the developer (% by weight), and C / D is the carrier concentration weight fraction in the developer (weight). %), Ρt is the true density of the toner (g / cm ³ ), and ρc is the true density of the carrier (g / cm ³ ). But 30 <R <40
And developing while applying an alternating bias voltage in which a DC voltage and an AC voltage are superimposed, and a position where the magnetic brush of the developer finishes rubbing with the photosensitive drum surface. The tangential magnetic force X is 430 gauss or more or the tangential magnetic force X is less than 430 gauss and the normal magnetic force Y is Y ≧ −X + 800 (gauss) on the developing sleeve surface located on the line connecting the center of the developing sleeve. Is set, and the magnetic force distribution is set so as to satisfy the following condition.

The present invention can further be characterized in that the maximum magnetic force on the sleeve surface is 1500 gauss or less.

The present invention can be characterized in that the developing sleeve is used with a diameter of 20 mm or less.

The normal direction is the radial direction of the sleeve, and the magnetic force in the normal direction means a value in the normal direction when the magnetic force is vector-decomposed. The tangential direction refers to the direction of the tangent when a tangent is drawn on the circumferential surface of the sleeve at the position where the developer finishes rubbing, and the tangential magnetic force is the tangential direction when the magnetic force is vector-decomposed. Value.

(Function) The present invention is directed to developing conditions, that is, the amount of the developer applied per unit area of the sleeve (M; g / g) so that the above-mentioned formula (1) is satisfied.
cm ² ), the distance on the line connecting the centers of both the photosensitive drum and the sleeve (H; cm, also referred to as the DS distance), the toner weight fraction (T / D) in the developer, and the toner True density (ρt; g
/ cm ³ ), the carrier weight fraction in the developer (C / D) and the true density of the carrier (ρc; g / cm ³ ) significantly improve the flow state of the two-component developer in the development area. Thus, toner scattering is effectively suppressed even under developing conditions where the image density is high, and the magnetic force at the position of the developing sleeve surface at which the developer finishes rubbing with the photoconductor and the direction of the magnetic force are changed. By setting the specific range, it is possible to sufficiently prevent carrier pulling during development, in particular, to prevent defects at the rear end of a solid image portion due to carrier pulling. This is based on the finding that dot-type electrostatic images can be developed with good image quality by applying an alternating bias voltage between the sleeve and the photoreceptor surface.

In the present invention, R defined by the above formula (1) indicates the volume ratio (%) of the two-component developer in the volume of the development area, and this developer volume occupancy (R)
Setting to a value greater than 30% and less than 40%
This is extremely important in preventing toner scattering.

First, when the development occupation ratio (R) becomes 30% or less, D
The volume occupied by the developer in the -S development area is reduced, and the magnetic brush in this area entrains air from above the valley between DS and transports it to below the valley between DS,
An airflow is generated, and the toner tends to be scattered together with the airflow inside the apparatus outside the developing device. On the other hand, when the developer occupation ratio (R) is 40% or more, the developer is excessively clogged in the valley between DS and D, and the developer does not flow smoothly. In addition, the rotation of the sleeve is not performed smoothly, so that the developer is disturbed, and the toner is easily scattered on the upper side of the valley.
On the other hand, within the range specified in the present invention, D
While the flow of the developer is smoothly performed through the valley between -S, the above-described generation of the air flow is also prevented, and the toner scattering is effectively prevented even when the toner concentration is high.

In the present invention, the relationship between the developer occupancy (R) and the various factors of the developing conditions is clear from the above equation (1). That is, R increases as the amount M of developer applied to the sleeve increases, and R decreases as the distance H between DS becomes larger. In general, ρt <ρc (3). Therefore, as the toner concentration (weight fraction) in the two-component developer increases, the developer occupancy increases.

In the present invention, the application amount (that is, the supply amount) of the developer on the developing sleeve surface is in the range of 0.06 to 0.25 g / cm ² , particularly 0.1 to 0.2 g / cm ² per unit area of the developing sleeve. The DS distance (H) is 0.04 to 0.16 cm, particularly 0.06 to 0.
The toner concentration of the developer used is in the range of 3 to 8% by weight, particularly 3.5 to 7.5% by weight. Within this range, the above-mentioned developer volume occupancy (R) is larger than 30%. And set to be less than 40%.

Further, in the present invention, as is clear from FIG. 5 obtained by an experimental example described later, the state of magnetism that appears on the developing sleeve surface when the developing layer is rubbed is important. It is important that the magnetic force X in the tangential direction on the surface of the developing sleeve (the position indicated by P in FIG. 2) located on the line connecting the position where the rubbing is completed and the center of the developing sleeve is 430 gauss or more. . As described above, the tangential direction means that the direction of the line of magnetic force is in a direction parallel to or inclined with respect to the sleeve surface. This can be set by the overall relationship between the strength and distance of the magnetic poles of the N and S poles provided alternately in the developing sleeve and the sleeve diameter. When the magnetic force X in the tangential direction satisfies the above range, the magnetic brush as a developer layer is sufficiently bent with respect to the photoconductor surface at a position away from the photoconductor.
It is understood that such a brush state acts largely also on the rubbing part, and even when the diameter of the sleeve is small and the strength of the main pole in the rubbing part cannot be sufficiently secured, there is no carrier pull, or An image with no missing image trailing edge is obtained. If the magnetic force X in the tangential direction is less than 430 Gauss, it is important to regulate the magnetic force Y in the normal direction at the rubbing portion end position, and the magnetic force Y in the normal direction is Y ≧ −X + 800 (Gauss).
It is important that The normal direction is a direction extending perpendicular to the sleeve surface, and means a state in which the magnetic brush of the developer is raised. As is clear from Table 1 of the embodiment described later, in the apparatus satisfying the above relationship, no carrier pulling occurs, and the developer sticks to the sleeve surface of the rubbing portion as in the case of X ≧ 430 Gauss. In this state, the above operation is sufficiently exhibited.

In the rubbing part, the magnetic brush of the developer is bound so as to stick to the surface of the sleeve, so that the magnetic force in the normal direction can be reduced and a carrier with low saturation magnetization can be used. It can be formed for sharp development. It is also desirable that the alternating magnetic poles in the sleeve, that is, the maximum magnetic force appearing on the sleeve surface in the normal direction be 1500 Gauss or less, particularly 1200 Gauss or less. If the magnetic force of the main pole is too large, a soft magnetic brush cannot be formed depending on the diameter of the sleeve, and a clear image cannot be obtained.

In the present invention, it is important to perform development while applying an alternating bias voltage, which is a combination of a DC voltage and an AC voltage, between the developing sleeve and the photosensitive drum. In the normal development or the reversal development, a constant DC bias electric field is formed between the developing sleeve and the photoconductor drum so that the toner is easily transferred to the latent image portion on the photoconductor surface. An AC bias electric field is superimposed on such a DC bias electric field to oscillate the bias potential. Such an alternating bias potential is desirably equal to or lower than the main charging potential of the photosensitive drum and equal to or higher than the residual potential. Further, the cycle depends on the peripheral speed of the sleeve.
It is preferably in the range of 4 kHz to 4 kHz.

Normally, the toner scattering described above appears around a dot portion which is an electrostatic image regardless of whether a normal image (surface potential is positive) or reversal development (surface potential is negative), and this toner is excessively transferred. The toner is not considered to be electrically attracted to the latent image part, and is considered to be the result of excessive amount of toner losing its place, and is physically or slightly electrically attached around the latent image part. it is conceivable that. However, when the alternating bias potential is overlapped as in the present invention, the toner physically attached to the periphery of the dot is again adsorbed and collected on the carrier having the opposite polarity when the bias potential is periodically low. As a result, adhesion of unnecessary portions due to toner scattering around the dots is prevented, and the image becomes clear. in this case,
As described above, since the carrier occupies the development occupation and the magnetic field at a specific value, the carrier has a degree of freedom on the surface of the developing sleeve and is apt to be slightly moved by the electrical amplitude. It is believed that this will make recovery more effective.

Therefore, by superimposing the alternating bias potential between the photoconductor and the developing sleeve, the image of the electrostatic portion formed with dots in a good state of the carrier is made clear.

(Embodiments of the Invention) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 to FIG. 3 are main part explanatory diagrams of the developing device according to the present invention.

In FIG. 1 for explaining a magnetic brush developing method used in the present invention, a magnet roll 11 having a large number of magnetic poles N and S is accommodated in a developing sleeve 12 made of a non-magnetic material such as aluminum. A photosensitive drum 15 including a base 13 and an electrophotographic photosensitive layer 14 provided thereon is provided with a small gap, that is, H, from the developing sleeve 12. The developing sleeve 12 and the photosensitive drum 15 are rotatably supported by a machine frame (not shown), and are driven so that the moving direction (arrow) at the nip position is the same direction (the rotating directions are opposite to each other). You. The developing sleeve 12 is located at an opening of the developing device 16, and a mixing and stirring device 17 for a two-component developer (that is, a mixture of a toner and a magnetic carrier) 18 is provided inside the developing device 16. Above it, a toner supply mechanism 20 for supplying toner is provided. After the two-component developer 18 is mixed by the stirrer 17 and the toner obtains a triboelectric charge, the toner is supplied to the developing sleeve 12,
The magnetic brush 21 is formed on the surface. This magnetic brush 21
Of the electrophotographic photosensitive layer
The photosensitive drum 14 is conveyed to a nip position where the electrostatic latent image is formed on the photosensitive layer 14 with toner.

The developing sleeve 12 is located at the opening of the developing device generally indicated by 23, the above-described scissor mechanism 22 is disposed on the supply side to the developing sleeve, and on the circulation side from the sleeve to the developing device. A developer receiver 25 having an opening edge 24 is disposed.

The developer application amount M can be set to a predetermined value by changing the peripheral speed of the sleeve 12, and by adjusting the interval between the sleeve 12 and the ear-cutting mechanism 22.

As shown in FIG. 2, the sleeve 12 is provided so as to be driven and rotated in the direction of the arrow, that is, counterclockwise. A magnetic brush, which is a two-component developer layer 21, is formed on the outer peripheral surface of the sleeve 12, and the magnetic brush 21 moves in the same direction as the sleeve rotation direction with the rotation of the sleeve 12.

The electrostatic latent image formed on the photoreceptor surface of the opposing photoreceptor layer 14 has a development area, that is, a rubbing portion with a magnetic brush (A in FIG. 2).
Portion), only the toner is transferred, whereby the latent image portion is developed. A point P shown in FIG. 2 on the surface of the sleeve 12 corresponds to a position where the rubbing of the developer ends, and a straight line connecting the rubbing end position on the photosensitive layer 14 to the center of the magnet roll and a developing sleeve. This is the intersection with the surface.

In the present invention, as shown in FIG. 3, a predetermined magnetic force acts from the internal magnet roll 11 at a point P, and the magnetic force is vectorized in a normal direction Y (perpendicular to the sleeve surface) and a tangential direction X. Disassemble and measure the scalar amount,
The value is set in a certain range. FIG. 4A shows a chart of the magnetic force acting on the sleeve surface in the normal direction. FIG. 4 (B) shows a chart of the magnetic force acting on the sleeve surface in the tangential direction. The equidistant reference circle of the sleeve 12 indicates the scalar amount (Gauss) of the magnetic force, and indicates the strength of the magnetic field in the normal direction and the tangential direction on the sleeve surface.

In the present invention, the magnetic force in the tangential direction X at the sleeve surface point P at which the rubbing is completed is X ≧ 430 Gauss,
The formation of such a magnetic force is performed by the magnet roll in the sleeve 12.
The adjustment is performed by adjusting the positional relationship between the N and S poles and the distance according to the radius of the sleeve. Also, the tangential direction X
Is less than 430 gauss, the value in the normal direction Y is limited, and is set so that Y ≧ −X + 800 gauss.

Development conditions The peripheral speed of the development sleeve is 60 to 800 cm / sec, especially 90 to 4
The cutting length is 50 cm / sec, and the cutting length depends on the magnetic flux density, but the range of 0.6 to 1.6 cm, particularly 0.8 to 1.4 mm is appropriate.

Further, the DS distance (H) is 0.4 to 1.6 mm, particularly 0.1 mm.
It is better to select from the range of 6 to 1.4 mm. The diameter of the developing sleeve 12 in the present invention can be used in the range of 15 to 50 mm, and particularly when the diameter is 20 mm or less, the occupied volume of the developing sleeve 12 in the developing mechanism section becomes small.

As the photoconductor, a photoconductor conventionally used in electrophotography, for example, a selenium photoconductor, an amorphous silicon photoconductor,
A zinc oxide photoreceptor, a cadmium selenide photoreceptor, a cadmium sulfide photoreceptor, and various organic photoreceptors are all used.

As a developing condition, a DC bias voltage applied between the developing sleeve and the photoconductor conductive substrate has an average electric field strength of 10
It is preferable that the voltage is in the range of 0 to 1000 V / mm, particularly 125 to 800 V / mm, and the alternating bias voltage superposed thereon is
A voltage having an amplitude of 100 to 800 V, particularly 300 to 700 V is used, and it is desirable that the superposed potential is between the surface potential of the photoconductor surface and the residual potential. Further, it is desirable that the cycle (frequency) of the alternating bias potential is in the range of 0.2 to 4 kHz, particularly 0.5 to 3 kHz.

Developer The magnetic carrier depends on the carrier concentration C / D, but generally has a density ρc of preferably 3.50 to 6.50 g / mm, particularly preferably 4.00 to 5.50 g / mm, and particularly a ferrite-based magnetic carrier is used. You.

Conventionally, as ferrite, for example, iron oxide zinc (ZnFe
₂ O ₄ ), yttrium iron oxide (Y ₃ Fe ₅ O ₁₂ ), cadmium iron oxide (CdFe ₂ O ₄ ), gadolinium iron oxide (Gd ₃ Fe
₅ O ₁₂ ), copper iron oxide (CuFe ₂ O ₄ ), lead iron oxide (PbFe
₁₂ O ₁₉ ), nickel iron oxide (NiFe ₂ O ₄ ), iron neodymium oxide (NdFeO ₃ ), iron barium oxide (BaFe ₁₂ O ₁₉ ), iron magnesium oxide (MgFe ₂ O ₄ ), iron manganese oxide (MnFe)
Sintered ferrite particles having a composition of one or more of ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ), and the like are used. Soft ferrite containing at least one, and preferably two or more, of the metal components used, for example, copper-zinc-magnesium ferrite, among these ferrites,
Those that satisfy the above conditions are used.

Carrier saturation magnetization is 40 to 65 emu / g, especially 45 to 56 em
It is preferably in the range of u / g. As the magnetic carrier, a ferrite carrier that satisfies the above conditions, particularly a spherical ferrite carrier, is preferable, and the particle size is 20 to 14 μm.
It is preferably in the range of 0 μm, especially 50-100 μm.

The electrical resistance of the ferrite carrier naturally varies depending on its chemical composition, but also varies depending on its particle structure, production method, coating type and thickness. Generally, its volume resistivity is 5 × 10 ^{8 to} 5 × 10
^It is preferably in the range of ¹¹ Ω · cm, particularly 1 × 10 ^{9 to} 1 × 10 ¹¹ Ω · cm.

The toner generally has a density ρt of 1.00 to 1.40 g / mm, particularly 1.10 to 1.20 g / mm, although it depends on the density of the magnetic carrier and the toner concentration.

The toner used in the present invention is obtained by blending a colorant and a charge control agent or a toner compounding agent known per se in a fixing resin medium. The toner used in the present invention also includes
1 × 10 ^{-11 to} 5 × 10 ^-8 S / cm, especially 5 × 10 ^{-10 to} 1 × 10
^It preferably has a conductivity of ^-9 S / cm, and its dielectric constant is preferably in the range of 2.5 to 4.5, especially 2.5 to 4.2.

The fixing resin medium for the toner, the colorant, the charge control agent and the other compounding agents for the toner are preferably selected and combined so as to obtain the above-mentioned properties. First, as a fixing resin medium,
A styrene resin, an acrylic resin, a styrene-acrylic resin, a polyester, an epoxy resin, a rosin-modified maleic resin, a silicone resin, a xylene resin, a polyvinyl butyral resin, and the like are used. Further, the resin used generally preferably has an acid value of 0 to 25. Further, from the viewpoint of fixability, the glass transition temperature (T
g).

As the colorant to be contained in the resin, any known inorganic or organic pigment or dye or the like may be used alone or in combination of two or more. For example, carbon black such as furnace black and channel black; iron black such as triiron tetroxide; titanium dioxide such as rutin type or anatase type; phthalocyanine blue; phthalocyanine green; cadmium yellow; And the like.

Examples of the charge control agent include any charge control agent known per se, for example, oil-soluble dyes such as nigrosine base (CI50415), oil black (CI20150), and spiron black, and 1: 1 or 2: 1 metal Complex salt dyes, metal (complex) salts of (alkyl) salicylic acid and naphthoic acid and the like are used.

The particle size of the toner particles, as measured by a Coulter counter, is preferably in the range of 8 to 14 μm, particularly 10 to 12 μm in terms of volume-based median, and the particle shape was determined by a melt kneading / pulverization method. It may be of a regular shape or a spherical shape produced by a dispersion or suspension polymerization method.

The toner weight fraction T / D in the developer is 3 to 8% by weight,
In particular, the concentration is set to a low concentration range of 3 to 7.5% by weight.

The electric resistance of the whole developer is preferably in the range of 1 × 10 ^{8 to} 1 × 10 ¹¹ Ω · cm, particularly 5 × 10 ^{9 to} 5 × 10 ¹¹ Ω · cm. In the present invention, when the toner weight fraction (T / D) in the developer is increased, it is necessary to decrease the developer application amount (M) and increase the DS distance (H) to increase the toner scattering. Effective for prevention.

 Hereinafter, experimental examples in which examples and comparative examples are shown are shown.

(Experimental Example 1) On the basis of the following developing conditions, the developer application amount M, the toner weight fraction T / D, the carrier weight fraction C / D, the distance between the drum and the sleeve, and the cutting gap were variously changed. An image was displayed.

Developing conditions Developing sleeve diameter: 20 mm, developing sleeve peripheral speed: 210 mm / se
c, photoconductor drum diameter: 60mm, photoconductor drum peripheral speed: 70mm / se
c, photoreceptor drum: organic photoreceptor for negative charging, photoreceptor surface potential: -700V, developing bias potential: -500V, developing magnetic pole: magnetic force of 330 gauss normal at point P, tangential at point P Magnetic force of 440 gauss, toner: polyester with carbon black dispersed, volume-based median diameter 11 μm, true density 1.
11g / cm ³ toner, carrier: Ferrite core resin-coated with saturation magnetization of 55 emu / g and electrical resistance of 5 × 10 ⁹ Ω ·
true density of 5g / cm ³ carrier cm.

From the results in Table 1, it was found that those having a developer occupancy in the range of 30 to 40% can prevent toner scattering and obtain a high-density image. Furthermore, 3 of the developer occupancy was applied amount expand the ear switching gap between 0.111 g / cm ² for those of No.1
When the image was displayed at 7.3%, toner scattering was prevented and the image density was improved. Also, for No. 3, when the distance between the drum and the sleeve was reduced to 0.07 cm and the developer occupancy was set to 40.2, density unevenness occurred in the image,
In addition, toner scattering occurred. As a result, the effectiveness of setting the developer occupancy to 30 to 40% was confirmed. On the other hand, although these images are good in image density and toner scattering, the rear end of the solid image is chipped, the carrier is swept in the image area, and the carrier is developed in some places in the non-image area. There was something.

(Experimental example 2) No. 2 and No. 3 of Experimental example 1 and the occupancy rate after 37.3%
Under the developing conditions described above, images were produced using developing magnets having various magnetic intensities. As shown in FIG. 5, the magnetic force in the tangential direction on the surface of the developing sleeve corresponding to the development end portion of the development area was reduced as shown in FIG. If it is 430 gauss or more, or if it is a magnetic force relationship that is above the straight line with the straight line of Y = -X + 800 in the figure, the image density can be maintained at a satisfactory level from the image, and the sweep trace by the magnetic carrier from the image It was confirmed that carrier adhesion was eliminated. In the drawing, ● indicates that carrier pulling or sweeping traces due to carriers on the image have occurred, and ○ indicates that the above-mentioned problem has not occurred.

(Experimental Example 3) Under the conditions using the developing magnet represented by ○ in FIG. 5 of Experimental Example 2, an AC voltage (frequency: 1 kHz) [-150 to -650 V, -150 to- 800
V, -50 to -650 V, -50 to -750 V], the toner was reduced at the periphery of the dot image. In particular, the effect was remarkable when applied in the range of the peak to the peak, and a clear and sharp good image was obtained. On the other hand, under the condition (1), the degree of fog was slightly inferior to that obtained by applying only the DC voltage. In the case of the sample, the carrier adhesion was slightly inferior to that in the case where only the DC voltage was applied. In the case of the toner, the toner scattering was slightly inferior to that in the case where only the DC voltage was applied.

As a result, the scattering of the toner around the dot image is suppressed by the application of the AC voltage. Was confirmed.

(Effects of the Invention) As described above, according to the present invention, the composition and density of the developer, the amount of the applied developer, and the distance between the drum and the sleeve satisfy the above (1) in the development zone during development. With such a setting, a high-density image without toner scattering can be formed in a state in which the developer passing through the developing area has good fluidity.

Also, the magnetic force generated on the developing sleeve surface, particularly the magnetic force in the tangential direction at the point where the developer layer finishes rubbing, is set to a specific range, or the magnetic forces in the tangential direction and the normal direction are set to a specific range. As a result, carrier pull during development can be reduced. In addition, it is possible to form a soft developer layer by using a carrier having a low saturation magnetization by reducing the magnetic force in the developing sleeve. Further, since the carrier has a degree of freedom and the alternating bias potential is superimposed, it is possible to prevent toner scattering around the electrostatic image portion formed by dots.

[Brief description of the drawings]

FIGS. 1, 2, and 3 are explanatory views of a main part of the developing method and the apparatus according to the present invention, and FIGS. 4 (A) and (B) are
FIG. 5 is a diagram showing a magnetic force distribution chart at a point P, and FIG. 5 is a diagram showing a magnitude relationship between a magnetic force in a normal direction and a magnetic force in a tangential direction.

Continuation of the front page (72) Inventor Masahiko Kubo 1-2-28 Tamazo, Chuo-ku, Osaka-shi, Osaka Inside Mita Industries Co., Ltd. (72) Inventor Kazuhisa Edahiro 1-2-28 Tamazo, Chuo-ku, Osaka-shi, Osaka (56) References JP-A-63-4281 (JP, A) JP-A-2-79878 (JP, A) JP-A-62-192757 (JP, A) Patent 2647237 (JP, B2) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G03G 15/08, 15/09

Claims (3)

(57) [Claims] 1. A two-component developer comprising a magnetic carrier and a toner is supplied onto a developing sleeve having a magnet therein, and the developer is supplied to a developing area between the developing sleeve and the photosensitive drum. A developing method for developing an electrostatic latent image formed on the photoconductor drum by conveying the photoconductor drum in the form of a magnetic brush and rubbing against the surface of the photoconductor drum; Is the distance between the DS indicating the distance between the two closest positions is 0.04 to 0.16 cm
The toner concentration in the developer is set in a range of 3 to 8% by weight.
The magnetic brush of the developer is supplied to the developing area after being cut off to a height of 0.6 to 1.6 mm, and is supplied to the developing area at the amount of 06 to 0.25 g / cm ^2. M × (T / D × 1 / ρt + C / D × 1 / ρc) ÷ H In the formula, M is the supply amount (g / cm ² ) of the developer per unit area of the sleeve, and H is the D- The distance between S (cm), T / D is the toner concentration weight fraction in the developer (% by weight), and C / D is the carrier concentration weight fraction in the developer (% by weight). , Ρt is the true density of the toner (g / cm ³ ), and ρc is the true density of the carrier (g / cm ³ ). R <40
And developing while applying an alternating bias voltage in which a DC voltage and an AC voltage are superimposed, and a position where the magnetic brush of the developer finishes rubbing with the photosensitive drum surface. The tangential magnetic force X is 430 gauss or more or the tangential magnetic force X is less than 430 gauss and the normal magnetic force Y is Y ≧ −X + 800 (gauss) on the developing sleeve surface located on the line connecting the center of the developing sleeve. A magnetic field distribution is set so as to satisfy the following. 2. The developing method according to claim 1, wherein the maximum magnetic force on the surface of the developing sleeve is set to 1500 Gauss or less. 3. The developing method according to claim 1, wherein a developing sleeve having a diameter of 20 mm or less is used.