JP3047074B2 - High density 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 which can obtain high-density image quality by using the method and can reduce the size of the 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 into a magnetic brush shape 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 a subsequent stage and development is performed.

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, the toner density is suppressed to a lower level. However, generally, the developing efficiency tends to be low, and the density of a solid portion or the like tends to be 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 the above proposal is optimal as a countermeasure for such defective charged particles, the degree of freedom of the developer in the development area, that is, the development nip portion is small, so that the developer strongly hits the photosensitive member, After the image is swept easily, the image may be deteriorated. For this reason, there are methods of lowering the saturation magnetization of the carrier and lowering the magnetic strength of the magnet roll in the developing sleeve. However, such a simple method cannot prevent carrier pulling.

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

In recent years, miniaturization has been desired in the development of full-color developing systems and the like, and development of a developing device using a sleeve having a diameter of 20 mm or less and having no carrier pulling is urgently required.

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 device and 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 a range of 3 to 10% by weight, and the developer is contained in a 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 ). 30 <R <75
Developing is performed under the condition satisfying the following condition. At a developing sleeve surface located on a line connecting a position where the magnetic brush of the developer finishes rubbing with the photosensitive drum surface and the center of the developing sleeve, a magnetic force in a tangential direction is applied. X is 430 gauss or more, or tangential magnetic force X is less than 430 gauss and normal magnetic force Y is Y ≧ −X + 800 (gauss)
And the position Yp on the developing sleeve surface where the normal direction magnetic force is maximum.
Is positioned 0.035 to 0.5 radians upstream from the position closest to the surface of the photosensitive drum with respect to the developer conveyance direction.

The present invention can also be characterized in that the maximum magnetic force on the sleeve surface is 1000 gauss or less.

The present invention can further 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 ), a distance H (also referred to as a distance between DS and DS) on a line connecting the centers of both the photosensitive drum and the sleeve, a toner weight fraction (T / D) in the developer, and a true density of the toner (Ρt; g / c
m ³ ), the carrier weight fraction in the developer (C / D) and the true density of the carrier (ρc; g / cm ³ ), the flow state of the two-component developer in the development zone is remarkably improved. hand,
Even under the developing conditions where the image density is high, toner scattering is effectively suppressed, and the magnetic force and the direction of the magnetic force at the position of the developing sleeve surface at which the developer finishes rubbing with the photoreceptor are set in a specific range. Is set based on the finding that carrier pulling is sufficiently prevented during development, and particularly, defects at the rear end of a solid image portion due to carrier pulling are prevented.

Further, in the present invention, the position Yp at which the normal direction magnetic force on the developing sleeve surface is maximized is positioned 0.035 to 0.5 radians upstream from the position closest to the photosensitive drum surface with respect to the developer transport direction. . That is, assuming that the radius of the developing sleeve is r, the position Yp is set at a distance of 0.035r to 0.5r from the center of the developing area (located on a straight line connecting the center of the photosensitive drum and the center of the developing sleeve). It is important to shift to the upstream side in the developer transport direction. When the position Yp at which the normal magnetic force is maximized is set at such a position, the degree of freedom of the magnetic brush in the development area increases, and the volume occupancy (R) of the developer occupying the development area is greatly increased. As a result, even when a small developing sleeve is used, an image with good image quality can be formed.

That is, the volume occupancy (R) of the developer is represented by the above formula (1).
Can be set to an extremely wide range of more than 30% and less than 75%. By setting the volume occupancy (R) within such a range, toner scattering is effectively prevented, High density images can be formed.

First, when the developer occupation ratio (R) becomes 30% or less,
The volume occupied by the developer in the DS-developing 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.

In the case where the developer tends to be clogged between DS, the state of the developer brush has a great effect, and the state of the developer brush is influenced by the maximum value of the magnetic force in the normal direction described later. In this case, the developer occupation ratio (R) is 75
% Or more, the developer is too tight in the valley between DS and
The developer does not flow smoothly, and a considerable load is applied to the developer sleeve due to the effect, the rotation of the sleeve is not performed smoothly and the developer is disturbed, and the toner is easily scattered on the upper side of the valley. . On the contrary,
In the range specified by the present invention, the flow of the developer is smoothly performed through the valley between DS in the development area, while the above-described airflow is prevented, and the toner scattering is prevented even when the toner concentration is high. Is effectively prevented.

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 10% by weight, especially 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 75%.

Further, in the present invention, as is clear from FIGS. 4 and 5 obtained by an experimental example described later, the state of the magnetic force that appears on the surface of the developing sleeve when the developing layer is rubbed is important. It is important that the magnetic force X in the tangential direction on the developing sleeve surface (the position indicated by P in FIG. 2) corresponding to the position where the rubbing with the photosensitive member surface ends 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 is sufficiently resilient to the photoconductor surface at a position away from the photoconductor. Such a brush state has a great effect on the rubbing portion, which is a development area, and there is no carrier pulling even when the diameter of the sleeve is small and the strength of the main pole in the rubbing portion cannot be sufficiently secured, 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 device satisfying the above-mentioned relationship, no carrier pulling occurs and the device is stuck on the sleeve surface at the sliding portion as in the case of X ≧ 430 Gauss. The above function is sufficiently exhibited.

Further, in the present invention, the position Yp at which the magnetic force in the normal direction on the developing sleeve surface is maximized is set to the position closest to the photosensitive drum surface (the center of the developing area;
From the position indicated by) to the upstream side with respect to the developer conveyance direction by 0.035 to 0.5 radians. The fact that the magnetic force in the normal direction is maximum at such a position means that the magnetic brush is attracted by the magnetic force toward the tangential direction in the developing area and is in a state of being neglected on the sleeve surface. . In this case, it is possible to satisfy the tangential magnetic force value at the point P, which is important as described above. As described above, the fact that the magnetic force in the normal direction becomes maximum at the above-mentioned position means that the magnetic brush does not strongly hit the photoconductor in the development area during development, and the developer occupancy (R)
In addition to the effect of the above, the degree of freedom of the magnetic brush is increased. In such a state of the developer brush, the image quality can be improved and the effective rubbing area can be largely expanded, so that the diameter of the developing sleeve can be reduced and reduced.

Further, 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 to use a carrier having a low saturation magnetization, and the magnetic brush of the soft developer can be used. A sharp development can be performed by forming a brush. Also, alternating poles in the sleeve,
That is, it is desirable that the maximum magnetic force appearing on the sleeve surface in the normal direction be 1000 Gauss or less, particularly 900 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.

(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. The point S shown in FIG. 2 of the sleeve 12 is the position of the sleeve surface at the shortest distance between the photoreceptor surface 14 and the surface of the sleeve 12, and the point P corresponds to the position where the rubbing of the developer is completed. This is the intersection of the straight line connecting the rubbing end position on the photoreceptor surface 14 and the center of the magnet roll with the surface of the developing sleeve.

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.

In the present invention, from the position of the point S, 0.035r to 0.5r (r is the radius of the sleeve), especially 0.14r
The maximum value Yp in the normal direction is set in the range of 0.42r to 0.42r, and the maximum magnetic force may be either N or S pole, but is preferably set to 1000 Gauss or less, particularly 900 Gauss or less. On the sleeve set in such a range, the magnetic brush tends to be kept soft in the sprung state in the developing area.

The diameter of the developing sleeve 12 in the present invention is 15 to 50.
It is possible to use the developing sleeve 12 within a range of mm, and particularly when the developing sleeve 12 is used at a distance of 20 mm, the area occupied by the developing sleeve 12 in the developing mechanism is reduced.

Further, the developer application amount (the supply amount M of the developer per unit area of the sleeve) and the DS distance are within the above-mentioned ranges in which the volume occupancy (R) of the developer represented by the above formula (1) is obtained. Set as follows.

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 / m ³ , particularly 1.10 to 1.20 g / mm ³ , 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
It 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,
Styrene resins, acrylic resins, styrene-acryl resins, polyesters, epoxy resins, rosin-modified maleic resins, silicone resins, xylene resins, polyvinyl butyral resins, 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, it is preferable that the glass transition temperature (Tg) is 50 to 65 ° C.

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 rutile 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 10% by weight,
In particular, it is in the range of 3.5 to 7.5% by weight.

The electric resistance of the whole developer is preferably in the range of 1 × 10 ^{8 to} 1 × 10 ¹² Ω · cm, particularly 5 × 10 ^{9 to} 5 × 10 ¹¹ Ω · cm.

Other Development Conditions The amount M of the developer applied is preferably in the above-described range.
This depends on both the peripheral speed of the developing sleeve and the magnetic flux density and the spike length of the developing sleeve. For this reason, the magnetic pole of the developing sleeve is generally 500 to 1000 Gauss, especially 650
~ 850 Gauss is good, the peripheral speed of the developing sleeve is 60 to 800 cm / sec, especially 90 to 450 cm / sec,
The cutting length depends on the magnetic flux density, but 0.6 to 1.6 mm, especially
A range of 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.

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 another developing condition, the bias voltage applied between the developing sleeve and the photoconductor conductive substrate has an average electric field strength of 10
Those having a range of 0 to 1000 V / mm, particularly 125 to 800 V / mm are preferable.

 Hereinafter, experimental examples and comparative examples according to the present invention will be described.

(Experimental Example 1) Based on the following developing conditions, the positions of 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 position of the cutting gap are variously changed. Changed the image.

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, photoconductor drum: organic photoconductor for negative charging, photoconductor surface potential: -700V, developing bias potential: -500V, developing magnetic pole: the position of the maximum magnetic force in the normal direction is at the center between the magnet roller and the photoconductor drum. On the connecting line, the magnetic force in the normal direction at point P is 63
0 gauss, 150 gauss tangential magnetic force at point P, toner:
Toner with a true-density of 1.11 g / cm ³ with a median diameter of 11 μm based on a volume of carbon black dispersed in polyester, carrier: Ferrite core resin-coated with a saturation magnetization of 55 em
Carrier with u / g, electrical resistance of 5 × 10 ⁹ Ω · cm and true density of 5 g / cm ³ .

From the results in Table 1, when the position Yp where the magnetic force in the normal direction on the developing sleeve surface is maximum is located at the center of the developing area, toner scattering and fogging are prevented and a high density image is obtained. The volume occupancy (R) of the developer is 30-40%
It can be seen that it is limited to a very narrow range.

For example, in Experiment No. 1, when the ear-cut gap was widened and the developer application amount M was set to 0.111 g / cm ² (volume occupancy R = 37.3%), toner scattering and fogging were effectively prevented. , A high density image was obtained (Experiment No.
1 '). Further, in Experiment No. 3, when the distance H between DS was set to be 0.07 cm narrower (volume occupancy R = 40.2
%), Toner scattering occurred, and density unevenness occurred in the image (Experiment No. 3 ').

(Experimental Example 2) In Experiment No. 3 'and Experiment No. 4 of Experimental Example 1, the position Yp of the maximum magnetic force in the normal direction of the developing magnetic pole was set to 0.04 radian from the center of the developing area to the upstream side in the developer conveying direction. At the end of the development zone (point P in FIG. 2).
A similar experiment was performed with 590 Gauss and the tangential magnetic force X set to 220 Gauss.

As a result, the occurrence of toner scattering and fogging was effectively suppressed, and further, a high-density clear image was obtained without sweeping of the image area by the carrier or adhesion of the carrier.

Therefore, by moving the position Yp of the maximum magnetic force in the normal direction from the center of the developing area to the upstream side in the transport direction of the developer, even when the volume occupation ratio R of the developer exceeds 40%, toner scattering or fogging can occur. It can be seen that high density images can be obtained.

(Experimental Example 2) The developer occupancy of Experimental Example 1 was 40.2% and 43.2% (No. 4).
Under the condition (1), the position of the maximum magnetic force in the normal direction of the developing magnetic pole is moved 0.04R (R is the radius of the developing roller) to the upstream side in the rotation direction of the developing sleeve, and the magnetic force in the normal direction at the point P is reduced by 59.
When the magnetic force in the tangential direction at point 0 gauss and point P was 220 gauss, toner scattering and fogging were suppressed, and a high-density clear image was obtained with no sweeping of the image area by the carrier and no carrier adhesion.

(Experimental Example 3) By shifting the position of the maximum magnetic force in the normal direction of the developing magnetic pole in the rotating direction of the developing sleeve in Experimental Example 2, the effective developer occupancy is increased, and the sweeping of the image area by the carrier and Since it was confirmed that carrier adhesion can also be suppressed, the developer occupancy rate was changed variously,
An image was obtained by changing the positions of the magnet roller and the magnetic pole. 4 (A) and 4 (B) are magnetic force distribution charts at points S and P under the conditions of No. 6, and FIG.
FIG. 5 is a magnetic force distribution chart at points S and P in FIGS. 5 (A) and (B). The results are shown in Table 2 below.

From Table 2, the magnet roller is changed to move the position of the maximum magnetic force in the normal direction of the developing magnetic pole within a specific range to the upstream side in the rotation direction of the developing sleeve, and to move the position on the developing sleeve at the end of the rubbing area. It was confirmed that those having a specific relationship of magnetic force had good image density and fine line reproducibility, and were able to form high-quality images without image fogging, carrier adhesion, and no sweeping marks caused by carriers in the image area.

FIG. 6 is a plot of the magnetic force in the normal direction and the tangential direction on the developing sleeve and the presence or absence of carrier adhesion (sweeping trace due to carrier) on the developing sleeve in the end region of the developing rub in each experimental example. According to the figure, the relationship between the magnetic force (Y) in the normal direction and the magnetic force (X) in the tangential direction is Y ≧ −X + 800 (X <430),
It can be seen that carrier adhesion does not occur when ≧ 430.
In the drawing, ● represents the occurrence of carrier adhesion, and ○ represents the absence of carrier adhesion.

(Experimental Example 4) Under the developing conditions indicated by ○ confirmed in Experimental Example 3, as a magnetic carrier (saturation magnetization: 55 emu / g, particle size: 70)
μm, volume resistivity: 1 × 10 ⁹ −cm, carrier A (saturation magnetization: 45 emu / g, particle size: 65 μm, volume resistivity: 3 × 10 ¹⁰⁾
The same image formation was performed using the carrier B (Ω-cm), but in each case, a high quality image having excellent image characteristics without carrier adhesion and no trace of sweeping by the carrier was obtained.

(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 in the development zone during the development are expressed by the above formula (1). The volume occupancy (R) of the developer represented by the formula is more than 30% and 75%
High-density images with no toner scatter in a state of good fluidity of the developer passing through the development area because the position of the maximum value of the magnetic force in the normal direction is set to a specific position. Is formed, and the diameter of the developing sleeve can be reduced to reduce the size of the entire developing device.

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.

[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
Magnetic force distribution charts at points S and P, FIGS. 5A and 5B show magnetic force distribution charts at different points S and P, and FIG. 6 shows normal and tangential directions. FIG. 4 is a diagram showing a magnitude relationship of magnetic force of FIG.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihiro Watanabe 1-2-28 Tamazuki, Chuo-ku, Osaka-shi, Osaka Inside Mita Kogyo Co., Ltd. (72) Inventor Yoshihisa Kuramae 1-2-2 Tamazuki, Chuo-ku, Osaka-shi, Osaka No. 28 Mita Kogyo Co., Ltd. (56) References JP-A-63-4281 (JP, A) JP-A-2-79878 (JP, A) JP-A-62-192757 (JP, A) JP-A-4- 86868 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/09 G03G 15/08

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 10% 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 <75
Developing is performed under the condition satisfying the following condition.The tangential magnetic force is applied to the developing sleeve surface located on a line connecting the position where the magnetic brush of the developer finishes rubbing the photosensitive drum surface and the center of the developing sleeve. The magnetic force distribution is set so that X is 430 Gauss or more, or the magnetic force X in the tangential direction is less than 430 Gauss and the magnetic force Y in the normal direction satisfies Y ≧ −X + 800 (Gauss). At the developing sleeve surface where
Is a method in which a high-density developing method is characterized in that 0.035 to 0.5 radians is located on the upstream side of the developer conveying direction from the position closest to the surface of the photosensitive drum. 2. The developing method according to claim 1, wherein the maximum magnetic force on the developing sleeve surface is set to 1000 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.