JPH0774922B2 - High quality development method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high image quality development method in which toner scattering is prevented in electrophotography, and more specifically, high density and fine line reproducibility are also prevented while preventing toner scattering. The present invention relates to a developing method capable of obtaining a good clear image.

(Prior Art) In electrophotography, a two-component developer composed of a sensible toner and a magnetic carrier is used, and the developer is supplied onto a magnet sleeve to form a magnetic brush. The toner image is obtained by rubbing the formed electrostatic latent image carrier.

However, in this magnetic brush development method, it is not easy to obtain a sufficient image density, to prevent toner scattering, and to maintain these characteristics for a long time.

The optimum image means not only the image density but also the fine line faithfully reproduced and unnecessary toner not scattered around the image (hereinafter, simply referred to as toner dust). As a general tendency, the toner density is When it becomes higher, the high image density is obtained, but the toner supply amount in the thin line portion is inevitably increased, and the thin line may be reproduced thickly. Further, when the toner concentration is increased, the triboelectric charge of the toner is likely to be insufficient, and the toner has a low ability to combine with the carrier, and the toner flows in and out of the developing device violently. Also tends to increase.

Therefore, in the conventional two-component developing method, the toner density is set to be low in order to prevent toner scattering and toner dust, but generally the developing efficiency is low and the density of the solid portion is low, which causes toner scattering. Prevents toner dust, and
It is quite difficult to form a high-quality image with high density and good reproducibility of fine lines.

For example, in JP-A-62-63970, an alternating electric field that violently vibrates a magnetic brush is formed between an electrostatic latent image carrier and a sleeve, and a magnetic carrier occupies a volume between a drum and a sleeve. It has been proposed to use a volume in the range of 1.5-30% to obtain high image quality. This method uses a developer with a high toner concentration and sets the absolute amount of the developer (magnetic carrier and toner) conveyed in the development area to a small value, while the peak potential is the maximum potential of the electrostatic latent image (bright part potential). ) Above and below the minimum potential (dark portion potential) respectively, the toner is ejected by the vibration of the magnetic brush to increase the effective developing toner amount to obtain a high density image. .

(Technical problem to be solved by the invention) In a two-component developer, matching between a magnetic carrier and a toner is important, but it is easy to eliminate defective charged particles in the toner obtained from the current toner manufacturing method. is not. This is because the toner is a resin particle in which various additives such as a charge control agent are dispersed in a binder resin, and there is a possibility that these additives are not contained or there is a small content. is there. For this reason, when developing with a high toner density in order to obtain a high density image, the influence of uncharged or low charged defective charged particles is further increased, which causes toner scattering and toner dust. Further, as a result of repeated studies by the present inventors, when the ratio of air in the space in the developing region increases, the electrostatic latent image carrier and the developing sleeve rotate with respect to each other. It was found that an air flow is generated toward the upstream side), and this air flow is a factor that scatters the toner out of the developing device.

Therefore, the inventors of the present invention have a key point in the flow state of the developer passing through the development area in the developing method using the two-component developer including the magnetic carrier and the toner, and the development conditions are related to this flow state. When the toner density is set to a certain range, a high density image can be obtained while preventing toner scattering and toner dust even when using a toner having a high toner density and containing a large amount of uncharged or low charged particles. We found that the fine lines were faithfully reproduced.

Therefore, it is an object of the present invention to provide a developing method using a two-component developer capable of obtaining a good image having high density and excellent fine line reproducibility while preventing toner scattering.

Further, it is an object of the present invention to provide a developing method using a two-component developer which prevents adverse effects of uncharged and weakly charged particles.

(Means for Solving the Problems) According to the present invention, a two-component developer including a magnetic carrier and toner is conveyed from a developing device to a developing area by a developing sleeve, and the electrostatic latent image bearing member on the electrostatic latent image bearing member is conveyed in the developing area. In the developing method comprising developing the latent image and circulating the developer of the developer to the developing device, the following formula 30 <M × (T / D × 1 / ρ _t + C / D × 1 / ρ _c ) ÷ H × 100 <40 (1) In the formula, M is the coating amount of the developer per unit area of the sleeve (g / cm ² ), and H is the closest contact between the electrostatic latent image carrier and the sleeve. Distance (cm), T / D is the toner weight fraction in the developer, C / D is the carrier weight fraction in the developer, and ρ _t is the true density of the toner (g / cm ³ ). And ρ _c is the true density of the carrier (g / cm ³ ).

And develop by applying an alternating voltage between the electrostatic latent image carrier and the developing sleeve, which has the same polarity as the electrostatic latent image and forms an alternating electric field between the highest potential and the lowest potential of the electrostatic latent image. There is provided a high image quality development method which prevents toner scattering.

(Operation) In the present invention, the developing conditions satisfying the above formula (1), that is,
Application amount of developer per unit area of sleeve (M, g / c
m ² ), the closest distance between the electrostatic latent image carrier and the sleeve (H,
cm), toner weight fraction in developer, carrier weight fraction in developer, toner true density (ρ _t , g / cm ³ ), and carrier true density (ρ _c , / cm ³ ). When developing is performed while applying an AC voltage between the electrostatic latent image carrier and the developing sleeve, which has the same polarity as the electrostatic latent image and forms an alternating electric field between the highest potential and the lowest potential of the electrostatic latent image, Based on the new finding that the flow state of the developer in the area is remarkably improved, the toner scattering is effectively prevented, and both the image density and the fine latent reproducibility are satisfied, and the toner dust around the image can be reduced. Is.

That R = M × (T / D × 1 / ρ t + C / D × 1 / ρ c) ÷ H × 100 ... (1
R defined in a) indicates the volume ratio (%) occupied by the two-component developer in the dimensionless development area volume.
By keeping the value of above 30% and below 40%, toner scattering can be effectively prevented. When the developer occupancy ratio R is 30% or less, the volume occupied by the developer in the developing area is small, and the magnetic brush in this area sucks air from above the valley between the developing sleeve and the image carrier to form the developing sleeve. It is recognized that the toner tends to be carried under the valleys between the image bearing members to generate an air flow and to be scattered along with the air flow inside the machine outside the developing device. On the other hand, when the developer occupancy rate (R) is 40% or more, the developing area is electrostatic latent image bearing member-
The developer clogs in the valley between the developing sleeves (D-S) and the developer does not flow smoothly. As a result, an equal load is applied to the developing sleeve and the sleeve does not rotate smoothly, and the developer is disturbed. Instead, the toner is likely to be scattered. On the other hand, in the range defined by the present invention, the developer flows smoothly through the valleys between D and S in the developing area to supply an appropriate amount of toner to the electrostatic latent image, while The generation of toner is also prevented, and toner scattering is effectively prevented even if the toner concentration is high. Further, in the present invention, in the flow state of the developer occupancy ratio, an alternating electric field is formed between the electrostatic latent image bearing pair and the developing sleeve with the same polarity as the electrostatic latent image and between the bright portion potential and the dark portion potential of the electrostatic latent image. The magnetic brush is finely moved by applying an AC voltage that forms a magnetic field, thereby softening the contact of the magnetic brush with the surface of the image carrier to prevent excessive supply of toner to the line image and disturbance of the toner image. At the same time, unnecessary toner scattered in the non-image area is picked up, so that fine line reproducibility is improved and toner dust can be suppressed.

In the present invention, it is important that the peak value of the alternating voltage that generates the alternating electric field is between the light portion potential (minimum potential) and the dark portion potential (highest potential) of the electrostatic latent image. If the value is too large, the vibration of the magnetic brush becomes too violent to cause unevenness in image quality, or image fogging or dust on the toner may occur due to toner flying, or carrier particles may drop off.

In the conventional developing method described in JP-A-62-63970 described above, a developer having a high toner concentration is used with a small developer amount such that the volume ratio of the carrier in the developing region is 1.5 to 30%. However, a high-voltage AC voltage is applied so that the peak voltage is between the bright part potential and the dark part potential of the electrostatic latent image, and the magnetic brush is vibrated violently for development. Then, the rubbing pressure on the image bearing member is reduced and the toner is supplied to the electrostatic latent image by the flying force of the toner. According to the present invention, the toner is rubbed while finely moving the toner to the electrostatic latent image. It is essentially different from the method described in JP-A-62-63970 in that it depends on the amount of developer (magnetic brush) conveyed and that no consideration is given to the air flow generated in the developing area. It is a thing.

In the present invention, the relationship between the developer occupancy (R) and various factors of the developing conditions is clear from the above formula (1a), and R increases as the developer coating amount M on the sleeve increases. Also, when the distance H between the image bearing member and the developing sleeve increases, the void R decreases. Further, since the true density ρ _c of the carrier is generally larger than the true density ρ _t of the toner, the higher the toner concentration in the two-component developer, the higher the developer occupancy rate. More specifically, M is generally from 0.06 to 0.25 g / cm ² , especially from 0.1 to 0.2 g / cm ² , and H is generally from 0.04 to 0.16 cm, especially from 0.06 to 0.14 cm,
Further, the toner weight fraction in the developer is 0.03 to 0.08, particularly 0.
From the range of 035 to 0.075, the developer occupancy rate is determined so that R when these are combined satisfies the expression (1).

Further, as already pointed out, the AC voltage applied between the image bearing member and the developing sleeve is such that the magnetic brush is slightly moved, and the peak voltage between the light potential and the dark potential of the electrostatic latent image. It is preferable that the voltage is applied so that the peak-to-peak voltage is -100V to -600V when the dark portion potential of the electrostatic latent image is -700V and the light portion potential is -70V. As a guideline, the potential difference between the dark part potential and the bright part potential
It is preferable that peak-to-peak is formed in the range of 60 to 90%.

(Preferred Embodiment of the Invention) In FIG. 1 for explaining the developing method of the present invention, a magnet roll 11 having a large number of magnetic poles and N, S is housed in a developing sleeve 12 made of a non-magnetic material such as aluminum. ing. A minute gap from this developing sleeve 12, that is, H
The base 13 and the electrophotographic photosensitive layer provided thereon.
An electrostatic latent image carrier 15 composed of 14 is provided. The developing sleeve 12 and the electrostatic latent image carrier 15 are rotatably supported by a machine frame (not shown) so that the moving directions at the developing nip position 23 are the same direction (rotational directions are opposite to each other). Driven. The developing sleeve 12 is located at the opening of the developing device 16, and inside the developing device 16, a mixing and stirring device 17 for a two-component developer (that is, a mixture of toner and magnetic carrier) 18 is provided. A toner supply mechanism 20 for supplying the toner 19 is provided above. Two-component developer
18 is mixed by a stirrer 17 and after the toner obtains a triboelectric charge,
It is supplied to the developing sleeve 12 and the magnetic brush 21 is
To form. And the developing sleeve 12
An alternating voltage is applied between the image carrier 15 and the image carrier 15, and the length of the spikes is adjusted by the spike-cutting mechanism 22 so that the magnetic brush 21 is conveyed to the nip position 23 of the electrophotographic photosensitive layer 14, and the electrophotographic photosensitive layer is formed. The electrostatic latent image on 14 is visualized with toner 19.

At the developing nip position 23, the magnetic brush 21 makes fine movements to come into contact with the photosensitive layer 14, and the photosensitive layer-developing sleeve has the narrowest distance between the photosensitive layer 14 and the developing nip central portion 23a.
The toner is supplied during the passage of the toner. Then, in the central portion 23a of the developing nip, there is no useless space that causes scattering, and the developer flows smoothly without being clogged. Next, after passing through the central portion 23a, the density of the developer is gradually lowered, and the magnetic brush (developer) 21 that slightly moves between the photosensitive layer 14 and the photosensitive layer 14 collects the toner scattered around the image portion on the photosensitive layer. It is collected in the developing device while being taken, and a good image with high density and good reproducibility of the fine point image and reduced toner dust in the peripheral portion of the image can be obtained. The developer application amount M is
By changing the peripheral speed of 12 also, the sleeve 12
It can be set to a predetermined amount by adjusting the distance between the cutting device and the panicle cutting mechanism 22.

The magnetic carrier generally has a density ρ _c of 3.50 to 6.50 g / cm ³ , particularly 4.00, although it depends on the carrier concentration C / D.
It is preferable that the particle size is from 5.50 cm ³ to 5.50 cm ³ , and examples thereof include iron tetraoxide, ferrite, iron powder and the like known per se. A ferrite carrier is particularly preferable.

The average particle size of this magnetic carrier is generally 20 to 200 μm.
m, particularly 40 to 130 μm, and the saturation magnetization is 30 to 70 emu / g, especially 53 to 65 emu / g.
Those within the range are preferable.

The electrical resistance of the carrier generally has a volume resistivity of 5 × 10 ⁸
To 5 × 10 ¹¹ Ω ・ cm, especially 1 × 10 ^{9 to} 1 × 10 ¹¹ Ω ・ cm
It is good to have a range of.

As the toner, a colored toner having a sensible property and a coloring property is used. Resin particles having a particle size of 5 to 30 μm in which a color pigment, a charge control agent, etc. are dispersed are used, and a density ρ _t is 1.00 to 1.40 g /
cm ³ and especially 1.1 to 1.30 g / cm ³ are used. As the binder resin which is the toner component, a thermoplastic resin,
An uncured or precondensate thermosetting resin is used.
Suitable examples thereof are, in order of importance, vinyl aromatic resins such as polystyrene, acrylic resins, polyvinyl acetal resins, polyester resins, epoxy resins, phenolic resins, petroleum resins, olefin resins and the like.

As the color pigment, for example, one or more of carbon black, cadmium yellow, molybdenum orange, pyrazolone red, fast violet B, phthalocyanine blue and the like are used.

As a charge control agent, for example, nigrosine base (CI5041
5), oil black (CI26150), oil-soluble dyes such as spirone black, metal salts such as salicylic acid, naphthoic acid and naphthenic acid, fatty acid metal soaps, resin acid metal soaps, metal-containing azo dyes, etc. are used as necessary. It

The toner may also be 1 × 10 ^{8 to} 3 × 10 ^{9 and} especially 2 × 10 ^{8 to} 8
Those having a volume resistivity of × 10 ⁹ Ω · cm are preferable,
Further, it is desirable that its dielectric constant is in the range of 2.5 to 4.5, particularly 3.9 to 4.0.

The toner weight fraction T / D in the developer is generally 0.03 to 0.1.
It is preferably in the range of 0, particularly 0.035 to 0.080. Also,
The developer as a whole has an electric resistance of 1 × 10 ^{9 to} 1 × 10 ¹¹
It is preferable for the purpose of the present invention that the range is from 5 × 10 ^{8 to} 4 × 10 ¹⁰ Ω · cm.

The developer application amount M depends on the magnetic flux density of the developing sleeve, the brush length, and the peripheral speed of the developing sleeve. The magnetic strength of the main pole of the magnet is preferably 500 to 1000 gauss, particularly 650 to 850 gauss. , The peripheral speed of the developing sleeve is 60 to 800c
m / sec, particularly 90 to 450 cm / sec, and the length of the cutting edge is 0.6 to 1.8 mm, particularly 0.8 to 1.6 mm, although it depends on the magnetic flux density.

The distance between the image carrier and the developing sleeve is 0.4 to 1.6m.
It is preferable to select from the range of m, especially 0.6 to 1.4 mm.

As the photoconductor, all photoconductors conventionally used in electrophotography, such as selenium photoconductors and organic photoconductors, can be used.

(Effect of the Invention) According to the present invention, the flow state of the developer in the developing area is improved, the air flow generated between the electrostatic latent image carrier and the developing sleeve is prevented, and the toner to the electrostatic latent image is prevented. It is possible to prevent the disturbance of the toner image due to the rubbing pressure of the magnetic brush while keeping the supply amount of the toner stable, and to obtain a high-quality image with high density and fine line reproducibility without toner scattering or fog. be able to. Further, it is possible to effectively prevent the dust of the toner around the image.

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

(Experimental Example 1) Using a laser printer LPX-1 (trade name) modified by Mita Kogyo Co., Ltd., a light part potential of -70 V and a dark part potential of -7 were used.
The electrostatic latent image formed at 00V was image-formed by changing the AC voltage value applied between the image carrier and the development leaf and the developer, and the image was evaluated. The results are shown in Table-1.

From Table 1, it can be seen that according to the developing method of the present invention, good results can be obtained in all of image density, line image reproducibility (resolution), fog / toner scattering, and toner dust.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a developing device to which the developing method of the present invention is applied.

Claims (1)

[Claims] 1. A two-component developer comprising a magnetic carrier and toner is conveyed from a developing device to a developing area by a developing sleeve, and in the developing area, an electrostatic latent image on an electrostatic latent image carrier is developed to in the developing method which comprises circulating the developer in the developing device, the following formulas 30 <M × (T / D × 1 / ρ t + C / D × 1 / ρ c) ÷ H × 100 <40 formula, M is The amount of developer applied per unit area of the sleeve (g / cm ² ), H is the closest distance (cm) between the electrostatic latent image carrier and the sleeve, and T / D is the weight of the toner in the developer. C / D is the carrier weight fraction in the developer, ρ _t is the true density of the toner (g / cm ³ ), and ρ _c is the true density of the carrier (g / cm ³ ). In addition to satisfying the above condition, an alternating voltage that forms an alternating electric field between the highest potential and the lowest potential of the electrostatic latent image with the same polarity as the electrostatic latent image is applied between the electrostatic latent image carrier and the developing sleeve. A high image quality development method, which comprises: