JPH0782256B2 - High quality development method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-quality image development method in which toner scattering is prevented in electrophotography, and more specifically, high density and high resolution while preventing toner scattering. It relates to a developing method for obtaining an image.

(Prior Art) In electrophotography, a two-component developer composed of a sensible toner and a magnetic carrier is used, and a harmful developer is supplied onto a magnet sleeve to form a magnetic brass. The latent image is visualized by rubbing against the surface of the photosensitive drum on which the toner image has been formed to obtain a toner image.

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

Further, the final image means that not only the image density but also the resolution is good, and as a general tendency, when the toner concentration becomes high, a high image density can be obtained, but the triboelectric charge of the toner tends to be insufficient, Since the ability to bind to the carrier is reduced and the toner flows in and out of the developing device, the toner scattering tends to increase.
Therefore, in the conventional two-component developing method, the toner density is set low in order to prevent toner scattering, but generally the developing efficiency is low and the resolution is good to some extent, but the density of solid areas tends to be low. Therefore, it is more difficult to obtain a high-density and high-resolution image while preventing toner scattering.

For example, in JP-A-62-63970, an alternating electric field is formed between the drum and the sleeve, and the volume occupied by the magnetic carrier per volume between the drum and the sleeve is 1.5.
It is proposed to use in the range of -30% to obtain high image quality.

(Problems to be Solved by the Invention) In a two-component developer, matching between a magnetic carrier and a toner is important, but it is not easy to eliminate defective charged particles in a toner obtained from a current toner manufacturing method. Absent. 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 probability that these additives are not contained or there is a small content. Therefore, when developing with a high toner density in order to obtain a high density image, the influence of these uncharged particles and low-charged particles is further increased, and toner scattering and fogging are likely to occur.

The inventor of the present invention has a key point in the developer using a two-component developer consisting of a magnetic carrier and a toner, and there is a key point in the flow state of the developer passing through the development zone. It has been found that when the range is set, a high density image can be obtained while preventing the toner scattering and the resolution is improved even when a toner containing a relatively high toner density and uncharged or low charged particles is used. .

An object of the present invention is to provide a developing method capable of preventing toner scattering when a two-component developer composed of a magnetic carrier and a toner is used and obtaining a high-density solid image and a high-resolution image.

(Means for Solving Problems) According to the present invention, a two-component developer composed of a magnetic carrier and toner is conveyed from a developing device to a developing area by a sleeve, and the electrostatic latent image on the photosensitive drum is developed in the developing area. In the development method, which comprises developing the toner and circulating the developed developer to a developing device, the toner scattering is prevented, which is characterized in that the development is carried out under the conditions satisfying the following formulas (1) and (2). A high quality development method is provided.

33 <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 distance (cm) on the line connecting the centers of the photosensitive drum and the sleeve. Yes, T / D is the toner concentration weight fraction in the developer, C / D is the carrier concentration weight fraction in the developer, and ρ _t is the true density of toner concentration (g / cm ³ ). , Ρ _c is the true density of the carrier (g / cm ³ ).

1.25d / x ≦ K ≦ 2d / x (2) In the formula, d is the particle size (μm) of the magnetic carrier, x is the saturation magnetization (emu / g), K is the peripheral speed ratio between the photosensitive drum and the sleeve. Represent

Further, according to the present invention, a two-component developer composed of a magnetic carrier and toner is conveyed from the developing device to the developing area by the sleeve, the electrostatic latent image on the photosensitive drum is developed in the developing area, and the developed image is developed. In a developing method comprising circulating an agent to a developing device, a spherical carrier having a circularity of 0.9 or more is used, and the developing is carried out under conditions satisfying the following formulas (2) and (3). There is provided a high image quality development method which prevents toner scattering.

31 <M × (T / D × 1 / ρ t + C / D × 1 / ρ c) ÷ H × 100 <50
(3) In the formula, M is the coating amount of the developer per unit area of the sleeve (g / cm ² ), and H is the distance (cm) on the line connecting the centers of the photosensitive drum and the sleeve. Yes, T / D is the toner concentration weight fraction in the developer, C / D is the carrier concentration weight fraction in the developer, and ρ _t is the true density of toner concentration (g / cm ³ ). , Ρ _c is the true density of the carrier (g / cm ³ ).

1.25d / x ≦ K ≦ 2d / x (2) In the formula, d is the particle size (μm) of the magnetic carrier, x is the saturation magnetization (emu / g), K is the peripheral speed ratio between the photosensitive drum and the sleeve. Represent

(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 distance (H, cm) on the line connecting the centers of the photosensitive drum and the sleeve, the toner concentration weight fraction in the developer,
Carrier concentration in developer Weight fraction, true density of toner (ρ
_t , g / cm ³ ) and the true density (ρ _c , / cm ³ ) of the carrier are set, and the particle size (μm) of the carrier and the saturation magnetization (emu / When the peripheral speed ratio between the photoconductor drum and the developing sleeve is determined according to g), the flow state of the two-component developer in the developing area is significantly improved, and the toner scattering occurs even under the developing condition where the image density becomes high. It is based on the new knowledge that the resolution is good while effectively suppressing the above.

That is, R defined by R = M × (T / D × 1 / ρ _t + C / D × 1 / ρ _c ) ÷ H indicates the volume ratio of the two-component developer in the dimensionless development area volume. And the value of this R
By maintaining a value of more than 33% and less than 40%, toner scattering is effectively prevented and a high density image is obtained. That is, when the developer occupancy R becomes 33% or less, the volume occupied by the developer in the inter-DS developing region decreases, and the magnetic brush in this region sucks in air from above the valley between DS to cause the valley between DS. There is a tendency that the toner is scattered below the developing unit to generate an air flow and to be scattered along with the air flow inside the developing unit. On the other hand, this developer occupancy (R) is 40
%, The developing area is too clogged in the valleys between the DSs, the developer does not flow smoothly, and the equivalent load is applied to the developing sleeve due to the effect, and the sleeve does not rotate smoothly, Is disturbed and the toner is more likely to scatter. In the present invention, the peripheral speed ratio between the photosensitive drum and the developing sleeve for transporting the magnetic brush is determined according to the above formula (2) in accordance with the particle diameter d of the carrier and the saturation magnetization x within the preferable range of the developer occupancy ratio. Is determined so as to satisfy the condition, the rubbing force (developing pressure) of the developer flowing on the photosensitive member in the developing region becomes preferable, and the resolution becomes good. That is, when the peripheral speed ratio K between the photoconductor drum and the developing sleeve becomes larger than 2d / x, the rubbing force on the photoconductor in the developing area becomes too large and the obtained image disturbs the toner image and has a resolution. When it is lower than 1.25 d / x, the image density may be lowered and toner may be scattered when the flow state of the developer is slightly changed due to a change in environment.

In the present invention, the developer occupancy R increases as the developer coating amount on the sleeve increases, and decreases as the DS distance H increases. 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 in the range 0.06 to 0.25 g / cm ² , especially 0.1 to 0.2 g / cm ² , and H is generally 0.04 to 0.16 cm, especially 0.06 to
From the range of 0.14 cm, and the toner weight fraction in the developer is 0.
From the range of 03 to 0.08, especially 0.035 and 0.075, the developer occupancy rate is determined so that R when these are combined satisfies the expression (1). Then, the peripheral speed ratio between the photosensitive drum and the developing sleeve is adjusted in accordance with the saturation magnetization x and the particle diameter d of the magnetic carrier within a range satisfying the above occupancy ratio to improve the image quality.

On the other hand, the spherical carrier is superior in fluidity due to its shape as compared with the amorphous carrier. Roundness of this carrier (D)
If is 0.9 or more, in the developer in the above development area,
Since the carrier particles are arranged uniformly and evenly, it is possible to prevent the generation of air flow, increase the adhesive force with the toner, and set the toner concentration to a higher concentration. Therefore, R = M
× (T / D × 1 / ρ t + C / D × 1 / ρ c) The preferred range of the developer occupancy ratio defined by ÷ H is expanded to 31 <R <50. In addition, the spherical carrier ensures uniform development pressure,
There is also an advantage that unevenness in image quality is reduced. The roundness referred to here is represented by the following equation (4).

In the formula, r _L represents the major axis of the carrier, and r _s represents the minor axis of the carrier.

(Preferred Embodiment of the Invention) 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 preferably in the range of 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 shape of the magnetic carrier may be either an irregular shape or a spherical shape. In the case of a spherical shape, if the roundness (D) is 0.9 or more, more preferably 0.93 or more, the suitable range of the developer occupancy is Expanded.

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 should be in the range of.

As the toner, a colored toner having a sensible property and a coloring property is used, which is generally called in the binder resin.
Particle size of 5 to 30μ in which color pigments, charge control agents, etc. are dispersed
of a granular composition of m having a density ρ _t of 1.00 to 1.40 g / cm ³
In particular, 1.1 to 1.30 g / cm ³ is used. As the binder resin which is the toner component, a thermoplastic resin or a thermosetting resin of an uncured or initial condensation product 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, carbon black, cadmium yellow, molybdenum orange, pyrozolone red,
One or more kinds of fast violet B, phthalocyanine blue, etc. are used.

As the 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 be of any shape, i.e., spherical or spherical, as long as it has the above particle size range. If it is preferably spherical, the presence of the developer becomes more uniform in the developing area. The toner is also preferably one having a volume resistivity of 1 × 10 ^{8 to} 3 × 10 ^9, especially 2 × 10 ^{8 to} 8 × 10 ⁹ Ω · cm, and its dielectric constant is 2.5 to 4.5, particularly 3.9 to 4.0. Those in the range of are desirable.

The toner weight fraction T / D in the developer is generally 0.03 to 0.10,
Particularly, it is preferable that it is in the range of 0.035 to 0.080. The developer as a whole has an electric resistance of 1 × 10 ^{9 to} 1 × 10 ¹¹ ,
In particular, the coating amount of 5 × 10 ^{8 to} 4 × 10 ¹⁰ Ω · cm developer depends on the magnetic flux density of the developing sleeve, the brush length, and the peripheral speed of the developing sleeve, and the magnetic strength of the magnet main pole is 500 to 1000 gauss. , Especially 650 to 850 gauss, the peripheral speed of the developing sleeve is 60 to 80
The cutting length is 0 cm / sec, particularly 90 to 450 cm / sec, and the cutting length is appropriately 0.6 to 1.8 mm, particularly 0.8 to 1.6 mm, although it depends on the magnetic flux density.

Further, the distance between DSs may be selected from the range of 0.4 to 1.6 mm, particularly 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.

As other developing conditions, the bias voltage applied between the developing sleeve and the photoconductor conductive substrate has an average electric field intensity of 10
The range is set to 0 to 1000 V / mm, particularly 125 to 800 V / mm.

(Effect of the Invention) According to the present invention, in the magnetic brush developing method comprising a magnetic carrier and a toner, the composition of the developer, the density, the coating amount,
The drum-sleeve distance is selected so as to satisfy the above formulas (1) and (3), and the peripheral speed ratio between the drum and the sleeve is determined by the particle size of the magnetic carrier and the saturation magnetization. It is possible to obtain a high-density solid image and a high-resolution line image while preventing the toner from scattering by improving the flow state of the developer passing through and the sliding force (developing pressure) on the photosensitive drum. Become.

Hereinafter, the present invention will be described in more detail with reference to experimental examples.

(Experimental Example 1) Using a modified laser printer LPX-1 (trade name) manufactured by Sanda Kogyo Co., Ltd., a black toner having an average particle diameter of 11 μm for various negative charges having different true densities was used as the toner, and the true density was used. , Grain size, saturation magnetization, different electric resistance 10 ⁸ ~ 10 ⁹ Ω
An imaging test was conducted under various conditions using a cm ferrite carrier. The results are shown in Table-1, sample NO, 7,8,9 and 11 are spherical carriers with roundness of 0.93, 0.940.93, 0.95, and the others have roundness of 0.9.
It is less than or indefinite.

From Table 1, those in which the occupancy rate of the developer satisfies the above formula (1) and the peripheral speed satisfies the above formula (2), prevent the toner from scattering and have a high density (4.5 mm / line). It can be seen that the above image is obtained. Furthermore, it can be seen from Samples Nos. 6 and 7 that when a spherical carrier having a circularity of 0.9 or more is used, the suitable range of the developer occupancy rate is expanded and the allowable range is expanded.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-63970 (JP, A) JP 62-112170 (JP, A) JP 62-192757 (JP, A) JP 1- 102588 (JP, A) JP 61-128261 (JP, A) JP 63-208867 (JP, A)

Claims (3)

[Claims] 1. A two-component developer comprising a magnetic carrier and toner is conveyed from a developing device to a developing area by a sleeve, an electrostatic latent image on a photosensitive drum is developed in the developing area, and a developed developer is developed. A high-quality developing method in which toner scattering is prevented, characterized in that the developing is carried out under conditions satisfying the following formulas (1) and (2). 33 <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 distance (cm) on the line connecting the centers of the photosensitive drum and the sleeve. Yes, T / D is the toner concentration weight fraction in the developer, C / D is the carrier concentration weight fraction in the developer, and ρ _t is the true density of toner concentration (g / cm ³ ). , Ρ _c is the true density of the carrier (g / cm ³ ). 1.25d / x ≦ K ≦ 2d / x (2) In the formula, d is the particle size of the magnetic carrier (μm), x is the saturation magnetization (emu / g), K is the peripheral speed ratio between the photosensitive drum and the sleeve. Represent 2. A two-component developer comprising a magnetic carrier and toner is conveyed from a developing device to a developing area by a sleeve, an electrostatic latent image on a photosensitive drum is developed in the developing area, and a developed developer is developed. In a developing method of circulating in a container, a spherical carrier having a circularity (D) of 0.9 or more is used as a magnetic carrier, and development is performed under conditions satisfying the following formulas (2) and (3). A high-quality image development method that features the prevention of toner scattering. 31 <M × (T / D × 1 / ρ t + C / D × 1 / ρ c) ÷ H × 100 <50
(3) In the equation, M is the coating amount of the developer per unit area of the sleeve (g / cm ² ), and H is the distance (cm) on the line connecting the centers of the photosensitive drum and the sleeve. Yes, T / D is the toner concentration weight fraction in the developer, C / D is the carrier concentration weight fraction in the developer, and ρ _t is the true density of toner concentration (g / cm ³ ). , Ρ _c is the true density of the carrier (g / cm ³ ). 1.25d / x ≦ K ≦ 2d / x (2) In the formula, d is the particle size of the magnetic carrier (μm), x is the saturation magnetization (emu / g), K is the peripheral speed ratio between the photosensitive drum and the sleeve. Represent 3. The developing method according to claim 1, wherein the magnetic carrier has a particle size of 20 to 200 μm and a saturation magnetization of 30 to 70 emu / g.