JP2637572B2 - Development method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developing method, and more particularly, to a two-component magnetic developer using a color toner and an organic photoreceptor, The present invention relates to a developing method capable of obtaining a high-quality color image by magnetic brush development.

(Prior Art) In the field of commercial electronic copying, magnetic brush development using a two-component magnetic developer is widely used for developing electrostatic images. As a two-component magnetic developer, a mixture of a magnetic carrier composed of iron or sintered ferrite particles and a toner particle obtained by dispersing a compounding agent such as a colorant and a charge control agent in a fixing resin is widely used. It is used.

A typical developing mechanism using a developer has a structure as shown in FIG. 1, and a box-shaped toner supply mechanism 4 is provided in the development mechanism 2 and toner 6 is supplied from above. Is done. The toner 6 is supplied to a lower developing unit 10 through a supply port 8 with a feeder, and is stirred by a stirrer 12 with a carrier in the developing unit 10 to form a two-component developer 14.

A developing sleeve (developer carrying member) 16 having a large number of magnetic poles is arranged in the developing device 10, and the developing sleeve 16 is supplied with a developer 14 after toner obtains a triboelectric charge. A magnetic brush 18 is formed on the surface by a developer. The spike length of the magnetic brush 18 is adjusted by a spike cutting mechanism 20, and the magnetic brush 18 is conveyed to a nip position with a surface photosensitive layer 24 of an electrophotographic photosensitive drum (image carrier) 22. Photosensitive drum 22 is Haise a distance D _DS from the developing sleeve 16, the moving direction of the rotatably supported in the nip position to the developing sleeve 16 and the photosensitive drum 22 is a machine frame (not shown) (arrow ) Are driven in the same direction (the rotation directions are opposite to each other).

Around the photoreceptor drum 22, a corona charger 26 and an exposure optical system 28 connected to a variable high-voltage power supply 24 are disposed upstream of the developing device 10 to form an electrostatic latent image having a predetermined surface potential. It can be formed. Also, the photosensitive drum 22
A bias power supply 33 having a voltage adjusting mechanism 30 is connected between the photosensitive drum 24 and the developing sleeve 12, and an arbitrary value (bias potential) having the same polarity as the surface potential and lower than the surface potential is provided on the photosensitive layer 24. It can be applied. Further, a transfer mechanism 34 for transferring a toner image to a copying machine is provided around the photosensitive layer 24 and downstream of the developing unit.

In such a configuration, the developer 14 is
The magnetic brush 18 is formed thereon, and reacts with the electrostatic latent image on the photosensitive layer 24 at the nip position to form a visible image 36 of the toner on the photosensitive layer 24. The formed visible image 36 is transferred to a transfer material (not shown), and then a toner image is fixed by a transfer mechanism 34 to form a direct image.

(Problems to be Solved by the Invention) By the way, at the time of forming a color image, the selection of the color dye and the pigment is more restricted than the black dye such as carbon, so that the electrical resistance (the reverse of the conductivity) of the color toner is reduced.
Tend to be higher. For this reason, the image density (ID) may not be maintained at a high density. Conventionally, in order to solve such a problem, the supply amount of toner is increased by reducing the particle size of the magnetic carrier, or the electric resistance of the magnetic carrier is reduced. However, even if the physical properties of the magnetic carrier are changed as described above, a sufficient ID may not be obtained for a color image, and a satisfactory ID may not be obtained particularly for a red toner having low conductivity. Further, it is conceivable that the above-mentioned DD-S width is made smaller than before so as to improve the color image density. But,
In this case, stress is applied and there is a problem that carrier pulling occurs.

In recent years, an organic photoreceptor that has good workability and is advantageous in terms of manufacturing cost and has a high degree of freedom in functional design has been used as a photoreceptor for electrophotography. There are two types of organic photoreceptors: negatively charged type and positively charged type. Negatively charged type photoconductors cause contamination of the copy environment, so use of positively charged photoconductor (OPC) is expected. Have been.

However, such a positively charged photoreceptor tends to have a residual potential higher than that of a conventional Se-based photoreceptor, and when using a positively charged photoreceptor, the bias potential must be used at 250 V or more. . The increase in the bias potential increases the charge repulsion between the magnetic carrier and the developing sleeve, thereby making carrier pulling more likely. Therefore, in color development of a positively charged photoreceptor, there has been a problem of improving carrier drawing and image density.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a developer having a high-density image and no carrier pulling even when a toner having a low conductivity is used.

Another object of the present invention is to provide a red developer capable of obtaining a high-density red image.

A further object of the present invention is to provide a color developer for OPC, which has recently been frequently used, particularly for a positively charged OPC.

(Means for Solving the Problems) According to the present invention, a developing method in which a two-component magnetic developer is transported in the form of a magnetic brush by a developing sleeve to develop an electrostatic image formed on an organic photoreceptor In the magnetic developer, a non-magnetic toner having a conductivity of 3.0 × 10 ⁻¹⁰ s / cm or less and a 50% diameter of a weight average particle diameter of 80 to 100 are used.
μm, 25% of the weight average particle size (D ₂₅ ) and 7 of the weight average particle size
The difference from the 5% diameter (D ₇₅ ) is in the range of 5 to 20 μm and 25
A magnetic carrier having a particle size distribution in which particles of 0 mesh or less are 8% by weight or less is used in a weight ratio of 2:98 to 5:95. Interval (D _DS ) and
There is provided a developing method characterized in that development is performed by setting the thickness to less than 1.0 mm and applying a bias voltage of 250 V or more.

(Function) In the present invention, in a color toner having a low electric conductivity, the particle size distribution of the magnetic carrier is selected to a specific value.
This is based on the finding that the developer provides an image having a very high color density and does not cause carrier pulling or the like.

Color toners and the like are limited in the types of dyes and pigments, and tend to be low in toner conductivity. In particular, in the case of red color, a dye or pigment that increases the electrical conductivity has not been sufficiently obtained. A developer using such a low-conductivity color toner cannot form a sufficiently high-density color image under conventional developing conditions.

Less than 1.2mm and D _DS width of the developer in the present invention, especially in the developing conditions of less than 1.0 mm, moreover by using a high bias potential state, in which enhanced color image density. Unlike the conventional development conditions, the transfer of the color toner to the photoconductor is facilitated by reducing the DD-S width and increasing the bias potential. For this reason, the color density of the visible image on the photoconductor is increased. On the other hand, carrier development may occur under such developing conditions, but the developer of the present invention has been solved by setting the particle size distribution of the carrier to specific requirements.

In the present invention, 50% of the weight average particle diameter D of the carrier
₅₀ is 80 to 100 μm, and the particle size difference between D ₂₅ and D ₇₅ is 5 to 20
In the case of a constant range of μm, the bias potential is high, that is, the development condition and the d _DS
Even when used under developing conditions with a width of less than 1.2 mm, high density images can be obtained with almost no carrier pull.

The sharpening of the carrier particle size distribution reduces the presence of carriers with small particle diameters compared to conventional carriers, and the presence of small particle size carriers reduces the DDS width when the bias potential is increased and the _DDS width is reduced. It is understood that it may have the effect of inducing a carrier pull at times. On the other hand, it is well known that reducing the particle size of the carrier can achieve higher density of a solid image.

In the present invention, when the particle size distribution is sharpened based on the characteristics of the carrier, high image density is maintained or improved despite the small amount of the small particle size carrier, but carrier pulling occurs. It is something that has not been found. It is understood that simply removing small particle size carriers from the entire carrier does not provide sufficient developer.

Further, as shown in FIG. 2, in the conventional developer, the carrier pull increases as the bias potential increases. This is understood because the magnetic carrier gradually increases the charge repulsion with the developing sleeve, so that the carrier is easily transferred to the photoconductor. In general, the current value and other electrostatic effects of a magnetic carrier are largely influenced by the carrier pull, and the size of the carrier particle is of little importance because all carriers are uniformly charged. How

However, in the developer of the present invention, even if the bias potential is increased, the carrier pull is significantly suppressed by setting the particle size distribution of the magnetic carrier of 250 mesh or less to 8% by weight or less, particularly 5% by weight or less. Making the particle size distribution of the fine particle carrier of 250 mesh or less 8% by weight or less means that a part of the fine particle carrier is removed as compared with the conventional carrier. It is not clear how the removal of such a fine particle size affects the carrier pulling, but this is because the developer of the present invention has a bias potential of 250 V, especially
It is understood that it can be used above 280V.

Increasing the bias potential can reduce the influence of the residual potential of the photoconductor. That is, even if the residual potential of the photoconductor is a high potential of at least about 150 V, the photoconductor can provide excellent image quality without causing carrier pulling. Positively charged photoconductors (OPCs) are examples of such high residual potentials.
Are provided with conditions under which the developer of the present invention can be suitably used. Further, an increase in the bias potential reduces a development potential difference given by a difference between the potential and the surface potential, and in some cases, low-potential development is forced. Such low-potential development deteriorates gradation and image density. However,
D _DS width is less than 1.2 mm, if particular development conditions of less than 1.0 mm, tone reproduction, is maintained also excellent image density, does not occur carrier pull. Thus, the color developer of the present invention can be sufficiently applied to a positively charged organic photoreceptor.

(Preferred Embodiment of the Invention) Hereinafter, a preferred embodiment of the developer according to the present invention will be described.

The developer of the present invention is a two-component developer composed of a magnetic carrier and a toner. The magnetic carrier, the toner, and the developer will be described in detail sequentially.

Magnetic Carrier In the present invention, as the magnetic carrier, any one can be used as long as the particle size distribution and the saturation magnetization are within the above-mentioned ranges. it can.

That is, the carrier particles generally are divided Mashiku a spherical, 50% diameter of the weight average particle diameter (hereinafter, D ₅₀ that.) Is intended to satisfy the range of 80 to 100 [mu] m, also, the D ₂₅ Those having a particle size difference from D ₇₅ satisfying the range of 5 to 20 μm have a sharp particle size distribution, and have a _DS width described later of 1
Even if the length is further reduced from less than mm, there is no carrier pull. That is, raising the particle size based on the sharpening of the carrier particle size distribution reduces the torque and reduces the drum circumferential friction when the image carrier and the developer carrier are in the form of a drum.

In addition, to prevent carrier pulling, 25
It is desirable to eliminate carriers having a small particle size of 0 mesh or less.
The amount of the carrier having a particle size distribution of 250 mesh or less preferably satisfies the range of 8% by weight or less, particularly 5% by weight or less,
In a developer satisfying such a range, carrier pulling can be sufficiently prevented even when the bias potential is high.

A magnetic carrier having a saturation magnetization satisfying the range of 50 to 70 emu / g is used.In particular, a magnetic carrier having a saturation magnetization of 60 to 70 emu / g is suppressed to be lower than the saturation magnetization of the conventional developer carrier. The softening of the ears in the magnetic brush promotes the softening of the ears in comparison with the carrier of the present invention, and the softening of the ears reduces the drum stress. In the present invention, since the interval (D _DS ) between the organic photoreceptor and the developing sleeve is set to a small interval of less than 1.0 mm, a soft magnetic brush having the above saturation magnetization and forming a soft magnetic brush is formed. It is particularly preferred to use the resulting carrier.

Further, the current value of the carrier used in the present invention when 200 V is applied is desirably 10 to 70 μA, particularly 30 to 50 μA, and the carrier has a fluidity of 15 to 50 μA.
Those satisfying the range of 35 sec / 50 g, particularly 20 to 30 sec / 50 g are desirable.

Specifically, as ferrite, for example, zinc iron oxide (Zn
Fe ₂ O ₄ ), yttrium iron oxide (Y ₃ Fe ₅ O ₁₂ ), cadmium iron oxide (CdFe ₂ O ₄ ), gadolinium iron oxide (CdFe ₂ O)
₁₂ ), lead iron oxide (PbFe ₁₂ O ₁₉ ), nickel iron oxide (NiFe ₂
O ₄ ), neodymium iron oxide (NdFeO ₃ ), barium iron oxide (BaFel ₂ O ₁₉ ), magnesium iron oxide (MgFe ₂ O ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ), etc. Sintered ferrite particles having a composition of one or more of the following are used, and in particular, at least one metal component selected from the group consisting of Cu, Zn, Mg, Mn, and Ni, preferably 2 Soft ferrites containing more than one species, for example copper-zinc-magnesium ferrite, are used.

As the coating resin, use one or more of silicone resin, fluorine resin, acrylic resin, styrene resin, styrene-acryl resin, olefin resin, ketone resin, phenol resin, xylene resin, sialyl phthalate resin, and the like. Can be. Among these resins, a straight silicone resin, that is, a silicone resin composed of an organopolysiloxane such as dimethylpolysiloxane, diphenylsiloxane and methylphenylpolysiloxane and having a network structure is most preferable. Reticulation (cross-linking) of the silicone resin is carried out by allowing a functional group such as a trimethoxy group or the like which can be initially decomposed or a functional group such as a silanol group to be present in an organopolysiloxane unit. Is effected. The resin coating amount is generally in the range of 0.5 to 3 parts by weight, preferably 0.8 to 1.5 parts by weight, per 100 parts by weight of ferrite.

Color toner The toner used in the present invention is obtained by blending a colorant such as a red pigment or dye and a charge controlling agent or a toner compounding agent known per se in a fixing resin medium, and the dielectric constant of the color toner is 3.0 × 10 ^-10 s / cm or less, especially 2.6 × 10 ^-10
It satisfies the range of s / cm or less. The fixing resin medium for the toner, the colorant, the charge control agent, and the other compounding agent for the toner are used in an appropriate combination within a range having the above characteristics.

First, a styrene resin, an acrylic resin or a styrene-acrylic copolymer resin is generally used as the fixing resin medium. Examples of the styrene monomer include styrene, vinyltoluene, α-methylstyrene, and α-methylstyrene. Examples thereof include chlorostyrene, vinyl xylene, and vinyl naphthalene. Among them, styrene is preferred.

On the other hand, as the acrylic monomer, for example, ethyl acrylate, methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, acrylic acid,
And methacrylic acid. Further, in addition to those described above, an ethylenically unsaturated carboxylic acid or an anhydride thereof, for example, maleic anhydride, fumaric acid, maleic acid, crotonic acid, itaconic acid, or the like can also be used.

Styrene-acrylic copolymer resin is one of the suitable resin media, and styrene monomer (A) and acrylic monomer (B) are A: B = 50: 50-90. :Ten,
In particular, the range is preferably 60:40 to 85:15. 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 coloring agent to be contained in the resin, various dyes and pigments known per se used in this field are used.

Red pigment Bengala, cadmium red, lead red, cadmium mercury sulfide, permanent red 4R, permanent red
FNG, Risor Red, Pyrazolone Red, Watchinga Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake, Brilliant Carmine 3B, Spiron Red.

Purple pigment Manganese purple, Fast Violet B, Methyl Violet Lake.

Blue pigment Navy blue, cobalt blue, alkali blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, Fast Sky Blue, Indasulene Blue BC.

Orange pigments Red-mouthed lead, molybdenum orange, permanent orange GTR, Piazolo orange, Vulcan orange, Inzathrene brilliant orange RK, Benzidine orange G, Induslen brilliant orange GK.

Yellow pigment Yellow lead, zinc yellow, cadmium yellow, navel yellow, naphthol yellow S, Hanser yellow G, Hanser yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NC
G, tartrazine lake, green pigment chrome green, pigment green B, malachite green lake, final yellow green G.

White pigment Zinc white, titanium oxide, antimony white, zinc sulfide.

Next, as the charge control agent, any charge control agent known per se, for example, oil-soluble dyes such as nigrosine base (CI 50415), oil black (CI 26150), and spiron black, metal salts of naphthenic acid, fatty acids and the like Soaps and resin acid soaps 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. Also,
The surface of the toner may be coated with hydrophobic silica fine particles or carbon black to improve its fluidity.

Developer The developer is preferably used by mixing the above-mentioned magnetic carrier and toner in a weight ratio of usually 98: 2 to 95: 5. The initial charge amount of the developer is 5
It is desirable to satisfy the range of 30 to 30 μc / g, especially 10 to 25 μc / g. The loose specific gravity of the developer is 1.7 to 2.1.
Those satisfying g / cm ³ , especially 1.8 to 2.0 g / cm ³ are preferable for the purpose of the present invention.

The developer of the present invention has an image carrier-developer carrier distance D _DS.
It is desirable to use it under a condition of less than 1 mm and a development potential difference of 500 V or less. An image bearing member and the developer carrying member used developing mechanism may be a drum form shown in planar form or Figure 1, it is desirable that D _DS satisfies the above range.

In the present invention, the magnetic brush development is performed by setting the D _DS width in the range of less than 1.0 mm, tone reproduction even at a low potential development,
It can provide excellent color image density,
In consideration of the requirements of the carrier, carrier pulling or the like does not occur. In addition, the ear cutting width in accordance with the reduction of D _DS width
It is desirable to provide it in the range of 0.5 to 1.3 mm, especially 0.7 to 0.9 mm.

The developer of the present invention has a development potential difference of 500 V, especially 480 V
Under the following conditions, when the surface potential of the photosensitive drum is applied to 750 to 850 V, the bias potential is set to 250 to 3
It is possible to use a photosensitive drum or the like applied with a voltage of 50 V or more. In such a rise in the bias potential, the photosensitive drum can be used even when the residual potential thereof is about 150 V or more, particularly about 200 V or more.

As the photoreceptor, photoreceptors used in conventional electrophotography, such as selenium photoreceptor, amorphous Shinkon photoreceptor,
Zinc oxide photoreceptor, selenide cadmium photoreceptor, can be used cadmium sulfide photoconductor or the like, when these are used in D _DS width as described above, to provide tone reproduction, the development of excellent color image density Can be.

Further, in the present invention, it is desirable to use a developer for a positively charged photoconductor (OPC). In a positively charged photoreceptor, a charge generation material and a charge transport material are mainly mixed in one layer, so that electrons and holes move in one layer, and either one becomes a trap and the residual potential increases. There is a tendency. Such a photoreceptor must be used at a bias potential of at least 250 V, and in some cases, at 280 V or more. The developer of the present invention provides an excellent image even at such a bias potential, and does not cause carrier pull.

As a specific positively charged photoreceptor, a photoreceptor in which a well-known charge generating material and a charge transporting material are combined can be used. desirable.

According to the present invention (Effect of the Invention), conductivity using the following toner 3 × 10 ^-10 s / cm, and a weight average particle 50% diameter D ₅₀ of the diameter of the carrier 8
Since the particle size distribution is adjusted to a range of 0 to 100 μm and the particle size distribution of 250 mesh or less to 8% by weight or less, the developer does not cause carrier pulling and the like, and a high density color image can be provided. Conventionally, a sufficient red image has not been obtained due to a problem of toner conductivity, but the developer of the present invention can provide a high-density red image.

In addition, the developer of the present invention can be sufficiently applied as a developer for OPC, which has recently been frequently used, particularly as a positively charged OPC developer.

(Example) Hereinafter, an example and a comparative example are shown. The present invention is not limited to the scope of the embodiment.

 The components of the developer and the developing conditions were set as follows.

Ingredients The magnetic carrier used was a spherical non-coated ferrite carrier, and its physical properties are shown in Table 1.

As the toner, a toner whose particle diameter, pigment component, conductivity, etc. are known is used. The physical properties are shown in Table 1.

The developer was a mixture of toner and carrier at a weight ratio of 4.5: 95.5, and the basic physical properties are shown in Table 1.

Development conditions D _DS width, bristle cutting width, developing potential difference, the bias potential and the photosensitive member are shown in Table 1.

Table 1 shows the results of development using the developer having the above conditions and components (carrier pull, image density).

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a developing mechanism, and FIG. 2 is a characteristic diagram showing a relationship between a bias potential and carrier pulling.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takachi Fukumoto 1-2-2, Tamazo, Chuo-ku, Osaka City, Osaka Prefecture Inside Mita Kogyo Co., Ltd. (56) References JP-A-62-42163 (JP, A) JP-A-63-170660 (JP, A) JP-A-63-301960 (JP, A) JP-A-62-49361 (JP, A) JP-A-56-140357 (JP, A)

Claims (1)

(57) [Claims] 1. A developing method in which a two-component magnetic developer is transported in the form of a magnetic brush by a developing sleeve to develop an electrostatic image formed on an organic photoreceptor. Non-magnetic toner having a ratio of 3.0 × 10 ⁻¹⁰ s / cm or less, and a 50% diameter of the weight average particle diameter of 80 to 100 μm
m, 25% of the weight average particle size (D ₂₅ ) and 75 of the weight average particle size
% Diameter (D ₇₅ ) is in the range of 5 to 20 μm and 250
A magnetic carrier having a particle size distribution of 8% by weight or less of particles having a mesh size of less than or equal to 8% by weight, wherein a weight ratio of 2:98 to 5:95 is used, and a distance between the organic photoreceptor and the developing sleeve is used. (D _DS ) and 1.
A development method characterized in that development is performed by setting the thickness to less than 0 mm and applying a bias voltage of 250 V or more.