JPH02296268A - Developing device - Google Patents

Abstract

PURPOSE:To prevent the firm adhesion of developer fine particles by providing a movable developer carrying member with a coating layer which conductive fine particles are dispersed in a resin and allowing the distributing secondary particles formed of the conductive fine particles on the surface of the coating layer to form a rugged surface with the resin and the secondary particles. CONSTITUTION:The developer carrying member 7 is provide with the coating layer 6 made of the resin in which the conductive fine particles are distributed. The secondary particles 6' formed of the resin and the conductive fine particles are distributed on the surface of the coating layer 6 so that the rugged surface is formed by the secondary particles. Thus the abnormal charge-up of a developer is prevented even in low humidity environment and toner triboelectrifying quantity is stabilized. Moreover since a triboelectrifying quantity distribution is sharpened, proper developing images are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an electrostatic latent image developing device using a one-component developer.

[Prior art and problems]

Developing devices using a one-component developer are often used in electrophotographic copying machines and electrophotographic printers. (In this specification, a one-component developer refers to a dry developer that does not contain carrier particles contained in a so-called two-component developer. However,
Not limited to those containing only toner particles, one or more types that improve the fluidity of the developer, control the amount of charge of the toner, and clean the surface of the image carrier in addition to the toner particles. A developer to which an auxiliary agent is externally added is also called a one-component developer. ) Compared to a developing device that uses a two-component developer, a developing device that uses a one-component developer is easier to downsize and does not require a means to maintain the mixing of toner particles and carrier particles. It has the advantage that the configuration is simple.

By the way, in a developing device using a one-component developer, toner particles are charged to a polarity for developing a latent image due to friction between the toner particles and the developer carrying member. On the other hand, the developer is not consumed in the region of the carrier member facing the non-image area of the image carrier, but if this state of not being consumed continues, the developer will be exposed to fine powder on the carrier, which is thought to be due to electrostatic mirroring force. The developer layer strongly adheres to the image area of the image carrier and is not easily consumed, but also reduces the amount of charge of the developer on the fine powder developer layer. For this reason, a ghost image is generated on the developed image and the image quality is deteriorated.

For example, it is not known to externally add substances such as vapor-phase silica (hereinafter referred to as dry-process silica) or wet-process silica (hereinafter referred to as dry-process silica) to toner to control the amount of triboelectric charge of a one-component developer. ing.

For example, magnetite is added to styrene-acrylic copolymer.
For a negatively charged magnetic toner containing 0 parts by weight, dry silica fine powder (100rr? vapor phase silica) exhibiting strong negative charging properties,
By externally adding (added at a ratio of 0 parts by weight and heat-treated), the amount of triboelectric charge as a developer increases. Using this developer, a known jumping developing device as shown in FIG. 1 (for example, see US Pat. No. 4,292,387)
When a thin developing layer is formed on the sleeve 8 and development is performed, the image density increases and images with less roughness are obtained compared to a developer without external addition of silica.
This is widely known.

However, in the case of a developer externally added with silica having a strong negative charge characteristic to negatively charged toner, a sleeve ghost, which is the history of the print pattern, occurs on the developing sleeve, and this ghost also appears on the printed image. The sleeve ghost that occurs in the case of a developer in which negatively charged silica is externally added to negatively charged toner causes a developed image having a positive ghost, as shown in FIG.

In other words, because there was a continuous non-printing area (white background), even if printing was performed, only light development was performed (a), and because printing continued, a dark phenomenon occurred (b).
There is uneven density between different parts. According to the experiments and considerations of the present inventors, the mechanism of this ghost formation is deeply related to the layer of fine powder (particle size of 5 to 6 microns or less) formed on the sleeve.

In other words, there is a clear difference in the particle size distribution of the toner bottom layer of the developing sleeve between the toner consumed area and the toner unconsumed area, and a fine powder layer is formed in the toner bottom layer in the unconsumed area. Because fine powder has a large surface area per volume, it has a larger amount of triboelectric charge per weight than particles with a large diameter, and due to mirroring force, it
It is electrostatically strong (restricted). Therefore, the toner on the part where the fine powder layer is formed cannot be sufficiently charged by friction with the developing sleeve, reducing the developing ability and appearing as a ghost on the image. Put it away.

Further, under high temperature and high humidity, particularly high humidity environments, the developer, especially silica, absorbs moisture, resulting in a decrease in the amount of charge of the developer.

Even if the image density is good in a low-humidity environment or a normal environment, the image density generally decreases in a high-humidity environment and the image becomes rough.

For this reason, several attempts have been made to prevent moisture absorption under high humidity conditions by subjecting externally added silica to hydrophobization treatment.

However, although developers to which hydrophobized silica is externally added show stable charging under high humidity conditions, the amount of charging increases too much under low humidity environments, and in particular, fine particles are charged up.
There is a strong tendency for the above-mentioned ghost image to occur. In particular, when hydrophobized silica having negatively charged characteristics is externally added to negatively charged toner, the difference in density of a ghost image is large.

In addition, the volume average particle size of the magnetic toner in a dry one-component developer conventionally used as a developer is generally within the range of 10 to 14 μm, especially in typical jumping development. Regarding the particle size, the volume average particle size of the magnetic toner is 12 μm.Moreover, this magnetic toner has a volume average particle size of 6.35 μm or less, which accounts for about 20% or less in the number distribution. A toner containing toner having a diameter of 20.2 μm or more in a volume distribution of about 2% or less is used.

However, in recent years, efforts have been made to further reduce the particle size of toner in order to improve the image quality of electrophotographic devices. for example,
In terms of electrophotographic laser beam printers, the printing density has been doubled from the conventional 300 dpi to 600 dpi (23,6
pe+), it is relatively easy to increase the sharpness after resolution and faithfully reproduce the electrostatic latent image by using toner with a particle size of about 8 μm to 6 μm. An example of such a toner with a small particle size is a volume average particle size of 6.0 μm.Moreover, this -component magnetic toner has a number of toners with a volume average particle size of 3.5 μm or less. This is a toner containing particles having a volume average particle size of 16 μm or more at a ratio of about 20% or less in terms of volume distribution, and about 1% or less in volume distribution. If this toner is a positively charged toner containing nigrosine or the like as a charge control agent, approximately 0.8% by weight of silica treated with amino-modified silicone oil is added to the toner as an external additive.
It is used as a developer after being added externally.

However, since such small particle size toner has a larger specific surface area per volume than conventional toner, the amount of charge per volume/weight increases by about 30% when measured using the two-component tripometry method. In addition, as mentioned above, the particle size is 5μ
As the amount of fine powder below m becomes thicker (increases), the resin component in these small particle size toners becomes abundant, and as a result, the high tripo fine powder from these small particle size toners makes it difficult for developers such as developing sleeves to The surface of the carrier is easily contaminated, which tends to cause ghost images as described above.

Conventionally, as a countermeasure against the above phenomenon, by bringing a scraper into contact with the developing sleeve, all of the toner after development is scraped off from the developing sleeve, or the toner after development is electrostatically transferred from the developing sleeve to the image bearing surface. There are methods such as applying a different bias to the sleeve than during development so that the toner is transferred to the body, or placing a grounded metal plate or roller facing the developing sleeve to remove the toner after development from the developing sleeve. However, these methods all have the drawbacks of complicating the equipment and increasing costs.

[Purpose of the invention and outline of the structure]

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that can prevent fine developer powder from strongly adhering to a developer carrying member and produce developed images with good density.

In the present invention, the developer carrying member has an outer covering layer in which conductive fine particles are dispersed in a resin, and a secondary layer formed of the resin and conductive fine particles is provided on the surface of this outer covering layer. The particles are distributed so as to form an uneven surface, or the developer carrying member has an outer coating layer in which fine graphite particles are dispersed in a resin.

〔Example〕

The binder resin for the magnetic toner, which is the main component of the one-component magnetic developer used in the following examples, includes monopolymers of styrene and its substituted products such as polystyrene and polovinyltoluene; styrene-propylene copolymers; Styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-
Ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer,
Styrene-dimethylaminoethyl acrylate copolymer,
Styrene-methyl methacrylate copolymer, styrene-
Ethyl methacrylate copolymer.

Styrene-butyl methacrylate copolymer, styrene-
Dimethylaminoethyl methacrylate copolymer, styrene-vinyl methyl ether copolymer.

Styrene-vinylethyl ether copolymer, styrene-
Styrenic copolymers such as vinyl methyl ketone copolymer, styrene butadiene copolymer, styrene-isoprene copolymer, styrene-maleic acid copolymer, and styrene-maleic acid ester copolymer; polymethyl methacrylate, poly Butyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, Tenbel resin, phenolic resin, aliphatic or alicyclic hydrocarbon resin,
Aromatic petroleum resins, paraffin wax, carnauba wax, etc. can be used alone or in combination.

Further, as coloring materials that can be further added to the magnetic toner, conventionally known carbon black, copper phthalocyanine, iron black, etc. can be used.

The magnetic fine particles contained in the magnetic toner are materials that become magnetized when placed in a magnetic field, such as iron.

Powder of ferromagnetic metal such as cobalt or nickel, or magnetite, r-Fe203. Alloys and compounds such as ferrite can be used.

These magnetic fine particles preferably have a BET specific surface area of 1 to 20 nil/g, particularly 2.5 to 12 r.
r? /g', and more preferably a magnetic powder having a Mohs hardness of 5 to 7. The content of this magnetic powder is 10 to 10% based on the weight of the toner.
70% by weight is good.

Further, the toner may contain a charge control agent if necessary, and a negative charge control agent such as a metal complex salt of a monoazo dye, a metal complex salt of salicylic acid, alkyl salicylic acid, dialkyl salicylic acid, or naphthoic acid is used. Furthermore, the toner has a volume resistivity of 10I0Ω・cm or more, especially 1o12
It is preferable that it is Ω·cm or more in terms of frictional charge retention and electrostatic transferability. The volume resistivity referred to here means that the toner is 1
Molded at a pressure of 00 kg/crd, and then
It is defined as a value calculated from the current value after 1 minute has passed after applying an electric field of 0 V/cm.

The amount of frictional charge of negatively charged toner is -8μc/g to 20μ
It is preferable to have c/g. When it is less than -8 μc/g, the image density tends to be low, and the effect is particularly noticeable under high humidity. On the other hand, if it exceeds -20 μc/g, the toner charge is too high, resulting in thin line images and poor images especially under low humidity.

Negatively charged toner particles are 25°C, 150-60% RH.
Toner particles left overnight in an environment of 200~
A non-resin-coated carrier iron powder with a main particle size of 300 mesh (e.g. EFV20 manufactured by Nippon Iron Powders)
0/300) 90g and approximately 200c under the above environment,
Mix thoroughly (by hand and lift up and down approximately 50 times) in an aluminum pot with a volume of 40
The amount of triboelectric charge on the toner particles is measured by a conventional blow-off method using an aluminum cell having a screen of 0.0 mm. By this method, toner particles whose measured triboelectric charge is negative are defined as negatively chargeable toner particles.

Silica fine particles used as an external additive to improve fluidity before development are so-called dry silica produced by vapor phase oxidation of silicon halide compounds, so-called dry silica called fumed silica, or so-called dry silica produced from water glass, etc. Wet silica and the like can be used, but dry silica, which has fewer silanol groups on the surface and inside and does not produce any manufacturing residue, is preferred. In addition, for dry silica, it is also possible to obtain a composite fine powder of silica and other metal oxides by using other metal halide compounds, such as aluminum chloride or titanium chloride, together with silicon halide compounds in the manufacturing process. Also includes.

Furthermore, the silica fine particles are preferably hydrophobically treated. For the hydrophobization treatment, a conventionally known hydrophobization method is used, and hydrophobization is imparted by chemically treating with an organosilicon compound that reacts with or physically adsorbs the silica fine powder. A preferred method is to treat fine silica powder produced by vapor phase oxidation of a silicon halide compound with an organosilicon compound after or simultaneously with the silane coupling agent.

Finally, the degree of hydrophobicity of the treated silica fine powder was determined to be 30 as measured by methanol titration test.
When the developer is hydrophobized so as to exhibit a value in the range of .about.80, the triboelectric charge amount distribution of the developer containing such fine silica powder becomes sharp and exhibits uniform negative chargeability, which is preferable.

Here, the methanol titration test is an experimental test to confirm the degree of hydrophobization of fine silica powder having a hydrophobized surface.

It is defined herein to evaluate the degree of hydrophobization of treated silica fine powder. The "methanol titration test" is carried out as follows. 0.2 g of sample silica fine powder in a capacity of 25
Add to 50 m 12 of water in a 0 m 12 Erlenmeyer flask. Methanol is titrated from the burette until all of the silica is wetted. At this time, the solution in the flask is constantly stirred using a magnetic cooler. The end point is observed when the entire amount of fine silica powder is suspended in the liquid, and the degree of hydrophobization is expressed as the percentage of methanol in the liquid mixture of methanol and water when the end point is reached.

Further, the applied amount of these silica fine particles is 0.05 to 3 parts by weight per 100 parts by weight of toner to exhibit an effect, and particularly preferably 0.1 to 2 parts by weight to achieve excellent stability. It is possible to provide a developer that exhibits charging properties. A preferred form of addition is one in which 0.01 to 1 part by weight of the silica fine powder is attached to the surface of the toner particles based on the weight of the developer.

As long as it does not have a substantial adverse effect on the developer,
Furthermore, other additives such as tetrafluoroethylene resin, a lubricant such as zinc stearate, a fixing aid (such as low molecular weight polyethylene), or a metal oxide such as tin oxide as a conductivity imparting agent may be added. .

In producing toner, the constituent materials are thoroughly kneaded using a thermal kneader such as a hot roll or kneader-extruder, and then obtained by mechanical crushing and classification, or by dispersing the materials in a binder resin solution. After that, the toner is obtained by spray drying, or the toner is produced by a polymerization method in which the monomers that should constitute the binder resin are mixed with a predetermined material to form an emulsified suspension and then polymerized to obtain the toner. This method can be applied.

Examples of the developing device will be described below.

In FIG. 4, an image carrier, for example, an electrophotographic photosensitive drum 1, carrying an electrostatic latent image formed by a known process rotates in the direction of arrow B. As shown in FIG. The developing sleeve 8 as a developer carrying member carries the one-component magnetic developer 4 supplied by the hopper 3, and by rotating in the direction of arrow A, conveys it to the developing area where the sleeve 8 and the drum 1 face each other. . The sleeve 8 is used to magnetically attract and hold the developer onto the sleeve 8.
A magnet 5 is arranged inside.

In order to regulate the layer thickness of the developer transported to the developing area,
A regulating blade 2 made of ferromagnetic metal is attached to a developing sleeve 8.
It hangs down from the surface so as to face the developing sleeve 8 with a gap width of about 200 to 300 μm. magnet 5
A thin layer of magnetic developer is formed on the sleeve 8 by concentrating the lines of magnetic force from the magnetic pole N1 on the blade 2. It is also possible to use a non-magnetic plate as the blade 2.

The thickness of the thin developer layer formed on the sleeve 8 is preferably thinner than the minimum gap between the sleeve 8 and the drum 1 in the developing area. The present invention is particularly effective in a device that develops a latent image using such a thin layer of developer, that is, a non-contact development type developing device. but,
The present invention can also be applied to a developing device in which the thickness of the developer layer in the developing area is greater than the minimum gap between the sleeve 8 and the drum 1, that is, a contact development type developing device. In order to avoid complication of explanation, the following explanation will be given using a non-contact development type developing device as an example.

A developing bias voltage is applied to the sleeve 8 by a power source 9 in order to cause the developer to fly from the developer layer supported on the sleeve 8 toward the drum 1 . When using a DC voltage as this bias voltage, a voltage with a value between the potential of the image area of the latent image (the area where the developer is attached and becomes visible) and the potential of the background area is applied to the sleeve 8. It is preferable that On the other hand, in order to increase the density or improve the gradation of the developed image, an oscillating electric field may be formed in the developing area by applying an alternating bias voltage to the sleeve 8. In this case as well, it is preferable to apply to the sleeve 8 an alternating bias voltage in which a DC voltage component having a value between the potential of the image area and the potential of the background area is superimposed. (Refer to Japanese Patent Publication No. 58-32375) In addition, in so-called regular development, in which toner is attached to the high-potential portion of a latent image having a high-potential portion and a low-potential portion to make it visible,
A toner that is charged to the opposite polarity to that of the latent image is used.On the other hand, in so-called reversal development, in which toner is attached to the low potential area of the latent image and visualized, the toner is charged to the same polarity as the latent image. Use toner. Note that high potential and low potential are expressions using absolute values. In any case, the toner is charged to the polarity required to develop the latent image due to friction with the sleeve 8. The externally added silica particles are also charged by friction with the sleeve 8.

In the developing device shown in FIGS. 5 and 6, a material having rubber elasticity such as urethane rubber or silicone rubber, or a material having metal elasticity such as phosphor bronze or stainless steel is used as a member for regulating the layer thickness of the developer. An elastic plate 20 is used, and this elastic plate 2o is brought into pressure contact with the sleeve 8. With such an apparatus, a thinner developer layer can be formed. And Figure 4,
The apparatus for forming a thin layer of developer as shown in Figure 5 is suitable for both those using a -component magnetic developer and those using a one-component non-magnetic developer whose main component is non-magnetic toner. ing. Since the toner is rubbed onto the sleeve 8 by the elastic plate 20, the amount of charge on the toner increases, contributing to an improvement in image density. Therefore, it is suitable for dealing with insufficient charging of toner in a high humidity environment.

Now, the above-mentioned developing sleeve 8 is made up of a metal cylindrical base 7 made of aluminum, stainless steel, brass, or the like, with an outer coating layer 6 attached to the surface.The outer coating layer 6 supports the developer. The developer is triboelectrically charged. The outer covering layer 6 is made of conductive fine particles dispersed in resin. A large number of conductive fine particles are exposed on the resin surface.

As the conductive fine particles, carbon fine particles, carbon fine particles and graphite fine particles, or graphite fine particles are preferable.

An example of the outer covering layer will be described below. A thermosetting phenolic resin was used as the resin.

The carbon used here is RAVEN 1035 manufactured by Columbia Carbon Japan. The volume average particle size of this is about 20 mμ. The coating was applied to the surface of the aluminum cylindrical substrate 7, which had been blasted with #400 Alundum abrasive grains, by a dipping method or a spraying method to a thickness of about 1.0 to 1.5 microns. In this experiment, since phenolic resin, which is one of the thermosetting resins, was used, it was heated at 150 degrees C-30 in a drying oven.
Heat curing was performed for 1 minute.

When ghost images were compared using a negative polarity toner in a developing device incorporating the thus-formed developer carrier 8, it was found that the positive ghost prevention effect improved as the formulas 1 to 3 went from formulation 1 to formulation 3. The development at this time was carried out using a non-contact jumping development method. The developing bias is AC bias Vpp 1600V.

Frequency 1800Hz, spacing between sleeve and drum approximately 3
00 microns. The thickness of the outer coating layer is 1.0 to 3.
．． The ghost prevention effect was higher at around 0μ.

Therefore, in response to these phenomena, the inventors believed that there was a close correlation between the electrical resistance of the outer coating layer and ghosts, and developed RA.
We proceeded with the study using highly conductive carbon, which has higher conductivity than VEN1035.

(Formulation 4) The effect conditions and film production method are as described above.

Further, regarding the film thickness, a study was conducted on a film thickness of 0.5 to 30 microns. As a result, when negative toner was evaluated under the same developing conditions as above in a low-humidity environment where positive ghosting is said to be most severe, it tended to be better than Formulation 1 to Formulation 3 above. Further, when the amount of conductive carbon was varied from 20% to 90% relative to the resin, a ghost prevention effect was observed.

However, when negative polarity toner is used, the anti-ghost effect may be insufficient in low humidity environments where positive ghosting is considered to be severe. Therefore, the inventors decided to consider the leakage site of the electric charge of the fine powder toner from a viewpoint other than resistance.

It is clear that the resistance of the outer coating layer is also effective in the above-mentioned formulations 1 to 4, but the resistance should be lower without the outer coating layer.

In this regard, we inventors paid attention to the following points. If the surface of the outer covering layer is made uneven, so-called charge concentration occurs due to the conductive particles, and the charge flows to the sleeve. This allows the charge of the charged-up fine powder to be removed.

From this point of view, when we changed the average particle size of the secondary particles, which are a mixture of resin and conductive carbon, by changing the dispersion state of carbon particles in the resin in the above-mentioned Formulation 4, we obtained a positive ghost prevention effect. There was a correlation between the size and distribution of secondary particles. That is, according to observation using a scanning electron microscope, (1) 2 formed on the surface of the outer coating layer;
When the average size of the secondary particles is about 1 micron or less, almost complete ghost prevention effect is exhibited even under low humidity, but when the average size is larger than that, the effect decreases. (2) If the secondary particles are so densely packed that they cannot be recognized on the surface of the outer coating layer and there are no gaps at all, that is, if an almost flat surface is formed, the ghost prevention effect will be reduced and the secondary particle spacing will be reduced. A high ghost prevention effect is observed when the average diameter is 0.05 μm to 2.0 μm. Note that the depth of the voids between the secondary particles at this time should be approximately one particle or more of the average size of the secondary particles. In other words, within the range of film thickness 0.1 μm
~30.0 μm.

(3) Although there is a preferable range for the electrical resistance of the outer coat layer when it has a ghost prevention effect, the shape of the portion of the outer coat layer in contact with the toner is more important than the volume resistance of the outer coat layer.

A brief summary of the above results is shown in the table below.

Relationship between the state of the outer coating layer and positive ghost (in the case of conductive carbon) In the above example, the average volume resistivity of the outer coating layer is 7X10~
It was found that the ghost prevention effect becomes higher when the resistance is within the range of 7×10 −2 Ω·cm. Also, 2 on the surface of the outer coating layer
The average particle size is 0.1 to 0.3 μm, and 2
When the gap between the secondary particles is 0.1 to 0.4 μm on average, the ghost prevention effect is higher.

Here, the term "secondary particles" refers to a state in which conductive particles are dispersed in a resin, and the resin is aggregated into particles. Such secondary particles may be formed by the layer being broken up by the paths through which the diluent evaporates and escapes, or when applied by spraying, the ejected droplets may It is assumed that this is the cause of the formation.

FIG. 1 is a reproduction of an electron micrograph of the surface of the outer covering layer in which the secondary particles shown above are distributed in a gravel road pattern on the outer covering layer surface.
FIG. 2 is a schematic cross-sectional view of the sleeve 8, and FIG. 3 is a schematic perspective view. Reference numerals 6' indicate secondary particles, and as shown in the figure, a large number of secondary particles 6' are distributed on the surface of the outer covering layer, forming an uneven surface resembling a gravel road. In this way, the outer coat layer in which the secondary particles 6' are distributed like a gravel road has succeeded in reducing the apparent contact resistance between the toner and the outer coat layer (creating leak sites). This made it easy to leak the fine powder toner charge. In addition, the volume resistivity of the outer coating layer is important because if a conductive sleeve is not used for insulating toner, the phenomenon of toner charge-up will occur on a macroscopic level, resulting in a decrease in development density as well as ghosting. The scope is naturally limited. In this sense, the volume resistivity of the outer covering layer is preferably 10 8 Ω·cm or less. Regarding the thickness of the outer coating layer, for a thin one, a lower limit is naturally determined from the relationship between the density of leak sites caused by toner and secondary particles. Therefore, the outer layer is 0.5μ
It is preferable that it is more than m. Furthermore, regarding the upper limit of the thickness of the outer coating layer, the conductive fine particle-containing resin layer of the present invention:
Since metal has a high volume resistivity, it is clear that if it is made too thick, the effect will be reduced.

Therefore, the thickness of the outer covering layer is preferably 30 μm or less.

The present inventors confirmed the effect by comparing the amount of charge of the toner in the upper layer and the amount of charge of the toner in the lower layer in a thin layer coating of the developer. FIG. 7 shows the difference in toner charge amount between the white area (sleeve area facing the latent image background area) and the black area (sleeve area facing the latent image area). The horizontal axis is the toner coating position, and the vertical axis is the charge amount difference, expressed as tribo difference (△Q/M) - white area Q/M - black area Q/M (Q/M is the toner charge amount). .

In contrast to conventional sleeves, charged-up toner exists in the toner core 1/lower layer as shown by the broken line.
It can be seen that in this example (prescription 4), the charged up toner is considerably reduced.

In the following example, in order to further ensure the positive ghost prevention effect especially under low humidity conditions than in the previous example, the developer carrier is Graphite was mixed into the outer layer of the body as conductive fine particles with solid lubricating properties. Other conditions were the same as in the previous example. In this case, a developer carrier having an extremely high positive ghost prevention effect was obtained.

(Formulation 5) (Formulation 6) In the following example, carbon as conductive fine particles and graphite as conductive fine particles with lubricating properties are dispersed in a photocurable resin, and this conductive fine particle-containing resin layer has an average volume of The resistivity is in the range of 102 to 10-2 Ω・cm, the thickness is between 0.5 micron to 5 micron, and the size of secondary particles made of conductive fine particles and resin is 1.0 micron or less. Moreover, it is shown that positive ghost in negative toner can be eliminated or reduced by forming a coating film in which secondary particles are distributed so that the outermost layer has a gravel road shape. .

The formulation of the coating agent in this example is shown below.

In this example, the anti-ghost effect was evaluated in the same manner as in the previous example, and very satisfactory results were obtained.

In addition, in a sleeve having an outer coating layer in which fine graphite particles are dispersed in a resin, the number of secondary particles of 1 μm or less on the surface is small, and the surface is made up of secondary particles as shown in Figures 1 to 3. It was found that the ghost prevention effect is higher than that of conventional developing sleeves even in low-humidity environments, even when the road is not a gravel road. This is because graphite has high lubricity, which reduces the amount of fine powder adhering to the sleeve surface.However, even in this outer layer, since fine powder is mixed in, the surface has extremely fine irregularities. Many are formed.

Incidentally, in order to improve the resolution of a developed image, a toner having a small particle size is suitable. In this case, the volume average particle diameter is 9 μm
The thickness is preferably 4 μm or more. The reason why this range is preferable is that when the volume average particle size is 9 μm or more, 19 pel
This is because when reproducing a latent image of 23.6 pels, there is not much improvement in sharpness, and if the volume average particle size is 4 μm or less, it is technically difficult to stably contain magnetic powder such as magnetite in the resin. This is because it is difficult to produce a magnetic toner with a volume average particle size of 4 μm or less because it is difficult to produce a magnetic toner with a volume average particle size of 4 μm or less, and the cost of pulverization and 2-classification is too high. In any case, in such a developer, the amount of fine powder increases, but according to the present invention,
By forming a conductive resin layer containing, for example, carbon particles as a conductivity imparting agent on the surface of the developing sleeve,
It becomes possible to improve sleeve ghost and durable density reduction caused by the formation of a toner fine powder layer on the surface of the developing sleeve.

As a sleeve for a developing device that uses such small particle size toner, the outer cover layer 6 is made of a resin layer containing conductive fine particles such as carbon powder with an average particle size of about 20 millimicrons, Average volume resistivity is 10-3~
It is in the range of 102Ω・cm, and the thickness is from 1.0 microns.
It is preferable that the size of the conductive fine particles is between 20 microns and that the conductive fine particles are present on the surface layer, and that the size of secondary fine particles composed of the conductive fine particles and the resin is 1.0 microns or less.

The content of the conductive fine particles contained in the outer cover layer 6 to impart conductivity is 30 to 70% by weight. At that time, graphite may be contained in the conductive fine particles described above in an amount of 30 to 100% by weight.

An example of the formulation of the outer covering layer material is shown below.

(Prescription 7) At this time, the thickness of the conductive resin layer 6 formed on the cylinder 7 was about 4 μm.

With the developing device shown in FIG. 4 having such a developing sleeve, development is carried out in a low humidity environment using a small particle diameter toner as a developer,
As a result of evaluating the occurrence of ghosts, it was found that the occurrence of ghosts was significantly reduced compared to conventional metallic conductive sleeves.

The toner used in the above examples had a styrene-acrylic copolymer as its main component, contained 90 parts by weight of magnetite as a magnetization agent, 2 parts by weight of nigrosine as a charge control agent, and was crushed and classified. Positively charged toner having a volume average particle size of 6 μm has a number distribution of 20% or less with a volume average particle size of 3.5 μm or less, and 1% or less in volume distribution with a volume average particle size of 6 μm or more. To this toner, 0.8 parts by weight of amino-modified silicone oil-treated silica was externally added in order to improve fluidity and stabilize the toner charge, and was used as a developer.

It is believed that with conventional sleeves whose metal surfaces have been roughened by sandblasting or the like, an insulating layer of oxide film is formed on the metal surface, which causes insufficient charge leakage of the fine powder, and thus a desirable effect cannot be obtained. It should be noted that, among metal plating, only the Au plating developing sleeve produced an excellent effect, and this fact seems to support the estimation of the present inventors.

Next, another example will be described.

(Prescription 8) At this time, the outer covering layer 6 formed of the above material has a thickness of about 6
In μm, the volume resistivity was measured using the four-point needle method and was found to be 5.
0x10°Ω・cm, and its surface resistivity is 7.3
It was XIO”Ω/mouth.

The sleeve with this outer coating layer was incorporated into the developing device shown in Figs. 5 and 6, and development was performed using small particle size toner to evaluate the occurrence of ghosts. Compared to the case where a conductive sleeve and a developing sleeve according to the above (prescription 7) were used, the reduction in density and the occurrence of ghosts were greatly improved.

Note that the small particle size toner used in the above examples is as follows:
A negatively charged toner containing a styrene-acrylic copolymer as a main component, 90 parts by weight of magnetite as a magnetization imparting agent, and 2 parts by weight of a monoazo metal-containing complex as a charge control agent was used. The volume average particle size of this toner is 6 μm,
The number distribution of particles with a volume average particle size of 3.5 μm or less is 20.
% or less, and those with a volume average particle diameter of 16 μm or more account for 1% or less in volume distribution.

To this toner, 0.8 parts by weight of dry negatively charged silica treated with hexamethylene disilane was externally added in order to increase the fluidity and stabilize the toner charge, and was used as a developer.

When this negatively charged small particle size toner was used to develop the latent image formed on the photosensitive drum 1, ghosting and durable density reduction were worse than the positively charged small particle size toner used in the above-mentioned example. . Therefore, when comparing positively charged small particle size toner and negatively charged small particle size toner, there is a difference in the amount of charge of the toner.
The value of the negatively charged small particle size toner is approximately -25μc/g by the two-component tribometry method, and the value of the positively charged small particle size toner is +18μc/g.
It was found that it is considerably higher than g. This is because the resin component of the toner inherently has a higher ability to be charged.

Therefore, it is considered that negatively charged small particle diameter toner is more susceptible to ghosting and lowering of durability density.

For a developer using this negatively charged small particle size toner, in a system using a developing sleeve according to the above-mentioned formulation 7, ghosts,
The effect on reducing durability density decline is insufficient, and 10
After developing and printing 0.00 to 2000 sheets, the level decreased to the same level as a system using a normal metal conductive sleeve (however, the number of prints before the effect deteriorates is greater than that of a metal sleeve).

When this developing sleeve was analyzed, it was found that the surface of the developing sleeve 8 was contaminated by the resin components and silica in the toner, and in fact, the surface of the developing sleeve 8 was cleaned or wiped with a cloth dampened with water. Wipe vigorously (by doing so, the image density and ghost prevention effect were restored to their initial levels).

Therefore, the present inventors believe that by including graphite having a surface with solid lubricating properties, particularly graphite having a cleavable crystal surface, in the outer coating layer, fine toner powder does not become easily separated from the surface of the developing sleeve. Considering this, they added graphite to the conductive fine powder. As a result, the surface of the developing sleeve 8 containing graphite in the outer coating layer was completely free from contamination by the resin components in the toner and silica even after printing 10,000 sheets.

The carbon fine powder has a volume average diameter of 5 to 100 m.
Preferably, the graphite has a volume average diameter of 0.5 to 10 μm. In addition, when using a mixture of fine carbon powder and fine graphite powder as the conductive fine powder, the graphite is 4 times the weight of carbon.
It is more preferable that the content is more than 90% by weight and less than 90% by weight. On the other hand, the weight ratio of the conductive fine powder (carbon or a mixture of carbon and graphite) to the resin as a binder is more preferably 1:4 to 2:l. If the resin component is too large, the surface will become smooth, and if it is too small, the mechanical strength of the outer coating layer will decrease, making it unsuitable for use as a developing sleeve.

As the resin, that is, the binder, in addition to the examples mentioned above, thermosetting resins such as polystyrene, butyral, vinyl salt and acetate, PMMA, ultraviolet curing resins such as epoxy acrylate, water-based polymers such as casein, glue, etc. can also be used. Also Ti
The mechanical strength of Pai Goo may be improved by dispersing O2, SnO□, and Si alkoxide-based conductive ceramic powder in the binder.

Further, as the conductive fine particles, fine metal powders such as fine stainless steel powder and fine zinc powder can also be used.

Further, as the cylindrical substrate 7 to which the outer coating layer is attached, it is also possible to use one whose surface has been blasted with spherical abrasive grains, or one which has a smooth surface.

As toner, non-magnetic toner can also be used in the present invention.

That is, the present invention is applicable not only to -component magnetic developers but also to component non-magnetic developers.

〔effect〕

According to the present invention, even in a low humidity environment, abnormal charge-up of the developer can be prevented and a good developed image can be obtained.

Further, according to the present invention, the amount of triboelectric charge of the toner can be stabilized, and the distribution of the amount of triboelectricity can be made sharp.

Further, according to the present invention, even if a negatively charged toner is used, or even if a negatively charged hydrophobized silica is used, the ghost phenomenon can be suppressed and a good developed image can be obtained.

Furthermore, according to the present invention, the fluidity of the developer on the surface of the developer carrying member is improved, so the efficiency of developer utilization during development is improved, and the charge polarity of the developer is also prevented from being reversed. , it is also possible to suppress the occurrence of fog due to toner of opposite polarity.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electron micrograph of the surface of a sleeve outer coating layer according to an embodiment of the present invention, FIG. 2 is an enlarged schematic diagram of a sleeve cross section, FIG. 3 is an enlarged needle-view schematic diagram of a sleeve surface, and FIG. The figure is an explanatory diagram of one embodiment of the present invention, FIG. 5 is an explanatory diagram of another embodiment of the present invention, FIG. 6 is an explanatory diagram of still another embodiment of the present invention, and FIG. 7 is an explanatory diagram of toner charge amount. FIG. 8 is an explanatory diagram of the conventional developing device, and FIG. 9 is an explanatory diagram of the ghost. 1 is an electrophotographic photosensitive drum, 4 is a developer, 6 is an outer coating layer, 6
' is a secondary particle, and 7 is a sleeve base. To Ding-tsu-hi

Claims (21)

[Claims] (1) In a developing device in which a one-component developer is carried by a movable developer carrying member and transported to a developing area, this carrying member has an outer covering layer in which conductive fine particles are dispersed in a resin. A developing device characterized in that secondary particles made of resin and conductive fine particles are distributed on the surface of the outer coating layer so as to form an uneven surface. (2) The developing device according to (1), wherein the conductive fine particles include carbon fine particles. (3) The developing device according to (1), wherein the conductive fine particles include graphite fine particles. (4) The developing device according to (1), wherein the conductive fine particles include carbon fine particles and graphite fine particles. (5) The average volume resistivity of the outer coating layer is 10^-^3~1
Claims (1) to (4) falling within the range of 0^2Ω・cm
The developing device according to any one of the above. (6) The developing device according to any one of claims (1) to (5), wherein the thickness of the outer covering layer is within a range of 0.5 to 30 μm. (7) The developing device according to any one of claims (1) to (6), wherein the size of the secondary particles is 1.0 μm or less. (8) The developing device according to any one of (1) to (7), wherein the supporting member frictionally charges the toner of the one-component developer to a negative polarity. (9) The developing device according to (8), wherein the one-component developer contains hydrophobized silica that is negatively charged. (10) The developing device according to any one of claims (1) to (9), wherein the one-component developer contains toner having a volume average particle diameter of 4 to 9 μm. (11) The developing device according to any one of claims (1) to (10), further comprising a bias power source that forms an alternating electric field in the developing area. (12) Claims (1) to (1) wherein the carrying member includes a regulating member that regulates the thickness of the developer layer conveyed to the developing area to a thickness thinner than the minimum gap between the carrying member and the image carrier.
10) The developing device according to any one of 10). (13) The thickness of the movable developer carrying member that carries a monocomponent developer and conveys it to the developing area and the developer layer that the carrying member conveys to the developing area is determined by the minimum gap between the carrying member and the image carrier. In a developing device that includes a regulating member that regulates the thickness to be thinner than a thickness of A developing device comprising: (14) The developing device according to claim 13, wherein carbon fine particles are further dispersed in the resin. (15) The average volume resistivity of the outer coating layer is 10^-^3 ~
15. The developing device according to claim 14, wherein the resistance is within the range of 10^2 Ω·cm. (16) The developing device according to claim 15, wherein the thickness of the outer coating layer is within a range of 0.5 to 30 μm. (17) The developing device according to any one of (13) to (16), wherein the supporting member frictionally charges the toner of the one-component developer to a negative polarity. (18) The developing device according to (17), wherein the one-component developer contains negatively charged hydrophobized silica. (19) The developing device according to (17) or (18), wherein the one-component developer contains a magnetic toner having a volume average particle diameter of 4 to 9 μm. (20) The developing device according to any one of (13) to (19), wherein the power source applies a DC bias voltage to the carrier. (21) The developing device according to any one of (13) to (19), wherein the power source applies an alternating bias voltage to the carrier.