JP4554854B2 - Development device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device, and more particularly to a developing device capable of binary development and low development potential and capable of obtaining a good image.
[0002]
[Prior art]
In recent years, in electrophotographic apparatuses such as copiers, printers, facsimiles, and the like, particularly in the field of small machines, the maintenance has been simplified, and a developing system for non-magnetic one-component toner has been put into practical use.
As a developing method for non-magnetic one-component toner, a contact developing method for a photosensitive drum using a developing roller made of a rubber or elastomer elastic material is generally proposed, and various developing rollers have been proposed. . In the contact development method for the photosensitive drum, an elastic developing roller is brought into contact with the photosensitive drum on which the electrostatic latent image is formed, and the toner thinned on the surface of the developing roller is applied in accordance with the developing electric field. The toner is moved to make a visible image. This method has the advantage that colorization is easy without using a magnetic material for the toner.
[0003]
In addition, in order to increase the life of the system, in particular, to increase the life of the photosensitive drum, there is a tendency to reduce the hazard during charging by lowering the charging potential. Therefore, a system capable of developing at a low developing potential is required. It is coming.
Further, from the viewpoint of improving the image quality, there is a demand to change from multiple values to binary values, and therefore, it has become necessary to make development γ stand as much as possible and to make the saturation development potential as small as possible.
[0004]
A conventional non-magnetic one-component toner developing device will be described with reference to FIG.
As shown in FIG. 8, the toner T is stored in the case 1, and the toner T is stirred by the toner stirring member 2. The stirred toner T is conveyed to the developing roller 4 by the replenishing roller 3, and the toner T attached to the developing roller 4 is formed to a predetermined thickness by the toner layer forming member 5. The toner T adhered to the developing roller 4 with a predetermined thickness is conveyed to the photosensitive drum 6 and carried on the surface of the photosensitive drum 6. Reference numeral 7 denotes a bias power source.
[0005]
In the non-magnetic one-component developing method using the developing device having such a configuration, the toner adheres to the toner thin layer blade (toner layer forming member 5), the toner filming onto the developing roller 4, and the time on the surface of the developing roller 4 Due to the problems such as the occurrence of scratches such as streaks, the toner charge amount due to the deterioration (stress) of the toner T, the change in the toner adhesion amount on the developing roller 4 with time, the soiling at the time of toner replenishment, etc. It must be in the form of a cartridge that can be replaced by k-level printing (tens of thousands of prints).
However, because of the problem of global environmental pollution caused by the disposal of the cartridge and the maintenance problem (for example, contamination with toner when the cartridge is replaced, the number of sheets is as small as about 20,000), the development of the stationary type without the above problem A device is sought.
[0006]
In order to solve such a problem, as in the prior art, as disclosed in Japanese Patent Application Laid-Open No. 7-20714, a toner brush is started up with a two-component developer, and a magnetic brush formed on a magnet roller is used on the developing roller. By supplying the toner, the contact member to the developing roller is eliminated, and the stress on the toner is reduced, so that a stationary type developing device can be realized. Xerox Docucentre 650 (trade name) is a product using a developing device having the same configuration as that disclosed in Japanese Patent Laid-Open No. 7-20714.
[0007]
[Problems to be solved by the invention]
However, the Docucentre 650 developing device uses a belt-like photosensitive drum, and the developing roller has a high resistance and high hardness. Therefore, it is not suitable for binary development and low development potential.
Further, in the case of this method (Developer of Docucentre 650), the toner thin layer formation (adhesion amount adjustment) method on the development roller is electrically adjusted by the electric field from the magnet roller (replenishment roller). For this reason, the electrical characteristics of the developer have a great influence on the toner thin layer formability, and consequently the image characteristics. In particular, when a solid image is continuously output, the image density of the second and subsequent turns of the developing roller is lowered due to carrier resistance, so that there is a problem on the image that a negative afterimage is generated.
In order to secure a stable toner supply amount to the developing roller and obtain a good image, it is necessary to increase the toner density.
[0008]
Accordingly, an object of the present invention is to provide a developing device capable of binary development and low development potential and capable of obtaining a good image.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention described in claim 1 carries a two-component developer including a developing roller for carrying a toner on the surface and transporting the toner to a developing area facing the latent image carrier, and a toner and a carrier. And a toner supply roller that transports the toner to a toner supply area facing the developing roller and supplies only the toner from the two-component developer to the developing roller. The developing roller is elastic with the surface layer. The actual resistance of the surface layer is 1.0 × 10 ⁸ Ω or less when measured in the direction of the developing roller surface with an applied voltage of 1 V , and is smaller than the actual resistance of the elastic layer, The volume resistance of the developing roller is 2.2 × 10 ³ Ω · cm or more and 1.0 × 10 ⁷ Ω · cm or less when measured in the circumferential direction of the developing roller with an applied voltage of 1 V , and the latent image carrier and the two-component Except for the developer, the development When there is no member in contact with the image area of the roller and the developing roller is used, the difference between the surface potential of the image portion on the latent image carrier and the developing bias is 150 V or less, and the toner on the latent image carrier The adhesion amount is saturated. By eliminating the conventional contact member to the developing roller, the stress on the toner is reduced, so that it is possible to prevent the toner from adhering to the developing roller, filming, scratching, and the like.
Also, the reason for this configuration will be described. Development γ (toner adhesion amount on the photosensitive drum) does not saturate at a development potential of 150 V or less. As for the relationship between the resistance and the development γ, there is a tendency that the slope of γ becomes steep when the resistance is low, and the slope is slanted when the resistance is high. The development potential of 150V is much lower than conventional systems. By reducing the resistance, the developing bias can be lowered. Accordingly, since the developing bias can be set low, the life of the photosensitive drum is extended.
That is, the charging potential of the photosensitive drum can be lowered (for example, 300 V), and in this case, the potential of the image portion can be several tens of volts. Therefore, when the background potential is considered as 100 V, the developing bias is 200 V. It becomes as follows. In that case, if the potential of the image portion is 50V, the development potential is 150V, and it is necessary to saturate at 150V or less in order to achieve binary development. The validity of the development potential of 150V is not so much at present, but the target of future developed products is 100V development, and the target value + α is set to 150V (low potential considering the conventional).
Further, the reason for this configuration will be described. As a relationship between the volume resistance of the developing roller and the surface resistance, in order to reduce the roller resistance including the surface layer, conventionally, the resistance of the elastic layer has to be lowered due to the resistance configuration of the elastic layer ≦ the surface layer, It must be highly filled with a conductive agent such as carbon black. However, when the conductive agent is highly filled, the hardness is increased, so that the required hardness cannot be satisfied. Therefore, by adopting a resistance configuration of elastic layer> surface layer, the entire roller surface acts as an electrode, so that a large amount of current flows, and thus the resistance becomes lower than the resistance of the elastic layer alone.
In order to achieve low potential saturation development, a low resistance is required, and the resistance can be easily reduced by adopting a resistance configuration of elastic layer> surface layer. Conventionally, the reason why the low resistance roller is not used is that the gradient of γ is important in order to obtain the gradation of the image. The resistance environment fluctuates greatly because of leakage to the photosensitive drum due to application of a high bias, and it is used in an intermediate resistance region where resistance control is unstable. As an effect of using low resistance, it is expected that variation in manufacturing is reduced and resistance variation due to environment is also reduced.
[0010]
The invention described in claim 2 is the developing device according to claim 1,
The two-component developer has a carrier resistance of 1.0 × 10 ^{8 to} 1.0 × 10 ¹⁰ Ω at an electric field strength of 2.2 × 10 ⁴ V / cm.
In this way, by increasing the carrier resistance, it is possible to improve the toner supply performance to the developing roller, so that the toner thin layer rises on the developing roller (for example, corresponding to the development from the first sheet to the second sheet). (Rise at the time) can be made faster.
[0011]
Further, the invention according to claim 3 is the developing device according to claim 2, wherein the carrier of the two-component developer is coated with a polymer having an average particle diameter of 70 μm or less and a surface having a polarity opposite to the charged polarity of the toner. It is characterized by being.
Thus, by making the carrier have a small particle diameter, the toner concentration can be increased, and as a result, the toner supply performance can be increased. Further, by increasing the toner concentration, the number of rotations of the supply roller can be decreased, so that toner scattering can be prevented. The reason for coating the carrier is to increase toner chargeability and to prevent spent (toner filming) on the carrier.
[0015]
According to a fourth aspect of the present invention, in the developing device according to the first aspect, a ratio of the developing roller diameter (Rd) to the toner supply roller diameter (Rs) is Rs / Rd> 1. . The reason for this configuration will be described. By making the supply roller diameter larger than the developing roller diameter, it is possible to improve toner supply performance. When the supply roller diameter is smaller than the developing roller diameter, the toner supply amount is insufficient, so that the image density is lowered. Therefore, if Rs / Rd> 1, an image having a good image density can be obtained.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on the illustrated embodiments.
(1) Apparatus FIG. 1A is a side sectional view showing a developing apparatus of the present embodiment, and FIG. 1B is a side sectional view of a developing roller.
As shown in FIG. 1A, the developer (two-component developer) G is composed of a toner T and a carrier C. The toner T is charged by the toner T and the carrier C supplied to the toner supply unit 11. The first and second toner stirring members 12 and 13 are used for stirring and mixing. The developer G is adjusted to an appropriate amount by the doctor blade 15 by the supply roller 14 composed of a magnet roller, and then is conveyed to a supply portion (toner supply & thin layer forming portion 21) with the development roller 16 to be magnetic brush (illustrated). In this case, only the toner T is supplied onto the developing roller 16.
[0019]
The toner T supplied onto the developing roller 16 is conveyed by the developing roller 16 to the electrostatic latent image portion of the photosensitive drum 17 which is a “latent image carrier”, and the developing portion 22 develops the latent image. The supply roller 14 and the development roller 16 are “non-contact”, and the development roller 16 and the photosensitive drum 17 can be used either “contact or non-contact”, but contact development is preferable from the viewpoint of image quality. That is, in the image area of the developing roller 16, a photosensitive drum (image bearing member) 17 and a developer (two-component developer) against touch to that member is not configured other than G to the developing roller 16.
[0020]
Although not shown, a bias voltage is applied between the supply roller 14 and the developing roller 16 and between the developing roller 16 and the photosensitive drum 17 via a power source. The bias to the developing roller 16 may be “direct current” or “direct current + alternating current”, but the direct current bias is desirable from the viewpoint of cost.
[0021]
By using the developing device having such a configuration, the number of members in contact with the developing roller 16 is reduced, so that filming on the developing roller 16 and damage to the developing roller 16 can be prevented.
Further, the problem of toner sticking to the blade, which has been a problem with the conventional blade toner thin layer type developing device, is eliminated. In addition, since a gap is formed between the doctor blade 15 and the supply roller 14, the toner does not adhere.
Furthermore, the supply roller 14 needs to rotate the supply roller 14 faster than the development roller 16 in order to stably supply the toner onto the development roller 16. The reason is that if the diameter of the supply roller 14 is smaller than the diameter of the developing roller 16, the toner supply becomes insufficient, and an afterimage or a decrease in image density as described later at (3) the developing roller 16 occurs.
[0022]
(2) Developer G
The developer G is composed of toner T and carrier C. The toner T is a mixture of a resin such as polyester, polyol, styrene acrylic, and a charge control agent (CCA) and a colorant. The fluidity is increased by adding substances such as these. The particle size of the additive is usually in the range of 0.1 to 1.5 μm. Examples of the colorant include carbon black, phthalocyanine blue, quinacridone, and carmine. The charging polarity is negative charging in the present embodiment.
As the toner T, a toner obtained by externally adding the above-mentioned type of additive to a base toner in which wax or the like is dispersed and mixed may be used.
The range of the volume average particle diameter of the toner T is preferably 3 to 12 μm, but in the present embodiment, it is 7 μm and can sufficiently cope with a high resolution image of 1200 dpi or more.
[0023]
For carrier C, a magnetic material such as iron powder, magnetite, ferrite, or the like is used as it is, or a coating layer such as a silicone resin is provided on the surface for the purpose of improving toner chargeability or preventing toner T filming. Used by coating.
The particle size of the carrier C is about 30 to 100 μm, and in the present embodiment, the carrier C of 50 μm is used. The smaller the carrier particle size, the higher the toner concentration. Therefore, the toner can be supplied stably.
[0024]
Further, in this system, the toner supply performance is improved by making the supply roller 14 rotate faster than the developing roller 16, but if the supply roller 14 rotates fast, a problem such as toner scattering occurs. If the toner density can be increased, the rotation speed of the supply roller 14 can be decreased. In order to stably supply the toner T from the toner supply roller 14 to the developing roller 16, the carrier resistance at an electric field strength of 2.2 × 10 ⁴ V / cm needs to be 1.0 × 10 ^{8 to} 1.0 × 10 ¹⁰ Ω. It becomes. As shown in FIG. 2, the carrier resistance is measured by applying a voltage of 200 V between the doctor blade 15 and the aluminum sleeve (supply roller 14), rotating at 600 r / min, and determining the resistance value after 5 minutes as the carrier resistance. did.
[0025]
(3) Developing roller 16
As shown in FIG. 1B, the developing roller 16 used in the present embodiment forms an elastic layer (rubber layer) 16b on a metal core shaft (core metal) 16a, and a coating layer (surface layer). 16c is provided.
As the elastic layer 16b, for example, a known rubber or elastomer such as ethylene propylene rubber, butadiene rubber, nitrile rubber, styrene rubber, isoprene rubber, silicone rubber, urethane rubber or foam can be used. As the hardness, in order to improve the dot reproducibility of the image, it is better that the nip width is not too wide, and the hardness for that purpose is preferably 25 to 50 degrees in JIS-A hardness.
[0026]
The surface layer 16c having a film thickness of 10 to 30 μm is formed by applying various known coatings such as a dip method, spray coating, and roll cotoner around the elastic layer 16b.
The important characteristics of the developing roller 16 as used in the present invention are electrical characteristics (resistance, capacity). With the recent longevity of the system (especially the photosensitive drum), there has been an attempt to reduce the deterioration of the photosensitive drum by lowering the charging potential, and accordingly, the developing bias has to be set low. Furthermore, in order to change from multivalue to binary, high development γ is required. In order to meet this requirement, the resistance of the developing roller is set to a low resistance that is different from the conventional medium resistance region. In order to obtain conductivity, a conductive agent such as carbon black or metal oxide is added.
A method for measuring the resistance of the developing roller 16 is shown in FIG. In FIG. 3, reference numeral 23 is an ohmmeter, and 24 is a metal electrode.
[0027]
(4) Examples and Comparative Examples FIG. 4 shows carrier characteristics (resistance) used in Examples and Comparative Examples. For toner T constituting developer G, a polyester resin is used as a base material. FIG. 5 shows the characteristics of the developing roller 16 used in the examples and comparative examples.
In the developing roller 16, an elastic layer 16b of urethane elastomer was formed on a cored bar 16a by a one-shot method using polyol and isocyanate in which carbon black was dispersed. Thereafter, the elastic layer 16b having a thickness of 4 mm was obtained by adjusting to φ16 or φ20 mm by outer diameter grinding. Thereafter, a melamine resin was added as a curing agent to a water-based urethane paint in which carbon black was dispersed, and a coating layer having a thickness of 10 to 20 μm was applied by a spray coating method, followed by heat curing at 130 ° C. for 1 hour.
The resistance was adjusted by adjusting the amount of carbon black added to the polyol and the amount of carbon black added to the water-based urethane coating.
[0028]
The diameter of the supply roller 14 used in the examples and comparative examples is shown below.
Supply roller 1: φ18mm, Supply roller 2: φ20mm
The supply roller 14 has a magnet fixed inside, and has a structure in which a non-magnetic non-magnetic sleeve is rotatably disposed on the outer periphery thereof (not shown). In the present embodiment, the sleeve is made of aluminum and has a V-groove (not shown) in order to improve the transportability of the developer G.
An experiment was conducted using a combination of the carrier C, the developing roller 16 and the supply roller 14 under the conditions shown in FIGS. The evaluation items were the presence or absence of negative afterimage generation on the image and the saturation development potential. The afterimage evaluation method and the saturated development potential will be described with reference to FIGS. FIG. 6A is a test chart, and FIG. 6B is a characteristic diagram showing the relationship between the development potential and the toner adhesion amount on the photoreceptor.
FIG. 7 shows the experimental results.
[0029]
<Afterimage evaluation method>
Evaluation is performed as an afterimage rate (%).
Measure ID (reflection density) of (1) and (2) in FIG.
Afterimage ratio (%) = (▲ 1 ▼ − ▲ 2 ▼) / (▲ 1 ▼ + ▲ 2 ▼) × 100
Here, when the afterimage rate is negative, a negative afterimage is indicated, and when it is positive, a positive afterimage is indicated. The target for the afterimage rate is 2% or less.
As is apparent from FIG. 6B, when the development potential is 150 V or less, the development γ (toner adhesion amount on the photosensitive drum) is not saturated. As for the relationship between the resistance and the development γ, there is a tendency that the slope of γ becomes steep when the resistance is low, and the slope is slanted when the resistance is high. The development potential of 150V is much lower than conventional systems. By reducing the resistance, the developing bias can be lowered.
[0030]
Although the photosensitive drum is used in the above-described embodiment, the present invention can of course be applied to a belt-type photosensitive member.
[0031]
【The invention's effect】
As described above, according to the present invention, the following effects can be exhibited. According to the first aspect of the present invention, in the image area of the developing roller, the stress on the toner can be reduced by eliminating the contact member other than the latent image carrier (photosensitive drum) and the two-component developer. In addition, toner adhesion to the developing roller and toner filming can be prevented, scratches on the developing roller can be prevented, and coating layer wear can be reduced. According to the first aspect of the present invention, the difference between the surface potential of the image portion on the photosensitive drum (latent image carrier) and the developing bias is 150 V or less, and the toner adhesion amount on the photosensitive drum is saturated. By doing so, leakage to the photosensitive drum does not occur despite the low resistance roller. Low potential binary development can be achieved. Since the charging potential of the photosensitive drum can be lowered, the life of the photosensitive drum can be extended. Furthermore, according to the first aspect of the present invention, when the actual resistance of the surface layer when measured in the roller surface direction with an applied voltage of 1 V is 1.0 × 10 ⁸ Ω or less, the development potential is 150 V or less. The toner adhesion amount on the electrostatic latent image can be saturated. As a result, the developing bias can be set low, leading to a long life of the photosensitive drum (latent image carrier). Furthermore, according to the first aspect of the present invention, the volume resistance when measured in the circumferential direction of the roller with an applied voltage of 1 V is set to 2.2 × 10 ³ Ω · cm or more and 1.0 × 10 ⁷ Ω · cm or less. The toner adhesion amount on the electrostatic latent image can be saturated with a developing potential of 150 V or less. As a result, the developing bias can be set low, leading to a long life of the photosensitive drum (latent image carrier). According to the second aspect of the present invention, the toner supply performance from the supply roller to the developing roller is improved by setting the carrier resistance at an electric field strength of 2.2 × 10 ⁴ V / cm to 1.0 × 10 ^{8 to} 1.0 × 10 ¹⁰ Ω. Since it can be increased, afterimages on the image can be prevented.
[0032]
According to the third aspect of the invention, the carrier has an average particle diameter of 70 μm or less and the surface thereof is coated with a polymer having a polarity opposite to the charging polarity of the toner, thereby increasing the toner concentration and supplying the developing roller to the developing roller. The toner supply performance can be improved and the rotation speed of the supply roller can be reduced. Further, the coating on the carrier surface can improve the toner charging property and can prevent spent (toner filming) on the carrier .
[0033]
According to the fourth aspect of the present invention, since the ratio of the developing roller diameter (Rd) to the toner supply roller diameter (Rs) is set to Rs / Rd> 1, stable toner supply from the supply roller to the development roller can be achieved. In addition, it is possible to prevent a decrease in image density and an afterimage.
[Brief description of the drawings]
1A and 1B are diagrams showing an embodiment of the present invention, in which FIG. 1A is a side sectional view of a developing device, and FIG. 1B is an enlarged sectional view of a developing roller;
FIG. 2 is a diagram showing a carrier resistance measurement method in the embodiment;
FIG. 3 is a diagram illustrating a developing roller resistance measurement method according to the embodiment;
FIG. 4 is a diagram showing carrier data in the embodiment.
FIG. 5 is a diagram showing development roller data in the embodiment;
6A is a diagram showing a test chart in the same embodiment, and FIG. 6B is a diagram graphing experimental results.
FIG. 7 is a diagram showing experimental result data in the embodiment.
FIG. 8 is a side sectional view of a conventional non-magnetic one-component toner developing device.
[Explanation of symbols]
C ... Carrier G ... Developer (two-component developer)
T ... Toner 1 ... Case 2 ... Toner stirring member 3 ... Supply roller 4 ... Developing roller 5 ... Toner layer forming member 6 ... Photoconductor drum 7 ... Bias power supply 11 ... Toner supply unit 12 ... First toner stirring member 13 ... First 2 toner agitating member 14 ... supply roller 15 ... doctor blade 16 ... developing roller 16a ... core shaft 16b ... elastic layer 16c ... surface layer 17 ... photosensitive drum 18 ... bias power supply 19 ... ammeter 21 ... toner supply & thin layer formation Part 22 ... Developing part 23 ... Resistance meter 24 ... Metal electrode 30 ... Test chart

Claims (4)

A toner is carried on the surface and conveyed to a development region facing the latent image carrier, and a two-component developer containing toner and carrier is carried and conveyed to a toner supply region facing the development roller. A developing device including a toner supply roller that supplies only the toner from the two-component developer to the developing roller;
The developing roller has a surface layer and an elastic layer,
The actual resistance of the surface layer is 1.0 × 10 ⁸ Ω or less when measured in the direction of the developing roller surface with an applied voltage of 1 V, and is smaller than the actual resistance of the elastic layer,
The volume resistance of the developing roller is 5.5 × 10 ³ Ω · cm or more and 1.0 × 10 ⁷ Ω · cm or less when measured in the circumferential direction of the developing roller with an applied voltage of 1 V ,
Except for the latent image carrier and the two-component developer, there is no member that contacts the image area of the developing roller,
When the developing roller is used, the difference between the surface potential of the image portion on the latent image carrier and the developing bias is 150 V or less, and the toner adhesion amount on the latent image carrier is saturated. . 2. The developing device according to claim 1, wherein the resistance of the carrier of the two-component developer is 1.0 × 10 ^{8 to} 1.0 × 10 ¹⁰ Ω at an electric field strength of 2.2 × 10 ⁴ V / cm. .   3. The developing device according to claim 2, wherein the carrier of the two-component developer has an average particle size of 70 [mu] m or less and the surface is coated with a polymer having a polarity opposite to the charged polarity of the toner. .   2. The developing device according to claim 1, wherein a ratio of the developing roller diameter (Rd) to the toner supply roller diameter (Rs) is Rs / Rd> 1.

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