JPH11231654A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device which can stably transport toner without adjusting supply bias irrespective of environmental changes. SOLUTION: A potential difference is applied across a developer carrier 10 making developer adhere to a latent image carrier and a supply means 20 to be press-contacted with the developing carrier 10, and also, the resistance value of the supply means 20 is determined so that a 1st resistance value RH in a state at a high temperature and humidity is smaller than a 2nd resistance value RL in a state at a low temperature and humidity. And, the resistance value is to be arranged so that when it is high in temperature and humidity of 35 deg.C and 65%, the 1st resistance value RH takes 102 Ω or more, and when it is low in temperature and humidity of 10 deg.C and 15%, the 2nd resistance value takes 108 Ω or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a developing device used for an image forming apparatus such as a laser printer and a laser facsimile for forming an image by electrophotography.

[0002]

2. Description of the Related Art Conventionally, in order to obtain a high-quality image faithfully reproducing an electrostatic latent image on a latent image carrier in this type of electrophotographic apparatus, a toner layer having a uniform thickness is formed on a developer carrier. Is an important requirement, and various proposals have been made for that.

For example, Japanese Unexamined Patent Publication No. 61-238072 (known example 1) discloses a pressing roller 5 made of a conductive elastic material while stirring toner by an agitator 4 in a hopper 2.
The developing sleeve 1 having the electrode layer 1c supplied thereto and pressed against the surface layer 5b of the pressing roller 5 is turned in the same direction as the pressing roller 5 so that the toner charged at the contact portion C is placed on the developing sleeve 1. In FIG. 1, a voltage applying device 10 is provided so that a potential difference is formed between the pressing roller 5 and the developing sleeve 1.

[0004] For example, Japanese Patent Application Laid-Open No. 6-194944 (known example 2) has a developing roller 5 and a toner supply roller 6.
A bias voltage is applied from 6, 18;
In the figure, a bias voltage applied to the toner supply roller 6 is variably controlled in accordance with a change in physical properties of the toner supply roller 6.

[0005]

Although the above-mentioned known examples 1 and 2 can be expected in terms of the toner supply function, there is still room for improvement.

That is, in the prior art 1, the bias voltage is adjusted to stabilize the toner supply property, and the afterimage is improved. In the known example 2, the change in the physical properties such as the resistance and the hardness of the supply roller is caused. The toner supply property is only improved by changing the bias voltage in response to the change. The change in the chargeability and the supply property of the toner due to the temperature and humidity is not always sufficient, and the improvement is required.

A first problem to be solved by the present invention is to provide a developing device which can guarantee good toner supply without being particularly affected even when the environment such as temperature and humidity changes. That is.

A second problem to be solved by the present invention is to provide a developing device which does not need to change and adjust the supply bias condition even when the environment such as temperature and humidity changes.

A third problem to be solved by the present invention is that the supply of toner is improved in a high-temperature and high-humidity environment, and the excessive supply of the toner is suppressed in a low-temperature and low-humidity environment, so that the toner is always stable. An object of the present invention is to provide a developing device capable of maintaining the supply of toner.

A fourth problem to be solved by the present invention is to provide a developing device having a simplified structure because it is not necessary to change the supply bias condition.

[0011]

Means for solving the problems Specific means for solving the above-mentioned problems are as follows.

(1) A developing device for electrostatically attaching a developer to a latent image carrier to develop the developer, the developer carrier capable of attaching the developer to the latent image carrier, and the developer carrier A potential difference is provided between the supply means and the supply means pressed against the body, and the first resistance value RH in the "high temperature and high humidity" state of the resistance value of the supply means is the second resistance in the "low temperature and low humidity" state. Wherein the resistance value is relatively smaller than the resistance value RL.

(2) 35 ° C. in the “high temperature and high humidity” state,
The developing device according to (1), wherein the first resistance value RH is not less than 102 Ω at 65%.

(3) 10 ° C. in the “low temperature and low humidity” state,
The developing device according to the above (1) or (2), wherein the second resistance value RL is 10 8 Ω or less at 15%.

Since the resistance value of the supply roller is changed in accordance with environmental changes such as temperature and humidity by the above-mentioned corresponding means, the toner supply does not occur shortage or oversupply, and the toner is stably supplied to the developing roller. You can do it.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The specific contents of the present invention will be described below with reference to the drawings.

1. An electrostatic latent image is formed on a latent image carrier 60 such as a photosensitive member uniformly charged by a charging unit such as a charging roller or scorotron (not shown) by a charging unit such as a laser and an exposure unit such as a laser (not shown). The apparatus 1000, more specifically, the developing roller 10 that transports the toner (T) as a developer contacts the latent image carrier 60, and the toner (T) adheres to the electrostatic latent image by an electrostatic force, and The formation is made.

The developing device in this embodiment does not contact the latent image carrier with a gap when the normal developing operation is not performed (broken line in FIG. 1). The angle changes due to the movement of a cam (not shown) and comes into contact with the latent image carrier (solid line in FIG. 1).

At this time (at the position where the developing device comes into contact with the latent image carrier), the toner carried on the surface of the developing roller is adhered to the latent image carrier by electrostatic force and developed.

In this embodiment, the developing device is configured to be separated from and in contact with the photosensitive member. However, this is a preferred example for forming a color image, and the present invention is not limited to this. .

A supply roller is provided for supplying toner to the developing roller.

The supply roller is frictionally charged by rubbing the toner against the developing roller, and is brought into contact with the developing roller so as to electrostatically adhere to the developing roller so as to have a certain bite amount, and is rotated.

The developing roller and the supply roller are first,
It is rotatably supported by the second support shafts 12 and 22.

The developing roller is a hard roller made of SUS, aluminum, or the like, and the supply roller has at least a surface formed of an elastic material such as foam for carrying toner and rubbing against the developing roller.

A developing bias applying means 200 is disposed between the first support shaft 12 and the latent image carrier 60 to form an electric field corresponding to the electrostatic latent image formed on the latent image carrier, and The latent image is visualized.

A supply bias applying means 100 is provided between the first and second support shafts 12 and 22 to form an electric field between the developing roller and the supply roller, and the toner is supplied from the supply roller to the development roller. Of the developing roller, or conversely, the toner remaining on the developing roller without being developed is collected by the supply roller.

The resistance value of the supply means 20 is, for example, in a high temperature state of about 35 ° C. and 65%, for example.
In a high humidity state, the first resistance value RH is 1
In a low temperature state of, for example, about 10 ° C. and a low humidity state of, for example, about 15%, the second resistance value RL is autonomously changed so as to be about 10 6 Ω. Configured.

Numeral 40 shown in FIG. 1 denotes a toner (T) transfer means, which is a transfer fin 42 for turning the toner (T) stored in the hopper 41 in a counterclockwise direction (arrow A) in FIG. By means of 43 and 44, it can be transported toward the supply roller 20 while stirring so as not to solidify.

Numeral 50 denotes a regulating means, which holds the free end of an elastic body 53 provided at the outer end of a support frame 52 supported swingably by a biasing means 51 such as a coil spring on the surface 11 of the developing roller 10. Contact is made at a predetermined pressure.

2. Operation Next, prior to describing the operation when the developing device 1000 is used, it has been verified that the following causal relationship exists between the toner supply property and the guarantee of a high quality image.

That is, in general, it is desirable for the developing device of this type that the toner supply property is sufficient and stable. If the toner supply property is excellent, the required amount of toner on the developer carrier is required. Of toner will be supplied,
High-density toner image whose image density is approximately the saturation value,
In the case where a so-called solid image is continuously formed, for example, on substantially the entire surface of an image formable area on recording paper, a sufficient amount of toner is supplied from the supply roller so as to compensate for the amount of toner consumed on the developing roller. When a uniform image is formed, it is guaranteed that a uniform solid image is continuously formed, and the toner supply property can be detected from the amount of toner transported on the developing roller.

In this method, the supply of toner by the supply roller is detected from the amount of toner transported on the developing roller. When the supply of toner by the supply roller changes, the amount of toner transported on the developing roller changes accordingly. In order to do this, the change rate of the toner conveyance amount on the developing roller may be measured.

That is, if the rate of change of the toner transport amount on the developing roller is within a predetermined range, it can be said that the supply of toner by the supply roller is stable.

Therefore, in the present invention, the change rate of the toner conveyance amount on the developing roller is used as an index indicating the toner supply property, and this change rate of the toner conveyance amount is referred to as a toner supply rate.

Now, a specific definition of the toner supply rate is the weight per unit area of the toner carried on the developer carrying member without developing, that is, the leading end conveying amount indicating the conveying amount after the white image. This is expressed as a percentage of the rear end transport amount M2 indicating the weight per unit area of the toner carried on the developer carrying member at the rear end of the solid image with respect to M1.

Accordingly, regarding the toner supply rate, the percentage of the rear end supply amount M2 to the front end supply amount M1 is 100%.
%, The rear end supply amount M2 becomes closer to the front end supply amount M1 and the difference between the front end and rear end of the image is reduced, so that a high-quality image can be obtained.
It has been verified that desirably, at 90% or more, a uniform solid image with good supply properties can be obtained.

Conversely, if the toner supply rate is too high, the density of the leading edge of the image will decrease (120% because the leading edge density is too low, or toner is supplied so much that it cannot be carried on the developing roller). Less, desirably less than 110%.

The supply of the toner (T) is greatly affected by the environmental temperature and humidity. At high temperature and high humidity, the triboelectric charging performance is reduced. Since the amount of charged toner is insufficient and the supply amount of the toner from the supply unit to the developer carrier decreases, a supply potential difference is provided between the supply unit and the developer carrier to promote the supply of the toner, and a necessary toner amount is provided. In this case, when the resistance of the supply unit is high, a part of the supply potential difference provided for supplying the toner from the supply unit to the developer carrier is applied to the supply unit itself. As a result, the potential difference actually applied to the toner becomes small, and it becomes necessary to secure a larger supply potential difference in order to secure a necessary amount of toner.

On the other hand, at a low temperature and a low humidity, since the triboelectric charging performance is high, a relatively large amount of charged toner can be obtained so that the toner can be electrostatically attached to the developer carrying member. If the resistance of the supply means does not change due to the environment, if the supply potential difference is set so that the supply properties are good at high temperature and high humidity, excessive supply of toner to the developer carrier unnecessarily occurs, It has also been pointed out that toner that cannot be carried on the developer carrying member spills off from the developer carrying member and may cause an image or soil the inside of the image forming apparatus.

In the developing device 1000, the supply means 2 is provided by transfer fins 42 and 43 which are turned in the direction of arrow A.
The toner (T) such as the toner supplied on the top surface of the developer carrier 10 and the supply unit 20 are configured such that a supply potential difference is provided in advance when the supply unit 20 is turned clockwise (arrow B). And 21 are frictionally charged in the contact area and adhere from the surface 21 of the supply means 20 to the surface 11 of the developer carrier 10 and are regulated on the surface 11 of the developer carrier 10 which is turned in the direction of arrow B. 50 elastic bodies 5
3, a thin layer is uniformly formed, is opposed to the latent image carrier 60, and is attached to the latent image carrier 60 in accordance with an electrostatic pattern formed on the latent image carrier 60 turned in the direction of arrow A. Is developed.

By the way, in this embodiment, the material of the supply means 20 whose resistance value changes autonomously according to the environment is adopted, and the environment changes from a low temperature and low humidity environment to a high temperature and high humidity environment. , The resistance value also changes from RL to R
Changes to H.

RH is lower than RL.

The supply roller used in this embodiment has a resistance RL of 10 6 Ω in a low-temperature and low-humidity environment with a temperature of 10 ° C. and a humidity of 15% and a high-temperature and high-humidity environment with a temperature of 35 ° C. and a humidity of 65%. When the resistance RH changes to 10 5 Ω, the developer carrier 10 caused by the deterioration of the triboelectric charging property of the toner (T)
The toner (T) can be effectively supplied to the developer carrier 10 by sufficiently exerting the applied supply bias effect without causing supply failure to the developer.

Further, as the environment changes from a high temperature and high humidity environment to a low temperature and low humidity environment, the resistance value also changes from RH to RL.

RL is higher than RH.

The supply roller used in this embodiment has a resistance RH of 105 Ω in a high-temperature and high-humidity environment with a temperature of 35 ° C. and a humidity of 65% and a low-temperature and low-humidity environment with a temperature of 10 ° C. and a humidity of 15%. When the resistance RH changes to 10 <6> [Omega], the applied supply bias acts not on the toner (T) but on the supply means 20, and the supply bias effect is less likely to be exhibited, and the toner (T) having a high triboelectric charging property under low temperature and low humidity. This prevents the developer from being supplied to the developer carrier 10 more than necessary.

When the above operation was verified, the results shown in FIG. 2 were obtained.

That is, the toner supply rate (%) and the supply potential difference (V) (the potential difference between the supply means and the developer carrier in the direction of supplying the toner to the supply means and the developer carrier).
For example, when a negatively charged toner is used, the potential of the developer carrier
200 V, supply means potential -400 V, supply potential difference 2
00V), high temperature and high humidity HH,
As for the toner supply rate in the normal temperature and normal humidity NN and the low temperature and low humidity LL, for example, when the supply potential difference is 200 (V), the toner supply rate is 103% in the low temperature and low humidity LL and 95% in the high temperature and high humidity HH. It was confirmed that even if the supply potential difference was kept constant, the transition was favorable.

Incidentally, the magnitude of the supply potential difference applied for improving the toner supply property is affected by the resistance value of the supply means.

It was observed that the higher the resistance value of the supply means, the larger the supply potential difference for ensuring the toner supply property.

Therefore, even if the supply potential difference is set such that supply delay does not occur at high temperature and high humidity, the resistance of the supply means may increase at low temperature and low humidity, causing a supply delay. In addition, it is necessary to set a supply potential difference that does not cause excessive supply at high temperature and high humidity.

Experimentally, the supply roller of the present invention, which was experimentally manufactured with the resistance RL at low temperature and low humidity LL in the range of 10 3 to 10 8 Ω, has a resistance RH at high temperature and high humidity HH of RH <RL and 10 2 to 10 7 Ω. By setting the supply potential difference appropriately, good supply properties could be secured even when the environment changed.

However, if the resistance of the supply means exceeds 108 Ω, the applied supply bias acts on the supply means instead of the toner, or depending on the speed of the latent image carrier, the developer carrier and the supply means, the Since the required amount of supply current flowing between the supply means and the developer carrier due to the movement cannot flow, the effect of the supply potential bias was not obtained.

Therefore, the resistance of the supply means of the present invention is 10 8
Ω or less, and RL ≦ 10 even at low temperature and low humidity.
The relationship of 8 Ω was satisfied.

When the resistance of the supply means is less than 10 2 Ω, if the toner between the supply means and the developer carrier does not intervene as in the case of solid development or decreases, the supply means and the developer carrier Because the resistance between them is low, the supply potential difference cannot be held by a power supply normally used.

Therefore, the resistance of the supply means of the present invention is 10 2
Ω or more, and RH ≧ 10 even at high temperature and high humidity.
The relationship of 2 Ω was satisfied.

The resistance of the supply means was measured by placing the supply means on a conductive plate as shown in FIG. 5, applying a load of 500 g to both ends, and measuring the resistance between the rotating shaft of the supply roller and the conductive plate.

Comparative Example A comparative example for verifying the superiority of the above embodiment is as follows.

Low change in resistance due to environment, low temperature and low humidity L
Using a supply roller whose resistance RL at L and resistance RH at high temperature and high humidity are hardly changed and around 106 ohms, the supplyability when the environment is changed before and after endurance at room temperature and normal humidity NN and after endurance is confirmed. (FIGS. 4 and 3).

As a result, it has been found that even when the supply potential difference is provided, good supply properties cannot always be secured at a constant potential due to durability and environment, resulting in oversupply and supply delay.

Here, the durability is a test for continuously forming an image on substantially the entire surface of a recording sheet corresponding to 5000 A4 size sheets as a printing test.

FIG. 4 shows the toner supply rate (%) when the supply potential difference (V) between the BT before endurance and the AT after endurance of the normal temperature and normal humidity NN in the printing test is changed by using a supply roller having a small resistance change regardless of the environment. ).

According to this, the BT before endurance has a supply potential difference of 0
(V), that is, the toner supply rate was 98% even when the supply means 20 and the developer carrier 10 were set to the same potential, and good supply performance was obtained. The rate was 67%, causing a supply delay.

After the endurance, a supply potential difference of 200 (V) was necessary to ensure sufficient supply of AT.

In the case of before and after the endurance, the supply potential difference 200
With V, good supply properties can be secured.

FIG. 3 shows the relationship between the supply potential difference and the toner supply rate when the environment is changed after the endurance using the supply means having a small resistance change regardless of the environment.

As shown in FIG. 3, the toner supply rate is higher at low temperature and low humidity LL even at a low supply potential difference than at high temperature and high humidity HH, and at the same supply potential difference, low temperature and low humidity LL has better supply performance than high temperature and high humidity HH. Is obtained.

When the supply potential difference was set to 200 (V) so as to obtain a good supply property at normal temperature and normal humidity NN after the durability, supply delay occurred at high temperature and high humidity HH (toner supply rate 80%), and low temperature Conversely, in the low humidity LL, excessive toner supply occurred (toner supply rate 120%).

From this result, when a supply roller having a small resistance change was used irrespective of the environment, supply was barely secured before and after endurance at room temperature and normal humidity with a constant supply potential difference, but the environment was changed after endurance. Then, it turned out that the problem of supply delay and oversupply arises.

Therefore, as a countermeasure, good supply performance can be obtained by changing the supply potential difference depending on the environment. However, a sensor and a control device for changing the supply potential difference depending on the environment are required, and the apparatus becomes large. However, there is a problem that it becomes expensive.

In this regard, according to this embodiment, the resistance of the supply means 20 is reduced at high temperature and high humidity HH, and the toner (T) from the supply means 20 to the developer carrier 10 due to the difference in supply potential.
The supply of the toner (T) can be suppressed by suppressing the effect of the supply potential difference by increasing the supply of the toner (T) at low temperature and low humidity LL.

[0070]

The specific effects provided by each of the above described inventions are as follows.

The toner can be stably supplied even when the environmental temperature or the humidity changes.

The toner can be supplied effectively without changing and adjusting the supply bias condition.

In a high-temperature and high-humidity environment, the supply of toner can be improved, and in a low-temperature and low-humidity environment, excessive supply of toner can be suppressed.

The supply bias changing means is not required, and the configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a developing device according to an embodiment.

FIG. 2 is a characteristic diagram of the toner supply rate when the environment changes according to FIG. 1;

FIG. 3 is a characteristic diagram of a toner supply rate when an environment changes in a comparative example.

FIG. 4 is a characteristic diagram of a toner supply rate before and after endurance in a comparative example.

FIG. 5 is a schematic diagram schematically showing a supply roller resistance measuring device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 developing device 10 developer carrier 20 supply means 60 latent image carrier RH first resistance value RL second resistance value

Claims (3)

[Claims] 1. A developing device for electrostatically applying a developer onto a latent image carrier to develop the developer, the developer carrier being capable of attaching the developer to the latent image carrier, and the developer carrier And a first resistance value RH in the “high temperature and high humidity” state and a second resistance in the “low temperature and low humidity” state in the resistance value of the supply means. A developing device, wherein the developing device is configured to be relatively smaller than a resistance value RL. 2. 35 ° C., 6 in the “high temperature and high humidity” state
2. The developing device according to claim 1, wherein said first resistance value RH is not less than 10 @ 2 .OMEGA. At 5%. 3. A temperature of 10.degree.
3. The developing device according to claim 1, wherein the second resistance value RL is equal to or less than 10 @ 8 .OMEGA. When the value is 5%.