JP3364553B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias cleaning of a transfer member for preventing backside smearing of the transfer member caused by the toner smearing of the transfer member used in the image forming section of the electrophotographic image forming apparatus. The present invention relates to an improvement in a method, and more particularly to an image forming apparatus capable of efficiently preventing a transfer member from being stained by devising a combination of current values of cleaning biases applied to the transfer member.

[0002]

2. Description of the Related Art In an image forming apparatus utilizing an electrophotographic process such as a copying machine, a printer, a facsimile machine, etc., image information such as reflected light of a document is irradiated onto a photosensitive body which is uniformly charged in advance. An image is formed by developing the obtained electrostatic latent image with toner from a developing device, transferring the toner image onto a transfer material, and then heating and fixing the toner image. As a transfer means for transferring a toner image on a photoconductor onto a transfer material, a method of using a contact type transfer member such as a transfer roller is known, and this transfer means uses an image carrier (photoconductor ) Is always in contact with the transfer material, so that the transfer material is not located in the transfer portion, that is, while the transfer material is not present between the image carrier and the transfer member, or after a jam occurs, When a transfer material having a different paper width is passed, the toner on the image carrier directly adheres to the transfer member, and as a result, toner stains are formed on the back surface of the subsequent transfer material. As means for preventing such back stain, a method of separating the transfer member from the image carrier other than when the transfer operation is performed, or a position of the transfer material between the transfer member and the image carrier (transfer Position) to apply a bias to reversely transfer the toner on the transfer member onto the image carrier to electrically clean it, or mechanically remove the toner on the transfer member by installing a blade. There are known methods for doing so.

At present, a cleaning method using a bias (cleaning bias) is mainly used from the viewpoint of cost merit evaluation, but as such a conventional example, Japanese Patent Laid-Open No. 5-119645 discloses a method for continuous paper feeding. There is disclosed a technique in which cleaning biases having different polarities are alternately applied to the transfer roller while the transfer material is not present at the transfer position as in the case of non-sheet passing such as paper interval. In this method, when the transfer material is not present at the transfer position, a bias having the same polarity as the toner and a bias having the opposite polarity are sequentially applied for a predetermined time, so that the normally charged toner attached to the transfer roller and the reverse toner are reversed. Is also removed.

However, the above-mentioned prior art publications merely vaguely disclose a method of sequentially applying a bias having the same polarity as the toner on the photosensitive member and a bias having the opposite polarity.
Even if the bias cleaning is performed by this method, it is not possible to reliably remove the toner from the transfer member, and it is not always possible to prevent back smearing of the transfer material depending on the combination of current values applied for constant current control. There wasn't. Moreover, how to set this combination of current values is the most important factor that determines the back dirt prevention effect, so unless there is a certain guideline regarding the combination of current values, the optimum cleaning bias It should not be a solution for the application method.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a bias having the same polarity as the toner on the photoconductor and a bias having the opposite polarity are sequentially applied to the transfer member to charge the transfer roller. An invention that serves as a criterion for selecting an optimum combination of applied currents (polarity, current value) that is a factor that most affects cleaning performance in a cleaning method of removing toner and performing reverse transfer on a photoconductor Is intended to provide.

[0006]

In order to achieve the above object, the invention according to claim 1 is an image carrier for electrostatically carrying a toner image, and
Transfer unit that applies a transfer bias to the surface of the image carrier
Material and polarity when the transfer material does not exist at the transfer position
Bias applying means for sequentially applying a bias to the transfer member
In an image forming apparatus equipped with
The step has the same polarity as that of the toner forming the toner image and a current value.
After applying two or more same polarity currents of different
Two or more types of reverse polarity electrodes with opposite polarity and different current value from the toner
Current is applied, and each of the above currents by the bias applying means is applied.
In the application process, the absolute maximum of the same polarity current
The above reverse polarity current whose absolute value is larger than the current
It is characterized in that the voltage is applied at least once. Claim
In the invention described in 2, the above transfer bias and the transfer bias are provided.
The cleaning bias of the same polarity as
Output by the same bias applying means as voltage
Is characterized by. In the invention according to claim 3, the transfer member is
It is characterized by being composed of polyurethane.

[0007]

In the invention according to claim 1 or 3, the bias clear
Contamination of the transfer material can be
This can be reliably prevented. The invention according to claim 2
Then, transfer bias application means and cleaning bias
Achieved cost reduction by combining with the application means
it can.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. The characteristic configuration of the present invention is that when the transfer material is not present at the transfer position or after a jam, the transfer material having a different width is passed through and the same polarity as the charged toner on the photoconductor is used as a cleaning bias for the transfer member. After the bias is applied, the bias of the polarity opposite to that of the toner and larger than the absolute value of the bias of the same polarity is applied to prevent the back stain under all the conditions. . FIG. 1 is a configuration explanatory view of an example of an image forming unit of an image forming apparatus to which the present invention is applied. The electrophotographic image forming unit is charged around a photoconductor (image carrier) 1 rotating in a direction of an arrow. The container 2, the exposure unit 3, the developing unit 4, the transfer roller 5 (transfer member), the separating unit 6, the cleaning unit 7, the charge eliminating lamp 8 and the like are sequentially arranged. Registration rollers 10 and 11 are arranged on the upstream side of the conveyance path of the recording paper P centering on the transfer position where the transfer roller 5 is located, and a fixing device 14 (roller 15, roller 15 on the downstream side of the transfer position).
16) is arranged.

In the image forming operation, first, the surface of the photoconductor 1 is charged by the charger 2, and when the opposite surface is irradiated with the light according to the original image by the exposure means 3, the photoconductor is exposed. An electrostatic latent image is formed on. When the electrostatic latent image thus formed passes through the developing device 4, toner is supplied from the developing device to form a toner image. On the other hand, recording paper P (transfer material) for receiving image recording is stacked and stored in a paper feeding unit (not shown), and is fed and conveyed one by one by the cooperation of a pickup roller and a feed roller (not shown), and a registration roller. The nip portion (transfer position) between the photoconductor 1 and the transfer roller 5 is entered by the guide plates 9 and 10. The transfer roller 5 is arranged below the photoconductor 1 so as to press and sandwich the recording paper P between the transfer roller 5 and the surface of the photoconductor. A voltage having the opposite polarity to that of the charged toner is applied. By applying a reverse polarity current to the transfer roller 5 from the bias applying means 20 in a state where the recording paper is pressed against the transfer roller 5 and the photoconductor, the electrostatic force generated by the applied current causes an action. The toner image is transferred onto the recording paper P.

The recording sheet P carrying the toner image in this manner is de-charged by the separating means 6 so that the photoreceptor 1
And is held between the heat roller 15 and the pressure roller 16 which constitute the fixing device 14 after passing through the paper transport plate 13 and the toner image is fixed on the recording paper P by heat and pressure. Become. The surface of the photoconductor 1 after the transfer of the toner is removed by the cleaning means 7, and then the electric charge on the entire surface is neutralized by the charge eliminating lamp 8 to return to the initial state.
Image formation is performed by repeating the above cycle again. FIG. 2 is a diagram showing a configuration of an example of the transfer roller. The transfer roller 5 has both end portions in the axial direction cut at the end faces to prevent an edge discharge from the photoconductor. The axial width m of the transfer roller 5 is smaller than the width of the photosensitive layer of the photoconductor 1. As the transfer roller material, a conductive foam sponge or the like is used. Specifically, silicon,
Urethane, epichlorhydrin, EPDM or the like is used.

In the present invention, by using the above-mentioned image forming unit, assuming that the transfer roller 5 is most likely to be contaminated, a paper feed jam is artificially generated to contaminate the transfer roller 5 with toner. . Bias cleaning was performed by sequentially applying a bipolar cleaning current to the transfer roller 5 in such a state. It has been confirmed that the cleaning method according to the present invention is effective even when the transfer roller is contaminated due to a cause other than a jam.

In the first embodiment of the present invention corresponding to claim 1, the transfer roller 5 (transfer member) which is in contact with the photoconductor 1 and applies the transfer bias, and the polarity when the recording paper is not present at the transfer position. In the image forming apparatus including a bias applying unit that sequentially applies different biases to the transfer roller, the bias applying unit applies a current having the same polarity as that of the toner forming the toner image (the same polarity current). The characteristic is that a current having a polarity opposite to that of the toner and having a current value greater than or equal to the absolute value of the same polarity current (reverse polarity current) is applied thereafter.

That is, in this embodiment, first, the photoconductor 1 is charged to −850 V by using the charger 2, and the toner from the developing device 4 is adhered to the entire charged portion to clean the transfer roller 5. A bias was applied. Since the toner on the photoconductor is positively charged, cleaning was performed by first applying a positive current (same polarity current) and then a negative current (reverse polarity current) as a cleaning bias. If the toner on the photoconductor is negatively charged, a negative current is first applied as the same polarity current, and then a positive current is applied as the opposite polarity current. In both cases, good cleaning results are obtained. I was able to get

Table 1 shown in FIG. 3 shows the state of backside smearing in the transfer roller made of silicon (volume resistance: 10 ⁹ Ω · cm), and different values of the same polarity current and the opposite polarity current were combined. The resulting back stain is shown. As is clear from this table, when the absolute value of the current (reverse polarity current) of the opposite polarity to the charged toner on the photoconductor is larger than the absolute value of the current of the same polarity (same polarity current) as the charged toner, cleaning is performed. It can be seen that the effect of. In other words, as the absolute value of the reverse polarity current increases from 3 μA to 20 μA, the absolute value of the same polarity current is greater than or equal to (| the same polarity current value | ≦ | reverse polarity current value |). The generation of dirt is reduced. In the case of the silicon roller, since the cleaning property is good, good cleaning property may be obtained even if the absolute value of the reverse polarity current applied later is small.

Next, Table 2 in FIG. 4 is a diagram showing the state of backside smearing in the urethane transfer roller. In this case as well, as in the case of FIG. It can be seen that the cleaning effect is exhibited when the absolute value of the same polarity current) is larger than the absolute value. However, urethane roller (for example, polyurethane roller, volume resistance 10 ⁹ Ω
(Cm) has excellent wear resistance, but the range of combinations of cleaning biases (cleaning bias conditions) that can prevent the occurrence of back stains is narrower than that of silicon rollers. However, by performing the bias cleaning within the range of the above conditions, the back stain can be prevented, and therefore the practicability is sufficiently high. Therefore, when the present invention is applied to the urethane roller, its practical meaning becomes stronger.

Next, in a second embodiment of the present invention corresponding to claim 2, an image provided with bias applying means for sequentially applying biases having different polarities to the transfer member when the recording sheet is not present at the transfer position. In the forming apparatus, the bias applying unit 20 applies two or more kinds of same polarity currents having the same polarity as the charged toner forming the toner image on the photoconductor 1 but different current values, and then reverses the toner. 2 with different current value depending on polarity
More than one kind of reverse polarity current is applied, and in the process of applying each current by the bias applying means, a reverse polarity current having an absolute value larger than that of the same polarity current having the maximum absolute value is applied at least once or more. The point is that it is done.

That is, FIG. 5 is a diagram showing an example of the sequence of the cleaning current according to the second embodiment. In this example, the same polarity current (+) and the opposite polarity current (-) are different from each other by two or more kinds. The absolute value of the same polarity current is gradually increased (every rotation of the transfer roller), and the absolute value of the reverse polarity current is also gradually increased (every rotation of the transfer roller). It is controlled to increase gradually. In addition, the current (|
-20 μA |) was made larger than the current (| 15 μA |) having the largest absolute value among the same polarity currents. Therefore, as in the case of the first embodiment, the cleaning effect of the transfer roller can be enhanced and the backside stain of the recording paper can be effectively prevented.

Next, FIG. 6 shows a modification of the embodiment of FIG. 5, in which the same polarity current (+) as the cleaning bias is applied.
5 is different from the embodiment of FIG. 5 in that the absolute value of the current value in the reverse polarity current (−) is not increased gradually but “increased”. That is, the same polarity current increases and decreases between 5 μA and 10 μA for each rotation of the transfer roller, and the reverse polarity current similarly increases and decreases between −5 μA and −15 μA. Also in this embodiment, similarly to the embodiment of FIG. 5, the cleaning effect of the transfer roller is enhanced,
The backside of the recording paper could be effectively prevented. In addition,
The maximum absolute value of the reverse polarity current is larger than the maximum absolute value of the same polarity current as in the above embodiments.

FIG. 7 is a diagram showing a difference in cleaning effect between the embodiment shown in FIGS. 3 and 4 corresponding to claim 1 and the embodiment shown in FIGS. Immediately after that, the result of comparing the amount of toner adhered to the transfer roller with the amount of adhered toner after cleaning is shown. As a result,
It has been found that the cleaning effect is higher in the embodiment corresponding to claim 2 by switching the bias.

In a third embodiment of the present invention corresponding to claim 3, the transfer bias and the cleaning bias having the same polarity as the transfer bias are both constant current or constant voltage and output by the same bias applying means 20. The characteristic feature is the configuration. That is, a large cleaning effect can be obtained by executing the bias cleaning according to each of the above-described embodiments. Therefore, if a new bias applying unit is added, the cost is increased. Therefore, in the third embodiment, the polarity opposite to that of the toner is used. By making the power supply for the current common with the transfer current power supply, the cost increase is prevented. In the above embodiments, the bias is applied by the constant current, but the bias may be applied by the constant voltage, and the effect is the same.

Next, the reason why the cleaning effect on the transfer roller is enhanced by adopting the cleaning bias applying method of the present invention is considered as follows. First, the toner attached to the transfer roller includes not only the toner having the same polarity as the charged toner on the surface of the photoconductor but also the toner having the opposite polarity, so that only the toner having the same polarity is removed by applying the cleaning bias of the same polarity. This is because the cleaning effect is not sufficient, and the reverse polarity bias must be applied because the reverse polarity toner needs to be removed.

That is, FIG. 8 is a diagram showing the toner charge amount distribution on the transfer roller when a jam occurs, and the toner on the transfer roller immediately after the jam at the transfer position is distributed as shown in FIG. Therefore, if the bias is applied in the order of (+) → (−), the bipolar toners can be transferred to the photoconductor side, respectively. In the actual bias cleaning, when the (+) polarity bias is first applied, the toner having the (+) polarity in the toner on the transfer roller moves to the photoconductor side. However, the toner of the (-) polarity has a stronger attraction to the transfer roller than before the cleaning bias is applied. When the application of the (+) polarity bias is terminated, the (-) polarity toner adhered to the transfer roller with a strong force loses the force in the pressing direction against the transfer roller by the electric field, but the surface of the transfer roller generally used is foamed. Since it has a fine concavo-convex portion, the (-) toner has already entered the concavo-convex when the application of the (+) polarity bias is completed. As a result, the cleaning effect by applying the (−) polarity bias is lower than that before applying the (+) polarity bias. what if,
When the (-) polarity bias having the same absolute value as that of the (+) polarity bias applied first is applied, a part of the (-) toner that has entered the unevenness at most is pulled out to the roller surface. You can only do it. Therefore, by applying a (-) polarity bias having an absolute value exceeding the absolute value of the (+) polarity bias, extraction of all (-) toner in the unevenness and transfer to the photoconductor are realized at once. It becomes possible to do it. In each of the above-described embodiments, the transfer roller is illustrated as the transfer member, but any means may be used as long as it is a means for contacting the photoconductor to perform the transfer. For example, the present invention can be applied to a transfer device using a transfer belt.

[0023]

As described above, according to the first aspect of the invention, an image carrier for electrostatically carrying a toner image, and the image carrier.
A transfer member that contacts the body surface and applies a transfer bias,
Vias with different polarities when there is no transfer material at the transfer position
Biasing means for sequentially applying a bias to the transfer member,
In the provided image forming apparatus, the bias applying means includes
The toner that forms the toner image has the same polarity but a different current value.
After applying two or more kinds of currents of the same polarity,
Two or more types of reverse polarity currents with different polarity but different current values are printed.
In addition, the application of each of the currents by the bias applying means
The maximum absolute value of the same polarity current
The absolute value is larger than the current
Since both are applied once or more, the change in bias
Can effectively remove the toner on the transfer member.
It

According to a second aspect of the present invention, the transfer via is provided.
And a cleaning bias having the same polarity as the transfer bias.
Are both constant current or constant voltage, and the same bias applying means
Since it is output by, the cost can be reduced.
It

According to a third aspect of the present invention, the transfer member is a polyurethane resin.
Since the present invention is applied to the case where the
From the absolute value of the reverse polarity current applied from the same polarity before
The absolute value of the current of the
It has the effect of further increasing the practicality of the controller.

As described above, according to the present invention, a bias having the same polarity as that of the toner on the photoconductor and a bias having the opposite polarity are sequentially applied to the transfer member to remove the charged toner adhering to the transfer roller, thereby exposing the photoconductor. In the cleaning method for reverse transfer onto the body, it is possible to provide a criterion for selecting an optimum combination of applied currents (polarity, current value) that are the factors that most influence the cleaning performance.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view of an example of an image forming unit of an image forming apparatus to which the present invention is applied.

FIG. 2 is a structural explanatory view of an example of a transfer member.

FIG. 3 is a diagram showing a state where backside smear occurs in a silicon transfer roller.

FIG. 4 is a diagram showing a state where back stains occur on a urethane transfer roller.

FIG. 5 is a diagram showing an example of a cleaning current sequence according to a second embodiment.

FIG. 6 is a diagram showing an example of a cleaning current sequence according to a modification of the second embodiment.

FIG. 7 is a diagram showing a difference in cleaning effect between the embodiment of FIGS. 3 and 4 and the embodiment of FIGS. 5 and 6;

FIG. 8 is an explanatory diagram of the principle of the present invention.

[Explanation of symbols]

1 photoconductor (image carrier), 2 charger, 3 exposure means,
4 developing device, 5 transfer roller (transfer member), 6 separating means, 7 cleaning means, 8 static elimination lamp, 10, 1
1 registration roller, 14 fixing device, 20 bias applying means.

Claims (3)

(57) [Claims] 1. An image carrier for electrostatically carrying a toner image,
Transfer in which a transfer bias is applied by contacting the surface of the image carrier
The polarity is different when there is no transfer material at the transfer position
Bias applying means for sequentially applying a bias to the transfer member
In the image forming apparatus including a step, the bias applying unit includes a toner forming the toner image.
Two or more kinds of same polarity currents with the same polarity but different current values
After applying the voltage, the polarity is different from that of the above toner but the current value is different.
More than one kind of reverse polarity current is applied, and in the process of applying each current by the bias applying means,
The maximum absolute value of the same polarity current
The reverse polarity current, which has a larger absolute value than the
An image forming apparatus characterized by being applied more than once. 2. The transfer bias is the same as the transfer bias.
Both polarity cleaning bias is constant current or constant voltage
The same bias applying means to output.
The image forming apparatus according to claim 1, which is a characteristic. 3. The transfer member is made of polyurethane.
The image forming apparatus according to claim 1 or 2, characterized in that
Place