JPH03131885A - Image forming device - Google Patents

Abstract

PURPOSE:To stably obtain satisfactory transferability irrespective of environment, transfer material size, print-side order, etc., by making the first and second sides of a transfer material different from each other in coefficient value by which a voltage is multiplied. CONSTITUTION:In paper non-passing time at which the transfer material P does not exist in the transfer part where a transfer roller 2 abuts on a photosensitive body 1, the transfer roller 2 is controlled so that current is constant, by using the current set in advance; in paper passing time, the transfer roller 2 is controlled so that voltage is constant, by using the voltage obtained by multiplying the voltage in the paper non-passing time by a coefficient. The first and second sides of the transfer material P are made different from each other in coefficient value. Therefore, void on the first side and defective transfer on the second side both can be prevented. Thus, satisfactory transferability can be stably obtained irrespective of environment, transfer material size, print- side order, etc.

Description

Detailed Description of the Invention (1) Purpose of the Invention (Field of Industrial Application) This invention relates to an image forming apparatus that utilizes an electrostatic transfer process, such as an electrostatic copying machine or a printer, and particularly to a contact type transfer means. The present invention relates to an image forming apparatus equipped with the above-mentioned image forming apparatus.

(Prior Art and Problems to be Solved) An image bearing member and a transfer means that is in pressure contact with the image carrier are provided, and a transfer material such as paper is passed through the pressure nip between these two members, and a transfer bias is applied to the transfer means. An image forming apparatus has already been proposed in which a transferable toner image, which has been formed on the surface of an image carrier up to this point, is transferred to a transfer material.

FIG. 5 is a schematic side view showing a typical example of such an image forming apparatus.

To briefly explain this, the surface of a cylindrical image carrier (referred to as photoreceptor) l, which has an axis perpendicular to the plane of the paper and rotates in the direction of arrow X at a process speed of 23 mm/sec, forms an OPC photosensitive layer. and by power supply 4,
After being uniformly negatively charged via the charging roller 3, an image signal 7 such as an image-modulated laser beam is projected onto the charged surface to form an electrostatic latent image.

Next, negatively charged toner is supplied to this latent image by the developing device 9, and a toner image is formed by reversal development, and as the photoreceptor 1 rotates, the toner image is formed by the photoreceptor 1 and the low volume resistance material. When the transfer material P reaches the transfer site formed by contacting the transfer roller 2, the transfer material P is conveyed to the transfer site in synchronization with the toner image, and at the same time, the transfer material P is supplied with toner and toner by the power source 4. A transfer bias of opposite polarity is applied, and the toner image on the photoreceptor side is transferred to the transfer material by the action of the electric field formed.

FIG. 6 shows the operation sequence of the above device.

Thereafter, the transfer material carrying the toner image is conveyed to a fixing site (not shown), and the toner that was not transferred to the transfer material during transfer is removed by the cleaner 10, and the photoreceptor enters the next process.

Image forming apparatuses that use the contact-type transfer method described above are
Compared to conventional systems that use a well-known corona discharger, it is cost-effective because it does not require a high-voltage power supply.Since there is no wire as an electrode, there is no negative effect on the image due to contamination of the wire.Due to the presence of a high-voltage member. There are various advantages such as being able to avoid the generation of ozone, nitrogen oxides, etc. and the deterioration of image quality caused by this, but on the other hand, the characteristics of the transfer roller, which is a conductive member, vary greatly depending on the environment, so the voltage applied to it It is known that the relationship between the current and current (referred to as the V-I characteristic) changes significantly.

To briefly explain this, under a low temperature and low humidity environment (hereinafter L/L
) So, what is the resistance value of the transfer roller at room temperature? B It is several orders of magnitude higher than when it was under the m boundary (referred to as N/N). Furthermore, in a high temperature environment (referred to as H/H), the resistance value decreases by one to two orders of magnitude compared to N/N.

FIG. 7 shows changes in characteristics due to such environments.

In the same figure, the solid lines indicate when the charging roller 3 is crossed in the above-mentioned device during the pre-rotation, the paper gap and when the paper is not passing, and the broken line is when the A4 size transfer material passes through the transfer area. V-I of transfer roller 2 when both DC components are on
The characteristics are shown divided into L/L, N/N, and H/H.

In the case of the above-mentioned known device, in order to perform a good transfer, a transfer current of 0.5 to 4 μA is required during normal operation, and if the current exceeds 5 μA, a positive potential is applied to the OPC photosensitive layer. Experiments have shown that transfer memory remains and causes embedded fog in images.

From this, the appropriate transfer bias in the known device is approximately 300 to 500 V for H/H and approximately 4 V for N/N.
It can be seen that the voltage is about 1250 to 2000V at 00 to 500V and L/L.

In other words, if the transfer roller is controlled at a constant voltage of 500 V, for example, to ensure proper transfer in N/N, almost the same transfer performance will be obtained in H/H, but the transfer current will be zero in L/L. This results in poor transfer.

In addition, if the voltage is set to improve the transferability in L/L, OPC is
Positive transfer memory is generated on the photoreceptor, causing blur in the image, and especially in H/H, the transfer current increases during paper passing, and the charge penetrates the transfer material, changing the charging characteristics of negative toner to reverse polarity. This may cause transfer defects.

In order to deal with the above-mentioned problems, an image forming apparatus is equipped with an image carrier and a transfer means that comes into contact with the image carrier, and is configured so that the transfer material is inserted into the transfer site where the two come into contact. A method has been proposed in which the transfer means is controlled at a constant current when no material is present and paper is not passing, and the voltage at this time is multiplied by a coefficient R, and constant voltage is controlled when paper is passing (hereinafter referred to as ATVC control). .

However, the above control means causes the following problems.

That is, in the case of double-sided copying, which has been increasingly used in recent years, transfer defects may occur when copying the second side.

Considering this, in such a double-sided copy,
When copying the first side, heat fixing is performed before copying the second side in order to fix and fix the toner image electrostatically attached to the transfer material. In this case, heating dries the material and increases its resistance. For example, in N/N, after a transfer material with a surface resistance of 1010 Ωcm passes through a fixing device equipped with a heating means,
14Ωcm, which is comparable to L/L transfer material,
The ■-■ characteristics change greatly between the first side and the second side, and the appropriate bias value also changes, which is considered to cause transfer defects.

Figure 3 shows the V- of the first and second sides in the above case.
It is a graph showing changes in I characteristics.

The broken lines in the figure indicate the states of L/L, N/N, and H/H.
When both AC and DC components of the voltage applied to the charging roller 3 are turned on, the dotted line indicates the V-I characteristic of the transfer roller 2 when the first side of an A4 size transfer material passes through the transfer site. V of the transfer roller 2 when passes through the transfer site
-I characteristics are shown respectively.

As mentioned above, the current required to maintain good transferability is 0.
5 to 4 uA, and if it exceeds 5 μA, it will cause soil tension, so taking this into account, the appropriate bias value is about 500 V for H/H, about 800 V for N/N, and about 2 for L/L.
It turns out that the voltage is 000V.

In such a case, if the ATVC control is performed, when copying the second side, in H/H, the transfer bias in the image area is reduced to 2μ in the non-image area due to the ATVC control.
If constant current control is performed with A, the voltage in this case is 250V.
(Fig. 7) multiplied by a coefficient R=1.5, which is set to about 375V. In this case, a current of about 1 LLA flows on the first surface, resulting in good transfer performance, but on the second surface, a current of only about 0.2 μ flows (FIG. 8), resulting in poor transfer.

In addition, for N/N, approximately 60
The image area is subjected to constant voltage control with a voltage of 0.

In this case as well, a current of approximately 1 .mu.A is obtained for the first surface, but the transfer current for the second surface is approximately 0.1 .mu.A, resulting in defective transfer.

Furthermore, in L/L, if the non-image area is controlled with a constant current of 2uA, and the image area is controlled with a constant voltage of 1950V, which is the voltage at this time of 1300V multiplied by a coefficient R = 1.5, 1
The transfer current for the second side is about 0.5 μA, whereas the transfer current for the second side is about 1 uA, which may also cause transfer defects.

The present invention has been made to deal with the current situation as explained in detail above, and is applicable to an image forming apparatus that is equipped with a contact type transfer means such as a transfer roller and performs ATVC control. To provide an image forming apparatus that can always stably obtain good transfer performance by changing the value of the coefficient R, so that an appropriate bias can be applied in response to the change in transfer characteristics as described above. The purpose is to

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention comprises an image bearing member and a transfer means that comes into contact with the image carrier, and a transfer means that these two come into contact with. Image formation in which the transfer means is controlled at a constant current with a preset current when no transfer material is present in the area and paper is not passing, and the transfer means is controlled at a constant voltage when paper is passed using a voltage obtained by multiplying the voltage at this time by a coefficient. The apparatus is characterized in that the value of the coefficient is different between the first and second sides of the transfer material.

With this configuration, stable and good transfer performance can be obtained regardless of the environment or the size of the transfer material.

(Description of Embodiments) FIG. 1 is a side view schematically showing the configuration of an image forming apparatus suitable for applying the present invention, in which parts corresponding to those of the above-mentioned known apparatus are given the same reference numerals. There are, and explanations about them will be omitted.

It is assumed that a predetermined voltage is applied to the transfer roller 2 at a predetermined time by a power supply 4 that can control %ATVC.

When the CPU 12 receives a print signal from an external device such as a computer, the CPU 12 sends a main motor drive ON signal to a motor drive circuit (not shown) that drives the photoconductor 1, and at the same time sends a primary high voltage ON signal to the power source 4 to start charging. By applying a charging bias to the roller 3, the surface of the photoreceptor 1 is
For example, it is charged to a dark potential V o ” of 700 V.

Next, the CPU 12 drives an image information writing means (not shown), and a static XRlt image is formed on the charged surface of the photoreceptor by the image-modulated laser beam 7.

Further, when the CPU 12 outputs a transfer on signal to the power source 4, constant current and constant voltage control is performed with a predetermined current and voltage at a predetermined time.

FIG. 2 shows the operating sequence of the above device.

Upon receiving the transfer on signal, the power source 4 controls the transfer roller 2 with a constant current when the paper is not passing. For the device shown, 2μA
Assume that a current of

Next, the power supply 4 holds the voltage 1 at any time during the paper non-passing period, and during the first paper passing, the power supply 4 holds the voltage vi (V2=RX■,) which is obtained by multiplying this voltage by the coefficient R. The transfer roller 2 is controlled with constant voltage.

In this example, as soon as ■1 is held, constant voltage control is performed with v2. Also, there is some variation in the timing of v1 hold (but there is no problem.

After the first paper passing, the paper is not passed and the current is controlled at a constant current of 2μA.At this time, since the second transfer material is the second side, the second side copy signal is on, and the power supply 4 is turned on. The voltage V1° at that time is held.

Then, when the paper is fed, the voltage Vl' becomes M'2R.
'?&ff, knee voltage Vz (Vi = Vl
xR') controls the transfer roller 2 at a constant voltage.

In the case of the second side, since the resistance of the transfer material is large as described above, it is set so that R'>R.

By appropriately determining R1R' in consideration of the transfer memory capacity of the photoconductor, the uniformity of the resistance of the transfer roller, etc., excessive transfer current in the first transfer, resulting white spots in the image, and transfer current on the second side can be avoided. Transfer defects due to shortage can be suitably prevented.

The voltage V1 can be sampled several times during constant current and the average value taken. If the process speed is high, the current flowing when the paper is not passing can be kept small by setting the coefficients R and R'' to be large. , it can reduce the burden on the power supply, and it can also be used with photoreceptors that are prone to transfer memory and transfer rollers that have uneven resistance in the circumferential direction, expanding the range of usable materials.

FIG. 3 shows the V-I characteristics of the transfer roller for the first and second surfaces of the transfer material, divided into H/H, N/N, and L/L, and in the same figure, the broken line is for the first surface.

The dotted line indicates the state of the second side. Note that the coefficient is R=
1.5, and R' = 2.0.

According to FIGS. 3 and 7, under the H/H environment, the transfer roller 2 is controlled with a constant current of 2 μA when paper is not passing, the resulting voltage V, = 250V is held, and when paper is passing, this Voltage 375V (V,
=RV, =1.5X250) to perform constant voltage control.

Next, in the case of the second side, the coefficient WI R' is set to 2, and when passing the paper, v2°=R' V, = 2.0 x 250 = 500
Perform constant voltage control with V.

By doing so, a transfer current of about 1 uA can be obtained for the first side, and a transfer current of about 1 μA can be obtained for the second side, and good transfer can be achieved in both cases.

In this case, when paper is not passing, such as during pre-rotation, only 2 μA of current flows, which is less than the limit value of 5 μA mentioned above. There is no risk of blurring (and there is no deterioration of the photoreceptor 1 due to charging, and the life of the photoreceptor 1 can be extended).

Similarly, under the N/N environment, constant current control is performed at 2μA when paper is not passing, and the voltage V at this time is held at 400■, and when paper is passing, this is multiplied by the coefficient R = 1.5 to 600V. A transfer current of about 1 μA was obtained by controlling the constant voltage with 2
In terms of appearance, the coefficient R° is 2.0 and 800V (V,'
By controlling the constant voltage at (=R'V, =2.0×400), a transfer current of about 1 μA can be ensured at this time as well, and no transfer defects occur in either case.

Even under L/Ll conditions, constant current control is performed at 2μA when paper is not passing, and the voltage at this time is 1300V multiplied by the coefficient R, which is 1.
1 at 950V (V, = RVl = 1.5x1300)
Constant voltage control is applied when passing the first side, and 1300V is applied to the second side.
is multiplied by the coefficient R゛, 2600V (Vz' = R'
By controlling the constant voltage at V+ = 2.0 x 1300), a transfer current of about 1 μA can be obtained, and good transfer properties can be obtained on both sides.

As explained above, when using this device, regardless of the environment, it is possible to prevent both white spots on the first side and transfer defects on the second side, ensure good transfer performance on both sides, and when using constant current control. Since the current is small, deterioration of the photoreceptor due to charging can be prevented.

FIG. 4 is a sequence diagram showing another embodiment of the present invention.

In the case of printing one sheet, ATVC control is performed each time, and in the case of continuous sheet feeding, constant current control is performed every two sheets as shown in the figure, and the voltage at this time is
is held, and when paper is passed, constant voltage control is performed using a voltage multiplied by a coefficient R or Ro.

In the case shown, the first side and the second side are printed alternately, but it is of course not limited to this; continuous printing of only the first side or only the second side, and all other combinations are possible. be.

Further, it is not necessary to perform constant current control every two sheets, and the same effect can be obtained even if it is performed every arbitrary number of sheets.

Although the contact type transfer means has been described above, it goes without saying that the present invention can be applied to other transfer means such as a transfer belt.

(3) As described in detail, in accordance with the present invention, in an image forming apparatus equipped with an image carrier and a transfer means in contact with the image carrier, the size of the transfer material and the print surface can be adjusted under all environments. Regardless of the order, etc., stable and good transferability can always be obtained, which greatly contributes to obtaining high-quality images.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of the main parts of an image forming apparatus suitable for applying the present invention, FIG. 2 is a sequence diagram of the same as above, and FIG. 3 is a graph showing the transfer characteristics of the first and second sides of the transfer material. 4. A sequence diagram showing another embodiment of the present invention; FIG. 5 is a schematic side view showing the configuration and operation of a known image forming apparatus; FIG. 6 is a sequence diagram of the same as the above; FIG. This is a graph showing. 1...Photoreceptor, 2...Transfer roller, 3...Charging roller, 4...Power source, 9...Developer, 10...Cleaner, 12...CPU. Figure Figure Figure! 1. Indication of the case Patent Application No. 1-269093 2. Name of the invention Image forming device 3. Person making the amendment relationship

Claims (2)

[Claims] (1) An image bearing member and a transfer means that come into contact with the image carrier are provided, and when there is no transfer material in the transfer area where these two come into contact with each other, the transfer means is controlled with a constant current using a preset current; An image forming apparatus that controls a transfer means at a constant voltage during sheet feeding using a voltage obtained by multiplying the voltage at this time by a coefficient, and in which the value of the coefficient is made different between the first side and the second side of the transfer material. (2) During continuous printing, the transfer means is controlled at a constant current with a predetermined current during pre-rotation before image output, and the voltage at this time is used as the reference voltage for printing the first and second sides while printing a predetermined number of sheets. An image forming apparatus according to claim 1.