JP3005126B2 - Transfer device for 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 transfer device of an image forming apparatus using an electrophotographic system.

[0002]

2. Description of the Related Art As a conventional image forming apparatus, an LBP (La
ser Beam Printer), as shown in FIG.
The OPC drum 22 includes a photosensitive drum 22 (hereinafter, referred to as an OPC drum) on which a C (Organic Photoconductor) layer is formed.
Scorotron 2 as a charging means for uniformly charging 2
1. A semiconductor laser 23 that forms an electrostatic latent image on the OPC drum 22 according to a document image, and supplies toner to convert the electrostatic latent image formed on the OPC drum 22 into a visible toner image A developing tank 24, a transfer charger 26 as transfer means for transferring the toner image on the OPC drum 22 to a transfer material 25 such as OHP paper, and the like are arranged in this order.

In the above configuration, first, the surface of the OPC drum 22 is uniformly charged by the scorotron 21 in a dark place. Next, while the OPC drum 22 is rotating, the semiconductor laser 23 irradiates a laser beam in accordance with the original image on the surface of the OPC drum 22 to form an electrostatic latent image. Next, a toner charged to the same polarity as the charge on the OPC drum 22 is supplied from the developing tank 24 to the electrostatic latent image to form a visible toner image.

Then, the transfer material 25 is transferred to the OPC drum 22
The transfer charger 26 conveys the toner image to a portion opposite to the charged charge of the toner image. Then, the transferred toner image is fixed in a fixing unit (not shown) and becomes a permanent image. On the other hand, the OPC drum 22
The remaining toner is removed by a cleaner (not shown). The electrostatic latent image on the OPC drum 22 is irradiated with light from a static eliminator (not shown) to be neutralized, and then charged again by the scorotron 21, and the above-described series of processes is repeated.

In the above-described conventional transfer apparatus, a transfer charger 26 is used as a transfer unit, and a corona discharger is usually used as the transfer charger 26. Since this corona discharger requires a high applied voltage of several kV, the applied voltage power supply itself becomes large, the manufacturing cost of the applied voltage power supply increases, and the size and cost of the entire apparatus can be reduced. Has become difficult. Moreover, since the corona discharger is not in contact with the transfer material 25, unnecessary radiation is generated. Further, if the corona discharger itself is dirty, the transfer material cannot be sufficiently charged, and the charge of the transfer material cannot be sufficiently charged. The amount is not sufficient, and transfer failure is likely to occur, resulting in deterioration of image quality. In addition, scattered toner often adheres to the corona discharger, which tends to cause uneven density and missing characters, thereby causing a problem of deteriorating image quality.

However, recently, a transfer roller has been used instead of using the transfer charger 26 such as the corona discharger. This transfer roller requires a lower transfer application voltage than the transfer charger 26, and can reduce the applied voltage power supply itself.
The manufacturing cost can be reduced and the size of the apparatus can be reduced. In addition, since the transfer member is in the form of a roller and can be in direct contact with the transfer material, the transfer material can be sufficiently charged, transfer failures can be reduced, density unevenness and character omission are eliminated, and scattering toner A good image can be obtained without bleeding or the like due to adhesion to the transfer roller.

[0007]

Generally, the transfer roller is formed to have a predetermined resistance value by mixing carbon black into a rubber sponge made of, for example, silicon as a base material. However, it is difficult to form the transfer roller uniformly, and the resistance value at each portion of the transfer roller often varies. For this reason, when a voltage is applied to the transfer roller, the current concentrates on a portion having a small resistance value.
And, likely occur transfer failure insufficient current in large part of the resistance value. For example, when the low resistance portion is the non-image forming area on the roller end side and the high resistance portion is the image forming area near the center of the roller, the transfer current concentrates on the low resistance non-image forming area. since the high resistance of the image forming region is insufficient transfer current, transfer failure occurs in the vicinity of the center of the b over la.

Also, in the image forming area of the transfer roller, since the resistance value in each portion is different, the transfer current is not uniform in each portion, and the transfer material cannot be charged uniformly. At the time of halftone or solid black printing, density unevenness occurs in the high-resistance portion and the low-resistance portion every roller cycle. Further, after the transfer, the toner scattered on the transfer roller is generally removed by applying a voltage having a polarity opposite to that of the toner to the transfer roller. However, even in this case, since the voltage cannot be sufficiently applied to the high resistance portion of the transfer roller, the toner attached to the high resistance portion is not removed, and the toner is applied to the back of the transfer material at the time of the next transfer. Is adhered, and appears as back stain every cycle of the roller.

Accordingly, if there is variation in the resistance value of each portion of the transfer roller, it tends to occur transfer failure of the transfer bad or the like, a problem that it is impossible to obtain a good image occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a non-image forming apparatus on an end side of a transfer roller.
It is an object of the present invention to provide a transfer device of an image forming apparatus capable of eliminating a variation in a resistance value between an area and an image forming area near the center of a roller and obtaining a good image.

[0011]

According to a first aspect of the present invention, there is provided a transfer device for an image forming apparatus, comprising a transfer roller abutting on a photosensitive member via a transfer material, and both ends of the transfer roller in the axial direction. Each of the resistance values in the non-image forming area provided in each of the sections is from 1.2 of the resistance value in the image forming area substantially in the axial center of the transfer roller.
It is characterized in that it is set large within a range of up to 1.3 times .

[0012]

[0013]

According to the first aspect of the present invention, in the transfer roller, each resistance value in the non-image forming area is in a range of 1.2 to 1.3 times the resistance value in the image forming area.
Since the area is large, the transfer current flowing to the transfer roller can be prevented from being concentrated on the non-image area. As a result, a sufficient transfer current can be supplied to the transfer roller, particularly to the image forming area, and the shortage of the transfer current in the image forming area can be solved. Therefore, eliminating the transfer failure due to transfer current shortage in the image area, good good transfer it is possible to perform, it is possible to obtain a good image as a result.
In addition, in the transfer roller, the resistance values of the above two regions are appropriate.
The ratio is set to an appropriate ratio, so transfer defects can be more reliably prevented.
To obtain better images.
Play.

[0014]

According to the first aspect of the present invention , the resistance value (Rn) of each part of the transfer roller in the image forming area and the average of the resistance value of each part in the image forming area. The value (R) is | 1-Rn / R | ≤0.8
(N = 1, 2, 3,...) Is preferably satisfied. Here, the expression | 1-Rn / R is obtained by the resistance value (Rn) of each part in the image forming area of the transfer roller and the average value (R) of the resistance value in each part of the image forming area. |
The variation of the resistance value Rn can be obtained from the above equation. If the variation of the resistance value Rn is 0.8 or less,
It is possible to eliminate the deviation of the transfer current at each portion of the image forming area, eliminating the transcription defect in each section of the image forming area, transfer unevenness, it is possible to perform good transfer without density unevenness. Further, since the transfer current can be almost uniformly applied to the transfer roller, a voltage for cleaning the toner scattered on the transfer roller can be sufficiently applied, and the cleaning efficiency of the toner can be improved. The back contamination of the transfer material due to insufficient cleaning of the roller can be reduced. Therefore, if a transfer roller having a resistance value Rn variation of 0.8 or less in each portion in the image forming area is used, good transfer can be performed, and a good image without back stain can be obtained. .

[0016]

[Embodiment 1] An embodiment of the present invention will be described below with reference to FIGS.

The transfer device of this embodiment is, for example, an LBP (La
As shown in FIG. 3, it is disposed at a position facing the photosensitive drum 2 via a transfer sheet 5 as a transfer material.

Further, on the outer periphery of the photosensitive drum 2, for example, a scorotron 1 as charging means for charging the photosensitive drum 2, a semiconductor laser 3 for irradiating a laser beam to form an electrostatic latent image corresponding to a document image A developing tank 4 for developing the electrostatic latent image into a visible image; a transfer roller 6 for transferring the visible image formed on the photosensitive drum 2 to a transfer material 5 such as transfer paper or OHP (Over Head Projector) paper. Further, fixing rollers 8.8 for fixing the visible image transferred to the transfer material 5 by the transfer roller 6 are provided.

The photosensitive drum 2 has a cylindrical shape with an outer diameter of 30 mm, and has an OPC (Organic Photoconductor) on its surface.
ctor) layer is formed, and is uniformly charged at -600 V by the scorotron 1 as the charging means (hereinafter referred to as an OPC drum). In addition, this O
The PC drum 2 has a rotation axis perpendicular to the transfer direction of the transfer material 5, and rotates in the direction of the arrow at a peripheral speed of 48 mm / sec.

The scorotron 1 is for uniformly charging the surface of the OPC drum 2 to, for example, negatively (negative) after the charge remaining on the surface of the OPC drum 2 is erased by a static elimination lamp (not shown). Yes, other charging means having such a function, for example, a corotron or the like may be used.

The semiconductor laser 3 irradiates the surface of the OPC drum 2 uniformly charged by the scorotron 1 with a laser beam based on a signal based on image data, thereby increasing the potential of the irradiated surface portion. The electrostatic latent image for the original image is formed by being lowered.

In the developing tank 4, the toner is charged to the same polarity (minus) as that of the charged portion of the OPC drum 2 by stirring the toner with a toner while applying a negative voltage to the carrier via a magnet roller (not shown). It is made to let. When the negatively charged toner is supplied to the electrostatic latent image, the OPC drum 2
A toner image, which is a visible image corresponding to a document image, is formed on the front surface.

A voltage of 500 V is applied to the transfer roller 6 from a transfer application voltage power supply 7, and the transfer paper 5 is made to have a polarity (plus) opposite to that of the toner of the toner image by the applied voltage. It is designed to be charged.

On the other hand, the transfer roller 6 has an outer diameter of 15 mm and is arranged in parallel with the OPC drum 2. The transfer roller 6 is subjected to a conductive treatment by mixing carbon black into a rubber sponge made of silicon as a base material, and has a predetermined resistance. It has a value. The transfer roller 6 has shafts 6a at both ends.
6a (FIG. 1) is provided, is supported by a bearing (not shown), and is pressed toward the OPC drum 2 by a spring (not shown). The pressure of the spring at this time is 250 g for each shaft 6a of the transfer roller 6, and the transfer pressure by the transfer roller 6 is 500g. further,
The transfer roller 6 can rotate in the direction of the arrow at the same speed as the peripheral speed of the OPC drum 2 by adjusting the rotation drive gear.

The fixing rollers 8 are provided in a fixing section, and pressurize and fuse the toner of the toner image transferred to the transfer paper 5 by the transfer roller 6 to thereby transfer the toner onto the transfer paper 5. The image is fixed.

In the above configuration, image formation will be described below with reference to FIG. First, the surface of the OPC drum 2 is irradiated with light by a static elimination lamp (not shown),
Eliminates residual charge. Next, the surface of the OPC drum 2 is
It is uniformly charged by the scorotron 1 to which a voltage of 00V is applied. The OPC drum 2 rotates in the direction of the arrow to move the charged portion to the laser beam irradiation position of the semiconductor laser 3, and the charged portion is irradiated with a laser beam based on a document print pattern signal. An electrostatic latent image is formed by lowering the potential of the portion. Next, the toner that is negatively charged in the developing tank 4 is supplied to the electrostatic latent image formed on the surface of the OPC drum 2 to become a visualized toner image.

On the other hand, the transfer material 5 is supplied from a paper supply unit (not shown), and an OP is provided between the OPC drum 2 and the transfer roller 6.
It is carried in at the same speed as the peripheral speed of the C drum 2. At this time,
When the transfer paper 5 is detected to be carried in between the OPC drum 2 and the transfer roller 6 by a paper detection sensor (not shown), a voltage of 500 V is applied to the transfer roller 6 from the transfer application voltage power supply 7. The transfer material 5 carried in by applying the voltage to the transfer roller 6 is positively charged.

Thus, the toner image having a negative charge formed on the surface of the OPC drum 2 is transferred to the transfer material 5 having a positive charge. At this time, the transfer roller 6 transfers the toner image to the transfer material 5 while applying a transfer pressure of 500 g in the direction of the OPC drum 2.

The transfer material 5 to which the toner image has been finally transferred is
The fixing roller 8 is transported by a transport system such as a transport roller (not shown).
The toner on the transfer material 5 is conveyed to the pressure contact portion 8 and melted under pressure and fixed to the transfer paper 5.

Although the transfer roller 6 is formed so as to have an arbitrary resistance value as a whole, the resistance value is not always uniform. For example, the resistance value in the image forming area near the center of the roller often differs from the resistance value in the non-image forming area near the roller end. In such a case, for example, if the resistance value in the image forming area is high and the resistance value in the non-image forming area is low, the transfer current concentrates on the non-image forming area of the transfer roller 6 and sufficient transfer to the image forming area is performed. The current stops flowing. For this reason, a transfer failure due to an insufficient transfer current in the image forming area is likely to occur. Therefore, it is desirable to use a transfer roller having no variation in resistance between the image forming area and the non-image forming area of the transfer roller.

Here, a method of measuring the resistance value in the image forming area and the non-image forming area of the transfer roller 6 will be described below with reference to FIG.

The transfer roller 6 generally has an image forming area near the center of the roller and a non-image area near the end of the roller.
As shown in FIG. 1, conductive members 11 and 13 are provided at both ends,
A conductive member 12 is provided near the center. These conductive members 11 to 13 are made of SU having a thickness of 100 μm and a width of 10 mm.
It is made of S foil and is connected to the switch 10. The switch 10 switches the conductive members 11 to 13 respectively. One of the shafts 6a provided at both ends of the transfer roller 6 is connected in series with the switch 10 via a transfer application voltage power supply 7 and an ammeter 9 connected in series. By switching the switch 10, currents at both ends and near the center of the transfer roller 6 are respectively measured by the ammeter 9.

When the resistance value near the conductive member 11 is measured, for example, the switch 10 is first switched to the conductive member 11 side, and a voltage of 500 V is applied to the transfer roller 6 by the transfer application voltage power supply 7. Is measured by the ammeter 9. Then, a resistance value (hereinafter, referred to as R1) of the transfer roller 6 near the conductive member 11 is calculated from the current value. Similarly, based on the current values of the conductive members 12 and 13, the resistance value (hereinafter referred to as R
2) and a resistance value near the conductive member 13 (hereinafter, R
3) is calculated.

In this embodiment, the resistance values near the respective conductive members 11 to 13 are R1 = 3.6 × 10 ⁷ Ω and R2 = 3.0 ×
10 ⁷ Ω, R 3 = 3.9 × 10 ⁷ Ω, and Table 1 also shows the values of R 1, R 2, and R 3 in other transfer rollers and the results of the image quality of the formed image actually measured by the above method.

[0035]

[Table 1]

From Table 1, it can be seen that the relationship between R1, R2 and R3 is generally good if R1 and R3 ≧ 0.7R2.

By the way, normally, the transfer roller 6 has a resistance of 10 ⁵ Ω.
Since the resistance value of each part is measured by the above method, if the resistance value actually measured satisfies the relational expression of R1 and R3 ≧ 0.7R2 as described above, it is good. Image can be obtained. However, the transfer if the resistance value of the end portions 11, 13 of the roller 6 is less than 10 ⁵ [Omega] cm, the non-image area, concentrates the transfer current in the region on both ends that is, inevitably transfer bad, further, The concentration of the current to a portion having a small resistance value becomes extremely intense, resulting in deterioration of image quality, and the transfer roller 6 itself cannot be used as a transfer device.

Therefore, the resistance value of the transfer roller is 10 ⁵ Ωc
If m or more, the transfer roller is used such that the resistance values R1 and R3 in the non-image forming area are 0.7 times the resistance value R2 in the image forming area as described above. prevent concentration of transfer current to, Ru can flow the transfer current in the image forming region sufficiently. Therefore, the image area
In this case, it is possible to eliminate poor transfer due to insufficient transfer current and perform good transfer, and as a result, obtain a good image.

Embodiment 2 Another embodiment of the present invention will be described below with reference to FIGS. 2 and 3. For convenience of explanation, the same members as those used in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 2, the transfer roller 6 according to the present embodiment uses conductive members 14 to 16 instead of the conductive members 11 to 13 used in the first embodiment.
5 is provided at substantially the same position as the conductive member 12 (FIG. 1), but the other conductive members 14 and 16 are provided on the outermost side of the image forming area inside the conductive members 11 and 13, respectively.

[0041] In the image forming region of the transfer roller 6, generally, the resistance value of each part is different, it tends to occur a deviation of the transfer current in the image forming region portion, transfer <br/> bad is This tends to cause unevenness in density when printing solid black or the like. Therefore, it is desirable to use the transfer roller 6 in which the variation of the resistance value in the image forming area of the transfer roller 6 is reduced.

Here, the variation of the resistance value of each part in the image forming area of the transfer roller 6 is obtained.

First, the resistance value of each part in the image forming area of the transfer roller 6 is set in the same manner as in the first embodiment, and the resistance value R4 near the conductive member 14, the resistance value R5 near the conductive member 15, The respective values of the resistance value R6 near the conductive member 16 are obtained. In this embodiment, R4 = 5.6 × 10 ⁷ Ω, R5
= 4.0 × 10 ⁷ Ω, the R6 = 7.9 × 10 ⁷ Ω.

Next, the average value R of the respective resistance values obtained above is obtained, and the variations T _n (n = 4, 5, 6) for the respective resistance values R4 to R6 are obtained by the following equations.

T _n = | 1-R _n / R | where the variation in each resistance value is T ₄ = 0.0
4, T ₅ = 0.31, the T ₆ = 0.35. Hereinafter, similarly, the resistance values of the respective portions in the image forming area are obtained for the other transfer rollers, and the variation of these resistance values is obtained. Table 2 shows the results obtained in this manner.

[0046]

[Table 2]

From this result, if the variation in the resistance value in each portion is 0.8 or less, the quality of the formed image is good.

Therefore, if the resistance value of each part in the image forming area of the transfer roller 6 satisfies | 1-R _n /R|≦0.8, the resistance value of the transfer roller 6 in the image forming area varies. Is small, the transfer current flows almost uniformly, and the concentration of the transfer current in each part is eliminated, so that the density unevenness in each part is eliminated, and a good image is obtained.
The cleaning voltage to the transfer roller 6 can be applied uniformly and sufficiently, and the image quality can be prevented from deteriorating due to the back contamination of the transfer material 5 due to the adhesion of the toner on the transfer roller 6, and as a result, a good image Obtainable.

[0049]

As described above, the transfer device of the image forming apparatus according to the first aspect of the present invention has a transfer roller that comes into contact with a toner image formed on a photoreceptor via a transfer material. Each of the resistance values in the non-image forming areas provided at both ends in the axial direction of the transfer roller, respectively,
The resistance value is set to a large value in a range from 1.2 to 1.3 times the resistance value in the image forming area substantially at the center of the transfer roller in the axial direction.

[0050] Since this makes it possible to reduce the deviation of the transfer current in the image forming area and the non-image forming region of the transfer roller, it can camphor such a transfer failure due to transfer current shortage in the image area, the result of this, There is an effect that a good image can be obtained. In addition,
The resistance value of the above two regions to an appropriate ratio
Transfer can be prevented more reliably, and
This produces an effect that a good image can be obtained.

[0051]

[0052]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a method for measuring a resistance value of an image forming area and a non-image forming area of a transfer roller according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a method for measuring a resistance value of each part of an image forming area of a transfer roller according to another embodiment of the present invention.

FIG. 3 is an LBP (Laser Beam Print) according to FIGS. 1 and 2;
er) is a schematic configuration diagram.

FIG. 4 is a schematic configuration diagram of a conventional LBP (Laser Beam Printer).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Scorotron 2 OPC drum (photoreceptor) 3 Semiconductor laser 4 Developing tank 5 Transfer material 6 Transfer roller 7 Transfer applied voltage

Claims (1)

(57) [Claims] In a transfer device of an image forming apparatus having a transfer roller in contact with a photoreceptor via a transfer material, each resistance value in a non-image forming area provided at both ends in the axial direction of the transfer roller is Each of the transfer devices of the image forming apparatus is set to a large value in a range from 1.2 to 1.3 times the resistance value in the image forming area substantially at the center of the transfer roller in the axial direction.