JPH09244432A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily transfer a toner image by preventing resistance in a transfer roller from becoming irregular in its longitudinal direction due to heat. SOLUTION: The transfer roller 4 is obtained by cylindrically wrapping the periphery of a core metal 2 with an elastic layer 3. A cooling member (metal roller) 102 is obtained by covering the periphery of an insulation core 100 with a roller-like metal member 101. The length of the metal member 101 is equal to that of the elastic layer 3. To transfer a toner image on the second side of a transfer material 19, the transfer material 19 whose temperature has increased due to heat applied at the time of fixing on its first side is inserted. As a result, the temperature of the transfer roller 4 increases, in particular, resistances in both ends of the transfer roller 4 increase, and a transfer current in this parts decreases. From the elastic layer 3 to the metal member 101, heat is uniformly transmitted longitudinally, a distribution of the temperature of the elastic layer 3 in the longitudinal direction becomes uniform and, thus, the temperature irregularity is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as copiers and laser beam printers have been promoted to have higher speed and longer life, and at the same time, various equipments such as large-capacity sheet feeding for realizing high functionality. The number of cases where units, multi-stage paper output sorters, and automatic double-sided machines are installed is increasing.

By using these devices, a large amount of continuous printing (continuous printing) can be performed in a short time.

In the following description, the above-mentioned image forming apparatus will be described with reference to an image forming apparatus including a photosensitive drum as an image carrier and a transfer roller (transfer member) arranged in contact with the photosensitive drum. To do. Further, the above-mentioned transfer roller is composed of a metal cored bar and a conductive elastic layer surrounding the outer peripheral surface of the cored bar in a cylindrical shape. The elastic layer is pressed against the surface of the photosensitive drum by urging the elastic layer against the surface of the photosensitive drum to form a belt-shaped transfer nip portion with the photosensitive drum. When the toner image formed on the surface of the image carrier is transferred to a transfer material such as paper, the transfer material is nipped and conveyed at the transfer nip portion, and a transfer bias is applied to the transfer roller by a power source. I am trying to transfer with.

[0005]

However, when continuous printing is performed using the above-mentioned image forming apparatus, the temperature of the surface of the photosensitive drum rises, and further the temperature of the elastic layer of the transfer roller in contact with the surface of the photosensitive drum rises. Rises. It is generally known that the volume resistance value of the elastic layer rises as the temperature rises. Moreover, the increase in the volume resistance value is not uniform in the longitudinal direction (the direction along the core bar), but becomes more prominent in a portion where the contact pressure is higher in the transfer nip portion, that is, both end portions of the roller. As a result, when a voltage was applied from the power source, the transfer current was insufficient at both ends of the roller having high resistance, and the toner image was scattered on the transfer material. This splattering was particularly noticeable when continuous double-sided printing was performed by an automatic double-sided machine under a low temperature and low humidity environment.

FIG. 6 schematically shows changes in resistance distribution in the longitudinal direction of the transfer roller before printing (before use) and after continuous double-sided printing of 100 sheets in an automatic double-sided machine in a low temperature and low humidity environment. Show. In the figure, the horizontal axis represents the position in the longitudinal direction of the transfer roller when the longitudinal center of the transfer roller having a length of 300 mm is 0, and the vertical axis represents the volume resistance value of the transfer roller. The volume resistance value of the transfer roller before the printing shown by the solid line and after the continuous double-sided printing shown by the dotted line is shown as a relative value when the average value of the volume resistance values in the longitudinal direction of the transfer roller is 1. is there. In addition, in the same figure, when the volume resistance value shown by the horizontal line H or more, the scattering occurred.

The causes of the above are that the transfer roller is likely to have a high resistance in a low temperature and low humidity environment, and the transfer material once warmed by the fixing device is sufficiently cooled by fixing the first surface of the transfer material like an automatic double-sided machine. It is considered that since the toner image is transferred to the second surface without the transfer roller, the surface temperature of the transfer roller and the photosensitive drum in contact with the transfer material rises, and the resistance of the elastic layer of the transfer roller increases. Actually, 500 sheets of continuous double-sided printing were performed in a low-temperature and low-humidity environment, and when the temperature of the photosensitive drum and the total resistance value over the entire longitudinal direction of the transfer roller were measured, the temperature of the photosensitive drum rose 5 degrees, and the total resistance value of the transfer roller was increased. Was 1.4 times higher than the beginning.

Therefore, the present invention eliminates the resistance unevenness in the longitudinal direction due to the temperature rise of the transfer roller during continuous printing,
It is an object of the present invention to provide an image forming apparatus that enables good transfer without scattering and further good printing.

[0009]

According to a first aspect of the present invention, a toner image is formed on an image bearing member, and a transfer bias is applied to a conductive elastic roller arranged in contact with the image bearing member. In an image forming apparatus for transferring a toner image on an image carrier onto a transfer material and fixing the toner image on the transfer material by heating, a metal abutted in the longitudinal direction along a generatrix of the elastic roller surface. A cooling member having a member and an insulating member supporting the metal member is provided.

The present invention according to claim 2 is characterized in that the cooling member has a biasing member for biasing the metal member toward the elastic roller.

The present invention according to claim 3 is characterized in that the metal member is a plate-shaped member.

The present invention according to claim 4 is characterized in that the metal member is a roller-shaped member, and the insulating member is an insulating core material that penetrates the center of the roller-shaped member in the longitudinal direction. .

The present invention according to claim 5 is characterized in that the biasing means biases both end portions in the longitudinal direction of the insulating core material.

The present invention according to claim 6 is characterized in that the biasing means also serves as a pre-transfer guide disposed upstream of the transfer position in the transfer material transport direction.

According to a seventh aspect of the present invention, the elastic roller has a cored bar and an elastic layer surrounding the outer peripheral surface of the cored bar in a cylindrical shape, and the outer diameter B of the elastic layer and the cored bar. Between the outer diameter A and B
It has a relationship of /A≦1.5.

The present invention according to claim 8 relates to one of the transfer materials.
In order to automatically form an image on the first side and the second side, the image forming unit includes an automatic double-sided machine that reverses the transfer material image-formed on the first side and supplies the image again to the image forming unit. It is characterized by

[Operation] Since the metal member of the cooling member is abutted in the longitudinal direction along the generatrix of the elastic roller surface, when the elastic roller is heated, its heat is evenly distributed in the longitudinal direction of the elastic roller. It is transmitted to the metal member and radiated. Therefore, the surface temperature distribution in the longitudinal direction of the transfer roller can be made uniform, and the resistance unevenness in the longitudinal direction due to the difference in temperature can be eliminated. At this time, the metal member is
Since it is supported by the insulating member, when a transfer bias is applied to the elastic roller at the time of transfer, electric charge leaks through the metal member arranged in contact with the elastic roller,
It does not affect the transfer bias.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 shows an example of an image forming apparatus equipped with an automatic double-sided machine.

The image forming apparatus shown in FIG. 1 includes a drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 as an image bearing member inside an image forming apparatus main body 47. The photosensitive drum 1 is rotationally driven in the clockwise direction in the figure by a driving means (not shown).

The surface of the photosensitive drum 1 which is rotationally driven is uniformly charged by a primary charger 29, and then a laser beam according to an image signal from a host computer (not shown) is irradiated from an exposure device 28. Electrostatic latent image is formed.

The electrostatic latent image is developed (visualized) as a toner image with toner attached by the developing device 30.
On the other hand, a transfer material 19 such as paper is stored in a paper feeding unit 36 below the image forming apparatus, and is taken out one by one by a paper feeding roller 25 and sent to a pair of conveyance rollers 33 along a guide 34. The transfer material 19 is further guided by a guide 32 to be sent to a registration roller 31, and is sent to the pre-transfer guide 14 by the registration roller 31 in time with the toner image on the photosensitive drum 1.
The transfer material 19 is pressed between the transfer roller 4 disposed in contact with the photosensitive drum 1 and the photosensitive drum 1, and the toner image on the photosensitive drum 1 is transferred with a polarity opposite to the toner charge applied to the transfer roller 4. It is transferred to the surface of the transfer material (first surface) by the bias. The transfer roller 4 and the cooling member 102 arranged in contact with the transfer roller 4 will be described in detail later.

After the transfer of the toner image, the transfer residual toner remaining on the surface of the photosensitive drum 1 is removed by the cleaner 12, and the photosensitive drum 1 is used for the next image formation.

On the other hand, the transfer material 19 after the transfer of the toner image is in a state in which the unfixed toner image is carried on the first surface of the transfer material 1.
The charge passes through the charge eliminating needle 8 which applies a bias having a polarity opposite to that of the transfer bias in order to remove the charge on the toner 9, and is conveyed to the fixing device 13 through the conveying guide 10 by the driving of the transfer roller. The image is heated and pressed to fix it.

In the case of single-sided printing, the transfer material 19 is conveyed upward along the guide 38 due to the swingable flapper 37 being positioned below, and the paper discharge roller 45 causes the image forming apparatus main body 47. Paper ejection tray 4 formed on the top surface
6 is discharged.

When double-sided printing is performed by the automatic double-sided machine, the transfer material 19 after fixing is conveyed downward along the guide 39 by switching the flapper 37 upward. Then, the reversing roller 40 once sends the sheet to the reversing guide 41, and the reverse rotation of the reversing roller 40 causes a switchback to reverse the front and back. The inverted transfer material 19 then returns to the same conveying path as that of the first surface by the conveying roller pair 33 again via the guide 42, the conveying roller 43, and the guide 44, and then returns to the second surface in the same manner as the first surface. After the paper is printed and fixed, the paper output tray 46
Is discharged on top. The automatic double-sided machine is composed of each member from the flapper 37 to the guide 44.

FIG. 2 shows an enlarged view of the transfer roller 4 and the metal roller 102 as a cooling member which is a feature of the present invention. The transfer roller 4 includes a metal cored bar 2 having an outer diameter of 8 mm,
An outer diameter of 18 mm is formed by the elastic layer 3 surrounding the outer peripheral surface in a cylindrical shape. The elastic layer 3 is formed by foaming EPDM, and further has carbon dispersed therein to have a volume resistivity of the roller of 1.0 × 10 ^{5 to} 1.0 × 1.
It is adjusted within the range of 0 ¹⁰ Ω · cm. Also, 50
Reference numerals 51 and 51 are high-voltage power supplies for applying a bias to the core metal 2 and the charge eliminating needle 8 of the transfer roller 4, respectively. The transfer bias (output) V _t by the high-voltage power supply 50 is constant-current controlled so that the transfer material 19 reaches the hold voltage V _t0 before the transfer material 19 reaches the transfer nip portion formed by the photosensitive drum 1 and the transfer roller 4. The transfer bias V _t is determined by the following equation: V _t = a · V _t0 + b (a and b are constants).

The output V _d of the high voltage power source 51 is a value determined by separation of the transfer material 19 from the photosensitive drum 1, image scattering, paper conveyance, fixing offset, etc., and the tip of the transfer material 19 is discharged. It is applied after reaching the needle 8 until the trailing edge has finished passing through the transfer nip portion. Reference numeral 9 denotes a static elimination needle cover, and the above-mentioned output V _d also depends on the shape of the static elimination needle cover 9. In the present embodiment, a = 0.
9, b = 1.5, and a V _d = -1.2kV.

The metal roller 102 as the cooling member is P
Diameter 6 formed by OM (polyoxymethylene)
It is composed of an insulating core material (insulating member) 100 of mm and a roller-shaped metal member 101 made of aluminum and having an outer diameter of 14 mm surrounding the outer peripheral surface in a cylindrical shape. The metal roller 102 is formed to have the same length as the elastic layer 3 of the transfer roller 4, and both ends thereof are abutting means (not shown).
Is biased toward the transfer roller 4. At this time, a load of 200 g on each side is applied so that the contact pressure on the transfer roller 4 becomes uniform in the longitudinal direction. The metal roller 102 is driven to rotate in the direction of arrow R2 as the transfer roller 4 rotates in the direction of arrow R4.

FIG. 3 shows a comparison of the resistance distribution in the longitudinal direction of the transfer roller 4 after continuous printing on both sides when the metal roller 102 is not contacted and when it is contacted. As shown by the dotted line in the figure, when contacted, the volume resistance value at both ends of the transfer roller 4 and the central part of the transfer roller 4 compared to the case not contacted (only the transfer roller) are shown. The difference from the volume resistance value becomes small, and the contact of the metal roller 102 is caused by the transfer roller 4.
It was found that it has the effect of making the surface temperature distribution of the uniform. Comparing the images after printing at this time, the degree of "scattering" is also improved.

In the above, the core material 100 of the metal roller 102 is used.
Since the POM is used as this, the electric charge does not leak and the transfer bias V _t is not affected at all. As long as these conditions are satisfied, P
The core material 100 may be composed of a member other than the OM.

Further, if the thickness of the roller-shaped metal member 101 is smaller, the thermal conductivity in the longitudinal direction is improved accordingly, so that it may be thinner. For example, it is more preferable when the metal member 101 is formed in a pipe shape and only the shaft flange is made of POM. The contact with the transfer roller 4 may be always performed, but may be limited to only during double-sided printing.

Further, the material of the metal roller 102 is not limited to aluminum, but may be any other metal having a high thermal conductivity (for example, copper), and the shaft flange is not limited to POM. Any material may be used as long as it is made of insulating material such as a mixed material of nylon and glass.

The length in the longitudinal direction of the metal member 101 of the metal roller 102 may be longer than the length of the transfer roller 4, and does not necessarily have to be the same length.

In the above description, the roller-shaped metal member 102 is brought into contact with the transfer roller 4. However, this is not limited to the roller-shaped member, but instead of this, for example, a plate-shaped metal member may be brought into contact. Good. <Second Embodiment> A second embodiment will be described with reference to FIG. FIG. 4 is an enlarged view of the vicinity of the transfer roller.
The same reference numerals as in FIG. 6 have the same configuration and operation. In FIG. 4, 102 is the metal roller of the above-described first embodiment. On the other hand, 105 is a transfer roller, and the elastic layer 10
The outer diameter B of No. 4 remains 18 mm as in the first embodiment, and the outer diameter A of the core metal 103 is 14 mm (8 m in the first embodiment.
m) thickened. By thus reducing the thickness of the elastic layer 104, the heat from the transfer material 19 and the photosensitive drum 1 can be uniformly transferred in the longitudinal direction, so that the contact of the metal roller 102 of the first embodiment can be prevented. By combining them, the degree of “scattering” can be suppressed lower than in the first embodiment. Regarding the thickness of the elastic layer 104 of the transfer roller 105, as shown in FIG. 7, the ratio B / A of the outer diameter B of the elastic layer 104 and the outer diameter A of the core metal is 1.5 (3/2). It can be seen that the "scattering" can be eliminated by making it smaller.

Also in the second embodiment, the metal member 10 is used.
When the thickness of No. 1 is made thin or made into a pipe shape to improve the thermal conductivity, it is used in combination with the above-mentioned transfer roller 105, and a more remarkable effect can be obtained. <Third Embodiment> A third embodiment will be described with reference to FIG. The transfer roller 105 shown in FIG.
It is the same as that of the second embodiment shown in FIG. Further, the same symbols as those in FIG. 4 have the same configuration and operation. In FIG. 5, reference numeral 108 denotes a metal roller composed of a POM shaft 106 and a roller-shaped metal member 107 made of aluminum, and the shaft 106 is supported by the front end portion C of the pre-transfer lower guide 109. The pre-transfer lower guide 109 is
It is supported so as to be vertically swingable about a swing shaft 110 in the center, and a compression spring 111 that is shorter than the free length is attached to the base end. As a result, the metal roller 108 attached to the tip portion C of the pre-transfer lower guide 109.
Is in contact with the surface of the transfer roller 105 with a constant pressure. That is, the lower pre-transfer lower guide 109 of the upper and lower pre-transfer guides also serves as the biasing means of the metal roller 108. Since the metal roller 108 is located between the pre-transfer lower guide 109 and the transfer roller 105 as described above, the position of the tip portion C of the pre-transfer lower guide 109 is set to the transfer roller 105.
Transfer material 1 in front of the transfer nip part to keep it constant from the surface
It is possible to suppress the scattering of the toner image on the toner image 9 and to reduce the resistance unevenness of the transfer roller 105 in the longitudinal direction.

The swing shaft 11 of the pre-transfer lower guide 109
The biasing means by 0 and the compression spring 111 is not limited to this,
The metal roller 108 may be brought into contact with the transfer roller 105 with a constant pressure.

In any of the above embodiments, a metal member is used for the portion of the cooling member that directly contacts the transfer roller surface. This means that a member having excellent thermal conductivity is used. Of course, as long as this condition is satisfied, members other than metal may be used.

[0038]

As described above, according to the present invention,
Since the metal member of the cooling member is abutted in the longitudinal direction along the generatrix of the surface of the elastic roller, when the temperature of the elastic roller rises, the heat is evenly transferred to the metallic member in the longitudinal direction of the elastic roller to radiate heat. To be done. Therefore, the surface temperature distribution in the longitudinal direction of the transfer roller can be made uniform, and the resistance unevenness in the longitudinal direction due to the difference in temperature can be eliminated. As a result, it is possible to prevent a transfer failure due to uneven resistance of the elastic roller and form a high-quality image. Since the metal member is supported by the insulating member, when a transfer bias is applied to the elastic roller at the time of transfer, electric charge leaks through the metal member arranged in contact with the elastic roller or the transfer bias is applied. It has no effect.

The outer diameter B of the transfer roller and the outer diameter A of the cored bar
By using a transfer roller having a ratio B / A smaller than 1.5 smaller than 1.5 in combination with the above-described cooling member, it is possible to further reduce resistance unevenness in the transfer roller longitudinal direction.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a transfer roller, a metal roller, etc. according to the first embodiment.

FIG. 3 is a diagram showing a longitudinal direction distribution of transfer roller volume resistance values.

FIG. 4 is an enlarged cross-sectional view of a transfer roller, a metal roller, etc. according to the second embodiment.

FIG. 5 is an enlarged cross-sectional view of a transfer roller, a metal roller, etc. according to the third embodiment.

FIG. 6 is a diagram showing a longitudinal direction distribution of transfer roller volume resistance values after continuous printing in a conventional example.

[FIG. 7] Ratio B / of outer diameter B of transfer roller and accounting A of core metal
The figure which shows the relationship between A and a scattered image.

[Explanation of symbols]

 1 Image Carrier (Photosensitive Drum) 2, 103 Core Metal 3, 104 Elastic Layer 4, 105 Transfer Roller 19 Transfer Material 100, 106 Insulating Core Material (Insulating Member) 101, 107 Metal Member 102, 108 Cooling Member (Metal) Roller) 109 Energizing means (lower guide before transfer) 111 Compression spring

Claims (8)

[Claims] 1. A toner image is formed on an image carrier, and a transfer bias is applied to a conductive elastic roller arranged in contact with the image carrier to transfer the toner image on the image carrier onto a transfer material. In the image forming apparatus for fixing the toner image on the transfer material by heating, a metal member abutting in the longitudinal direction along a generatrix of the elastic roller surface, and an insulating member supporting the metal member, An image forming apparatus comprising: a cooling member having: 2. The image forming apparatus according to claim 1, wherein the cooling member has a biasing member that biases the metal member toward the elastic roller. 3. The image forming apparatus according to claim 1, wherein the metal member is a plate-shaped member. 4. The metal member is a roller-shaped member, and the insulating member is an insulating core material that penetrates the center of the roller-shaped member in the longitudinal direction. The image forming apparatus described. 5. The image forming apparatus according to claim 2, wherein the urging means urges both ends of the insulating core material in the longitudinal direction. 6. The pre-transfer guide arranged on the upstream side of the transfer position in the transfer material conveying direction, wherein the urging means also functions as a pre-transfer guide.
An image forming apparatus according to any one of the preceding claims. 7. The elastic roller has a cored bar and an elastic layer surrounding the outer peripheral surface of the cored bar in a cylindrical shape, and between the outer diameter B of the elastic layer and the outer diameter A of the cored bar. , B / A ≦ 1.5, wherein any one of claims 1 to 6 is satisfied.
An image forming apparatus according to any one of the preceding claims. 8. In order to automatically form an image on the first side and the second side of the transfer material, the transfer material image-formed on the first surface is reversed in the image forming section, and the image formation is performed again. 8. An automatic double-sided machine for supplying to a section is provided.
An image forming apparatus according to any one of the preceding claims.