This application claims priority to Japanese Patent Application No. 2009-184361 filed on Aug. 7, 2009. The entire disclosure of Japanese Patent Application No. 2009-184361 is hereby incorporated herein by reference.
1. Technical Field
The present invention relates to a transfer apparatus and an image forming apparatus which transfer an image carried by a transfer belt onto a transfer material by using a transfer belt having an elastic layer and a transfer roller having an elastic layer.
2. Related Art
In an existing electrophotographic type image forming apparatus using a liquid developer, there is a problem that transfer efficiency of an image carried by a transfer belt onto a transfer material such as transfer paper is not good. In particular, when an image which is carried by the transfer belt and on which a plurality of colors are superimposed is transferred onto the transfer material, deterioration in transfer efficiency becomes a problem.
Then, an image forming apparatus in which a long transfer nip is used for transferring has been proposed. Japanese Patent Application Publication No. 2001-166611 discloses such a nip as an example. The long transfer nip includes a pressure-contact nip which presses a transfer roller against a transfer belt and a winding nip which winds the transfer belt over the transfer roller and which is formed so as to be extremely longer than the pressure-contact nip. In the image forming apparatus, a transfer material contacts with an image with pressure on the transfer belt at the long transfer nip while a time during which a transfer bias is applied is made longer. This makes it possible to increase transfer efficiency.
However, if the long transfer nip is used and if the winding nip is long, an image transferred onto the transfer material is dragged to cause deviation at the time of transferring in some cases. The deviation of the image is considered to be caused by change in belt surface speed at the long transfer nip. In general, a surface layer portion of the transfer roller is formed to be softer than a backup roller of the transfer roller. Therefore, a surface layer portion of the transfer roller is concaved with respect to the circular circumference of the transfer roller at the pressure-contact nip and a surface of the transfer belt which carries an image is bent in the extension direction along the concave portion. On the other hand, a surface of the transfer belt is bent in the compression direction along an outer circumferential surface of the transfer roller at the winding nip. Thus, as the bending directions of the surface of the transfer belt differ at the transfer nip, the surface speed of the transfer belt changes between the pressure-contact nip and the winding nip. Then, as the winding nip is made longer, the change in the surface speed of the transfer belt is larger and image deviation tends to be caused.
An elastic layer of the transfer belt is compressed by a pressure load on the pressure-contact nip. Therefore, a net length of the belt is made short at the pressure-contact nip. On the other hand, the elastic layer of the transfer belt is hardly deformed because the pressure load is not applied to the transfer belt at the winding nip. Therefore, a difference in the surface speed of the transfer belt is caused between the pressure-contact nip and the winding nip.
Further, both of a contact area between the transfer belt and the transfer roller and a contact area between the transfer belt and the transfer material are increased by using the long transfer nip. Therefore, the transfer belt easily meanders due to a difference in the pressure load in the direction orthogonal to or substantially orthogonal to the transfer material movement direction, a position of the transfer material at the transfer nip (position different from a predetermined position), or a posture (skew) of the transfer material.
An advantage of some aspects of the invention is to provide a transfer apparatus and an image forming apparatus by which excellent transfer efficiency is obtained and which can suppress deviation of the transfer image and suppress meandering of the transfer belt.
According to one aspect of the invention, there is provided a transfer apparatus. The transfer apparatus includes a transfer belt being configured and arranged to carry an image. The transfer belt has an elastic layer. The transfer apparatus also include a transfer roller having an elastic layer and being configured and arranged to transfer the image from the transfer belt onto a transfer material, and a backup roller being configured and arranged to have pressure against the transfer roller with the transfer belt therebetween. The transfer nip portion includes a pressure-contact nip formed in an area where the transfer belt is in contact with the transfer roller and the backup roller by the pressure, and a contact nip formed in an area where the transfer belt is in contact with the transfer roller and is no contact with the backup roller. A length of the contact nip in a rotational direction of the transfer roller is smaller than half a length of the pressure-contact nip in the rotational direction of the transfer roller.
Referring now to the attached drawings which form a part of this original disclosure:
The present invention will now be described in terms of the explanatory embodiment with reference to the accompanying drawings.
An image forming apparatus 1 according to the first embodiment performs image formation by using a liquid developer containing toner particles and carrier liquid. As shown in
Each of charging portions 3Y, 3M, 3C, 3K is provided on the periphery of each of the photosensitive members 2Y 2M, 2C, 2K. Further, exposure portions 4Y, 4M, 4C, 4K, developing portions 5Y, 5M, 5C, 5K, primary transfer portions 6Y 6M, 6C, 6K and photosensitive member cleaning portions 7Y 7M, 7C, 7K are arranged in this order in the rotational direction a of the photosensitive members 2Y 2M, 2C, 2K from the charging portions 3Y, 3M, 3C, 3K, respectively. Each of the exposure portions 4Y, 4M, 4C, 4K writes a latent image onto each of the photosensitive members 2Y, 2M, 2C, 2K. Each of the developing portions 5Y, 5M, 5C, 5K develops the latent image carried by each of the photosensitive members 2Y, 2M, 2C, 2K by toner as the liquid developer so as to form a toner image as a developer image.
The image forming apparatus 1 includes an intermediate transfer belt 8, which is ring-shaped. The intermediate transfer belt 8 serves as an image carrier and as a transfer belt. The intermediate transfer belt 8 is arranged above the photosensitive members 2Y, 2M, 2C, 2K. The intermediate transfer belt 8 contacts with each of the photosensitive members 2Y, 2M, 2C, 2K with pressure at each of the primary transfer portions 6Y, 6M, 6C, 6K. Each of the primary transfer portions 6Y, 6M, 6C, 6K color-superimposes and transfers each toner image of each color carried by each of the photosensitive members 2Y, 2M, 2C, 2K onto the intermediate transfer belt 8. Therefore, a full-color toner image is carried by the intermediate transfer belt 8.
The intermediate transfer belt 8 is formed into a relatively soft elastic belt having a three-layered structure. Although not shown, the three-layered structure has a flexible base layer such as a resin, an elastic layer such as a rubber layer which is formed on a surface of the base layer, and a surface layer which is formed on a surface of the elastic layer. In this case, the base layer is located at an inner circumferential side and the surface layer is located on an outer circumferential side. As an example of the intermediate transfer belt 8, a resin such as a polyimide resin can be used as the base layer, and a rubber layer such as an urethane rubber can be used as the elastic layer. Further, for example, a fluororesin, a fluoro-rubber based material, or the like can be used as the surface layer. However, the intermediate transfer belt 8 is not limited thereto. The intermediate transfer belt 8 is stretched between the intermediate transfer belt driving roller 9 and the intermediate transfer belt tension roller 10. The driving force of an intermediate transfer belt driving motor (not shown) is transmitted to the intermediate transfer belt driving roller 9 and the intermediate transfer belt tension roller 10. Then, the intermediate transfer belt 8 is configured to rotationally move in the rotational movement direction β in a state where tension is applied to the intermediate transfer belt 8.
Arrangement orders of members such as the photosensitive members corresponding to each color of Y, M, C and K is not limited to the example as shown in
A secondary transfer portion 11, which is a transfer apparatus, is provided on the side of the intermediate transfer belt driving roller 9 with respect to the intermediate transfer belt 8. The secondary transfer portion 11 includes a secondary transfer roller 12, a tension roller 13 and a secondary transfer roller cleaning portion 14.
As shown in
A radius R1 (mm) of the outer circumferential surface of the elastic layer 12b of the secondary transfer roller 12 is set to be larger than a radius R2 (mm) of the intermediate transfer belt driving roller 9 (R1>R2). Further, in the image forming apparatus 1 according to the first embodiment, although not shown, the thickness (μm) of the elastic layer of the intermediate transfer belt 8 is set to be smaller than the radius R2 (mm) of the intermediate transfer belt driving roller 9. The secondary transfer roller 12 rotates in the rotational direction γ at the time of the image formation.
In the secondary transfer roller 12, the elastic layer 12b contacts with the intermediate transfer belt driving roller 9 with pressure through the intermediate transfer belt 8 by a biasing force of a biasing unit such as a spring (not shown). Therefore, as shown in
The tension roller 13 is arranged at a position which is after the intermediate transfer belt roller 9 and before the intermediate transfer belt tension roller 10 in the movement direction β of the intermediate transfer belt 8. The intermediate transfer belt 8 which has passed through the pressure-contact nip 11a is guided to the side of the secondary transfer roller 12 by being wound over the tension roller 13. Further, the intermediate transfer belt 8 which has passed through the pressure-contact nip 11a makes contact with (that is, is wound over) the elastic layer 12b of the secondary transfer roller 12. Therefore, the contact nip 11b is formed between the intermediate transfer belt 8 and the elastic layer 12b of the secondary transfer roller 12. The contact nip 11b is formed so as to follow a termination end of the pressure-contact nip 11a (an end of the pressure-contact nip 11a on the advanced side in the intermediate transfer belt movement direction β). That is to say, the contact nip 11b is formed as a contact nip by the contact of the intermediate transfer belt 8 and the secondary transfer roller 12 in a region where the intermediate transfer belt 8 and the secondary transfer roller 12 are not in contact with the intermediate transfer belt driving roller 9. The pressure-contact nip 11a and the contact nip 11b constitute a secondary transfer nip 11c which corresponds a transfer nip portion. With the transfer nip portion, a toner image carried by the intermediate transfer belt 8 is secondarily transferred onto a transfer material 15 such as transfer paper.
At the secondary transfer nip 11c, the transfer material 15 passing through the pressure-contact nip 11a is pinched together with the intermediate transfer belt 8 between the intermediate transfer belt driving roller 9 and the elastic layer 12b of the secondary transfer roller 12. Further, the transfer material 15 passing through the contact nip 11b is pinched between the intermediate transfer belt 8 separated from the intermediate transfer belt driving roller 9 and the elastic layer 12b of the secondary transfer roller 12. The transfer material 15 which has passed through the contact nip 11b is separated from the intermediate transfer belt 8 and moves in a state of being wound over the elastic layer 12b of the secondary transfer roller 12. Finally, the transfer material 15 is separated from the elastic layer 12b.
Accordingly, a position p1 is different from a position p2 with respect to a tangential direction ε at an intersection of a virtual line δ and an outer circumferential surface of the intermediate transfer belt 8. The virtual line δ is a line connecting the center 9a of the intermediate transfer belt driving roller 9 and the center 12c of the secondary transfer roller 12. Further, the tangential direction ε is a direction orthogonal to the virtual line δ. In this case, the intermediate transfer belt 8 is separated from the intermediate transfer belt driving roller 9 at the position p1. The transfer material 15 is separated from the intermediate transfer belt 8 at the position p2. To be more specific about the relationship between the position p1 and the position p2, the position p1 is located on the previous side in the movement direction β of the intermediate transfer belt 8 with respect to the position p2.
As shown in
In the image forming apparatus 1 according to the first embodiment, the contact nip width W2 (mm) is set to be smaller than half the pressure-contact nip width W1 (mm) (that is, W2<W1/2). In other words, a length of the contact nip 11b on the circumferential surface of the secondary transfer roller 12 in the rotational direction γ of the secondary transfer roller 12 is smaller than half a length of the pressure-contact nip 11a on the circumferential surface of the secondary transfer roller 12 in the rotational direction γ of the secondary transfer roller 12. Further, the contact nip width W2 is set to be larger than the thickness of the elastic layer of the intermediate transfer belt 8.
A method of measuring the secondary transfer nip width W (mm), the pressure-contact nip width W1 (mm) and the contact nip width W2 (mm) in the secondary transfer nip 11c will be described. As shown in
As described above, the secondary transfer nip width includes the pressure-contact nip width W1 (mm) and the contact nip width W2 (mm). Therefore, the secondary transfer nip width is formed as a long transfer nip which is longer than a transfer nip including only the pressure-contact nip width W1 (mm). However, since the contact nip width W2 (mm) is restricted to be smaller than the pressure-contact nip width W1 (mm), the contact nip width W2 (mm) is extremely small in comparison with the contact nip width in the image forming apparatus described in Japanese Patent Application Publication No. 2001-166611 in which the contact nip width is formed to be larger than the pressure-contact nip width.
Further, as shown in
Transfer mechanism in the secondary transfer portion 11 having such a configuration is assumed, as follows. The elastic layer of the intermediate transfer belt 8 is deformed by the pressure load at the pressure-contact nip 11a. Therefore, the surface of the intermediate transfer belt 8 follows irregularities on the surface of the transfer material 15. Therefore, adhesion between the toner image carried by the intermediate transfer belt 8 and the transfer material 15 is increased. In a state where adhesion between the toner image and the transfer material 15 is increased, an electric field is formed by the secondary transfer bias on the pressure-contact nip 11a. Therefore, the toner image carried by the intermediate transfer belt 8 is effectively transferred onto a surface of the transfer material 15 having irregularities.
When the toner image carried by the intermediate transfer belt 8 is transferred onto the surface of the transfer material 15 by the secondary transfer nip 11c including only the pressure-contact nip 11a, toner adhered to a convex portion on the surface of the transfer material 15 is relatively easily separated from the intermediate transfer belt 8. However, toner adhered to the concave portion on the surface of the transfer material 15 is not easily separated from the intermediate transfer belt 8 in comparison with the toner adhered to the convex portion of the transfer material 15. The reason of this is considered to be as follows. When the contact nip 11b is not formed, the transfer material 15 is separated from the intermediate transfer belt 8 at an outlet of the pressure-contact nip 11a (at a termination end of the pressure-contact nip 11a in the movement direction of the transfer material 15). At this time, a relatively large physical adhesion acts between the intermediate transfer belt 8 and the toner and between the transfer material and the toner by the pressure applied on the pressure-contact nip 11a. The pressure is drastically released near the outlet of the pressure-contact nip 11a so that the deformation of the elastic layer of the intermediate transfer belt 8 is recovered. Then, since a slight space is likely to be generated between the concave portion of the transfer material 15 and the intermediate transfer belt 8 at the concave portion of the transfer material 15, aggregation force by the toner positioned on the concave portion of the transfer material 15 becomes smaller. On the other hand, since a large physical adhesion between the intermediate transfer belt 8 and the toner is present near the outlet of the pressure-contact nip 11a, the aggregation force by the toner is smaller than the physical adhesion between the intermediate transfer belt 8 and the toner. Therefore, a toner film is divided in the film. As a result, a part of the toner located on the concave portion of the transfer material 15 is adhered to the transfer material 15. However, the remaining toner is kept being adhered to the intermediate transfer belt 8 so that the toner remained not to be transferred is considered to be present.
In the secondary transfer portion 11 according to the first embodiment, the contact nip 11b is formed so as to follow the pressure-contact nip 11a so that the secondary transfer nip 11c is formed to be a long transfer nip. In the contact nip 11b, a pressure contact between the intermediate transfer belt driving roller 9 and the secondary transfer roller 12 through the intermediate transfer belt 8 is released. Accordingly, when the transfer material 15 is passing through the contact nip 11b, a pressure is hardly applied to the toner pinched between the transfer material 15 and the intermediate transfer belt 8. Therefore, the physical adhesion between the intermediate transfer belt 8 and the toner image carried by the intermediate transfer belt 8 is relaxed. Further, a transfer current is generated by the secondary transfer bias at the pressure-contact nip 11a. However, the intermediate transfer belt 8 and the transfer material 15 are charged with the transfer current so as to generate an electric field at the contact nip 11b. Namely, when the transfer material 15 is passing through the contact nip 11b, the electric field acts on the toner in the state where the physical adhesion between the intermediate transfer belt 8 and the toner is relaxed. As a result, when the intermediate transfer belt 8 is separated from the transfer material 15, toner adhered to the concave portion on the surface of the transfer material 15 is easily separated from the intermediate transfer belt 8 by the effect of the electric field and the aggregation force with the toner adhered to the convex portion adjacent to the concave portion. In such a manner, the toner adhered to the concave portion of the transfer material 15 is relatively easily separated from the intermediate transfer belt 8 with the contact nip 11b formed so as to follow the pressure-contact nip 11a. This makes it possible to make transfer efficiency better.
The transfer material 15 passing through the pressure-contact nip 11a is pinched together with the intermediate transfer belt 8 between the intermediate transfer belt driving roller 9 and the elastic layer 12b of the secondary transfer roller 12 at the secondary transfer nip 11c.
The secondary transfer roller cleaning portion 14 removes the liquid developer adhered to the elastic layer 12b of the secondary transfer roller 12 with a cleaning member such as a cleaning blade. The liquid developers removed by the cleaning member are collected into a liquid developer container.
The transfer material 15 onto which the toner image is transferred at the secondary transfer portion 11 is transported to a commonly known fixing unit (not shown). Then, the toner image transferred onto the transfer material 15 is heat-pressed and fixed by the fixing unit. The transfer material 15 onto which the toner image is fixed is accommodated in a transfer material discharge tray (not shown).
According to the image forming apparatus 1 of the first embodiment, the secondary transfer nip 11c includes the pressure-contact nip 11a and the contact nip 11b so as to be formed as a long transfer nip which is longer than a transfer nip including only the pressure-contact nip. Accordingly, excellent transfer efficiency can be obtained in comparison with that in the transferring performed by using only the pressure-contact nip 11a.
The contact nip width W2 (mm) when the intermediate transfer belt 8 is wound over the secondary transfer roller 12 is made smaller than half the pressure-contact nip width W1 (mm). This decreases the winding amount of the intermediate transfer belt 8 wound over the secondary transfer roller 12. Therefore, the intermediate transfer belt 8 hardly bends in the compression direction along the outer circumferential surface of the secondary transfer roller 12. Accordingly, the bending direction of the surface of the intermediate transfer belt 8 hardly changes at the secondary transfer nip 11c so that change in the surface speed of the intermediate transfer belt 8 between the pressure-contact nip 11a and the contact nip 11b is suppressed. As a result, deviation of the image transferred onto the transfer material 15 can be suppressed at the time of the secondary transferring.
Further, when the pressure-contact nip 11a has a shape projecting to the side of the secondary transfer roller 12, the radius R1 (mm) of the secondary transfer roller 12 is made larger than the radius R2 (mm) of the intermediate transfer belt driving roller 9 so that the tension roller 13 easily guides the intermediate transfer belt 8 from the termination end of the pressure-contact nip 11a to the side of the intermediate transfer belt driving roller 9. Therefore, the contact nip width W2 (mm) can be made smaller, thereby effectively suppressing bending of the surface of the intermediate transfer belt 8 along the outer circumferential surface of the secondary transfer roller 12 in the compression direction.
Further, when the pressure-contact nip 11a has a shape projecting to the side of the secondary transfer roller 12, the thickness (mm) of the elastic layer 12b of the secondary transfer roller 12 is made larger than the contact nip width W2 (mm) so that the tension roller 13 easily guides the intermediate transfer belt 8 from the termination end of the pressure-contact nip 11a to the side of the intermediate transfer belt driving roller 9 in the same manner. Therefore, the contact nip width W2 (mm) can be made smaller, thereby further effectively suppressing bending of the surface of the intermediate transfer belt 8 along the outer circumferential surface of the secondary transfer roller 12 in the compression direction.
Further, when the pressure-contact nip 11a has a shape projecting to the side of the secondary transfer roller 12, the thickness (mm) of the elastic layer of the intermediate transfer belt 8 is made smaller than the contact nip width W2 (mm) so that the tension roller 13 easily guides the intermediate transfer belt 8 from the termination end of the pressure-contact nip 11a to the side of the intermediate transfer belt driving roller 9 in the same manner. Therefore, the contact nip width W2 (mm) can be made smaller, thereby further effectively suppressing bending of the surface of the intermediate transfer belt 8 along the outer circumferential surface of the secondary transfer roller 12 in the compression direction.
Further, when the secondary transfer nip 11c is formed so as to be a long transfer nip, the width of the secondary transfer nip 11c in the movement direction of the transfer material 15 can be made sufficiently short in comparison with the image forming apparatus described in Japanese Patent Application Publication No. 2001-166611. Both of a contact area between the intermediate transfer belt 8 and the secondary transfer roller 12 and a contact area between the intermediate transfer belt 8 and the transfer material 15 can be made smaller. Therefore, effect on the intermediate transfer belt 8 by the difference in the pressure load in the direction orthogonal to or substantially orthogonal to the movement direction of the transfer material 15, a position of the transfer material 15 at the secondary transfer nip 11c (a position different from a predetermined position), or a posture (skew) of the transfer material 15 can be made smaller. Accordingly, the meandering of the intermediate transfer belt 8 can be effectively suppressed.
Further, the movement direction β of the intermediate transfer belt 8 which has passed through the pressure-contact nip 11a can be made stable by arranging the tension roller 13 at a position advanced in the movement direction β of the intermediate transfer belt 8 with respect to the intermediate transfer belt driving roller 9. This makes it possible to suppress the wobble of the intermediate transfer belt 8 which has passed through the pressure-contact nip 11a in the movement direction β so as to reliably form the contact nip 11b. At the same time, the contact nip width W2 (mm) can be more reliably made smaller than half the pressure-contact nip width W1 (mm).
In addition, the movement speed of the intermediate transfer belt 8 can be made stable by driving the intermediate transfer belt 8 by the intermediate transfer belt driving roller 9 in the secondary transfer portion 11. Therefore, the movement speed of the transfer material 18 at the secondary transfer nip 11c can be made stable so that the image deviation of the transfer image is hardly caused.
In such a manner, according to the image forming apparatus 1 of the first embodiment, excellent transfer efficiency is obtained while suppressing the deviation of the transfer image. Moreover, the meandering of the intermediate transfer belt 8 can be effectively suppressed according to the image forming apparatus 1 of the first embodiment.
Other configurations and other operation effects in the image forming apparatus 1 according to the first embodiment are the same as those with an existing tandem type image forming apparatus using a liquid developer.
As shown in
A gripper 18, a gripper supporting member 19 and a separation claw 20 are arranged in the concave portion 17. The gripper 18 corresponds to a transfer material gripping unit, the gripper supporting member 19 corresponds to a transfer material gripping unit reception member on which the gripper 18 is seated, and the separation claw 20 corresponds to a transfer material separation member. Although not shown, a plurality of grippers 18 are arranged along an axial direction of the secondary transfer roller 12. The number of the grippers 18 is predetermined. Each gripper 18 is formed in a comb-tooth pattern. The gripper supporting members 19 are arranged so as to correspond to each gripper 18. Further, the separation claws 20 are arranged between the teeth of a comb of the grippers 18 and on both outer sides of the teeth of the comb.
Each gripper 18 is provided integrally with the gripper supporting member 19 so as to be rotationally movable in the rotation direction η between a gripping position as shown in
Immediately before the concave portion 17 reaches the secondary transfer nip 11c, the grippers 18 rotationally move toward the gripper supporting members 19 and grip the top edge 15a of the transfer material 15 fed from the gate rollers 16 in the feeding direction ζ between the grippers 18 and the gripper supporting members 19. The toner image carried by the intermediate transfer belt 8 is transferred onto the transfer material 15 at the secondary transfer nip 11c in a state where the grippers 18 grip the top edge 15a of the transfer material 15. Further, the transfer material 15 which has passed through the secondary transfer nip 11c is reliably separated from the intermediate transfer belt 8 because the top edge 15a of the transfer material 15 is gripped by the grippers 18. Thereafter, the grippers 18 rotationally move in the direction of leaving the gripper supporting members 19 so as to release the top edge 15a of the transfer material 15. Further, each separation claw 20 is projected to the projection position soon after the griping of the transfer material by the grippers 18 is released. Then, the rear face of the transfer material 15 is projected from each separation claw 20. Thus, the transfer material 15 is separated from the secondary transfer roller 12. Then, each separation claw 20 returns to the retreat position in the concave portion 17. Each operation of the grippers 18 and the separation claws 20 is controlled by a gripper control cam (not shown) and a separation claw control cam (not shown), respectively, by rotating the secondary transfer roller 12.
According to the image forming apparatus 1 of the second embodiment, the toner image carried by the intermediate transfer belt 8 is transferred onto the transfer material 15 in a state where the top edge 15a of the transfer material 15 is gripped by the grippers 18. Therefore, the transfer material 15 can be reliably separated from the intermediate transfer belt 8 after the transferring. Further, since the rear face of the transfer material 15 is projected from the outer circumferential surface by the separation claws 20, the transfer material 15 can be reliably separated from the outer circumferential surface of the elastic layer 12b of the secondary transfer roller 12 after the transferring.
Other configurations and other operation effects in the image forming apparatus 1 according to the second embodiment are the same as those in the image forming apparatus 1 according to the first embodiment.
As shown in
Further, a plurality of air flow nozzle holes 12g which penetrate through a cylindrical portion of the base material 12a and the elastic layer 12b are arranged on the secondary transfer roller 12. The number of the air flow nozzle holes is predetermined. These air flow nozzle holes 12g are arranged along the axial direction of the secondary transfer roller 12. In this case, the air flow nozzle holes 12g are arranged along the axial direction of the secondary transfer roller 12 in a single row as shown in
In the image forming apparatus 1 according to the third embodiment having such a configuration, the switching valve is set such that the air suction unit is connected to the air suction unit connection hole 12f and then the air suction unit is operated immediately before each air flow nozzle hole 12g reaches the secondary transfer nip 11c. Thus, the air in the base material 12a is sucked through the air suction unit connection hole 12f so that the air pressure in the base material 12a becomes a negative pressure. Then, the air near outside in the portion where the air flow nozzle holes 12g of the secondary transfer roller 12 are formed is sucked through each air flow nozzle hole 12g to inside the base material 12a. In this state, if the transfer material 15 is fed from the gate rollers 16 and the top edge 15a of the transfer material 15 reaches a portion where the air flow nozzle holes 12g of the secondary transfer roller 12 are formed, the top edge 15a of the transfer material 15 is sucked by the air flow nozzle holes 12g and adsorbed to the elastic layer 12b of the secondary transfer roller 12.
Then, the toner image carried by the intermediate transfer belt 8 is transferred onto the transfer material 15 at the secondary transfer nip 11c in a state where the top edge 15a of the transfer material 15 is adsorbed by the air flow nozzle holes 12g. Further, the transfer material 15 which has passed through the secondary transfer nip 11c is reliably separated from the intermediate transfer belt 8 because the top edge 15a of the transfer material 15 is adsorbed by the air flow nozzle holes 12g. Thereafter, the operation of the air suction unit is stopped to terminate the suction of the top edge 15a of the transfer material 15. Then, if the top edge 15a of the transfer material 15 reaches a separation position where the transfer material 15 is separated from the secondary transfer roller 12, the air feeding unit is operated and the switching valve is switched. Therefore, the air feeding unit is connected to the air suction unit connection hole 12f. Then, the air having a positive pressure is fed to the inside of the base material 12a and air having a positive pressure is flown out to the outside of the base material 12a through the air nozzle holes 12g. The transfer material 15 is easily separated from the secondary transfer roller 12 by the air flown out through the air nozzle holes.
According to the image forming apparatus 1 of the third embodiment, the toner image carried by the intermediate transfer belt 8 is transferred onto the transfer material 15 in a state where the top edge 15a of the transfer material 15 is sucked by the air flow nozzle holes 12g. Therefore, the transfer material 15 can be reliably separated from the intermediate transfer belt 8 after the transferring. Further, since the suction of the transfer material 15 by the air flow nozzle holes 12g is terminated after the transferring, the transfer material 15 can be easily separated from the outer circumferential surface of the elastic layer 12b of the secondary transfer roller 12.
Other configurations and other operation effects in the image forming apparatus 1 according to the third embodiment are the same as those in the image forming apparatus 1 according to the first embodiment.
As shown in
Other configurations and other operation effects in the image forming apparatus 1 according to the fourth embodiment are the same as those in the image forming apparatus 1 according to the first embodiment.
Next, Examples 1 to 4 according to the invention will be described.
Common Matters to Examples 1 to 4
Configuration of Image Forming Apparatus 1
A tandem type image forming apparatus as shown in
Configuration of Intermediate Transfer Belt 8
The intermediate transfer belt 8 has a three-layered structure having a base layer, an elastic layer arranged on a surface of the base layer (an outer circumferential side surface), and a surface layer arranged on a surface of the elastic layer (an outer circumferential side surface). The base layer is formed with a polyimide resin having thickness of 100 μm. Further, the elastic layer is formed with a rubber layer made of urethane rubber and the thickness of the rubber layer differs depending on Examples. The details thereof will be described later. Further, the surface layer is formed with a coating layer made of a fluororesin having thickness of 7 μm. A volume resistivity of all layers of the intermediate transfer belt 8 is 9.2×109 (Ω·cm) when the voltage of 100 V is applied thereto.
Configuration of Secondary Transfer Roller 12
The elastic layer 12b which is a rubber layer is arranged on an outer circumferential surface of the base material 12a made of iron in the secondary transfer roller 12. The elastic layer 12b is formed with a rubber layer made of urethane rubber and the thickness of the rubber layer differs depending on Examples. The details thereof will be described later. The width of the elastic layer 12b (the length of the elastic layer 12b in the axial direction of the secondary transfer roller 12) is 330 mm. Then, the intermediate transfer belt driving roller 9 (backup roller) is pressed through the intermediate transfer belt 8 by a pressing mechanism (not shown) of the secondary transfer roller 12.
Configuration of Tension Roller 13
A commonly known tension roller is used as the tension roller 13. In this case, the tension roller 13 is provided such that a position thereof can be adjusted in order to adjust the contact nip width W2 (mm).
Transfer Material
Two types of paper are used as the transfer material: coated paper (ULTRA SATIN KINFUJI 127.9 g manufactured by Oji Paper Co., Ltd.), and uncoated paper (J-paper manufactured by Fuji Xerox Co., Ltd.). Two types of transfer materials are used because difference in surface roughness between these transfer materials makes the transfer behavior different. A reason for the different transfer behaviors is considered hereinafter. Namely, in the transfer mechanism, aggregation force between toner particles, adhesion of toner particles to the transfer material and adhesion of toner particles to the intermediate transfer belt 8 are assumed to affect the transfer behavior. Further, separation behavior of the toner film from the intermediate transfer belt in the transfer nip and division behavior in the toner film are different depending on the types of transfer materials based on the surface roughness of the transfer materials. Therefore, the transfer behavior can differ depending on the types of transfer materials.
Method of Measuring Transfer Efficiency
The transfer efficiency is measured for three image patterns: a 2×2 dot image as shown in
As for the transfer efficiency, transfer efficiency is defined to be ((OD1−OD2)/OD1)×100(%) on the assumption that a concentration of toner (OD value) carried by intermediate transfer belt 8 before the secondary transferring is OD1 and the concentration of toner (OD value) remaining on the intermediate transfer belt 8 after the transferring is OD2. The concentration of the toner is measured by using an optical tester X-Lite. The transfer efficiency is measured while changing a secondary transfer bias. Then, a result at the transfer bias when the transfer efficiency is the maximum is adopted. Further, if the transfer efficiency is 90% or higher, the transfer efficiency is determined to be good. On the other hand, if the transfer efficiency is lower than 90%, the transfer efficiency is determined to be bad.
Method of Determining Image Deviation
Image deviation is determined for a horizontal line image of two dots which extends in the direction orthogonal to the movement direction (horizontal direction in
The pressure-contact nip width W1 is 4 mm and the contact nip width W2 is 1.9 mm. Therefore, W2<(W1/2) is satisfied. The width of the secondary transfer nip 11c in the transfer material movement direction is 5.9 mm. The radius R1 of the secondary transfer roller 12 is 40 mm and the radius R2 of the intermediate transfer belt driving roller 9 (backup roller) is 32 mm. Therefore, R2<R1 is satisfied. The thickness of the elastic layer 12b (rubber layer) of the secondary transfer roller 12 is 2.5 mm and the thickness of the elastic layer (rubber layer) of the intermediate transfer belt 8 is 250 μm. The pressure load of the secondary transfer roller 12 onto the intermediate transfer belt driving roller 9 (backup roller) is 80 kgf.
An evaluation result in Example 1 is shown in Table 1 below.
As shown in Table 1, the transfer efficiency was 90% or higher in both of the coated paper and the uncoated paper for all of the 2×2 dot image, the 8×8 dot image and the solid image. Accordingly, it is determined that excellent transfer efficiency was obtained in Example 1. Further, it is determined that image deviation was not caused in both of the coated paper and the uncoated paper because the rubbed marks in the horizontal image were not recognized.
The pressure-contact nip width W1 is 3 mm and the contact nip width W2 is 0.2 mm. Therefore, W2<(W1/2) is satisfied. The width of the secondary transfer nip 11c in the transfer material movement direction is 3.2 mm. The radius R1 of the secondary transfer roller 12 is 40 mm and the radius R2 of the intermediate transfer belt driving roller 9 (backup roller) is 24 mm. Therefore, R2<R1 is satisfied. The thickness of the elastic layer 12b (rubber layer) of the secondary transfer roller 12 is 5 mm and the thickness of the elastic layer (rubber layer) of the intermediate transfer belt 8 is 150 μm. The pressure load of the secondary transfer roller 12 onto the intermediate transfer belt driving roller 9 (backup roller) is 30 kgf.
An evaluation result in Example 2 is shown in Table 2 below.
As shown in Table 2, the transfer efficiency was 90% or higher in both of the coated paper and the uncoated paper for all of the 2×2 dot image, the 8×8 dot image and the solid image as in Example 1. Accordingly, it is determined that excellent transfer efficiency was also obtained in Example 2. Further, it is determined that image deviation was not caused in both of the coated paper and the uncoated paper because the rubbed marks in the horizontal image were not recognized.
The pressure-contact nip width W1 is 8 mm and the contact nip width W2 is 0.5 mm. Therefore, W2<(W1/2) is satisfied. The width of the secondary transfer nip 11c in the transfer material movement direction is 8.5 mm. The radius R1 of the secondary transfer roller 12 is 240 mm and the radius R2 of the intermediate transfer belt driving roller 9 (backup roller) is 67 mm. Therefore, R2<R1 is satisfied. The thickness of the elastic layer 12b (rubber layer) of the secondary transfer roller 12 is 1.5 mm and the thickness of the elastic layer (rubber layer) of the intermediate transfer belt 8 is 250 μm. The pressure load of the secondary transfer roller 12 onto the intermediate transfer belt driving roller 9 (backup roller) is 120 kgf.
An evaluation result in Example 3 is shown in Table 3 below.
As shown in Table 3, the transfer efficiency was 90% or higher in both of the coated paper and the uncoated paper for all of the 2×2 dot image, the 8×8 dot image and the solid image as in Example 1 and Example 2. Accordingly, it is determined that excellent transfer efficiency was also obtained in Example 3. Further, it is determined that image deviation was not caused in both of the coated paper and the uncoated paper because the rubbed marks in the horizontal image were not recognized.
The pressure-contact nip width W1 is 11 mm and the contact nip width W2 is 5 mm. Therefore, W2<(W1/2) is satisfied. The width of the secondary transfer nip 11c in the transfer material movement direction is 16 mm. The radius R1 of the secondary transfer roller 12 is 240 mm and the radius R2 of the intermediate transfer belt driving roller 9 (backup roller) is 67 mm. Therefore, R2<R1 is satisfied. The thickness of the elastic layer 12b (rubber layer) of the secondary transfer roller 12 is 10 mm and the thickness of the elastic layer (rubber layer) of the intermediate transfer belt 8 is 350 μm. The pressure load of the secondary transfer roller 12 onto the intermediate transfer belt driving roller 9 (backup roller) is 60 kgf.
An evaluation result in Example 4 is shown in Table 4 below.
As shown in Table 4, the transfer efficiency was 90% or higher in both of the coated paper and the uncoated paper for all of the 2×2 dot image, the 8×8 dot image and the solid image, as in Example 1 to Example 3. Accordingly, it is determined that excellent transfer efficiency was also obtained in Example 4. Further, it is determined that image deviation was not caused in both of the coated paper and the uncoated paper because the rubbed marks in the horizontal image were not recognized.
Note that in each of the above Examples 1 to 4, the contact nip width W2 was set to be doubled compared to the pressure-contact nip width W1 to evaluate the transfer efficiency and image deviation. Accordingly, the relationship between the pressure-contact nip width W1 and the contact nip width W2 is expressed as W1<W2 in Examples 1 to 4. As for the evaluation result in these cases, transfer efficiency was lowered in any cases. It is considered that this is because charges remaining on the transfer material and the intermediate transfer belt 8 on the contact nip 11b are relaxed as time passes and a sufficient electric field cannot be obtained as the contact nip width W2 is larger. Further, image deviation was slightly observed in any cases. It is considered that this is because the intermediate transfer belt 8 bends relatively largely in the compression direction along the outer circumferential surface of the secondary transfer roller 12 as the contact nip width W2 is larger. In such a manner, the bending direction of the surface of the intermediate transfer belt 8 changes at the secondary transfer nip 11c. Then, the surface speed of the intermediate transfer belt 8 changes between the pressure-contact nip 11a and the contact nip 11b to cause the image deviation.
It is noted that the transfer apparatus and the image forming apparatus according to the invention are not limited to those described in each of the above embodiments. For example, the image forming apparatus in each of the above embodiments is the image forming apparatus supporting four colors. However, the image forming apparatus may be an image forming apparatus supporting only one color. That means that various changes in design can be made within the range of the scope of the invention.
In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. Finally, terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.
While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
Number | Date | Country | Kind |
---|---|---|---|
2009-184361 | Aug 2009 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
3443808 | Siebke | May 1969 | A |
7587158 | Pargett et al. | Sep 2009 | B2 |
20040009012 | Kwak | Jan 2004 | A1 |
20090190979 | Tanaka | Jul 2009 | A1 |
Number | Date | Country |
---|---|---|
2001-166611 | Jun 2001 | JP |
Number | Date | Country | |
---|---|---|---|
20110033213 A1 | Feb 2011 | US |