JP2000219389A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate straightening of curling of a recording sheet. SOLUTION: This image forming device is constituted of image bearing bodies PRk, PRm, PRc on which electrostatic latent images are formed at latent image writing positions Q1k, Q1y, Q1m, Q1c set along a surface rotationally moving, unfixed toner image forming devices PRk+Dk, PRy+Dy, PRm+Dm, PRc+Dc having developers Dk, Dy, Dm, Dc to develop the electrostatic latent images on specified color toner images, a sheet transfer apparatus T2 to transfer an unfixed toner image on a recording sheet S passing a sheet transfer region Q4, a fixing device F to fix the unfixed toner image on the recording sheet S passing a fixing region Q5, a sheet carrier passage SH sequentially carry the recording sheet S stored in a sheet storage tray TR1 to the sheet transfer region Q4, the fixing region Q5 and a sheet discharge tray TR2 and a moisture giving device W to give moisture to the recording sheet S carried in the sheet carrier passage SH.

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 an electrophotographic copying machine and a laser printer, and more particularly to an image forming apparatus having a function of correcting a curl (curling) generated on a recording sheet.

[0002]

FIG. 9 is an enlarged view of a main part of a conventional image forming apparatus. 10A and 10B are explanatory diagrams of curl generated on a recording sheet. FIG. 10A is an explanatory diagram when a recording sheet passes through a fixing device. FIG. 10B is a diagram illustrating toner image formation on the recording sheet after the recording sheet passes through the fixing device. FIG. 10C is a diagram illustrating a state in which the surface is curled inward, and FIG. 10C is a diagram illustrating a state in which the recording sheet in a state in which the toner image forming surface is curled inward is retransmitted to the secondary transfer area. In FIG. 9, an electrostatic latent image is formed in the image writing area Q1 on the surface of the image carrier PR of the full-color image forming apparatus U capable of double-sided printing. In the developing area Q2, the electrostatic latent image is developed into a toner image Tn by the developing device D, and in the primary transfer area Q3, the toner image Tn is primarily formed on the surface of the intermediate transfer belt B by the roll-shaped primary transfer device T1. Transcribed.

The supply of the multi-toner image or the single-color toner image on the intermediate transfer belt B transferred to the secondary transfer area Q4 is adjusted in synchronization with the transfer timing. The recording sheet S in the paper tray TR1 is conveyed to the secondary transfer area Q4 by the sheet feeding path SH1 of the sheet conveying path SH. In the secondary transfer area Q4, the toner image is secondarily transferred to the recording sheet S by the secondary transfer roll T2. In the case of single-sided copying, the recording sheet S on which the toner image has been secondarily transferred is fixed in the fixing area Q5 by the fixing device F, and then discharged to the discharge tray TR2 by the sheet discharge path SH2 of the transport path SH. .

[0004] In the case of double-sided copying, the recording sheet S on which the toner image of the first side (one side) is fixed is reversed by the reversing path SH3, and then retransmitted to the secondary transfer area Q4 through the retransmission path SH4. The toner image is transferred to the second surface. The retransmission path SH4
Is provided with a curl correcting member Rc. In FIG. 10A, the fixing device F has a heating roll Fh and a pressure roll Fp, and a fixing nip (fixing area Q5) is formed by a pressure contact area between the heating roll Fh and the pressure roll Fp. Recording sheet S passing through the fixing nip
The surface on which the unfixed toner image is transferred (toner image forming surface) contacts the pressure roll Fh and is heated and fixed.

[0005] The recording sheet S having passed through the fixing nip
FIG. 10 shows that the toner cools and shrinks after a while.
As shown in B, an image curl occurs in which the center of the recording sheet S in the sheet conveying direction (the portion where the toner is attached) is concave. Further, there may be a case where an anti-image curl in which the toner image forming surface becomes convex due to the shape of the fixing nip is formed at both ends of the sheet in the sheet conveying direction where no toner is attached. The following techniques (J01) and (J02) are conventionally known as techniques for correcting the curl (image curl and anti-image curl) of the recording sheet S.

(J01) (Japanese Patent Application Laid-Open No. Hei 6-115791) In this publication, the curl is corrected by passing the curled recording sheet between a belt and a pressing roll pressing the belt surface. At this time, a technique is described in which the pressing roll is moved according to the type of the recording sheet and the image density, and the amount of pressing of the pressing roll against the belt surface is adjusted. (J02) (Technique described in JP-A-8-217313) In this publication, in the case of double-sided printing, the curled recording sheet is passed between a metal roll and an elastic roll whose surface is depressed by the metal roll. At this time, the distance between the rotation axes of the two rolls is adjusted according to the difference between the amount of toner on the first side and the amount of toner on the second side, and information such as the thickness and temperature and humidity of the recording sheet. A technique for adjusting the amount of pressing of the metal roll against the elastic roll is described.

[0007]

[Problems to be Solved by the Invention]
1), (J02)) The above-mentioned prior arts (J01), (J0)
In 2), the curl amount is corrected (the pressing amount is controlled) according to various conditions such as the image density, the thickness of the recording sheet, and the temperature and humidity. However, in the case of an image forming apparatus capable of performing double-sided printing, after heat-fixing one side (the first side) of the recording sheet S, the recording sheet S is dried to have low water content. The recording sheet S having a low water content has a problem that it is difficult to sufficiently correct the curl and correct it to a flat surface.

Further, as shown in FIG. 9, in the case of the image forming apparatus U capable of performing double-sided printing and having the intermediate transfer belt B, when the toner image is secondarily transferred to the second side, it is dried by fixing on the first side. There is a problem that peeling discharge occurs more vigorously between the recording sheet S having low water content and the intermediate transfer belt B than at the time of the secondary transfer to the one surface (the first surface).
As a result, the resistance of the intermediate transfer belt B decreases,
This leads to a reduction in belt life. Further, image quality defects occur due to scattering of toner due to the peeling discharge. Further, if the recording sheet S has a curl in which the toner image forming surface at the end in the sheet conveyance direction is convex, the recording sheet S is passed through the secondary transfer area Q4 (see FIG. 10C). Since the front end of the recording sheet S in the transport direction is curled toward the surface of the intermediate transfer belt B, there is a problem that the recording sheet S easily winds around the intermediate transfer belt B.

[0009] In view of the above problems, the present invention has the following technical content as a technical subject. (O01) To be able to easily correct the curl of a recording sheet.

[0010]

Next, a description will be given of the present invention which has solved the above-mentioned problems. In the description of the present invention, reference numerals in parentheses added after constituent elements of the present invention denote constituent elements of the present invention. Reference numerals of corresponding components of the embodiment described later. The reason why the present invention is described in association with the reference numerals of the components of the embodiments described later is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(Invention) In order to solve the above-mentioned problem, an image forming apparatus of the invention has the following requirements (A01) to (A05). Latent image writing positions (Q1k, Q1y, Q1m, Q1
1c) An image carrier (PRk,
PRy, PRm, PRc) and the image carriers (PRk, PR
developing devices (Dk, Dy, Dm, and Dm) for developing the electrostatic latent image into a toner image of a predetermined color in a developing area (Q2k, Q2y, Q2m, Q2c) set along the surface of the electrostatic latent image.
Dc) and an unfixed toner image forming apparatus (PRk + D
k, PRy + Dy, PRm + Dm, PRc + Dc), (A02)
Sheet transfer that is arranged in a sheet transfer area (Q4) for transferring the unfixed toner image to a recording sheet (S) and transfers the unfixed toner image to a recording sheet (S) that passes through the sheet transfer area (Q4) (A2), (A03) The printer is disposed in a fixing area (Q5) for fixing the unfixed toner image transferred to the recording sheet (S), and is undetermined on the recording sheet (S) passing through the fixing area (Q5). (A04) The fixing device (F) for fixing the formed toner image, (A04) the recording sheet (S) stored in the sheet storage tray (TR1) is transferred to the sheet transfer area (Q).
4), fixing area (Q5), and sheet discharge tray (TR
(A05) A water application device (W; W ') for applying water to the recording sheet (S) conveyed through the sheet conveyance path (SH).

(Operation of the Present Invention) In the image forming apparatus of the present invention having the above-described features, the unfixed toner image forming apparatus (PR
The image carrier (PRk, PRy, PRm, PRc) of k + Dk, PRy + Dy, PRm + Dm, PRc + Dc has a latent image writing position (Q1k,
An electrostatic latent image is formed at Q1y, Q1m, and Q1c). The unfixed toner image forming device (PRk + Dk, PRy + Dy,
PRm + Dm, PRc + Dc) developing units (Dk, Dy, Dm,
Dc) is the image carrier (PRk, PRy, PRm, PR
c) Development areas (Q2k, Q2y, Q2) set along the surface
In m, Q2c), the electrostatic latent image is developed into a toner image of a predetermined color. The sheet transport path (SH) sequentially transports the recording sheets (S) stored in the sheet storage tray (TR1) to a sheet transfer area (Q4), a fixing area (Q5), and a sheet discharge tray (TR2). The sheet transfer area (Q
The sheet transfer unit (T2) arranged in 4) transfers the unfixed toner image to the recording sheet (S) passing through the sheet transfer area (Q4). The fixing device (F) disposed in the fixing area (Q5) fixes an unfixed toner image on the recording sheet (S) passing through the fixing area (Q5). The water supply device (W; W ') is provided with the sheet conveying path (SH).
Is imparted to the recording sheet (S) conveyed. For this reason, the recording sheet (S) becomes softer than the low water content state and the curl size becomes smaller. When a curl correcting member (Rc; Rc ') for correcting the curl is provided on the sheet conveying path (SH), the curl correcting effect of the recording sheet (S) increases.

[0013]

(Embodiment 1) Embodiment 1 of the image forming apparatus of the present invention is characterized in that in the present invention, the following requirement (A06) is provided. (A06) In order to perform double-sided recording on the single-sided recording sheet (S) on which the fixed toner image has been recorded on one side when passing through the fixing area (Q5), the single-sided recording sheet (S) is inverted and then re-transmitted to the transfer area (Q4). The sheet conveying path (SH) having a re-sending path (SH4).

(Operation of the First Embodiment) In the first embodiment of the image forming apparatus of the present invention having the above-described configuration, the re-sending path (SH4) of the sheet conveying path (SH) is the same as the fixing area (Q5).
In order to perform double-sided recording on the single-sided recording sheet (S) on which the fixed toner image has been recorded on one side during the passage, the single-sided recording sheet (S) is turned over and then re-sent to the transfer area (Q4). When the water supply device (W) is disposed in the retransmission path (SH4), when water is supplied to the recording sheet (S) conveyed to the retransmission path (SH4) by the water supply device (W), The recording sheet (S) is softer than the low water content state and the curl size is reduced. Therefore, even in the case of double-sided copying, the curl of the recording sheet (S) can be easily corrected.

(Embodiment 2) Embodiment 2 of the image forming apparatus of the present invention is the same as Embodiment 1 of the present invention, except that
The following requirements (A08) are provided, (A0
8) A curl straightening member (R) composed of a pair of rotating members (6, 7) having cylindrical surfaces that are in pressure contact with each other and are arranged downstream of the water supply device (W) in the re-sending path (SH4).
c; Rc '), wherein the curl correction region (Q6) is formed by the region where the pair of rotating members (6, 7) press against each other.
Is a curl correcting member (Rc; Rc;) configured to correct the curl of the recording sheet (S) passing through the curl correcting area (Q6) because the surface of one of the rotating members (7) is concave.
Rc '). (Operation of the Second Embodiment) In the second embodiment of the image forming apparatus of the present invention having the above-described configuration, the curl correcting member (R
c; Rc ') is constituted by a pair of rotating members (6, 7) having cylindrical surfaces that are in pressure contact with each other and that are arranged downstream of the water supply device (W) in the retransmission path (SH4). The curl correction region (Q6) formed by the region where the pair of rotating members (6, 7) is pressed against each other is one of the rotating members (7).
The surface is concave, and the curl of the recording sheet (S) passing through the curl correction area (Q6) is corrected by the shape of the concave. Since the recording sheet (S) is curled after being softened by the provision of water by the water supplying device (W), the curl correcting effect is increased.

(Embodiment 3) An image forming apparatus according to Embodiment 3 of the present invention is different from Embodiment 1 of the present invention in that
The following requirements (A09) are provided, (A0
9) A curl correcting member (Rc; R) composed of a pair of rotating members (6, 7) having cylindrical surfaces pressed against each other.
c '), wherein the curl correction region (Q6) formed by the region where the pair of rotary members (6, 7) is pressed against each other has a concave surface on one of the rotary members (7), and the curl correction region (Q6). ), The curl correcting member (Rc; R) configured to correct the curl of the recording sheet (S) passing therethrough.
c ') and a water supply device (W') constituted by a water supply device (Ws) for supplying water to the surface of the one rotating member (7). (Operation of the Third Embodiment) In the third embodiment of the image forming apparatus of the present invention having the above-described structure, the water supply device (W ')
The curl correcting member (Rc; Rc ') is composed of a pair of rotating members (6, 7) having cylindrical surfaces that are pressed against each other. The water supply device (W) of the water application device (W ')
s) supplies water to the surface of the one rotating member (7). The curl correction area (Q6) formed by the area where the pair of rotating members (6, 7) are pressed against each other has a concave surface on one of the rotating members (7) and passes through the curl correction area (Q6) due to the depression. The curl of the recording sheet (S) to be corrected is corrected. Thus, the recording sheet (S) is softened and curled by the provision of water by the water supply device (Ws), and the curl correcting effect is increased. The curl correcting member (Rc; Rc ')
Constitutes a part of the moisture applying device (W '), it is not necessary to separately provide the curl correcting member (Rc; Rc') and the moisture applying device (W ').

[0017]

Next, examples (embodiments) of the embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. To facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, the up-down direction is the Z-axis direction, and arrows X, -X, Y, -Y, The directions indicated by Z, -Z or the sides indicated are forward, rearward, leftward, rightward, upward, downward,
Or, the front side, the rear side, the left side, the right side, the upper side, and the lower side.
Also, in the figure, those with “•” in “○” mean arrows pointing from the back of the paper to the front, and those with “x” in “○” indicate the arrow on the paper. From the back to the back.

Embodiment 1 FIG. 1 is an overall explanatory view of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is an enlarged explanatory view of a main part of FIG. 1, the image forming apparatus U has a main body Ua and an automatic document feeder Ub placed on a platen glass PG on the upper surface of the main body Ua. The image forming apparatus main body Ua has a UI (user interface) through which a user inputs an operation command signal such as a copy start signal.

The reflected light from a document (not shown) placed on the platen glass PG passes through an exposure optical system A,
R (red), G (green), B with CCD (solid-state image sensor)
(Blue) electrical signal. The IPS (image processing system) uses the R input from the CCD.
The GB electrical signal is converted into K (black), Y (yellow), M (magenta), and C (cyan) image data and temporarily stored, and the image data is stored at a predetermined timing for forming a latent image. The data is output to the laser drive circuit DL as image data.

The image writing data (laser driving data) of the four colors of KYMC output by the IPS are K, Y,
M, C laser drive signal output devices DLk, DLy, DLm, D
It is input to the laser drive signal output device DL having Lc.
The laser drive signal output devices DLk, DLy, DLm,
DLc transmits a laser drive signal corresponding to the input image data at a predetermined timing to the latent image writing devices ROSk,
Output to ROSy, ROSm, ROSc.

Each of the image carriers PRk, PRy, PRm, PRc is uniformly charged by each of the roll-shaped chargers CRk, CRy, CRm, CRc, and then an image writing area (latent image writing position) Q1k. , Q1y, Q1m, and Q1c, an electrostatic latent image is formed on the surface by the laser beams Lk, Ly, Lm, and Lc output from the latent image writing devices ROSk, ROSy, ROSm, and ROSc. The image carrier PRk, PRy, PRm, P
The electrostatic latent images on the Rc surface are developed areas Q2k, Q2y, Q2m, Q2
In c, the toner images are developed by the developing units Dk, Dy, Dm, and Dc. The developed toner image is conveyed to primary transfer areas Q3k, Q3y, Q3m, and Q3c that contact the intermediate transfer belt B. The primary transfer areas Q3k, Q3y, Q3m, Q3c
, The primary transfer devices T1k, T1y, T1m, and T1c in the form of rolls disposed on the back side of the intermediate transfer belt B are supplied with a polarity opposite to the charge polarity of the toner at a predetermined timing from the power supply circuit E controlled by the controller C Is applied. The toner images on the image carriers PRk to PRc are primarily transferred to the intermediate transfer belt B by the primary transfer units T1k, T1y, T1m, and T1c. The image carrier PRk after the primary transfer,
The residual toner on the surfaces of PRy, PRm, PRc is neutralized by the pre-cleaning corotron JCk, JCy, JCm, JCc, and removed by the image carrier cleaners CLk, CLy, CLm, CLc.
An unfixed toner image forming device (PRk + Dk, PRy + D) for K, Y, M, and C color toners is obtained from each of the image carriers PRk, PRy, PRm, and PRc and each of the developing devices Dk, Dy, Dm, and Dc.
y, PRm + Dm, PRc + Dc).

Below the image carriers PRk to PRc, a slide frame F1 (indicated by a two-dot chain line) is supported by a pair of left and right slide rails SR so as to be slidable back and forth (in a direction perpendicular to the paper). I have. A belt module (vertical moving member) F2 is supported on the slide frame F1 so as to be able to move up and down. The belt module F2 includes the intermediate transfer belt B, a belt drive roll Rd, a tension roll Rt, a walking roll Rw, an idler roll (free roll) Rf, and a backup roll T2a.
Belt support rolls containing (Rd, Rt, Rw, Rf, T2a)
And the primary transfer units T1k, T1y, T1m, and T1c. The intermediate transfer belt B is rotatably supported by the belt support rolls (Rd, Rt, Rw, Rf, T2a).

Below the backup roll T2a,
A secondary transfer slide frame Fs slidable back and forth (in a direction perpendicular to the paper surface) by a pair of left and right slide rails SR, SR is detachably supported on the image forming apparatus main body. A secondary transfer lifting frame Ft of the secondary transfer unit Ut is supported on the secondary transfer slide frame Fs so as to be rotatable up and down around a hinge axis Fta. The rotation of the secondary transfer lifting frame Ft allows the secondary transfer unit Ut to move between a raised use position and a lowered retreat position. The sliding movement of the secondary transfer slide frame Fs and the vertical movement of the secondary transfer unit Ut (rotation about the hinge axis Fta) are performed by operation handles (not shown) provided on the front surface of the secondary transfer slide frame Fs. The secondary transfer unit Ut includes a secondary transfer roll T2b, a roll support lever Lr, a post-transfer sheet guide SG2, a sheet transport belt BH, and the secondary transfer lift frame Ft that supports them. ing.

The roll support lever Lr is a rotatable lever that supports the secondary transfer roll T2b. In a state where the secondary transfer unit Ut is moved to the use position, the roll support lever Lr is rotated by a motor (not shown) to bring the secondary transfer roll T2b into contact with the intermediate transfer belt B. Is moved between the position and a standby position separated from the intermediate transfer belt B. The post-transfer sheet guide SG2 guides the recording sheet, which has passed through a secondary transfer area (sheet transfer area) Q4, which is a contact area between the secondary transfer roll T2b and the intermediate transfer belt B, to a downstream sheet transport belt BH. I do.

A contact roll T2c is in contact with the backup roll T2a.
A secondary transfer voltage having the same polarity as the charging polarity of the toner is applied to 2c from the power supply circuit E controlled by the controller C at a predetermined timing. 2 by the above-mentioned rolls T2a to T2c.
A secondary transfer unit (sheet transfer unit) T2 is configured.

The primary transfer areas Q3k, Q3y, Q3m, Q3c
The color toner images sequentially transferred and superimposed on the intermediate transfer belt B by the primary transfer units T1k, T1y, T1m, and T1c are conveyed to the secondary transfer area Q4. Recording sheet S of sheet storage tray TR1 disposed below intermediate transfer belt B
Are taken out by a pickup roll Rp, separated one by one by a separation roll Rs, and sent to a registration roll Rr by a plurality of sheet transport rolls Ra. The sheet conveying roll Ra is constituted by a pair of rolls. The registration roll Rr moves the recording sheet S from the pre-transfer sheet guide SG1 to the secondary transfer area in time with the timing when the color toner image formed on the intermediate transfer belt B is conveyed to the secondary transfer area Q4. Transfer to Q4. When the color toner image on the intermediate transfer belt B passes through the secondary transfer area Q4, the secondary transfer unit T2
Is transferred to the recording sheet S. After the secondary transfer, the intermediate transfer belt B is cleaned by a belt cleaner CLb.

The recording sheet S on which the toner image has been secondarily transferred is transferred to a sheet guide SG2 and a sheet conveying belt BH.
After being conveyed to the fixing area Q5 through the fixing device F, the sheet is discharged from the discharge roller Rh to the sheet discharge tray TR2. The switching gate GT1 disposed on the downstream side of the fixing device F moves the recording sheet S having passed through the fixing device F in a direction of the sheet discharge path SH2 or the reversing path SH3 connected to the discharge tray TR2. Switch. A plurality of the sheet conveying rolls Ra are arranged along the reversing path SH3. The reversing path SH3 is connected to the sheet feeding path SH1 via a retransmission path SH4. The sheet-shaped and comb-shaped mylar gate GT2 provided at the connection portion between the reversing path SH3 and the re-transmission path SH4 has an elastic deformation when the passing recording sheet S is conveyed to the left. Record sheet S that has been allowed to move to the left and passed Mylar Gate GT2
Is switched back, and is conveyed upward, and is directed to the direction of the retransmission path SH4. In the case of double-sided copying, the single-sided recording sheet S on which the toner image of the first side is fixed is inverted by the reversing path SH3, re-transmitted to the secondary transfer area Q4 via the re-transmission path SH4 and the sheet feeding path SH1, and is re-transmitted. The toner image is transferred to the second side. In addition, the code S
The sheet conveying path SH is constituted by the components indicated by H1 to SH4. In FIGS. 1 and 2, a water application device W is disposed in the reversing path SH3, and an image curl correcting member Rc is disposed downstream of the water application device W in the sheet conveying direction.

(Water supply device W) In FIG. 2, the water supply device W has a water storage section 1 and a water supply roll support section 2.
The water supply roll 3 is rotatably supported. One end of a water supply member 4 made of a cloth having good permeability in the first embodiment is immersed in the water in the water storage unit 1. The other end of the water supply member 4 is connected to the water supply roll 3
The water in the water reservoir 1 is supplied to the water supply roll 3 by the water supply member 4. The water supply roll 3 is provided with the reversing path SH3.
In this embodiment, the surface Sa of the recording sheet S passing through the reversing path SH3 is fixed to the surface Sa (toner image forming) of the recording sheet S, which is in contact with one surface of the sheet conveying roll Ra of the recording sheet S. Surface (see FIG. 3)).

(Image curl straightening member Rc) In FIG. 2, the image curl straightening member Rc is composed of a rotating hollow pipe 6 (made of SUS in this embodiment 1 and an outer diameter of 8 mm) and an elastic rotating member 7 (in this embodiment 1). Outer diameter 26 mm). A support shaft 8 is disposed inside the rotary hollow pipe 6, and the support shaft 8 is fixed through both ends of the closed rotary hollow pipe 6 in the axial direction (not shown). The support shaft 8 is connected to the secondary transfer frame Fs.
It is supported rotatably. The elastic rotating member 7 includes a rotating shaft 9 rotatably supported by the secondary transfer frame Fs and an elastic layer 1 formed on the outer periphery of the rotating shaft 9.
1. The rotating hollow pipe 6 and the elastic rotating member 7 are in pressure contact with each other to form a pressure contact area (curl correction area Q6). The shape of the curl correction region Q6 is a shape in which the surface of the elastic layer 11 of the elastic rotating member 7 is depressed by the rotating hollow pipe 6 (see FIG. 3).
The single-sided recording sheet S passes through the curl correction area Q6. At this time, the surface of the single-sided recording sheet S opposite to the toner image forming surface (the surface on which the toner image is transferred) Sa is in contact with the rotary hollow pipe 6.

(Operation of the First Embodiment) In FIGS. 1 and 2,
The single-sided recording sheet S on which the toner image is fixed on the toner image forming surface Sa by the fixing device F is supplied with water by the water supplying device W while being conveyed to the reversing path SH3. For this reason, the single-sided recording sheet S becomes softer than the low water content state. Therefore, when the single-sided recording sheet S to which the moisture is applied passes between the rotary hollow pipe 6 and the elastic rotary member 7 of the curl correcting member Rc, the effect of correcting the image curl of the single-sided recording sheet S is increased. Further, since the single-sided recording sheet S is not in a state of low water content, a toner image is formed on the second side of the single-sided recording sheet S.
During the next transfer, no peeling discharge occurs between the single-sided recording sheet S and the intermediate transfer belt B.

(Test Example of Example 1) FIG. 3 is an explanatory view of a test performed to examine the effect of correcting image curl when water is applied to a recording sheet. The conditions of the test example of Example 1 are as follows (1) to (3). (1) The rotary hollow pipe 6 is set such that the rotary hollow pipe 6 bites into the elastic layer 11 of the elastic rotary member 7 (bits from the circumferential surface in the radial direction) to 2 mm. (2) A4 LEF (A4 long edge feed, A
After the sheet passes through the fixing device F, the curl correction area Q between the rotating hollow pipe 1 and the elastic rotating member 2 is formed.
6 was passed at a speed of 450 mm / s. The single-sided recording sheet S in which the image curl was corrected was placed on a flat plate, and the sheet (recording sheet) edge lifting amount (unit: mm) was measured every predetermined time after passing through the fixing device F. The results are shown in Table 1. (Comparative Example 1 of Example 1) In Comparative Example 1, only the image curl correction was performed without adding moisture to the single-sided recording sheet S. The conditions of Comparative Example 1 and the method of measuring the amount of lifting of the sheet edge are the same as those in the above-described Test Example. The results are shown in Table 1. (Comparative Example 2 of Embodiment 1) In Comparative Example 2, after the single-sided recording sheet S (A4LEF) was passed through the fixing device F,
No image curl correction was performed. The single-sided recording sheet S passed through the fixing device F was placed on the flat plate, and the amount of lifting of the sheet edge was measured every predetermined time. The results are shown in Table 1. The elapsed time in Table 1 is the elapsed time after the recording sheet S has passed through the fixing device F.

Table 1 is a table showing the results of the test example and Comparative Examples 1 and 2.

[Table 1] In Table 1, the image area ratio is 0%, 100%, 200%,
300% is the rotating hollow pipe 6 used in the experiment.
When the single-sided recording sheet S that has passed between the elastic rotating members 7 is in a blank state, when a single-color solid image is fixed on the single-sided recording sheet S, the two-color solid image is fixed on the single-sided recording sheet S. Is fixed, it means that three-color solid images are fixed on the single-sided recording sheet S. The number with a “-” sign in Table 1 indicates that the curl is on the opposite side of the image surface (the surface opposite to the toner image forming surface Sa).
That is, the amount of paper edge lift (unit: mm) when the single-sided recording sheet S is anti-image curl is shown. The number without the “-” sign indicates that the image is curled (when curled to the toner image forming surface Sa side). Indicates the amount by which the paper edge rises.

As shown in Table 1, when the image curl is corrected in the above-described test example, the lifting amount of each sheet edge is determined when the sheet curls on the surface opposite to the toner image forming surface Sa and on the toner image forming surface Sa. In both cases, the curl was smaller than the sheet edge lifting amount in Comparative Examples 1 and 2. In the case of the image area ratio of 100%, the lifting amount of the paper edge in the test example was slightly larger than the lifting amount of the paper edge in Comparative Example 2, but the other image area ratios were 0%, 200%, and 300.
% Does not affect the image curl correcting effect in the case of the test example.

FIG. 4 is an enlarged view of a main part of an image forming apparatus according to a second embodiment. In the description of the second embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The second embodiment differs from the first embodiment in the following points, but has the same configuration as the first embodiment in other points.
In FIG. 4, the water application device W of the second embodiment is disposed so as to apply water to the toner image forming surface Sa of the single-sided recording sheet S. Further, the rotary hollow pipe 6 of the second embodiment is disposed so as to contact the toner image forming surface Sa, and the rotary hollow pipe 6 and the elastic rotary member 7
Thus, an anti-image curl correcting member Rc 'for correcting anti-image curl at the front end of the toner image forming surface Sa in the sheet conveying direction is configured.

(Operation of Embodiment 2) In FIG. 4, a single-sided recording sheet S on which a toner image is fixed on a toner image forming surface Sa is shown.
During the conveyance of the toner image on the toner image forming surface Sa, the water supplying device W supplies water to the toner image forming surface W while being conveyed to the reversing path SH3. For this reason, the recording sheet S becomes softer than the low water content state. Therefore, when the single-sided recording sheet S to which the moisture is applied passes between the rotating hollow pipe 6 and the elastic rotating member 7 of the anti-image curl correcting member Rc ', the anti-image of the front end of the single-sided recording sheet S in the sheet transport direction is obtained. The effect of curl correction is increased. Since the anti-image curl (curl along the surface of the intermediate transfer belt B) at the front end in the sheet conveying direction of the single-sided recording sheet S is corrected, the intermediate transfer belt is re-transmitted to the secondary transfer area Q4. Does not wrap around B.

(Test Example of the Second Embodiment) In the test example of the second embodiment, the rotating hollow pipe 6 of the anti-image curl correcting member Rc 'is arranged so as to contact the toner image forming surface Sa of the single-sided recording sheet. did. The conditions and measurement method of the test example of the second embodiment are the same as those of the test example of the first embodiment. Table 2 shows the results. (Comparative Example 1 of Example 2) Comparative Example 1 is the same as Example 1 described above.
Under the same conditions as in Comparative Example 1 and the method of measuring the amount of lifting of the sheet edge, only the anti-image curl correction was performed without adding moisture to the single-sided recording sheet S. Table 2 shows the results.

Table 2 shows the results of the test example of Example 2 and the result of Comparative Example 1.

[Table 2] In Table 2, the image area ratio is 0%, 100%, 200%,
300% and the numbers with “-” sign have the same meanings as in Table 1 above. In Table 2, when the image area ratio at which the toner is not adhered to the single-sided recording sheet S is 0%, the lifting amount of the paper end of the test example is slightly larger than the lifting amount of the paper end of the comparative example 1. Generally, when correcting the anti-image curl that occurs at both ends of the recording sheet where the toner does not adhere to the sheet in the sheet conveying direction, the recording sheet can be image curled. The image curl generated in the portion where the image is curled is strengthened and increased. For this reason, when correcting the anti-image curl at the front end in the sheet conveying direction, it is preferable to reduce the image curl at the center in the sheet conveying direction. As shown in Table 2, when the image area ratio was 0%, the lifting amount of the paper edge in the test example was slightly larger than the lifting amount of the paper edge in Comparative Example 1, but the toner adhered to the single-sided recording sheet S. When the image area ratios are 100%, 200%, and 300%, the sheet lifting amount of the test example is smaller than the sheet lifting amount of the comparative example 1. That is, in the test example of Example 2, when the anti-image curl at the front end in the sheet conveyance direction is corrected, the image curl at the center in the sheet conveyance direction can be reduced.

(Embodiment 3) FIG. 5 is an overall explanatory view of an image forming apparatus according to Embodiment 3 of the present invention. FIG. 6 is an enlarged view of the main part of FIG. In the description of the third embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. Example 3
Is different from the first embodiment in the following points, but is configured similarly to the first embodiment in other points. 5 and 6
In the third embodiment, the elastic layer 11 of the elastic rotating member 7 of the third embodiment
Is formed of a sponge, and a lower portion of the elastic rotating member 7 is immersed in water in a water storage container 12. Moisture is applied to the toner image forming surface Sa of the single-sided recording sheet S passing between the elastic rotating member 7 and the rotating hollow pipe 6, and the image curl is corrected by being pressed by the elastic rotating member 7 and the rotating hollow pipe 6. It has become so. The elastic rotating member 7 and the rotating hollow pipe 6 constitute an image curl correcting member Rc of the third embodiment, and the elastic rotating member 7 and the water storage container 12 constitute a water supply device Ws. The image curl correcting member Rc and the water supply device Ws constitute a water supply device W 'of the third embodiment. Also in the third embodiment, the same operation as in the first embodiment is achieved. Further, in the third embodiment, since the elastic rotating member 2 of the image curl correcting member Rc also serves as a part of the water supply device Ws, the number of parts can be reduced.

(Embodiment 4) FIG. 7 is an enlarged explanatory view of a main part of a water supply device provided in an image forming apparatus according to Embodiment 4 of the present invention. In the description of the fourth embodiment, the same reference numerals are given to the components corresponding to the components of the third embodiment, and the detailed description is omitted. The fourth embodiment differs from the third embodiment in the following points, but has the same configuration as the third embodiment in other points. In FIG. 7, a water level gauge 12a 'is provided in a water storage container 12' of the fourth embodiment.
Is provided, and the amount of water reduction in the water storage container 12 'can be determined by the liquid level gauge 12a'. The fourth embodiment has the same operation as the third embodiment.

(Embodiment 5) FIG. 8 is an explanatory view of a water supply apparatus used in an image forming apparatus according to Embodiment 5 of the present invention.
FIG. 8A is a schematic explanatory view of the moisture applying device, FIG. 8B is an explanatory diagram of an elastic rotating member provided in the moisture applying device, and FIG. 8C is a longitudinal sectional view of an end of the elastic rotating member. In the description of the fifth embodiment, components corresponding to the components of the second embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The fifth embodiment differs from the second embodiment in the following points, but has the same configuration as the second embodiment in other points.

In FIG. 8A, the water supply device Ws of the water supply device W 'according to the fifth embodiment has a water storage container 14, and the water storage container 14 has a liquid level gauge 14a,
A water supply pipe 14b for supplying water to the elastic rotating member 7 'of the anti-image curl correcting member Rc' is provided. The water supply pipe 14b is provided with a flow control valve 16.

8B and 8C, the elastic rotating member 7 'of the anti-image curl correcting member Rc' of the moisture supplying device W 'of the fifth embodiment has a shaft member 17. The shaft member 17 is connected to the water supply pipe 14b (see FIG. 8C), and is fixed to a secondary transfer slide frame Fs in the image forming apparatus main body U2. 8C, at both ends of the shaft member 17, rotating cylindrical members 18 (only one side is shown) are arranged. A bearing 19 is fitted and fixed to the outer end of the rotating cylindrical member 18, and the rotating cylindrical member 18 is rotatably supported on the shaft member 17 via the bearing 19. ing. The cylindrical wall of the shaft member 17 is formed with a plurality of water supply holes 17a for supplying inner water to the outer peripheral side.

The outer surface of the shaft member 17 has an inner hydrated layer 2
1. A cylindrical member 22 is arranged on the outer periphery of the inner hydrous layer 21. The inner ends of the rotating cylindrical member 18 are fitted and fixed to both ends (only one side is shown) of the cylindrical member 22. A plurality of water supply holes 22a are formed in the cylindrical member 22, and an outer water-containing layer 23 having elasticity is provided on the outer peripheral surface of the cylindrical member 22.
The water seeping out from the inner hydrated layer 21 is supplied to the outer hydrated layer 23 through a plurality of water supply holes 22 a of the cylindrical member 22. The surface of the outer hydrated layer 23 is covered with a permeable coating layer 24, and the water of the outer hydrated layer 23 oozes to the surface of the coating layer 24 by the pressing force of the rotating hollow pipe 6. Has become.

Also in the fifth embodiment, when the single-sided recording sheet S passes between the elastic rotating member 7 'and the rotary hollow pipe 6, moisture is applied to the toner image forming surface Sa of the single-sided recording sheet S. As a result, the single-sided recording sheet S is pressed against the elastic rotating member 7 and the rotating hollow pipe 6 to correct the anti-image curl at the front end in the transport direction of the single-sided recording sheet S.

(Modifications) Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments.
Various design changes can be made without departing from the invention as set forth in the claims. Modification examples of the present invention are exemplified below. (H01) In each of the above embodiments, the water imparting devices W and W '
Has been described as an example in which the sheet is disposed on the reverse feeding path SH3, but it can be installed at any position in the sheet transport path through which the single-sided recording sheet S passes. (H02) The moisture applying devices W and W 'are configured to be detachable from the single-sided recording sheet S according to the temperature and humidity, the type and thickness of the single-sided recording sheet S, the image density, and the like. It is possible to apply or not impart moisture to the recording sheet S. (H03) In each of the above embodiments, the image curl correcting member R
It is also possible to omit c or the anti-image curl straightening Rc ', and to reduce the size of the curl by applying moisture to the curled recording sheet S by the moisture applying devices W and W'.

[0046]

The above-described image forming apparatus of the present invention has the following effects. (E01) The curl of the recording sheet can be easily corrected.

[Brief description of the drawings]

FIG. 1 is an overall explanatory diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of a main part of FIG. 1;

FIG. 3 is an explanatory diagram of a test performed for examining an image curl correcting effect when water is applied to a recording sheet.

FIG. 4 is an enlarged view of a main part of an image forming apparatus according to a second embodiment.

FIG. 5 is an overall explanatory diagram of an image forming apparatus according to a third embodiment of the present invention.

FIG. 6 is an enlarged view of a main part of FIG. 5;

FIG. 7 is an enlarged explanatory view of a main part of a water supply device provided in an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 8 is an explanatory diagram of a water supplying device used in an image forming apparatus according to a fifth embodiment of the present invention. FIG. 8A is a schematic explanatory diagram of the water supplying device, and FIG. FIG. 8C is a longitudinal sectional view of an end of the elastic rotating member.

FIG. 9 is an enlarged view of a main part of a conventional image forming apparatus.

10A and 10B are explanatory diagrams of curl generated on a recording sheet. FIG. 10A is an explanatory diagram of a case where the recording sheet passes through a fixing device. FIG. 10B is a diagram illustrating the recording sheet after the recording sheet passes through the fixing device. 10C is a diagram showing a state where the toner image forming surface is curled inward, and FIG. 10C is a diagram showing a state where the recording sheet in a state where the toner image forming surface is curled inward is retransmitted to the secondary transfer area. is there.

[Explanation of symbols]

F: fixing device, PRk, PRy, PRm, PRc: image carrier, Q1k, Q1y, Q1m, Q1c: latent image writing position, Q2k, Q
2y, Q2m, Q2c: development area, Q4: sheet transfer area, Q5
... Fixing area, Q6 ... Curl correction area, Rc; Rc '... Curl correction member, S ... Recording sheet, SH ... Sheet conveyance path, SH
4 retransmission path, T2 sheet transfer unit, TR1 sheet storage tray, TR2 sheet discharge tray, W; W '... moisture supply device, Ws ... moisture supply device, (DK, DY, DM, DC) ... developer , (PRk + Dk, PRy + Dy, PRm + Dm, PRc
+ Dc): Unfixed toner image forming apparatus.

Claims (1)

[Claims] 1. An image forming apparatus comprising the following requirements (A01) to (A05): (A01) an electrostatic latent image at a latent image writing position set along a rotating surface; An unfixed toner image forming apparatus comprising: an image carrier on which is formed, and a developing device that develops the electrostatic latent image into a toner image of a predetermined color in a development area set along the surface of the image carrier. A02) A sheet transfer device arranged in a sheet transfer area for transferring the unfixed toner image to a recording sheet, and transferring the unfixed toner image to a recording sheet passing through the sheet transfer area. (A03) Transferring to the recording sheet A fixing device disposed in a fixing area for fixing the unfixed toner image, and fixing the unfixed toner image on the recording sheet passing through the fixing area; (A04) transferring the recording sheet stored in a sheet storage tray to the sheet; region, (A05) A moisture application device for applying moisture to a recording sheet conveyed through the sheet conveyance path.