JPH0330868B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a pressure fixing device that fixes a toner image by passing a support holding a toner image between a pair of fixing rolls using only pressure. [Prior Art] In dry type electrophotographic copying machines, printers, facsimile machines, etc., a pressure fixing device, for example, is used to fix a toner image held on a support such as paper after development or transfer. . As this pressure fixing device, for example,
A roller equipped with a pair of rollers as shown in Figure 4 of the publication or, for example, a
A roller having three rolls as described in Japanese Patent No. 48315 is generally used. In this type of pressure fixing device, in order to compensate for the deflection between a pair of press-contacted rolls and obtain a uniform pressure distribution in the axial direction, for example,
As described in Japanese Patent Laid-Open No. 55-4075, etc., it is common practice to make the axes of the pair of rolls intersect. Furthermore, in this type of pressure fixing device, it is virtually impossible to make the pressure distribution between the fixing rolls and the surface roughness of the rolls completely uniform in the axial direction, and the linear pressure between the fixing rolls is Also 10~25Kg/
It is as high as 1.2 cm, and paper wrinkles are more likely to occur compared to a heat roll type fixing device. In particular, if the amount of toner adhering to the support varies greatly in the axial direction, this may cause paper wrinkles. Furthermore, when a transfer paper such as plain paper is used as a support, in high humidity conditions, the paper absorbs moisture and is sent between rolls in a wavy state, making the paper particularly susceptible to wrinkles. Therefore, in order to prevent paper wrinkles, for example,
As described in Japanese Patent Publication No. 6911 and Japanese Patent Publication No. 57-3943, the circumferential speed of the fixing roll is set to be slower than the feeding speed of the paper to give the paper slack before it is inserted between the fixing rolls. ing. However, in conventional pressure fixing devices, the large amount of slack causes a large impact when the paper is caught between the fixing rolls, and this impact tends to cause disturbances in the toner image. As described in Publication No. 57-3943, if the paper guide is kept flat and parallel to the contact line of the pressure roller pair, and the leading edge of the copy paper is evenly bitten by the pressure roller pair, The impact is large, especially when there is variation in the amount of toner deposited across the width of the paper. In addition to the above-mentioned structure for preventing paper wrinkles, for example, Japanese Utility Model Application Publication No. 57-39063 discloses a guide member in which the leading edge protrudes toward the roll side at the center than at both ends. In addition, Japanese Utility Model Application Publication No. 57-60159 discloses the use of a paper guide whose tip is bent to form a downward slope substantially along the periphery of the upper roller.
However, in these cases, the shape of the paper guide becomes complicated, which poses a problem in practicality. [Objective] The object of the present invention is to solve the above-mentioned problems of the prior art, to prevent paper wrinkles with a simple structure, and to significantly reduce the impact when paper gets caught, thereby improving the toner image quality. It is an object of the present invention to provide a pressure fixing device capable of obtaining a high quality fixed image without disturbance. [Summary] The pressure fixing device of the present invention has at least a pair of fixing rolls arranged in pressure contact with each other, the axes of the fixing rolls are crossed by a small angle, and a support holding a toner image between the fixing rolls is provided. In a pressure fixing device, a guide member is installed in front of the fixing roll when viewed from the traveling direction of the support, and the tip of the guide member faces the surface of the fixing roll. is set substantially equal to the conveying speed of the support, and the gap between the tip of the guide member and the fixing roll is set to be substantially equal to the thickness of the support before fixing by at least a length near the center of the length of the fixing roll. The guide member is installed at a height of about 5 to 20 times the height of the fuser roll, and the tip of the guide member is set at the same or lower position than the contact portion of the fixing roll. [Example] The details of the present invention will be explained below with reference to the drawings. FIG. 1 is a schematic side view showing an example of a transfer electrophotographic copying machine, FIG. 2 is a cross-sectional view showing an embodiment of the pressure fixing device of the present invention, and FIG. 3 is an enlarged view taken along the line DD in FIG. 4 is a plan view of FIG. 2, and FIG. 5 is an enlarged view of section E in FIG. 2. First, in FIG. 1, reference numeral 1 denotes an image carrier drum (hereinafter simply referred to as drum) that rotates in the direction of the arrow shown in the figure, and a photoreceptor layer (not shown) made of, for example, Se, ZnO, etc. is formed on its surface. . After the surface of the drum 1 is uniformly charged by the corona charger 2, it is exposed to light by the optical system 3, and an electrostatic latent image (not shown) is formed on the surface.
is formed. This electrostatic latent image is developed by a developing device 4, and a toner image 5 is formed on the surface of the drum 1. Incidentally, as the developing device 4, a magnetic bright type developing device as described in, for example, Japanese Unexamined Patent Publication No. 55-138767 may be used. Then, when the toner image 5 reaches the transfer position, the transfer sheet 7 in the paper feed cassette 6 is conveyed by a paper feed roller 8 and a pair of conveyance rollers 9, and is superimposed on the toner image 5. Next, the transfer sheet 7 is transferred by the corona transfer device 10.
A transfer electric field is applied from the back side of the drum 1 to transfer the toner image 5 on the drum 1 onto the transfer sheet 7. After the transfer, the transfer sheet 7 is peeled off from the drum 1 by a separating claw 11, and then transferred to the pressure fixing device 1 by a conveyor belt 12.
Sent to 3. Here, the corona transfer device 1
Although not particularly shown, the separation claws 11 and the conveyor belt 12 are designed to be able to move integrally with respect to the drum 1, and are positioned lower than shown in the drawings except during transfer. The toner remaining on the drum 1 after the transfer is removed by a cleaning device 14 as described in, for example, Japanese Unexamined Patent Publication No. 55-64274. Next, the structure of the pressure fixing device of the present invention will be explained with reference to FIGS. 2 to 5. In FIGS. 2 to 5, the same functional parts as in FIG. 1 are indicated by the same reference numerals as in FIG. 1. In FIG. 2, the fixing roll 16 is rotatably supported by the side plate 15 via a bearing (not shown).
The fixing roll 17 is mounted within the side plate 15 so as to be movable up and down and is supported by a guide plate 19 via a bearing (not shown), and the pressure roll 18 is also mounted within the side plate 15 as a guide plate so as to be movable up and down. 20 via a bearing (not shown). A disc spring 21 and a washer 22 are mounted between the side plates 15 of the guide plate 20, and a pressure bolt 23 screwed onto the side plate 15 is in contact with the lower surface of the washer 22. Therefore, by appropriately tightening the pressure bolt 23, the fixing roll 1
6 and 17, fixing roll 17 and pressure roll 18
can be brought into pressure contact with each other and the pressure contact force can be adjusted. As each of the above-mentioned rolls, for example, a steel roll whose surface is plated with hard chrome may be used. In addition, in FIG.
This guide member 24 is fixed to the side plate 15 with screws 25 so that its tip forms a gap d with respect to the surface of the fixing roll. Furthermore, the guide member 24 is
As shown in FIG. 3, it is slightly curved along its length. Note that the guide member may be formed of, for example, a thin (about 1 mm thick) metal plate. Next, in the above pressure fixing device, in order to compensate for the deflection of the fixing roll 16 and the fixing roll 17, as shown in FIG.
1, the axis l2 of the fixing roll 17 is set at a small angle θ ₁
only crossed. Note that the axis l3 of the pressure roll 18 is configured to overlap the axis l1 when viewed from a plane. Therefore, the fixing roll 1
The contact lines 6 and 17 are located on a straight line 10 inclined by 1/2θ ₁ with respect to the axes l1 and l3 or the axis l2. That is, in the case of FIG. 4, the tip 7a of the transfer sheet 7 is not bitten uniformly across its axial direction, but the B side of the tip 7a is bitten first. In this pressure fixing device, the shaft end 16' of the fixing roll 16 is driven by a drive source (not shown) such as a motor. Then, the circumferential speed of the fixing rolls 16 and 17 is set to V ₁ ,
If the peripheral speed of the conveyor belt 12 is _V2 , then _V1 is
It is set so that 0.98V ₂ ≦V ₁ <V ₂ . In addition
V ₂ is normally set to be the same as the circumferential speed of the drum 1. In addition, the conveyor belt 12 (pulley 1
It goes without saying that the distance l from the center axis l' of roll 2' to the cross point (0) of the roll is generally set shorter than the length L of the paper. The operation of the pressure fixing device 13 having the above configuration will be explained as follows. The transfer sheet 7 separated from the drum 1 by the separation claw 11 is conveyed by the conveyor belt 12 in the direction of the arrow shown in the figure. Here, in a normal copying machine, since the transfer sheet 7 is located only on one end side of the drum 1 (in this embodiment, the A side), the transfer sheet 7 is placed on the B side (indicated by the broken line in the figure) on the separation belt 12 as shown in FIG. is transported in a floating state. After the leading edge of the transfer sheet 7 reaches the guide member 24, the transfer sheet 7 is conveyed along the surface of the guide member 24 and transferred to the fixing roll 16,
Sent between 17. Next, when the leading edge of the transfer sheet 7 is caught between the rolls, since V ₁ <V ₂ is set as described above, no restraining force is applied to the rear end of the transfer sheet 7. Paper wrinkles can be prevented. In this case, even if V ₁ < V ₂ , if V ₁ < 0.98V ₂ ,
As the amount of slack in the paper increases, the impact when the paper gets caught between the rolls increases, causing the transfer sheet 7
The toner on the top will scatter, causing disturbances in the toner image. On the other hand, if V ₁ <V ₂ and V ₁ ≧0.98V ₂ , the paper does not substantially sag, and the paper is fed between the rolls while roughly following the surface of the guide member. The impact when the paper is bitten is absorbed by the leading edge of the paper, so there is almost no toner scattering and no disturbance of the toner image. Further, in the pressure fixing device of the present invention, the fourth
As shown in the figure, since the contact line of the roll is inclined by a small angle θ' (=1/2θ ₁ ) with respect to the tip, the tip of the paper is not evenly bitten between the rolls, and one end (B side) is bitten first. Therefore, a portion of the leading edge of the paper receives the impact when the paper is caught between the rolls, minimizing toner scattering, thereby producing high-quality images with no toner image disturbance. is obtained. In this case, the minute angle θ' may be set according to the paper material, thickness, paper conveyance speed, etc.; however, if it is too large, it will cause paper wrinkles, while if it is too small, the effect will be lost. , is preferably set in a range of approximately 1/10 θ ₁ or more and approximately θ ₁ or less. The small angle θ' can be adjusted by tilting one end of the fixing device toward the conveyor belt. For example, in Figure 4, when θ ₁ is set to 1°08', if the driven side (B side) of the fixing device is left as is, and the driving side (A side) is tilted 0°25' towards the conveyor belt side. , θ′ becomes 9′. In addition, in FIG. 4, the transfer sheet 7 before fixing
Let θ ₂ be the angle between the traveling direction of the image (arrow Z) and the traveling direction of the transfer sheet 7 after fixing (arrow C), and let θ ₃ be the incident angle of the transfer sheet 7 with respect to the contact line l0, then θ ₂ = θ ₃ − (90+1/2θ ₁ ). in this case,
The difference between V ₂ and V ₁ (V ₂ −V ₁ =ΔV) is preferably set as shown in equation (1) below, where L is the length of the paper. ΔV≧(L−l)×tanθ ₂ (1) This is to prevent the paper from being constrained and wrinkles since the paper is stretched when it is caught between the rolls. However, if ΔV is too large, the paper will sag too much, so θ ₂ should be 05'~
It is preferable to set it in the range of 1°20', more preferably in the range of 10' to 1°00'.Furthermore, in the above equation (1), if ΔV>(L-l)× _tanθ2 , B The slack of the paper on the side increases, and the paper is no longer caught between the rolls along the surface of the guide member 22.
It is optimal to set ΔV=(L−l)×tanθ ₂ .
For example, as the transfer sheet 7, use B4 size paper (L
= 420mm), l is 150mm, θ ₁ is 1°08', θ ₃ is
When it is set to 91°, (L−l)×tanθ ₂ =2.0mm. Therefore, when V ₂ is, for example, 100 mm/sec, V ₁ ≦
If V ₂ is, for example, 200 mm/sec, V ₁ may be set to 198.0 mm/sec. here
When V ₁ = 98.0 mm/sec, the value of V ₁ /V ₂ is 0.98, and when V ₁ = 198.0 mm/sec, the value of V ₁ /V ₂ is 0.99. Next, the gap d between the tip of the guide member 24 and the fixing roll 16 is set to be larger than the thickness of the paper, where t is the thickness, in order to prevent paper jams, but only one sheet of paper is not necessarily transported. Since there are cases where about 5 sheets are transported in piles, it is necessary to adjust the attachment of the guide member 24 so that d is 5t or more. Although there are many types of transfer paper, their thickness t is usually 60 to 100 μm, so it is sufficient that d is about 0.5 mm or more. Furthermore, if the gap d is too large, the paper will not be accurately caught between the rolls, so it is preferably kept to 20 times or less the thickness t of the paper, and more preferably about 1.2 mm or less. Furthermore, the gap d does not need to be adjusted within the above range over the entire length of the guide member 22, but only by the length (W) near the center as shown in FIG. 3 (for example, if the length of the guide member is B When it corresponds to the width of the paper of the size, the length is only around 100 mm), and by adjusting the gap, the paper can be conveyed smoothly. By forming the guide member 24 to be slightly curved upward as shown in FIG. 3, the paper conveyed onto the guide member 24 is pulled on both sides, which is effective in preventing paper wrinkles. It is.
However, the maximum amount of warpage y of the guide member 24 should be 1.0 mm or less, because if it is too large, it will interfere with paper conveyance.
Preferably it is 0.7 mm or less. Further, it is effective to prevent paper wrinkles if the tip of the guide member 24 is placed at the same level as or below the contact line of the roll as shown in FIGS. 2 and 5. In the pressure fixing device shown in FIG.
Steel rolls 6 and 18 have an outer diameter of 34 mmφ and a length of 270 mm, and roll 17 has an outer diameter of 22 mmφ.
Using steel rolls with a length of 270 mm, rolls 16 and 1
Adjust the linear pressure between rolls 17 to 20 kg/cm, set the cross angle θ ₁ of roll 17 to 1°08', adjust θ' to 12', and install it into a commercially available copying machine (Copia SC120). A fixation test was conducted under the following conditions. The surfaces of all of the above rolls are plated with hard chrome. First of all, copy paper is A4 size and B4 size, and the thickness is
Using transfer paper with a high-resistance treatment on the surface of 80 μm, three types of images were formed on the transfer paper: (a) completely white, (b) completely black, and (c) Japan Institute of Electronics Chart paper.
Fixation was carried out under two types of environmental conditions: °C, 68% RH and 26 °C, 80% RH. The distance Δh between the tip of the guide member 24 and the contact line of the roll (see Fig. 5) is (a) +1.75 mm (center), +1.65 mm (both ends), (b) -0.10 mm (center). Department),
-0.20mm (both ends) and (C) -1.0mm (center),
Adjustments were made to -1.0mm (center) and -1.1mm (both ends). A fixing test was conducted on 200 sheets under each of the above conditions to determine the incidence of paper wrinkles, and the results shown in Table 1 were obtained. However, the paper wrinkles in this case include not only wrinkles that can be visually determined from the image surface, but also minute wrinkles that can be discerned from the back side of the image.

〔effect〕

As described above, according to the pressure fixing device of the present invention, the paper is structured so that at least no tensile force is applied to it, and the support is not simply inserted between the rolls in a slack state, and Since the structure is designed to soften the impact when the body bites, it is possible to obtain a high-quality fixed image without paper wrinkles or toner scattering. [Application Example] In the above embodiment, a pressure fixing device equipped with three rolls was explained as an example, but the present invention is not limited to this, but can also be applied to a pressure fixing device having two rolls. Of course. Furthermore, the present invention is not limited to the so-called PPC method including a transfer process.
Of course, it can also be applied to the so-called CPC method, which fixes immediately after development.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an example of a transfer type electronic copying machine, FIG. 2 is a sectional view showing an embodiment of the pressure fixing device of the present invention, and FIG. 4 is a plan view of FIG. 2, and FIG. 5 is an enlarged view of section E in FIG. 2. 16, 17: Fixing roll, 24: Guide member.

Claims (1)

[Scope of Claims] 1. A support having at least a pair of fixing rolls disposed in pressure contact with each other, the axes of the fixing rolls crossing each other by a small angle θ ₁ , and holding a toner image between the fixing rolls. In the pressure fixing device, a guide member is installed in front of the fixing roll when viewed from the direction of movement of the support, and the tip of the guide member faces the surface of the fixing roll _. , when the conveyance speed of the support is V ₂ , V ₁ <V ₂ and V ₁ ≧
The circumferential speed of the fixing roll is set to 0.98V ₂ , and the contact line of the fixing roll is 1/10θ ₁ with respect to a straight line perpendicular to the traveling direction of the support when viewed from a plane.
The fixing roll is arranged so as to be tilted by a small angle (θ') in the range of ~ _θ1 , and the distance between the tip of the guide member and the fixing roll is at least a length near the center of the fixing roll. The guide member is installed to have a thickness of about 5 to 20 times the thickness before fixing, and the tip of the guide member is set at a position equal to or lower than the contact portion of the fixing roll. Pressure fixing device. 2. Claim 1, characterized in that the guide member is curved upward along its length.
Section pressure fixing device.