JPH09218600A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device which prevents image quality deterioration even in image formation which is carried out immediately after a power source is turned on. SOLUTION: A pressure roller 36 is opposite a linear heating body 33 with a film 35 between them, and presses the heating body 33 with a specific pressing force. By rotating and driving the pressure roller 36 by a driving means M, the film 35 is rotated and driven round a film-internal-surface guide member 38 while its internal surface is slid in close contact with the underside of the heating body 33. In the condition where they are rotated and driven, a recording material P is passed through a fixing nip N, so that an unfixed image T is heated and fixed. Control is exerted so that the pressure roller 36 is made sufficiently warm, by rotating the fixing device for about 10sec. at an adjusted temperature of 170 deg.C before the start of printing, as in the case of paper insertion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording material (transfer material, electrostatic recording paper, electrofax paper, printing, etc.) in a recording section of an appropriate image forming principle and process such as electrophotography, electrostatic recording, magnetic recording and the like. A printer that forms and carries an unfixed image corresponding to the target image information on paper, printing paper, etc., and supplies this to a heat fixing device to heat and fix the unfixed image on a recording material to obtain an image recorded matter. The present invention relates to an image forming apparatus such as a copying machine, a recording device, and a facsimile.

[0002]

2. Description of the Related Art Conventionally, as a transfer device of an image forming apparatus using an electrophotographic system, there is a transfer device in which an image carrier 2 and a roller type transfer means 6 are arranged in contact with each other as shown in FIG. That is, the visible image formed on the surface of the image carrier 2 with toner or the like moves to the contact portion n by the rotation of the image carrier 2 in the direction of the arrow and is conveyed at a timing.
Transcribed above. By the way, in such a transfer device 60, a phenomenon such as a void in transfer occurs when the conveyance speed of the recording material P is slower than the rotation speed of the image carrier 2.

In order to solve such a problem, for example, in Japanese Patent Laid-Open No. 03-155584, the following measures are taken.

A roller having elasticity is used as the transfer means, and the peripheral speed of the roller is set to be higher than the peripheral speed of the image carrier.

Further, a heat roller system is used in a heat fixing device for heating a recording material having an unfixed image (toner image) to be fixed on the image, which is conveyed from the transfer device, and fixing the unfixed image on the recording material. Widely used.

In this heat roller system, as shown in FIG. 4, a metal heat roller 21 is internally provided with a heat source H such as a halogen heater and the temperature is controlled and controlled to a predetermined fixing temperature, and an elastic member which presses against the metal heat roller 21 is provided. The pressure roller 22 has a basic configuration, and the pair of rollers 21 and 22 are rotated to supply the recording material P from the recording unit A to the pressure contact nip portion (fixing nip portion) N of the pair of rollers to fix the fixing nip portion N. By sandwiching and passing the sheet, the unfixed image T is fixed on the recording material P by the heat of the heat roller 21 and the pressing force of the fixing nip portion N.

In the transfer device 60, 2 is, for example, an electrophotographic rotary photosensitive drum as an image bearing member, and a toner image T of desired image information is formed on its peripheral surface by an image forming process device (not shown), and the toner is the toner. The image is sequentially transferred onto the surface of the recording material P introduced into the pressure contact nip portion (transfer nip portion) n between the photosensitive drum 2 and the transfer roller 6 and conveyed to the heat fixing device 11.

In this heat roller system, since the heat capacity of the heat roller 21 is large, it takes a very long time (wait time, warming time) to raise the surface of the heat roller 21 to a predetermined fixing temperature. For this reason, in order to quickly execute the image output operation, the temperature of the heat roller surface must be controlled to a certain temperature even when the apparatus is not used, which causes a problem that power consumption increases. .

As a heat-fixing device which does not have such a problem, the one proposed by the applicant of the present invention is disclosed in, for example, JP-A-63-31.
There is a film heating type heat fixing device disclosed in Japanese Patent No. 3182, Japanese Unexamined Patent Publication No. 2-157878 and the like.

FIG. 5 shows a schematic structure of an example of the apparatus. 3
1, 32 and 33 are substantially parallel to each other, the first film suspension roller, the second film suspension roller, and the heat resistance
It is a low heat capacity heating element fixedly supported by a heat insulating heater support 34.

Reference numeral 35 denotes an endless belt-shaped thin heat-resistant film suspended and stretched between the three members 31, 32 and 33.

Reference numeral 36 denotes the heating element 3 with the film 35 sandwiched therebetween.
3, a pressure roller as a pressure rotating body having a rubber elastic layer having a good releasability such as silicon rubber, which is in pressure contact with the heating device 30 in a state of pressing the heating body 33 with a predetermined pressing force. .

The film 35 is a first film suspension roller 31 or a pressure roller 36, or an elastic roller 37 (2) which is pressed against the first or second film suspension roller 31 or 32 with the film 35 sandwiched therebetween. The dotted chain line) is used as a film driving roller, and the film is driven to rotate in the clockwise direction a by the frictional force between the driving roller and the inner surface or the outer surface of the film 35.

The heating element 33 is sandwiched by the film 35.
The recording material P to be image-fixed is introduced between the pressure roller 36 and the film 35 in the fixing nip portion N formed by the pressure roller 36, and the fixing nip portion N is nipped and conveyed together with the film 35. As a result, the heat of the heating body 33 is applied to the film 3
An unfixed image T on the recording material P is given to the recording material P via
Is heated and fixed on the surface of the recording material P. The recording material P that has passed through the fixing nip portion N is separated from the surface of the film 35 and conveyed.

The heating body 33 is, for example, as shown in FIG. 6, an elongated substrate 33 made of alumina or the like having heat resistance, insulation, and good thermal conductivity whose longitudinal direction is perpendicular to the transport direction a of the film 35.
a, an electric heating element (resistance heating element) 33b made of Ag / Pd or the like, which is formed by screen-printing linearly or in strips along the length of the substrate at a substantially central portion on the front surface side of the substrate,
Power supply electrodes 33c, 33c made of Ag or the like formed by screen printing or the like at both longitudinal ends of the electric heating element, overcoat layers 33d made of heat-resistant glass or the like for protecting the surface of the heating element on which the electric heating element is formed, a substrate A linear heating element (ceramic heater) having a low heat capacity as a whole, which is provided on the back surface side and includes a temperature detecting element 33e such as a thermistor for detecting the temperature of the heating element.

The heating element 33 is fixedly supported on a support 34 with the surface side on which the energization heating element 33b is formed facing downward, and the energization heating element 33b is lengthened by power supply between the both end electrodes 33c, 33c. The temperature rises due to heat generation over the entire length, the temperature rise is detected by the temperature detecting element 33e, and the detected temperature is fed back to a temperature control circuit (not shown) to maintain the temperature of the heating body 33 at a predetermined fixing temperature. The energization of the energization heating element 33b is controlled in such a manner.

The heat resistant film 35 generally has a total thickness of 1
A thin film having a heat resistance of less than 00 μm, preferably less than 40 μm, excellent releasability, durability, etc.
It is a film of (polyimide), polyetherimide or the like.

In such a film heating type fixing device, as the heating body 33, a heating body having a low heat capacity is used.
Since a thin, low heat capacity material can be used as 5, it is possible to save power and shorten the wait time (quick start property). The ability to perform a quick start eliminates the need for preheating during non-fixing operations, saves power in a comprehensive sense, suppresses the temperature rise inside the machine, and allows the fixing point and separation point to be set separately. It has an advantage that offset can be prevented.

However, in this type of device, since a strong tension acts on the entire circumference of the endless belt-shaped film 35 to drive it to rotate, the moving force toward the film in the rotational driving process, that is, the direction in which the film 35 is perpendicular to the rotation. The force of moving in the film width direction along the length of the film suspension tension members 31, 32, 33 is strong, and a complicated control mechanism is required to control the deviation.

Further, in the case of an apparatus in which the first film suspension roller 31 is used as a driving roller to drive the film 35 by the frictional force between the inner surface of the film and the driving roller 31, while driving from the inner surface of the film, There is a problem that the sliding resistance between the heating element 33 and the inner surface of the film must be reduced.

Therefore, the applicant of the present invention has disclosed a tension-free type film heating type heat fixing device in which the moving force toward the film is weakened in JP-A-4-44075-44083 and JP-A-4-204980-204984. is suggesting.

FIG. 2 shows a schematic structure of an example of the apparatus.
Reference numeral 38 denotes a film inner surface guide member having a substantially semicircular arc trough shape in cross section. A heating element fitting groove is provided along the longitudinal direction of the outer lower surface of the guide member 38 along the length of the member, and the low heat capacity linear heating element 33 is fitted and supported in the groove.

A cylindrical heat-resistant film 35 is loosely fitted onto the film inner surface guide member 38 with the linear heating element 33, and the pressure roller 36 is a film 35.
The heating element 3 is opposed to the heating element 33 with the pinch in between and the heating element 3 is pressed with a predetermined pressing force
It is pressed against the heating device 30 in a state of pressing 3.

The pressure roller 36 is used as a driving roller to be rotationally driven by the driving means M, and the cylindrical film 35 is made to face the inner surface of the linear heating element 33 downward by the frictional force between the roller 36 and the outer surface of the film. The inner surface of the film guide member 38 is driven to rotate while being brought into close contact with and sliding.

In this film rotation drive state, the recording material P is introduced between the film 35 and the pressure roller 36 and passes through the fixing nip portion N, so that the recording material P is the same as in the apparatus of FIG. In the process of P passing through the fixing nip portion N, the heat of the heating body 33 is given to the recording material P via the film 35, and the unfixed image T is heat-fixed.

In the case of the apparatus of FIG. 5 described above, a strong tension acts on the endless belt-shaped film 35 at the entire circumference during driving, but in the case of the apparatus of FIG. 2, the fixing nip portion N and this fixing nip portion are formed. The tension acts only on the film portion of the contact area B between the outer surface of the film inner surface guide member 38 and the film on the upstream side of the film rotation direction from N,
No tension acts on most of the remaining film.

In such a tension-free type apparatus, the deviation force of the film 35 when driving the film is smaller than that in the apparatus shown in FIG. 5, and the film deviation control means or the film deviation control means can be simplified. You can For example, the means for restricting the shift of the film can be a simple one such as a flange member for receiving the edge of the film, and the control means for the shift of the film can be omitted to reduce the cost and size of the apparatus.

[0028]

As in the tension-free type film heating type heat fixing device shown in FIG.
In the case where the pressure roller 36 that presses the heating body 33 through the film 35 is used as a drive roller to move and drive the film 35 and the recording material P, the diameter of the pressure roller 36 is thermally expanded by the heat of the heating body 33. Due to the change, the conveyance speed of the recording material P by the pressure roller 36 changes.

Therefore, when the recording material P is conveyed over both the transfer nip portion n of the transfer device 60 and the fixing nip portion N of the heat fixing device 11 as shown in FIG. Since the recording material conveying speed changes with the change in the diameter of the roller 36 due to the thermal expansion, the recording material portion between the transfer nip portion n and the fixing nip portion N is pulled or loosened to change the printing accuracy. That is, there is a problem in that the length of the image expands or contracts in the recording material conveyance direction, or the level of the void is changed.

Such a problem becomes noticeable in the image forming apparatus having a structure in which the transport path between the transfer nip portion and the fixing nip portion is shortened for cost reduction and size reduction. For example, comparing image forming apparatuses in which the transfer path between the transfer nip portion and the fixing nip portion is 50 mm and 150 mm, when the transfer path between the transfer nip portion and the fixing nip portion is 50 mm, A4 size paper is the transfer nip portion and the fixing nip portion. The transporting length of the pressure roller is 247 mm, and the transporting force of the pressure roller greatly affects the transportability of the recording material. On the other hand, when the conveyance path between the transfer nip portion and the fixing nip portion is 150 mm, the length of the A4 size sheet conveyed across both the transfer nip portion and the fixing nip portion is 147 mm, and the pressure roller The transporting force of P has little influence on the transportability of the recording material.

For this reason, in the image forming apparatus having the structure in which the conveying path between the transfer nip portion and the fixing nip portion is shortened,
The diameter of the pressure roller must be set in consideration of the conveying force when the pressure roller thermally expands. However, if the pressure roller diameter is set in this way, the pressure roller will not be sufficiently warmed up.
In the area where the recording material is conveyed across both the transfer nip portion and the fixing nip portion, there arises a problem that the conveyance speed of the recording material becomes slow and the hollowing level becomes worse.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object thereof is to prevent deterioration of image quality even when image formation is performed immediately after power-on. To provide a forming apparatus.

[0033]

SUMMARY OF THE INVENTION The present invention comprises a recording portion for forming an unfixed image on a recording material, a heating body and a pressure rotating body which is rotationally driven in pressure contact with the heating body. The recording material on which the unfixed image is formed is supplied from the recording unit to the pressure contact nip portion formed between the pressure contact member and the pressure contact member, and the pressure contact nip portion is nipped by the driving force of the pressure member. Transport
An image forming apparatus having a heat fixing device that heats and fixes an unfixed image on a recording material by the heat of the heating body, wherein control is performed to heat the pressure rotating body before starting image formation.

It is also possible to have control setting means for selecting whether or not to carry out the control, and to carry out the control based on the setting of the control setting means.

[0035]

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is a laser beam printer using an electrophotographic process.

As the heat fixing device, the tensionless type film heating type heat fixing device 11 shown in FIG. 2 is used. Here, the linear heating body 33, the film inner surface guide member 38, and the heat resistant film 35 constitute a heating body.

Reference numeral 1 is an apparatus casing, and 2 is an electrophotographic photosensitive drum, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed).

During the rotation of the photosensitive drum 2, the charging roller 3 uniformly performs a primary charging process to a predetermined polarity and potential.
Laser light L output from the laser scanning exposure device (laser beam scanner) 4 on the charged surface and modulated in accordance with the time-series electric digital pixel signal of the target image information.
Then, the electrostatic latent image corresponding to the desired image information is formed on the peripheral surface of the drum by scanning exposure.

The latent image is developed as a toner image by the developing device 5, and the toner image reaches the transfer nip portion n between the photosensitive drum 2 and the transfer roller 6.

On the other hand, the paper feeding roller 7 is used to feed the paper feeding cassette 8.
The recording material P in the inside is fed to one sheet by one-sided reference conveyance, is introduced into the transfer nip portion n at a predetermined timing through the sheet path 9, and has a polarity opposite to that of the toner from the back surface of the recording material P by the transfer roller 6. Is applied to transfer the toner image on the side of the photosensitive drum 2 to the surface of the recording material P.

Here, the electrophotographic photosensitive drum 2, the charging roller 3, the laser scanning exposure device 4, the developing device 5, and the transfer roller 6 constitute a recording portion A.

Upon receiving the transfer of the toner image, the transfer nip portion n
The recording material P that has passed through the sheet is separated from the surface of the photosensitive drum 2 and guided to the conveyance guide 10 and enters the heating and fixing device 11, where it passes through the fixing nip portion N to undergo the heat fixing of the toner image as described above, and the sheet is transferred. It is discharged to the outside of the device through the path 12.

After the transfer of the toner image onto the transfer material P, the surface of the photosensitive drum 2 is cleaned by the cleaning device 13 and repeatedly used for image formation.

The specifications of the transfer roller 6 and the heat fixing device 11 used in this embodiment will be described below. Transfer roller: Foamed EPDM rubber was used as the material.
The hardness of EPDM is 20-40 ° in Asker C hardness, and conductive ZnO is dispersed in order to impart conductivity.

Another material used for the roller is C
Examples thereof include R rubber, NBR, urethane rubber, Si rubber, and fluororubber.

Further, as the conductive substance dispersed in the roller for the purpose of imparting conductivity, carbon, ZnO,
Although metal fillers such as SnO ₂ can be mentioned, metal fillers having relatively high specific resistance so that they are not affected by environmental changes and easily controllable by the number of parts to be dispersed, preferably ZnO.

In the present invention, a rubber roller having an outer diameter of 16 mm was used. Fixing film 35; PTF on the outer surface of a cylindrical polyimide film having a length of 226 mm, an inner diameter of 24 mm, and a wall thickness of 45 μm.
E is coated with a thickness of 10 μm. Heater; width 6.5 mm, length 236 mm, thickness 0.63
A heating resistor pattern of silver-palladium was applied by screen printing as an energization heating layer 33b on a 5 mm alumina substrate 33a, and then baked to obtain 28.3Ω.

The thermistor 33e was mounted on the back side of the substrate 33a (the surface of the substrate opposite to the side of the electric heating element layer 33b) at a position 40 mm closer to the paper passage reference side than the longitudinal center of the substrate. Pressure roller 36: An aluminum shaft 36a having an outer diameter of 10 mm is provided with a silicon rubber roller layer 36b having a thickness of 3 mm, and a surface layer 36c is made of fluorine terax (GL made by Daikin).
30μ of S213 mixed with 10wt% of FEP)
m is coated and baked, hardness is 50 °
(Asker C). Film feed speed (paper feed speed); 23.8 mm / se
c The heating and fixing device 11 is incorporated in a printer so that a letter size A or A4 size paper (recording material) can be passed with a constant paper gap D of 50 mm.

(Comparative Example 1) With the above configuration, the image forming apparatus shown in FIG. 1 in which the conveying path 1 between the transfer nip portion n and the fixing nip portion N is 50 mm and the conventional image forming apparatus in which the conveying path 1 is 150 mm. Was used to print on A4 paper.

In the image forming apparatus having the conveyance path 1 of 50 mm, the length of the recording material conveyed across both the transfer nip portion and the fixing nip portion is 247 mm, and the conveyance force of the pressure roller conveys the recording material. Will greatly affect In the image forming apparatus of 1 = 50 mm used for the examination, the peripheral speed of the transfer roller is set to 1% of the peripheral speed of the photosensitive drum in order to prevent the hollow portion.
The transfer speed of the recording material at the transfer nip portion is set to be high. Further, the outer diameter and the peripheral speed of the pressure roller are set in consideration of the increase in the conveying force when the pressure roller thermally expands.
For this reason, if the pressure roller is not sufficiently warmed immediately after the power is turned on, the conveyance force of the pressure roller becomes smaller than the conveyance force at the transfer nip portion. Therefore, from the start of image formation to the passage of about 10 sheets, the leading edge 50 where the recording material is conveyed over both the transfer nip portion and the fixing nip portion.
From mm onward, the hollow portion gradually becomes worse, and becomes even worse near the trailing edge of the recording material. The deterioration of the hollow image was not so great on plain paper, but was remarkable on OHT.

(Comparative Example 2) Next, in the conventional image forming apparatus having the conveyance path 1 of 150 mm, the length of the recording material conveyed across both the transfer nip portion and the fixing nip portion is 147 m.
m, the influence of the conveying force of the pressure roller on the conveying property of the recording material is small. In the image forming apparatus of the conventional example as well, in order to prevent the hollow portion, the peripheral speed of the transfer roller is set to be 1% faster than the peripheral speed of the photosensitive drum, and the conveyance speed of the recording material at the transfer nip portion is set. When the conveyance path 1 is long in this way, the conveyance force of the pressure roller has little influence on the conveyance property of the recording material, so that the printing accuracy is not disturbed and the image is expanded or contracted due to thermal expansion of the pressure roller. The margin is small when setting the outer diameter of the pressure roller and the peripheral speed. In addition, in order to compare the level of the hollow in the transportability of the recording material when the transport path 1 is 50 mm and 150 mm, l = 150 mm
The outer diameter and peripheral speed of the transfer roller and the pressure roller of the image forming apparatus of No. 1 were set to be the same as those of the image forming apparatus of 1 = 50 mm, and printing was performed. In the morning condition, the hollow portion slightly deteriorated after 150 mm from the front end of the recording material, but did not worsen until the rear end of the recording material. The same was true for printing on the OHT.

In the present embodiment, an image formation having the same structure as in Comparative Example 1 in which the conveyance path between the transfer nip portion and the fixing nip portion is short and the conveyance force of the pressure roller greatly affects the conveyance property of the recording material. In order to improve the level of hollowing in the apparatus, especially immediately after the power is turned on, the pressure roller is controlled to be sufficiently warmed before the start of printing. Since the level of voids becomes worse on thick paper and especially on OHT, the information for selecting the control may be sent from the computer on the host side when these recording materials are passed, or the control may be selected for the image forming apparatus. A switch or the like may be attached. A sensor that detects the type of recording material is provided, and the recording material is thick paper or OHT.
The control may be performed when it is detected that In this case, the computer or switch on the host side constitutes the control setting means. Based on this information, before starting printing, the fixing device can be used for about 10 seconds in the same manner as when feeding paper.
By controlling the temperature at 70 ° C. and rotating it, the pressure roller was sufficiently warmed, and it was possible to prevent hollowing out near the trailing edge of the recording material immediately after the power was turned on.

From the above results, by carrying out the control of this embodiment, the conveying path between the transfer nip portion and the fixing nip portion is short, and the conveying force of the pressure roller greatly affects the conveying ability of the recording material. In the image forming apparatus, even when the outer diameter and the peripheral speed of the pressure roller are set so as to optimize the printing accuracy and the elongation of the image, it is possible to prevent the cardboard or the OHT from missing.

[0054]

As described above, according to the present invention,
Since the control for heating the pressure rotating body is performed before the start of image formation, even in the image forming apparatus in which the transportability of the recording material is greatly affected by the transport force of the pressure rotating body,
It is possible to prevent the deterioration of the image quality formed on the recording material immediately after the power is turned on. In addition, even when the outer diameter and peripheral speed of the pressure rotor are set to optimize printing accuracy and image elongation,
Since the pressure rotator is preheated, the change in the outer diameter and the peripheral speed is small, so that the deterioration of the image quality formed on the recording material can be prevented.

Since the control setting means for selecting whether or not to control the heating of the pressure rotating body before starting image formation is provided and the control is performed based on the setting of the control setting means,
The control can be selected when the recording material is a material such as thick paper or OHT that is likely to deteriorate in image quality, and the deterioration in image quality formed on the recording material can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus (laser beam printer) according to the present embodiment.

FIG. 2 is a schematic configuration diagram of a heat fixing device (tensionless type film heating system heat fixing device).

FIG. 3 is a schematic view showing a transfer device of a conventional example.

FIG. 4 is a schematic configuration diagram of a heat roller type heat fixing device.

FIG. 5 is a schematic view of an example of a tension type film heating type heat fixing device.

FIG. 6 is a partially cutaway plan view model in which a middle portion of a heating body is omitted.

[Explanation of symbols]

 2 Electrophotographic photosensitive drum 3 Charging roller 4 Laser scanner 5 Developing device 6 Transfer roller 11 Heat fixing device 33 Linear heating element 35 Heat resistant film 38 Film inner surface guide A Recording area P Recording material T Unfixed image N Pressure contact nip area

Claims (2)

[Claims] 1. A recording unit that forms an unfixed image on a recording material, and a heating body and a pressure rotating body that is rotationally driven by being in pressure contact with the heating body, and between the heating body and the pressure rotating body. The recording material on which the unfixed image has been formed is supplied from the recording portion to the pressure contact nip portion formed in, and the pressure contact nip portion is nipped and conveyed by the driving force of the pressure rotating body, and the heat of the heating body is heated. 2. An image forming apparatus comprising: a heat fixing device for heating and fixing an unfixed image on a recording material, wherein the pressure rotating body is heated before starting image formation. 2. The image forming apparatus according to claim 1, further comprising a control setting unit that selects whether to perform the control, and the control is performed based on the setting of the control setting unit.