JPH1063125A - Fixing device and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing method for high image quality where toner scattering, character blurring and offset are not found by preventing fluttering of the paper near a winding area in the case of a method where the supply quantity of heat to toner is increased to perform a high speed fixing by winding paper round a heat roll in a fixing device using a preheater used in an electrostatic recorder adaptable to continuous paper, and to provide a constitution of fixing device for executing double-sided fixing at a high speed. SOLUTION: The preheater 4 is turned centering around a rotary shaft 17 so as to wind the paper 6 round the heat roll 1. The preheater 4 is provided with curved surface-shaped paper guiding surface at its edge and a suction groove 11 having a suction port 19, so that the paper 6 stably travels along the surface of the preheater 4 without fluttering. After getting out of the preheater 4, the paper advances in the tangential direction of the surface of the roll 1 and is wound round the roll 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrostatic recording device such as a printer or a copying machine using an electrophotographic method, and more particularly to a fixing device for an electrostatic recording device for continuous paper and a control method thereof. .

[0002]

2. Description of the Related Art A heat roll fixing device including a heat roll and a backup roll has been used as a fixing device of an electrostatic recording apparatus such as a printer or a copying machine using an electrophotographic system. In this method, heat and pressure are applied to the toner on the paper when passing through the nip between the heat roll and the backup roll, and the toner is melted and fixed to the paper.

[0003] Printing speed from 100 ppm to 200 ppm
In a high-speed machine of the class, the time required for the paper to pass between the nips is shortened, so that the fixing energy is insufficient due to only the heat and pressure in the nip region alone, and a fixing failure occurs. For this reason, a method of providing a preheater for preheating the sheet temperature before entering the nip region is adopted. At higher speeds, the amount of heat is insufficient with the pre-heater alone. Therefore, a method has been proposed in which continuous paper passes through the pre-heater and then further winds the paper around the heat roll surface (DE2717).
260 C3). In this specification, this method is referred to as a "front winding method" and will be described with reference to FIG.

[0004] The paper 6 on which the toner image 7 is formed is
The sheet temperature rises by passing over the pre-heater 4 having the built-in heater 5, and the sheet is heated by bringing the pre-heater 4 closer to the heat roll 1.
After forming a winding area 16 by being wound around the surface of
The nip area 15 between the heat roll 1 and the backup roll 3 is entered. Thus, the amount of heat input to the toner can be increased.

[0005]

One of the objects of the present invention is to prevent the image quality from deteriorating at the time of forward winding fixing, and the other is to propose a fixing machine configuration for high-speed double-sided printing.

(1) Prevention of Deterioration of Image Quality at the Time of Front Winding Fixation FIG. 5 is a view for explaining the structure of a conventional preheater and the problem when fixing is carried out by the front winding method. The structure of the preheater 4 is described in the literature (IBM J. RES. DEVELO).
P. vol. 22, no. 1, 1978). As shown in FIG.
In the first embodiment, a suction groove 10 is provided on a paper contact surface of a paper guide saddle including a heater 5. This enhances the adhesion between the sheet and the preheater surface in order to improve the heat transfer from the preheater to the sheet. A suction port 19 is provided in the suction groove 10 and is connected to a suction blower (not shown). Further, a negative pressure suction box 12 is provided on the upstream side of the preheater, and a suction force is applied to the sheet by the suction port 20. Thus, the sheet enters the preheater in a stable state, and the adhesion between the sheet and the preheater is improved.

However, as shown in FIG. 5 (b), when continuous printing is performed by the front winding method, even if the paper is attracted to the pre-heater surface by the suction force in the negative pressure suction chamber or the suction groove, high-speed conveyance is performed. Occasionally, paper flapping 23 occurs near the leading end of the pre-heater, causing toner scattering 24.
Was found to occur. Further, in the area 16 wound around the heat roll, it was also found that the toner image on the paper came into contact with the preheater a plurality of times due to the flapping of the paper, which caused character blurring and offset after fixing, resulting in deterioration in image quality. In particular, when thick paper having a thickness of 150 μm or more is used, the flexibility is low. Therefore, the winding property from the leading end of the preheater to the heat roll is poor. As a result of the experiment, it was found that the deterioration of the image quality due to the folding of the sheet by the eyes was more remarkable. Patent DE271
7260 C3 does not describe the occurrence of such toner scattering or character blur, nor any countermeasures. On the other hand, as a patent related to the front winding method, a method of winding a sheet around a heat roll surface using a non-heated sheet guide saddle has been proposed (Japanese Patent Publication No. 5-504634). In this patent, it is described that a paper brake mechanism including a negative pressure suction chamber is provided just before entering a non-heated paper guide saddle to prevent flapping during paper traveling. However, even if the brake mechanism by the negative pressure suction chamber 12 is operated as described with reference to FIG. 5B, there is a problem in the stable conveyance of the paper near the front end of the preheater, and it is effective in preventing the occurrence of “character blur”. It turned out there was no. For this reason, new measures are needed.

(2) Configuration of a fixing machine for high-speed double-sided printing In a tandem type double-sided printing in which two electrostatic recording devices are used to perform first-side printing on the first and second-side printing on the second. During printing on the first side, the temperature of the pre-heater can be increased to 100 ° C. because there is no toner on the surface in contact with the pre-heater surface of the paper. On the other hand, the second side (back side) of the paper
When the toner image is fixed, the fixed toner image on the first surface (front surface) of the sheet comes into contact with the surface of the preheater. For this reason, the temperature of the pre-heater must be at least lower than the glass transition temperature (about 60 ° C.) of the toner resin.
Therefore, the amount of heat applied to the toner at the time of printing the second surface is smaller than the amount of heat applied to the toner at the time of printing the first surface, and the fixing strength is reduced. For this reason, new measures are needed.

[0009]

[Means for Solving the Problems]

(1) Prevention of deterioration of image quality at the time of fixing by wrapping forward The paper guide surface consisting of a curved surface is formed at the tip of the preheater,
A suction groove is provided on the paper guide surface. Further, the suction pressure is optimized according to the thickness of the sheet.

(2) Configuration of fixing machine for high-speed double-sided printing Instead of lowering the temperature of the preheater below the glass transition temperature of the toner, the paper is wound around a heat roll, and
After passing through the nip area between the heat roll and the backup roll, the paper is further wound around the heat roll (hereinafter, referred to as backward winding) to compensate for the shortage of heat in the preheater.

[0011]

FIG. 1 is a diagram for explaining an embodiment of the present invention. When loading paper 6, the backup roll 3
Is separated from the heat roll 1, the preheater 4 is also positioned below, and is separated from the heat roll 1. The sheet is fed by the loop tractor 8 over the negative pressure suction chamber 12, the preheater 4, and the backup roll 3.
Nipped by Reference numeral 9 denotes a buffer at the time of loading paper, running, and stopping. After loading the paper,
The backup roll 3 and the pre-heater 4 rise, the backup roll 3 is pressed against the heat roll 1 to nip the paper, and the pre-heater 4 rotates about a rotation shaft 17 to wind the paper 6 around the heat roll 1. The winding area is 16 and the nip area is 15. The paper 6 is tensioned by the spring force of the buffer 9 so as to be along the preheater surface. FIG. 2 shows the structure of the preheater 4 employed in the present invention. The preheater is made of metal and has a heater 5 inside,
The surface temperature is controlled to a value near 100 ° C. Before the paper enters the pre-heater, the suction port 20 of the negative pressure suction chamber 12 acts so that the direction of the paper travels along the pre-heater surface when the paper travels, and the suction groove 10 of the pre-heater improves the adhesion between the paper and the pre-heater surface. And improve the heat transfer to the paper. A paper guide surface 4a having a curved surface is formed at the tip of the preheater.

Further, the paper exits the preheater and then enters in the tangential direction of the heat roll surface and is wound by the curved shape of the paper guide surface and the suction force to the paper by the suction groove 11 according to the present invention. Suction ports 1 for suction grooves 11 and 10
9 and the exhaust blower 13 are connected by an exhaust tube 14. In the present invention, the suction groove 11 is provided with a plurality of suction ports so that the suction force of the sheet on the sheet guide surface can be improved.

The running speed of the paper is 50 inches / second (printing speed: 300 ppm or more), and the surface temperature of the heat roll is 1
High-speed fixing characteristics were evaluated using a styrene acrylic toner at 90 ° C. As a result, the following was found.

(1) Due to the shape of the paper guide surface at the leading end of the preheater and the suction force of the suction groove 11 provided therein, the flapping of the paper as shown in FIG. Can be prevented.

(2) The transport state of the sheet including flapping differs depending on the thickness and the type of the sheet. As the paper becomes thicker, the suction pressure is increased within a range that does not hinder the travel of the paper. If the paper thickness is 80 μm, the suction groove 1
It was found that when the suction pressure of No. 1 was 3 × 10 ⁶ Pa and the paper thickness was 125 μm, the suction pressure of the suction groove 11 should be 5 × 10 ⁶ Pa.

(3) Suction groove 11 newly added in the present invention
Is different from the operation of the suction groove 10. Suction groove 10
Is to close the gap between the paper and the heat roll in order to improve the thermal conductivity to the paper, and does not require a suction force. For heating the paper, increase the contact area,
The large attraction force, on the contrary, hinders the paper running.

On the other hand, the suction groove 11 is for preventing the paper from flapping and has a small contact area. Therefore, the suction force of the suction groove 11 needs to be larger than that of the suction groove 10.

When the paper thickness is 125 μm, the suction groove 11
2.5 × 10 ⁶ P which is the same as the suction force of suction groove 10
In the case of a, paper flapping occurred, so that 5 × 10 ⁶
When it was set to Pa, flapping of the paper could be prevented.

FIG. 3 shows a second embodiment. In the duplex printing, when the toner 7b on the second surface (back surface) of the paper is fixed,
The fixed toner 7 a on the first surface (front surface) of the sheet comes into contact with the heating surface of the preheater 4. For this reason, the temperature of the preheater must be at least equal to or lower than the glass transition temperature of the toner resin. Therefore, the amount of heat applied to the toner at the time of printing the second surface is smaller than the amount of heat applied to the toner at the time of printing the first surface, and the fixing strength is reduced. For this reason, the surface temperature of the preheater was set to 55 ° C. Further, a winding roll 21 is provided on the downstream side of the heat roll fixing machine to perform an operation of approaching and separating from the heat roll 1 in conjunction with the backup roll 3. With this configuration, the amount of heat input to the paper as shown in FIG. 6 can be obtained. FIG. 6 shows a change in the amount of heat between the first embodiment and the second embodiment. The second embodiment will be described below. At the time of printing, the paper 6 receives the heat quantity Q1 by the preheater 4, the heat quantity Q2 in the front winding area 16, the heat quantity Q3 in the nip area 15, and the heat quantity Q4 in the rear winding area 22, and the toner is melted and fixed to the paper. Preheater 4
The shortage of Q1 due to the decrease in the temperature of is compensated for by the heat quantity Q4 in the rear winding area. By making the total amount of heat applied to the toner the same, the fixing strength of the toner on the second surface could be secured.

A third embodiment will be described with reference to FIG. In the fixing method in which the paper is wound around the heat roll, the contact area between the paper and the heat roll is large, so that a large amount of heat is taken from the heat roll to the paper. The decrease in the surface temperature of the heat roll at the exit A in the nip area is about 140 to 160 ° C., depending on the thickness and printing density of the paper. Therefore, it is necessary to increase the heat roll temperature to around 190 ° C. before reaching the heat roll winding position B. For this reason, it is necessary to increase the power of the infrared lamp and the like provided inside the heat roll 1, but there is a limit in increasing the lamp power, and it is difficult to increase the number of lamps due to the space inside the heat roll. Therefore, as shown in FIG. 7, a heating element 27 (infrared wrap or the like) for heating the surface of the heat roll from outside is provided to help increase the surface temperature of the heat roll. The energization of the heating element is controlled based on the sensing of the heat roll surface temperature. This embodiment is an example of application to the case of the front winding method.
The external heating method can also be applied to a fixing method using both front and rear windings as shown in FIG. Such a configuration is, as in high-speed printing, the heating element 2 inside the heat roll.
Response is too high or the paper is too thick,
This is effective when the heat consumption is large.

[0021]

According to the fixing device having the pre-heater,
After passing through the preheater, the paper surface on which the toner image has been formed is wound around the heat roll surface, and then, in a fixing device employing a forward winding system which enters the nip region, a paper guide surface having a curved surface is formed at the leading end of the preheater. Formed and provided with a suction groove in the paper guide surface, the paper is conveyed in close contact with the preheater surface to near the leading end, and the paper exiting the preheater enters the tangential direction of the heat roll surface. In addition, "paper flapping" does not occur between the tip of the preheater and the region where the heat roll is wound. For this reason, the occurrence of toner scattering, offset, and character blur can be prevented.

Also, during duplex printing, the temperature of the pre-heater is set to be equal to or lower than the glass transition temperature of the toner, and by using a combination of the front winding method and the rear winding method, the shortage of heat input to the paper by the pre-heater is reduced. Can be compensated for, and the fixing strength can be secured. In addition, a decrease in the temperature of the heat roll during continuous printing can be compensated by heating the surface of the heat roll with an external heating device.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view for explaining a first embodiment of the present invention.

FIG. 2 is a perspective view showing a shape of a preheater used in the present invention.

FIG. 3 is a longitudinal sectional view showing a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a conventional technique of a front winding fixing method.

FIG. 5A is a perspective view showing a pre-heater shape according to a conventional technique. (B) It is a longitudinal section showing the problem of the prior art.

FIG. 6 is a graph showing a change in the amount of heat input to a sheet.

FIG. 7 is a longitudinal sectional view illustrating a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heat roll, 2 ... Infrared lamp, 3 ... Backup roll, 4 ... Preheater, 4a ... Paper guide surface, 5 ... Heater with a built-in preheater, 6 ... Paper, 7 ...
· Toner, 11 ··· Pre-heater tip suction groove, 12 ··· Negative pressure suction chamber, 13 ··· Blower, 15 ··· Nip area between heat roll and backup roll, 16 ··· Front winding area, 18 · ..Out rolls, 19: suction ports, 2
1: winding roll 22: rear winding area
23: paper flapping, 24: scattering of toner, 25
... regular fixing toner image, 26 ... character blur.

Claims (4)

[Claims] A heat roll having a heating source therein;
A heat roll fixing device including a backup roll that is in contact or non-contact with the heat roll,
The pre-heater comprises a pre-heater that can rotate toward and away from the heat roll, and at the time of printing, the backup roll contacts the heat roll to form a nip region, and the pre-heater pivots so as to approach the heat roll. After passing the preheater, the paper is wound around the heat roll surface, enters the nip region between the heat roll and the backup roll, and fixes the toner to the paper. Wherein the paper guide surface is formed and a suction groove is provided in the paper guide surface. 2. A heat roll having a heating source inside,
A heat roll fixing device including a backup roll that is in contact or non-contact with the heat roll,
The pre-heater comprises a pre-heater that can rotate toward and away from the heat roll, and at the time of printing, the backup roll contacts the heat roll to form a nip region, and the pre-heater pivots so as to approach the heat roll. After passing through the preheater, the paper is wound around the heat roll surface, enters the nip area between the heat roll and the backup roll, fixes the toner on the paper, and forms a curved paper guide surface at the leading end of the preheater. In a fixing device having a suction groove on a paper guide surface, a paper traveling state is controlled by changing a suction pressure of a suction groove provided at a leading end of a preheater according to a paper type and a paper thickness. Method of controlling fixing device 3. The printing method according to claim 1, wherein the unfixed toner image is formed on the back surface of the paper, and the surface temperature of the preheater is set to room temperature during the second surface printing when the fixed toner image surface formed on the front surface of the paper comes into contact with the preheater surface. 3. The method according to claim 2, wherein the temperature of the pre-heater is controlled so as to be higher than the glass transition temperature and lower than the glass transition temperature of the toner. 4. After leaving the nip portion of the fixing device,
4. The heat roll according to claim 2, wherein a roller for winding the paper around the surface of the heat roll is provided so that the paper is wound around the heat roll on the upstream side and the downstream side with the nip portion of the heat roll fixing device interposed therebetween. Method of controlling fixing device as described above