JPH04287077A - Fixing device for color image forming device - Google Patents

Abstract

PURPOSE:To perform fixing both in full colors and monochrome appropriately without heating a fixing roller abnormally by forming the surface temperature of the fixing roller in a standby operation and an image forming operation by enabling to be switched in the fixing in full colors and monochrome, respectively, and setting the surface temperature in the fixing in monochrome less than that in the fixing in full colors. CONSTITUTION:The surface temperature of the fixing roller 2 in the standby operation and the image forming operation are set at temperature less than that in the fixing in monochrome, respectively, and a heating means 1 is controlled. Therefore, the decreasing quantity of temperature after image formation is started can be reduced since standby surface temperature in the fixing in monochrome is set at a low level, and the difference of glossiness between first recording paper and following recording paper can be reduced. In addition to that, since the surface temperature in the fixing in monochrome is set at the low level, core temperature can be prevented from increasing over 200 deg.C, and a rubber layer can be prevented from peeling, and the increasing quantity of the surface temperature of the fixing roller 2 increased due to the delay of thermal responsiveness of the rubber layer after the image formation is performed can be reduced.

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 a color image forming apparatus such as a copying machine, a printer, or a facsimile machine.

0002

2. Description of the Related Art Color image forming apparatuses are known which are equipped with a developing device that accommodates developers of a plurality of colors and form monochrome or multicolor images of two or more colors.

In a color image forming apparatus, when forming a full color image, an electrostatic latent image formed by color separation exposure using red, green, and blue filters is developed with cyan, magenta, and yellow toner, and the toner is 2. Description of the Related Art It is common practice to transfer images onto recording paper in an overlapping manner and fix the transferred images.

[0004] In a full-color image forming apparatus, a color image is formed by fixing the above-mentioned three-color toner images, or four-color toner images including black if necessary, but the superimposed toner is not completely removed. Color reproduction will be good when the toner is melted and mixed sufficiently, but if the toner is unfixed or is not fully fixed and is semi-melted, the transparency of the toner will be poor and the color mixing will be insufficient.
The color reproducibility is dominated by the color of the last transferred toner, resulting in poor color reproducibility.

[0005] Toners used in full-color reimage formation are those with poor releasability in consideration of image glossiness. Therefore, when a fixing roller is used as a fixing device, a roller coated with silicone rubber having high mold release properties is used as the fixing roller.

In a fixing device having a fixing roller and a pressure roller, as shown in FIG.
The surface of the fixing roller 2, which has a built-in roller, is more flexible than the surface of the pressure roller 3, and the pressure roller 3 is formed in such a way that it sinks into the fixing roller 2 when pressed, as shown in FIG. In some cases, the pressure roller 3 is formed in a shape that is inserted into the pressure roller 3. The pressure roller 3 may also have a built-in heater if necessary. The surface temperature of the fixing roller 2 is detected by a temperature detection means 4, such as a thermistor.

In the nip shape shown in FIG. 1, the paper after the nip is fed out downward along the pressure roller 3, so it is called a downward nip shape, and in the nip shape shown in FIG. This is called an upward nip shape because in a downward nip shape, the amount of fixing heat is constant, but in an upward nip shape, the amount of heat changes, and the toner melts unevenly, resulting in glossy and non-glossy areas. Get out.

Therefore, it is preferable that the full-color image forming apparatus detecting device has a downward nip shape. In order to obtain this downward nip shape, the thickness of the silicone rubber coating layer of the fixing roller must be 1.5 mm or more.

Some color image forming apparatuses can perform monochrome image formation in which a toner image of one color is transferred and fixed, and full-color image formation in which a toner image of three or four colors is developed and transferred and then fixed. In this case, since the toner adhesion amount differs greatly between full color and single color, the energy required for fixing is greater for full color than for single color.

In order to cope with the difference in energy required for fixing single color and full color, for example,
No. 9-22226 proposes changing the conveyance speed of the transfer paper in the fixing device, that is, changing the speed at which the transfer paper passes through the heat source to increase the amount of heat in the case of full color printing. In this case, since there is a difference between the conveyance speed in the image forming section and the conveying speed in the fixing device, there is a distance between the image forming section (transfer section) and the fixing device equal to the length of the maximum size transfer paper that can form an image. The problem is that it requires a large amount of space.

[0011] In Utility Model Application Publication No. 15073/1983, it is proposed to change the nip width depending on the color mode.
In order to change the nip width, it is necessary to change the pressing force of the pressure roller against the fixing roller, which requires a device with a complicated structure, resulting in a problem of low reliability.

[0012] Japanese Patent Laid-Open No. 60-263173 proposes changing the set temperature of the pressure roller depending on the color mode, but the temperature of the fixing roller is constant.

Generally, it is preferable for control to make the copying linear velocity in the image forming section and the fixing linear velocity in the fixing device the same. In this case, if the structure uses one photoreceptor, for example, 24 photoreceptors (A
There is a difference between 4)/minute and 6 sheets (A4)/minute.
Full-color image formation speed becomes low.

For example, if the diameter is 60 mm and the silicone rubber thickness is 1.
In a fixing device that uses a 5 mm fixing roller and a pressure roller with a diameter of 60 mm and a silicone rubber thickness of 3 mm, if the heater 1 is controlled so that the surface temperature of the fixing roller 2 is 170°C, the fixing speed and the operation of the image forming section will change. Both image speeds are 180mm
/sec, if a single photoreceptor drum is used, 24 sheets (A4) / sec.
The copy speed is different from 6 sheets (A4) per minute in full color. If 20 or more sheets are continuously fed through this device, the core of the fixing device will reach a temperature of nearly 230° C. during monochrome image formation, exceeding the heat resistance temperature of silicone rubber and primer, and the rubber will peel off from the core. If the thickness of the rubber of the fixing roller is 1.5 mm or more, as shown in FIG. 5, the overshoot amount OS after the image forming process becomes large, causing a problem that hot offset occurs during the next image forming. This problem cannot be solved simply by changing the set temperature of the pressure roller of Utility Model Application No. 60-263173.

[0015]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides a color image forming apparatus that can properly fix both full color and single color without abnormally heating the fixing roller. The objective is to provide a compact fixing device.

[0016]

[Means for Solving the Problems] The present invention solves the above problem by forming an image using separated colors on one latent image carrier, transferring the image to a recording paper in an overlapping manner, and rotating at the same linear speed as the latent image carrier. In the fixing device of a color image forming apparatus that uses a heated fixing roller to fix images, the surface temperature of the fixing roller during standby and image formation can be switched between full color and single color, respectively, and the surface temperature during single color can be changed to full color. This problem has been solved by a fixing device for a color image forming apparatus, which is characterized in that the fixing device is set lower than the normal setting.

[0017]

[Function] According to the present invention, since the standby surface temperature during monochrome is set low, the amount of temperature drop after the start of image formation can be reduced, and the difference in glossiness between the first recording paper and the subsequent recording paper can be reduced. By setting the surface temperature low during fixing in single color, it is possible to prevent the core metal temperature from rising above 200℃, which prevents the rubber layer from peeling, and prevents the rubber layer from peeling off after image formation, that is, after paper feeding. The amount of increase in the surface temperature of the fixing roller due to the delay in thermal response, that is, overshoot, can be reduced because the temperature of the core metal can be lowered.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail based on embodiments shown in the drawings.

In the fixing device shown in FIG.
1.5 mm of RTV silicone rubber (room temperature vulcanized silicone rubber) is formed on an aluminum core metal to form a roller with a diameter of 60 mm. The pressure roller 3 is attached to an aluminum core metal.
mm silicone rubber is formed and finished to a diameter of 60 mm. The fixing roller 2 is driven to rotate at an image forming linear speed, for example, 150 mm/sec, which is the same linear speed as the transfer linear speed.

[0020] When the speed of monochrome image formation is 24 sheets (A4)/min, the speed of full color image formation is 6 sheets (A4) / min, and the fixing temperature setting is 170°C, the speed of full color image formation is 17 sheets (A4)/min.
The temperature is controlled at 0°C, and the temperature is controlled at 150°C since monochrome requires less energy. As shown in Figure 3, the fixing temperature, which was controlled at 170 degrees Celsius during standby, once fixing starts, heat is absorbed by the paper, so the temperature is temporarily reduced to 160 degrees Celsius, as shown at point A.
The roller surface temperature decreases from front to back, but in the case of full color, it is controlled at 170°C, so as curve C1 shows, the roller surface temperature decreases.
The temperature gradually recovers from around 60°C and is maintained at approximately 170°C. In the case of single color, the control temperature is 150℃, so curve C
As shown in No. 2, the temperature decreases to around 150°C. Taking advantage of the slow thermal response due to the low thermal conductivity of the silicone rubber layer, heater 1 was heated to 155°C, which is +5°C from the set temperature.
When the roller is turned on at a temperature of 150±1°C, the temperature of the roller surface can be controlled to 150±1°C.

Since the set temperature during image formation in the case of monochrome is set low, the temperature of the roller surface increases due to a delay in thermal response after image formation is completed, but the overshoot amount OS after completion of fixing is the same as before. Lower than the amount shown in Figure 5, even in the case of a single color, the temperature is 180°C on the roller surface and 200° on the core metal surface.
I was able to hold down.

In the above example, the fixing temperature is set at 170°C during standby, but if the temperature during standby is controlled to be low during full color, 170°C during full color, and 160°C during monochrome, image formation will start. The decrease in roller surface temperature during standby is low, and there is an advantage that the difference in image gloss between the first sheet and the fifth or sixth sheet during continuous copying can be small.

When the relationship between the surface temperature of the fixing roller and the glossiness of the toner image was determined, the results shown in FIG. 4 were obtained. It has been found that there is a correlation that the higher the surface temperature of the fixing roller, the higher the gloss. Therefore, in order to obtain a predetermined level of gloss, it is preferable to perform fixing using a narrow temperature range as the surface temperature of the fixing roller.

[0024]

[Effects of the Invention] According to the present invention, the standby temperature can be switched between monochrome mode and full color mode in consideration of the surface temperature drop at the start of copying, and furthermore, during image formation, the control temperature can be changed to monochrome mode in consideration of the difference in toner amount. By switching between the image forming mode and the full color mode, it was possible to prevent the rubber of the fixing roller from peeling off, reduce overshoot after image formation, and prevent offset due to overshoot. By making the conveyance speed of the image forming section and the fixing section the same, the fixing device can be moved closer to the image forming section, saving space and making it possible to downsize the device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a state in which a fixing roller has a nip shape facing downward.

FIG. 2 is a diagram showing a nip shape of the fixing roller in an upwardly facing state.

FIG. 3 is a diagram showing changes in the surface temperature of the fixing roller in the fixing device according to the present invention.

FIG. 4 is a diagram showing the relationship between fixing roller surface temperature and toner glossiness.

FIG. 5 is a diagram showing changes in the surface temperature of a fixing roller when a conventional fixing device is used for a single color.

[Explanation of symbols]

1 Heating means 2 Fusing roller 3 Pressure roller 4 Thermistor

Claims (2)

[Claims] [Claim 1] Fixing in a color image forming apparatus in which a separated color image is formed on one latent image carrier, transferred onto recording paper in layers, and fixed by a heating fixing roller rotating at the same linear speed as the latent image carrier. The device is characterized in that the surface temperature of the fixing roller during standby and image formation can be switched between full color and single color, and the surface temperature during single color is set lower than when full color. Fixing device for color image forming apparatus. 2. The heating means for the fixing roller is set to operate when the temperature of the latent image bearing member is +5° C. when the surface temperature falls during monochrome printing. Item 1. A fixing device for a color image forming apparatus according to item 1.