JPH06242695A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain the fixed image with high quality and reliability by sufficiently securing the contact area on the central part in the longitudinal direction of a fixing rotary body with a pressurizing rotary body, with a simple constitution. CONSTITUTION:This fixing device is composed of the fixing rotary body having a heat source such as a halogen lamp inside, the pressurizing rotary body 4 arranged opposite to the fixing rotary body and forming the contact area by constant pressing force and a thermosensitive element such as a thermistor coming into contact with the fixing rotary body and detecting the temperature of the surface and the pressurizing rotary body 4 is composed of the solid elastic layer 4a of a silicone rubber, etc., having a uniform outside diameter in the longitudinal direction and a core metal 4b worked to be the outside diameter on the central part smaller than that on both end parts.

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 a copying machine or an electrophotographic printer.

[0002]

2. Description of the Related Art Conventionally, in a fixing device of an image forming apparatus such as a copying machine or a printer to which an electrophotographic technique is applied, a fixing rotary member which is heated by radiant heat such as a halogen lamp provided therein and a fixing rotary member Then, the transfer material holding the unfixed toner image is nipped and conveyed by a pressure rotating body that presses with a constant pressure, thereby fixing the toner image on the transfer material.

A conventional image forming apparatus will be described below. FIG. 4 is a cross-sectional view of a fixing device of a conventional image forming apparatus, and FIG. 5 is an enlarged view of a pressure rotator constituting the fixing device of the conventional image forming apparatus. In FIGS. 4 and 5, a fixing device 1 has a heat source 2 of a halogen lamp inside and a transfer material 18
A fixing rotator 3 for fixing the unfixed toner 12 above
And the elastic layer 25a and the cored bar 25b having a uniform outer diameter, which presses the transfer material 18 against the fixing rotator 3 in a pinching manner, and the pressing rotator 25. The heat-sensitive element 5 such as a thermistor for detecting the temperature is included, and the incident guide 6 that guides the transfer material 18 between the fixing rotating body 3 and the pressing rotating body 25. The fixing rotator 3 maintains the surface temperature at a constant temperature by the control means based on the temperature detection value from the thermosensitive element 5, while the unfixed toner 12 on the transfer material 18 is kept.
Is fixed by the incidence guide 6 to the fixing rotator 3 and the pressure rotator 25.
And is output as a fixed image.

[0004]

However, in the above-mentioned conventional configuration, the elastic layer 25a of the pressing rotary member 25 has the outer diameter φ1.
A solid silicone rubber, which is a soft material having a rubber hardness of about 15 ° and a diameter of 5 mm, has an outer diameter of 20 mm and a wall thickness of 1.
When the unfixed toner 12 on the transfer material 18 is fixed with a 5 mm aluminum alloy steel using a 400 w halogen lamp as the heat source 2 and a process speed of 20 to 30 mm / s, pressure rotation is performed. When the total pressing force of the body 25 on the fixing rotator 3 is about 3.5 kgf, if the outer diameter of the core metal 25b of the pressure rotator 25 made of stainless steel or the like is set to φ8 mm or less,
The minimum required contact area area with the fixing rotary member 3 can be secured at both ends, but the required minimum contact area area cannot be secured due to the bending of the core metal 25b of the pressing rotary member 25 at the central portion, and continuous printing or solid black printing is possible. As a result, there is a problem that fixing failure occurs in the print center, and the function required for the fixing device of the image forming apparatus cannot be fully satisfied.

Even if the pressing force applied to the fixing rotary member 3 is increased to solve the above problem, the torque of the fixing device 1 is increased and the output torque of the drive motor for rotating the pressurizing rotary member 25 is increased. However, there is a new problem such as an increase in the size of the device, an increase in the size of the device body, and an increase in cost.

The present invention solves the above-mentioned problems and ensures a high quality and reliability by ensuring the minimum area of the fixing rotator and the pressure rotator required to obtain a fixed image with a simple structure. An object of the present invention is to provide an image forming apparatus having high property.

[0007]

SUMMARY OF THE INVENTION To achieve this object, the present invention provides a rotating roller made of metal that constitutes the core of a pressure roller of a fixing device so that the outer diameter of the central portion is smaller than the outer diameters of both end portions. did.

[0008]

According to the present invention, due to the above structure, the contact area of the fixing roller and the pressure roller can be sufficiently secured even in the central portion.

[0009]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of an image forming apparatus according to a first embodiment of the present invention. In FIG.
Reference numeral 7 denotes an image carrier having an inorganic or organic photoconductive layer provided on a conductive drum substrate, which is rotatably supported by a support shaft 8. The corona discharge of the charger 9 causes uniform negative charge on the surface. Granted. A desired electrostatic latent image is formed on the image carrier 7 to which this negative charge is applied by the light emitted from the LED print head 10. Reference numeral 11 denotes a process cartridge, which includes a detachable and replaceable toner cartridge 13 for containing a heat-melting toner, a supply roller 14 and agitator 15 for supplying and stirring toner.
It is composed of a developing roller 16 and an image carrier 7. The toner supplied from the toner cartridge 13 is thinned on the surface of the developing roller 16, and the electrostatic latent image on the image carrier 7 is developed by the toner. On the other hand, the transfer material 18 supplied from the paper feed tray 17 is transferred to the transfer roller 21 and the image carrier 7 via the conveyance path 20 by the half-moon shaped paper feed roller 19.
And the toner image on the image carrier 7 is transferred to the transfer material 18
Transcribed on.

The transfer material 18 on which the toner image is transferred has a fixing rotating body 3 having a halogen lamp as a heat source 2 therein.
A pressure rotator 4 which is disposed opposite to the pressure rotator 4 and has a contact area by a certain pressing force; a thermosensitive element 5 such as a thermistor which contacts the fixing rotator 3 to detect the surface temperature; and a transfer material 18.
The unfixed toner image is fixed on the transfer material 18 after passing through the fixing device 1 composed of the incidence guide 6 for guiding between the fixing rotating body 3 and the pressure rotating body 4, and the discharge roller pair 22 Is discharged to the discharge tray 23.

FIG. 2 is an enlarged view of the pressure rotator 4 constituting the fixing device 1 of the image forming apparatus according to the first embodiment of the present invention. The pressure rotator 4 includes an elastic layer 4a and a cored bar 4b. It is configured. The elastic layer 4a is made of a solid elastomer such as silicone rubber having a uniform outer diameter D over the length L in the longitudinal direction. On the other hand, the core metal 4b is processed so that the outer diameter d2 of the central portion is smaller than the outer diameter d1 of both end portions.

In practice, the pressure rotary member 4 shown in FIGS.
The elastic layer 4a has a length L of 222 mm and an outer diameter of φ15.
15 ° a rubber hardness in mm, metal core 4b is a stainless steel or free-cutting steel in φ8mm outer diameter length l ₁ of the both end portions in 59 mm, a length l ₂ of the central portion outer diameter at 104 mm 7 mm in diameter The fixing rotator 3 is made of aluminum alloy steel having an outer diameter of 20 mm and a wall thickness of 1.5 mm, and the heat source 2 is a halogen lamp of 400 w, which constitutes the fixing device 1 and is used under the condition of a process speed of 20 to 30 mm / s. In this case, even if the total pressing force of the pressure rotator 4 against the fixing rotator 3 is 3.5 kgf or less, the contact area area formed by both rotators is maintained in the central portion in the longitudinal direction without being significantly reduced. The unfixed toner image on the transfer material 18 can be sufficiently fixed regardless of the mode and the print pattern.

(Embodiment 2) FIG. 3 is an enlarged view of a pressure rotating body which constitutes a fixing device 1 of an image forming apparatus according to a second embodiment of the present invention. The shape of a core metal 24b of the pressure rotating body 24 is shown in FIG. The outer diameter is d1 at both ends, and the outer diameter is d2 at the center (d1> b2)
The same effect can be obtained by forming the elastic layer 24a so that the outer diameter D becomes uniform over the length L in the longitudinal direction by processing into an inverted crown shape such that

As described above, according to the first and second embodiments, the pressure bar 4 or the core metal 4 of the pressure bar 24 is used.
By making the outer diameters of b and 24b smaller in the central portion in the longitudinal direction than in both end portions, it is possible to secure a sufficient contact area area with the fixing rotary member 3 also in the central portion.

[0015]

As described above, according to the present invention, the outer diameter of the central portion of the rotating roller made of metal which constitutes the core of the pressure roller of the fixing device is made smaller than the outer diameters of the both end portions. Also in this case, since the contact area area between the fixing roller and the pressure roller can be sufficiently secured, it is possible to obtain a high quality and highly reliable fixed image without fixing failure.

[Brief description of drawings]

FIG. 1 is a sectional view of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a pressure rotating body that constitutes the fixing device of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is an enlarged view of a pressure rotating body that constitutes a fixing device of an image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a fixing device of a conventional image forming apparatus.

FIG. 5 is an enlarged view of a pressure rotating body that constitutes a fixing device of a conventional image forming apparatus.

[Explanation of symbols]

 1 Fixing Device 3 Fixing Rotating Body 4 Pressurizing Rotating Body 4a Elastic Layer 4b Core Bar 18 Transfer Material 24 Pressurizing Rotating Body 24a Elastic Layer 24b Core Bar

Claims (2)

[Claims] 1. A transfer material comprising a fixing roller having an internal heat source for fixing an unfixed toner image adhered to a transfer material, a rotating roller made of metal, and an elastic body covering the rotating roller. An image forming apparatus comprising: a fixing device having a pressure roller that is pressed against a roller and nipped and conveyed; and an outer diameter of a central portion of the rotating roller is smaller than outer diameters of both end portions. 2. The image forming apparatus according to claim 1, wherein the rotating roller has an inverted crown shape.