JPH02230175A - Fixing device - Google Patents

Abstract

PURPOSE:To decrease the pressure difference between the edge parts and the central part of a roller and to make fixing property uniform by forming a heat fixing roller so that its outer diameter is the prescribed length or below and the peripheral shape of a cross-section is linear, and forming a pressure roller so that the peripheral shape of a cross-section is formed in a crown shape which has the diameter difference having the fixed length or above between the central part and the edge parts. CONSTITUTION:In the heat fixing roll 1, its outer diameter is <=25mm and the peripheral surface of the cross-section including an axial line is formed with straight lines. The pressure roll 2 is formed so that its outer diameter is formed in a crown shape which has the diameter difference h/2 >=50mum between the central part and the edge parts. Therefore, the radius of the roll 1 is identical in the central part and the edge parts, and the feeding velocity of a transfer paper is identical to prevent paper from wrinkles. In addition, the pressure difference between the central part and both edge parts is minimized, so that fixing property is made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device used in a copying machine or printer using electrophotography.

[Prior Art] Such a fixing device includes a heat fixing device that rotates a heat fixing roller and a pressure roller in pressure contact with each other, and conveys a transfer material having an unfixed 1-toner image under pressure between both rollers to fix the image. or conventionally widely known. This heating constant device is constructed as shown in FIG. 2 of the accompanying drawings.

In the figure, reference numeral 8 denotes a fixed roller, in which the surface layer of a hollow core metal 6 made of aluminum or iron is coated with a resin layer of PTFE or PF8 or coated with a material such as silicone rubber. A heater 3 such as a halogen lamp is housed in the hole to heat the fixing roller 8.

On the other hand, 9 is a pressure roller with a core metal such as iron or stainless steel.
O is coated with an elastic body 7 having type III properties such as silicone rubber. The above fixed roller 8 and pressure roller 9
They are pressed together by means such as springs (not shown). A temperature measuring element (not shown) such as a thermistor is placed in contact with the outer peripheral surface of the fixing roller 8 .
It is designed to detect the temperature of Depending on the temperature detected by the thermistor, a temperature control circuit (not shown) or energization of the heater 3 is controlled to control the surface temperature of the fixing roller 8 to a predetermined value.

In medium-speed machines and high-speed machines, the cross-sectional shape of the fixing roller mentioned above has a maximum outer diameter of 60 mm or more and a diameter of 10 {)μ.
More than m. It has an I- inverted crown shape. The pressure roller has a maximum outer diameter of 60 m or more and a linear cross-sectional shape.

[Problem to be solved by the invention] Fixing devices are also becoming smaller in small and low-speed machines. Therefore, if only the diameters of the fixing roller and pressure roller are reduced and their shapes are made as in the conventional example mentioned above, for example, the outer diameter of the heated fixing roller is 20.00 ms at the center and 20.00 ms at the ends. 120g of inverted crown hanging for 12 servings
m, and the outer diameter of the pressure roller that comes into pressure contact with it is 16cm (
A problem will arise if the plate has a linear shape with a wall thickness of 3 mm.

Even if the heat-fixing device roller has a straight shape, the pressure roller usually receives the pressure contact force against the heat-fixing roller at both ends, so the contact pressure is applied more towards the center than at both ends. There is a tendency that the contact pressure distribution is not uniform in the axial direction. In addition to this, if the heat fixing roller is made into an inverted crown shape as shown in item 12, the difference in pressure between the edges and the center becomes even larger, and the roller as described above has a nip difference of more than 1 mm. Therefore, even if pressure is applied to the roller to obtain good fixing properties at the edges, the center part is not fixed at all.

In addition, in order to solve this problem, we need to provide good fixation in the center area.
When you apply enough pressure to get tt, a small boy like this! It also had drawbacks such as requiring a high torque that the machine could not handle, which could cause gears to slip out of alignment or be damaged.

Furthermore, when using such a small diameter roller, A
4.When passing one sheet vertically (approximately 300 mm), the heat fixing roller rotates about 5 times, so there is a paper feed misalignment of about 2 mm at the center and edges, and as a result, the transfer paper There was also the problem of wrinkles at the edges.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that reduces the pressure difference between the ends and the center of the roller to achieve uniform fixing performance, and also solves the problem of paper wrinkles caused by differences in feed speed.

[1000 Steps to Solve the Problems] According to the present invention, the 12th object is to transfer an unfixed toner image to a nip formed by a heat fixing roller and a pressure roller that rotates in pressure contact with the heat fixing roller. In the fixing device that fixes the unfixed toner image onto the transfer material by passing the toner image through the transfer material, the outer diameter of the heating fixing roller is 25 mm or less, and the circumferential shape of the cross section in the plane including the axis is a straight line. None, this is achieved because the pressure roller has a circumferential shape in cross section in a plane including the axis, or a crown shape with a difference in diameter of 50 JLm or more between the center and the ends.

[Function] According to the present invention, since the heat fixing roller has a linear outer circumferential surface whose surface deformation is generally less than that of the pressure roller, the diameter of the central portion and the end portions are the same. The peripheral speed at which the transfer paper is fed is also the same. However, the paper does not wrinkle due to feeding.

In addition, since the crown shape is such that when pressure is applied at both ends of the pressure roller, the diameter becomes larger at the center, there is a difference in pressure contact between the center and both ends, which tend to press strongly. It won't come out.

[Embodiments] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

Figure 1 (A). (B) is a sectional view and a side view showing the general configuration of the device of this embodiment. In the figure, the heating fixing roller l has an outer diameter of 20.00 m, a wall thickness of 211 m, and has a straight outer peripheral surface in a cross section including the axis.

On the other hand, the pressure roller 2 that rotates in pressure contact with the heating roller is
It has a crown shape with an outer diameter of 161mm at the center and 15.95mm at the ends, with a diameter difference of 50μ, and the thickness of the silicone rubber at the center is 311111mm.

The base material of the roller, the layer structure formed thereon, their materials, and other incidental parts are the same as in the conventional example of No. 211Sj, so repeated explanation here will be omitted. In addition, the process speed (transfer paper conveyance speed) is 25
mmlsec, the rotational drive of the fixing device is done by the fixing roller, and the rotational speed of the fixing roller is approximately 20 mm/sec. OO
1 is set so that the speed is exactly equal to the above process speed.

The device of this embodiment is as described above, and for comparison purposes, a test was conducted with the conventional device shown in FIG. 3, so this will be explained here. Note that roller Jl is fixing roller 6
The outer diameter is 20.00tm at the center and 20.00tm at the ends.
．． The diameter of the pressure roller was 16 mm (wall thickness: 3 II m). The total pressure P applied between the rollers is 5 kg, the temperature control temperature T of the fixing heating roller is 16 {1℃, and the silicone rubber used for the pressure roller is 10' (JI
S-A).

In such a system, the nip width (circumferential length of the pressure welding part)
is 1.5ms at the center, 2.7+s+s at the ends, and 1.5ms between the two. There is a difference in Zysm, low temperature (10'c)
Looking at the fixation rate (=density after rubbing with a weight etc./original density), the fixation rate was good (90% or more) at the edges, or 60% or more at the center. This will cause problems with the image. In order to improve the constant-II rate at the center, the controlled temperature was raised to 170°C, but this resulted in high temperature offset (a phenomenon in which toner adheres to the fixing roller) at the edges. Therefore, I tried to test the fixing rate by increasing the total pressure between the rollers to 7 kg while keeping the temperature control as it was.In this case, the torque acting on the fixing device became extremely high, and has been damaged. In order to improve this problem, the motor and gears must be replaced with high-strength ones that can withstand more torque, which is an inappropriate measure for small machines where cost is an important consideration. If this is graphed, it will look like Figure 3. Unless the above gear is improved, a good fixing rate can be obtained in the center and the edges (range A (condition)) and a good fixing rate can be obtained in the edges. The overlapped area with range B is small. Also, in terms of transportability, if you use transfer paper that is not stiff, A4
The feed rate for one sheet is approximately 2 am/s at the center and edges.
Since the EC is also different, the transfer paper ends up being folded and wrinkled when being transported.

Next, in the case of the present embodiment, using the fixing roller and pressure roller described above as shown in FIG. 1
When the nip radius and fixation rate were investigated for 'C', the nip width was 2.2+ss at both the center and the ends, and there was no difference at all. The fixation rate is 85% for both the center and edges.
It has a relatively high fixation rate and does not disturb the image.

In terms of transportability, there are no creases like in the conventional example. This is because the fixing device is driven by the fixing roller, so as long as a linear roller is used, there is no difference in the feeding speed of the transfer paper between the center and the edges, and since the pressure roller is crown-shaped, the nip This is due to the fact that the applied pressure is no longer different between the center and the ends.

[Effects of the invention] As explained below, by making the small-diameter fixing roller in a straight shape and the pressure roller in a crown shape in a fixing device used in a small, low-speed machine, it is possible to achieve sufficiently excellent fixing performance and conveyance performance. The town became interested in providing an inexpensive fixing device.

[Brief explanation of the drawing]

FIG. I(A) shows l! of the apparatus according to the present invention. 1(B) is a side view of the device shown in FIG. 1(A), and FIG. 2 is a sectional view showing the main components of the device. FIG. 3 is a sectional view showing the main components, and FIG. 2 is a diagram showing the fixing performance of the apparatus.

Claims (1)

[Claims] The unfixed toner image is transferred onto the transfer material by passing the transfer material having the unfixed toner image through a nip formed by a heating fixing roller and a rotating pressure roller that comes into contact with the heat fixing roller. In the fixing device for fixing, the heating and fixing roller has an outer diameter of 25 mm or less, the circumferential shape of the cross section on the plane including the axis is a straight line, and the pressure roller has a circumferential shape of the cross section on the plane including the axis. A fixing device characterized in that its surface has a crown shape with a diameter difference of 50 micrometers or more between the center and the ends.