JPH11282297A - Thermal fixing roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal fixing roller capable of suppressing the abnormal heating of its both end parts when temperature rapidly rises and having uniform temperature distribution even in a steady state. SOLUTION: This thermal fixing roller is constituted so that heating resistors 5 having a positive resistance temperature coefficient are serially disposed in the inside or at the inside surface of the roller 1. Then, the heating density of both end parts of the roller 1 are higher than that of the central part and the resistance temperature coefficients of the heating resistors A disposed at both end sides of the roller 1 are larger than those of the heating resistors B disposed at the central part. Besides, the volume resistance values of the resistors A are lower than those of the resistors B at the room temperature and higher than them at the heating temperature in the steady state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing roller provided with a resistance heating element capable of rapidly increasing the temperature and heating the entire area of the heater to a constant temperature during the temperature increase. It is suitable as a heat fixing roller used in an electronic copying machine or the like.

[0002]

2. Description of the Related Art In a copying machine, a heat fixing roller for applying pressure and heat to predetermined copy paper to fix toner on the copy paper is used. Such a roller is, for example, shown in FIG.
As shown in FIG. 2, in order to heat the surface of the roller 1 uniformly, a belt-shaped heating resistor 5
Are spirally disposed. When the pitch of the strip-shaped heating resistors 5 is exactly the same over the entire length of the roller 1, the heat at both ends A of the roller 1 is more easily dissipated than at the center A. There is a phenomenon that it is lower than the part.

In order to eliminate such non-uniformity of the surface temperature, the pattern of the heating resistor 3 is designed so that the pitch at both ends A is smaller than that at the center B of the roller. Thus, it has been proposed that the lowering of the surface temperature at the both end portions A of the roller is eliminated and the surface temperature distribution of the heat fixing roller is made uniform.

[0004] On the other hand, the fixing roller should be able to quickly heat up the surface temperature of the heater after turning on the power so that the copying operation can be performed immediately upon starting of the copying machine. It is desired that the residual heat time can be shortened.

[0005]

In the above-mentioned heat fixing roller, since the heat generation density at both ends is higher than that at the center, the surface temperature distribution of the roller is uniform in a steady state,
In the heating process, the temperature at both ends tends to be higher than that at the center.

[0006] Since this tendency becomes more remarkable as the temperature is increased by applying a large amount of electric power, when the temperature is rapidly increased, the temperature due to abnormal heating at both ends is attached to the end of the roller. There has been a problem that the temperature becomes higher than the heat resistant temperature of parts such as a resin gear for driving the rotor, and these parts are damaged. Therefore, conventionally, the heating rate of the heater has to be slowed so that the temperature at both ends does not exceed a prescribed temperature at the time of heating.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a heat fixing roller which suppresses abnormal heating at both ends of the roller against rapid temperature rise and has a uniform temperature distribution even in a steady state. It is.

[0008]

The inventor of the present invention has conducted various studies on the above-mentioned problems, and as a result, has arranged a heating resistor having a positive temperature coefficient of resistance in series inside or inside the roller. Wherein the heat generation density at both ends of the roller is higher than that at the center, and the resistance temperature coefficient of the heating resistor (A) disposed at both ends of the roller is at the center. The heating resistor (A) has a volume resistivity at room temperature lower than that of the heating resistor (B), which is larger than the temperature coefficient of resistance of the provided heating resistor (B), and the heating temperature in a steady state. It has been found that the above object can be achieved by controlling the volume specific resistance of the heating resistor (A) to be higher than that of the heating resistor (B).

In the above roller, the heat generating resistor is spirally disposed inside or on the inner surface of the roller, and the pattern pitch between the heat generating resistors at both ends of the roller is set at the center of the heat generating resistor. It is desirable that the pitch be smaller than the pattern pitch between them.

[0010]

Generally, in an electric circuit in which resistors having a positive temperature coefficient of resistance are arranged in series, when a constant voltage is applied to both terminals of the circuit, the heat value of each part is proportional to the temperature of that part.

According to the present invention, a heating resistor (A) having a large temperature coefficient of resistance is disposed at both ends having a high heat density in a steady state, and a heating resistor (A) having a small temperature coefficient of resistance is disposed at a center portion having a low heat density. Place B). Further, the heating resistor (A) and the heating resistor (B) have a lower volume specific resistance at room temperature than the heating resistor (B), and the heating temperature in a steady state. Are such that the volume resistivity value of the heating resistor (A) is higher than that of the heating resistor (B).

Thus, when the roller surface temperature is low immediately after energization, the temperatures at the center and both ends are equal according to the volume specific resistance value of each resistor and the pitch difference between the heating resistors at a low temperature. Further, as the temperature rises, the heat density at both ends becomes larger than that at the center, and when the temperature reaches a steady state, the surface temperature distribution of the roller ends up at the heat density that should be uniform.

As a result, as compared with the case where the entire roller is made of a resistor having the same temperature coefficient of resistance, the rapid temperature rise immediately after the energization prevents a sharp rise in temperature at both ends, and the thermal fixing also occurs in the steady state. The surface temperature distribution of the roller can be kept uniform.

[0014]

FIG. 1 is a schematic sectional view showing an example of a heat fixing roller according to the present invention. According to FIG. 1, a substrate 2 of the heat fixing roller 1 is made of a cylindrical metal member such as aluminum, and a release coating 3 such as Teflon is formed on an outer surface thereof. On the other hand, a cavity is formed in the base material 2, an insulating layer 4 is formed on the inner wall surface, and a heating resistor 5 is formed on the surface of the insulating layer 4.
Are formed.

A metal support shaft 6 is provided at one end of the heat fixing roller 1, and a metal drive shaft 7 serving also as a support shaft is provided at the other end of the roller base 2. Fitted on the inner surface. Further, a resin gear 8 for transmitting rotational torque is attached to the drive shaft 7. Further, the support shaft 6
The drive shaft 7 is electrically connected to the heating resistor 5 provided on the inner surface of the roller, and both the support shaft 6 and the drive shaft 7 also serve as electrode terminals.
The power is supplied to the heating resistor 5 via the slip ring 9, the support shaft 6, or the drive shaft 7.

The heating resistor 5 is moved linearly along the central axis 11 by a thermal spray gun 10 or the like while rotating the roller base 2 at a constant speed with respect to the central axis as shown in FIG. A resistance material such as stainless steel, nickel, aluminum, or tungsten paste to the insulating layer 4
Spiral is formed by spraying on the surface of
The pattern pitch and thickness between the heating resistors 5 can be easily controlled by the linear moving speed of the spray gun 10 at this time.

According to the present invention, the roller surface temperature at both ends is lower than that at the center due to the difference in heat dissipation between the center and both ends of the roller 1, so that the roller surface temperature becomes uniform in a steady state. Thus, the heat generating resistor 5 is formed such that the heat density of the roller end portions A is higher than that of the central portion B.

More specifically, as shown in FIG. 2, by reducing the linear movement speed of the spray gun 10 at both ends A, the pattern pitch between the heating resistors at both ends A of the roller is reduced to the center B. Are formed so as to be smaller than the pattern pitch between the heating resistors. The pitch P ₁ in the roller central portion at this time, the pitch P ₂ of the opposite end portions, in consideration of the heat generation density of the central portion and both end portions 0.
It is set to 5P ₁ ~0.95P _1.

According to the present invention, both end portions A of the roller are provided.
And the roller central portion B are formed of different heat generating resistors, and the temperature coefficient of resistance of the heat generating resistor (A) disposed at both ends A of the roller is determined by the heat generating resistor (B) disposed at the central portion B. )
, The volume resistivity at room temperature is lower than that of the heating resistor (B), and the volume resistivity at a heating temperature in a steady state. However, the heating resistor (A) is set to be higher than the heating resistor (B).

The resistor (A) having a large temperature coefficient of resistance.
Is desirably applied to both end regions where the temperature drop due to heat dissipation is large in a steady state, in other words, to both end regions formed so that the pattern pitch is smaller than the central portion. It is appropriate that the length of one side of the both ends B is equivalent to 3 to 20% of the entire length L of the roll.

A resistor (A) having a large temperature coefficient of resistance
For example, the material of the resistor (B) forming the central portion may be changed to a material having a large temperature coefficient of resistance that is completely different from the material of the resistor (B) forming the central portion, or the temperature coefficient of resistance of the resistor (B) forming the central portion may be changed Can be easily controlled by mixing an appropriate amount of nickel, rhenium, or the like having a large value.

In the above example, the heating resistor 5 is
Although the heating resistor 5 is formed on the inner surface of the cylindrical roller, the heating resistor 5 is not limited to this, and may be a structure buried inside an insulating base material.
This is not limited to thermal spraying with a thermal spray gun. It is also possible to change the thickness, and in those cases, the heating resistors at both ends may be formed of a material having a large temperature coefficient of resistance.

[0023]

EXAMPLE: Length 320 mm, diameter 40 mm, wall thickness 1.4
An insulating layer made of polyimide was formed on the inner surface of a cylindrical substrate made of aluminum having a thickness of 1 mm, and a heating resistor was formed in a spiral shape on the surface of the insulating layer by thermal spraying. At this time, two types of heating resistors having the characteristics shown in Table 1 were used, and a heating resistor (B) having a small temperature coefficient of resistance (TCR) was formed at a central portion at a pattern pitch of 15 mm. In both end regions of 50 mm from the portion, a resistor (A) having a large temperature coefficient of resistance was used and formed at a pattern pitch of 10 mm. The thickness of each heating resistor was 5 μm, and the line width was 3 mm. FIG. 3 shows resistance temperature curves of the two types of heating resistors shown in Table 1.

[0024]

[Table 1]

Further, as a conventional example, the heating resistor is formed in exactly the same manner as described above except that the heating resistor (B) having only a small temperature coefficient of resistance is formed at both the center and both ends of the roller. Thus, a heat fixing roller was manufactured.

When a voltage of 200 V is applied to the two heat fixing rollers from the initial temperature of 25 ° C. for 2.25 seconds, the applied voltage is reduced to 24 V to saturate the temperature. 4 (present invention) and FIG. 5 show the change in the temperature of the roller surface at each point with respect to the time after voltage application.
(Conventional product).

As is clear from the results shown in FIGS. 4 and 5, the conventional heat fixing roller showed a uniform temperature distribution in the steady state, but the central part after 2.25 seconds after the rapid temperature rise. Is as large as 18 ° C and the temperature at the end is 1
Above 73 ° C and 170 ° C (temperature in a steady state), it was found that abnormal heating occurred.

On the other hand, in the heat fixing roller of the present invention, even at the time of rapid temperature rise of 2.25 seconds, the temperature difference from the center is as small as 5 ° C., and the temperature at the end is 170 ° C. (steady state). ), Which was within an acceptable range. Further, the temperature distribution in the steady state also had a uniform distribution from the center to both ends.

[0029]

As described in detail above, according to the present invention,
By using at least two types of resistors with different temperature coefficient of resistance and a specific resistance value for the heating resistor inside the roller, abnormal heating at both ends of the roller against rapid temperature rise is suppressed and steady It is possible to provide a heat fixing roller having a uniform temperature distribution even in the state.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view according to an example of a heat fixing roller of the present invention.

FIG. 2 is a schematic diagram for explaining an example of a method of forming a heating resistor in the heat fixing roller of the present invention.

FIG. 3 is a diagram showing a temperature curve of resistance of a heating resistor used in an example of the present invention.

FIG. 4 is a diagram showing a temperature distribution at the time of rapid temperature rise by the heat fixing roller of the present invention.

FIG. 5 is a diagram showing a temperature distribution at the time of rapid temperature rise by a conventional heat fixing roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat fixing roller 2 Base material 3 Release coating 4 Insulating layer 5 Heating resistor 6 Support shaft 7 Drive shaft 8 Resin gear 9 Slip ring 10 Thermal spray gun 11 Central shaft

Claims (2)

[Claims] 1. A heat-fixing roller in which heat-generating resistors having a positive temperature coefficient of resistance are arranged in series inside or on an inner surface of a roller, wherein the heat density of both ends of the roller is higher than that of a central portion. In addition, the temperature coefficient of resistance of the heating resistor (A) disposed at both ends of the roller is larger than the temperature coefficient of resistance of the heating resistor (B) disposed at the center, and the volume specific resistance at room temperature. The value of the heating resistor (A) is lower than that of the heating resistor (B), and the volume specific resistance at a heating temperature in a steady state is higher than that of the heating resistor (B). ), A heat-fixing roller characterized by high 2. The heating resistor is spirally disposed inside or on an inner surface of a roller, and a pattern pitch between the heating resistors at both ends of the roller is larger than a pattern pitch between the heating resistors at a central portion. 2. The heat fixing roller according to claim 1, wherein the heat-fixing roller is also small.