JPH08286537A - Heat generating resistor and heater for fixing device of electrophotographic printer - Google Patents

Abstract

PURPOSE: To provide a heat generating resistor in which the temp. rising speed of the heater is increased to reduce the rising time to a stabilized temp. and to provide a heater for a fixing device of an electrophotographic printer using this resistor. CONSTITUTION: This heat generating resistor is produced by mixing a base resin and a conductive powder and has a temp. controlling function. The resin contains a Ti2 O3 powder and a conductive powder having <=4×10<-5> Ω.cm resistivity as a conductive powder. As for the conductive powder having <=4×10<-5> Ω.cm resistivity, at least one kind of powder of RuO2 , Ag, Cu and Ni is used. The obtd. heat generating resistor is used as a heater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat generating resistor having a temperature adjusting function, and more particularly to a heat generating resistor having a rapid temperature rise and a heater for an electrophotographic printer fixing device using the heat generating resistor.

[0002]

2. Description of the Related Art Conventionally, as a technique related to a heating resistor having a temperature adjusting function, for example, Japanese Patent Publication No. Sho 61-35223.
Is disclosed in Japanese Patent Application Laid-Open Publication No. HEI 9-203 (1995). This technology discloses a composite material in which a conductive metal, a conductive oxide, carbon black, etc. are mixed with a resin (polyimide, etc.). According to this composite material, a heating resistor formed using this It is said that the temperature dependence of the resistance value of 1 depends largely on the thermal expansion coefficient of the resin (polyimide or the like) as the base material. That is, at room temperature, the resistance network is formed by the contact of the conductors in the base material, but as the temperature rises, the distance between the conductor powders increases due to the thermal expansion of the base material, and the contact between the powders in the resistance network is eliminated. This is because the number of resistance networks will decrease and the number of resistance networks will decrease.

Since the number of resistance networks decreases as the temperature rises, the resistance value of the heating resistor made of the composite material increases with the temperature rise. As a result, PTC characteristics (Positive Temperature Coefficien
t). The PTC characteristic means that the coefficient of resistance value change with temperature is positive, that is, the resistance increases as the temperature rises. By the way, when a voltage is applied to the heating resistor and its temperature rises due to heat generation (Joule heat) of the resistor, the resistance of the resistor rapidly increases and becomes a high resistance. Since it is limited, the temperature control function of stabilizing the temperature of the resistor at a certain temperature is exhibited in this resistor.

[0004]

However, although the heater using the heating resistor has a temperature adjusting function, it is necessary to shorten the time (rise time) until the temperature reaches a stable temperature, as will be described below. There is a problem that you cannot do it. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heating resistor capable of speeding up the temperature rise of a heater and shortening the rise time to a stable temperature, and using the heating resistor. Another object of the present invention is to provide a heater for an electrophotographic printer fixing device.

[0005]

Means for Solving the Problems The inventors of the present invention have earnestly studied to solve the above-mentioned problems, and as a result, have obtained the following findings. Generally, the relationship of the following formula (1) is established between the electric energy applied to the heating resistor and the temperature rise of the heating resistor.

[Equation 1] IVdt = HdT + D (T−Troom) dt (1) IVdt; electric energy entering the heating resistor within dt time, HdT; thermal energy spent for raising the temperature dT of the heating resistor , D (T-Troom) dt; heat dissipation amount lost from the heating resistor of temperature T in dt time D: dissipation coefficient (W / K), T; temperature of heating resistor (K), Troom; heating resistance Ambient temperature of the body (room temperature) (K). Then, the temperature rising rate of the heating resistor is expressed by the following expression (2) from the expression (1).

## EQU00002 ## dT / dt = [IV-D (T-Troom)] / H (2)

[0006] Here, when the temperature stabilizes after a sufficient time has elapsed, the temperature rise of the heating resistor stops, and in that case dT
Since / dt = 0, IV = D (T-Troom) and the input electric energy and the heat dissipation amount are equal. For voltage constant, the input energy of the heating resistor is determined by V ² / R (T), hence V ² / R (T)
Since = D (T-Troom), the temperature dependence of the resistance value determines the temperature T when the temperature is stable.

FIG. 5 is a graph showing the temperature dependence of the relationship between the temperature of the heating resistor and the voltage application time. Further, FIG. 6 is a graph showing the temperature dependence of the relationship between the input energy [V ² / R (T)] and the heat dissipation amount [D (T-Troom)]. As the heating resistor used for the measurement,
Ru on epoxy resin (PR-52; manufactured by Ciba-Gaiki)
O ₂ powder [ruthenium (IV) oxide] was mixed with epoxy resin:
A heating resistor prepared by mixing RuO ₂ powder = 69 wt%: 31 wt% was used.

From FIG. 5, the stable temperature (saturation temperature) rises as the applied voltage rises (120 ° C. at 20 V, 1 at 40 V).
It can be seen that the temperature is 65 ° C and 180 ° C at 60V). Then, from this result, the heat dissipation amount [D (T-Troom)] at 120 ° C., 165 ° C., and 180 ° C. is obtained.
From the obtained values, the D (T-Troom) curve in FIG. 6 is obtained.

From the above equation (2), in order to increase the temperature rising speed to a stable temperature, the rising speed increases as the difference between the input electric energy and the heat dissipation amount increases.
This shows that the rise time to the stable temperature is shortened. Further, in order for the difference between the input electric energy and the heat dissipation amount to become large, the increase in the input electric energy V ² / R (T) due to the temperature increase needs to be larger than the increase in the heat dissipation amount due to the temperature increase. is there.

FIG. 7 shows the ideal input energy [V ² /
R (T)] changes due to temperature rise are shown. Furthermore, when the temperature dependence of the resistance value satisfying this temperature change of the input electric energy is obtained, it can be seen from W = V ² / R that the NTC characteristic (Negative T
It is necessary to show the emperature coefficient, and to show the NTC characteristic after the temperature just before the stable temperature. That is, in order to speed up the temperature rise of the heater and shorten the rise time to the stable temperature, the NTC is maintained until the temperature just before the stable temperature.
Therefore, it is necessary to form a heat generating resistor having the characteristics and the PTC characteristics from the temperature immediately before the stable temperature. In addition,
The NTC characteristic means that the coefficient of temperature change of the resistance value is negative, that is, the resistance decreases as the temperature rises.

The present inventor has based on such findings.
The present invention is completed by the means described below.
Solved the problem. That is, the heating resistor of the present invention is
Temperature control formed by mixing conductive powder with resin used as material
A heating resistor having a node function, which is made of the conductive powder.
, Ti ₂O₃Powder and resistivity of 4 × 10^-FiveΩ · cm or less
It contains the lower conductive powder. This heating resistance
In the body, as the base material resin, epoxy resin or
Polyimide resin is preferably used.

The Ti ₂ O ₃ powder is a conductive powder whose resistance value changes with temperature and has an NTC characteristic, and therefore imparts NTC characteristics to the heat generating resistor obtained up to a temperature just before its stable temperature. It is a thing. Note that Ti ₂
As shown in FIG. 2, the O ₃ powder has a resistivity of room temperature (1
000 / 300K = 3.33) to 200 ° C (1000
/473K=2.11) from 10 ^-2 Ω · cm (that is, 10 ⁻⁴ Ω · m) to 2 × 10 ⁻⁴ Ω · cm (that is, 2)
X 10 ⁻⁶ Ω · m).

Further, as a conductive powder having a resistivity of 4 × 10 ⁻⁵ Ω · cm (that is, 4 × 10 ⁻⁷ Ω · m) or less (hereinafter referred to as low resistance powder), the resistivity is 4 ×. 10 ^-5 Ω ・ c
RuO ₂ powder having m (that is, 4 × 10 ⁻⁷ Ω · m), and one or more kinds selected from powders such as Ag, Cu, and Ni having a lower resistivity than that are used. Here, this low resistance powder is used together with the Ti ₂ O ₃ powder and mixed with the base material resin so that the resistivity of Ti ₂ O ₃ at room temperature is 10 ⁻² Ω · cm (that is, 10
^-4 Ω ・ m), the resistivity is 4 × 10 ^-5 Ω ・ cm
This is because the resistance value of the obtained heating resistor at room temperature is lowered by mixing the low resistance powder having a low value (ie, 4 × 10 ⁻⁷ Ω · m) or less.

[0014] The mixing ratio of these matrix resin and a conductive powder, although varies depending on the kind of the resin type and the conductive powder, generally, with respect to 100 parts by weight of the matrix resin, Ti ₂
It is preferable that the total amount of the O ₃ powder and the low resistance powder is about 50 to 250 parts by weight. That is, when the total amount of the conductive powder is less than 50 parts by weight, the conductivity of the obtained heating resistor becomes too low, and when used as a heater, the applied voltage must be increased because of high resistance. If the total amount of conductive powder exceeds 250 parts by weight, the resin component of the base material becomes too small and molding defects occur when molding into a heating resistor, or the ratio of expensive conductive powder increases. This is because the cost will increase.

The mixing ratio between the conductive powders is T
40 to 40 parts of low resistance powder to 100 parts by weight of i ₂ O ₃ powder.
It is preferably 100 parts by weight. That is, if the low resistance powder is less than 40 parts by weight, the resistance of the heat generating resistor obtained becomes too high, and if it exceeds 100 parts by weight, the effect of adding the Ti ₂ O ₃ powder becomes low and This is because when the generated heating resistor is used as a heater, it is not possible to sufficiently shorten the rise time until the heater reaches a stable temperature.

In the heater for the electrophotographic printer fixing device of the present invention, the heating resistor is used as the means for solving the above problems. Here, as the heater for the fixing device including the heating resistor, a so-called surf (Surface Ra) is used.
pid Fusing) method, or on-demand method, which is configured as a general type.

[0017]

According to the heating resistor of the present invention, as the conductive powder, Ti ₂ O ₃ whose resistance value changes with temperature has NTC characteristics.
Since the powder is used, the heating resistor has NTC characteristics up to a temperature just before its stable temperature. Therefore, the heating resistor of the present invention has an increased temperature rising rate in comparison with the conventional one in the range having the NTC characteristics.

[0018]

EXAMPLES The heating resistor of the present invention will be described in detail below with reference to examples. An epoxy resin (PR-52; manufactured by Ciba-Geigy) having a glass transition temperature of 120 ° C. was used as a base material resin. Then, with this base material resin, Ti ₂ O ₃
Powder and RuO ₂ powder with epoxy resin: Ti ₂ O ₃ :
RuO ₂ = 47 wt%: 35 wt%: 18 wt% were mixed. In addition, the used Ti ₂ O ₃ powder,
For RuO ₂ powder, the powder particle size is Ti ₂
Those having O ₃ of less than 10 μm (average particle size 8 μm) and RuO ₂ of less than 1.0 μm (average particle size 0.2 μm) were used. Then, after mixing each of these materials by a known method, the mixture is heated at 150 ° C. for 30 minutes to be cured, and the width is 0.2 c.
A thin-film heating resistor (hereinafter, referred to as a product of the present invention) having m, a length of 2.5 cm, and a thickness of about 0.01 cm was obtained.

For comparison, only the RuO ₂ powder is added to the epoxy resin, and the epoxy resin: RuO ₂ = 69.
wt%: 31 wt% were mixed, that is, formed so as to be the same as the conventional heating resistor shown in FIGS. 5 and 6, and the heating resistor having the same size as the product of the present invention (hereinafter, The conventional product) is obtained. Then, electrodes of the present invention product and the conventional product were formed on both ends in the lengthwise direction by silver paste.

With respect to the heat generating resistors (product of the present invention, conventional product) thus obtained, change in resistance value with temperature, that is, temperature dependence of resistance value was examined, and the result is shown in FIG. From FIG. 1, it can be seen that the product of the present invention exhibits NTC characteristics from room temperature to near the glass transition temperature and has a thermistor function (temperature adjusting function) from 150 ° C. On the other hand, it can be seen that the conventional product exhibits PTC characteristics at room temperature and has a thermistor function at 120 ° C.

Further, the same input electric energy (7 W) is applied to the product of the present invention and the product of the related art through electrodes formed respectively.
Through, the time change of the temperature rise of the resistor was measured. FIG. 3 shows the obtained results. From FIG. 3, the input electric energy is equal when a voltage is applied, and both show a temperature rise rate of about 12 ° C./sec. However, the temperature rise rate at the time when the temperature rises to 100 ° C. Since it is 10 ° C./sec and that of the conventional product is about 2 ° C./sec, it can be seen that the temperature rise of the product of the present invention is faster than that of the conventional product.

Therefore, from such a result, the present invention has the following effects. Generally, a matrix resin, for example, an epoxy resin, has a coefficient of thermal expansion of α ₁ and α ₂ around the glass transition temperature tg. These thermal expansion coefficients α ₁ and α ₂ are both positive values, and α ₁ is α
It is less than ₂ . By the way, the heating resistor forms a resistance network at room temperature by contact with the conductor in the base material as described above. Then, as the temperature rises up to the glass transition temperature, the base material thermally expands, which increases the distance between the conductor powders, making it impossible to make contact between the powders in the resistance network and decreasing the number of resistance networks. . Therefore, the resistance value of the heating resistor formed of the composite material gradually increases with the temperature increase up to the glass transition temperature. Further, at the glass transition temperature or higher, the coefficient of thermal expansion α _{2 of the} base material is larger than that of α ₁ , so that the increase in the distance between the powders due to the temperature rise is larger than that at the temperature of tg or lower. The contact between them cannot be suddenly stopped and the resistance value rapidly increases.

As a result, the heating resistor formed of the composite material exhibits a small PTC characteristic at a temperature of tg or lower,
At the above temperature, large PTC characteristics are exhibited. Therefore, when voltage is applied to this heating resistor, when the temperature of the resistor rises due to heat generation (Joule heat) of the resistor, the resistance of the resistor rapidly increases and becomes high resistance, and the flowing current value is limited. That is, the temperature regulation function that the temperature becomes stable at a certain temperature is exhibited.

As shown in FIG. 1, the product of the present invention exhibits NTC characteristics from room temperature to 150 ° C., whereas the conventional product exhibits PTC characteristics from room temperature. Therefore, its input electrical energy is W = V ² / R,
As shown in FIG. 4, the product of the present invention is 1 more than R = V ² / W.
While the temperature continues to increase up to 50 ° C, the conventional product will continue to decrease. Here, the amount of heat dissipation [D (T-Troo
m)] increases as the temperature rises as shown in FIG.

At this time, the temperature rising rate of each resistor is determined by the difference between the input electric energy and the amount of heat dissipation according to the equation (2), so that the temperature of the product of the present invention is higher than that of the conventional product. The climb will be fast. On the other hand, when the voltage is applied, since the input power is equal to 7 W, the rate of temperature rise is equal to about 12 ° C./sec in both cases. However, the temperature rising rate at 100 ° C. is about 10 ° C./sec for the product of the present invention as determined from FIG. 3, whereas it is as small as about 2 ° C./sec for the conventional product. This is 100 ℃ in Figure 4
Looking at IV-D (T-Troom), the value of the present invention is approximately three times that of the conventional product.

The increase in the temperature rise rate is an action caused by the temperature change of the resistance value of the product of the present invention depending on the range of NTC characteristics. Therefore, in such a product of the present invention, when it is used as a heater, the temperature rises quickly, and thus the rise time to a stable temperature is short. Further, when such a heating resistor of the present invention is used as a heater for a fixing device for an electrophotographic printer, the temperature rise time becomes short because of the above reason. It should be noted that the configuration of the fixing device heater for the electrophotographic printer is the same as that of the conventional one except that only the heat generating resistor is replaced, and other components are the same, so a detailed description of the other components will be omitted. .

[0027]

As described above, the heat generating resistor of the present invention uses Ti ₂ O ₃ powder having a resistance change with temperature as the NTC characteristic as the conductive powder, so that the temperature immediately before its stable temperature is reached. Since it has NTC characteristics,
In the range having the NTC characteristics, the temperature rising speed is increased as compared with the conventional one. Therefore,
When this is used as a heater, the temperature rise rate increases as described above in addition to the thermistor function (temperature adjustment function) originally possessed, so it is possible to shorten the time until the temperature rises to a stable temperature. it can. Therefore, for example, if this heating resistor is used as a fixing heater for an electrophotographic printer, a fixing device with a short temperature rise time can be manufactured.

[Brief description of drawings]

FIG. 1 is a graph showing the temperature dependence of the resistance value of a heating resistor.

FIG. 2 is a graph showing the temperature dependence of the resistivity of Ti ₂ O ₃ .

FIG. 3 is a graph showing the time change of the temperature rise of the heating resistor.

FIG. 4 is a graph showing temperature dependence of input electric energy and heat dissipation amount.

FIG. 5 is a graph showing the relationship between the temperature of the heating resistor and the voltage application time.

FIG. 6 is a graph showing the temperature dependence of the relationship between input energy and heat dissipation.

FIG. 7 is a graph showing temperature dependence of ideal input energy.

FIG. 8 is a graph showing temperature dependence of ideal resistance value.

Claims (3)

[Claims] 1. A heat-generating resistor having a temperature adjusting function, which is formed by mixing conductive powder into a resin as a base material, wherein the conductive powder is Ti ₂ O ₃ powder and has a resistivity of 4
A heat-generating resistor, characterized in that it contains a conductive powder of ^{x10 -5} Ω · cm or less. 2. The conductive powder having a resistivity of 4 × 10 ⁻⁵ Ω · cm or less is made of at least one kind of powder of RuO ₂ , Ag, Cu and Ni. Item 3. A heating resistor according to item 1. 3. A heater for an electrophotographic printer fixing device, wherein the heating resistor according to claim 1 is used as a heater.